2021-04-13_HYDROLOGY - M1977342 - Laserfiche WebLink

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April 2021 MNGW-I pH Memo♦6 4.0 WATER QUALITY SAMPLING RESULTS AND TRENDS Per the GWMP, POC monitor well MNGW-1 has been monitored triannually since third quarter 2012 for the parameters listed in Table 2. More frequent monthly monitoring of MNGW-1 was initiated in August 2013 for these indicator parameters.Also beginning in 2013, Henderson began collecting surface water samples from the nearby diversion ditch portion of No Name Gulch(NNG-50;Figure 2).MNGW-3 and MNGW-4 were sampled twice in fourth quarter 2014 following their installation, development, and testing and sampled monthly beginning in June 2015 for the same indicator parameters. During the summer of 2017,a monitoring program was initiated along No Name Gulch.Flow rates and field parameter measurements were collected during seven bi-weekly events between mid June and early-September. Following this program, a new surface water monitoring location was established on No Name Gulch just upstream of the Mine surface facilities (NNG-40; Figure 1). The NNG-40 monitoring location was added to the sampling program in 2018. Analytical results from 2014 thru 2020 are presented in Table 3 for all three monitoring wells and surface water locations NNG-40 and NNG-50. Tabulated analytical data from MNGW- 1 prior to 2014 are presented in the 2013 Groundwater Quality Memorandum (AJAX/Clear Creek,2013). The following is a summary of pH measurements collected from monitoring locations east of the Henderson Mine surface facilities (Table 3). Figure 7 is a graph showing historical pH measurements recorded in MNGW-1 since 1995.Figure 8 shows pH measurements recorded in MNGW-1, MNGW-3, MNGW-4, NNG-4 , a-n NNG-50. A summary o t e pH results recorded in the monitoring wells is presented below. • The first reading of MNGW-1 pH that was less than 6.5 s.u. was recorded in January 1999 (6.46 s.u.).