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Waste Characteristics

Two HRS values are needed to calculate waste characteristics.

  • The highest product of toxicity and persistence for any substance available to the surface water pathway.

    • These are substances that are found in a source with a non-zero containment value against either overland flow or flood, or substances that are found in an observed release to surface water.

  • The quantity value from HRS table 2-6, based on the sum of the quantities for all sources that have a non-zero containment value against either overland flow or flood.

Assign Toxicity and Persistence

  • You will find these values in SCDM. Section 2.4.1.1, pages 51589-51590 of the HRS rule describes how the toxicity values in SCDM were derived. Section 4.1.2.2.1.2, page 51612 describes how the persistence values were derived. If SCDM does not contain values for a substance that is critical to your site, contact EPA.

  • There are two persistence values for each substance in SCDM: one for lakes and the other for rivers, oceans, coastal tidal waters, and the Great Lakes.

    • In rivers, oceans, coastal tidal waters, and the Great Lakes, flows and tides are assumed to carry a substance to the target distance limit more quickly than in lakes. The assigned values for "River" or "Lake" are based on half-life calculations that include hydrolysis, biodegradation, photolysis, and volatilization as loss mechanisms. For substances that tend to sorb and be preserved in the sediments, a low persistence value based on half-life is over-ridden by a persistence value based on the octanol/water partition coefficient.

  • Select "River" or "Lake" based on the predominant water body type between the PPE and the nearest intake.

  • If the nearest intake is 5 miles down the river and 2 miles across the reservoir, should you select "River" or "Lake"? ANSWER

Calculate Hazardous Waste Quantity

  • Sum the quantity values for all the sources that have a non-zero value for containment against either overland flow or flood.

    • Sources that have a zero value for containment generally meet RCRA closure standards and are treated as though they did not exist in the HRS assessment — no quantity, no hazardous substances, no distance measurements.


  • Enter this sum in HRS Rule table 2-6, page 51591 and select the value for hazardous waste quantity for the surface water pathway. The same value is used for all three threats.

    • Remember that the minimum value of 100 is used if any target, in any of the three threats, is subject to actual contamination.

    • Also remember that the minimum value of 100 is used when there has been a qualifying removal at the site, and when the quantity value before the removal was 100 or greater.

    • Carefully examine the supporting documentation for any sum of source quantities that fall near a breakpoint in HRS table 2-6. A change in value here can triple the drinking water threat score or reduce it to one third.

Calculate the score for waste characteristics.

  • Multiply the value for toxicity/persistence by the value for hazardous waste quantity, cap the product at 108, and find the score for waste characteristics from HRS table 2-7, page 51592.

  • An unknown quantity of PCBs has been deposited into a wetland that is contiguous to a river and reservoir and has been shown to be present at observed release levels. The toxicity and persistence values (both river and lake) for PCBs are 10,000 and 1, respectively. Calculate the score for waste characteristics for the drinking water threat. ANSWER

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