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Additional Groundwater Investigation and Remediation Feasibility Evaluation Work Plan Stockton Center Site Authority-University Park - i �. January 25,2005 f Page 6 and deeper water-bearing units. The three deep wells will allow evaluation, monitoring, and potential remediation'of the deep groundwater beneath the site should several quarters of groundwater monitoring show persistent contaminant levels. Proposed deep monitoring well locations are shown on Figure 7 {. (Appendix A). The monitoring well borings will be advanced using,15-inch outside diameter, continuous-flight, hollow- stem auger. The hollow-stem auger and other down-hole equipment will be decontaminated between borings by steam cleaning to prevent cross-contamination. The borings may be advanced to a depth of ' approximately 85 feet bgs, and approximately one to two feet into a clay-rich unit anticipated at that depth based on interpreted CPT results. The actual depth and screened interval for the deep monitoring wells are not known at this time, however. The actual well specifications will be selected based on conditions . t encountered and observed during the continuous coring. Condor will attempt to identify the likely vertical extent of the contamination in the source area and the potential lower, contamination limiting unit(clayey aquatard), if present. The well construction will be designed to case off the upper contaminated units (with the conductor casing, described below) and screen the potentially non-contaminated water bearing unit (sandy aquifer) below the potentially present aquitard. The continuously cored monitoring well boring up-gradient of the source area will be advanced first, prior to the source area borings, to assist in anticipating the lithology of the source area borings. a, Following installation of the 15-inch diameter boring as described eight and five-eighths inch conductor casing fitted with a wooden end plug will be lowered into the boring and the outer annulus will be grouted } from the bottom of the boring utilizing a tremie pipe and a grout mixture of Type 1/11 neat cement containing less than 5% bentonite solids. The grout in each boring will be allowed to cure for 48-hours. The conductor casing will then be reentered with eight-inch hollow-stem auger and advanced 4 approximately five to six feet into the sandy unit which is anticipated to underlie the clayey unit. All drilling activities will be supervised by a Condor geologist in accordance with SJCEHD and CRWQCB guidelines and requirements. ' Drill cuttings from the monitoring well borings will be logged according to the Unified Soil Classification System(USCS). Descriptions of soil types encountered and any other pertinent field observations will be recorded on boring logs. In addition, cuttings will be placed in a polyethylene bag and checked with a PID for the presence of hydrocarbons. All visual observations and PID measurements will be noted on the boring logs. R Continuous core samples will be collected from each boring by advancing a 3/2-inch by 5-foot core barrel r fitted with an acetate liner inside the hollow-stem augers during continuous-flight hollow-stem"auger k drilling. The 5-foot sample will be retained for use in geological logging, PID measurements, and r laboratory analyses. At least three and as many as five soil samples per boring will be retained for chemical analyses to aid in defining the vertical extent of soil contamination beneath the site: Each sample will be cut from the acetate liner; sealed at the ends with Teflon® sheeting; capped; and labeled. The samples will be placed in a cooler with ice and delivered under chain-of-custody procedures to a California-certified laboratory for chemical analyses. Six to eight soil samples are expected to be retained from each boring for analyses of physical properties of various units encountered. Samples will be cut from the acetate liner; sealed at the ends with Teflon® sheeting; capped and taped to retain moisture characteristics; labeled; and delivered to a qualified lab to perform the analyses. In addition, the soil from the capillary fringe and upper saturated zone will be retained and sent to a qualified laboratory for bench �. scale testing to determine the feasibility of 'remediation techniques, including ozone injection and r bioremediation. Soil sampling equipment will be cleaned prior to collecting each sample using laboratory- grade,non-phosphate detergent and de-ionized water, and double'rinsed with de-ionized water. CONDOR I � -