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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division
<br />Rationale - Page 2, Permit No. CO-0000906
<br />• III. RECEIVING STREAM
<br />A. Surface Water
<br />An assessment of the stream standards, low flow data, and ambient stream data has been performed to determine the
<br />assimilative capacities for the Middle Fork of the Purgatoire River and the Left Fork of Apache Canyon Creek for potential
<br />pollutants of concern. This information, which is contained in Appendix A to this rationale, also includes an antidegradation
<br />review, where appropriate. The Division's Permits Section has reviewed the assimilative capacities to determine the
<br />appropriate water quality-based effluent limitations as well as potential limits based on the antidegradation evaluation,
<br />where applicable. The limitations based on the assessment and other evaluations conducted as part of this rationale can be
<br />found in Tables VI-I through VI-7 of this rationale.
<br />The outfalls listed in Table ll-1 will be the authorized discharge points to the waters; Outfalls 002A and 003A, which are not
<br />included in Table II-1, are not existing outfalls at this facility. According to the permit application and the Division of
<br />Reclamation, Mining & Safety (DRMS), Pond 5, from which Outfall 005A originated, no longer exists (see later discussions
<br />in this rationale). Consequently, despite the permit application containing Outfall 005A, this permit does not authorize
<br />discharges from Outfall 005A. Outfall 006A, which is also not listed in Table 11-1 and which originated at Pond 6, is a non-
<br />discharging Outfall. Note that Pond 6 receives domestic sewage and coal preparation wastewater, which discharges solely
<br />to groundwater (as discussed in the subsection that follows). Outfall 006A was not authorized as part of the past permit and
<br />the permit application did not contain a request for authorization to discharge to surface water via Outfall 006A. Thus, this
<br />permit does not authorize the discharge of domestic sewage or coal preparation industrial wastewaters to surface waters.
<br />Finally, the facility applied to discharge via internal Outfall 033A in its permit application; Internal Outfall 033A is the
<br />discharge of treated domestic sewage from an activated sludge package plant, prior to entering Pond 6. In the previous
<br />permit, monitoring requirements, only, were included for Internal Outfall 033A. However, as part of this permit, limitations
<br />will be established and groundwater monitoring requirements will also be included as discussed in the subsection that
<br />follows. Additionally, Outfall 3001 has been included as the influent to the package treatment plant; this outfall is required to
<br />ensure that influent data are available to calculate percent removal rates.
<br />This permit is being set up based on tiered flow rates from the facility. Initially, the mine will be dewatered at a 2500 gpm
<br />flow rate, and then based on historical flow rates, the flow is expected to decrease to 200 gpm once the mine is dewatered. A
<br />mid level flow tier is also being included and will be set at 900 gpm. Outfalls 001A and 009A will be the 2500 gpm flow tier,
<br />Outfalls 0013 and 009B will be the 900 gpm flow tier, and Outfalls 001 C and 009C will correspond to the 200 gpm flow tier.
<br />Additionally, monitoring, only, outfalls corresponding to those discharge locations subject to water quality-based effluent
<br />limitations, specifically, Outfalls MONI and MON9, have been included in the permit at the same locations as the
<br />corresponding numbered outfalls listed in Table II-1 as discussed later in this rationale (e.g., Outfall 001 and Outfall MONI
<br />are at the same location and Outfall 009 and Outfall MON9 are at the same location). Note that Outfalls 004A, 007A and
<br />008A, which are not subject to water quality-based effluent limitations (see the water quality assessment in Appendix A for
<br />more information) do not have corresponding monitoring, only, outfalls.
<br />B. Groundwater
<br />Discharges to groundwater occur from this facilityfrom various ponds used for treatment at this facility. However, for
<br />groundwater discharges consisting solely of industrial process water, the groundwater discharges are regulated by the
<br />Division of Reclamation, Mining and Safety (DRMS). For groundwater discharges from domestic sewage, whether
<br />commingled with industrial process water or not, the Division has regulatory authority. Therefore, for Pond 6, which
<br />receives commingled treated domestic wastewater and coal preparation plant industrial wastewater, conditions for the
<br />protection of groundwater standards will be imposed in this permit contingent upon whether or not the facility meets the
<br />"allowable seepage " rate as set forth in Section 61.14(9)(a) of the Colorado Discharge Permit System Regulations.
<br />A groundwater monitoring program consistent with Division procedures has not yet been initiated by this facility and
<br />therefore this permit will incorporate the first round of permitting for compliance with groundwater standards. This will
<br />include the installation of upgradient and downgradient monitoring wells. Consistent with Division nomenclature, the
<br />upgradient monitoring well will be named monitoring well 050A and the downgradient monitoring wells will be named
<br />monitoring wells 050B, 0500 and 050D.
<br />1. Identification: Limited information is available concerning soil types in the area of * the mine. Available information
<br />suggests that the soil is categorized as "Mine Dump " with variable composition.
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