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3.1 Calibrating a Groundwater Plow Model for Pumping llesiv-i Condor has performed additional computer modeling of the groundwater system in an attempt to better predict the response of the system to pumping from wells in the vicinity of MW-6. Tlie numeric computer model used is Visual Modflow, an adaptation of the USGS Modflow and Modpath codes. 7lre simulation system was set up using piezometric heads from early observations, before potential impacts from bioremediation activities began. The intent was to see if the model can reasonably estimate the plume location as observed in 1992. The result is shown in Figure 3. Recharge through the former rinsewater pond was simulated assuming 16 weeks of operations discharging 4,000 gallons/day 6 days a week. Particle tracking was applied at the rinsewater pond to generate flow lines away from the source. 7lre flow lines successfully recreate observations prior to 1992, which show the plume contained between wells MW-3, MW-5 and MW-7. Based on this result we assume the model is a reasonable representation of the system, limited, of course by uncertainties in hydraulic conductivity and aquifer heterogeneities. 3.2 11-inming_From Existing Monitoring Well MW-4A MW-4A has historically yielded the highest chloroform levels and it makes sense to remove this most contaminated water as early as possible from the flow stream. A second advantage of pumping from this well is that it removes water from other pumping activities which is recirculating through the former,rinsewater pond, thus relieving somewhat the mounding that tends to disperse percolating water, and helping to contain the plume in an east-west direction. Pump testing of MW-4A indicated that 15 gpm would sustain a 14 foot drawdown without drying out the well, however subsequent pumping from MW-4A could not sustain 5 gprn. This may be due to inadequate development of the well. Therefore MW-4A will be re-developed with surge block and bailer until it runs clear before pumping is resumed. Development water will be released to the aeration pond (former rinse water pond). All necessary electrical and plumbing connections to pump water from MW-4to the aeration pond have been installed with the exception of an in- line flow device. This will be installed during redevelopment. The pond will also be instrumented with a pressure transducer to monitor water levels. The existing pump will be re-installed near the bottom of the well. Maximum pumping will be initiated during a trial period in order to (1) promote rapid development of a cone of depression, (2) to assess the efficiency of the well and pond aeration system, and (3) to evaluate the capacity required for the excess-water overflow system, if possible (see disposal section). Water-handling systems will be modified as required. N�_ L19 CONDOR