1. Justification of Review of Water Quality Standards for Nutrients and other Constituents Randy Pahl, NDEP

2. Background on Review of Truckee River Water Quality Standards (WQS) Truckee River standards haven’t been reviewed since 1993 – Science has progressed siginificantly NDEP encourages review of WQS prior to TMDL development Jan 6, 2011 – NDEP announces triennial WQS Review process, solicits input – Feb 22, 2011 – Third Parties submit letter to NDEP requesting review of Total Phosphorus (TP) and Total Nitrogen (TN) WQS NDEP 5-year plan promotes review of WQS before TMDL development Inconsistencies between the existing TMDL and TP WQS Legal, technical and operational changes in the watershed warrant a review – Truckee River on NDEP list of priority waters for Triennial Review of Water Quality Standards

3. What Are the Current Nutrient WQS? Parameter NDEP: CA to McCarran Blvd NDEP: McCarran Blvd to Wadsworth PLPT: Wadsworth and downstream TN mg/L (Annual Average) na 0.75 TN mg/L (Single Value) na 1.2 Ortho-P mg/L (Single Value) 0.05 na Ortho-P mg/L (Annual Average) na 0.05 TP (as P ) mg/L (Annual Average) 0.10.05 na

4. Basis for Existing Nitrogen WQS State of science relating nitrogen to DO has progressed significantly since WQS were developed Established in 1980, updated 1984 (unit conversion applied) Documentation of criteria development is limited Suggests they were set to protect beneficial uses yet based upon observed local WQ data that existed at that time WQS does not reflect site-specific conditions Consistent with PLPT total nitrogen criteria

5. Basis for Existing Phosphorus WQS Established in 1980, updated 1984 (unit conversion applied) Documentation of criteria development is limited Suggests they were set to protect beneficial uses yet based upon observed local WQ data that existed at that time Annual average TP < 0.1 mg/L based on EPA’s 1976 “Red Book” WQS does not reflect site-specific conditions Inconsistent with PLPT dissolved reactive phosphorus (DRP) criterion State of science relating phosphorus to DO has progressed significantly since WQS were developed

6. Compliance with Dissolved Oxygen (DO) Standard is Key Element for Aquatic Life Beneficial Use 6 Truckee River downstream of Lake Tahoe Dissolved Oxygen Sunlight Flow Algae Aeration Nutrients (N&P) Temperature Organic Matter

7. Complex Relationship Between Nutrients and Dissolved Oxygen Nutrient WQS developed to help control excess growth of algae Nutrients, by themselves, are not a problem – Nutrients  excess algae  low dissolved oxygen The relationship between nutrients and DO is: – Not a direct relationship – System-specific – Highly depending on flow in river Compliance with oxygen standards is best evaluated using a model to “link” nutrients to the DO under site- specific conditions 7

8. How Will the Nutrient WQS Be Reviewed? Use WQ models to develop technical rationale for any proposed changes – WQ models to provide linkage between nutrient loading to the Truckee River and resulting dissolved oxygen levels – Incorporates other factors (temperature, light, organic matter, aeration) Models will help ensure nutrient WQS… – Reflect site-specific response of the Truckee River to nutrient loads – Protect beneficial uses