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53 FR 37082-37247 Friday, Sept. 23, 1988 40 CFR Parts 280 and 281, Underground Storage Tanks; Technical Requirements and State Program Approval; Final Rules--Preamble Section IV. Analysis of Today's Rule--A. Program Scope

PREAMBLE
(37107-37125)

 


IV. Analysis of Today's Rule

A. Program Scope

1. Applicability

2. Regulatory Exclusions

3. Deferral of Regulations

4. Definitions


IV. ANALYSIS OF TODAY'S RULE

A. Program Scope

1. Applicability

As described previously, this rule generally applies to all owners and operators of UST systems containing regulated substances. Regulated substances consist of either petroleum or any substance defined in section 101(14) of CERCLA (but not including any substance regulated as a hazardous waste under Subtitle C). The following sections discuss the tank systems subject to exclusions from today's requirements and the deferral of regulation for other UST systems.

2. Regulatory Exclusions

The regulatory exclusions in today's final rule are based on a number of statutory provisions and regulatory considerations. Section 9003(a) of RCRA requires the Administrator to establish an UST program "as may be necessary to protect human health and the environment." In addition, Section 9003(b) allows the administrator to consider such factors as tank size and quantity of substances stored when establishing necessary requirements. The Agency believes that this statutory language allows some flexibility for EPA to concentrate its resources on tanks that pose the greatest potential environmental threat. Section 9001 defines the universe of the UST program and indicates that EPA should regulate tanks containing an "accumulation" of regulated substances. Section 9001 also excludes tanks regulated under Subtitle C from the jurisdiction of Subtitle I. Finally, section 1006 of RCRA generally requires integration of RCRA with the Federal Water Pollution Control Act; the Safe Drinking Water Act; the Marine Protection, Research, and Sanctuaries Act; and the Atomic Energy Act.

Based on these provisions, the Agency is today excluding from regulation several types of tank systems. These exclusions will decrease the regulatory burden on implementing agencies so they can focus their resources on types and classes of tanks that pose a significant threat to human health or the environment. Unlike statutory exclusions, regulatory exclusions may be modified by the Agency in the future should new information show that regulation of such an excluded tank type is necessary.

Four classes of tanks are excluded from regulation in the final rule: UST systems containing mixtures of hazardous waste and regulated substances; equipment and machinery that contain regulated substances for operational purposes; wastewater treatment tanks regulated under the Clean Water Act; and UST systems excluded via one of three de minimus exclusions. A specific regulatory exclusion for UST systems containing mixtures of hazardous waste and regulated substances was included in the proposed rule (52 FR 12687). The preamble of the proposal also discussed de minimus exclusions. The other two regulatory exclusions were regulatory deferrals in the proposal. The rationale for these exclusions is discussed below.

a. Tanks Regulated Under Subtitle C of RCRA. Because USTs containing a mixture of hazardous wastes (regulated under Subtitle C of RCRA) and regulated substances (regulated under Subtitle I) are subject to dual jurisdiction from Subtitle C and Subtitle I, EPA is today excluding these tanks from Subtitle I regulation. As evidenced by the exclusion of substances covered under Subtitle C within the statutory definition of "regulated substance," the Agency believes that this exemption is consistent with Congressional intent not to have redundant requirements under these two programs. Because of the continued coverage of these tanks by Subtitle C, the exclusion of these tanks from Subtitle I regulations will not present a risk to human health and the environment, and, thus, Subtitle I regulation is not "necessary to protect human health and the environment."

Several commenters pointed out that in the proposed rule this exclusion applied only to mixtures of hazardous wastes and hazardous substances. This wording would subject tanks that contain mixtures of hazardous wastes and petroleum to regulation under both Subtitle C and Subtitle I. The commenters requested that the wording be changed so that all mixtures with hazardous wastes regulated under Subtitle C would be excluded from these regulations.

The original wording in the proposal was based upon the statutory jurisdiction of the program. Under section 9001(2)(A), the exclusion of tanks regulated under Subtitle C pertains only to tanks containing hazardous substances, not to tanks containing petroleum. EPA, however, agrees with the commenters that dual regulation of tanks containing hazardous wastes and petroleum is not necessary and has changed the wording of this exclusion appropriately. This exclusion now applies to all tanks subject to regulation under Subtitle C that contain mixtures of hazardous wastes and either petroleum or non-petroleum regulated substances.

b. Equipment and Machinery that Contain Regulated Substances for Operational Purposes. Equipment and machinery that contain regulated substances for operational purposes, such as hydraulic lift tanks and electrical equipment, are excluded from today's regulations. These specific tank categories were deferred from regulation in the proposal, and the Agency requested comments on whether, and to what extent, these tanks should be subject to regulation under the UST program. Several commenters responded to this request and gave several reasons why these tanks should not be regulated as USTs. Their comments included three main points: the tanks are self-monitoring; the tanks pose a minimal risk to human health and the environment; and there have been few leaks.

Because these tanks contain regulated substances solely for operational purposes, the commenters argued that the loss of regulated substance would be accompanied by faulty operation of the equipment or machinery and thus the equipment is "self-monitoring." Second, the threat to human health and the environment was judged to be minimal because the tanks contain small amounts of regulated substances. Also, the commenters said that these devices rarely leak. Data submitted for leaks from electrical equipment, for example, show a leak incidence much lower than that for other types of tanks such as those at service stations.

This category of tanks includes hydraulic lifts and electrical equipment. Although commenters did not suggest other specific types of tanks that would fall within this class, EPA believes that other tanks of this type would also be included, provided that the tanks meet two major criteria: the equipment or machinery contains small amounts of regulated substances solely for operational purposes; and a loss of regulated substance is accompanied by faulty operation of the equipment or machinery, such that a loss of fluid causes knowledge of the loss.

In excluding this category of tanks, the Agency agrees with the commenters that these types of tank systems pose a relatively low level of risk compared to other types of storage tanks for the reasons given above. Moreover, the Agency recognizes that these tanks, although within Subtitle I jurisdiction, are not central to the Congressional concerns that created this program. Thus, regulation of these tank systems appears at this time to be unnecessary under section 9003(a).

EPA also believes that this potentially overwhelming large universe would require considerable effort on the part of implementing agencies even for just notification, with very little discernable environmental benefit. For example, the universe of hydraulic lift tanks alone has been estimated at 350,000 to 600,000 lifts. These figures do not include elevator lifts. Regulation of these types of tanks would unnecessarily divert implementing agency resources from other, more serious health threats. Therefore, today's final rule excludes such tanks.

c. Wastewater Treatment Tanks Regulated Under the Clean Water Act. The Agency is today excluding all wastewater treatment tanks, including any oil-water separators, that are subject to regulation under either section 402 or 307(b) of the Clean Water Act (CWA) (33 USC 1151 and following). These tanks, including tanks at most publicly owned treatment works and many private treatment facilities, would otherwise be subject to dual regulation. Because these tanks are subject to regulation under the CWA, further regulation under Subtitle I is unnecessary to protect human health and the environment and would be inconsistent with section 1006(b) of RCRA. This exclusion is analogous to the "wastewater treatment unit" exclusion under the RCRA Subtitle C program (see 40 CFR 260.10, 264.1, and 265.1).

In addition, tanks that treat wastewater or storm water, but which are not covered by the applicable sections of the CWA, are being deferred from today's final regulations. Such tanks might include many oil-water separators found at various facilities. Further discussion of these tanks can be found under the deferral section of this preamble.

d. De Minimis Exclusions. Today's final rule has been modified to exclude the following tanks: (1) those that have a capacity of less than 110 gallons; (2) those holding a very low concentration of regulated substances; and (3) those that serve as emergency backup tanks, hold regulated substances for only a short period of time, and are expeditiously emptied after use.

The statutory definition of tank includes all devices that "contain an accumulation of regulated substances." Although legislative history provides no guidance on the meaning of the phrase "accumulation of regulated substances," the Agency believes the statutory language provides some flexibility to define the universe of regulated facilities in a manner that focuses regulatory resources on the tanks posing substantial risk from storage of regulated substances and, thereby, fosters development of a program that most effectively protects human health and the environment. Thus, sections 9001 and 9003(a) authorize EPA to exclude from its regulations tanks containing de minimis amounts of regulated substances. EPA requested comment in the proposed rule concerning de minimis exclusion criteria.

A number of comments addressed the issue of including a de minimis exclusion in the rule for tanks that hold a small quantity of regulated substances. The overwhelming majority of the commenters believed that such an exclusion should be part of the final rule. Some commenters suggested that a small-capacity exclusion would reduce the regulatory burden on the implementing agencies and, thus, result in a more effective program. Some commenters believed that a small-capacity exclusion was justified because small quantities of regulated substances pose less of a health risk than do larger quantities.

In deciding to include a regulatory exclusion for tanks that contain small quantities of regulated substances in today's rule, the Agency had to balance the benefits and drawbacks of such an exclusion. The Agency agrees with the commenters who thought that without an exclusion such as this, the regulated universe could be overwhelmingly large. Such a large universe would require considerable efforts by the implementing authorities even for notification, diverting their attention away from other, more potentially environmentally hazardous classes of tanks. The Agency agrees that small tanks pose less danger to the environment than larger tanks, generally, due to the smaller quantity of regulated substances available to leak. In certain cases, however, the mismanagement of even small quantities of regulated substances could pose serious danger to human health and the environment. Nevertheless, the Agency has decided that the detriments of attempting to regulate these small tanks greatly outweigh any potential benefits from regulation of this class of tank and has, therefore, adopted this exclusion.

Several comments were received with suggested sizes for a de minimis cutoff. These sizes ranged from 100 gallons to 5,000 gallons. State and local agencies with de minimis exclusions use cutoffs that range from 60 to 2,100 gallons. Because it was apparent that there was no standard size for the de minimis exclusion, the Agency chose the size limit of 110 gallons capacity. According to one commenter, this size is below the smallest petroleum product tank routinely mass produced (275 gallons), and a 110-gallon level coincides with the Department of Transportation definition for minimum portable tank for the transportation of hazardous materials. Tanks likely to be exempted under this exclusion include many small sumps and other atypical tanks.

The Agency is also today excluding tanks that contain de minimis concentrations of regulated substances. Because "an accumulation of regulated substances" could include within the regulated universe USTs holding regulated substances in any amount, no matter how small, the regulated universe could include a vast number of tanks that contain regulated substances only in small concentrations. These very small concentrations could occur accidentally (through contamination) or by design (for example, underground tanks storing food that contains a preservative that is a regulated substance). The Agency has not included a specific percentage threshold as the de minimis cutoff because of the many difficulties with measuring tank contents for low concentrations. Instead, on a case-by-case basis, the implementing agencies will determine if tanks that hold very low concentrations of regulated substances are excluded via the de minimis concentration rationale. Tanks that are likely to meet this criteria include those that are used to treat storm water and municipal wastewater, tanks that store potable water that has been treated with chlorine, and in-ground swimming pools. EPA believes that such tanks pose a minimal threat to human health and the environment, and the inclusion of such tanks in the regulated universe would impose an undue burden on the implementing agencies because of the potentially large numbers of such tanks. Other types of tanks with very low concentrations of regulated substances may also be excluded.

The third de minimis exclusion included in today's rule pertains to tanks that are emergency spill protection tanks or overflow tanks, and are emptied expeditiously following use. This exclusion is analogous to the exclusion for emergency response treatment and containment under the RCRA Subtitle C program (see 40 CFR 264.1 and 265.1). Included in this category are many types of sumps and secondary barrier tanks. This exclusion does not specify a maximum time a tank may hold material, but applies only to tanks that are rarely used and are emptied shortly after use. The purpose of this exemption is to allow appropriate immediate response to emergency situations. These tanks are used for temporary storage of substances in response to a leak, spill, or other unplanned occurrences. Regulation of such tanks is unnecessary because they are rarely used and expeditiously emptied and, therefore, are unlikely to have any long-term leaks. Many of these tanks may also be able to be visually inspected because they rarely hold regulated substances. Several commenters expressed concern that the way the proposed rule was written, the Agency may have been requiring infinite layers of secondary containment. For example, in the proposal, an UST system was defined to include a secondary containment system, but there were references to requiring secondary containment for a hazardous substance UST system. Thus, it appeared that secondary containment was required to surround secondary containment. By including this exclusion in the final rule, the Agency believes that any potential confusion regarding the need for secondary barriers (containment) for secondary barrier (containment) systems has now been eliminated.

Sumps designed to store petroleum or hazardous substances during periodic cleaning or maintenance of machinery or equipment are not included in this exclusion. An example of this type of sump is turbine oil sumps that are used during maintenance of electric power generation turbines.

3. Deferral of Regulations

In the proposal preamble (52 FR 12687), EPA discussed its proposed deferral of requirements for the following categories of UST systems: wastewater treatment tanks, sumps, systems containing used oil, systems containing radioactive waste, systems containing electrical equipment, underground bulk storage tanks, and hydraulic lift tanks. The Agency requested comments on whether the deferrals were appropriate for each category and, if not, what regulations would be necessary.

In today's final rule, the Agency has revised the proposal in several ways. As a result of these revisions, tanks in some of these categories will fall within the scope of the regulatory exclusions described above, some will be subject to full regulation, and some will continue to be deferred from regulation. Tanks that are deferred rather than excluded are subject to interim UST requirements, but excluded tanks are not subject to any regulatory requirements. These revisions are briefly summarized below:

o Wastewater treatment tanks now fall under two parts of today's final rule. Wastewater treatment tanks, including oil-water separators, that fall under the jurisdiction of sections 402 or 307(b) of the CWA are excluded from today's regulatory requirements (as discussed above in IV.A.2.). The remaining wastewater treatment tanks continue to be deferred from Subparts B, C, D, E and G of today's regulations, but are subject to interim requirements under Subpart A and corrective action under Subpart F.

o Many sumps are excluded from regulation under the CWA-regulated wastewater treatment exclusion, and others via one or more of the de minimis exclusions; others may be excluded as part of the statutory exclusion for storm-water and wastewater collection systems. Many of those that are not excluded continue to be deferred from Subparts B, C, D, E and G under the "field-constructed tank" deferral. Such UST systems are subject to the interim prohibition under Subpart A and corrective action under Subpart F. Sumps that are neither excluded nor deferred from regulation are subject to today's regulation.

o Field-constructed tanks, which include many tanks classified as underground bulk storage tanks in the proposal, are deferred from Subparts B, C, D, E and G but are subject to interim requirements under Subpart A and corrective action under Subpart F.

o UST systems that contain radioactive wastes and other radioactive materials have been deferred from Subparts B, C, D, E and G but are subject to interim requirements under Subpart A and corrective action under Subpart F.

o UST systems containing electrical equipment and hydraulic lift tanks, which had been deferred in the proposal, are both examples of equipment or machinery using regulated substances for operational purposes. As discussed above in IV.A.2., both types of tanks have been excluded from regulation under Subtitle I.

o Tanks containing used oil are no longer deferred but are subject to full regulation under today's final rule.

Today's final rule also includes deferral of some subparts of the regulations for the following additional categories of tanks:

o Airport hydrant fueling systems and tanks storing diesel fuel for emergency power generation at plants regulated by the Nuclear Regulatory Commission are deferred from the technical standards set forth in Subparts B, C, D, E and G but are subject to interim requirements under Subpart A and corrective action under Subpart F.

o UST systems that store fuel solely for use by emergency power generators are deferred from the release detection requirements under Subtitle D. All other regulatory requirements apply to these tanks.

EPA's decision making on these various tank types is discussed in more detail in the sections below.

a. Wastewater Treatment Tanks. In the proposal, EPA deferred wastewater treatment tanks from UST regulation in order to gather more information on the need to regulate these tanks and the appropriate type of regulation. EPA included oil-water separators (which are considered treatment tanks) within the scope of wastewater treatment tanks.

In the proposal preamble, EPA specifically requested comments on whether wastewater treatment tanks should be regulated under Subtitle I (52 FR 12687). Almost all comments submitted were opposed to regulating wastewater treatment tanks under UST regulations. The commenters stated that wastewater treatment tanks are process devices and flow-through process tanks, not storage tanks; thus, they should not be regulated under the UST program. Several commenters also stated that wastewater treatment tanks contain large volumes of water and only small amounts of oil or hazardous materials and, thus, pose no major threat to human health or the environment. It was also stated that wastewater treatment tanks that are currently excluded by RCRA are, however, currently covered by the CWA. They should not, therefore, be regulated under UST regulations. In addition, several commenters pointed out that if wastewater treatment tanks were to be included in the final rule, there is presently no practical method of performing a tightness test on these tanks because the tanks are typically open to the atmosphere. Inventory reconciliation is not feasible because the very high throughput would require more accurate metering than is currently available.

EPA does not agree with the commenters who argued that wastewater treatment tanks are outside the scope of Subtitle I as "flow-through process tanks" or part of a storm-water or wastewater collection system, which are excluded from the jurisdiction of this program under section 9001(1). Wastewater treatment tanks are not part of a production process, nor are they part of a collection system. See section IV.A.2. for further discussion of the scope of the flow-through process tank and storm-water and wastewater collection system exclusions. EPA does, however, agree with commenters that the universe of treatment tanks could add a large administrative burden that could reduce the ability of the implementing agencies to regulate more serious threats to the environment.

After review of all available information, EPA now believes that wastewater treatment tanks that are currently covered by sections 402 and 307(b) of the CWA should be excluded from UST regulations as discussed in the previous section. In addition, some of these treatment devices, such as those treating municipal sewage, typically contain de minimis concentrations of regulated substances and are therefore excluded under today's rule.

Wastewater treatment tanks not covered by the CWA or otherwise excluded will continue to be deferred under these regulations. Oil-water separators and other similar treatment devices fall under the definition of "wastewater treatment tank" under today's rule. The deferral for those wastewater treatment tanks not regulated by the CWA reflects the Agency's uncertainty regarding the nature of this tank population and the appropriateness of some of the UST regulations for these tanks. For example, some types of leak detection (such as tightness testing) and inventory reconciliation would not appear to apply to treatment tanks.

b. Sumps. In the preamble of the proposal (52 FR 12687), the Agency requested that commenters submit information on the number, location, and substances stored in sumps; how sumps are protected to prevent releases from occurring; leak history; and whether the proposed UST regulations would be appropriate for sumps. Most of the commenters who responded believed that regulations for sumps should continue to be deferred because sumps are small, temporary storage facilities that are frequently visually monitored and that contain mostly water and only small amounts of petroleum or hazardous substances. Also, commenters stated that regulation of sumps would pose an unmanageable regulatory burden for the implementing agencies and would require an individualized approach for each location. Some commenters suggested that de minimis size, time, and throughput exclusions be developed to prevent sumps from becoming subject to the regulations. The only commenters who supported regulation of sumps did not believe that Subtitle I was the appropriate regulatory authority.

Although commenters did not submit data that would enable EPA to determine the total number of sumps nationwide, the Agency realizes that that the number of sumps potentially subject to Subtitle I is very large and could pose an unmanageable regulatory burden. In addition, the Agency agrees with the commenters that many sumps are small, temporary storage facilities that contain only small amounts of petroleum or hazardous substances. No information was submitted concerning whether sumps pose a significant threat to human health or the environment.

As discussed above, today's final rule contains de minimis size, time, and concentration exclusions that are expected to apply to many sumps. Also, sumps that are part of a storm-water or wastewater collection system are excluded by statute from UST regulations. These exclusions will allow the implementing agencies to focus their resources on UST systems that are a more significant threat to the environment and human health. The Agency believes, however, that large sumps that contain significant quantities of regulated substances over a period of time do not warrant such exclusion, because they are indistinguishable from other regulated tanks. Therefore, factory-built sumps are subject to all requirements under today's final rule if they are not subject to any other exclusion. Field-constructed tanks, including field-constructed sumps, are deferred until information can be obtained on what regulations (if any) are appropriate for these systems as discussed in the following section. Therefore, the final rule no longer contains a deferral for sumps.

c. Field-Constructed Tanks. In the proposal preamble, EPA specifically requested comments concerning the applicability of Subtitle I (52 FR 12688) to underground bulk storage tanks (UBSTs). In the proposal preamble, EPA considered UBSTs as those tanks whose total capacity was 20,000 gallons or greater. Several commenters stated their belief that because UBSTs pose a major environmental concern and are closely related to other USTs, they should be regulated under Subtitle I in the final rule. It was also stated by some commenters that secondary containment of UBSTs is feasible and other existing leak detection methods are applicable to UBSTs. On the other hand, there were some commenters who opposed the inclusion of UBSTs in the regulation stating that the differences between UBSTs and normal USTs are too great and that many leak detection and leak prevention methods are not applicable to UBSTs. There were also requests by some commenters that the definition of UBST be clarified and included not only in the preamble but also in the final regulation.

After reviewing the comments, EPA has modified the deferral of UBSTs to a deferral for tanks that are field-constructed. Although many bulk tanks are expected to be deferred because they are field-constructed, the capacity of these tanks no longer determines their regulatory status.

Field-constructed tanks are usually constructed of steel or concrete, shaped like flat vertical cylinders, and have a capacity of greater than 50,000 gallons. In contrast, factory-constructed bulk tanks are typically long, horizontal cylinders and are less than 12 feet in diameter. Tanks that are principally factory-built but are assembled in the field are considered factory-built tanks. For example, welding two halves of a factory-constructed tank together in the field does not qualify the tank as a field-constructed tank.

The deferral of regulation for field-constructed tanks is largely based on the fact that design and construction methods for field-constructed tanks are different from those for factory-built tanks. EPA has not had sufficient time to develop appropriate regulations related to design and construction for such tanks.

Comment was divided on the applicability of present leak detection and leak prevention methods to bulk tanks. Some commenters argued that existing leak detection methods are applicable to UBSTs, while others stated that the differences between UBSTs and normal USTs are too great to use most presently available leak detection and prevention methods for such tanks. EPA believes that the division of bulk tanks into field-constructed and factory-built tanks simplifies this issue.

EPA believes that because of the different design and construction methods used for field-constructed tanks, as well as the very large size of some field-constructed tanks, the majority of the leak detection methods presently available do not work for such tanks. Leak prevention methods may also differ for such tanks. The deferral for these tanks is due in part to this restricted availability of appropriate leak detection methods.

By contrast, EPA believes that currently available leak detection methods are applicable to factory-built tanks. Factory-built tanks, even those that are very large, generally conform to standard design and construction methods that allow the use of widely available leak detection methods.

EPA agrees with commenters that tanks that hold large amounts of regulated substances do pose a relatively larger potential danger to human health and the environment than other, smaller tanks. However, until regulations are developed to govern design and construction of field-constructed tanks, they will be deferred.

d. Systems Containing Radioactive Materials. At proposal, the Agency requested comment on the issue of whether tanks containing radioactive materials, including high-level radioactive waste and tanks containing mixtures of low-level radioactive waste and other materials, should meet the proposed standards or whether separate standards should be developed. No commenters supported regulation of these USTs under Subtitle I. The commenters stated that radioactive waste and materials tanks at nuclear facilities are regulated by the Nuclear Regulatory Commission (10 CFR 50.34a) and that further regulation of these tanks under Subtitle I would be duplicative and possibly inconsistent. One commenter noted that these tanks are typically made of stainless steel and have a capacity of approximately 1,000 gallons. The tanks are pressure tested before the nuclear facility is licensed to operate and are retested every 10 years. In addition, they are constantly monitored for loss of pressure and radiation leakage. Commenters also noted that the current Department of Energy management program for tanks containing high-level radioactive waste is as stringent as, and in some cases exceeds, the proposed UST rule.

Because tanks containing radioactive wastes and other radioactive materials at nuclear facilities are regulated by the Nuclear Regulatory Commission, these tanks could be subject to overlapping jurisdiction under Subtitle I and the Atomic Energy Act of 1954 (42 U.S.C. 2011 and following). The Agency, however, lacks complete information on whether these regulations fully cover all appropriate areas addressed under Subtitle I. The Agency, therefore, is deferring regulation of these tank systems until more information can be gathered.

e. Systems Containing Electrical Equipment. Under the proposed definition of "tank," large numbers of utility units in urban and residential areas (e.g., underground transmission cables and vaulted transformers for large trunk lines) could be subject to regulation. At the time of the proposal, the Agency deferred regulation of these structures based on its belief that inclusion of these structures in the UST program would be impractical and unnecessary. EPA requested that commenters submit information on the number, location, and substances stored in these units; how they are protected to prevent releases; leak history; and whether the proposed regulations would be appropriate for these units.

All of the commenters in this area were opposed to inclusion of electrical equipment structures in the UST program. The commenters stated that these units are not primarily used for storage and that the utilities industry already takes many precautions to prevent releases. Dielectric fluids, typically naphthenic mineral oil and synthetic fluids such as polybutene or alkylbenzene, are used in underground cable piping and vaulted transformers to prevent the cables and transformers from overheating. Underground cable piping is cathodically protected and is coated to prevent corrosion. The piping is subjected to pressure tests both before and after insertion of the cable and addition of the dielectric fluid. Electronic monitors at the utility's control center indicate potential releases of fluid (i.e., when the required oil pressure cannot be supplied by the associated pumping station). In addition, transmission line routes are routinely inspected to identify potential sources of piping damage, such as the misuse of construction equipment. Information submitted by commenters showed that from 1978 to 1985, utilities nationwide reported an average of less than 1 leak per 100 circuit miles of cable. In 1985, there were 23 reported leaks involving low-pressure systems and 6 reported leaks involving high-pressure systems. Of the low pressure system leaks, only one occurred belowground.

The Agency believes that there are already strong incentives for the utilities industry to prevent releases from underground equipment because these leaks could result in system malfunctions and widespread power outages. The industry has developed release response procedures for notification, containment, and cleanup in the event of a release. In addition, despite its widespread use, underground electrical equipment appears to pose a minimal threat to the environment because of the low leak incidence for such UST systems. Moreover, many of these systems also fall within the statutory exclusion for storage tanks situated on or above the floor of underground areas, such as basements and cellars. Therefore, to allow the implementing agencies to focus their limited resources on more significant potential threats, the Agency has decided to exclude underground electrical equipment from the final rule as equipment and machinery that contain regulated substances solely for operational purposes.

f. Hydraulic Lift Tanks. In the proposal preamble, EPA deferred the application of the proposed technical standards to hydraulic lift tanks; however, these tanks would have been subject to Subparts F and G of the proposed rule (i.e., corrective action). "Hydraulic lift tanks" are those tanks used to store fluid used in hydraulic lifts at service stations and similar devices such as lubrication oil reservoirs for elevators. After review of all available information, EPA has now decided that, like the electrical equipment tanks discussed above, hydraulic lift tanks will be excluded in the final rule as equipment or machinery that contain regulated substances solely for operational purposes.

In the proposal preamble, EPA specifically requested comments on whether hydraulic lift tanks should be regulated, and if regulated, to what extent (52 FR 12689). In response, several commenters stated that hydraulic lift tanks should not be regulated under the final rule because they are not used for storage and many of them are almost completely aboveground. It was suggested by several other commenters that hydraulic lift tanks not be regulated because they pose either minimal or no threat to human health or the environment and are self-monitoring. If problems do arise, the lifts cease to operate when they lose fluid. It was also mentioned by several commenters that due to the location of hydraulic lift tanks (e.g., under buildings), the cost impact involved in bringing these tanks under regulation would be substantial. Finally, several commenters stated that the inclusion of hydraulic lift tanks in the regulation would cause severe impacts on the implementing agency; the number of hydraulic lifts has been estimated at over 800,000. Several commenters suggested, however, that special standards be developed specifically for hydraulic lift tanks. It was also suggested that only those hydraulic lift tanks that exceed 100 gallons be regulated under the final rule.

EPA deferred regulation of hydraulic lift tanks at proposal to allow time to gather additional information on the subject. In the preamble to the proposal, however, EPA identified several reasons why, based on preliminary information, the Agency felt that regulation of such tanks would be unnecessary. After reviewing all comments submitted, EPA believes that it is appropriate to exclude all hydraulic lift tanks from regulation. EPA agrees with those commenters who stated that hydraulic lift tanks pose a minimal threat to the environment and are self-monitoring. The Agency is today excluding these types of tanks as equipment that contains regulated substances solely for operational purposes (see section IV.A.2.b. above).

g. Used Oil USTs. The Agency proposed to defer regulation of used oil USTs. The Agency indicated, however, that it might apply the proposed technical standards to used oil USTs in the final rule following public comment on the appropriateness of the technical standards for used oil USTs. EPA considered the many comments received on this issue and has decided to include used oil USTs in the final regulation. Public comments received by EPA and proposed revisions to the final rule as they relate to the appropriateness of the technical standards for used oil USTs are discussed below.

In the preamble to the proposed regulations, EPA requested comments on the following issues relating to used oil:

o Are the petroleum UST requirements appropriate for recycled used oil and/or used oil bound for disposal?

o Do the minor constituents found in used oil (such as water and metals) alter the appropriateness of the requirements?

o Is it appropriate to have different standards for relatively smaller tanks, such as those used by used oil generators and burners, than for larger tanks, such as those used by used oil processors?

In addition, EPA also requested comment on the impact of the proposed regulations on the recycling of used oil.

In a supplemental Federal Register Notice (52 FR 48638, December 23, 1987), EPA requested comment on the appropriateness of using alternative methods of release detection for used oil USTs, to supplement those listed in § 280.41 of the proposed rule. The Agency specifically requested comments on the use of static inventory control as a method of release detection for smaller used oil USTs. This request was prompted by the Agency's belief that some of the release detection methods proposed in § 280.41 may not be practical or effective for used oil USTs due to the physical characteristics of used oil. On the other hand, the Agency believes that the static inventory method of release detection may be very effective and practical for use with small used oil USTs. "Static inventory control" has been renamed as "manual tank gauging" in the final rule and in the rest of this preamble's discussion of this method of release detection.

The Agency believes that the risks associated with releases from used oil USTs may be different from those of other USTs, but the overall level of risk is similar to that of other petroleum products. Releases from used oil USTs may be less likely to occur than from petroleum USTs, but the health risks posed may potentially be greater because of the possibility of contaminants in the used oil. The appropriateness of further regulation, under RCRA Subtitle C, will be determined by results of studies currently in progress. At this time, the Agency has determined that used oil USTs should be regulated under Subtitle I because there is evidence of leaks that indicates a significant threat to human health and the environment.

In reply to EPA's request for comments about the appropriateness of the proposed regulation for used oil USTs, public comment was divided. Several commenters stated that used oil USTs should be covered by Subtitle I regulations because the risk to ground water was essentially the same as for other petroleum products, and that management of all underground tanks at a facility that had both used oil tanks and other Subtitle I regulated tanks (e.g., a service station) would be facilitated by a single, inclusive regulation (Subtitle I). In contrast, some commenters stated that the risk from used oil USTs was insignificant and, thus, used oil USTs should permanently be exempted from regulation. Others stated that used oil USTs should be regulated under RCRA Subtitle C because the hazardous constituents in used oil make it more dangerous than other petroleum products.

The Agency agrees with those commenters who noted that used oil presents risks similar to other petroleum products and that Subtitle I regulations are appropriate. Today's final rule reflects this by applying the petroleum UST requirements to used oil USTs, with limited exceptions discussed below. Releases from both used oil USTs or other petroleum USTs can be prevented, or at least limited, by sound management practices. As a result, the Agency has decided to require used oil USTs to meet the same upgrading, operation and maintenance, corrosion protection, corrective action, and closure requirements that are applicable to other petroleum USTs.

The Agency received comments requesting an exemption from Subtitle I regulations for small tanks. Recommended cutoff sizes ranged from 100 to 3,000 gallons. In addition, several commenters also requested regulatory exemptions for small vessels used to trap used oil, as well as tanks holding regulated substances for short time periods. As discussed above, in today's final rule EPA is exempting from the regulations USTs that are 110 gallons or less. Thus, small traps are excluded from regulation. With respect to tanks that hold regulated substances for short periods of time, today's rule includes an exemption for emergency spill collection tanks. The regulations do, however, apply to any other used oil USTs, the majority of which are the 500- and 550-gallon tanks often found at gasoline service stations. Most of these USTs are old and are believed to be a common source of releases of used oil. USTs that contain used oil that is used as substitute for heating oil are excluded.

The Agency received several comments noting particular characteristics associated with used oil or used oil USTs that make some of the proposed technical standards in Part 280 inappropriate for used oil USTs holding less than 1,100 gallons. In response to these comments, today's final rule contains different requirements for small used oil USTs in two areas: release detection and overfill/spill protection. First, with respect to release detection, many commenters noted their support for manual tank gauging (formerly called "static inventory control") by itself as an alternative leak detection method for used oil USTs. Today's final rule allows the use of this alternative release detection method as the sole method of release detection for any petroleum UST with a capacity of 550 gallons or less. Manual tank gauging may be used in combination with periodic tank tightness testing on petroleum tanks with a capacity between 55 and 1,000 gallons. (These provisions are discussed in more detail in section IV.D. of this preamble.)

Today's final rule also provides an exemption from the rule's spill and overfill protection controls for USTs that are filled in small increments. (This is also discussed in more detail later in this preamble under spill and overfill prevention for new USTs.) The Agency agrees with the commenters that used oil USTs that are filled manually in small increments do not pose the same risk to human health and the environment from spills and overfills as other USTs.

The Agency received additional comments related to design standards and agrees with those who requested cathodic protection for new used oil tanks. In addition, EPA is requiring that owners and operators upgrade or replace their used oil USTs according to the time period of today's final rule (10 years). EPA disagrees, however, with the commenters who argued that these tanks should be subject to secondary containment. Because the physical and chemical characteristics of used oil are similar to petroleum products, the release detection and corrective action technologies should be similarly applicable to used oil. Thus, the final rule subjects used oil USTs to the release detection requirements applicable to petroleum UST systems rather than secondary contaminant required for hazardous substance UST systems.

h. Airport Hydrant Fueling Systems. A number of commercial airports and airports at Department of Defense bases use hydrant fueling systems. These systems generally consist of one or more bulk storage tanks that may be either below or aboveground and that are connected by underground piping to various aircraft fueling locations on the airport. Hydrants, otherwise known as fuel dispensers, are connected to the pipe networks and dispense fuel into aircraft. These systems are, in some cases, very large in size and contain great volumes of fuel. Many airports have miles of piping, which is typically 8 to 24 inches in diameter, and the total capacity of the systems can be many millions of gallons.

Through a brief investigation of these systems, the Agency believes that some of these systems do not meet the statutory definition of an UST system, and are thus outside of the jurisdiction of Subtitle I. Hydrant systems that have aboveground storage tanks are not regulated tank systems unless 10 percent or more of the capacity of the system is in the belowground pipelines.

However, hydrant systems with belowground storage tanks and those with aboveground storage tanks but whose pipelines account for 10 percent or more of the system's capacity are within to Subtitle I jurisdiction as UST systems. The special problems posed by requiring hydrant systems to meet many of the requirements in today's final rule have motivated the Agency to look further at these systems, and have led to today's deferral of regulations for these systems.

The Agency continues to examine questions regarding the construction, operation, maintenance, and monitoring of hydrant systems. Preliminary information indicates that hydrant systems typically have cathodic protection, and are monitored for leaks on a daily, monthly, and annual basis. Inventory monitoring is often used, but the sensitivity of this technique is very limited due to the large volume these systems typically handle. No single leak test, however, appears to be an industry standard.

Since proposal, the Agency has become aware of several leak incidents from hydrant systems that resulted in environmental damage. Because of limited information on this subject, however, the Agency is unclear about the extent of this problem. In addition, to the nature of these systems, especially the typically large amount of piping, certain requirements in today's rule (such as leak detection for piping systems) may not be feasible for hydrant systems. For these reasons, the Agency is deferring regulation of Subparts B, C, D, E and G for all airport hydrant systems, including the underground tank portions of those systems, to allow more time to gather information.

i. Backup Diesel Tanks at Nuclear Facilities. Following publication of the proposed regulations, a commenter raised the issue of the applicability of the UST regulations to tanks at nuclear power plants that store diesel fuel for use in emergency situations. According to the commenter, these tanks are already extensively regulated by the Nuclear Regulatory Commission (NRC), and further regulation by EPA could result in an overly burdensome program if the regulations were inconsistent. Not only would these nuclear facilities be required to meet dual regulatory programs, but structural changes to the systems as a result of the UST regulations could result in an amendment to the plant's license, according to a commenter. The commenter also pointed out that any shutdown of the backup fuel system (e.g., for retrofitting) could result in the entire nuclear power plant being shut down.

The Agency is today deferring the requirements of Subparts B, C, D, E and G for these tanks pending completion of a review of the NRC regulations (10 CFR 50 Appendix A) governing these tanks to determine whether further regulation is necessary to protect human health and the environment or would be inconsistent with NRC regulations for proposes of section 1006. If this research indicates that the NRC regulations are not adequate or are not as complete as the UST regulations, EPA may require these tanks to be subject to Subtitle I regulations, or it may develop a separate set of standards applicable to this class of tank.

j. UST Systems Associated with Emergency Generators. In today's rule, EPA is deferring Subpart D requirements for UST systems associated with emergency power generators. Such tanks are common in the telephone industry and the electric utility industry. These tanks often store diesel fuel which serves as a source of backup power in remote locations (for example, at telephone switching locations). This is a deferral of the release detection requirements only; owners and operators of these systems must comply with all other subparts of this rule.

Several commenters argued that these tanks should not be regulated at all for the following reasons: they are generally small in size (typically under 500 gallons); most are less than 5 years old; they are often at unmanned stations in remote locations; they contain diesel fuel, which is less mobile than gasoline due to its higher viscosity; and many are filled only annually.

The Agency does not agree that these reasons merit an exclusion from the UST regulations. The requirement that these tanks be monitored each month is unworkable, however, because they are often located in remote areas and are visited very infrequently. Therefore, EPA is deferring Subpart D requirements for these tanks to allow time to develop workable release detection requirements for these tank systems.

4. Definitions

The following sections address many of the terms that are used in the statutory language and elsewhere in the final regulations. Since proposal, many terms have been redefined or clarified as a result of comments. The following sections contain the revised definitions, the rationale for the changes, and the Agency's interpretation of these terms.

a. Definitions of Terms in the Statute. (1) Underground Storage Tank. Underground storage tank is defined in the statute as any one or a combination of tanks (including underground pipes connected thereto) that is used to contain an accumulation of regulated substances, and the volume of which (including the volume of the underground pipes connected thereto) is 10 percent or more beneath the surface of the ground.

Today's rule sets forth the following definitions for terms used in the statutory definition of underground storage tank:

(a) Tank is a stationary device designed to contain an accumulation of regulated substances and constructed of non-earthen materials (e.g., concrete, steel, plastic) that provide structural support.

Several commenters stated that the definition of tank in the proposed rule was too broad, and included devices that do not store regulated substances but rather use, treat, collect, or capture regulated substances. By expanding the scope of tank beyond just storage tanks, say the commenters, EPA departed from its Congressional mandate and created a program that is overly inclusive and difficult to manage. The commenters also argued that the inclusion of hydraulic lift tanks, electrical equipment, oil-water separators, sumps, treatment tanks, and other devices not normally regarded as storage tanks would overwhelm the Agency's ability to adequately enforce the regulations. Also, the added burden of regulating these devices would be disproportionate to their potential environmental harm. Few of these devices have documented leak histories, according to the commenters.

Throughout the development of the UST regulations, where there has been ambiguity in the terms defining the jurisdiction of the Subtitle I program, it has been the Agency's policy to define the scope of the UST regulations broadly and interpret the exclusions relatively narrowly. By taking this approach, the Agency hoped to avoid prematurely eliminating from its jurisdiction tanks that may pose an environmental threat. This policy has afforded the Agency the opportunity to gather more information on the various classes of tanks in the potential regulated universe. EPA has retained the prerogative to narrow the scope of the program by regulation rather than statutory interpretation, taking into account potential environmental and health risks, implementability, and administrative burden. The Agency decided that this approach would result in a program that provides maximum protection to human health and the environment while taking into account the regulatory burdens associated with the program. Further explanation of these regulatory exclusions is found earlier in this preamble under IV.A.2. Regulatory Exclusions, many of which deal with precisely those tanks about which commenters expressed concern.

Accordingly, EPA disagrees with commenters who argued that EPA's definition of "tank" results in an unauthorized expansion of its regulatory program under Subtitle I. Although EPA acknowledges that this program includes only "storage" tanks, Congress defined "storage" in section 9001 of RCRA as "containing an accumulation of regulated substances." EPA's interpretation of the Subtitle I jurisdiction to encompass any devices holding an accumulation of any regulated substances (unless subject to a statutory exclusion) is thus not inconsistent with the statute. Moreover, this definition is the same as that which has been used in the Subtitle C tank program for years.

(b) Underground pipes connected thereto means all underground piping, including valves, elbows, joints, flanges, and flexible connectors attached to a tank system through which regulated substances flow. For the purpose of determining how much piping is connected to any individual UST system, the piping that joins two UST systems should be allocated equally between the systems. Tanks that are simply manifolded together are considered as one UST system. However, if an exempt tank is connected by piping to a regulated tank, half of the piping is allocated to each tank system. This allocation of connected piping is an attempt to reconcile two conflicting statutory provisions: section 9001(1) states that an UST system includes the tank and all underground pipes connected thereto but also states that a statutorily excluded UST system also includes all of the piping connected to it. As a result, half of the piping is allocated to the regulated tank system and half to the excluded tank system if two are connected.

In the RCRA Subtitle C tank rules, the starting point of the "connected piping" is the point at which the contained substance is initially considered to be a hazardous waste. It should be noted that the above terms as they apply here, while similar, are different than the Subtitle C definition.

(c) Regulated Substance. Today's definition of "regulated substance" in the final rule codifies the statutory definitions of "regulated substance" and "petroleum" and provides additional clarificati on concerning the coverage of certain substances and mixtures of these substances under the regulations.

(i) Overview. In the April 17 proposal, the Agency codified the statutory definition of regulated substance. Thus, "regulated substance" was defined to include: (1) any substance listed under section 101(14) of CERCLA, except those regulated as hazardous waste under Subtitle C of RCRA; and (2) petroleum, including crude oil or any fraction of crude oil that is liquid at standard conditions of temperature and pressure. The term "petroleum" was also separately defined as crude oil, crude oil fractions, and refined petroleum fractions including gasoline, kerosene, heating oils, and diesel fuels. The proposal addressed mixtures of petroleum and any hazardous substance with a "50 percent rule," and under which, for example, an UST system containing a mixture that was 50 percent or more petroleum was proposed to be a "petroleum UST system."

In the Supplemental Notice of December 23, 1987, the Agency proposed further clarification of these definitions by requesting public comment on a specific list of substances and blends that would be subject to the petroleum UST requirements. This list was intended to be comparable to the list of CERCLA hazardous substances (not including hazardous wastes). Thus, an owner or operator would have to comply with the UST regulations only if one or more of the stored substances were on either of the two lists of regulated substances. The proposed list of petroleum substances would also be used to determine, for purposes of release detection requirements, if a substance would be regulated as a petroleum UST system.

The few comments the Agency received about the proposed definition of regulated substance asked for further clarification of the term petroleum. The commenters' concern was whether the release detection requirements for new hazardous substance USTs (i.e., secondary containment), or those for new petroleum USTs, applied to particular substances. EPA also received numerous comments on the proposed list of petroleum substances contained in this Supplemental Notice. In general, most commenters expressed preference for this proposed list because it was more specific and clarified which substances had to meet the release detection requirements for petroleum USTs. However, some other commenters questioned this approach because of the difficulty in preparing a complete list and the loss of flexibility such a specific list would entail as the composition of petroleum products changed over time. Numerous commenters provided suggestions for adding or deleting specific substances from the list.

In today's final rule, the proposed list of petroleum substances in the Supplemental Notice is not used, although the general categories from the list have been included in the final definition of regulated substance. Thus, the definition of regulated substance retains the statutory language that was originially proposed, except that it has been revised to reference the petroleum refining process and include a list of seven basic categories of petroleum or petroleum-based substances considered by EPA to be "regulated substances." This addition to the federal definition is intended to respond to those commenters who requested more clarity about the scope of petroleum substances included within Subtitle I jurisdiction. The final rule also includes definitions for hazardous substances UST systems and petroleum UST systems for the purpose of clarifying, as requested by some commenters, which regulated substances are subject to the secondary containment requirements for new USTs storing hazardous substances and which are subject to the release detection requirements for new USTs storing petroleum or petroleum products. (These terms and their use to discern how mixtures are treated are discussed in section IV.A.4.b.)

(ii) Revisions in the final rule and public comments on the proposal. In the final rule regulated substance is defined as: "(a) any substance defined in section 101(14) of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (but not including any substance regulated as a hazardous waste under Subtitle C), and (b) petroleum, including crude oil or any fraction thereof that is liquid at standard conditions of temperature and pressure (60 degrees Fahrenheit and 14.7 pounds per square inch absolute). The 'regulated substance' includes but is not limited to petroleum and petroleum-based substances comprised of a complex blend of hydrocarbons derived from crude oil through processes of separation, conversion, upgrading, and finishing, such as motor fuels, jet fuels, distillate fuel oils, residual fuel oils, lubricants, petroleum solvents, and used oils." In summary, the proposal's codification of the statutory definition of "regulated substance" has been retained in sections (a) and (b) of the final definition (see above). Also, the proposal's elaboration of the meaning of petroleum in a separate definition of the term has been deleted (see section (iii) below), but several general categories in that proposed definition have been listed in the final definition of regulated substance to respond to some commenters' requests for clarification of the scope of the substances covered by the regulations.

The first part of today's final definition of regulated substance (section (a)) refers to the specific list of substances (both chemicals and discarded chemical products) that are defined by regulation under CERCLA (see 40 CFR Part 302). The Subtitle I program covers all hazardous substances except those that are hazardous wastes. Few comments were submitted concerning this list or section (b) of the proposed definition (the statutory definition of petroleum). The two questions raised in most public comments were (1) whether the storage of a particular substance was regulated under Subtitle I, and (2) what release detection was required for new UST systems storing a particular substance (see section (iii) below).

EPA originally proposed to define petroleum as crude oil, any fractions of crude oil and refined petroleum fractions, such as gasoline, kerosene, heating oils, and diesel fuels. In the Supplemental Notice to the proposal, EPA requested comment on the appropriateness of adding to the definition a specific list of substances that was based on the fundamental petroleum refinery process. Many commenters agreed with the proposed use of the crude oil separation processes as the basis for determining which substances should be subject to petroleum UST standards. However, others believed that basing the definition of petroleum strictly on the steps in the separation process was inappropriate. These commenters pointed out that this approach could result in similar substances being regulated differently, such as unleaded motor gasoline being considered a petroleum substance and leaded motor gasoline a hazardous substance because lead is added in steps subsequent to basic separation processes. Other commenters pointed out the difficulty in determining the exact point in the refinery process at which a substance is considered petroleum and at which point it becomes a chemical product distinct from petroleum.

In the refinery process, separation involves two steps: atmospheric and vacuum distillation. Heat is applied to crude oil, which separates into individual fractions because of differences in boiling points or boiling ranges. Some of these fractions can be used directly from a distillation tower; however, many of the products must go through further treatment. This treatment is known as conversion, which includes such processes as hydrocracking, catalytic cracking, coking, and alkylation. These processes are used to change the molecular weight and boiling ranges of the fractions. Upgrading is the process of improving the quality of the petroleum fraction by removing sulfur, nitrogen, and oxygen. The heating involved with this process adds stability and removes waxes, allowing lower pour points. Finishing does not mean distillation to pure chemical products, but is the final step before a petroleum product is sold at retail. An example of finishing is the addition of certain chemicals to motor gasoline. Additives may include octane enhancers, which either raise or lower octane ratings, dyes for product identification by color, and detergents that remove deposits from engines. These additives may be listed hazardous substances. The complexity of this process, the variety of chemical products produced, and the variety of chemical additives mixed with petroleum products in the refinery process has led to some confusion about which substances are "petroleum" or "hazardous substance" under Subtitle I.

To overcome this confusion and respond to comments received on the proposal, the final rule does not include a separate definition of petroleum. Instead, the final rule language for "regulated substance" has been amended to clarify what petroleum and petroleum-based substances, hazardous substances, and mixtures are within the regulated universe.

The final definition of regulated substance has been revised to refer to products from the refinery process, and it lists seven general categories of petroleum and petroleum-based substances so that the breadth of the coverage of the regulations is clear. Each of these general categories in fact consists of many specific individual products or substances. By not individually listing these different products and grades, EPA intends that any future adjustments in specific product composition (for example, changes made to respond to market demands) will not affect the product's classification as a "regulated substance." These seven categories correspond to the major categories in the list of petroleum substances and mixtures proposed in the Supplemental Notice. Nearly all petroleum products in use today are included in the seven categories listed in the definition. The general reference in the definition to the products from the refining process (discussed above) will aid in identifying the remaining unlisted regulated substances. Under this approach, EPA will not need to continually update the list (for example, motor gasolines is a category of regulated substance now and in the future, although new blends of motor gasoline, such as "mid-grade," may be developed or new additives may be used).

The Agency believes that this approach will make it easier to determine the regulatory status of an individual substance or blend under Subtitle I and ease the implementation burdens on the UST owner and operator, and the implementing agency. Any owner or operator trying to determine whether a tank system contains "regulated substances" and is subject to Subtitle I requirements must first determine if the substance belongs to one of the seven general categories of regulated petroleum substances. If not, then the owner or operator next must determine whether the stored material is included within the production process and physical properties description for petroleum products. If not, then the owner or operator must finally determine whether the substance is listed as a hazardous substance under section 101(14) of CERCLA (see 40 CFR Table 302.4), except for those listed as "hazardous wastes" under Subtitle C of RCRA. If the substance has not met one of these three definitions, then it is not a regulated substance.

(iii) Petroleum. The proposed definition of petroleum has been deleted from the final rule. A separate definition of petroleum was not included in the final rule because now no regulatory distinctions are based solely on whether the stored substance is "petroleum" or a "hazardous substance." However, regulatory distinctions concerning the selection of release detection equipment are based on whether a new tank system is a "petroleum UST system" or a "hazardous substance UST system." All other technical requirements are the same for all UST systems storing regulated substances.

In response to commenters' concerns about how to determine what type of release detection is applicable to a new UST system, the final rules include definitions that distinguish between "petroleum UST systems" and "hazardous substance UST systems." Owners and operators of new petroleum UST systems may utilize a variety of release detection methods because petroleum or petroleum-based substance releases are more predictable in their fate and transport underground, create relatively well-known exposure risks, and are subject to more widely available release detection and corrective action technologies. For regulatory purposes, petroleum UST systems may store petroleum or petroleum-based substances, petroleum and de minimis hazardous substance mixtures (e.g., used oil), or hazardous substances with properties similar to petroleum products. Thus, the types of stored substances subject to the release detection requirements for new petroleum UST systems are somewhat broader in scope than what constitutes simply "petroleum." This is reflected in a revised definition of "petroleum UST system," which includes a replacement of the proposal's 50-percent rule for petroleum-hazardous substance mixtures with a de minimis rule. (See the discussion in section IV.A.4.b. concerning the definitions of "hazardous substance UST system" and "petroleum UST system.")

The Agency will continue to use the statutory definition of "petroleum" for purposes of the LUST Trust response program under section 9003(h). Except for the requirement that petroleum must be a liquid at standard conditions of temperature and pressure, the term has the same definition as the term "petroleum" defined under CERCLA sections 101(14) and 101(33). The Agency interprets these terms to include the same substances, i.e., crude oil and refined fractions of petroleum, including gasoline and diesel fuels. The term "petroleum" includes the inherent "hazardous substance" constituents in crude or refined oil but does not include contaminants present in or mixed with the petroleum. Under section 9003(h), the Agency may undertake or order corrective action with respect to a release of petroleum from an UST system. The response program, however, is not limited to UST systems containing solely petroleum but, rather, requires only that the release from the UST contain petroleum. Thus, petroleum-hazardous substance mixtures would also be subject to the section 9003(h) corrective action authorities. This is consistent with Congressional statements concerning the jurisdiction of the section 9003(h) program. (See H.R. Conf. Rep. No. 962, 99th Congress, 2d. Sess., p. 228 (1986).)

(d) A tank is 10 percent or more beneath the surface of the ground if its volume (including the volume of its connected underground piping) is 10 percent or more beneath the ground surface or otherwise covered with earthen materials.

This definition reflects the intent of the UST regulations to govern underground tanks that could leak directly into the ground undetected. Thus, the following types of tanks are included within UST jurisdiction: tanks that are underground; in-ground open-top tanks; and tanks that are above grade but are covered with earthen materials (for example, to comply with fire codes). Tanks that are above the ground surface and are covered with non-earthen materials are not included within the scope of this definition.

The phrase "so that physical inspection is precluded" has been removed from this definition since proposal. One commenter argued that this phrase could be construed to bring under the jurisdiction of the UST program any totally aboveground tank that is permanently covered or shielded from view (e.g., by insulation). EPA agrees with this commenter that such tanks, as long as their volume, including the volume of connected underground piping, is not 10 percent or more beneath the surface of the ground, are not the focus of this program and should not be subject to UST regulations. These tanks are not subject to the same corrosive forces as are underground tanks and may be more easily inspected visually than other belowground tanks.

Other commenters referred to aboveground tanks that are enclosed in concrete vaults and are surrounded by inert material such as sand or vermiculite. The commenters believed that these tanks should not be defined as USTs. Under the changes to this definition in today's rule, aboveground tanks surrounded by sand would be within the scope of these regulations, because sand is an earthen material and has the potential to create corrosion. Vermiculite is not considered an earthen material and would not promote corrosion, and, therefore, tanks that are covered by this material are not considered USTs.

The statute excludes nine types of tanks from the definition of underground storage tank. Eight of these nine types of exclusions are described below. The ninth, on septic tanks, is not discussed because no changes have been made to the proposal and no comments were submitted to EPA on this exclusion.

(2) Farm or Residential Motor Fuel Tank Exclusion. The first group of tanks excluded by the statute is "farm or residential tanks of 1,100 gallons or less capacity used for storing motor fuel for noncommercial purposes." Following are definitions for the key terms of this exemption.

(a) A farm tank is a tank located on a tract of land devoted to the production of crops or raising of animals, including fish. To be exempt from UST jurisdiction, a farm tank must be located on the farm property. "Farm" includes fish hatcheries, rangeland, and nurseries with growing operations.

"Farm" does not include laboratories where animals are raised, land used to grow timber, and pesticide aviation operations. Moreover, this definition does not include retail stores or garden centers where the product of nursery farms is marketed, but not produced. This definition, as promulgated, is unchanged from the proposal.

One commenter argued that tanks at golf courses are essentially the same as tanks at sod farms; both types are used to hold fuel in support of sod and turf development. For these reasons, the commenter contended, these tanks deserve to be included under the farm exemption. The Agency does not agree that the similarities between sod farms and golf courses merit inclusion of tanks at golf courses within the farm tank exclusion. The Agency does not believe the term "farm" under section 9001 of RCRA, reasonably interpreted, includes golf courses or other places dedicated primarily to recreational, aesthetic, or other non-agricutural activities.

(b) Motor Fuel in today's rule means petroleum or a petroleum-based substance that is motor gasoline, aviation gasoline, No. 1 or No.2 diesel fuel, or any grade of gasohol, and is typically used in the operation of a motor engine.

As originally proposed, motor fuel was defined as petroleum-based fuel used in the operation of an engine that propels a vehicle for transportation of people or cargo. In the general interpretation of this phrase, motor fuel was limited to motor gasoline and diesel fuel used in automobiles, trucks, and buses. Many commenters felt that gasohols should be added to the list of motor fuels, because alcohol-type fuels are an alternative energy source encouraged by many states such as California. Commenters also felt that the term motor fuel should not be restricted to vehicles used for transportation purposes because some motors are stationary engines. The Agency agrees that the proposed definition was unnecessarily restrictive.

The final rule lists five types of motor fuel that are typically used to operate motor engines. Gasohols are included as motor fuels because EPA agrees with public comment that these are commonly used as and understood to be motor fuels. The proposed language restricting "motor fuel" to fuels used in transportation has been deleted from the definition because the term "motor fuel" does not in itself describes a use of the fuel, but rather describes a type of fuel. The statutory exclusion already contains a "use" limitation by restricting the exclusion to motor fuels stored for "noncommercial" purposes.

Accordingly, today's final rule defines motor fuel in terms of specific types of fuel. The definition lists typical uses to give descriptive, not restrictive, information about these substances. The final rule thus includes fuels used in stationary motors. The structure of this definition parallels that of heating oils.

(3) Heating Oil Tanks Exclusion. The second group of tanks excluded from UST jurisdiction by statute are tanks used for storing "heating oil for consumptive use on the premises where stored." Following are definitions for key terms of this exclusion:

(a) Heating Oil means petroleum that is No. 1, No.2 , No. 4-light, No. 4-heavy, No. 5-light, No. 5-heavy and No. 6 technical grades of fuel oil; other residual fuel oils (including Navy Special Fuel Oil and Bunker C); and other fuels when used as substitutes for one of these fuel oils. Heating oil is typically used in the operation of heating equipment, boilers, or furnaces.

The proposed rule defined heating oil as either one of eight technical grades of fuel oil (No. 1; No. 2; No. 4-light; No. 4-heavy; No. 5-light; No. 5-heavy; No. 6; and residual) or fuel oil substitutes such as kerosene or diesel when used for heating purposes. This definition has been revised in the final rule to clarify which technical grades of fuel oil the Agency believes are heating oil. In addition, the definition has been revised in response to comments on the use of heating oil substitutes.

The list of grades of fuel oils has been reworded because, since proposal, the Agency has discovered that "residual" is not a specific technical grade of fuel oil, but refers to several grades of fuel derived from certain operations in the refinery p rocess. Also, Navy Special Fuel Oil and Bunker C are included in the final definition as examples of residual fuels.

Several commenters suggested changes to the definition to modify the applicability of the heating oil exclusion to tanks storing fuel oil substitutes. Several commenters stated that both No. 2 diesel fuel and kerosene should be included as heating oil because their chemical makeup is similar to each other and No. 2 fuel oil. Additional commenters thought that the exclusion should not be limited to oil used for heating purposes. The Agency agrees that the heating limitation is inconsistent with the statutory language of the exclusion that limits "use" only by requiring "consumptive" use. The final rule definition, therefore, includes heating as a typical use of the fuels but does not limit the exclusion to fuels so used. The exclusion does, however, limit the use of substitutes to those situations where the substitute is actually used in place of one of the technical grades of fuel oil. For example, tanks that contain used oil at a typical retail gas station are not excluded unless the used oil is consumed on-site as a substitute for fuel oil (burned in an on-site space heater, for example). Tanks that store used oil awaiting recycling pickup are not heating oil tanks. Another example of a tank that is not a heating oil tank is one that stores diesel fuel for an on-site motor generator. Even though diesel fuel is sometimes burned in boilers as a substitute for heating oil, it is the fuel of choice for internal combustion engines. It is, thus, not a substitute for one of the technical grades of heating oil in this situation.

Thus, heating oil is defined in the final rule in terms of specific grades of oil or their substitutes. A sentence has been added to the definition listing typical uses of heating oil. This list provides descriptive, not restrictive, information about these substances and parallels the definition of motor fuel.

(b) Consumptive use means used on the premises. Accordingly, this exclusion applies to tanks at residential, commercial and industrial facilities storing heating oil that is used at the same site. The heating oil exclusion does not apply to the storage of heating oil for resale, marketing, or distribution.

In the preamble to the proposed rule, EPA stated that "consumptive use" was not intended to be limited to only space heating purposes, and described other uses of heating oil that would qualify for this exclusion. This definition has been modified since the proposed rule to clarify that tanks holding heating oil for any on-site use, such as heating or to power a generator, are exempt from regulation.

Several commenters supported this interpretation of consumptive use. Heating oil used to produce steam, process heat, electricity, and emergency power were among the consumptive uses that the commenters thought should be included in the heating oil exclusion. Today's definition clarifies that these uses are within the scope of this exclusion.

Several commenters argued that tanks storing diesel fuel for use in emergency generators should be exempt as tanks storing heating oil. As explained above, no restrictions are being placed on the use of the heating oil under this exclusion, except that it be used consumptively on-site.

(c) On the premises where stored means tanks located on the same property where the stored heating oil is used. Tanks are excluded as long as the oil is stored anywhere on the same property. "On the premises" is not limited to the building where the heating oil is stored. Thus, centralized heating units using heating oil that serve more than one building on the same property would be excluded.

In addition, several commenters provided suggestions that would result in narrower interpretations of this exclusion by regulating one of the following segments: all residential and commercial tanks; all commercial tanks; all tanks at commercial and government buildings; all residential buildings of six or more units; or all tanks above a certain size. The Agency recognizes the concerns expressed by these comments but believes that the statutory language prevents adoption of such suggestions. Under the statute, the exclusion of heating oil tanks is not limited to certain categories of heating oil tanks (e.g., only residential or only tanks less than 1,100 gallons). Congress did recognize, however, that heating oil tanks may require some regulation and required that EPA study this universe of exempt tanks and make recommendations concerning regulation (section 9009).

(4) Pipeline Facilities Exclusion. The fourth exclusion covers "any pipeline facility (including gathering lines) (1) regulated under the Natural Gas Pipeline Safety Act of 1968 (49 USC App. 1671, et seq.), (2) regulated under the Hazardous Liquid Pipeline Safety Act of 1979 (49 USC App. 2001, et seq.), or (3) which is an intrastate pipeline facility regulated under state laws comparable to the provisions of the laws referred to above.

"Pipeline facilities (including gathering lines)" include new and existing pipe rights-of-way and any equipment, facilities, or buildings used in the transportation of gas (or hazardous liquids, which include petroleum and any other liquid designated by the Secretary of Transportation) or the treatment of gas or designated hazardous liquids during the course of transportation.

The definition of pipeline facilities was adapted from the definition of that term as used in the Natural Gas Pipeline Safety Act of 1968 (NGPSA) and the Hazardous Liquid Pipeline Safety Act of 1979. "Pipeline facility" may also include any such intrastate facility as defined and regulated under state laws comparable to these two federal statutes. This definition includes sumps, drip tanks, skimmer pits, lubrication oil collection devices, and any other containers that are directly connected to regulated oil or gas pipelines or gas plants. This equipment would qualify as equipment used in the transportation of gas or hazardous liquid or the treatment of gas or hazardous liquids during the course of transportation.

One commenter pointed out that the definition of pipeline facilities in this rule differs from the definition which appears in the NGPSA. This commenter believed the Agency was mandated by Congress to adopt the definition from the NGPSA. The Agency intended that the definition that appears in these regulations mean the same as that definition that appears in NGPSA; the word changes were only for abbreviation. The Agency has retained the wording from the proposed rule.

(5) Surface Impoundments, Pits, Ponds and Lagoons Exclusion. The fifth exclusion covers any "surface impoundment, pit, pond or lagoon." A surface impoundment is defined as a natural topographic depression, man-made excavation, or diked area formed primarily of earthen materials (although it may be lined with man-made materials) that is not an injection well.

Since the proposed regulations, this definition has been changed and no longer stipulates that the surface impoundment be designed to hold an accumulation of regulated substances. This phrase created confusion among commenters and was considered unnecessary.

(6) Storm-Water or Wastewater Collection Systems Exclusion. The sixth exclusion covers a "storm-water or wastewater collection system." A storm-water or wastewater collection system is defined as all piping, pumps, conduits, and any other equipment necessary to collect and transport the flow of surface water runoff resulting from precipitation, or domestic, commercial, and industrial waste water to and from detention areas or areas where treatment is designated to occur. The collection of storm water and wastewater does not include treatment except where incidental to conveyance.

This definition is substantially the same as the proposed definition, with one addition to clarify that treatment is not included as part of a collection system.

The Agency received several comments on the definition of a collection system and also on the applicability of the UST regulations to wastewater treatment tanks. In general, the commenters were critical of any attempt by the Agency to define collection system so that treatment tanks, including oil-water separators, would be regulated. The various reasons and arguments used by commenters are discussed below.

Several commenters stated that treatment tanks are logically included as part of the collection system, and that Congress intended to exclude the tanks from these regulations. The word "system" implies that everything related to the collection of storm water and wastewater, including piping and tanks, should be excluded, according to commenters.

Two commenters stated that it is illogical to exclude the pipes and pumps of a collection system but not the treatment tanks. The sole purpose of these tanks, one commenter pointed out, is to reduce the degree of contamination of the water and lessen the threat of environmental harm. Another commenter stated that regulation of wastewater treatment tanks would penalize those who pretreat at the request of a POTW, and regulation may discourage on-site treatment. Both comments disagreed with any attempt to regulate these tanks. Several commenters argued that treatment tanks, and in particular oil-water separators, should be excluded because they are flow-through process tanks. Several commenters believe that treatment tanks are already regulated under other federal laws, including the Clean Water Act and the Safe Drinking Water Act. Further regulation under Subtitle I would be unwarranted and unnecessary, according to the commenters.

EPA does not agree with commenters who argued that a collection system includes tanks where treatment is designated to occur. Collection and treatment are separate and distinct functions. The Agency continues to believe that the collection system includes all piping, pumps, and conduits that extend to and from areas where treatment is designated to occur.

The Agency does not believe that it is illogical to regulate wastewater treatment tanks, although their purpose is to lessen the concentration of regulated substances in the water. Such tanks serve as receptacles for regulated substances, and may leak as any other tanks may leak, with adverse results. To categorically exclude all such tanks from regulation may risk environmental damage.

EPA also does not agree with commenters who argued that treatment tanks, particularly oil-water separators, should be classified as flow-through process tanks and therefore excluded. Treatment tanks do not form part of a production process, so they cannot be classified as flow-through process tanks.

EPA does agree, however, with the commenters who argued that some wastewater treatment tanks are adequately regulated by other federal regulations. After reviewing the comments, EPA has decided not to regulate any wastewater treatment tanks that are part of a wastewater treatment facility that is subject to regulation under either section 402 or 307(b) of the Clean Water Act. The primary reason for this decision is that, because such tanks are already subject to regulation under the CWA, additional regulation under Subtitle I is unnecessary to protect human health and the environment. Other wastewater treatment tanks may be excluded because they contain only de minimis concentrations of regulated substances. Wastewater treatment tanks that are not subject to regulation by the CWA sections 402 or 307(b) and that contain greater than de minimis concentrations of regulated substances will continue to be deferred from regulation. This deferral reflects the Agency's uncertainty regarding the nature of these tanks and the appropriateness of the UST regulations to wastewater treatment tanks. More discussion on wastewater treatment tanks is provided under that heading in section IV.A.3.

(7) Flow-Through Process Tank Exclusion. The seventh exclusion covers any flow-through process tank. Under today's final rule, a flow-through process tank is a tank that forms an integral part of a production process through which there is a steady, variable, recurring, or intermittent flow of materials during the operation of the process. Flow-through process tanks do not include tanks used for the storage of materials prior to their introduction to the process or for the storage of finished products or by-products from the production process.

Today's definition differs from the proposed definition in several respects. This exclusion now applies to tanks that are a part of a production process, rather than to tanks that are part of an industrial or commercial process. It now applies not only to tanks with steady or uninterrupted flow, but also to tanks with variable, recurring, or intermittent flow. The exclusion also now applies to tanks that hold intermediates.

The scope of the flow-through process tank exclusion has been one of the most difficult to define and most controversial interpretative issues, due to the lack of legislative guidance and a commonly understood technical meaning, as well as the potential for the exclusions, broadly interpreted, to encompass nearly all of the UST universe.

Although the definition of the terms "flow-through" and "process" have undergone several changes since EPA's first interpretation in the April 1986 guidance, these changes have been intended to clarify the Agency's interpretation of the scope of the exclusion and not to fundamentally alter that interpretation. EPA believes that this exclusion encompasses tanks that are an integral part of a production process and through which materials flow during the operation of that process. Application of leak detection or other tank standards to such tanks would generally be difficult to implement and potentially disruptive to vital production processes. The changes to this definition since the April 1986 guidance have resulted from comments on the April guidance, on the proposed definition, and on the Supplemental Notice. These comments are discussed below.

The original definition of this term that appeared in the April 1986 guidance document defined flow-through process tank to include any tank that was part of a "manufacturing" process that had "steady or uninterrupted flow." The original definition did not refer to tanks that held intermediates. This definition was thought by many commenters to be too restrictive in two respects: they stated that not only manufacturing tanks but also other industrial and commercial tanks should qualify; and that the requirement that the flow be steady would mean many tanks that operate in a batch fashion outside the scope of this exclusion.

The Agency agreed to some degree with these early commenters and, thus, included in the 1987 proposal a different definition than the one that appeared in the 1986 guidance. The proposed definition applied to "industrial and commercial" tanks, rather than to "manufacturing" tanks. The definition continued to restrict this exclusion, however, to tanks with a "steady or uninterrupted" flow of materials but added "during the operation of the process" in an attempt to accommodate commenters' concerns regarding batch processes. The proposed definition also stipulated that tanks that stored intermediates were not flow-through process tanks.

In the proposal preamble, the Agency expressed concern over what types of tanks would qualify as "flow-through process tanks" if the definition were expanded to include non-steady flow. Specifically, EPA was concerned that tanks at gasoline stations, airports, rental car agencies, and other such "commercial" locations could be construed to be flow-through process tanks if the flow of materials was allowed to be recurring. Thus, such an interpretation could exclude most tanks from the regulated UST universe. These concerns, in part, led to the issuance of a supplemental notice requesting comments on clarifying "process" to mean "production process" rather than "industrial and commercial process" as proposed in April 1987.

Several commenters addressed the issue of the types of facilities where flow-through process tanks may be located, in response to requests for comments in both the proposed rule and the supplemental notice. Comments in response to the proposed definition showed general agreement with the change (since the April guidance) to "industrial and commercial" from "manufacturing." One commenter stated that no qualifiers should be included on the term "process." Examples of non-manufacturing processes given by one commenter included oil and gas production, gas processing, wastewater collection and treatment, and recycling tanks. Other commenters suggested that hydraulic lifts, oil-water separators, and electrical equipment should be flow-through process tanks.

Several commenters supported the change proposed in the Supplemental Notice to "production process" from an "industrial or commercial process." According to commenters, this change "makes sense," "is in accordance with Congressional intent," and "clarifies that storage tanks are not flow-through process tanks." Several commenters, however, argued that the change to "production process" would be a narrowing of the exclusion that is not supported by Congressional intent. This change would also not be easier to implement, according to one commenter. One commenter suggested that flow-through process tanks used in the distribution of electric power were an example of a flow-through process tank that is clearly "industrial or commercial process," but is not necessarily "production." Another commenter stated that "production" implies a tangible good is produced, and thus a "production process" is no different than a "manufacturing process." Specifically, this commenter referred to tanks in the dry cleaning industry, which would be outside the scope of this exemption if a tangible good was required to be produced.

With respect to the interpretation of the term "flow-through," several commenters believed that the requirement that the flow be steady or uninterrupted (during the operation of the process) was too restrictive, and would result in the regulation of many tanks that the commenters believed qualify for this exclusion. For example, these commenters pointed out that many tanks in a process stream are batch tanks, where the flow of materials is recurring or interrupted. Such tanks are common in the chemical industry. The commenters also cited process tanks with variable flows, for which there is no flow some or most of the time, as examples of the type of tank that should be included in this exclusion.

The preamble to the proposed rule discussed allowing tanks that have an interruption in steady flow due to periodic maintenance or emergency shutdown to remain within the scope of this exclusion. The proposal preamble also stated that if a flow-through process tank regularly stores materials during period of interruption, it is a storage tank and not a flow-through process tank. Several commenters stated that tanks that "store" substances under these circumstances should still qualify for this exclusion because it may not be possible to remove all the material from the tank, and that this requirement seemed to imply that these tanks must be completely empty when the process was not in operation.

In the proposal preamble, the Agency also asked for comments on whether "integral to the process" would include governmentally required wastewater treatment tanks that are a necessary part of the industrial or commercial process. Several commenters stated that wastewater treatment tanks, including oil-water separators, should be considered flow-through process tanks because treatment of wastes is a process and is an integral part of any facility. One commenter stated that oil-water separators should not be considered flow-through process tanks because they are covered in UL 1316.

The discussion of flow-through process in the proposal preamble stated that tanks that store intermediates were not flow-through process tanks. Several commenters argued that tanks storing intermediates are a necessary part of the process in order for the process to be conducted safely and to allow for an adequate supply of raw materials to be used in batch-operated processes. They further stated that intermediate tanks store materials on a very temporary basis and consequently do not pose the same hazards as a tank that is in use at all times.

EPA also requested factual information, in particular process diagrams, indicating what tanks should be excluded as flow-through process tanks, given the nature of the specific process and function of the tank. One commenter provided the following examples: holding tanks; feed tanks; mixing tanks; tanks that hold materials being cut in concentration; and other tanks in the process train.

As discussed above, the definition of flow-through process tank as promulgated today is different in several respects from the proposed definition. The major differences are: the substitution of the phrase "production process" for "industrial or commercial process"; the change to "steady, variable, recurring, or intermittent" flow from "steady or uninterrupted" flow; and that tanks storing intermediates are now included as flow-through process tanks.

With respect to the interpretation of the term "process," the Agency agrees with those commenters who supported the change to "production process" from "industrial and commercial process," and is incorporating that phrase into the definition of flow-through process tank. EPA does not agree with commenters who argued that this wording is an unauthorized narrowing of the interpretation of this term. In response to the commenter who stated that the word "production" implies "making" or "manufacturing," and that the phrase "production process" would then be interpreted as "manufacturing process," the Agency does not intend to limit this exclusion only to manufacturing processes. Rather, any process at manufacturing, commercial, or industrial facilities where a tangible good or service is produced or performed may be considered a production process. Production processes include a wide variety of facilities and processes, including many at petroleum refineries, chemical manufacturing facilities, and automobile assembly plants. EPA does not agree, however, that "process" should be unqualified. Allowing the interpretation of this term to be unrestricted could result in an unreasonable interpretation of this exclusion, which, in effect, removes virtually all tanks from UST regulation since a tank related to any process through which there is a periodic flow of materials describes most storage tanks.

The Agency has changed its previous definition to allow steady, variable, recurring, or intermittent flow. Based on comments received on the proposed rule, the Agency realized that the revised definition did not effectively include batch process tanks, contrary to the Agency's intention, because batch processing can involve flows that are other than steady or uninterrupted during the operation of the process. In addition, EPA limited "flow-through" to steady or uninterrupted flow, rather than "recurring" flow to avoid eliminating jurisdiction over tanks with periodic inflow and outflow, including UST systems at gasoline filling stations. The Agency now believes, however, that by allowing variable or recurring flow, but limiting this exclusion to production processes, this concern is no longer relevant. Tanks that do form a part of a production process are often operated in a batch fashion, where inflow and outflow are periodic rather than steady or uninterrupted. EPA believes that the inclusion of such tanks is consistent with the intent of this exclusion, which is to preclude regulation of tanks that form an integral part of a production process.

Under the same rationale, EPA agrees with commenters that tanks that hold intermediates may be an integral part of a production process. Accordingly, tanks that store intermediates as part of a production process are flow-through process tanks. Similarly, the Agency agrees with the commenter who suggested that holding tanks, pulse tanks, feed tanks, mixing tanks, tanks that hold material being cut in concentration, and other tanks in the process stream are flow-through process tanks.

The Agency does not agree, however, that wastewater treatment tanks, including oil-water separators, are flow-through process tanks. These tanks do not form an integral part of a production process. Wastewater treatment tanks typically follow the production process, and in no way contribute to the production itself. Many of these treatment tanks, however, fall within the regulatory exclusion for tanks that are subject to CWA requirements or are excluded because they contain de minimis concentrations of regulated substances; wastewater treatment tanks that are not excluded are deferred from these regulations (see section IV.A.3.). For the same reasons, hydraulic lifts and electrical equipment, which commenters suggested should be defined as flow-through process tanks, are not. Hydraulic lift tanks and electrical equipment do not form part of a production process.

One commenter requested clarification on whether processes in service industries, specifically the dry cleaning industry, would qualify as "production processes." In the dry cleaning industry, the main "product," the cleaning of garments, is really a service. As stated above, EPA does not intend to restrict the phrase "production process" solely to industries where a tangible good is produced. Tanks that contain regulated substances that are integral to the dry cleaning process are eligible for consideration as flow-through process tanks. The tanks in dry cleaning machines, however, store regulated substances prior to their introduction to the cleaning process. Thus, these tanks are not flow-through process tanks.

(8) Liquid Traps or Gathering Lines Related to Oil or Gas Production and Gathering Operations. The eighth exclusion covers "liquid traps or associated gathering lines directly related to oil or gas production and gathering operations." The liquid trap exclusion refers to sumps, well cellars, and other traps used in association with oil and gas production, gathering, and extraction operations (including gas production plants), for the purpose of collecting oil, water and other liquids. Such liquid traps may temporarily collect liquids for subsequent disposition or reinjection into a production or pipeline stream, or may collect and separate liquids from a gas stream.

This exclusion applies only to traps and gathering lines, and does not include other storage tanks at oil and gas production sites. Similarly, although liquid traps are often used in activities other than oil and gas production, the only liquid traps excluded from UST jurisdiction under this provision are liquid traps used for the purpose of separating oil and gas liquids from water at oil and gas production facilities. Liquid traps used in conjunction with landfill methane gas production facilities are within this exclusion and would not be subject to UST jurisdiction. Liquid traps such as grease and oil traps at gas stations, however, are not within this exclusion.

Gathering lines are defined as any pipeline, equipment, facility, or building used in the transportation of oil or gas during oil or gas production or gathering operations.

Several commenters argued that EPA misinterpreted Congressional intent because the proposal preamble implied that this exclusion was limited to unused oil. The commenters suggested it should apply to both used and unused oil at oil and gas production sites. The Agency agrees with these commenters because this exemption is aimed generally at collection traps and gathering lines at oil and gas production facilities and does not distinguish between produced oil, used oil, or unused oil at those facilities.

Although many petroleum pipeline facilities are regulated under the Hazardous Liquid Pipeline Safety Act of 1979, and thus excluded from Subtitle I jurisdiction, tanks associated with gathering lines in rural areas are statutorily exempt from Department of Transportation regulations. Tanks associated with rural oil and gas pipelines, however, are exempted as "gathering lines" under this exclusion. Thus, tanks associated with rural pipelines that are not excluded from Subtitle I jurisdiction via the exclusion for pipeline facilities would be subject to this exclusion.

(9) Underground Areas Exclusion. The ninth exclusion covers "storage tanks situated in an underground area (such as a basement, cellar, mine working, drift, shaft, or tunnel) if the storage tank is situated upon or above the surface of the floor."

This exclusion applies to "underground rooms" in which tanks are located on or above the floor surface. The purpose of this exclusion is to remove from UST jurisdiction tanks that are technically underground but that also are, in a practical sense, no different from aboveground tanks. They are situated so that, to the same extent as tanks aboveground, physical inspection for leaks is possible. Thus, the requirement to be able to physically inspect the tank for leaks is consistent with the purpose of this exclusion.

Tanks located in a below-grade structural vault, cellar, basement, mine or other underground room would be included in this exclusion if the tanks sit upon or above the surface of the floor and there is sufficient space to enable physical inspection of the tank, but not necessarily the tank bottom. An underground tank that has a secondary containment system that allows physical inspection of the tank would also qualify for this exclusion.

b. Definition of Terms Used in the Regulations. In addition to the preceding definitions of terms that clarify the statutory exclusions in section 9001 of Subtitle I, the Agency is setting forth the following definitions of terms used in the rule. This section today contains several terms that were not defined in the proposed rule. These terms have been included today in response to requests from commenters or to clarify other terms used in today's rule. These terms include cathodic protection tester, dielectric material, maintenance, pipe or piping, repair, and upgrading. Several terms that appeared in the proposed rule do not appear in this section of the preamble because they are no longer defined in the final rule. These terms are discussed (along with comment summaries and responses) in section IV.D. of today's preamble and include interstitial monitoring, inventory control, secondary barrier, and tank tightness testing. Also, liquid trap is now defined and discussed in the statutory exclusion section in IV.A.1.

Finally, several terms have not changed, did not receive public comments since proposal, and thus are not included here: electrical equipment; operational life; overfill release; positive sampling, test, or monitoring results; release detection; and underground release. Explanations of these terms are found in the preamble to the April 1987 proposal.

(1) Aboveground Release. "Aboveground release" means any release to the surface of the land or to surface water. This includes, but is not limited to, releases from the aboveground portion of an underground storage tank system and aboveground releases associated with overfills and transfer operations as the regulated substance moves to or from an UST system.

Two commenters asked if the applicability of this term is determined by where the material escapes the UST or where it is eventually found. Commenters stated that a release from below the ground may eventually migrate to the surface, and a spill to the ground could infiltrate into the subsurface. The Agency has interpreted this term to apply to all leaks from the aboveground portion of an UST, including spills and overfills. The source of a leak, rather than its ultimate destination, is the determinant in assigning a leak to this category.

(2) Ancillary Equipment. "Ancillary equipment" means any devices including, but not limited to, such devices as piping, fittings, flanges, valves, and pumps, that are used to distribute, meter, or control the flow of petroleum or hazardous substances to and from an underground storage tank.

This definition has not changed since the proposed rule. Some commenters asked if certain equipment, such as aboveground meters and pumps, was considered to be ancillary equipment, and to what extent such equipment would be regulated. EPA has clarified the discussion of ancillary equipment in the section on release detection to address the commenters' concerns.

(3) Belowground Release. "Belowground release" means any release to the subsurface of the land and to ground water. This includes, but is not limited to, releases from the belowground portions of an underground storage tank system and belowground releases associated with overfills and transfer operations as the regulated substance moves to or from an underground storage tank.

This definition is slightly different from the proposed rule, which contained different definitions for this term in the preamble and the rule. EPA has adopted the more general definition set forth in the proposal preamble. The definition in the final rule has also been clarified by substituting the term "regulated substance" for "petroleum" to include all regulated UST systems.

(4) Cathodic Protection. "Cathodic protection" is a technique to prevent corrosion of a metal surface by making that surface the cathode of an electrochemical cell. For example, a tank system can be cathodically protected through the application of either galvanic anodes or impressed current.

The phrase "for example" has been added to this definition since the proposed rule to emphasize that cathodic protection may be provided by either galvanic anodes or impressed current, but is not required to be one of the two. Any other technique that provides cathodic protection may also be used.

(5) Cathodic Protection Tester. "Cathodic protection tester" means a person who can demonstrate an understanding of the principles and measurement of all common types of cathodic protection systems as applied to buried or submerged metal piping and tank systems. This person must have education and experience in the measurement of cathodic protection of buried metal piping and tank systems. This definition was also added to the final rule in response to comments on the qualifications necessary for corrosion protection test personnel and is discussed in more detail in section IV.C.2. of this preamble.

(6) Compatible. "Compatible" means the ability of two or more substances to maintain their respective physical properties upon contact with one another for the design life of the tank system under conditions likely to be encountered in the UST.

One commenter suggested that the proposed definition, which based compatibility upon whether substances could maintain physical and chemical properties "upon contact with one another for extended periods of time and under varied environmental conditions (i.e., at different temperatures)," was ambiguous due to the phrases "extended periods of time" and "varied environmental conditions (i.e., at different temperatures)." The Agency agrees that these terms were vague and has replaced the phrase with "for the design life of the tank system under conditions likely to be encountered in the UST."

(7) Corrosion Expert. A "corrosion expert" is a person who, by reason of thorough knowledge of the physical sciences and the principles of engineering and mathematics acquired by a professional education and related practical experience, is qualified to engage in the practice of corrosion control on buried or submerged metal piping systems and metal tanks. This person must be accredited as being qualified by the National Association of Corrosion Engineers (NACE) or be a registered professional engineer who has certification or licensing that includes education and experience in corrosion control of buried or submerged metal piping systems and metal tanks.

As proposed, this definition required NACE certification. One commenter pointed out that NACE provides accreditation, not certification of corrosion expertise. NACE does in fact accredit and certify corrosion expertise. The final definition has been modified to take this into account. NACE also has recently introduced a certification program for cathodic protection specialists and cathodic protection testers.

Several commenters argued that the requirements for a corrosion expert were unnecessarily strict, and that their use would exclude many qualified people from work on UST systems. Many people, the commenters argued, did not have NACE certification or a professional engineering degree but were highly qualified based on their experience. The requirements of the definition (specifically, that a corrosion expert be accredited by NACE or have other types of licensing or certification) are not expected by EPA to exclude such qualified persons from work as corrosion experts unless they cannot satisfy the tests for accreditation. Thus, they are intended to provide some type of assurance to tank owners and operators, as well as implementing agencies, that a corrosion expert actually has achieved a minimum degree of expertise and experience needed to ensure corrosion is managed in a way that prevents leaks from UST systems and hereby protects human health and the environment. People who have attained the necessary qualifications through experience should be able to easily become NACE accredited.

(8) Dielectric Material. A "dielectric material" is one that does not conduct direct electric current. Dielectric coatings are used to electrically isolate UST systems from the surrounding soils. Dielectric bushings are used to electrically isolate portions of the UST system (i.e., tank from piping). This definition was added to the final rule in response to comments; see section IV.B.3.b. of today's preamble for further discussion of this issue.

(9) Excavation Zone. "Excavation zone" is defined as the volume containing the tank system and backfill material bounded by the ground surface, walls, and floor of the pit and trenches into which the UST system is placed at the time of installation.

The Agency has changed this term in the final rule from excavation "area" to excavation "zone" to indicate measurement in three dimensions.

(10) Existing Tank System. "Existing tank system" means a tank system used to contain an accumulation of regulated substance or for which installation has commenced on or before the effective date of this regulation. Installation is considered to have commenced if: (1) the owner or operator has obtained all federal, state, and local approvals or permits necessary to begin physical construction of the site or installation of the tank system; and (2) if either: (a) a continuous on-site physical construction or installation program has begun, or (b) the owner or operator has entered into contractual obligations--which cannot be canceled or modified without substantial loss--for physical construction at the site, or installation of the tank system, to be completed within a reasonable time.

Existing tanks that are converted from tanks storing non-regulated substances to tanks storing regulated substances after the effective date of the rules are considered "new tank systems" and are required to meet new tank standards.

One commenter stated that the language in the preamble to the proposed rule implied that UST systems that were permanently taken out of service or decommissioned before the effective date of the regulations are "existing tank systems." Tanks that have been taken out of service would not meet the definition of "existing tank system" if they contained no regulated substances. However, the definition of "existing tank system" is only relevant to the determination of when certain requirements must be met, not which requirements apply. Certain regulatory requirements apply to out-of-service tanks that were used in the past for the storage of regulated substances. Subpart G (§ 280.70) addresses out-of-service tanks, and this issue is addressed in section IV.G. of this preamble.

(11) Free Product. "Free product" refers to a regulated substance that is present as a non-aqueous-phase liquid (e.g., liquid not dissolved in water).

The proposal defined free product as "regulated substance in the non-aqueous phase (e.g., liquid not dissolved in water) that is beneath the surface of the ground." One commenter suggested that this phrase should include a non-aqueous phase regulated substance that is on surface water. The Agency agrees that this is free product and has modified the definition accordingly. Other commenters suggested that EPA clarify the definition to clearly exclude vapors from this definition. The Agency agrees that vapors are not free product and has added the term 'liquid' to the definition. Another commenter suggested a lower thickness limit of one-eighth of an inch be used as a cutoff; any layer of product with thickness lower than this should not be considered free product. The Agency does not agree with this concept because in some instances very thin layers may still be retrievable. The regulations require that free product must be removed to the maximum extent practicable as a part of the total site cleanup.

Other commenters suggested that the definition be modified to include a field criteria for use in corrective action. The Agency has chosen to not include this type of criteria because determining the presence of free product and the extent to which it can be removed depends on site conditions and the technology employed. EPA believes that it is preferable to leave this determination to the discretion of the implementing agency. This issue is discussed in more detail in section IV.F. of this preamble.

(12) Hazardous Substance UST System. "Hazardous substance UST system" means an UST system containing either (a) hazardous substances defined in section 101(14) of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (but not including any substance regulated as a hazardous waste under Subtitle C) or (b) any mixture of such substances and petroleum that is not regulated as a petroleum UST system. Thus, the final rule, in effect, defines a hazardous substance UST system as any UST system storing regulated substances which is not a petroleum UST system. It is essentially a catchall for any UST system for which the effectiveness of petroleum release detection and corrective action technology is uncertain. By contrast, in the proposed rule, a hazardous substance tank system was defined as a system containing an accumulation of hazardous substances or a mixture of such substances and petroleum in which hazardous substances comprise greater than 50 percent of the weight or volume of the mixture. The change from the proposed to the final definition eliminates the proposed 50-percent mixture rule for distinguishing tanks subject to the petroleum release detection requirements.

Many commenters agreed with the Agency's proposal in the Supplemental Notice that a substance not found on the petroleum list but listed under CERCLA should be regulated as a hazardous substance. Other commenters felt that if a hazardous substance was a constituent in petroleum, then that substance should be regulated like petroleum when it is stored in its pure form. Other commenters stated the converse argument: that because some hazardous substances are constituents in petroleum, then petroleum should be regulated as a hazardous substance.

The final rules distinguish petroleum and petroleum-based substances from other hazardous substances or mixtures for the purposes of determining which type of release detection requirements apply to new UST systems. UST systems storing petroleum, including its natural or refinery-added "hazardous substance" constituents (and stored materials with petroleum-like characteristics), are allowed to use a wide range of release detection methods in today's rule because petroleum has chemical and physical properties that make it highly detectable and amenable to a wide array of available corrective action technologies. A hazardous substance in its pure form, however, does not necessarily retain the same characteristics when it is a constituent in petroleum. Thus, the storage of such hazardous substances in new UST systems is governed by the release detection requirements for non-petroleum regulated substances, i.e., secondary containment. In the final rule, the determination of which type of release detection requirement is appropriate at an UST storing a regulated substance is not based on the Agency's interpretation of the definition of "petroleum" or "hazardous substance." (For further discussions of the differences between petroleum and hazardous substance USTs and their associated release detection requirements, see also section IV.D.2. on hazardous substance release detection, and section III.C.3. on alternative approaches to hazardous substance UST systems.)

In the proposed rule, an UST system was regulated as either a petroleum or hazardous substance UST system based on whether "petroleum" or "hazardous substances" were stored in the system. The problem of how to regulate a mixture of petroleum and hazardous substance was addressed in the proposed definitions of hazardous substance UST and petroleum UST by the "50-percent rule." A mixture of regulated substances was subject to either the petroleum UST system requirements or hazardous substance UST system requirements depending on which of these substances comprised more than 50 percent of the mixture. At proposal, the Agency thought this was a straightforward way to decide which release detection requirements for new UST systems were applicable to a mixture or blend of petroleum and hazardous substances. After proposal, however, the Agency became concerned that this approach would prove to be unworkable because of the difficulty of measuring constituent concentrations and the uncertainty of how to address constituents of petroleum that are also hazardous substances. In addition, there is not a single percentage value that is applicable to all mixtures and blends for determining when the substance will no longer be reliably detected by one of the release detection technologies allowed under the rule for petroleum USTs, and there is a wide variation in the degree of "hazardousness" among the many substances listed in section 101(14) of CERCLA.

For these reasons, in the Supplemental Notice, the Agency considered replacing the 50-percent rule with a specific list of all substances and blends of regulated substances that would be regulated under petroleum UST requirements. Any other blend or mixture of regulated substances would be subject to hazardous substance UST requirements. Many commenters supported the proposed 50-percent rule because it was clear and because it would be difficult to list all petroleum substances. Others supported the 50-percent rule approach but recommended alternative percent values ranging from 1 percent to 50 percent. Many commenters, particularly state agencies, supported the idea of a list because it would lessen the need for determining how to regulate a particular stored mixture, and thereby decrease the burden on the implementing agencies. It was also believed to give the owner and operator clear guidelines in determining the status of blends and, therefore, which release detection method to use. These commenters said that any percentage method would be cumbersome and difficult to enforce because it would be difficult to measure concentrations in the UST system.

After consideration of all of these comments, EPA concluded that neither a percentage rule nor a comprehensive list of petroleum or petroleum-based substances is a practical solution to the problem of how to determine which blends and mixtures of regulated substances must meet the release detection standards for new UST systems storing hazardous substances. (See the discussion concerning "regulated substance" in section IV.A.4.a. earlier in this preamble for the reasons why the Agency rejected the proposed comprehensive list approach.) The main drawback to the percent approach is the variability of a meaningful value. For example, 5-percent pesticide mixed in oil or 5-percent pentachlorophenol mixed in mineral spirits for application purposes should be stored in USTs with secondary containment and interstitial monitoring because of the high toxicity of these substances and the unavailability of highly effective corrective action technologies and release detection. In contrast, a hazardous substance such as methanol that is highly flammable as a pure product can be blended in relatively high proportions with motor gasoline and not change the flammable nature of the motor gasoline. It can be safely stored in a protected single-walled tank because release detection and corrective action technology are available for the petroleum-methanol mixture; and these methods are the same or very similar to those used for petroleum products. Thus, the appropriate percentage value to use in determining the release detection requirements that must be used at a new UST storing a mixture of regulated substances should be determined by the implementing agency based on a consideration of the following factors: the availability of reliable and sensitive release detection, the availability of effective corrective action technologies, and the inherent toxicity of the substance stored.

The final rule, therefore, does not contain a "50-percent rule" to determine how mixtures of petroleum and hazardous substances should be regulated. Rather, the final rule lists specific substances subject to the petroleum UST system requirements and uses a de minimis standard to determined when other mixtures of petroleum and hazardous substances are subject to petroleum UST system standards. A "petroleum UST system" is, thus, one which contains petroleum or petroleum and de minimis amounts of other regulated substances. Any other UST system is a hazardous substance UST system and must be provided with secondary containment or obtain a variance. The de minimis amount of hazardous substance mixed with a petroleum product is that amount in which the additional hazardous substance does not alter the detectability, effectiveness of corrective action, or toxicity of the petroleum to any significant degree.

(13) Hydraulic Lift Tank. "Hydraulic lift tank" means a tank holding hydraulic fluid for a closed-loop mechanical system that uses compressed air or hydraulic fluid to operate lifts, elevators, and other similar devices.

One commenter stated that the definition of this term in the proposal did not include elevator lifts. In response, the Agency changed this definition to include lifts that operate by compressed air or hydraulic fluid. This change properly includes all elevator lifts within the hydraulic lift definition.

(14) Implementing Agency. "Implementing agency" means EPA, or, in the case of a state with a program approved under section 9004 (or pursuant to a memorandum of agreement with EPA), the designated state or local agency responsible for carrying out an approved UST program.

As the definition states, section 9004 empowers the Agency to approve a state program to operate in lieu of the federal program. The state agency responsible for carrying out an approved program is the lead implementing agency for the UST program. A state may decide to work through designated local agencies to carry out the approved program. It is important to note that the local or state agency responsible for the enforcement of the UST regulations, particularly once the state program is approved, is expected to be an owner and operator's first contact in any situation involving a leaking UST system. The state and local agencies could then contact EPA if necessary.

(15) Maintenance. "Maintenance" is the normal operational upkeep to prevent an UST from releasing product. This definition has been added since proposal in response to requests by several commenters for clarification of this term. The comments and the use of this term are discussed further in section IV.C.2. of this preamble.

(16) New Tank System. "New tank system" means a tank system that will be used to contain an accumulation of regulated substance and for which installation has commenced after the effective date of this regulation.

Existing tanks that are converted after the effective date of this regulation from tanks storing non-regulated substances to tanks storing regulated substances are considered new UST systems and are required to meet new tank standards.

(17) Petroleum UST System. "Petroleum UST system" means an UST system containing petroleum or mixtures of petroleum with de minimis quantities of other regulated substances. Such systems include those containing motor fuels, distillate fuel oils, residual fuel oils, lubricants, petroleum solvents, or used oils.

In the proposed rule, a petroleum UST system was defined as a system that contained an accumulation of petroleum or a mixture of regulated substances and petroleum in which petroleum comprised greater than 50 percent of the weight or volume of the mixture. In the Supplemental Notice, the Agency proposed the development of a list of petroleum or petroleum-based substances subject to the petroleum UST system requirements. Based on public comment, however, the Agency has decided that it would be unworkable, time consuming, and largely unnecessary to specifically identify all possible petroleum products, petroleum-based substances, and mixtures of these substances with hazardous substances that should be subject to petroleum UST standards.

The definition for petroleum UST systems has been revised in two ways in the final regulation. The 50-percent rule for mixtures has been deleted and replaced with a limitation of non-petroleum regulated substances to de minimis levels. Use of this approach is intended to better determine if an UST system qualifies for the new petroleum UST release detection methods (see also definition of hazardous substance UST system). In addition, a list consisting of seven general categories of substances has been added to the petroleum UST system definition to more clearly identify the major types of petroleum and petroleum-based substances that may be stored in new protected single-walled tanks with release detection rather than only in UST systems that meet the secondary containment requirements. These categories are not substances that necessarily must be defined as petroleum under CERCLA, but instead are substances for which the Agency has determined single-walled tanks with cathodic protection and monthly release detection are adequate to protect human health and the environment. Other mixtures of regulated substances (for example, petroleum products mixed with non-indigenous hazardous substances or contaminated petroleum products) will have to be considered on a case-by-case basis by the implementing agency, using the de minimis rule. The EPA anticipates that few blends and mixtures will present interpretation difficulties. See part (12) of this section for an explanation of the application of the de minimis rule.

(18) Pipe or Piping. A "pipe" or "piping" is any hollow cylinder or tubular conduit that is constructed of non-earthen materials. This definition has been added since the proposed rule at the suggestion of a commenter (see sections IV.B.1. and IV.C.5. of this preamble for further discussion).

(19) Repair. "Repair" means to restore a tank or UST system component that has caused a release of product from the UST system.

This term has been added since proposal in response to public comments requesting additional clarification concerning the differences between repair, upgrading and maintenance. Refer to section IV.C.5. of today's preamble for further discussion of this issue.

(20) SARA. "SARA" means the Superfund Amendments and Reauthorization Act of 1986.

(21) Sump. This term has been deleted from the final rule.

Several commenters stated that this definition was ambiguous due to the inclusion of the term "temporarily." They suggested it be removed or that an actual time be substituted. The Agency agrees and has eliminated the definition from the final rule. This definition is no longer needed because the final rule no longer contains any requirements or provisions specific to sumps.

(22) Upgrade. An "upgrade" is the addition or retrofit of some portion of an UST systems, such as cathodic protection, lining, and spill and overfill controls, to improve the ability of the UST to prevent the release of product in accordance with § 280.21.

Although this term was not defined in the proposal, it has been added at the recommendation of commenters. Further discussion of upgrading is presented in section IV.B.3. of today's preamble.

(23) UST System or Tank System. "UST system" or "tank system" means an underground storage tank, connected underground piping, underground ancillary equipment, and containment system, if any. This definition has been changed to include within the UST system only underground ancillary equipment.

Two commenters suggested that the phrase "underground piping" be defined to exclude any non-wetted piping such as vent lines. EPA does not agree with the commenters. Because such "non-wetted" piping can contain regulated substances, particularly when the tank is overfilled, EPA believes that certain requirements in this rule are applicable to this type of piping. Clarification has been added in today's rule regarding which requirements are applicable to "non-wetted" piping.

(24) Wastewater Treatment Tank. "Wastewater treatment tank" means a tank that is designed to receive and treat an influent wastewater through physical, chemical, or biological methods.

This definition has been changed since the proposal so that it no longer includes only tanks regulated under the Clean Water Act. This term now refers to any tanks that are designed to treat wastewater. Of these, only some are regulated under the CWA. This change was required due to the different regulations for CWA-regulated and non-CWA-regulated wastewater treatment tanks.

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