CORRESPONDENCE_2007 (1/07 - 6/07)

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An increasing trend of nitrate as nitrogen and a decreasing trend in pH has been noted in MW -4. In 2003, improvements were made to minimize infiltration and reduce ponding. This has had a positive impact on the groundwater quality in this area. Trends of chloride, total dissolved solids (TDS), and electrical conductivity (EC) are also increasing. Chloride, TDS and EC were reported at 90 mg/l, 690 mg/l, and 1218 umhos/cm in October 2005 for MW -5. The trend in pH is decreasing for MW -5 in July 2003 the pH was reported at 7.03; in October 2005 the pH was reported at 6.94. Run-off/Run-on facilities The Corral Hollow Sanitary Landfill utilizes several methods to control run-off and run- on to the facility. A perimeter road/berm around the waste management unit prevents any run-on to the unit. Run-off is directed into two retention ponds via a mid -slop berm and perimeter ditches. The most likely release that will require corrective action is an elevation of VOCs in groundwater rather than an elevation of inorganics. The hypothetical release scenario for the Corral Hollow Sanitary Landfill is as follows: 1. Release occurs from the unlined landfill, potentially in three directions (north, south or east 2. Deep landfill gas (carrying VOCs) beyond the influence of the existing landfill gas extraction wells escapes from the bottom of the landfill. 3. The escaped landfill gas travels to groundwater resulting in low level (<50 µg/1) VOC concentration in groundwater. An Evaluation Monitoring Program (EMP) may be required to investigate the lateral and vertical extent of a hypothetical release from Corral Hollow Sanitary Landfill in the shallow aquifer. This EMP will consist of work plan preparation and approval by the agencies, implementation of field investigation and preparation report of the findings. An EMP work plan will be submitted to the RWQCB in accordance with Section 20425 (a) and (b) of Title 27. The EMP will include a soil gas and groundwater step-out/step- down investigation of the northern, eastern and southern boundaries of the site similar to the program now requested by RWQCB staff. Corrective Action Financial Assurance Cost Estimate 3 May 25, 2007 Corral Hollow Sanitary Landfill San Joaquin County Public Works