ARCHIVED REPORTS XR0010083 - Laserfiche WebLink

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Reconnaissance Groundwatei Sampling Four boreholes were sampled using push or dnll rods or hollowstem auger as temporary casing Boring PB-14 collapsed which prevented the collection of a groundwater sample Depth to groundwater measurements were made to the nearest one-one hundredth of one foot from existing grade, and also checked for the presence of separate phase product The groundwater sample was carefully collected with a clean disposable bailer and poured into the appropriate laboratory prepared container with minimum cavitation and headspace Each water sample was labeled, logged onto a chain-of-custody form, and placed in a chilled ice chest on crushed ice Subsurface Conditions Five exploratory borings were drilled at the locations shown on Figure 1, the deepest of which was advanced to a termination depth of 26 feet The site is underlain by silty clay to depths of about 8- to 10-feet This clay is underlain by interbedded clay, clayey sand, silty sand, and sand to depths of about 20- to 24 feet, and compose the aquifer strata The sand is locally very clean and tends to flow and caused partial or total borehole collapse in all bonngs The aquifer strata are underlain by interbedded silty clay and clayey silt, which are the underlying confining strata Groundwater occurred at depths of about 12- to 14-feet and rose to about 9-feet indicating the aquifer strata are unconfined to very weakly confined On the basis of selected field groundwater measurements, groundwater appears to flow to the north, however there was insufficient time for levels to equilibrate for adequate data to plot a contour flow direction The historic groundwater flow direction as mapped in the existing monitoring wells is consistently northerly Regional lithologic lateral and vertical variation are present in the shallow aquifer strata and underlying confining strata, which are typical for river and floodplain deposits in this portion of the San Joaquin Valley (see Geologic Cross Section, Figure 1) While regional lateral and vertical variation are present in the aquifer and confining strata, these strata as a whole form the aquifer stratigraphy (or hydrostratigraphy) between about 10- to 24-feet The underlying confining strata display some lateral lithologic variations and were not observed to yield water In our opinion, on the basis of these observations, both aquifer strata the underlying confining strata are interpreted to have some lateral extent underlying the immediate site vicinity Chemical Analysis Eleven soil samples including two "underlying confining strata" soil samples, and four groundwater samples were analyzed at a Chromalab Inc State certified analytical laboratory from the exploratory borings These samples were tested for the following, Total Petroleum Hydrocarbons as Gasoline (TPHG) and Diesel (TPHD), Benzene (B), Toluene (T), Ethylbenzene (E) and Xylene (X), Methyl-tert-butyl-ether (MTBE) and fuel oxygenates, using EPA Methods 3510/8015, 8020, 8240 and 8260 The results are tabulated and presented in the attached Tables 1 and 2 below Page 3