ARCHIVED REPORTS XR0006610 - Laserfiche WebLink

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it . Correc,tive Action Plan—Tosco(76)Service Station No 11192, Stockton, California March 13, 2002 4.0 Work Plan for Additional Delineation To perform additional vertical and lateral delineation of the MtBE plume, GR proposes to install one onsite shallow groundwater monitoring well and two offsite deeper groundwater monitoring wells The onsite shallow well will be installed to provide onsite downgradient delineation of the plume The two deeper wells will provide additional data for lateral and vertical delineation of the MtBE plume GR also proposes to install twelve microsparge points to initiate remediation of the known hydrocarbon plume Ten of the proposed sparge points will target the shallow impacted zone, and two points will target the deeper impacted zone in the vicinity of well MW-11 The proposed locations of the wells and sparge points are presented on Figure 3 4 1 Pre-Field Activities GR will update the site-specific safety plan and obtain the necessary well installation permits from the San Joaquin County PHS-EHD In order to install the off-site groundwater monitoring wells GR will obtain encroachment permits from the San Joaquin County Department of Public Works A private utility locator will be contracted to locate any underground utilities near the proposed well locations and Underground Service Alert (USA) will be notified 48 hours prior to drilling • 4 2 Drilling and Sampling Drilling and well construction activities will be performed by a California licensed driller A GR geologist will observe the drilling,collect soil samples for chemical analyses, describe the encountered soil, and prepare a log of the boring The borings will be advanced using 8-inch-diameter hollow-stem augers and a truck-mounted drill rig 4 3 Monitoring Well and Sparge Point Installation The groundwater monitoring wells will be constructed of 2-inch-diameter Schedule 40 polyvinyl chloride (PVC)well casing and 0 02-inch machine slotted PVC well screen The screened interval of the shallow well will extend from 10 to 30 feet bgs to accommodate known groundwater fluctuations in the area The screened interval of the deeper wells will extend from 70 to 80 feet bgs Proposed well construction details are shown on Figures 4 and 5 The sparge points will be constructed with 2-inch diameter sparge points attached to 3/4-inch blank schedule 80 PVC casing installed through the hollow-stern augers The sparge points are composed of 30-inch long sections of microporous plastic The shallow sparge points will be installed to a depth of approximately 30 feet bgs, and the two deep sparge points will be installed to an approximate depth of 80 feet bgs The two deep sparge points will each be nested in a boring with a shallow sparge point Proposed sparge point construction details are presented on Figures 6 and 7 140245 08 13