SITE INFORMATION AND CORRESPONDENCE

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Mosquito Abatement District Page 3 Site Status Following the removal of the underground storage tanks, soil contamination was 7 excavated .to 27 feet below ground surface., Residual soil contamination. was detected,up .to, 12 ppm TPH. However, the detection limits used for BTX were too: ,.. high and sidewall samples were not collected. On April 13, 1987, to verify that the on site well was not affected by the petroleum hydrocarbon release, a sample was collected and analysis indicated that the well was not contaminated and that,,groundwater within the well was noted at 28:feet below. 4 i ground surface. Subsequently, two new tanks (#9 and #10) were installed in the area excavated. On December 4, 1991, a UAR and Prop,65 notification were filed,by..PHSIEHD. Correspondence prepared by PHSIEHD dated December 23, 1991 informed,you that a UAR was fled and that additional investigation of the site was required- On February 3, 1994, you were notified that,a work plan to install monitoring wells and to continue the soil investigation should be submitted—Jin-July seven soil . F boring were drilled,three of which were converted into monitoring wells and two were continued to allow the collection of groundwater samples using a hydropunch. The results from this investigation indicated that there was possible residual,soil contamination 'in'the area of former tanks41, #2 and #4. • -, In order to confirm that groundwater.has .not-been impacted,,additional groundwater monitoring and sampling should be scheduled by March 31, 1995. As _P.HS/EHD requested during the recent meeting, a summary,of,all:the prior soil and Y groundwater analytical results.from the tank,removals, over-excavation, soil borings, , groundwater monitoring wells and hydropunches should be,prepared,and. submitted. immediately. A-corrective action plan estimating the volume and concentration of residual soil contamination should be submitted by May 15;" 995. As'you in the District is evaluating the necessity of retaining use of tanks #9 and #10. If these tanks are removed, it will likely occur sometime between April and June 1995 and at that time additional remedial investigation will occur. If you have any questions.or to schedule a site inspection to�witness sampling, please contact Mary Meays at (209) 468-0337..' Donna-Heran, RENS; Director , 4 Environmental Health Division Mary Meays,'Senior REHS, 7 -Diane M. Hinson, RENS -r Site Mitigation Unit .. : Y=`Supervisor MM/MOSQUITO w cc: Elizabeth Thayer, Central Valley Regional Water Quality Control Board