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NOW <br /> T ICI- TE <br /> ALTH SERVICES <br /> P`JBL <br /> SAN JOAQUIN COUNTY <br /> ENVIRONMENTAL HEALTH DIVISION t. <br /> Karen Furst, M.D., M.P.H., Health Officerq <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 95202 �.� <br /> 209/468-3420 �` E <br /> is <br /> BOB CARTWRIGHT' NOV 19 M7 J <br /> TRI VALLEY GROWERS ASSOCIATION <br /> ENVIRONMENTAL SERVICES ti <br /> P O BOX 1211 <br /> MODESTO CA 95353 . <br /> Re: Plant T: 26200 North Gait Road (Nowell Road) <br /> Site Code: 1920 <br /> nvironmental Health /EHD) has <br /> San Joaquin County Public Health <br /> lth of SEices, E COR rove ligation and RecomFmendations for Additional <br /> completed review of the <br /> "Analysis <br /> E Work" dated August 5, 1997 and the "Results of Monitoring Well <br /> SHapd ng Third Quarter <br /> 1997" dated September 11, 1997,both of which were prep Y <br /> PHS/EHD has the following comments for your consideration. <br /> Harding and Lawson sampled the existing monitoring wells on August 7, 1997,monitored the <br /> on August 6,_1997,and determined that the direction of groundwater <br /> depth to groundwater. <br /> j flow was to the south-southwest. The casing of mo ito i.ng s ill, The reportreportedly <br /> indicated <br /> fractured during sampling. Please submit a plan to p <br /> that the wells would be resurveyed as necessitated by the apparent erroneous measurements <br /> obtained from MW3d Mommends that theth to ewells be surveyed byr measurements ea licensed red greater surveyor one <br /> foot). PHS/EHD further <br /> The concentrations of contaminants detected during the August 1997 sampling event were <br /> significantly reduced as compared to the last sampling event which occurred June 1994. <br /> Please be aware that the maximum groundwater concentrations evidenced in June 1994 were <br /> 260 ppb TPH-gas and`11 ppb benzene while the maximum groundwater concentrations <br /> evidenced in August 1.997 were 54 ppb TPH-gas and 0..68 ppb benzene. Whether or not <br /> bioremediation was the primary process of remediation is unknown;however,it can be <br /> concluded that it was`Iikely that natural attenuation has occurred. Full-scale bench tests of <br /> bioremediation generally require the characterization of boundary conditions that are <br /> indicative of biological processes. Characterization of pre-bioremediation and post- <br /> bioremediation conditions have not yet occurred at this site to make the conclusion that <br /> bioremediation has occurred. Also, please note that bioremediation is not a passive process. <br /> t <br /> The work plan that recommended additional investigation to determine the vertical and <br /> horizontal extent of the soil and groundwater contamination is approved with conditions. The <br /> work plan proposed to advance two soil borings in the approximate locations of borings, SB-9 <br /> and SB-10 to investigate the soil and groundwater contamination in the area of the former <br /> underground storage tanks and one soil boring in the approximate location of HAI to <br /> investigate the soil and groundwater contamination beneath the shop building. Since distinct <br /> lithological units have been indicated, three groundwater samples will be collected from <br /> distinct depth intervals in each boring. <br /> Also, the work plan proposed to install a monitoring well in the area of the former <br /> underground storage tanks to assess the maximum groundwater contamination which remains <br /> after the 1994 cessation of the pump and treat groundwater remediation system. <br /> A Division of San Joaquin County Health Care Services <br />