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19 June 1992 <br /> (GeoAudit CV 30-34E3-1. 33) <br /> Page 3 of 4 <br /> Due to the fact that it is not feasible to provide <br /> hermetical seals between the targeted zones, causing <br /> short circuiting, we refrain from using a cluster well <br /> design. <br /> C) It is our experience that aquifer materials, unless a <br /> layer of free-floating product was previously present, <br /> typically do not contain elevated levels of hydrocarbon <br /> contaminants, if the water table had dropped. During the <br /> proposed soil gas survey, a VOC reading of the standing <br /> vapor level in MW-1, MW-3 and MW-5 is now scheduled to be <br /> obtained. If necessary, these wells can be directly used <br /> as extraction wells. The same vacuum extraction technique <br /> as described in the FRP will be used. <br /> 3 . a) We were not aware of the fact that MW-4 was dry during <br /> the December 1991 sampling. In this case, a new and <br /> deeper ground water extraction well is required. The well <br /> is to be installed as close as possible to the center of <br /> the worst impacted area, which will be close to MW-4. The <br /> design of the well is depicted on Figure 1. This well is <br /> used as the main ground water extraction well to capture <br /> the contaminants near the source. Ground water extraction <br /> from EW-1 needs to be performed occasionally to contain <br /> as much as contaminants within the property boundaries. <br /> b) Due to less than ideal aquifer conditions (the upper <br /> alluvial aquifer materials tend to be less homogeneous) <br /> and the fact that most wells do not penetrate the entire <br /> aquifer, aquifer tests in the environmental field rarely <br /> yield accurate data. Fortunately, accurate aquifer data <br /> in the environmental field for extraction or discharge <br /> purposes are not that crucial. A steady flow rate is not <br /> required, and as a matter of fact, the extraction plan <br /> calls for alternating on and off periods for a more <br /> effective flushing effect (Page 13 - FRP) . <br /> The hydraulic conductivity (K) values calculated by the <br /> previous consultants, PES, match closely to those of a <br /> fine sand aquifer. This data appears to be acceptable. In <br /> numerous cases, we notice that the calculated value <br /> differ significantly from the actual field value. Of the <br /> suggested aquifer tests, we believe that an additional <br /> capture radius analysis deserves a merit. For this <br /> purpose, we suggest an actual field test by extracting <br /> water from the extraction well to be installed and by <br /> monitoring/measuring the drawdown in the surrounding <br /> wells. <br />