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n - ; <br /> low levels at 23 and 48 feet, However, the 48 feet contamination <br /> in this boring is almost certainly related to contact with <br /> groundwater. Laboratory results are summarized on Table l and <br /> the laboratory reports are attached. <br /> The distribution of contamination indicates a significant line <br /> leak occurred near 5812 but that the product migrated largely <br /> vertically and the tank pit area may not contain significant, <br /> levels of hydrocarbons. An estimate of the area of contaminated <br /> soils is shown on Figure 2. <br /> The boring data provide good constraint on the lateral and <br /> vertical extent of soil contamination• is The <br /> defit ition Of <br /> ab ured <br /> vertical extent of contamination, however, <br /> by the effects of seasonal and draught-induced fluctuations in <br /> groundwater level. Historically, groundwater <br /> levels <br /> have <br /> been <br /> this <br /> much higher, perhaps within 25 feet of ground <br /> area (DWR. Bulletin No. 146). it appears likely that free product <br /> traveled, vertically until reaching the capillary fringe and the <br /> migrated .laterally and vertically with the water table. I'. <br /> should also be recognized that a significant capillary fringe (5- <br /> 10 feet) can form above the water <br /> restsvery <br /> on the zonegrained <br /> of <br /> sediments and that any free p <br /> capillarity.. <br /> In considering the remediation options at this site it .is clear <br /> that vapor extraction would be difficult at best. For instance <br /> in.GTI soil boring number 1. 33 feet of the 46 feet drilled and <br /> sampled .was comprised of clay. similarly. in WaterWork boring <br /> Sg12, which has documented contamination throughout, less than ll <br /> out :of 44 feet is comprised of reasonably permeable sediment <br /> (logs attached). <br /> Based an the above we propose to excavate all <br /> contaminated soils at the site to the greatest possible depth,_ <br /> estimated to be 30-40 feet below grade. Any soils remaining <br /> below this level are ' within the zone of historic groundwater <br /> fluctuation: an <br /> of the future <br /> d can be addressed as part <br /> groundwater remediation plan. <br /> - The soil, n, will. be directed using a PID for preliminary <br /> screening Confirmation samples will be taken after ' field <br /> evidence indicates all contaminated soil has been .removed. , This <br /> sample: for each 20 �inear feet .of <br /> sampling: will consist of one <br /> pit wall and will be analyzed for BTEX and TPH as gasoline by EPA <br /> methods 8020/8015. <br /> The removed material will be stockpiled on-site, covered and <br /> secured with plastic sheeting pending sampling and approval of <br /> an aeration permit from the Air Quality Control Berard: A <br /> -- -- <br /> --- compasita,sample,_consisting of four separate grab samples, will <br /> be collected..for ea <br /> Will <br /> yards of stockpiled soil. --Camposit ng -- <br /> wili be performed in the laboratory to prevent volatilization <br />