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Mr. Don O. Culbertson rroject 2560-203.01 September 13, 1995 Page 3 At least one petroleum-affected sample from Area 4 and a background sample from the upgradient monitoring well should be analyzed for total and soluble metals using the waste extraction test using deionized water as the extractant. During field activities conducted by Raney Geotechnical (Raney), a soil sample was collected from Area 7 and submitted for chemical analysis for Title 22 metals. The report prepared by Raney describes the soil sample as discolored soil and states that it appeared to contain the least weathered soil contaminant. The results of the metal analysis of this sample, which are summarized in Table 1 of the work plan prepared by EMCON, indicate that metal concentrations in petroleum-hydrocarbon impacted site soils have already been characterized. Furthermore, detected concentrations of metals in the above mentioned sample were within regional background metal concentrations as established by soils analyzed by the United States Geological Survey (USGS) and summarized in USGS Open-File Report 81-1971. This indicates that petroleum hydrocarbons have not influenced metal concentrations in site soils. Piezometers should be installed in the Geoprobe borings to estimate the ,groundwater level and gradient for placement of the monitoring wells. At least two wells should be downgradient of the pipeline. An interim report of the Geoprobe investigation, includingI?radient information, should be submitted for approval prior to installing the monitoring wells borings to confirm their locations. During geoprobe field activities, EMCON will install temporary, well casing in at least three borings. The borings will be selected so that they are as far apart as possible from one another. After the water level has stabilized in these borings, the depth to water will be recorded and the sites will be surveyed for position and elevation. This information will be used to construct a groundwater contour map which will be included in an interim letter report describing the results of the geoprobe program. After review of this data and consultation with representatives of the RWQCB and the Rural California Housing Corporation, Chevron Pipe Line Company and EMCON will select sites for the proposed monitoring wells. 'Boerngen,J.G.and Shaklette,H.T. 1981. Chemical Analyses of Soils and Other Surficial Materials of the Conterminous United States: United States Geological Survey,Open-File Report 81-197. H:\WINW0RD\215ADDN.D0C-95W:1