SITE INFORMATION AND CORRESPONDENCE

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John Johnson Page 2 The potential exposure pathway discussion will be useful for performing a risk assessment for the site. While the results of a risk assessment are not accepted by the Central Valley Regional Water Quality Control Board(CVRWQCB)or EHD as stand-alone criteria for site closure,they are one factor considered for site closure. At this time,EHD is more interested in identifying migration pathways through the subsurface that will influence the potential for the contaminants to impact sensitive receptors or impact additional groundwater supplies,thereby degrading their beneficial use. Theses issues may also be addressed in a revised SCM that incorporates the findings from the next phase of work. The remedial alternatives for impacted soil and groundwater discussed in the Report comprise a sort of CAP,but are presented as general descriptions of the alternatives without incorporation of site specific data,estimates of costs,or estimates of effectiveness. EHD cannot evaluate the alternatives as discussed at this time,but does note that the shallow depth to groundwater on the site and the predominance of fine-grained soil at shallow depth,limit the potential for use of soil vapor extraction and,therefore, also limits the potential use of insitu air sparing. ATC proposes to delineate the vertical extent of impacted soil and groundwater by advancing three CPT borings onsite to characterize the hydrogeologic framework of the site and collect soil and groundwater samples for laboratory analysis.. EHD approves the scope of work noting that sufficient data should be collected to identify and correlate all major potential permeable hydrological units. Include the compounds ethanol and methanol in future soil and groundwater analyses. EHD does not agree that shallow impacted soil has been fully delineated. Most soil samples collected between 6 and 7 feet below surface grade(bsg)have been impacted and probably represent the capillary fringe smear zone. EHD recommends that the proposed CPT boring locations be sampled at approximately 6 or 7 feet bsg and that additional shallow borings be advanced at the following locations: two borings adjacent to the north of each dispenser; one boring approximately 20 feet west of monitoring well (MW-5); one boring approximately 20 feet northwest of MW-1; one boring approximately 20 feet west of boring,B-13; and one boring midway between MW-4 and boring,BH-4. The latter six borings to collect shallow soil samples may be advanced by geoprobe or another cost-effective method, and based on the findings from the CPT borings, it may be necessary to collect deeper soil samples from one or more of the recommended additional shallow borings. Please submit a work plan by May 10,2004,that addresses EHD's recommendations presented in this letter. Submit a drilling permit application for advancing the 3 CPT borings,along with an $89.00 fee, and notify EHD at least 72 hours prior to commencing the fieldwork. Please contact Vicki McCartney,REHS,at(209)468-3456 or vmccartneyRsjcehd.com if you have questions regarding this letter. Donna Heran,REHS,Director Environmental Health Department Vicki McCartney,REHS Nuel C.Henderson,Jr.,RG Unit IV-Site Mitigation Unit IV-Site Mitigation cc: Drew Van Allen-ATC James L.L.Barton-CVRWQCB