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GEOSYNrEC CONSULTANTS Ms. Amy Terrell 31 January 2005 Page 2 As part of ongoing site investigations, in December 2003 GeoSyntec implemented ' a grab groundwater sampling program to investigate the downgradient extent of site- related compounds in groundwater. Results of the grab groundwater sampling program were reported to the RWQCB along with recommendations for follow-up work3. In ' their 23 August 2004 response letter, the RWQCB agreed with the proposed work, but also requested that JTF conduct a soil investigation to locate possible soil source areas ' contributing to chemicals found in perimeter monitoring wells. Specific chemicals cited by the RWQCB in the source area investigation request ' section of their 23 August 2004 response letter include bromacil and dinoseb. While these constituents have been detected in water samples at the site, the maximum historical concentrations of these constituents in groundwater samples are below all applicable state and federal screening criteria set fourth in the Compilation of Water Quality Goals. For example, the maximum concentration of bromacil ever detected in a ' monitoring well sample from the site is 7.8 ug/L4, less than 10% of the most restrictive goal for this compound, the U.S. EPA "Suggested No-Adverse-Response Level" (SNARL) of 90 ug/L. This SNARL is the level that is acceptable for drinking every ' day over the course of one's lifetime, and does not pose any health concerns. The RWQCB has stated that California Water Code mandates that all beneficial uses of water be protected, and that cleanup to background pollutant concentrations are the primary cleanup goal regardless of screening criteria5. JTF and GeoSyntec understand this position, but caution that regional background concentrations have not been established, and will not be known until the upgradient investigation is complete. The lack of significant concentrations of bromacil or dinoseb in groundwater reflect ' the probable lack of concentrated "source areas" in soil at the site. It is not practical to attempt to identify each soil area with very low levels of bromacil or dinoseb that may 3 GeoSyntec Consultants, 2004. "December 2003 Downgradient Delineation Report, John Taylor Fertilizers Co., Inc.,Stockton, California Facility." 30 March. ' 4 GeoSyntec Consultants, 2004. "December "2004 Annual and Semi-Annual Groundwater Monitoring Report,John Taylor Fertilizers Co., Inc.,Stockton, California Facility." 30 October. s RWQCB, 2000. "Conditional Approval of monitoring Well Installation Work Plan, Review of Site ' Investigation Work Report, John Taylor Fertilizers, Stockton, San Joaquin County". 13 March letter to John Taylor Fertilizer Company,Inc. P:\PRJ2003REM\Wilbur-Ellis\WrO250(JTF)\STOCKTON\S 1.X\2005 Source Area Invest\SSI Work Plan.doc i� AccvcLEo AND aEcvcueLE r