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May 2014 Groundwater POC Update Memorandum♦8 <br /> ' these deeper sections is unclear. The water level elevation at MLGW-17 is over 70 feet lower <br /> than the Williams Fork River at its nearest point, so a through-flowing aquifer system to the <br /> Williams Fork River is not supported. Water may reside in shallow depressions in the <br /> bedrock surface for extended periods of time or it may continue to follow the sloping <br /> ' bedrock contact toward the north, where the glacial sediments are even deeper. When <br /> groundwater has been observed in MLGW-20, it appears to be the result of transient and <br /> temporary perched water conditions. The abrupt appearance of groundwater in the spring <br /> and early summer is consistent with a localized meteoric recharge and not a distal source. <br /> Seepage affects from 3-Dam are not indicated by water chemistry results from monitor wells <br /> MLGW-17 and MLGW-20. Both wells show low or non-detect concentrations of seepage <br /> ' indicator parameters. The maximum concentrations of sulfate in MLGW-17 and MLGW-20 <br /> are 33.5 and 75.6 mg/L are interpreted to be within the range of background natural <br /> ' concentrations for the Qd aquifer at the site, and are well below concentrations measured in <br /> seepage or seepage-impacted groundwater (>1,000 mg/L). Manganese and other dissolved <br /> ' metal concentrations do not indicate seepage impacts in these monitor wells. <br /> Based on these results, AJAX and Clear Creek recommend that monitor well MLGW-17 be <br /> ' established as a POC monitor well for 3-Dam. Of the five wells installed, MLGW-17 is the <br /> only well that regularly has groundwater and is located within the interpreted groundwater <br /> ' flowpath east of 3-Dam. Groundwater in MLGW-20, located adjacent to MLGW-17, is <br /> interpreted to be localized and transient, with perched water occurring in the well only in <br /> response to late spring/early summer snowmelt. Based on geology and water level <br /> observations in other nearby monitor wells,groundwater in MLGW-20 is not interpreted to <br /> ' follow a laterally extensive flowpath leading from the 3-Dam facility. Therefore, MLGW-20 <br /> is not considered a representative monitoring location for 3-Dam. Downward vertical <br /> ' gradients are indicated from MLGW-20 toward the deeper MLGW-17, further supporting <br /> the selection of MLGW-17 as a more representative 3-Dam monitoring location. <br /> r <br />