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L <br /> DIRK orainLP <br /> Ms Margaret Lagorio <br /> San Joaquin County Public Health Services <br /> February 4, 2000 <br /> Page -3- <br /> Task 4—Estimation of Petroleum Hydrocarbon Mass in Soil and Groundwater <br /> As part of the data evaluation, the vertical and horizontal extent of petroleum hydrocarbons in <br /> groundwater have been estimated based on groundwater monitoring data from the March/April 1999 and <br /> September 1999 groundwater monitoring events and the discrete vertical groundwater sampling In <br /> addition, the historical soil analytical data are being depicted horizontally and vertically to evaluate the <br /> extent of petroleum hydrocarbons in soil These data are being used to estimate the mass of petroleum <br /> hydrocarbons in soil and groundwater The results will be included in the report <br /> Task 5—Natural Attenuation Evaluation <br /> Natural attenuation of TPH-G and benzene have been evaluated using current and historical groundwater <br /> monitoring data, inorganic analyses (nitrate and sulfate), and water quality parameters (pH, conductivity, <br /> and dissolved oxygen)to assess the potential for natural degradation of residual petroleum hydrocarbons <br /> A discussion on natural attenuation has been included in the report <br /> . On behalf of Caltrans District 10, we appreciate your patience Following the submittal of the report, <br /> URSGWC will complete a human health risk assessment and groundwater impact analysis and the <br /> evaluation of remedial alternatives <br /> If you have any questions, please feel free to contact Saiyed Ali of Caltrans at (209) 948-7873, or George <br /> Piantka at(805) 964-6010 <br /> Sincerely, <br /> URS Greiner Woodward Clyde <br /> George L Piantka, P E <br /> Project Manager <br /> c Lori Duncan, San Joaquin County <br /> Saiyed Ali, Caltrans <br /> Carlos Lopez, Caltrans <br /> Attachments <br /> Figure 1-1 Site Location Map <br /> Figure 5-1 Vertical Groundwater Sampling Results <br /> Figure 5-2 Groundwater Elevation Contour Maps <br /> Figure 5-3 Discrete Sampling Results and Quarterly Monitoring Results <br /> ONSITE Analytical Data <br /> 11SBA11SHAREDNPROJW1D4010DO41SYYARDIS CPHSLTRSTKTNYDDOG 242000 <br />