DWQ-2023-200008

Utah Division of Water Quality
Statement of Basis
ADDENDUM
Wasteload Analysis and Antidegradation Level I ReviewDate:November 21, 2023Prepared by:Suzan TahirStandards and Technical ServicesFacility:Utah Iron, LLC - Iron Mountain Mine
UPDES No. UT0026298Receiving water: Unnamed Tributary of Iron Spring Creek (2B, 3D)
This addendum summarizes the wasteload analysis that was performed to determine water quality based effluent limits (WQBEL) for this discharge. Wasteload analyses are performed to determine
point source effluent limitations necessary to maintain designated beneficial uses by evaluating projected effects of discharge concentrations on in-stream water quality. The wasteload
analysis also considers downstream designated uses (UAC R317-2-8). Projected concentrations are compared to numeric water quality standards to determine acceptability. The numeric criteria
in this wasteload analysis may be modified by narrative criteria and other conditions determined by staff of the Division of Water Quality.DischargeOutfall 001: Unnamed tributary Iron
Spring CreekOutfall 002: Unnamed tributary Iron Spring CreekThe total design capacity for the proposed discharges is 0.4 MGD.Receiving WaterThe receiving water for Outfalls 001 & 002
is an unnamed tributary to Iron Spring Creek.The beneficial uses for the West Desert region are not defined but this region is defaulted to the 2B and 3D designated beneficial uses.
Class 2B - Protected for infrequent primary contact recreation. Also protected for secondary contact recreation where there is a low likelihood of ingestion of water or a low degree
of bodily contact with the water. Examples include, but are not limited to, wading, hunting, and fishing.
Class 3D - Protected for waterfowl, shore birds and other water-oriented wildlife not included in Classes 3A, 3B, or 3C, including the necessary aquatic organisms in their food chain.FlowTypically,
the critical flow for the wasteload analysis is considered the lowest stream flow for seven consecutive days with a ten-year return frequency (7Q10). The facility discharges to a dry
wash and no flow records are available. Therefore, critical flow was assumed to be zero. The effluent limits revert to the water quality standards. TMDLAccording to Utah's 2022 303(d)
Water Quality Assessment Report, there are no defined assessment units and no listed impairments for the watershed proximal to the facility, which is the West Desert Region of the Lower
Sevier River Basin. The West Desert region does not have identified beneficial uses. There have been no TMDL studies completed for this watershed and therefore, no TMDL implementation
requirements at this time. Protection of Downstream UsesPer UAC R317-2-8, all actions to control waste discharges under these rules shall be modified as necessary to protect downstream
designated uses. For this discharge, 3D numeric aquatic life use criteria apply to the immediate receiving water (Iron Spring Creek). Ambient Water Quality Data and Mixing Zone
The maximum allowable mixing zone is 15 minutes of travel time for acute conditions, not to exceed 50% of stream width, and 2,500 feet for chronic conditions, per UAC R317-2-5. Since
there is no ambient stream flow data, no mixing zone is allowed and therefore, end of pipe water quality standards must be met. Parameters of Concern
The primary parameters of concern identified for the discharge/receiving water are pH, TSS, and Total Iron as determined from 40 CFR 440 Subpart N in consultation with the UPDES Permit
Writer. Additional potential parameters of concern, such as sulfate, ammonia, selenium or other metals may become apparent as a result of reasonable potential analysis, technology-based
standards, or other factors as determined by the UPDES Permit Writer.
Effluent Limitation for Total Ammonia based upon Water Quality Standards
In-stream criteria of downstream segments for Total Ammonia will be met with an effluent
limitation (expressed as Total Ammonia as N) as follows:
SeasonConcentrationLoad
Summer4 Day Avg. – Chronic5.1mg/l as N17.0lbs/day
1 Hour Avg. – Acute15.4mg/l as 51.5lbs/day
Fall4 Day Avg. – Chronic4.3mg/l as N14.3lbs/day
1 Hour Avg. – Acute11.2mg/l as N37.2lbs/day
Winter4 Day Avg. – Chronic4.0mg/l as N13.4lbs/day
1 Hour Avg. – Acute12.8mg/l as N42.5lbs/day
Spring4 Day Avg. – Chronic4.3mg/l as N14.3lbs/day
1 Hour Avg. – Acute11.2mg/l as N37.2lbs/day
Acute limit calculated with an Acute Zone of Initial Dilution (ZID) to be equal to 100.%.WET LimitsTypically, the percent of effluent in the receiving water in a fully mixed condition,
and acute and chronic dilution in a not fully mixed condition are calculated in the WLA in order to generate WET limits. The LC50 (lethal concentration, 50%) percent effluent for acute
toxicity and the IC25 (inhibition concentration, 25%) percent effluent for chronic toxicity, as determined by the WET test, needs to be below the WET limits, as determined by the WLA.
When applicable, the WET limit for LC50 is typically 100% effluent and does not need to be determined by the WLA. Antidegradation Level I ReviewThe objective of the Level I ADR is to
ensure the protection of existing uses, defined as the beneficial uses attained in the receiving water on or after November 28, 1975. No evidence is known that the existing uses deviate
from the designated beneficial uses for the receiving water. Therefore, the beneficial uses will be protected if the discharge remains below the WQBELs presented in this wasteload.A
Level II Antidegradation Review (ADR) is required for this discharge since the facility is a new discharge and the pollutant concentration and load is increasing from ambient conditions
under this permit. WLA Documents:IronMt_WLA_Summary_2023.docxIronMt-Memo-2023.docxReferences:Utah Division of Water Quality. 2021. Utah Wasteload Analysis Procedures Version 2.0.