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HomeMy WebLinkAboutDWQ-2025-004928 Page 1 of 4 Utah Division of Water Quality Statement of Basis ADDENDUM Wasteload Analysis and Antidegradation Level I Review Date: June 9,2025 Prepared by: Suzan Tahir Standards and Technical Services Facility: Huntington Wastewater Treatment Facility Castle Valley Special Service District UPDES Permit No. UT0021296 Receiving water: Huntington 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 of Water Quality. Discharge Outfall 001: Huntington Creek (Stream Discharge) → Cottonwood Creek → San Rafael River → Colorado River 0.8 MGD maximum daily design discharge, 0.4 MGD maximum monthly design discharge Receiving Water Per UAC R317-2-13.1(b), the designated beneficial uses for Huntington Creek and tributaries, from the confluence with Cottonwood Creek to Highway U-10 crossing are 2B, 3C and 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. Utah Division of Water Quality Wasteload Analysis Autoliv ASP Inc., UPDES Permit No. UT0024911 Page 2 of 4 Site Specific Total Dissolved Solids Criteria Site-specific total dissolved solids (TDS) criteria are associated with this use. Huntington Creek and tributaries from the confluence with Cottonwood Creek to Highway U-10 is 4,800 mg/l total dissolved solids. Critical Low Flows Typically, the critical flow for the wasteload analysis is considered the lowest stream flow for seven consecutive days with a ten-year return frequency (7Q10). Flow data was insufficient to calculate the annual or seasonal 7Q10 values. Due to a lack of flow records for Huntington Creek, the seasonal 20th percentile flow measurements taken immediately upstream of the outfall were calculated to estimate the critical flow in the receiving water (Table 1). Results were calculated using data from DWQ monitoring station 4930520 HUNTINGTON CREEK ABOVE HUNTINGTON LAGOONS OUTFALL for the period 2015-2025.The critical flow values for winter and spring season however were based of best professional judgment according to the limited data. Table 1.Seasonal Critical Flows (cfs) Season 20th percentile Flow Data (cfs) Summer 1.4 Fall 1.4 Winter 13.0 Spring 30.0 Annual Overall 7.5 Receiving Water Quality Ambient receiving water quality was characterized using data from DWQ monitoring station 4930520 HUNTINGTON CREEK ABOVE HUNTINGTON LAGOONS OUTFALL for the same period (2015-2025). The average seasonal value was calculated for each constituent with available data in the receiving water. Effluent parameters were characterized using data from the monitoring site 4930510 HUNTINGTON LAGOONS OUTFALL. Total Maximum Daily Load (TMDL) According to the Utah's 2024 303 (d) assessment, the receiving water for the discharge, Huntington Creek (Huntington Creek-1, Huntington Creek and tributaries from confluence with Cottonwood Creek to Highway 10, UT14060009-010_00) is impaired for dissolved selenium. assessment Site Specific Total Dissolved Solids Criteria A site-specific standard for total dissolved solids was adopted for Huntington Creek to address the impairment. The site specific criterion is based upon the EPA approved Total Maximum Daily Utah Division of Water Quality Wasteload Analysis Autoliv ASP Inc., UPDES Permit No. UT0024911 Page 3 of 4 Load (TMDL) Price River, San Rafael River, and Muddy Creek TMDLs for Total Dissolved Solids, West Colorado Watershed Management Unit, Utah (MFG Inc., 2004). The standard is as follows per UAC R317-2-14.1, Footnote (4). Huntington Creek and tributaries from the confluence with Cottonwood Creek to Highway U-10 is 4,800 mg/l total dissolved solids. 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 is 2500 ft, per UAC R317-2-5. Water quality standards must be met at the end of the mixing zone. The actual length of the mixing zone was not determined; however, it was presumed to remain within the maximum allowable mixing zone dimensions. Acute limits were calculated using 50% of the seasonal critical low flow. Parameters of Concern The potential parameters of concern identified for the discharge/receiving water were selenium, total suspended solids (TSS), dissolved oxygen (DO), BOD5, total phosphorus (TP), total nitrogen (TN), total ammonia (TAN), E. coli, pH, and total residual chlorine (TRC) as determined in consultation with the UPDES Permit Writer. Additional parameters of concern may become apparent as a result of reasonable potential analysis, technology-based standards, or other factors as determined by the UPDES Permit Writer. WET Limits 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. The WET limit for LC50 is typically 100% effluent and does not need to be determined by the WLA. Table 2: WET Limits for IC25 Outfall Percent Effluent Outfall 001 46.9% 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 Utah Division of Water Quality Wasteload Analysis Autoliv ASP Inc., UPDES Permit No. UT0024911 Page 4 of 4 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 the Wasteload Addendum. The effluent limits for DO, BOD5 and total residual chlorine in order to meet minimum DO criteria in the receiving water was evaluated using the Utah River Model. The analysis is summarized in the Wasteload Addendum. Models and supporting documentation are available for review upon request. Antidegradation Level I Review The 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. Antidegradation Review Level II A Level II Antidegradation Review (ADR) is not required for this facility. The proposed permit is a simple renewal of an existing UPDES permit. No increase in effluent flow or concentration of pollutants over those authorized in the existing permit is being requested. Documents: WLA Document : Huntington_POTW_WLA_2025.docx Wasteload Analysis and Addendums: Huntington_POTW _WLA_2020.xlsm References: Utah Division of Water Quality. 2024. Final 2024 Integrated Report on Water Quality Utah Division of Water Quality. 2021. Utah Wasteload Analysis Procedures Version 2.0. Lewis, B., J. Saunders, and M. Murphy. 2002. Ammonia Toxicity Model (AMMTOX, Version2): A Tool for Determining Effluent Ammonia Limits. University of Colorado, Center for Limnology. MFG Inc. 2004. Price River, San Rafael River, and Muddy Creek TMDLs for Total Dissolved Solids, West Colorado Watershed Management Unit, Utah. Utah Division of Water Quality. Utah Division of Water Quality. 2012. Utah Wasteload Analysis Procedures Version 1.0. Utah Division of Water Quality Salt Lake City, Utah WASTELOAD ANALYSIS [WLA]9-Jun-25 Addendum: Statement of Basis 4:00 PM Facilities: Castle Valley SSD - Huntington Lagoons UPDES No:UT-0021296 Discharging to:Huntington Creek I. Introduction 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 [R317-2-8, UAC]. Projected concen- trations are compared to numeric water quality standards to determine acceptability. The anti-degradation policy and procedures are also considered. The primary in-stream parameters of concern may include metals (as a function of hardness), total dissolved solids (TDS), total residual chlorine (TRC), un-ionized ammonia (as a function of pH and temperature, measured and evaluated interms of total ammonia), and dissolved oxygen. Mathematical water quality modeling is employed to determine stream quality response to point source discharges. Models aid in the effort of anticipating stream quality at future effluent flows at critical environmental conditions (e.g., low stream flow, high temperature, high pH, etc). The numeric criteria in this wasteload analysis may always be modified by narrative criteria and other conditions determined by staff of the Division of Water Quality. II. Receiving Water and Stream Classification Huntington Creek:2B, 3C, 4 Antidegradation Review:Level I review completed. Level II review not required. III. Numeric Stream Standards for Protection of Aquatic Wildlife Total Ammonia (TNH3)Varies as a function of Temperature and pH Rebound. See Water Quality Standards Chronic Total Residual Chlorine (TRC)0.011 mg/l (4 Day Average) 0.019 mg/l (1 Hour Average) Chronic Dissolved Oxygen (DO) 5.00 mg/l (30 Day Average) N/A mg/l (7Day Average) 3.00 mg/l (1 Day Average) Maximum Total Dissolved Solids 4800.0 mg/l Background Page 1 Utah Division of Water Quality Salt Lake City, Utah Acute and Chronic Heavy Metals (Dissolved) 4 Day Average (Chronic) Standard 1 Hour Average (Acute) Standard Parameter Concentration Load*Concentration Load* Aluminum 87.00 ug/l**0.580 lbs/day 750.00 ug/l 5.003 lbs/day Arsenic 150.00 ug/l 1.001 lbs/day 340.00 ug/l 2.268 lbs/day Cadmium 2.39 ug/l 0.016 lbs/day 7.38 ug/l 0.049 lbs/day Chromium III 268.22 ug/l 1.789 lbs/day 5611.70 ug/l 37.434 lbs/day ChromiumVI 11.00 ug/l 0.073 lbs/day 16.00 ug/l 0.107 lbs/day Copper 30.50 ug/l 0.203 lbs/day 51.68 ug/l 0.345 lbs/day Iron 1000.00 ug/l 6.671 lbs/day Lead 18.58 ug/l 0.124 lbs/day 476.82 ug/l 3.181 lbs/day Mercury 0.0120 ug/l 0.000 lbs/day 2.40 ug/l 0.016 lbs/day Nickel 168.54 ug/l 1.124 lbs/day 1515.92 ug/l 10.112 lbs/day Selenium 4.60 ug/l 0.031 lbs/day 20.00 ug/l 0.133 lbs/day Silver N/A ug/l N/A lbs/day 41.07 ug/l 0.274 lbs/day Zinc 387.83 ug/l 2.587 lbs/day 387.83 ug/l 2.587 lbs/day * Allowed below discharge **Chronic Aluminum standard applies only to waters with a pH < 7.0 and a Hardness < 50 mg/l as CaCO3 Metals Standards Based upon a Hardness of 400 mg/l as CaCO3 Page 2 Utah Division of Water Quality Salt Lake City, Utah IV. Numeric Stream Standards for Protection of Agriculture 4 Day Average (Chronic) Standard 1 Hour Average (Acute) Standard Concentration Load*Concentration Load* Arsenic 100.0 ug/l lbs/day Boron 750.0 ug/l lbs/day Cadmium 10.0 ug/l 0.03 lbs/day Chromium 100.0 ug/l lbs/day Copper 200.0 ug/l lbs/day Lead 100.0 ug/l lbs/day Selenium 50.0 ug/l lbs/day TDS, Summer 4800.0 mg/l 16.01 tons/day VII. Mathematical Modeling of Stream Quality Model configuration was accomplished utilizing standard modeling procedures. Data points were plotted and coefficients adjusted as required to match observed data as closely as possible. The modeling approach used in this analysis included one or a combination of the following models. (1) The Utah River Model, Utah Division of Water Quality, 1992. Based upon STREAMDO IV (Region VIII) and Supplemental Ammonia Toxicity Models; EPA Region VIII, Sept. 1990 and QUAL2E (EPA, Athens, GA). (2) Utah Ammonia/Chlorine Model, Utah Division of Water Quality, 1992. (3) AMMTOX Model, University of Colorado, Center of Limnology, and EPA Region 8 (4) Principles of Surface Water Quality Modeling and Control. Robert V. Thomann, et.al. Harper Collins Publisher, Inc. 1987, pp. 644. Coefficients used in the model were based, in part, upon the following references: (1) Rates, Constants, and Kinetics Formulations in Surface Water Quality Modeling. Environmen- tal Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Athens Georgia. EPA/600/3-85/040 June 1985. (2) Principles of Surface Water Quality Modeling and Control. Robert V. Thomann, et.al. Harper Collins Publisher, Inc. 1987, pp. 644. VIII. Modeling Information The required information for the model may include the following information for both the upstream conditions at low flow and the effluent conditions: Flow, Q, (cfs or MGD)D.O. mg/l Temperature, Deg. C.Total Residual Chlorine (TRC), mg/l pH Total NH3-N, mg/l BOD5, mg/l Total Dissolved Solids (TDS), mg/l Metals, ug/l Toxic Organics of Concern, ug/l Page 3 Utah Division of Water Quality Salt Lake City, Utah Other Conditions In addition to the upstream and effluent conditions, the models require a variety of physical and biological coefficients and other technical information. In the process of actually establishing the permit limits for an effluent, values are used based upon the available data, model calibration, literature values, site visits and best professional judgement. Model Inputs The following is upstream and discharge information that was utilized as inputs for the analysis. Dry washes are considered to have an upstream flow equal to the flow of the discharge. Current Upstream InformationStream Critical Low Flow Temp.pH T-NH3 BOD5 DO TRC TDS cfs Deg. C mg/l as N mg/l mg/l mg/l mg/l Summer (Irrig. Season)1.4 17.0 8.1 0.03 2.00 7.04 0.00 1411.7 Fall 1.4 3.4 8.2 0.03 2.40 --- 0.00 1982.0 Winter 13.0 2.0 7.8 0.03 1.50 --- 0.00 1982.0 Spring 30.0 9.0 8.6 0.02 1.50 --- 0.00 1982.0 Dissolved Al As Cd CrIII CrVI Copper Fe Pb Metals ug/l ug/l ug/l ug/l ug/l ug/l ug/l ug/l All Seasons 7.09 0.98 0.23 1.01 2.50 2.60 3.5 0.68 Dissolved Hg Ni Se Ag Zn Boron Metals ug/l ug/l ug/l ug/l ug/l ug/l All Seasons 0.0000 0.86 0.44 0.56 6.39 10.0 * 1/2 MDL Page 4 Utah Division of Water Quality Salt Lake City, Utah Projected Discharge Information Season Flow, MGD Temp.TDS mg/l TDS tons/day Summer 0.80000 17.7 3230.00 10.77312 Fall 0.80000 15.0 3230.00 10.77312 Winter 0.80000 12.0 3230.00 10.77312 Spring 0.80000 15.0 3230.00 10.77312 All model numerical inputs, intermediate calculations, outputs and graphs are available for discussion, inspection and copy at the Division of Water Quality. IX. Effluent Limitations Current State water quality standards are required to be met under a variety of conditions including in-stream flows targeted to the 7-day, 10-year low flow (R317-2-9). Other conditions used in the modeling effort coincide with the environmental conditions expected at low stream flows. Effluent Limitation for Flow based upon Water Quality Standards In-stream criteria of downstream segments will be met with an effluent flow maximum value as follows: Season Daily Average Summer 0.800 MGD 1.238 cfs Fall 0.800 MGD 1.238 cfs Winter 0.800 MGD 1.238 cfs Spring 0.800 MGD 1.238 cfs Flow Requirement or Loading Requirement The calculations in this wasteload analysis utilize the maximum effluent discharge flow of 0.8 MGD. If the discharger is allowed to have a flow greater than 0.8 MGD during 7Q10 conditions, and effluent limit concentrations as indicated, then water quality standards will be violated. In order to prevent this from occuring, the permit writers must include the discharge flow limititation as indicated above; or, include loading effluent limits in the permit. Effluent Limitation for Whole Effluent Toxicity (WET) based upon WET Policy Effluent Toxicity will not occur in downstream segements if the values below are met. WET Requirements LC50 >EOP Effluent [Acute] IC25 >46.9%Effluent [Chronic] Page 5 Utah Division of Water Quality Salt Lake City, Utah Effluent Limitation for Biological Oxygen Demand (BOD) based upon Water Quality Standards or Regulations In-stream criteria of downstream segments for Dissolved Oxygen will be met with an effluent BOD limitation as follows: Season Concentration Summer 25.0 mg/l as BOD5 166.8 lbs/day Fall 25.0 mg/l as BOD5 166.8 lbs/day Winter 25.0 mg/l as BOD5 166.8 lbs/day Spring 25.0 mg/l as BOD5 166.8 lbs/day Effluent Limitation for Dissolved Oxygen (DO) based upon Water Quality Standards In-stream criteria of downstream segments for Dissolved Oxygen will be met with an effluent D.O. limitation as follows: Season Concentration Summer 5.00 Fall 5.00 Winter 5.00 Spring 5.00 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: Season Concentration Load Summer 4 Day Avg. - Chronic 5.8 mg/l as N 38.6 lbs/day 1 Hour Avg. - Acute 23.0 mg/l as N 153.1 lbs/day Fall 4 Day Avg. - Chronic 47.8 mg/l as N 318.9 lbs/day 1 Hour Avg. - Acute 117.0 mg/l as N 780.4 lbs/day Winter 4 Day Avg. - Chronic 34.5 mg/l as N 230.3 lbs/day 1 Hour Avg. - Acute 72.3 mg/l as N 482.3 lbs/day Spring 4 Day Avg. - Chronic 5.4 mg/l as N 35.9 lbs/day 1 Hour Avg. - Acute 16.2 mg/l as N 107.9 lbs/day Acute limit calculated with an Acute Zone of Initial Dilution (ZID) to be equal to 100.%. Page 6 Utah Division of Water Quality Salt Lake City, Utah Effluent Limitation for Total Residual Chlorine based upon Water Quality Standards In-stream criteria of downstream segments for Total Residual Chlorine will be met with an effluent limitation as follows: Season Concentration Load Summer 4 Day Avg. - Chronic 0.022 mg/l 0.15 lbs/day 1 Hour Avg. - Acute 0.039 mg/l 0.26 lbs/day Fall 4 Day Avg. - Chronic 0.022 mg/l 0.15 lbs/day 1 Hour Avg. - Acute 0.039 mg/l 0.26 lbs/day Winter 4 Day Avg. - Chronic 0.116 mg/l 0.77 lbs/day 1 Hour Avg. - Acute 0.208 mg/l 1.39 lbs/day Spring 4 Day Avg. - Chronic 0.253 mg/l 0.00 lbs/day 1 Hour Avg. - Acute 0.455 mg/l 0.00 lbs/day Effluent Limitations for Total Dissolved Solids based upon Water Quality Standards Season Concentration Load Summer Maximum, Acute 8632.9 mg/l 28.79 tons/day Fall Maximum, Acute 7987.8 mg/l 26.64 tons/day Winter Maximum, Acute 8875.8 mg/l 29.60 tons/day Spring 4 Day Avg. - Chronic 9107.7 mg/l 30.38 tons/day Colorado Salinity Forum Limits Determined by Permitting Section Effluent Limitations for Total Recoverable Metals based upon Water Quality Standards In-stream criteria of downstream segments for Dissolved Metals will be met with an effluent limitation as follows (based upon a hardness of 400 mg/l): 4 Day Average 1 Hour Average Concentration Load Concentration Load Aluminum N/A N/A 1,170.2 ug/l 7.8 lbs/day Arsenic 318.57 ug/l 1.4 lbs/day 531.8 ug/l 3.5 lbs/day Cadmium 4.82 ug/l 0.0 lbs/day 11.4 ug/l 0.1 lbs/day Chromium III 570.49 ug/l 2.5 lbs/day 8,785.2 ug/l 58.6 lbs/day Chromium VI 20.62 ug/l 0.1 lbs/day 23.6 ug/l 0.2 lbs/day Copper 62.06 ug/l 0.3 lbs/day 79.4 ug/l 0.5 lbs/day Iron N/A N/A 1,563.6 ug/l 10.4 lbs/day Lead 38.83 ug/l 0.2 lbs/day 746.1 ug/l 5.0 lbs/day Mercury 0.03 ug/l 0.0 lbs/day 3.8 ug/l 0.0 lbs/day Nickel 358.22 ug/l 1.5 lbs/day 2,372.9 ug/l 15.8 lbs/day Selenium 9.30 ug/l 0.0 lbs/day 31.1 ug/l 0.2 lbs/day Silver N/A ug/l N/A lbs/day 64.0 ug/l 0.4 lbs/day Zinc 819.32 ug/l 3.5 lbs/day 603.6 ug/l 4.0 lbs/day Page 7 Utah Division of Water Quality Salt Lake City, Utah Cyanide 11.08 ug/l 0.0 lbs/day 34.4 ug/l 0.2 lbs/day Effluent Limitations for Heat/Temperature based upon Water Quality Standards Summer 21.2 Deg. C.70.2 Deg. F Fall 7.6 Deg. C.45.7 Deg. F Winter 25.0 Deg. C.77.0 Deg. F Spring 59.5 Deg. C.139.1 Deg. F Page 8 Utah Division of Water Quality Salt Lake City, Utah Effluent Targets for Pollution Indicators Based upon Water Quality Standards In-stream criteria of downstream segments for Pollution Indicators will be met with an effluent limit as follows: 1 Hour Average Concentration Loading BOD (mg/l)5.0 mg/l 33.4 lbs/day Nitrates as N 4.0 mg/l 26.7 lbs/day Total Phosphorus as P 0.05 mg/l 0.3 lbs/day Total Suspended Solids 90.0 mg/l 600.4 lbs/day Note: Pollution indicator targets are for information purposes only. Effluent Limitations for Protection of Human Health [Toxics Rule] Based upon Water Quality Standards (Most stringent of 1C or 3A & 3B as appropriate.) In-stream criteria of downstream segments for Protection of Human Health [Toxics] will be met with an effluent limit as follows: Maximum Concentration Concentration Load Metals Antimony ug/l lbs/day Arsenic ug/l lbs/day Asbestos ug/l lbs/day Beryllium Cadmium Chromium (III) Chromium (VI) Copper ug/l lbs/day Cyanide ug/l lbs/day Lead Mercury ug/l lbs/day Nickel ug/l lbs/day Selenium Silver Thallium ug/l lbs/day Zinc Dioxin Dioxin (2,3,7,8-TCDD)2.98E-08 ug/l 1.99E-10 lbs/day Metals Effluent Limitations for Protection of All Beneficial Uses Based upon Water Quality Standards and Toxics Rule Class 4 Acute Agricultural Class 3 Acute Aquatic Wildlife Acute Toxics Drinking Water Source Acute Toxics Wildlife 1C Acute Health Criteria Acute Most Stringent Class 3 Chronic Aquatic Wildlife ug/l ug/l ug/l ug/l ug/l ug/l ug/l Page 9 Utah Division of Water Quality Salt Lake City, Utah Aluminum 1170.2 1170.2 N/A Antimony 1364.0 1364.0 Arsenic 213.1 531.8 0.0 213.1 318.6 Barium 0.0 Beryllium 0.0 Cadmium 21.0 11.4 0.0 11.4 4.8 Chromium (III)8785.2 0.0 8785.2 570.5 Chromium (VI)212.0 23.6 0.0 23.64 20.62 Copper 423.3 79.4 79.4 62.1 Cyanide 34.4 852.5 34.4 11.1 Iron 1563.6 1563.6 Lead 212.4 746.1 0.0 212.4 38.8 Mercury 3.76 0.32 0.0 0.32 0.026 Nickel 2372.9 9803.6 2372.9 358.2 Selenium 106.1 31.1 0.0 31.1 9.3 Silver 64.0 0.0 64.0 Thallium 1.1 1.1 Zinc 603.6 603.6 819.3 Boron 1598.2 1598.2 Summary Effluent Limitations for Metals [Wasteload Allocation, TMDL] [If Acute is more stringent than Chronic, then the Chronic takes on the Acute value.] WLA Acute WLA Chronic ug/l ug/l Aluminum 1170.2 N/A Antimony 1363.98 Arsenic 213.1 318.6 Acute Controls Asbestos 0.00E+00 Barium Beryllium Cadmium 11.4 4.8 Chromium (III)8785.2 570 Chromium (VI)23.6 20.6 Copper 79.4 62.1 Cyanide 34.4 11.1 Iron 1563.6 Lead 212.4 38.8 Mercury 0.320 0.026 Nickel 2372.9 358 Selenium 31.1 9.3 Silver 64.0 N/A Thallium 1.1 Zinc 603.6 819.3 Acute Controls Boron 1598.20 Other Effluent Limitations are based upon R317-1. E. coli 126.0 organisms per 100 ml X. Antidegradation Considerations Page 10 Utah Division of Water Quality Salt Lake City, Utah The Utah Antidegradation Policy allows for degradation of existing quality where it is determined that such lowering of water quality is necessary to accommodate important economic or social development in the area in which the waters are protected [R317-2-3]. It has been determined that certain chemical parameters introduced by this discharge will cause an increase of the concentration of said parameters in the receiving waters. Under no conditions will the increase in concentration be allowed to interfere with existing instream water uses. The antidegradation rules and procedures allow for modification of effluent limits less than those based strictly upon mass balance equations utilizing 100% of the assimilative capacity of the receiving water. Additional factors include considerations for "Blue-ribbon" fisheries, special recreational areas, threatened and endangered species, and drinking water sources. An Antidegradation Level I Review was conducted on this discharge and its effect on the receiving water. Based upon that review, it has been determined that an Antidegradation Level II Review is not required. XI. Colorado River Salinity Forum Considerations Discharges in the Colorado River Basin are required to have their discharge at a TDS loading of less than 1.00 tons/day unless certain exemptions apply. Refer to the Forum's Guidelines for additional information allowing for an exceedence of this value. This doesn’t apply to facilities that do not discharge to the Colorado River Basin. XII. Summary Comments The mathematical modeling and best professional judgement indicate that violations of receiving water beneficial uses with their associated water quality standards, including important down- stream segments, will not occur for the evaluated parameters of concern as discussed above if the effluent limitations indicated above are met. Page 11 Utah Division of Water Quality Salt Lake City, Utah XIII. Notice of UPDES Requirement This Addendum to the Statement of Basis does not authorize any entity or party to discharge to the waters of the State of Utah. That authority is granted through a UPDES permit issued by the Utah Division of Water Quality. The numbers presented here may be changed as a function of other factors. Dischargers are strongly urged to contact the Permits Section for further information. Permit writers may utilize other information to adjust these limits and/or to determine other limits based upon best available technology and other considerations provided that the values in this wasteload analysis [TMDL] are not compromised. See special provisions in Utah Water Quality Standards for adjustments in the Total Dissolved Solids values based upon background concentration. Utah Division of Water Quality 801-538-6052 File Name: Huntington_POTW_WLA_2025.xlsm Suzan Tahir Page 12