SITE HISTORY - Laserfiche WebLink

Home Browse Search

Additional Soil and Grou-�water Investigation Report California Central Traction Company, 1645 Cherokee Lane, Stockton,CA September 22, 2008 Page 5 MTBE was detected in the grab groundwater sample from boring B-17 at a concentration of 1.9 pg/L. All other analytes were below their respective laboratory reporting limits. 6.3 GROUNDWATER MONITORING AND ANALYTICAL RESULTS Based on the measured depth to groundwater in wells MW-5, MW-6, and MW-7 following well development, the groundwater beneath the Site flows to the northeast at a calculated hydraulic gradient of o.ol feet per foot. Historically, the reported groundwater flow direction beneath the Site was to the northwest. Based on a review of groundwater flow data obtained from nearby sites, the groundwater flow direction in the Site vicinity ranges from northwest to northeast. TPH-d was detected in all three wells,�tirith a maximum concentration of 320 gg/L reported in well MW-7. TPH-g and benzene were also detected in well MW-5 at concentrations of 50 µg/L and 0.77 pg/L, respectively. All other analytes were below their respective laboratory reporting limits. Analytical results of the soil, grab groundwater, and monitoring well groundwater samples are presented in Tables 1, 2, and 3, respectively. Soil and groundwater analytical reports and chain- of-custody records are included in Appendix E. 7.0 4A'ASTE DISPOSAL Soil cuttings and purge water generated during drilling, well development, and sampling activities were placed in California Department of Transportation (DOT) approved 55-gallon drums and temporarily stored on site pending profiling and disposal. On August 1, 2oo8, Environmental Logistics, Inc. transported 17 drums of soil and to drums of purge water to the Filter Recycling Services disposal facility located in Rialto, California.A copy of the waste manifest is included in Appendix F. 8.o CONCLUSIONS AND RECOMMENDATIONS Soil analytical data from the six borings did not indicate the presence of any significant residual soil impacts with the possible exception of the sample from boring B-17 collected at a depth of 50 fbg. However,this sample was collected at the approximate depth of the soil-groundwater interface and is likely more representative of current groundwater conditions at that location. Based on quantity of impacted soil removed from the Site to date, and on the post-excavation confirmation soil data and the soil analytical data collected as part of this recent investigation, TRC recommends no further action with respect to Site soils. Groundwater analytical data from the six grab samples,and subsequently from the three monitoring wells, are generally consistent with results reported historically from wells MW-1, MW-2, and MW-3. Unfortunately,wells MW-1, MW-2,and MW-3, as well as well MW-4,were not installed to sufficient total deep within the water-bearing zone to consistently obtain groundwater samples given seasonal fluctuations in groundwater depth. The deeper construction of the three newly installed wells (MW-5, MW-6,and MW-7),each installed to a total depth of 67 fbg,will provide more consistent groundwater data throughout the year and the longer well screens will accommodate larger fluctuations in groundwater depth.