2021-09-03_PERMIT FILE - C1981019A (8)

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RULE 2 PERMITS the wells and field measurements for pH, electrical conductivity, and temperature were monitored monthly. Quarterly monitoring included a full suite of analyses on each well. Water samples from the wells were filtered in the field and preserved for analysis of dissolved metal concentrations. Groundwater samples were also collected in Collom permit expansion area wells in 1984-1985, 1996-1997, and 1999- 2000 as part of earlier studies; pertinent data from those data sets are included in the discussion presented in this section. Figures 2.04.7-36 and 2.04.7-37 present trilinear diagrams illustrating water quality for representative bedrock and valley fill monitoring wells from the data collected during baseline monitoring in 2004-2006. Groundwater samples for water quality analysis were collected from the bedrock and monitoring wells in 2004 to 2006. Water samples were also collected from well C -04-16B (this well was one of several monitoring wells around exploration hole C-04-16), constructed for use in a long-term aquifer test in the Collom Pit area, to characterize the groundwater that would be produced during Collom Pit dewatering operations. Additional data collected in 1996 and 1997 from wells UL -95-01, W-95-11 and UL -95-40 were also available. The locations of these wells are shown on Map 1013. A summary of the sampling history and results is provided in Table 2.04.7-42 for the bedrock wells. Table 2.04.7-42 also lists the Federal drinking water maximum contaminant levels (MCLs) and secondary drinking water quality criteria. Although these criteria are not specifically applicable, they provide a basis for comparison. The inorganic chemistry of the bedrock groundwater changes as a function of depth and distance downdip along groundwater flow paths. Groundwater samples from the F sandstone are calcium/magnesium— bicarbonate waters and fall within Region 1 on Figure 2.04.7-39. Within Region 1, the downdip wells show a gradual evolution toward sodium -bicarbonate water. Samples from the F/G sequence contain higher percentages of bicarbonate and occupy Region 2. These wells also evolve towards a more sodic chemistry with distance down dip. Samples collected from well C -04-16B, which is screened over the 400 -ft interval from the D coal to the H sandstone, fall into to this region and most closely resemble the groundwater from well MWC-04-13FG. Groundwaters in the H sandstone are all sodium bicarbonate types, with the sodium content a function of the distance down dip. These groundwaters generally plot in Region 3 on Figure 2.04.7-39. The inorganic chemistry of some of the samples collected from wells MWC-04-33H and MWC-04-13H plots in Region 1. Well MWC-04-033H is actually screened in the lower part of the G sequence and plots near Region 2, as would be more typical for its construction. Two samples from well MWC-04-13H plot in Region 1, close to the samples from well MWC-04-13FS, suggesting either a hydraulic connection or possibly a handling issue with those samples from well MWC-04-13H. The other samples from well MWC-04-13H plot at the extreme far end of Region 3, as expected. Historic data from well UL -95-01, located a short distance northeast of well cluster MWC-04-33 and completed in the Fab coal seam, indicate groundwater quality that plots in Region 2 on Figure 2.04.7-39. The chemistry of this groundwater is very similar to a majority of samples from upgradient F sandstone wells. Samples from well UL -95-01 collected between September 1996 and August 1997 show relatively little variation over time. Samples from well W-95-11, located on the ridge crest between Jubb and Wilson Creeks, plot in Region 2, indicating that the well is screened in the F/G sequence. The samples show little variation between October 1996 and August 1997. Total dissolved solids (TDS) ranged between 500 and 1,000 milligrams per liter (mg/L), which exceeds the secondary drinking water MCL of 500 mg/L. The pH of the samples is slightly alkaline, ranging from 7.6 to 8.1. Concentrations of dissolved metals were generally low. Problematic metals (cadmium, lead, mercury and selenium) were not detected above the laboratory reporting limits. Concentrations of iron and manganese exceeded their respective drinking water criteria of 0.3 and 0.5 mg/L in all bedrock groundwater samples except those from wells C-04-1613, MWC-04-1FG, MWC-04-05H, and MWC-04-13FG (Table 2.04.7-41). Collom — Rule 2, Page 27 Revision Date: 4/7/17 Revision No.: RN -07