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6E5� GENESIS ENGINEERING&REDEVELOPMENT Howard F. Hold, P.G. May 29, 2009 Page 3 quality screening criteria for this Site was discussed with Dr. Jon Marshack, D.Env. of the RWQCB. Because municipal and domestic water supplies are the most sensitive beneficial uses for surface and groundwater in the vicinity of the Site, drinking water standards were used to select the lowest critical use screening criteria for groundwater beneath the Site. With only one exception (thallium), none of the laboratory reporting limits exceeded their respective water quality screening criteria. The method detection limit for thallium has consistently exceeded the California Water Quality Goal,but not the maximum contaminant level ("MCL"). RWQCB Comment: "The Discharger must develop a monitoring program for groundwater that includes a plan for defining the vertical and lateral extent of the plume. This proposed monitoring plan shall be submitted no later than 1 August 2009." As noted above,the six on-Site monitoring wells have been sampled quarterly since June 2008. In our April 16,2009 meeting, we requested that this monitoring frequency be reduced to semi- annual. The RWQCB staff stated that no monitoring reductions would be considered until sufficient data have been collected to conduct statistical analyses,typically eight sampling events. Furthermore, as discussed in that meeting, and as noted in your letter,the vertical and lateral extents of groundwater impacts in the vicinity of well MW-5 have not yet been delineated. GE&R proposes to complete delineation of the lateral and vertical extent of the groundwater impacts prior to proposing a revised groundwater monitoring program. Specifically, we propose to submit a work plan for delineation of the inorganic impacts to groundwater in the vicinity of well MW-5 by June 30, 2009. Once the lateral and vertical extent of these impacts is understood, and sufficient background water quality data have been collected to establish concentration limits, a Groundwater Monitoring Plan will be prepared for RWQCB approval. Until a new Groundwater Monitoring Plan is approved for the Site, GE&R will continue to conduct quarterly groundwater monitoring of all Site monitoring wells. RWQCB Comment: "The Discharger recommended seven scenarios for completing closure at the DePaoli property. Staff evaluated the proposals and concurs with following the proposals to either clean close the site or consolidate the waste under an alternative cover design. Therefore, no later than 1 August 2009, a closure plan that incorporates one of the two above site closure proposals shall be submitted. As discussed in our 16 April 2009 meeting,this plan must include detailed cost analysis for each proposed scenario."