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N <br /> PUBLIC HEALTH SERVICES <br /> p44 ! ,N <br /> SAN JOAQUIN COUNTY <br /> r.� <br /> ENVIRONMENTAL HEALTH DIVISION y; , <br /> Ernest M. Fujimoto, M.D . , M.P.H. , Acting Health Officer <br /> 304 E.Weber Ave. , 3rd Floor • P. O. Box 388 • Stockton, CA 95201-0388 <br /> 209/468-3420 r ° n <br /> �\ = -J Py <br /> ROGER LISTON <br /> 3450 EL CAMINO MAILED AUG 011995 <br /> CERES CA 95307 <br /> t RE: Gasco Service Station SITE CODE: 1060 <br /> 749 East Charter Way <br /> Stockton CA 95206 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has reviewed the June <br /> 30, 1995 Activity Report prepared by California Geophysical Group (CGG) for the above referenced site. <br /> The report contains summary tabulations of soil and groundwater analytical results, depth to water <br /> measurements and hydraulic gradients to date. The report describes hydropunch technique and field <br /> conditions encountered during the two recent hydropunches HP-1 advanced on June 19, 1995 and HP-2 <br /> advanced June 26, 1995 . Using the data from the hydropunches and the monitoring well sampling which <br /> occurred on April 25, 1995 and June 19, 1995 the report makes findings and draws conclusions. <br /> The conclusion CGG stated in the report is that an offsite upgradient groundwater plume is migrating onto the <br /> Darpetro site. The reports continues to state that the proposed vapor extraction system will treat the <br /> contamination in the unsaturated zone and probably will have an effect on groundwater; therefore, the <br /> possibility of remediating the plume on this site is not completely possible in the presence of the offsite plume. <br /> CGG requests recognition of the offsite plume by this department. <br /> y Based upon the data presented in the CGG report, PHS-EHD does not agree with the conclusion that an offsite <br /> plume exists. Analytical results from Monitoring Wells BM1 , BM4, BM7 and BM9 demonstrate expected <br /> attenuation values of 40.50 ppm Benzene to 3 .34 ppm Benzene. The elevated levels of Benzene present in <br /> BM9 may be attributed to calculation, sampling and handling errors, or BM9 may be a location where <br /> contamination has pooled. These elevated levels do not represent a significant difference in contaminant <br /> concentrations. <br /> PHS/EHD recommends that the investigation of the upgradient portion of this plume proceed as with any other <br /> offsite plume investigation. You are the recognized discharger of the plume which originates from assessors <br /> parcel number (APN) 147-343-09 the Darpetro site. Monitoring well BM-9 and the two hydropunches HP-1 <br /> and HP-2 were advanced on APN 147-343-10 the site west of, adjacent to and upgradient of the Darpetro site <br /> known as the location of Suns Garden Restaurant. Since the groundwater beneath this site is contaminated, <br /> the investigation should proceed with groundwater data from APN 147-343-11 which is west of, adjacent to <br /> and upgradient of the Suns Garden property, which is currently operating as an ARCO station . <br /> PHS/EHD recommends that CGG proceed with due diligence to complete the installation of the vapor <br /> extraction system . It is the understanding of PHS/EHD that there is one vapor extraction machine available <br /> and that machine will be available for this site b September. It is also the understanding of PHS EHD that <br /> Y P g / <br /> the vapor extraction system manifold has been installed but the vapor extraction wells have not been installed . <br /> A Division of San Joaquin County Health Care Services <br />