2013-04-10_PERMIT FILE - C1981019A (11)

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RULE 2 PERMITS 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 a 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 -1613, 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 -1 FG, MWC- 04 -05H, and MWC- 04 -13FG (Table 2.04.7 -41). Water quality data are available for the valley -fill monitoring wells from 2004 through 2006. Additional data collected in 1996 and 1997 from wells MJ- 95 -01, MJ- 95 -02, and MJ -95 -03 were reviewed. Results of the valley -fill well samples are summarized in Table 2.04.7 -42. The complete dataset is provided in Appendix 5.K of the WMC (2005) report (Exhibit 7, Item 21), as are laboratory analysis sheets for samples collected in 1995 -1996. Table 2.04.7 -42 also lists the Federal MCLs and secondary drinking water quality criteria. All samples except from well MJ -95 -02 exceeded the secondary drinking water MCL for TDS of 500 mg/L. Water quality in several wells also exceeded the secondary drinking water MCLs for iron (0.3 mg/L) and manganese (0.05 mg /L). Groundwater Use — Groundwater use in the Colowyo revised permit area is limited due to the depth to water, the generally poor quality, and its limited overall availability. Colowyo installed and developed two wells in the late 1970s to supply a portion of the domestic needs. The two deep wells, Taylor Creek Nos. 1 and 3, are located in Section 33, T4N, R93 W, and in Section 4, T3N, R93 W, respectively (Map 11C). Taylor Creek No. 1, completed to a depth of 850 ft in the Williams Fork Formation, produced 40 gpm. Taylor Creek No. 3, completed to a depth of 2,284 ft in the Iles Formation, produced 20 gpm. Neither well has been pumping since the early 1980s. Colowyo installed a new potable water supply well in 2004. That well was completed above the KM bed (depth 1,000 ft) and is located in the NW' /4 of Section 3, T3N, R93 W. The production rate is less than four gpm. Collom — Rule 2, Page 40 Revision Date: 9/28/11 Revision No.: PR -03