SITE INFORMATION AND CORRESPONDENCE

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al � Mosquito Abatement District Page 3 Site Status „ Following the removal of the underground storage tanks, soil contamination was excavated to 27 feet below ground surface. Residual soil contamination was detectedup to 12 ppm TPH. However; the' detection limits used for BTEX 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 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. In July 1994, seven soil 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 tanks #1, #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 'PHS/EHD requested during the recent meeting, a summary' of all the prior soil and, 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, 1995.- As you indicated, 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. r If you have any questions or to schedule a site inspection to witness sampling, please contact Mary Meays at (209) 4168-0337. { Donna Heran, RENS, Director Environmental Health Division Mary Meays, Senior REHS:' Diane M. Hinson, REHS Site Mitigation Unit Supervisor MM/MOSQUITO cc: Elizabeth Thayer, Central Valley Regional Water Quality Control Board