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' Revised Work Plan for Pilot Study 2 9 March 2011 Deuel Vocational Institution Burn Pit ' Tracy, San Joaquin County The contingency plan will be implemented if either baseline or background ' concentrations are exceeded by 20% at the transition well. Should this occur, two monthly consecutive sampling events would occur at the impacted well(s) and background well. URS is not proposing to conduct removal actions unless a compliance ' well is impacted for 6 months (above 120% of baseline and background). Should this occur, URS will evaluate injection of calcium polysulfate into the impacted well(s) and/or extraction of groundwater from the compliance wells. ' I concur with the Work Plan with the understanding the Work Plan will incorporate following comments: 1. URS proposes waiting 6 months to evaluate any unwanted impacts found in a contingency well, prior to implementing a removal action. Although some ' unwanted by-products may be generated in the treatment zone, they should be diminishing in the transition wells, and any concentrations greater than 20% of background or baseline concentrations at the compliance zone wells will require ' implementation of active remedial technologies. 2. URS has proposed evaluating barium, arsenic, iron and manganese as remedial ' targets during the Pilot Study, and is not considering total or hexavalent chromium, or salts as targets. Please incorporate total and hexavalent chromium in the analytical suites. ' 3. As a contingency measure, URS has proposed in situ remediation with calcium polysulfide or another reagent to remove inorganic constituents from the ' groundwater. This methodology should be evaluated prior to use as these reagents proposed for use to counteract the unwanted by-products of OES may also create additional unwanted by-products. This contingency measure is not ' approved, at this time. 4. URS is considering the re-start of the existing pump and treat system should ' groundwater extraction be needed. Since the system has not been operated since 2007, please evaluate and confirm if this system will function for use as a contingency measure. ' 5. Groundwater sampling for the Pilot Study is proposed to be conducted quarterly for four quarters (three quarters and an annual sampling event), upon which time the Pilot Study will be concluded. Based upon URS's estimate of groundwater flow velocity, impacts to the transition wells MW-24BP and MW-25BP may not be seen for 1-3 years, and may not be evident in the compliance wells for 3-7 ' California Environmental Protection Agency ' ¢Recycled Paper