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• • <br /> 12 July 1991 <br /> Well Sampling Frequency <br /> -4- <br /> DDRW, Sharpe Site <br /> The concentrations of TCE <br /> Monitor wells 4408 and 440C are to be temporarily deleted whereas 440 <br /> is to be retained for quarterly monitoring• 1 respectively based C <br /> in the A, B and C zones are 3.4, 1 .5 and 5.2 µg/ , ears to <br /> on the January to March 1991 quarter) results. <br /> ng since this is unclear <br /> why <br /> was not retained for quarterly <br /> entrations. Therefore, we recommend that this well <br /> have the highest conc <br /> cluster be sampled annually. in the 503 and 506 <br /> It is unclear why the deeper monitor wells (B and <br /> and the other <br /> clusters have been proposed to be temporarily <br /> wells in the cluster have been retaie sampled annually or every other <br /> ned for annual sampling. We <br /> recommend that the entire clusters bedge <br /> year due to the distance of these wells from the lWells9betwfe <br /> between the <br /> plume and the presence of other monitor or supply <br /> plume and these wells. <br /> cy for the wells to be temporarily <br /> Depending on the monitoring frequen <br /> deleted, we recommend that two other wells be considered for addition to <br /> this list. Monitor wells 414A and 452A gradient locationsould not be tanddthatethe <br /> frequently than annually due to their upg <br /> concentrations of TCE in trespectively.he January to <br /> arch 1991 sampling round were <br /> less than 0.5 and 0.6 Mg/l , <br /> Page 3-5. The recommendations include analysis for VOC using the Environmental <br /> Protection Agency (EPA) Methods 601 and 602 for all annual sampling. <br /> Analysis for TCE and tetrachloroethylene (PCE) was proposed for <br /> quarterly samples. It is unclear why the 602 analysis is needed for <br /> most of the wells since generally only VOCs purgeable halocarbons are <br /> the contaminants of concern. Unless purgeable aromatics have been <br /> historically detected in samples from a monitor well , we recommend that <br /> analysis using EPA Method 602 be deleted from the monitoring program. <br /> In addition, it is unclear why only TCE and PCE are listed as analytes <br /> for the quarterly sampling. It is our understanding that other VOCs are <br /> detected using the EPA Method 601 for analysis. The analytical results <br /> for all purgeable halocarbons should be reported for the quarterly <br /> sample results. <br /> Page 3-6. Table 3 lists those wells judged to be redundant and are therefore <br /> recommended for deletion from the monitoring program. We do not concur <br /> with the deletion of all of the wells listed in this table. <br /> Monitor well 425A is listed in this table as redundant and therefore to <br /> be deleted from the monitoring program. However, this well should be <br /> retained for quarterly or annual sampling due to the fact that the <br /> sample from this well had up to 120 µg/l of TCE in the January to March <br /> 1991 quarterly sampling round. Other wells in the vicinity of this well <br /> cluster should be considered for deletion due to redundancy, unless the <br /> concentrations are significantly higher than what is reported in samples <br /> from 425A. <br /> Monitor well cluster 427 should be retained for annual sampling because <br /> there are three wells in this cluster that can be used to gather <br />