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Messers Trommer and Larson Page 2 Re: Annual Five-Year Review Various Sites 08 June 2009 Page 2 of 2 well MW-3 appears to have rebounded from 790 pg/L and 2.5 pg/L to 86,000 pg/L and 270 pg/L, respectively. Concentrations of the same analytes in MW-7 are also elevated at 2,100 pg/L and 230 pg/L, respectively. Impacted ground water around MW-3 is delineated by monitoring wells in three directions while it is similarly delineated in only one direction around MW-7. The impacted groundwater is in an area of high groundwater usage, in fact MW-7 is approximately 15 feet from a domestic well believed to be only 140 feet deep. In August 2008, an MIP investigation in the core areas was conducted, but the results have not been submitted to the EHD for review. At this time the EHD believes additional monitoring of the core and inboard wells is warranted to more fully understand the import of the recently reported monitoring results, quarterly monitoring of MW-3 and MW-7 would also be helpful. The EHD also believes it would only be prudent to review the report of findings for the recent MIP investigation before making or concurring with a closure recommendation. The EHD would appreciate your reconsideration of the closure recommendation on this site at this time. 15 E. Grant Line Road — Your draft letter recommends site closure consideration. The EHD believes the site is nearly ready for closure consideration but has been seeking to have the vertical delineation of the plume of impacted groundwater completed and the down-gradient extent confirmed. The EHD has approved installation of monitoring wells to delineate the vertical extent based on significant hits in a cone penetration testing (CPT) investigation on site and in grab samples collected offsite in the down-gradient direction. The EHD has reevaluated the approved scope of work and reinterpreted the TPHg plume history on the site and now believes new grab groundwater samples will be sufficient to conclude the issue. The EHD plans to issue a directive rescinding the approval for the additional monitoring wells and recommending the acquisition of grab groundwater samples to complete the delineation requirements for site closure consideration. The EHD would appreciate your reconsideration of a site closure recommendation at this time. 2315 N. California Street—Your draft letter repeats last year's recommendation for site closure consideration. Two additional groundwater monitoring wells have been installed to complete the lateral delineation of impacted groundwater. The three sampling events conducted to date have yielded no quantifiable detections of contaminants of concern, although the EHD would prefer to have an additional monitoring event on these new wells, the EHD will proceed with recommending site closure consideration and requesting submission of a site closure summary report. If you need more information to complete your review of these sites, contact Nuel Henderson, Engineering Geologist, at (209)468-3436 or by mail (address on the letterhead). Nuel C. Henderson, Jr., PG Engineering Geologist C: Jim Barton, PG, CVRWQCB, 11020 Sun Center Dr. #200, Rancho Cordova, CA 95670 5-Year Review Comment Letter 0609.doc