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RMENEM- ME Pill P . r .{ r ^S.. x ..w. *. - SSB 91-1035 Thrifty oil Company Station No. 172 Page 7 7647 Pacific Avcnuc Stockton,Califorrsia 3.3 11Sonitnrin� Nell Inst^llution and Sur+ev Four 2-inch diameter ground-:nater monitoring welis were instailed at the site. After installation, each well was developed, sampled, and a level survey was conducted to determine will head • elevations. Elevations relat've to sea level were determined from City of Stockton benchmark labeled IN-5 located on a traffic island at the intersection of Rivara and Thornton (Pacilac). Monitoring well installation, sampling, and chain-of-custody procedures are presented in Appendix D1. The well construction details are prese,..tted in Appendix D2- Plate P-3 shows the locations and the well head elevations of each monitoring well. 3.4 5�b'ective Anal sis of Ground-Water Sam les Each monitoring well was developed by surging followed by bailing until the water produced was essentially sediment free, and temperature, pH, and electrical conductivity measurements stabilized. The final readings for these properties are presented in Tsble 4. TABLE 4 STABILIZED READINGS -TEMPERATURE, pH, AND EC FOR GROUND-WATER, SAMPLES � Thrifty Oil Company Sta.:ion No. 172 7647 Pacific A••c11ue Stockton, California Well Date Temperature (°F) Ph EC (umhoslcm) MW-1 616191 68.3 7.33 1,257 MW-2 616191 67.2 7.17 1,068 MW-3 616191 64.5 7.17 1,040 MW-4 616191 63.7 6.97 1,309 Prior to development and purging,and again before sampling,each well was subjectively analyzed for visual evidence of floating product and odor. None of the examined samples contained floating product. A slight sheen and hydrocarbon odor were noted is the witer sample collected from MW-2• ssit ENVIRONMENTAL CONSULTANTS,INC.