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n 0 r If the sample indicates VOC impacts that are consistent with those observed in the existing site monitoring wells, then the temporary well will be removed, and the borehole will be abandoned in accordance with requirements of the San Joaquin County Environmental Health Department guidelines. Another borehole will be drilled using the groundwater equipotential data to establish a downgradient direction and the chemistry data to extrapolate a distance where VOCs should be below the respective detection limits (i.e., at an approximate zero VOC concentration line). This process will be repeated as feasible until sample results indicate non-detectable VOC concentrations. At these final locations, permanent wells will be constructed by reaming the borehole to ten inches in diameter, advancing the borehole approximately 20 feet into the saturated zone, and completing well construction in accordance with State of California and San Joaquin County guidelines. Specific drilling, well construction, well development, sampling and analytical procedures are presented in the following sections. The locations of the County's three replacement EMP borehole/monitoring wells described herein have been negotiated with Caltrans, and access to these locations are subject to the terms of an encroachment agreement between the County and Caltrans. If additional drilling is required to define the "zero concentration" line, these well locations would likely be considered on properties not owned by the County or Caltrans. For these replacement wells, additional access/encroachment agreements would need to be obtained from the property owners, and the EMP deliverable schedule would likely need to be revised. The County would notify the RWQCB immediately should it be necessary to revise the project schedule again. 3.2 MONITORING WELL LOCATIONS AND RATIONALE As required by the Order, a minimum of three new monitoring wells are proposed to be constructed to evaluate VOC migration in the shallow aquifer outside of the property boundary. As shown on Figure 3, replacement wells MW -9A and MW -10A would be cross - gradient or down -gradient from the landfill, constructed to the west/northwest of existing wells MW -5 and MW -8. Well MW -11A would be constructed downgradient of well SB -1, to the northeast of SR -580. The construction of these three wells will help further define groundwater flow direction and gradient of the shallow aquifer, if not the extent of the shallow aquifer. It is anticipated that exploratory boreholes will be drilled to depths of approximately 90 feet. Temporary monitoring wells will be drilled to depths of no greater than 95 feet. Site- specific data suggest that the depth to the Corcoran Formation is approximately 60 feet, and groundwater is found approximately 10 to 20 feet into the Corcoran Formation. Temporary wells will extend approximately 5 feet past the first encountered groundwater or to the bottom of the Corcoran clay unit, whichever it encountered first. 2011-0115 CHSL EMP Workplan Revision 2 —January 11, 2012 0 Geo -Logic Associates