SITE INFORMATION AND CORRESPONDENCE

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1./ 880 Victor,Lodi Page 2 For example,EHD notes that 7 of the 13 analyzed samples collected from the SVE borings were sand,2 were sand or silt(boring logs show both lithologies) and 4 were silt samples underlying the sand units,all were collected between 14 and 30 feet bsg. MTBE,having little affinity for soil in general,is least likely to sorb to the sand,only the 4 silt samples should have been comparable to the previously collected data. Of twelve older soil samples having more than 1 mg/kg MTBE,all were collected at 25 feet bsg or deeper,eleven were silt or from an interval with a silt/sand transition,one was collected from a sand interval at 50 feet bsg. It appears to EHD that lithology and sampling depth may also have a significant influence on MTBE occurrence. EHD believes that the dissolved MTBE concentrations in groundwater may be declining due to degradation of MTBE to TBA as discussed at the June 9,2005,meeting with you and your consultant at the EHD office. Cambria has interpreted the low MTBE mass recovery during the SVE pilot test, the apparent decline of MTBE in soil data and the declining dissolved MTBE data to indicate a reduction of sorbed MTBE mass such that the remaining mass poses little additional threat to groundwater and that further remediation is not necessary.These three observations form a reasonable basis for that interpretation,but as noted above,EHD believes that the reduction of MTBE in soil and groundwater may be related to other factors and is concerned that a threat to groundwater may remain. Taking the conservative course protective of human health and groundwater resources, EHD directs you to advance at least one confirmation soil boring near one of the borings formerly known to encounter impacted soil in the close proximity of the UST pit to test the Cambria interpretation. If you would like to incorporate this work with the installation of the monitoring wells, submit an addendum to the work plan with your proposal for drilling, sampling and placement of the soil boring. In a telephone conference with you and Cambria on July 25,2005,EHD agreed with your proposal to conduct interim groundwater extraction at the site. You were to submit a groundwater extraction work plan. In later conversations with EHD staff,Cambria proposed conducting some initial groundwater extraction to determine the most effective pumping rate,propose a frequency of conducting interim groundwater extraction,and determine if a permanent groundwater extraction system could be installed at the site. Interim groundwater extraction has not been implemented to date. You are directed to begin implementation of interim groundwater extraction by October 12, 2005,and submit a report of the groundwater extraction activities with a recommended interim groundwater remediation schedule and system to EHD by November 12,2005. If you have any questions contact Jeffrey Wong,Senior REHS,at(209) 468-0335. Donna Heran,REHS,Director Environmental Health Department cl P, v&'' Y�AylL 6 Jeffrey Wong,Senior REHS Margaret Lagorio,REHS LOP/Site Mitigation Unit Supervisor C: CRWQCB, Central Valley Region—James L.L.Barton,RG C: Cambria Environmental Technologies, Inc. —Aubrey Cool