SITE INFORMATION AND CORRESPONDENCE_FILE 1

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2 . SITE INVESTIGATION On the basis of previous investigations, and in accordance with r requirements of the Regional Water Quality Control Board, EA installed three off-site wells to delineate the extent of the ` contaminant plume and to define other possible sources of hydro- carbons in the ground water (Figure 2 ) . One well (MW8 ) was �- installed upgradient of the site in the west sidewalk of Pershing Avenue, beside a Shell service station; one ( MW9 ) quasi- upgradient on Pershing Avenue beside a 7-Eleven store with gaso- line dispensers, and one (MW10 ) downgradient from the site beside the parking lot of the Chateau Convalescent Hospital, at 1221 Rosemarie Lane. ` 2 . 1 WELL DRILLING AND SOIL SAMPLING .. Drilling, soil sampling and well installation were supervised by a state-registered geologist. Boreholes were drilled using a truck-mounted rig and hollow-stem auger of 10-inch outside dia- meter . The boreholes were drilled to depths between 34 and 38 feet below grade. The depth of drilling was determined by a competent clay layer occurring throughout the investigated area. During drilling, soil samples were collected using California modified split-spoon sampler lined with three 6-inch long brass tubes. The lowermost tube was sealed with aluminum foil and PVC caps, taped, labeled, and placed on ice in a cooler. Soil in the remaining two tubes was screened with a Foxboro volatile organics analyzer for the presence of hydrocarbons, and classified according to the Unified Soil Classification System. Samples screening positive for hydrocarbons were selected for analysis and shipped under chain of custody to the California-certified Brown and Caldwell Laboratories in Emeryville, California, where they were analyzed for total petroleum hydrocarbons (TPH ) and for selected volatile gasoline constituents: benzene, toluene, xylenes, and ethylbenzene (BTXE) . Between sampling, the sampler e20/73942 2