Laserfiche WebLink
f � Monitoring Well Installation Report-Tosco(Former BP)SS#11195,Lathrop California <br /> July 24,2002 <br /> feet bgs. The poorly graded sand is underlain by silty sand to approximately 9 feet bgs, followed by <br /> silt to 16 feet bgs. Well-graded sand was observed from approximately 16 to 20 feet bgs and silt <br /> with sand encountered at 20 feet bgs (total depth). Detailed descriptions of the soil encountered <br /> during this investigation can be found in the boring logs in Appendix B. <br /> 4.2 Soil Analytical Results <br /> All soil samples analyzed were non-detect for all hydrocarbon constituents, except for soil sample <br /> MW-16-S9.5, which contained an MtBE concentration of 0.040 ppm. The stockpile soil sample, <br /> Comp-1 (A;B,C,D), contained a concentration of lead that was acceptable for disposal at Allied <br /> Waste's Forward Landfill. The analytical results from the soil samples are summarized in Tables <br /> 3 and 4. <br /> 4.3 Ground-water-Analytical Results <br /> MtBE was detected in all groundwater samples collected from the newly installed monitoring wells <br /> (MW-13 through MW-17)in concentrations ranging from 28 to 3,900 ppb. All other hydrocarbon <br /> constituents and oxygenates were non-detect. Groundwater analytical data are summarized in Tables <br /> 1 and 2. <br /> =? 5.0 CONCLUSIONS AND RECOMMENDATIONS <br /> All soil samples collected during the installation of monitoring wells MW-13 through MW-17 were <br /> non-detect for TPHg,BTEX,oxygenates, 1;2-DCA,or EDB,except soil sample MW-16-S9.5, which <br /> contained MtBE at 0.040 ppm. The groundwater samples collected from the new monitoring wells <br /> contained concentrations of MtBE ranging from 28 to 3,900 ppb, but were non-detect for all other <br /> analyzed constituents. <br /> Current and historical data indicate that the groundwater flow direction beneath the site is toward the <br /> southwest with a gradient range from 0.006 to 0.02 (GR, lst Quarter 2002). Based on groundwater <br /> elevation data collected during development of the new wells; the groundwater flow direction is <br /> generally consistent with historical data. GR recommends that the new wells be added to the quarterly j <br /> monitoring and sampling program. An additional off-site investigation is warranted to further <br /> delineate the impacted groundwater known to exist beneath the site. GR will submit a Work Plan <br /> for additional off-site investigation by September 20, 2002. <br /> 140193.12-2 <br /> 7 <br /> i <br />