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Cease and Desist Order R503-XXXX - 5 - San 5 -San Joaquin County Department of Public Works Corral Hollow Sanitary Landfill San Joaquin County Monitoring Program work plan to characterize the nature and extent of shallow groundwater impacted from the release from the WMU. The work plan required a minimum of three additional off site groundwater monitoring wells. 29. On 10 October 2011, the County drilled three temporary borings offsite to assess the extent of the release from the WMU as required by the Order. VOCs were detected in the grab groundwater samples collected from the three temporary wells, and according to the approved work plan, the County initiated step out borings to define the VOC plume. The three initial temporary borings were abandoned per San Joaquin County guidelines. 30. During February 2012, the County advanced three step-out borings to fulfill the requirements of the EMP. Three borings were constructed as permanent groundwater monitoring wells MW-9A through MW-11A. Groundwater samples were collected and analyzed for VOCs. Sampling results indicated that several VOCs were detected at low concentrations in all three step-out wells. 31. In a letter dated 26 September 2012, Board staff issued a Notice of Violation requesting that the County provide a work plan to conduct additional off site investigation to define the VOC plume northeast of the site, to conduct a water supply well search within a 1-mile radius of the site, and to propose the installation of a minimum of two soil gas probes along the northern site boundary to monitor migrating landfill gas. 32. In a letter dated 29 October 2012 the County submitted a work plan proposing to conduct a water supply well search and install two soil gas probes. The letter also confirmed a meeting between the County and Board staff discussing the 26 September NOV and staff's request for further off-site investigation. The County insisted that additional work in the northeast direction to further define the plume would not affect the approach to corrective action. A complete EMP Report and Engineering Feasibility Study (EFS) to evaluate corrective action measures as required by the 13267 Order is pending. 33. The Third Quarter 2012 Groundwater Monitoring Report indicates that VOCs continue to affect water quality beneath the site and off site in newly installed wells MW-10A and 11A. Up to six VOCs were detected in both wells MW-5 and MW-8 and up to three VOCs were detected in off site wells MW-10A and MW-11A. PCE was detected above the PHG in wells MW-5, MW-8, MW-10A, and MW-11A. The highest PCE concentration was reported in well MW-5 at 4.2 pg/L. 34. According to the EMP Report submitted, VOCs are being detected approximately 1,000 feet downgradient of the point of compliance. The release from the landfill has been detected in groundwater since 1991 and the County has installed 44 LFG extraction wells to address impacts to the vadose zone and groundwater. LFG extraction has been in place since 2001, yet this corrective action does not appear to be effectively controlling the source as evidenced by off site migration.