Critical Conditions Review Nancy Vignali │ Water Quality Assessment Team

Where We Fit in the Permitting Process Applications Standards Critical Conditions DO Modeling Biomonitoring Permit Writers

Mixing Zone Regulations EPA allows states to adopt their own mixing zone regulations as part of the states water quality standards (40 CFR §131.13). TCEQ’s mixing zone regulation has been approved by EPA and can be found outlined in the Texas Surface Water Quality Standards (TSWQS) http://www.tceq.texas.gov/waterquality/ standards/eq_swqs.html

Which Applications Receive Critical Condition Reviews? All Industrial wastewater permits All Municipal wastewater permits with biomonitoring requirements Municipal wastewater permits with design flows of ≥ 1.0 MGD

Critical Conditions Workflow Outfall Mapping TEXTOX Menu Determination Mixing Zone Determination 7Q2_HM Or Effluent % Calculation

TEXTOX Menu Determination Standards Assessment Worksheet Details the characteristics of all receiving water bodies within 3 miles of the discharge point using TSWQS Determine receiving waters uses and associated criteria; aquatic life use, toxicity (acute/chronic) and human health criteria – incidental, sustainable, public water supply Capture any change in human health criteria for downstream receiving waters within three miles of the point of discharge

Immediate Receiving Water Water Body Within 3 Miles Menu # Immediate Receiving Water Water Body Within 3 Miles 1 Intermittent water body ──── 2 Perennial ditch, stream, or river 3 4 Lake or lake-like water body 5 Wide tidal water body or narrow tidal with no upstream flow data 6 Narrow tidal water body with upstream flow data 7 Intermittent stream w/perennial pools 8 9 Narrow tidal water body w/ upstream flow 10

What is a Regulatory Mixing Zone? A mixing zone is an area where wastewater discharged from a permitted facility enters and mixes with a stream or water body A mixing zone is an established area where water quality standards may be exceeded as long as acute toxic conditions are prevented and all beneficial uses, such as drinking water, fish habitat, recreation human health and other uses are protected

Types of Mixing Zones Zone of Initial Dilution (ZID) – Acute aquatic life criteria applies at the edge of the ZID Mixing Zone (MZ) – Chronic aquatic life protection applies at the edge of the MZ Human Health Mixing Zone (HH) – Chronic human health protection applies at the edge of the HH

Aquatic Life Mixing Zone (MZ) Human Health Mixing Zone (HH) 400 ft. Aquatic Life Mixing Zone (MZ) ZID 200 ft. 50 ft. Point of Discharge

Mixing Zone & Human Health MZ ZID Point of Discharge Direction of Flow 20 ft. 60 ft. ZID 100 ft. 300 ft. Point of Discharge

Critical Conditions – Final Result In flowing waters, the river or stream’s: Low-flow metric (7Q2) is the critical condition for receiving-water flow which is based on a consecutive Seven-day, Two-year Low Flow recurrence interval. Harmonic Mean (HM) is calculated to establish human health limits In pooled water bodies, freshwater and saltwater: Percentages of effluent are calculated for water bodies at the edge of the MZ, ZID, and HH in the receiving water body by using the jet plume equation. These percentages are often referred to as the “critical dilution”.

Critical Conditions Contact Information Jeff Borski x5599 Jeffrey.Borski@tceq.texas.gov cubicle 200 Nancy Vignali x1303 Nancy.Vignali@tceq.texas.gov cubicle 197 June 2010 Procedures to Implement the Texas Surface Water Quality Standards http://www.tceq.texas.gov/assets/public/permitting/waterquality/standards/docs/june_2010_ip.pdf 2014 Texas Surface Water Quality Standards http://www.tceq.texas.gov/waterquality/standards/eq_swqs.html

Questions?