WORK PLANS FILE 2 - Laserfiche WebLink

Home Browse Search

y "Moe Cleo logluI nchgics 11tc. Page 10 Interim Remedial Action Plan Project No.723.2 March 7, 2005 sections detail the methods to achieve hydraulic control of the on site plume and prevent further dispersion of the contaminants. 3.2.1. Extraction Well A sustained pumping rate of 3 gpm was achieved in well EW-1 during the July 2004 pilot test. This well demonstrated that the site's soils are conducive to groundwater extraction technology. If pumping had continued in EW-1 then the drawdown would have produced a cone of depression further exposing soil to be influenced by vapor extraction. The bottom of this well is at 54.5 feet bgs. However, the contamination present in off site, down-gradient well MW-208 indicates that the aquifer is impacted in its screened level of 76 feet bgs (or approximately 37 feet below the water table). This well contained 4,020 ug/l TPH-G on October 21, 2004 (see Figures 4A & 4B for geology, soil and groundwater contamination in well set MW-8/108/208). A sand unit was identified in on site boring MW-101 at 70- 77 feet bgs and sands were also recorded at this depth in MW-208. The sands may be acting as a preferential pathway for contaminant transport to the northeast of the site. The bottom of EW-1 is 15 feet higher than this level and an additional groundwater extraction well is needed because no on site well intercepts this interval. GTI recommends installing one additional well, EW-2, to extract groundwater from the sand units in question. The proposed well EW-2 is shown on Figure 5: Cross Section C —C'. 3.2.1.1 Soil Boring Figure 2 includes the proposed well boring location. Well EW-2 will be installed adjacent to the former dispenser island and in proximity to the existing extraction wells to facilitate plumbing design. Prior to commencing work, encroachment permits and soil boring/monitoring well permits will be secured and the SJC/EHD will be notified 48 hours in advance. The subsurface will .r be cleared of underground utilities by notifying Underground Service Alert. The borings will be drilled using a 10-inch outside diameter continuous flight hollow stem auger. The borehole will be advanced to a depth of 77 feet below the ground surface (bgs). Soil cuttings will be containerized in DOT approved 55-gallon steel drums and held on site pending disposal. 3.2.1.2 Soil Sampling Soil samples will be collected for geological evaluation with continuous logging starting at 25 feet bgs and then to total depth. This continuous sampling is designed to fill data gaps resulting from the five foot sampling interval previously used at the site. Historically heaving sands have been experienced at the site and if encountered they will be bypassed as necessary without sampling. Boring logs will be developed by a professional geologist under the supervision of a registered geologist. The logs will be prepared using the U.S.C.S. and field V