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Placement of the recovery wells in the utility trench backfill was seen as critical to <br /> (1) assess the extent of the hydrocarbon plume in this direction; (2) take advantage <br /> of the barrier to offsite migration provided by the intersecting underground utilities, <br /> and (3) enhance ground water recovery using the higher permeability to be expected <br /> in backfill material. <br /> 4 2 Soil Boring. Sampling. and Well Installation <br /> Prior to commencement of drilling activities, a permit for the proposed recovery wells was <br /> obtained from SJCPHS. A copy of the permit is presented in Appendix B. <br /> On October 29 and November 19, 1991, Alton Geoscience supervised the drilling of two <br /> 10-inch-diameter soil borings to depths of 14 and 16 5 fbg The soil borings were <br /> subsequently converted into 4-inch-diameter ground water recovery wells (AMW-5 and <br /> AMW-6) <br /> Prior to drilling, each hole was hand excavated to 5 fbg During drilling of AMW-5, soil <br /> samples were collected at 2.5 and 6 fbg Soil samples were not collected from AMW-6 due <br /> to the shallow ground water condition (ground water was encountered during initial hand <br /> augering) and insufficient recovery in the sampler during drilling Drilling procedures and <br /> soil sampling protocol are presented in Appendix C, while boring logs are presented in <br /> Appendix D. <br /> 4.3 Ground Water Recovely Well Construction and Develo ment <br /> Ground water was initially encountered during drilling of AMW-5 and AMW-6 at <br /> approximately 7 and 6 fbg The recovery wells were constructed of 4-inch-diameter, flush- <br /> threaded, Schedule 40, polyvinyl chloride (PVC) blank casing and 0.020-inch, slotted, PVC <br /> casing Recovery well construction details and installation procedures are presented with <br /> the boring logs in Appendix D. <br /> During installation, each well was surged prior to sealing the wells to- (1) compact the filter <br /> pack, and (2) reduce borehole side wall mudcake. The recovery wells were developed on <br /> December 5, 1991, by removing 10 casing volumes of ground water from each Recovery <br /> Well AMW-6 exhibited slow recharge characteristics with a calculated recharge rate of <br /> approximately 0 4 gallons per minute (gpm). Due to the initial slow recharge characteristics <br /> exhibited in Recovery Well AMW-6, this well was redeveloped on March 10, 1992, by surge <br /> block and pumping Recharge characteristics of AMW-6 were observed to be lower then <br /> during the initial development, with an estimated recharge rate of less than 0.2 gpm. <br /> General field procedures for recovery well development and field survey forms are <br /> presented m Appendix E. <br /> ID <br /> 4 <br />