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�y �' - s r":df:i9 — __ _ _ — _ _ _ •' .. ..'qy �`:a r M 3. PREVIOUS INVESTIGATIONS The following summary of the work completed at the site is organized by task, not necessarilyb chronology.y Because of the large number of site visits by both GTI and FA, this format pro- vides the most succinct summary. 3. 1 UNDERGROUND TANK REMOVAL AND SOIL SAMPLING Three 8,000-gallon fuel tanks and one 500--gallon waste oil tank were removed on 4 February 1986 by American Environmental Manage- ment Corporation of Rancho Cordova, California. GTI personnel monitored the tank removal and screened the soils in the tank excavations with an HNU photoionization detector. Single soil samples were collected from six locations (S-1 through S-6, Figure 6) at the time of the tank excavation. The samples were taken from areas where petroleum odors and soil discoloration were detected and from the areas below the product tanks .and the waste oil tank. .These samples were collected fly..removing soil with the backhoe and then placing the soil in brass tubes. The: analytical results from.the testing of these samples are shown in Table 8. The extent of the soil contamination`in the tank pit was desck ibed' in ,the GTI report as "localized- Prior to back filling of the tank pit, "representatives from Groundwater : Technology and the San Joaquin Local Health District determined ( that. exca1va.tion,,of the minor amount of contaminated soil was... i unnecessary" (GTI. 1986a) 3.2 DRILLING 'AND .EAMPLING. OF' SOIL BORINGS r On 8,. and 9' January 1986,. soil borings for two monitoring wells a (MW1 , NW2, Figure -6:)' were.;.drilled on the site under GTI's super- vision Borings for these wells here drilled to`a depth of 70 feet. Soil samples were collected from these borings "at' var ous, depths" using a split-spoon sampler. The soil samples were screened .at tYe ,surface using an HNU phatoionization detector, e35/71050/2--90/tx 19 .'ter 1991 Mimi