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Corral Hollow LFG System Audit and Upgrade Report INTRODUCTION ' SCS Engineers (SCS) was retained by the County of Joaquin Department of Public Works (County) to prepare this Landfill Gas (LFG) Extraction System Evaluation and Upgrade Report ' for the Corral Hollow Landfill (CHLF or Site). This report was specifically prepared to comply with Item No. 2, on page 10 and 11 of the Cease ' and Desist Order R5-2013-0024 (CDO) issued by the Central Valley Regional Water Quality Control Board (RWQCB, April 16, 2013) for the CHLF and includes an audit and evaluation of the Site's current LFG gas collection and control system(GCCS). ' The CDO was issued in response to the detection of volatile organic compounds (VOCs) in shallow groundwater monitoring wells MW-5, MW-8 and'two off-site monitoring wells. The ' presence of these compounds is thought to have been caused by LFG from the Site, in particular from an area near MW-5. The VOC detections are most likely from LFG not captured by the existing GCCS, which includes an approximate 1.6-acre area without a final cover (RWQCB, t2013). Given the above, this Report provides a description of these and other measures that have been taken to provide and maintain continuous negative pressure in each LFG extraction well. This report also provides an Operational Procedures Document that describes ongoing procedures implemented to ensure that LFG extraction is continuously optimized. SCOPE OF WORK ' SCS's work under this assignment included: • Review of County-provided information on site conditions, GCCS operation and soil gas ' monitoring at the Corral Hollow Landfill. • Perform a GCCS operations review via field inspection, monitoring and testing during October, 2013. Results of this review are provided in Appendix A. • Perform an engineering evaluation of the effectiveness of the GCCS and the system's ' ability to capture and control LFG, including the newly-installed LFG wells. Included herein are descriptions of system components, current performance and measures that have been taken to provide and maintain, to the extent possible, continuous negative ' pressure in each LFG extraction well. • Prepare this summary audit/evaluation report,which includes: o Evaluating the ability of the system to prevent additional LFG from migrating into the vadose zone or groundwater. ' o A description of the measures that have been taken to provide and maintain continuous negative pressures in each LFG extraction well. 1 December 2013