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Section 8.4 of the HRS Guidance Manual (HRSGM), page 244

SURFACE WATER CONTAINMENT FACTOR

:This section provides definitions for many of the terms used in the surface water containment descriptions and explains how to score the containment factor in the surface water pathway. If an observed release to a watershed cannot be established, then that watershed is evaluated based on potential to release. Two factors are used to evaluate the potential to release factor: potential to release by overland flow and potential to release by flood. The containment factor is a measure of the methods (either natural or engineered) that have been used to restrict the release of hazardous substances from a source to the watershed or to prevent released substances from entering surface water.

:Containment criteria have been compiled for several types of sources on a numerical scale selected to provide a relative degree of discrimination among different levels of containment. HRS Table 4-2 includes containment factor rating descriptions for the following specific categories of hazardous waste sources: surface impoundments, land treatment facilities, containers, and tanks. The table also provides containment factor rating descriptions that apply to all other hazardous waste sources, including landfills, piles, and contaminated soil.

:The containment factor is evaluated for each source for the watershed being evaluated, and the highest containment factor value for any source that meets the minimum size requirement is assigned as the containment factor value. If none of the sources meets the minimum size requirement, the highest containment factor value of any source is assigned.


RELEVANT HRS SECTIONS
Section 4.1.2.1.2.1.1: Containment
Section 4.1.2.1.2.2.1: Containment (flood)
Section 4.1.2.1.2.2.2: Flood frequency
Section 4.1.2.1.2.2.3: Calculation of factor value for potential to release by flood
Section 4.1.2.1.2.3: Calculation of potential to release factor value

DEFINITIONS

The following definitions elaborate on terms used in the containment descriptions in HRS Table 4-2.

Above-ground Tank: Any tank that does not meet the definition of a below-ground tank (including any tank that is only partially below the surface).

Associated Containment Structures: As used in HRS Table 4-2, constructed barriers (e.g., liners, dikes, berms) that may have been placed under, over, or around a source (e.g., a landfill or a waste pile) to prevent the release of hazardous substances to the environment.

Below-ground Tank: A tank with its entire surface area below the surface and not visible; however, a fraction of its associated piping may be above the surface.

Bulk Liquids: Noncontainerized liquids deposited directly into a source by pipe, tanker truck or other means of transport.

Essentially Impervious Base: A base underlying containers that is free from cracks and gaps and prevents the penetration of leaks, spills, or precipitation.

Evidence of Hazardous Substance Migration: Chemical analyses and/or visual evidence that demonstrate hazardous substances attributable to a source have migrated away from that source into the surrounding soil, ground water, surface water, or air (e.g., leachate containing hazardous substances coming out of the source; stained or contaminated soil that can be attributed to migration from the source; evidence of overflow from a surface impoundment containing hazardous substances).

Free Liquids: Liquids that readily separate from the solid portion of a substance under ambient temperature and pressure.

Freeboard: Vertical distance between the top of a tank or surface impoundment dike and the surface of the hazardous substance contained therein. Freeboard is intended to prevent overtopping resulting from normal or abnormal operations, wind and wave action, rainfall, and/or run-on.

Land Treatment Zone: Soil area in the unsaturated zone of a land treatment unit within which hazardous substances are intended to be degraded, transformed, or immobilized.

Liner: A continuous barrier that covers all the earth likely to be in contact with a source so that hazardous substances or leachate containing hazardous substances would not migrate to the surrounding earth. The barrier may be synthetic material (e.g., a thick, continuous, polyethylene membrane) or engineered, compacted natural, material (e.g., re-worked and low permeability clay). An in-situ clay layer that has not been re-engineered by compaction or other methods is not considered a liner.

Maintained Engineered Cover: Vegetated cover, usually made of compacted clean soil. It is generally placed over a source at its closure and is designed and constructed to minimize the migration of liquids through the closed source, function with minimum maintenance, and accommodate settling and subsidence. Maintenance of the integrity and effectiveness of the final cover may include repairing the cap as necessary to correct the effects of settling, subsidence, erosion, and other events.

Run-on Control/Runoff Management System, Functioning and Maintained: A functioning and maintained, engineered system or structure designed to prevent flow into or onto a source or, alternatively, to control runoff from a source and prevent hazardous substance migration.

Secondary Containment: As used in HRS Table 4-2, secondary containment is applicable to the evaluation of the containment factor for tanks. Methods of secondary containment include a liner external to the tank, a vault, a double-walled tank, or an equivalent device.

Tank and Ancillary Equipment: Tanks and associated pipes, pumps, sumps, manifolds, fittings, flanges, and valves used to distribute, meter, or control flow of hazardous substances to or from the tank.


SCORING SURFACE WATER CONTAINMENT FOR OVERLAND FLOW

(1)  Identify the sources at the site. (See Section 4.1 for discussion of potential sources.) HRS section 1.1 defines a source as "any area where a hazardous substance has been deposited, stored, disposed, or placed, plus those soils that have become contaminated from migration of a hazardous substance." The HRS divides sources into five categories for evaluating ground water containment: surface impoundments, land treatment, containers, tanks, and all other sources. Each category has a separate list of criteria used to assign containment values.

(2)  Determine if one or more sources are located in surface water in the watershed being evaluated (e.g., intact sealed drums in surface water).

  • If so, assign a containment factor value of 10 for that watershed.

  • If not, continue to Step (3).

(3)  For each source within the watershed, determine whether the source hazardous waste quantity value is 0.5 or greater.

  • Only sources with a source hazardous waste quantity value of 0.5 or greater can be used to assign the containment value, unless no source for the watershed being evaluated has a source hazardous waste quantity value of 0.5 or greater. This limitation is referred to as "minimum size requirement." Highlight 8-25 summarizes the measurements of sources that will give a source hazardous waste quantity value of 0.5. Any of the hazardous waste quantity tiers can be used to determine whether a source meets the minimum size requirement. Detailed guidance on determining hazardous waste quantity values is provided in Chapter 6.

  • If no source meets the minimum size requirement, evaluate containment for all sources.

(4)  Assign a containment value to each eligible source.

  • Use the definitions provided above to interpret the containment criteria in HRS Table 4-2.

  • Highlight 8-26 summarizes the information requirements to evaluate source containment.

(5)  Assign a containment factor value for the potential to release by overland flow component for the watershed.

  • Assign the highest containment value for those sources with hazardous waste quantity values greater than or equal to 0.5 as the containment factor value for the watershed.

  • If none of the sources in the watershed being evaluated at the site has a source hazardous waste quantity value greater than or equal to 0.5, assign the highest containment factor value from all eligible sources for the watershed as the containment factor value for the watershed.

SCORING SURFACE WATER CONTAINMENT FOR FLOOD

Assign the flood containment factor value as described below.

(1)  Identify the sources at the site. (See Section 4.1 for discussion of potential sources.)

(2)  Determine if each source meets the minimum size requirement.

  • Only sources with a source hazardous waste quantity value of 0.5 or greater can be used to assign the containment value, unless no source for the watershed being evaluated has a source hazardous waste quantity value of 0.5 or greater.

  • If no source meets the minimum size requirement, evaluate containment for all sources.

(3) Assign potential to release by flood factor value to each eligible source in the watershed.

  • Determine the floodplain category in which the source (or portion of the source) lies.

  • Assign a floodplain frequency value (see HRS Table 4-9) for each applicable floodplain category.

  • Assign a containment factor value (see HRS Table 4-8) for each floodplain category in which the source is located.

  • Multiply the floodplain containment value by the floodplain flood frequency value for each floodplain in which the source is located.

  • Select the highest product as the source's potential to release by flood factor value.

(4)  Assign the highest potential to release by flood factor value for the watershed from sources meeting the minimum size requirement.

  • Assign the highest potential to release by flood factor value for those sources with hazardous waste quantity values greater than or equal to 0.5 as the factor value for this component of the surface water pathway.

  • If none of the sources in the watershed being evaluated at the site has a hazardous waste quantity value greater than or equal to 0.5, assign the highest potential to release by flood factor value from all eligible sources for the watershed as the factor value for this component of the surface water pathway.

TIPS AND REMINDERS

  • Regardless of source type, if there is evidence of hazardous substance migration from the source, assign a containment factor value of 10 for the overland flow component for that watershed.

  • Any hazardous waste quantity tier can be used to determine that a source meets the minimum size requirement.

 

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