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u a • • Second Quarter 1993 Groundwater Morutonng Report Krug Island Resort, Stockton,CA(Sete Code 1557) Project No W0367 01 Page 2 TPHG TPHD was not detected to any site monitoring well The approximate extent of dissolved contaminants (benzene) is shown on Figure 3 Analytical results are summarized in Table 2 Laboratory reports with chain-of-custody documents are included in Attachment 2 To further define the extent of dissolved hydrocarbon impaction at the site, RESNA proposes to install an additional groundwater monitoring well downgradient of well MW4 (Figure 4) This additional proposed monitoring well (MW6) will be positioned to define the downgradient extent of the contaminant plume, and provide a sampling point downgradient of well MW4, which provides questionable data due to continued silting. PROPOSED FIELD METHODS The following section will serve as an addendum to RESNA's Preliminary Report/Assessment of Potential Soil and Groundwater Contamination, December, 1990, which outlined field methodology for the installation of initial groundwater monitoring wells That workplan was approved by your office with no modifications • Drilling will be conducted by a C-57 licensed company using a hollow stem auger drill rig Eight-inch outside diameter continuous flight augers will be used for boring and well construction. The boring will be advanced to approximately 18 feet below grade (15 feet below the depth of saturation) and converted to a two-inch diameter groundwater monitoring well The actual completion depth will be determined in the field based on hydrogeologic conditions encountered. All procedures and protocol for groundwater monitoringfwell construction will conform to State of California and San Joaquin County water well standards Well completion depth will be based on the setting of the well screen 15 feet below and one foot above the saturated zone In order to allow for seasonal fluctuations in water level However, if a significant aquitard is encountered below the point of saturation, the well will be terminated within the aquitard All necessary permits will be obtained prior to initiating field work. The wells will be constructed of two-inch diameter F480 threaded PVC screen/casing No glues or solvents will be used Screen slot size will be 0 010-inch Sand pack material will be #2 pre-washed silica sand The well annulus above the sand pack will be sealed with hydrated bentonite and/or neat cement, in accordance with state and local guidelines Proposed well construction is presented in Figure 5 Drill cuttings and core samples will be logged continuously for characterization of contamination and soil type by an experienced geologist using the Unified Soil Classification System Descriptions of soils encountered and monitoring well construction details will be recorded on �s 2QR-1993 FNL