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Well Sampling Frequency -3- 12 July 1991 <br /> DDRW, Sharpe Site <br /> We recommend that monthly water quality samples be collected for a year <br /> only in those areas that there is planned expansion or installation of a <br /> treatment system. Sample collection may then be further reduced based <br /> on the response of the aquifer to the remedial actions. Quarterly <br /> monitoring may only be needed for two years and may then be reduced <br /> further to semiannual thereafter, provided the hydraulics of the system <br /> are well understood. <br /> Page 2-2. Figure 1 in the Report is the logic flow diagram for the proposed <br /> revisions to the well monitoring schedule. We are concerned that 15 <br /> micrograms per liter (µg/1 ) of trichloroethylene (TCE) was used for the <br /> information criteria rather than USATHAMA's detection limit of 1. 1 µg/l <br /> for this constituent. If 15 µg/l is used as the information criteria <br /> then it is possible that wells downgradient and outside of the plume <br /> will not be tracked. Wells which have concentrations of TCE below the <br /> Primary Drinking Water Standard (DWS) of 5 µg/l but above the detection <br /> limit in 1990 may exceed these concentrations in the future but would <br /> not be included in the monitoring program. We recommend that <br /> information criteria be changed to include the DWS for each of the <br /> constituents. <br /> Page 3-3. Table 1 lists those wells proposed to be permanently removed from the <br /> well monitoring program. We do not concur with the deletion of all of <br /> the wells listed in this table. In addition, any wells which are <br /> proposed to be permanently deleted from the monitoring program should <br /> not be abandoned or destroyed because the needs of the monitoring <br /> program may change and these wells may again need to be monitored in the <br /> future for verification. <br /> Monitor well cluster 401 should not be permanently dropped from the <br /> monitoring program. This cluster should be monitored annually as it is <br /> the furthest most upgradient well cluster in the South Balloon Area. If <br /> monitor well cluster 401 is retained for annual monitoring, then it <br /> would be more appropriate to drop monitor cluster 501 from the <br /> monitoring program as this well cluster is also upgradient of the South <br /> Balloon Area but is off-site. <br /> Monitor well cluster 419 should remain in the well monitoring program <br /> because it is immediately down gradient of the Oxidation Pond. In the <br /> January to March 1991 quarter, ground water from 4198 had 36.5 µg/l of <br /> 1,1,1-trichloroethane. The Oxidation Pond is to be converted to a storm <br /> water retention basin and may not be lined. Therefore, the 419 well <br /> cluster should be kept in the monitoring program to monitor potential <br /> discharges from the future storm water retention basin. Use of a storm <br /> water basin may result in additional and separate ground water <br /> monitoring in the vicinity of the basin. <br /> Page 3-4. Table 2 lists those wells to be temporarily deleted from the ground <br /> water monitoring program. We do not concur with the selection of all of <br /> the wells listed in this table. In addition, the plan did not indicate <br /> what "temporarily deleted" meant. Sharpe needs to define the frequency <br /> of sampling for the wells to be temporarily deleted from the monitoring <br /> program. <br />