COMPLIANCE INFO - Laserfiche WebLink

Home Browse Search

Revised Work Plan for Additional Site Investigation Raymond Investment Corporation Former Helena Chemical Facility February 27,2018 Page 7 5.2.3 Proposed Monitoring Wells Condor proposes drilling and installing two (2) additional shallow groundwater monitoring wells (MW-4 and MW-5) at the Site. One monitoring well (MW-4) will be placed approximately 190 to 200 feet south of well MW-3, on the east side of the main office/warehouse building to evaluate the extent of dissolved Nitrate-N and 1,2,3-TCP in shallow groundwater in that direction. One monitoring well (MW-5) will also be placed approximately 140 feet southeast of well MW-2 to evaluate the extent of dissolved Nitrate-N and 1,2,3-TCP in the presumed downgradient direction (south-southeast) from well MW-2 and boring B39/GW12. No additional monitoring well is proposed northwest of well MW-1, because historical "grab" groundwater samples collected in that direction (B28/GW6 and B29/GW7 contained Nitrate-N at concentrations less than the established MCL of 10 mg/L. During installation of the proposed monitoring wells, soil samples will be collected at a depth of approximately 10 feet bgs and submitted to a California-certified laboratory for analyses. The approximate locations of proposed monitoring wells are shown on Figure 5 (Appendix A). 5.3 SOIL BORING DRILLING AND SAMPLING METHODOLOGY Soil borings will be advanced using a Geoprobe direct push drilling rig by a drilling company licensed by the State of California (C-57 drilling license). The direct push borings will be hydraulically advanced using a 2.25-inch diameter sampling bit. Continuous core soil samples will be collected from each of the borings with a 2-inch outside diameter (OD), 4-foot-long core barrel fitted with a clean, single use, polyethylene liner. During the sampling, the core barrel will be driven in four-foot intervals. The sample liner will be extracted from the core barrel and used for geological logging in general accordance with the Unified Soil Classification System (USCS), and for field observations. Samples selected for laboratory analyses will be cut above and below the selected sample interval to separate the sample from the rest of the four-foot tube, capped with Teflon® tape and plastic end caps, and placed into a pre-cooled ice chest pending shipment to an analytical laboratory under chain-of-custody procedures. A generalized soil boring diagram is included as Figure 6 (Appendix A). Upon completion of sampling activities, each boring will be backfilled with neat cement grout from the bottom of the bore hole to the ground surface pursuant to EHD guidelines. Due to the presence of shallow groundwater beneath the Site (<10 feet bgs) all sealing material will be placed using a tremie pipe. If soil conditions prevent the Geoprobe drilling rig from reaching the target depth, then the drilling location may be completed using a drilling rig equipped with hollow stem augers, at the discretion of the Condor professional geologist. 5.4 "GRAB" GROUNDWATER SAMPLING METHODOLOGY Condor will collect "grab" groundwater samples at from each of the proposed borings, as described in section 5.2.1. A "grab" groundwater sample will be collected at each boring location from the shallow water- bearing zone (approximately 10-12 feet bgs) and from selected locations at depth (approximately 30 feet bgs). Groundwater samples will be collected from selected borings using either a hydropunch groundwater sampler driven to the desired depth, or from temporary %-inch PVC screen installed into the bore hole. If installed, the temporary screen will be inserted into the boring after the soil sampling tool is removed. The groundwater samples will be retrieved from the hydropunch sampler or temporary screen with a length of new 3/8-inch polyethylene tubing equipped with a check valve at the bottom. The tubing will be moved up and down by hand to draw groundwater up inside the tubing. The groundwater samples will be discharged directly from the tubing into laboratory suiSplied sample containers. CONDOR