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PHASE VI SUBSURFACE INVESTIGATION Site Code 2163 Montgomery Ward Auto Service Center 5400 Pacific Avenue,Stockton, CA geologists The borings MW-4 through MW-6 were drilled to a depth of 68 feet bgs, while boring MW-3 had a termination depth of 67 feet bgs (see Figure 2) The borings were dnlIed using 10'/4-inch outside diameter continuous flight hollow stem augers Mr Mike Infurna of the County was on-site during most of the drilling and sampling activities All borings were logged ' in accordance with the Unified Soil Classification System (see Appendix A) Soil samples were obtained from each boring beginning at approximately five feet bgs and at approximately five-foot intervals thereafter until 65 feet bgs The samples were collected using six 2'/2-inch diameter by three-inch long brass tubes mounted within a 2'/z-inch inside diameter Modified California split-spoon drive sampler The sampler was attached to the down-hole hammer, lowered to the sampling depth, and then driven into the formation for the length of the ' sampler Hammer counts per six-inch of penetration of the barrel sampler were recorded to measure the consistency of the formation After sample recovery, the ends of the lowermost three-inch long tube were covered with aluminum foil and plastic caps taped over the ends ' Prior to use, all tubes were washed in a solution of Alconox detergent and tap water, rinsed with tap water and then with distilled water The samples were labeled with the sample point identification, EAT project number, depth interval, time and date, individually sealed in "Ziploc" ' plastic bags, and immediately placed into an ice chest chilled using crushed ice The samples were kept chilled until delivered to the laboratory for analytical testing All samples «ere logged on chain of custody record forms (see Appendix B) An HNU Model DL-101 Phototonizer/Datalogger calibrated against an isobutylene gas standard was used on soil contained in the second tube from the bottom of the shoe, at each sampling interval within the borings to determine if volatile hydrocarbon vapors were emanating directly from the soil Each sample was placed in an airtight "Ziploc" plastic bag The samples were allowed to sit in the sun, and then the head space in the bags was analyzed using the IDI U Photoionizer The results of this testing were recorded on the boring logs (see Appendix A) ' 3 2 MONITORING WELL CONSTRUCTION & DEVELOPMENT Borings MW-3 through MW-6 were converted to ground water monitoring wells MW-3 through ' MW-6, respectively (see Figure 2) Appendix C contains the County permit issued for construction of the wells All wells are constructed of four-inch inside diameter flush threaded Schedule 40 polyvinyl chloride (PVC) well casing The wells are designed with a slotted section ' (0 02-inch x two-inch slots) which extended from approximately 48 feet bgs to the termination depth of each well The annular space between the borehole wall and well casing was backfilled with grade #3 Morie sand to about two feet above the slotted section Aur e block was then used on the well to help develop the well and to set the sand pack surrounding the casing After ' using the surge block, additional sand was added to the annular well space until the top of the sand pack was two feet above the slotted section A two-foot thick layer of hydrated quarter- inch diameter bentonite pellets was placed directly on top of the sand pack as a sanitary seal, and ' the remaining annular space was backfilled with cement grout to the surface The grouting material used was Portland Neat Cement type II Potable water was used for mixing grouting materials Flush mounted lockable traffic grates are placed on all the wells Further, the grates are designed to prevent sheet flow from entering the wells appendix D contains the specific well construction details for each well Mr Mike Infurna of the County was present during the grouting of the wells The wells were developed on February 8, 1995 approximately two weeks after well installation Well development was performed by V & W Drilling Inc , using a Mobil B-61 HDX rig equipped with an eight-foot long, 3'/2-inch diameter stainless steel bailer The balling equipment 1 Project No 1232 5 ENVIRONMENTAL AUDIT, INC