ARCHIVED REPORTS XR0006254 - Laserfiche WebLink

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1 SECTION 4 RESPONSE TO LETTER FROM THE COUNTY 1 In this section, ERM and Safeway address the concerns of the County, as expressed in the letter to Safeway dated May 14, 1992 (Appendix C) • The site lacks a well upgradient of the former underground storage tank (UST) location The three monitoring wells (MW-1, MW-2, and MW-3) that were closed in November 1991 were considered to be upgradient Analytical results illustrated in Figures 2-4, 2-5, and 2-6 indicate that the area affected is south of the former tank locations, which is consistent with the flow direction established. While groundwater movement has no doubt been altered by prolonged drought and increased pumping throughout the area, groundwater movement has been steady for at least the past two years Should the direction of groundwater movement begin to change in a significant manner, we would agree that another well may be advisable IThe County correctly states that no detailed investigation of the soils or groundwater below the UST pipeline has been done At this time, however, additional data regarding soils beneath the pipeline is not critical to understanding site conditions Also, a well along the fuel lines would be considered upgradient and, as previously discussed, is not crucial to the current monitoring • Diesel-contaminated soil poses a threat to water quality Elevated concentrations of TPH-diesel in the soil have been identified on the Safeway property and below Navy Drive to the south The soil in question is found a minimum depth of 25 feet below grade Well sampling has shown that groundwater has not been significantly affected. It should be emphasized that HydroPunch data, used primarily as a screening tool, often yields elevated analytical results that are not duplicated in well samples Analyses of the HydroPunch sample from boring B-21 in November 1991, for example, showed a concentration of 6 9 mg/kg of TPH-diesel Boring B-21 was converted into monitoring well I 4-1