2020-03-30_HYDROLOGY - M1981021 - Laserfiche WebLink

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SUNDAY MINE COMPLEX-HYDROGEOLOGIC REPORT collected on the same day). The later samples collected on September 24, 2014, October 16, 2019, and February 18, 2020, were reported as 4.4 mg/L , non-detect, and non-detect, respectively (all with a PQL of 20 mg/L). Hydroxide was generally not present in wells MW- SUN2 and MW-SUN3. The presence of hydroxide and absence of bicarbonate is expected in waters of high pH, as observed in well MW-SUN1, where pH ranged from 9.4 to 12.26 standard units (s.u.). Chloride in well MW-SUN1 is understandably non-detected in the first two samples when a high PQL of 250 mg/L was used, and subsequent samples show a concentration range of 156 to 190 mg/L. However, the most recent sample, collected on February 18, 2020 showed a result of 8.3 mg/L. This result is suspect and is being investigated. Well MW-SUN2, which did not have high PQLs in the early samples, also showed non-detected chloride concentrations. This appears to indicate a potential analytical problem. Nitrate concentrations are generally low in the groundwater samples from the monitoring wells, and even though concentrations were periodically affected by laboratory-established PQLs of 10 mg/L, well concentrations were less than 0.61 mg/L (well MW-SUN2). The highest measured levels came from underground samples of mine water where one sample attained a concentration of 10 mg/L, the state standard for drinking water, in a West Sunday Mine sample collected on September 16, 2015. This relatively high nitrate concentration may be attributable to the ammonia nitrate and fuel oil (ANFO) that is used in underground blasting operations. Sulfate shows high concentrations in well MW-SUN1 ranging from 1290 to 1580 mg/L, regardless of PQLs. Whereas well MW-SUN2 shows inconsistent sulfate concentrations overtime ranging from non-detected at 0.665 to 193 mg/L. Well MW-SUN3 has sulfate concentrations ranging from 144 to 199 mg/L, with five instances of non-detections when a PQL of 250 mg/L was used. Calcium, magnesium and potassium occur in relatively low concentrations in the monitoring wells, while potassium and sodium occur in notably higher concentrations than what is typically found in shallow aquifers. The absence of numerous minor and trace metals is expected in groundwater with a high pH. Denison (2012) presented groundwater analytical data for wells installed in the West Sunday Mine near the interface of the flooded workings. The purpose of the work was to evaluate ambient groundwater quality in the vicinity of the mine workings. The analytical results of water Western Water& Land, Inc. 36