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Jonas & Associates Inc <br /> ' In soil borings where headspace analyses indicated no hydrocarbon presence, <br /> samples were chosen by criteria 1 and 2 The water table was estimated in the field <br /> as the depth where the first apparently saturated sample was recovered (typically 7 <br /> ' to 9 feet below ground surface) <br /> Soil samples were submitted to Clayton Environmental Consultants, Inc , a State- <br /> certified analytical laboratory for analysis <br /> ' Chain-of-custody forms were completed for samples submitted for laboratory <br /> analysis <br /> 23 Groundwater Investigation <br /> 2 3 1 Groundwater Monitoring Well Design, Installation, and Development <br /> ' Six groundwater monitoring wells (OW-1 through OW-6) were installed at the Site <br /> between December 22, 1987 and February 18, 1988 The well locations were <br /> ' chosen based upon data obtained from the soil vapor assessment <br /> Monitoring well OW-2 was located where the highest organic vapor readings were <br /> encountered Monitoring well OW-1 was located beyond the estimated eastern extent <br /> of the vapor plume Wells OW-4, OW-6, and OW-5 were located beyond the <br /> estimated northern extent of the vapor plume Well OW-3 was located near an <br /> ' isolated elevated organic vapor reading encountered south of the former tank <br /> location <br /> Each well was constructed of flush-threaded Schedule 40 polyvinyl chloride (PVC) <br /> casing Four-inch casing with 0 02-inch slots was used for wells OW-1 and OW-4 <br /> Two-inch casing with 0 01-inch slots was used for wells OW-2, OW-3, OW-5, and <br /> ' OW-6 The filter pack material for all wells was Lone Star #2/12 sand This sand <br /> was selected primarily to match the casing slot size, since gram size analyses <br /> performed on soil samples collected during the initial investigation showed greater <br /> ' than 90 percent of the sample passing the No 200 sieve (making a designed filter <br /> pack infeasible) Stainless steel centralizers were used at each well to ensure an <br /> evenly distributed filter pack(PG&E, 1988) Well construction details are presented <br /> ' in Appendix C <br /> The borehole for each well was advanced with 10-inch hollow stem augers When <br /> ' the augers had been advanced to the desired depth of the well (approximately 25 feet <br /> below grade), the PVC well casing was lowered down the center of the augers and <br /> set to the appropriate depth The annular space between the augers and the <br /> 4 <br /> 1 <br />