ARCHIVED REPORTS_XR0002855 - Laserfiche WebLink

Home Browse Search

3.0 LABORATORY ANALYSIS ' The groundwater samples were transported to Severn Trent Laboratories, Inc. (STL), a state-certified laboratory, located in Pleasanton, California. The groundwater samples were analyzed in accordance ' with San Joaquin County Environmental Health Department's March 2004 letter as follows: ■ Well MW-1R was analyzed for the presence of TPH-G, MTBE,DIPE, TAME, ETBE,TBA; ' ■ Wells MW-2, MW-5 and MW-8 were analyzed for the presence of TPH-G, BTEX, MTBE, DIPE, TAME, TBA, ETBE; ■ Wells MW-3 and MW-10 were analyzed for the presence of MTBE; ' ■ Well MW-4 was analyzed for TPH-G,BTEX and MTBE; ■ Well MW-6 and MW-9 were analyzed for BTEX and MTBE; and ■ Well MW-7 was analyzed for MTBE,DIPE, TAME, ETBE, and TBA. ' The selected analytical constituents were analyzed by US EPA Method 8260B. Copies of the laboratory analytical report and chain of custody record are provided in Appendix C. ' 4.0 SUMMARY OF RESULTS Based on groundwater elevation data for December 14, 2004, the groundwater flow direction in both the ' upper and lower aquifers was towards the southeast at gradients of approximately 0.003 feet per foot (ft/ft) and 0.002 ft/ft, respectively (Figures 3 and 4). The groundwater flow directions and gradients noted during this sampling event are consistent with historical trends. tAnalytical laboratory results of groundwater samples collected on December 14, 2004 indicate that TPH-G was reported at a concentration of 730 micrograms per liter (gg/L) in upper aquifer monitoring ' weIl MW-5. TPH-G was also reported in lower aquifer wells MW-1R and MW-4 at concentrations of 69 p.g/L and 74 gg/L, respectively: The reported gasoline concentrations were flagged by the laboratory for hydrocarbons reported in the gasoline range not matching the gasoline standard and for quantities of unknown hydrocarbon(s)in the sample based on gasoline. 64so i;n.-, WAJ Gels a rr?tr f..,4 l of '7/ ' love- lab ke.a� .,C f'C3uY Qt i]nn[lvi d..,rY p .�/4► BTEX compounds were reported below method detection limit concentrations in analyzed samples ' except MW-4 where toluene was reported at a- concentration of 48 gg/L. 'MTBE was reported in groundwater samples collected from upper aquifer wells MW-5, MW-7 and MW-10 at concentrations of 310 gg/L, 0.69 gg/L and 0.63 µg/L, respectively. MTBE was also reported in lower aquifer wells MW- JR, MW-2, and MW-9 at concentrations of 1.3 4g/L, 19 pg/L and 0.88 gg/L, respectively. Figures 5 and 6 provide maps of TPH-G, benzene and MTBE concentration distributions in site wells based on the December 14, 2004 sampling event. ' The fuel oxygenates DIPE, ETBE and TAME were not detected in groundwater samples collected from any of the monitoring wells sampled this quarter. However, TBA was reported in groundwater samples collected from wells MW-2 and MW-5 at concentrations of 12 µg/L and 280 pg/L, respectively. Both ' TBA and MTBE concentrations in water samples from MW-2 and MW-5 have trended downward significantly during year 2004. Cumulative analytical results of groundwater samples collected from current and past sampling events are presented in Tables 1 and 2. Well construction details are provided in Table 3. 9 ' Quarterly GW Monitoring Report-4th Qtr 2004 "Wic Quik Stop No. 132 Quik Stop Markets,Inc. ATC Project No.75.82503.3205 January 11,2005 Page 2 of 4