ARCHIVED REPORTS_2010_22 - Laserfiche WebLink

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Mr. Robert McClellon October 1 , 2010 Page b • New Probe Spacing—In accordance with CCR Title 27 §20925(b),the LFG probes will be installed at a horizontal spacing not to exceed 1,000 feet. The estimated horizontal spacing between each proposed probe is shown in Table 3. Final horizontal spacing intervals may vary due to site conditions,but shall be within 1,000 feet as required in Title 27 §20925(b). • Probe Depth—In accordance with CCR Title 27 §20925(c), LFG perimeter monitoring probes shall be installed (1)below the maximum planned waste depth; (2) above the permanent low seasonal groundwater table; and/or(3) above bedrock. Based on groundwater data since 2005, groundwater appears to range between approximately -10 ft msl and -25 ft msl, which is below the maximum planned waste depth, and therefore, is not expected to be encountered as part of this installation. Bedrock is not expected to be encountered during the installation,based on boring logs from the site. Therefore,the proposed probes are required to be installed to a depth below the maximum waste elevation. The minimum waste elevation in the planned expansion is -5 ft msl. The new probes are proposed to be completed to a depth of 40 ft bgs, which will bring the total depth below the planned waste depth but above the water table. The proposed depths are subject to change due to conditions encountered in the field at the time of installation. Table 3 lists the proposed depths for the new probes. Construction Details The proposed LFG probe construction details are shown in Figure 5 and the total depths and screened intervals are provided in Table 1. A triple-completion LFG probe will be installed at each proposed location. The probe casing will consist of%2-inch diameter or greater flush-thread schedule 80 PVC. The probe screen will consist of%Z-inch diameter or greater flush-thread schedule 80 PVC 0.010-inch well screen. The bottom of the screen for each interval will be capped with a secured end cap. No glue or solvents will be used during any part the construction of the probe. The deep interval will be installed to the total depth of the borehole. After the deep probe is in place,the borehole will be backfilled to the top of the screen with a filter pack consisting of pea gravel. A five-foot thick(minimum) layer of bentonite, hydrated to the manufacture's specifications, will be installed on top of the pea gravel to isolate the deep screened interval from the overlying screened interval. The bentonite and sand pack will be placed through the auger, and the auger withdrawn as the boring is filled to prevent borehole collapse. The sand and bentonite shall be tagged frequently with a weighted measuring tape to ensure proper placement of each material. If necessary, native soil cuttings may be used as fill above the bentonite layer to bring the borehole depth to the bottom of the next screened interval. The method utilized to install the intermediate interval will be the same as that used to install the deep interval. The shallow interval will be installed with the screened interval from 5-10 ft bgs [per CCR §20925(c)(1)(A)]. A five foot bentonite seal will be placed above the shallow screened interval. The surface of each probe will be protected by installing a locking metal monument box encased in an approximately 2-ft x 2-ft concrete apron. If necessary, a traffic-rated flush-mounted well box may be installed in place of the monument in high-traffic areas. The surface completion will