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' May 2014 Groundwater POC Update Memorandum♦9 <br /> ' 5.0 SUMMARY AND RECOMMENDATIONS <br /> ' The results of recent investigations and groundwater monitoring were used to develop the <br /> following POC recommendations for the areas east of 1-Dam, in the Potato Gulch drainage, <br /> ' and east of 3-Dam. <br /> • Groundwater elevation and water quality data from MLGW-15 continue to support <br /> ' that both MLGW-7 and MLGW-15 be considered POC locations for the area east of <br /> 1-Dam. Monitor well MLGW-15 should be included in the triannual POC <br /> monitoring program along with MLGW-7 and sampled for the list of indicator <br /> parameters as specified in the GWMP. <br /> ' • Based on existing geologic and hydrologic information, including the existence of a <br /> bedrock ridge northeast of 1-Dam and the intermittent occurrence of groundwater in <br /> ' existing monitor wells, there continues to be no basis for establishing a POC well <br /> north of 1-Dam or in the Potato Gulch drainage. <br /> • The results of quarterly groundwater monitoring at 3-Dam support the original <br /> interpretation that a laterally extensive aquifer system does not exist at 3-Dam. Of <br /> ' the five monitor wells installed, only one (MLGW-17) has had measureable <br /> groundwater during all monitoring events and is located within the interpreted <br /> ' groundwater flowpath east of 3-Dam. All other wells have at times been dry. Based <br /> on these results,AJAX and Clear Creek recommend that monitor well MLGW-17 be <br /> ' established as a POC monitor well for 3-Dam. <br /> • As discussed in Section 4.0, pH measurements in MLGW-17 have ranged as low as <br /> ' 6.4 s.u.. This level is lower than the NPL established for other Henderson No POC <br /> locations in the GWMP. Since water quality results indicate MLGW-17 is not <br /> ' affected by seepage, the lower pH measurements are interpreted to represent <br /> background conditions. Therefore, it is recommended that a modified pH range be <br /> adopted as an NPL for MLGW-17 and other POC wells as discussed in in the <br /> ' Groundwater Quality Assessment for MLGW-7 Technical Memorandum (AJAX and <br /> Clear Creek,2014). <br />