Laserfiche WebLink
Windsor East Mine, Exhibit G – Water Information September 2022 <br /> Page 6 | 11 <br />Following mining, each cell will be lined to form a hydraulically isolated reservoir. The effect of the clay liner on the <br />groundwater within the aquifer will be the formation of a hydraulic mound upgradient of the cell where water levels <br />will be several feet higher than under pre-mining conditions. Downgradient of the cell, the groundwater levels will be <br />several feet lower due to a “shadow effect” behind the reservoir. These changes in groundwater levels due to the <br />clay-lined cells are expected to have minimal effect on the groundwater in the surrounding area due to the proximity <br />of the river adjacent to and downgradient of the lined cells. Downgradient of the lined cells, groundwater levels will <br />reach an equilibrium with the river due to its proximity, thereby minimizing the “shadow effect” <br />1.5 AVAILABLE SATURATED THICKNESS <br />The drilling and installation of monitoring wells at the Windsor East site in August 2022 indicated that bedrock was <br />encountered between 15 and 22.5 feet below land surface. Water levels measured on August 12, 2022, ranged <br />from 7.9 to 10.4 feet bgs. Based on this data, the saturated thickness of aquifer present beneath the site ranges <br />from approximately 5 to 13.5 ft (Table 3). The lowest saturated thickness was recorded in MW-11 on the eastern <br />side of the site, which is likely showing the direct impact from dewatering activities associated with the adjacent <br />Parsons mine. <br />Dewatering activities required as part of mining in the absence of a hydraulic barrier wall result in drawdown of the <br />water table and associated decrease in saturated thickness of the alluvium. This has the potential to impact other <br />wells nearby if the decline in water levels is sufficient to prohibit the well owner from extracting the associated <br />water rights from the well. <br />Table 4 presents historic information about the variability in saturated thickness near the site and the impact from <br />mining based on available data. Four of the monitoring wells that were installed at the Parsons Mine Site to <br />observe water levels at the Parsons Mine site, provide evidence of the saturated thickness of alluvium nearest to <br />the Windsor East property. Water levels measured during pre-mining and mining conditions illustrate the expected <br />decline in saturated thickness at a distance of approximately 100 feet from the gravel mines. In particular, the <br />Parsons Mine monitoring well MW-12 is located approximately 100 feet west of a cell that began dewatering and <br />mining in 2019. The water level record for the well shows the range of saturated thickness for the alluvium before <br />and during dewatering activities at this distance. MW-12 is located on the eastern edge of the Windsor East <br />property and is therefore expected to be representative of the conditions at the site as well as of the expected <br />impacts from dewatering during mining near the property boundary. <br />Before 2019, the water table was an average of 6.3 feet above the top of the bedrock at MW-12 and fluctuated <br />over a range of approximately 1 foot above or below this average. During dewatering, the depth to water <br />increased, and the saturated thickness decreased until it was an average of 1.7 feet above the top of the bedrock, <br />with a variation range of approximately 1 to 1.5 feet. <br />Water wells completed in sand and gravel aquifers typically provide approximately 25 to 30 gallons per minute per <br />foot of drawdown of saturated thickness in the well. Domestic wells are typically permitted for maximum pumping <br />rates of 15 gallons per minute (gpm). As a result, less than 2 feet of saturated thickness above the pump intake is <br />therefore likely to be required to provide the allowed pumping rates of 15 gpm. The reduction of saturated <br />thickness of 4.6 ft at MW-12 to 1.7 ft above bedrock suggests that the potential for impact to a domestic well at <br />this distance is likely, however wells located further from the lease boundary will have more saturated thickness <br />and hence will likely be able to pump the permitted rates. <br />1.6 MODELED HYDRAULIC IMPACTS <br />The hydraulic impacts associated with dewatering around the planned mine cells are expected to spread outward <br />as a function of the aquifer properties of the alluvium, the time elapsed since dewatering began, and the distance <br />of observation from the point of dewatering. The previous observations of the depressed water table (drawdown) <br />due to mining at the adjacent Parsons mine (noted in the previous section) are useful for predicting the impact of <br />the Windsor East mine. In particular, the observations at Parsons well MW-12 (located directly between a <br />dewatered cell and the Windsor East site) represent an ideal location from which the effects of dewatering in the