Modeling of Storm Water Needs

In the 1996 CWNS, EPA used a model to estimate the SW (Category VI) needs. While SW represents a substantial part of the total water quality problem, few States have systematically documented their SW needs. EPA developed a model to help build a more complete picture of these needs.

What Are the Phase I SW Program Requirements?

Pollutants in SW discharges from urban areas are a significant source of degradation of the nation's waters. SW runoff can impair the beneficial use of water resources and pose health risks. Pollutants commonly found in SW runoff include pathogens, nitrogen, phosphorus, sediment, heavy metals, pesticides, herbicides, and synthetic organic compounds. Further, pollutants in SW runoff can deplete a waterbody's oxygen level. In addition to pollutants, the increased quantity of SW discharged from rapidly urbanizing areas also poses a threat to aquatic ecosystems by physically altering the receiving waterbody.

To help improve the quality of SW discharges, Congress amended the CWA in 1987 to add Section 402(p). This section directs EPA to establish phased NPDES permit requirements for SW discharges. Accordingly, EPA published the Phase I SW Program permit application requirements on November 16, 1990. These requirements applied to certain categories of SW discharges associated with industrial activity, and SW discharges from MS4s serving populations of 100,000 or more. At this time, EPA is evaluating the requirements for Phase II SW sources, generally covering those urban or urbanized areas with smaller populations.

MS4s that are covered by the Phase I SW Program regulations include: storm sewer systems located in incorporated places with populations of 100,000 or more; systems located in 47 counties identified by EPA as having populations of over 100,000 in unincorporated, urbanized areas; and systems that are designated by the EPA Administrator or the State. Those MS4s identified under the Phase I SW Program regulations were required to submit an NPDES permit application. Approximately 266 Phase I SW Program NPDES permits will be issued, covering about 850 municipal entities. A few small communities are included in the program because they are associated with larger systems or because they are designated by the State.

Part 1 of the permit application requires information about any existing SW management programs and what means are available for controlling pollutants in SW discharges. Part 1 also requires a field screening analysis of major outfalls to detect any illicit connections to the storm sewer system. Building on the Part 1 information, Part 2 of the permit application requires a limited amount of representative discharge characterization data, and a description of a proposed SW management program. EPA is committed to the goal that all Phase I municipal SW Program permits will be issued by the end of September 1997.

Section 402(p)(3) of the CWA specifies that Phase I SW Program permits must meet a new statutory standard that requires controls to reduce the discharge of pollutants to the maximum extent practicable. MS4 permits must also ensure compliance with State water quality standards. According to EPA's Interim Permitting Approach for Water Quality Based Effluent Limits in Storm Water Permits (August 1, 1996), SW permitsshould require MS4s to develop and implement site-specific SW management programs based on best management practice (BMP) requirements rather than numeric water quality-based limitations. While this policy applies only to EPA, the Agency also encourages States to adopt similar policies for SW permits. The NPDES permitting authority (EPA or the State) and the permittee under the Phase I SW Program will jointly develop components of an MS4 SW management program to provide for attainment of water quality standards.

What Are the Goals for SW in the 1996 CWNS?

For the 1996 CWNS, EPA used a two-pronged approach to estimate the SW needs. First, EPA obtained available technical data to estimate the documented needs. Second, EPA developed a model to generate national needs estimates. The goal for SW in the 1996 CWNS is both to estimate the SW needs for the 1996 CWNS and to build a base for future refinements and additions as better planning and cost information become available. In addition, the SW model for the 1996 CWNS was designed to reflect more accurately SW management costs under the Phase I SW Program, especially costs for structural controls and BMPs that may be eligible for SRF funding. Under the 1992 CWNS, only the costs of implementing NPDES municipal SW programs on a nationwide basis were estimated. For the 1996 CWNS, the model was expanded based on available information on SW controls and BMPs proposed in MS4 SW management programs to produce a refined estimate of both State-by-State and national SW needs.

The SRF-eligible portions of the Phase I SW Program consist of capital costs for developing and implementing municipal SW management programs. Capital costs include: construction costs for structural controls and BMPs; program development costs; and program implementation costs. Examples of the latter costs include: drafting new ordinances or regulations; preparing training materials and training staff; and producing public education materials.

What Is the Modeled Estimate for the 1996 Phase I SW Program Needs?

The modeled estimate of the SW needs is $7.4 billion. This represents only the estimated SRF-eligible portion of the costs that the MS4s are expected to incur to develop and implement a SW management program in response to the Phase I SW Program regulations. While not included in the model, O&M costs for the continued operation of MS4 SW management programs as well as O&M costs for SW controls and BMPs are significant. State-documented needs under the Program amount to $3.2 billion.

The distribution of modeled SW needs is depicted in Figure 4 in the "Key Results" section. A State-by-State tabulation is presented in Table A-4 of Appendix A.

What Cost Estimating Methodology Was Used?

The objective of the model was to estimate both State-by-State and national SW needs, but not to predict the needs for individual MS4s. Estimated needs for the Phase I SW program were modeled as follows:

• Develop decision rules based on climatic criteria to create a set of SW management approach groups representing broad climatic characteristics that determine the choice of SW controls or BMPs;
• Assign each MS4 to a SW management approach group by applying the decision rules based on climatic criteria to each MS4;
• Assign appropriate SW controls or BMPs to each SW management approach group;
• Estimate the scale of the applicable SW controls or BMPs for each MS4 in a SW management approach group;
• Use cost formulas, developed for each SW control or BMP, to estimate the capital cost during a 20-year period for each applicable SW control or BMP, for each MS4, in January 1996 dollars;
• Sum the costs of all the applicable SW controls or BMPs for an MS4 to estimate total capital costs; and
• Aggregate costs nationally and by State.

The model used to estimate the Phase I SW needs was peer reviewed by a panel of outside experts. Several points related to the O&M costs, estimated by the model, were raised by the peer review and did not affect the modeled capital needs presented in this report. The second major area receiving comment is that this report presents only one estimate of needs instead of a range. EPA agrees that, depending on the complexity of each individual SW problem and the variability of local circumstances, a range rather than a single estimate could be developed.

However, given the objective of the CWNS to estimate the needs for pollution control, one set of assumptions was selected for use in the report. If the model was to be used for economic analysis, then a number of assumptions would have been utilized to develop upper and lower cost bounds.

What Are the Limitations of the SW Cost Modeling?

The following types of costs were not included in the SW needs modeling due to insufficient information or ineligibility for SRF funding:

• O&M costs for SW management (ineligible);
• Land acquisition costs (ineligible);
• Permitting and mitigation costs (ineligible);
• Capital costs for some SW controls or BMPs that are not widely used or had insufficient cost information;
• Developer-financed SW controls or BMPs and other private costs. (For some SW controls, such as erosion and sediment controls for construction site runoff, most capital costs are borne by developers and private costs are ineligible for SRF funding. However, public costs for establishing a program and for training municipal inspectors to review private erosion and sediment controls would be capital costs eligible for SRF funding. These were included in estimated SW needs.);
• Costs to provide SW controls or BMPs for future development. (It would be difficult to predict the size and location of future development throughout the nation. In addition, many of those SW controls or BMPs would probably be developer-financed and ineligible for SRF funding.);
• Costs for designated MS4s that are not associated with cities or counties (e.g., departments of transportation and special districts);
• Costs associated with developing Part 1 and Part 2 SW NPDES permit applications;
• Costs associated with SW permits for industrial activities owned and operated by municipalities;
• Costs associated with SW permits for construction activities under the Phase I SW Program;
• Costs associated with the industrial component of the Phase I SW Program; and
• Costs associated with the Phase II SW Program.

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