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yUbbUb-_)J4 UUw--;C <br /> Plan for the WCC investigation called for field filtration of the sample <br /> portion collected for metals analysis prior to field preservation with <br /> acid. This is done to remove particulate matter and metals sorbed onto the <br /> particulates. While some very fine particulates may be transported through <br /> the aquifer, the majority of the particulates are likely to derive from <br /> construction and development of the well and thus not represent the actual <br /> state of the water in the aquifer. Also, analytical results from <br /> unfiltered samples may not be reproducible, especially from a monitoring <br /> well , due to the variation which may occur in the amount of suspended <br /> sediments from one sampling event to the next. Thus, the Radian metals <br /> values in groundwater are not comparable with other values in this <br /> investigation, and are not considered valid. <br /> 4.3.5.5.5 The USATHAMA report did not detect arsenic above a detection <br /> limit of 10 ug/l in any of the 11 water samples analyzed. However, Radian <br /> reported a "trace" of arsenic in four wells out of 43 onsite wells <br /> sampled. Since the detection limit for arsenic was 60 ug/1 , compared to an <br /> MCL of 50 ug/l , Radian concluded that the four "trace" results indicated an <br /> arsenic source on the site. Again, Radian' s samples were not field- <br /> filtered, however, and thus, are likely to have included arsenic sorbed to <br /> particulates in the well . Radian also cited the concentration of four <br /> positive, if unquantified, results in the northern part of the Depot as <br /> evidence that the arsenic found was a site-related contaminant. <br /> 4.3.5.5.6 WCC sampled most of the wells (LM 47 through LM 92) for arsenic, <br /> with seven samples found to contain arsenic above the detection limit of <br /> 3 ug/1 . The maximum level found, however, was 4.7 ug/l , well below the MCL <br /> of 50 ug/1 . Again, the positive results were concentrated in the northern <br /> and northeastern part of the Depot, and in the near offsite wells, <br /> generally, within 500 feet of the Depot boundary. Arsenic was not detected <br /> in any farther offsite wells, nor was arsenic detected above the detection <br /> limit of 10 ug/l in any of the private wells sampled. Generally, the wells <br /> where arsenic was found are in or just downgradient of Contaminant Areas 1, <br /> 2, 3, and 4. <br /> 4-186 <br />