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Groundwater elevation monitoring at eight (8) piezometers on the Wattenberg Lakes site <br /> began in 2002 (see MW locations in Figure 1). The primary slurry wall was installed <br /> surrounding the Phase I — Pond 3 Mining Area in the spring of 2013 and mining and <br /> dewatering activities were mainly confined to within the slurry wall boundary until the fall <br /> of 2017. In November 2017, mining and dewatering activities began in Phase II (Pond 1 <br /> Mining Area and Mining Area 3) and in Phase III (Mining Area 2). As mining was <br /> completed in each mining area, backfilling activities began. Monthly groundwater <br /> elevation monitoring is still being performed, with monitoring results being evaluated for <br /> trends and potential off-site impacts. <br /> Baseline Groundwater Monitoring. Prior to the slurry wall installation, over 10 years of <br /> monthly monitoring established baseline groundwater elevations, gradients, and seasonal <br /> trends. In general, groundwater elevations within each piezometer varied by several feet <br /> during the baseline monitoring period (see Figure 2). Seasonal trends included increased <br /> groundwater elevations in the spring and summer months, and declining elevations in the <br /> fall and winter months. As the elevations varied through the years and seasons, the <br /> groundwater gradient across the Wattenberg Lakes site remained consistently from the <br /> southwest to the northeast(Figure 3). <br /> A small mining pit was excavated and dewatered on the north side of the property for <br /> several months during the baseline monitoring period (see Figure 3). However, <br /> groundwater impacts from the pit dewatering were localized and temporary (Figure 1). <br /> Other potential impacts to baseline groundwater elevations included changes in agricultural <br /> land use and irrigation practices,both on and off the Wattenberg Lakes site, and aggregate <br /> mining operations immediately south of the site. <br /> Slurry Wall Installation. In addition to the slurry wall installation in 2013, persistent rain <br /> in September of that year created site flooding, including South Platte River over-bank <br /> flows. Following slurry wall installation and flooding in 2013, groundwater elevations in <br /> some of the site piezometers increased relative to the most recent baseline data,but overall <br /> groundwater elevations and gradients did not change significantly from baseline <br /> conditions (see Figure 2). <br /> Mining and Dewatering. While Phase 11 (Pond 1 Mining Area and Mining Area 3) and <br /> Phase III (Mining Area 2) mining and dewatering activities began in November 2017, <br /> effects of the dewatering did not become immediately obvious in the monitoring data. <br /> Although groundwater elevations dropped in adjacent and nearby monitoring wells, <br /> groundwater elevations typically decrease in the winter months due to seasonal variations. <br /> It was not until February 2018 that groundwater elevation decreases, not likely due to <br /> seasonal variability,were observed(Figure 2). Effects were observed in upgradient wells <br /> (MW-7), adjacent wells (MW-5 and MW-8), and in downgradient wells (MW-1, <br /> MW-2, MW-3). <br /> As mining in each area was completed, and backfilling in each area progressed, the <br /> groundwater elevations appeared to begin to rebound from the dewatering effects (see <br /> Figure 2). Similar to the typical seasonal trend, groundwater elevations in most of the <br /> piezometers increased during the spring months of 2018. The primary exception to this <br /> observation was MW-2;the monitoring piezometer directly downgradient from the mining, <br /> Page 2 of 3 <br />