SITE INFORMATION AND CORRESPONDENCE

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WALLACE KUHL 6,ASSOCIATES,TUC. LAMROP PROPERTY WKA No. 1184.02 October 10, 1991 Page 2 between 5 to 50 feet northerly of the northerly edge of East Thomsen Road. Confirmatory soil samples were obtained from the bottom and sidewalls of the excavation and it was then backfilled with clean material upon the approval of the San Joaquin County Environmental Health Division. We determined that the particular contaminants found in the stockpiled soils at the subject property could be successfully remediated by aeration; the stockpiled soils were therefore placed on construction grade plastic and spread across an approximate 18,900-square foot area for aeration. Aeration of the contaminated soils continues, although samples of the aerating soils obtained on September 3, 1991, indicate that contaminant concentrations in eight of eleven composite samples are below 50 parts per million (ppm) petroleum hydrocarbons; Ali Othman with the San Joaquin County Air Pollution Control District informed us at the time of the aeration permit approval that contaminated soils are considered successfully remediated when total petroleum hydrocarbon concentrations are less than 50 ppm. We will obtain three additional samples of the aerating soils on October 11, 1991, to confirm that all aerating soils have been remediated to less than 50 ppm total petroleum hydrocarbons. We installed three ground water monitoring wells on the property on September 3, 1991, to evaluate ground water quality and determine the hydraulic gradient beneath and near the previously excavated and backfilled area of subsurface soils contamination; one of the wells was installed in the central portion of the backfilled area, i.e. at a location most likely to have experienced ground water contamination. The wells were sampled on September 9, 1991; laboratory analysis of the samples indicated non-detectable concentrations of petroleum hydrocarbon-related contamination in each well. Based on ground water elevation measurements taken at the time of the well sampling, we determined that the hydraulic gradient beneath the subject property is 0.0006 with a flow direction of approximately N 47' E. Based on this flow direction, monitoring well W2 is a "downgradient" well; it is a requirement on sites of this nature that at least one well be installed downgradient relative to the area of suspected contamination. The attachments to this letter are a registered civil engineer's survey of the ground water monitoring wells on the property with respect to a known datum and a proposed lot-split prepared by the current property owners. The locaticns of the monitoring wells are well within the proposed boundaries of the lot-split and one well is in the downgradient direction from the former area of contaminated soils; the first round of sampling and analysis of the ground water wells indicates non-detectable concentrations of petroleum hydrocarbon contaminants. Our site characterization work indicated that the former area of contaminated soils did not