Justification of Review of Water Quality Standards for Nutrients and other Constituents

Randy Pahl, NDEP

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

What Are the Current Nutrient WQS?

ParameterNDEP: CA to

McCarran Blvd

NDEP: McCarran

Blvd to Wadsworth

PLPT: Wadsworth

and downstream

TN mg/L (Annual Average)

na 0.75 0.75

TN mg/L (Single Value)

na 1.2 1.2

Ortho-P mg/L (Single Value)

0.05 na na

Ortho-P mg/L (Annual Average)

na na 0.05

TP (as P ) mg/L(Annual Average)

0.1 0.05 na

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

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

Compliance with Dissolved Oxygen (DO) Standard is Key Element for Aquatic Life Beneficial Use

6Truckee River downstream of Lake Tahoe

Dissolved Oxygen

Sunlight

Flow

Algae

AerationNutrients (N&P)

Temperature

Organic Matter

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

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