SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr.Russell Chapin 1766 W.Monte Diablo Avenue Page 7 of 7 fine-grained and sand layers of contrasting hydraulic conductivities and variable thicknesses. • The contaminant mass reduction due to natural attenuation through biological activity has not been demonstrated or isolated from the engineered causes of mass reduction. The rate of natural attenuation has not been estimated. • A health risk assessment for an area of mixed land use and known depths of water as shallow as 10 feet bsg has not been conducted. There has been no demonstration that the current remediation activity, groundwater extraction, is not effective for mass removal or cost-effective. It should be kept in mind that the EHD does not run the models, but evaluates the input utilized for the models; therefore, all data manipulations and calculations should be provided for evaluation in the supporting model documentation. This would include figures of all contoured data and model output comparisons utilized to assign model input parameters. For the reasons stated above, the EHD still does not concur with the recommendation by ATC for immediate site closure. As you have filed an appeal with the State Water Resources Control Board (SWRCB)for closure consideration, the EHD will not issue further directives to you at this time. The groundwater extraction and treatment program, as well as the quarterly groundwater- monitoring program, should continue until directed otherwise by this agency or by the SWRCB. Questions or comments may be directed to Margaret Lagorio at (209) 468-3449 or to Nuel Henderson at (209)468-3436. Donna Heran, REHS, Director Environmental Health Division Nuel C. Henderson, Jr., RG Margar Lagorio, R HS Unit IV - Site Mitigation, LOP Supervisor, Unit IV, LOP C: James L.L. Barton—CVRWQCB Dennis Parfitt- SWRCB David Hankins—ATC Drew Van Allan -ATC Victor Mow— San Joaquin County Board of Supervisors, Supervisor District 3