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TRAC 5/28-29/98

Staff Paper # 4.1


TOPIC:
ISSUES ASSOCIATED WITH DRINKING WATER ASSESSMENTS

BACKGROUND:

CURRENT APPROACH (Since November 1997)

CASE STUDIES:

QUESTIONS THAT TRAC MIGHT ADDRESS:

  1. Should EPA consider another approach as an alternative to its current approach of use the best available data along with existing models and scientific judgment in assessing drinking water exposure? Should there be any limitation for pesticides that are clearly persistent and mobile in the environment?

    Description: Some have suggested that, given the current wide variation in data availability and quality, the Agency should generally defer extensive consideration of drinking water exposure. In such cases, the need for retaining some or all of the FQPA safety factor because of uncertainty in the drinking water exposure also needs to be addressed. In specific cases, where sufficient reliable data are available, the Agency could conduct refined exposure assessments as part of its aggregate exposure analysis.

  2. Considering the range of data availability for pesticides, how should OPP select a reasonable high end value (or values) from available valid monitoring data? How would one define a "reasonable high end value"?

    Description: Data show that a particular pesticide does not degrade rapidly in soils and water in certain areas of the country and that it does not bind strongly or readily to soils. Available surface water and groundwater monitoring data are of variable quality. The majority of monitoring data are from studies not designed to specifically look for the pesticide, and we do not know whether it was actually used in these areas. Many of the values (thousands of values) reported in these non-specific monitoring studies are "zeroes" (that is, "below the limits of detection"). Maximum measurements in these general surface water studies range between 0.012 ppb and 17 ppb. Maximum measurements in these general groundwater studies range between 0.17 ppb and 36.6 ppb. There are four groundwater studies and two surface water studies that did specifically look for the pesticide, using controlled field trials. Maximum measurements in these specific surface water studies are 23 ppb and 150 ppb. Maximum measurements in the specific groundwater studies are 3.0 ppb, 9.0 ppb, 51 ppb and 71 ppb.

    Given these data, and a strong scientific basis for believing that water contamination at some levels in some locations is likely, how should EPA factor this information on the potential for drinking water exposure into the tolerance decision? Specifically, how should OPP approach the selection of a value or values for use in the human health dietary risk assessment?

  3. In the absence of monitoring data, or where time is very short, as with emergency exemption requests, what should EPA do to address the drinking water issue in the context of complying with FQPA?

    Description: Currently, in the absence of monitoring data, OPP uses model estimates to screen out those pesticides that are not likely to pose any significant "threat" to drinking water. For those that are not cleared, OPP's risk managers make decisions as to the need for surface water and/or groundwater monitoring and/or interim risk mitigation measures while monitoring is conducted.

    Section 18s pose a special problem, in that there are surface water and/or groundwater monitoring data available in some cases--but, given the emergency nature of the action (and the tight time constraints), OPP often lacks the time to collect, thoroughly analyze, and fully consider these data. Given the nature of section 18 decisions (to allow or not to allow) and the tight timeframes, what role should model estimates play in making this decision?


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    updated May 17, 1998