Monitoring Issues and Resolutions. Monitoring issues specific to WMA C have been identified in the above discussions of the ground- water monitoring plan. These issues are reiterated in this section for clarity along with solutions to solve monitoring problems. The specific issues are as follows: • The water table is essentially flat across the 200 East Area making it difficult to use the water table gradient alone to determine the local flow direction across the. Because the local flow can be quite different from the regional flow and flow directions may change as the B-Pond mound diminishes, regional water table contours and/or regional plume directions are unreliable for determining local flow across the site. • Based on consistent water levels referenced to a more recent well elevation survey, data from the gyroscope surveys that correct for vertical borehole deviations, and data from colloidal borescope measurements that measure the in situ flow directions, the current flow direction is to the southwest ranging from 200 degrees to 235 degrees azimuth. • The current network was designed for flow specifically to the west. Determination of this flow direction was based on a presumed regional flow due to the presence of the B-Pond mound. No xxxxx were placed to allow for changes in flow direction over time. • Model studies using a southwest flow direction result in a monitoring efficiency of 73%, suggesting contamination entering the groundwater under one fourth of the WMA may not be detectable with the current location of xxxxx. • Revisions to the Part A Permit for WMA C added the 244-CR vault, eight diversion boxes, and ancillary equipment to the WMA. The existing groundwater-monitoring network was not designed to monitor the facilities recently added to the WMA • Finally, with the present rate of water table decline, some xxxxx in the network may be unusable in about six years. A monitoring network that includes the existing monitoring xxxxx and new downgradient xxxxx has a closer well spacing providing sufficient coverage to detect contamination originating from WMA C. The modified network will account for monitoring the 244-CR vault and seven of the eight diversion boxes that were recently incorporated into the WMA. Consideration will also be given to existing xxxxx that may eventually become unusable due to declining water levels. The design modifications to the existing network will account for current conditions and eventual changes in flow direction. Future well locations will als...
