DWQ-2024-001771

Utah Division of Water Quality
Statement of Basis
ADDENDUM
Wasteload Analysis and Antidegradation Level I Review Date:February27, 2024Prepared by:Suzan TahirStandards and Technical ServicesFacility:Weir Minerals, UPDES Permit No. UT0024767Receiving
water: Mill Creek (2B, 3C,4)
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 takes into account 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 ofWater Quality.DischargeOutfalls: 001 & 002(Internal
Outfall), combined discharge to storm drain (via Outfall 001) with a maximum design flow rate of 0.12 MGD.Receiving WaterPer UAC R317-2-13.5(a), the designated beneficial uses of Mill
Creek (Salt Lake County) fromconfluence with Jordan River to Interstate 15 are 2B, 3C, 4.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 3C -Protected for nongame fish and other aquatic life, including the necessary aquatic organisms in their food chain.Class 4 - Protected for agricultural uses including
irrigation of crops and stock watering.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, 3B numeric aquatic life use criteria apply to the immediate receiving water (Jordan River).
Flow
The critical background flow for the wasteload analysis is considered the lowest stream flow for seven consecutive days with a ten-year return frequency (7Q10). Daily flow records were
obtained for Salt Lake County flow gage 490 Mill Creek at 460 West for the period 2012-2022. (Table 1). Table 1: Mill Creek critical low flow (7Q10)
Season
Flow (cfs)
Summer
7.3
Fall
7.5
Winter
6.2
Spring
14.4
Receiving water quality
Receiving water quality was characterized using data from DWQ Monitoring Station #4992505, MILL CK. AB CENTRAL VALLEY WWTP OUTFALL, for the period 2014-2024.TMDL
According to the Utah’s 2022 303(d) Water Quality Assessment Report,the receiving water for the discharge, Mill Creek1-SL City (UT16020204-026_00), which extends from the confluence
of the Jordan River to Interstate 15 crossing is impaired for a loss of benthic macroinvertebrates community. Additional downstream impairments of the Jordan River are outlined in Table
2. Table 2. Jordan River Segments and Impairments Downstream of Discharge.Assessment Unit NameAssess Unit DescriptionAssessment UnitImpairment CauseJordan River-4Jordan River from 2100
South to the confluence with Little Cottonwood CreekUT16020204-004_00Benthic macroinvertebrate assessments and total dissolved solids
Jordan River-3
Jordan River from North Temple to 2100 South
UT16020204-003_00
Benthic macroinvertebrate assessments and phosphorous
Jordan River-2
Jordan River from Davis County line upstream to North Temple Street
UT16020204-002_00
Benthic macroinvertebrate assessments
Jordan River-1
Jordan River from Farmington Bay upstream contiguous with the Davis County line, except North Canyon Creek
UT16020204-001_01
Benthic macroinvertebrate assessmentsTwo Total Maximum Daily Loads analyses are applicable to these waters. The Jordan River Watershed E. coli TMDLs addresses elevated E. coli impairments
in the Mill Creek1- SLCity, Jordan River-4, Jordan River-3, and Jordan River-2 assessment units. This TMDL was approved in January 2023 (UDWQ, 2023). The second TMDL is the Jordan River
Total Maximum Daily Load Water Quality Study - Phase I, which addressed the dissolved oxygen impairment in Jordan River segments assessments Units UT16020204-001 through 003, was completed
in July 2013 (UDWQ, 2013). A TMDL has not been completed for the other impaired constituents.Mixing Zone
The maximum allowable mixing zone is 15 minutes of travel time for acute conditions, not to exceed 50% of stream width, and for chronic conditions, per UAC R317-2-5. Water quality standards
must be met at the end of the mixing zone. The mixing zone model showed complete mixing within 2,500 feet for chronic conditions. Acute limits were calculated using 50% of the seasonal
critical low flow.
Parameters of Concern
The potential parameters of concern identified for the discharge were TDS, TSS, E. coli, Oil & Grease, Lead, Zinc, Total Phosphorus, and Copper as initially determined by Federal Effluent
Limitations Guidelines found in 40 CFR Part 28 Subpart E, as well as determined by the impairment status of the receiving water, existing TMDLs, and a review of the previous permit.
As part of the E. coli TMDL, all permittees shall meet the E. colinumeric criteria stated underR317-2-14, where the numeric criteria for E. coli are 206 MPN and 668 MPN, 30 Day geometric
mean #/100 ml and daily maximum, respectively. Additional parameters of concern may become apparent as a result of a reasonable potential analysis, other emerging technology-based standards,
or other factors as determined by the UPDES Permit Writer. WET LimitsThe 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. The WET limit for LC50 is typically 100% effluent

and does not need to be determined by the WLA. IC25 WET limits for Outfall002should be based on 2.5% effluent.Wasteload Allocation Methods
Effluent limits were determined for conservative constituents using a simple mass balance mixing analysis (UDWQ 2012). The mass balance analysis is summarized in the Wasteload Addendums.
The water quality standard for chronic ammonia toxicity is dependent on temperature and pH, and the water quality standard for acute ammonia toxicity is dependent on pH. The AMMTOX
Model developed by University of Colorado and adapted by Utah DWQ and EPA Region VIII was used to determine ammonia effluent limits (Lewis et al. 2002). The analysis is summarized in
theWasteloadAddendum.Models and supporting documentation are available for review upon request.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 notrequired for this facility. The proposed permit is a simple renewal of an existing UPDES permit. No increase in flow or concentration of pollutants over those authorized
in the existing permit is being requested.Documents:WLA Document:WeirMinerals_WLADoc_2024.docxWasteloadAnalysis and Addendums:WeirMinerals_WLA_2024.xlsmReferences:Utah Division of Water
Quality2023,Jordan River Watershed E.Coli Total Maximum Daily LoadsUtah Division of Water Quality 2022,Final 2022 Integrated Report on Water QualityUtah Division of Water Quality 2021,Utah
Wasteload Analysis Procedures Version 2.0. Utah Division of Water Quality 2013,Jordan River Total Maximum Daily Load Water Quality Study - Phase ISalt Lake County Rain Flow Websites:https://rain-flow.slco.org/sensor/?time_zone=US%2FMountain&site_id=82&site=07368bfd-e9e1-4d61-865b-11ac14719ba7&device_id=2&device=0c8aad55-53e1-41d8-bff2-97f37e281ebc&bin=3600&range=Custom%20Range&markers=false&legend=true&thresholds=true&refresh=off&show_raw=true&show_quality=true&data_start=2021-01-01%2000%3A00%3A00&data_end=2021-12-31%2023%3A59%3A59https://rain-flow.slco.org/dashboard/?dashboard=f9d8b446-42b3-4e8d-a5a0-d11210f82bac#widget_72ca8f52303e40b6b9cf62449649a3a5