DWQ-2025-004956

Utah Division of Water Quality
Statement of Basis
ADDENDUM
Preliminary Wasteload Analysis and Antidegradation Level II ReviewDate:June 10, 2025Prepared by:Suzan TahirStandards and Technical ServicesFacility:Grantsville Wastewater Treatment Facility
UPDES No. UT0021130Receiving water: Blue Lakes (2B, 3B, 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 ofdischarge 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 ofthe Division ofWater Quality.DischargeOutfall 001: Drainage Ditch
Blue Lakes Irrigation CanalThe maximum hourlyflow is 8.0 MGD and the maximum monthly design discharge is 3.0 MGD for the facility. Currently the lagoons are discharging at 1.5 MGD.Receiving
WaterThe receiving water for Outfall 001 is an unnamed drainage ditch that is tributary to Blue Lakes, which outlets to an irrigation canal. As per UAC R317-2-13.10, the receiving ditch
is classed 2B, 3E. As per R317-2-13.2(v), the designated beneficial uses of Blue Lake are 2B,3B, 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 3B - Protected for warm water species of game fish and other warm water aquatic life, including the necessary aquatic organisms in their food chain.
Class 4 - Protected for agricultural uses including irrigation of crops and stock watering.Critical Flow:Typically, the critical flow for the wasteload analysis is considered the lowest
lake elevation averaged over seven consecutive days with a ten-year return frequency (7Q10). No stage records were found for Blue Lakes and no water was assumed present during critical
conditions.Parameters of Concern
The potential parameters of concern identified for the discharge/receiving water were total suspended solids (TSS), dissolved oxygen (DO), BOD5, total ammonia (TAN), total phosphorus
(TP), E. coli, and pH as determined in consultation with the UPDES Permit Writer. Addition 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.TMDLAccording to DWQ’s 2024 Integrated Report and 303(d) Assessment, there is no defined assessment unit.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,
3Bnumeric aquatic life use criteria apply to the immediate receiving water (Blue Lake).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. Water
quality standards must be met at the end of the mixing zone. Due to the lack of dilution in Blue Lakes during critical conditions, no mixing zone is allowed.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. Table 1: WET Limits for
IC25
Season
Percent Effluent
Dilution Ratio
Annual
100%
0Effluent Limits
Effluent limits were determined using a mass balance mixing analysis (UDWQ 2012). Due to the lack of dilution from the receiving water during critical conditions, the WQBELs were set
at the water quality criteria. The mass balance analysis is summarized in Appendix A.
The toxicity of some metals is dependent on the hardness of the water. Due to the lack of sampling data, a hardness of 300 mg/L as CaCO3 was assumed.
The water quality criteria for chronic ammonia toxicity is dependent on temperature and pH, and for acute ammonia toxicity is dependent on pH. The water quality standards for ammonia
are summarized in Appendix B.Due to the lack of monitoring data, it was not possible to assess the effects of TP, TN, DO and BOD5 in the effluent on the DO in the downstream receiving
waters; therefore, it is presumed that secondary standards for BOD5, water quality criteria for DO, and technology-based limits for TP are sufficiently protective of the receiving water.
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.Antidegradation Level II Review
A Level II Antidegradation Review (ADR) is required for this discharge since this is a UPDES permit renewal with an expansion of modification of an existing wastewater treatment works
and pollutant concentrations and load is increasing under this permit renewal. Documents:WLA Document :Grantsville_WLA_2025.docxWasteload Analysis: Grantsville_WLA_2025.xlsmGrantsville
WLA_2025_Appendix A and C.pdfReferences:Utah Division of Water Quality. 2021. Utah Wasteload Analysis Procedures Version 2.0.