2012-03-07_HYDROLOGY - C1981033 - Laserfiche WebLink

Home Browse Search

Sandra Brown March 7, 2012 Page 10 expression of the same warm groundwater seepage evident within the eastern half of the extensional head scarp trough, directly up slope from the spring. Previous investigators did not observe these warm vapors and seep areas in the scarp trough directly up slope from the spring, so there was no evidence then to link the spring with a potential groundwater source at the base of the slide." He discovered strong evidence that some portion of the seep was groundwater presumably discharging from the C -Seam subcrop above the seep location. The present day seep is lower at about the elevation of the Edwards Mine portal but approximately twenty feet to the west. There is likely some component of B -Seam mine inflow water discharging at the subcrop /outcrop due to the gradient being to the north towards the river. The Mesa Verde Formation is known to have stratigraphic units with very low transmissivity, so you would expect a small amount of inflow mine workings. It is also possible that the Edwards Mine B- Seam portals have failed to some degree due to the landslide activity potentially contributing discharge to the seep area as well. The Edwards Mine portals were "Pre -Law" so reclamation liability is not relevant and as such, if Edwards Mine is the sole source for the water then ownership of the water also remains irrelevant and inconclusive. I conclude that the primary source of the seep is groundwater discharge with some component of mine water discharging from the B -Seam and C -Seam subcrop. With regard to the heat source the Division has concluded that there is not substantial evidence to conclude that a mine fire associated with the Bear or Edwards workings is the source for the heat exhibited by the warm spring. Based on our investigation by members of our Inactive Mines Reclamation Program, the underlying fire does not seem to be large or intensive enough to provide sufficient heat to significantly raise the temperature of nearby groundwater. It is possible that heating of groundwater results from subsurface geothermal activity potentially related to the Tertiary intrusive rocks of the nearby West Elk Mountains. It is interesting to note that the nearby West Elk Mine encountered warm fault - related water of a similar temperature while mining in the B -Seam to the east of the Bear Mine. There are also documented hot springs that exist in the region and there are other seeps and springs along the bedrock outcrops in the North Fork of the Gunnison River valley. All of this evidence leads me to conclude that the source of the elevated temperatures in the warm spring are more likely the a result of geothermal heating. Based on the testing performed by the Division and BCC, it is safe to conclude that the water discharging from the hillside seep above the Bear No. 3 Mine is benign. None of the CDPS permit limits are exceeded even prior to treatment in the pond. If the water were discharged to the river directly then the applicable standards would be the Colorado Department of Public Health and Environment Water Quality Control Commission (WQCC) Regulation No. 35 — Classification and Numeric Standards for Gunnison and Lower Dolores River Basins. It was determined that the appropriate stream segment is segment 2 — Mainstream of North Fork of the Gunnison River from the confluence of Muddy Creek and Coal Creek to the Black Bridge. The numeric in- stream standard for total recoverable iron is 1000 ug/1. As seen from the mass balance equation described above the impact that seep would have on the river with regard to iron concentration is minimal. This does not even take into account mixing and dilution. It has been previously determined that the ratio of flow of the North Fork of the Gunnison River to the Mountain Coal and Bear Coal WWTF's combined designated flows ... is more than 150:1 at low