ARCHIVED REPORTS XR0001539 - Laserfiche WebLink

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i w • Chemical Analysis Seven groundwater samples were analyzed at Kiff Analytical, LLC, a State certified analytical laboratory 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, 1,2 Dichloroethane and Ethylene Dibromide using EPA Methods 3510/8015, 8020, 8240 and 8260 The analyses were run on a "normal" turnaround (five- to ten working days) The results are tabulated and presented in Table 2 Discussion The sample results show that TPHG and BTEX contaminants were observed in monitoring wells MW-2 and MW-3 The most elevated concentrations occurred in MW-2 and are consistent with historic sampling data The sampler removed 0 01 ounce of product from MW-2 The presence of product is interpreted as drainage with declining groundwater levels The other wells showed that contaminants were not detected Wright recently completed exploratory boring and sampling additional subsurface assessment work This data appears to show an upgradient off-site source of TPHG and 1,2-DCA Groundwater levels declined from the previous quarter measurements and the decline is attributed to natural aquifer discharge. A small groundwater depression appears to center around well MW-2 where plotted groundwater elevation contours "hook" steeply around that well This may indicate some vertical leakage within the aquifer strata in the uppermost aquifer Conclusions and Recommendations Wright has competed the quarterly monitoring for the Stefanos site The monitoring data show that TPH contaminants are present in MW-2 and MW-3 Additional subsurface investigation for groundwater sampling has been completed Wright has completed a proposed workplan for PHS EHD regarding initial soil vapor extraction and ozone infection for interim cleanup Wright recommends that the quarterly monitoring program for TPHG, TPHD and BTEX and MTBE and oxygenates continue and the existing monitoring wells are scheduled for sampled in the next quarter Limitations This report has been prepared specifically for Stefanos site at 1419 East Charter Way, Stockton, California and was done according to the State and local agency suggested guidance documents for these investigations The interpretations, conclusions and recommendations made herein are based on professional judgment of the data and analysis for the soil and water samples collected on-site and should be reviewed in the context of this report and other site reports Wright Environmental Services, Inc. is not responsible for errors in laboratory analysis and reporting, or for information not available during the course of the study, and no warranty or guarantee is expressed or implied therein 0. Page 2