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Additional Soil and Grouftwwater Investigation Report - California Central Traction Company, 1645 Cherokee Lane,Stockton,CA September 22,2oo8 Page 4 5.3 MONITORING WELL INSTALLATION At the request of the SJCEHD, and as agreed to in the December 17, 2007 Additional Soil and Groundwater Investigation Work Plan Addendum ,TRC converted three (3) of the borings to 2- inch diameter groundwater monitoring wells in order to further evaluate groundwater quality and determine the hydraulic gradient and flow direction. Monitoring wells were completed to a depth of 67 fbg based on lithologies observed during drilling. Twenty(20) feet of.020 well screen was installed in each monitoring well. Monitoring well construction specifications are shown on the boring logs included in Appendix B. 5.4 MONITORING WELL DEVELOPMENT AND SAMPLING On June 24, 20o8, the wells were developed(surged and bailed) to improve hydraulic communication between the geologic formation and the well. Approximately 10 casing volumes of water were removed from each monitoring well during development. Following well development, and after the water level in each well had recovered to at least 80 percent of the pre- purge level, the three newly installed wells (MW-5, MW-6, and MW-7) were gauged and sampled to provide more representative groundwater analytical data from those three locations. Groundwater samples were collected from wells MW-5, MW-6,and MW-7 and analyzed for TPH- d by EPA Method 8015, and for TPH-g, BTEX, and fuel oxygenates including MTBE by EPA Method 826oB. The well development and sampling field sheets are included in Appendix C. 5.5 MONITORING WELL SURVEY On August 16, 2oo8, the three monitoring wells were surveyed by Virgil Chavez Land Surveying,a " professional survey company. Each wells was surveyed to determine the northing and easting and the top of casing elevation relative to the surrounding site wells and to the nearest benchmark. The monitoring well survey report is included in Appendix D. 6.o SOIL AND GROUNDWATER DATA 6.1 SOIL ANALTYICAL RESULTS TPH-d was detected in three of the twelve soil samples analyzed at a maximum concentration of 410 milligrams per kilogram (mg/kg) in boring B-17 collected at a depth of 50 fbg. TPH-d was also detected in boring B-14/MW-7 at a concentration of 1.5 mg/kg at a depth of 6o fbg, and in boring B-12 at a concentration of 2.2 mg/kg at a depth of 65 fbg. TPH-g was only detected in boring B-17 at concentrations of 0.31 mg/kg at a depth of 50 fbg. All other analytes were below their respective laboratory reporting limits. 6.2 GRAB GROUNDWATER ANALTYICAL RESULTS TPH-d was detected in grab groundwater samples collected from five of the six borings. The maximum concentration of TPH-d reported in groundwater was 1,300 micrograms per liter (µg/L) in the grab groundwater sample collected from boring B-12/MW-5. TPH-g was detected in grab groundwater samples from borings B-12/MW-5 and B-17 at concentrations of 73 pg/L and 6o pg/L, respectively. Benzene was detected in grab groundwater samples from borings B- 12/MW-5 and B-17 at concentrations of 0.73 pg/L and o.6o pg/L, respectively.