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Longston's Alarket 15615 Seventh Street, Lothi op, California October 5, 1995 Interim Secondary.Sorxrce Rettict*al c Page: 9 1 ' a field log (Appendix D, Table 4) Instruments calibrated to known standards were used to monitor these parameters At least five well volumes were evacuated from each well, and more, if necessary, until the above parameters had stabilized ' Wells that are de-watered before evacuation of five well volumes have been accomplished will be sampled upon eighty percent recovery of the initial water level The wells or other sampling points were sampled in order of the least to the ' most contaminated, as best known or estimated The samples were pumped from a stainless steel bladder pump or carefully poured from a Teflon bailer into clean glass vials with Teflon-lined screw caps and half gallon plastic, containers provided ' by the laboratory Care was taken to ensure that no aii space exists in the vials by inverting to check for bubbles and re-sampling if necessary ' The samples were analyzed of ex i i acted wither. 14 days according to their EPA methods Water samples collected for snalrsis wfll lir aiialy,cd try EPA method 602 for BT1 &E compounds and method 5030 LU17T fa ga iczline range ' hydrocarbons The minimum detection hinits ased for �ach analyte ;ball be 0 5 pg/L for BTX&E and 50 µg/L for gasoline (Table 2 1, Append,x 13) Daring this scope of work, analyses were conducted by Cal,foriha Laboratory Services, a State-certified laboratory in Rancho Cordova, California, Monroe Laboratories, Inc , a State-certified mobile lau from San Jose, California, and GeoAnalytical Laboratories, a State-certified laboratory in Modesto, California 4.0 Soil Conditions Zhe subsurface lithology at the Langston's Market site in Lathrop, California is characterized by interbedded sands, silts and -lays Phis is typical of the valley fill deposits in the region The beds are fairly consistent across the site, except for a blue clay (locally known as the "Stockton BIue") that was not found in boring MW Contamination may I have migrated downward in the area whet e the clay underwent a fes change to silt in MW-3 (14 - 27 foot interval) This would allow contaminants to enter an underlying clayey sand (SC) and move down-gradient towards EW-1 Contamination was found in the EW-1 soil sample at 34 feet (Table 1 1, Figure 5) Soil sampling in the excavation show, minor contamination to the northeast, north and west walls (Table 16) The southwest wall and all floor samples were "ND" ontamination remains in the east, southeast acid south walls where excavating could not continue due tot a location of city streets (Figure 3) Boring W-i s ow+ ccintamination extending southeast from the excavation toward the intersection of L and 7th Streets Boring SB-10 was "NE)", indicating the plume does not extend to the south across L street, at this time All soil samples fiuni the down-gradient boring, MW-2 were also