Applying Nutrient Standards in Wadeable Streams in Montana Vicki Watson, University of Montana Michael Suplee, Montana DEQ Presented at Nitrate in Montana Hydrologic Systems, Helena, MT April 23, 2014

Excess nutrients & nuisance algae –one of top 5 causes of impairment of Montana’s wadeable streams 17% of MT impaired stream miles impaired by excess nutrients Cladophora in Clark Fork River, 1980s

MT Numeric Nutrient Criteria In 2008, DEQ developed preliminary ecoregion- specific numeric criteria for nutrients and algae, based on regional stressor-response studies and reference-stream data for mountains and plains ecoregions (Level III) Harm to beneficial uses began around: 90 th percentile of reference in mountains 90 th percentile of reference in mountains 75 th percentile of reference in plains 75 th percentile of reference in plains  So criteria were set near these levels

How were the 2008 Criteria Derived? Based on nutrient concentrations where impact to these sensitive beneficial uses begins to occur Based on nutrient concentrations where impact to these sensitive beneficial uses begins to occur – Fish and aquatic life – Recreation & aesthetics Impact-to-use thresholds determined using: Impact-to-use thresholds determined using: – Stressor-response studies (e.g., TN vs. DO) – Public opinion surveys on nuisance algae levels Final criteria derived by: Final criteria derived by: – Comparing impact threshold concentrations to ecoregional reference data

< (Summer mean) >250 > mg chlorophyll a per square meter 150 (Summer max) 35g AFDW per square meter

Stressor-response Studies vs. Reference-site Data (in contrast to EPA’s suggestion of using the 25 th percentile of all streams)

Level III Ecoregions & Stream reference sites (white) Cities (red dots)

MT’s Draft Level III Ecoregion Nutrient Criteria, 2008 In addition to N and P criteria, attached-algae criteria were suggested for western mountainous ecoregions. Plains criteria set to maintain acceptable DO levels. Note seasonality..

In 2012, MT nutrient criteria were refined, in light of: additional stressor response studies additional stressor response studies additional reference site data additional reference site data  Made it possible to look at small scale level-IV ecoregions small scale level-IV ecoregions within some Level III ecoregions within some Level III ecoregions Greater emphasis was placed on dose-response studies, and criteria were no longer linked to specific percentiles in the reference distribution

N:P Ratios also Considered Nuisance growths of Didymosphenia (rock snot) noted in low P streams with high N:P ratios (N:P 34:1) Nuisance growths of Cladophora noted in high P streams with low N:P ratios

Didymo Distribution U.S. EPA. Retrieved

Level III Ecoregions & Stream reference sites (white) Cities (red dots)

Level IV ecoregion within Middle Rockies: Absaroka-Gallatin Volcanic Mountains

TN criteria 250 µg/L ( >100 th percentile of reference) TN criteria 250 µg/L ( >100 th percentile of reference) TP criteria: 105 µg/L (75 th percentile of reference) N:P Ratio of Criteria: 2:1 N:P Ratio of Reference Sites: 1:1 TN criteria 300 µg/L (93 th percentile of reference) TP criteria: 30 µg/L (80 th percentile of reference) N:P Ratio of Criteria: 10:1 N:P Ratio of Reference Sites: 11:1 Absaroka-Gallatin Volcanic Mountains (17i) Middle Rockies (17)

Middle Rockies Stream Bloody Dick Creek Bloody Dick Creek

Absoroka-Gallatin Volcanic Mountain Streams E. Rosebud Cr. Gardner River

NW Glaciated Plains (gray), Mountain-to-plains transition zone level IV ecoregions (dark gray)

Total Nitrogen: 1,300 µg/L (65 th percentile) Total Phosphorus: 110 µg/L (75 th percentile) N:P Ratio of Criteria: 12:1 N:P Ratio of Reference Sites 18:1 Total Nitrogen: 560 µg/L (80 th percentile) Total Phosphorus: 80 µg/L (75 th percentile) N:P Ratio of criteria: 7:1 N:P Ratio of Reference Sites: 7:1 Northwestern Glaciated Plains (42) Mountain-to-plains transition zone (various)

Northwestern Glaciated Plains Streams Battle Cr. Porcupine Cr.

TransitionalStream Clear Creek, Flowing down From the Bear Paw Mountains on to the Glaciated Plains

Northwestern Great Plains(gray), Wyoming Basin (light gray). Mountain-to-plains transition zone level IV ecoregions (dark gray)

Total Nitrogen: 1,300 µg/L (68 th percentile) Total Phosphorus: 150 µg/L (77 th percentile) N:P Ratio of Criteria: 9:1 N:P Ratio of Reference Sites 13:1 Total Nitrogen: 440 µg/L (98 th percentile) Total Phosphorus: 33 µg/L (87 th percentile) N:P Ratio of criteria: 13:1 N:P Ratio of Reference Sites: 13:1 Northwestern Great Plains (43) Mountain-to-plains transition zone (various)

Northwestern Great Plains Streams Box Elder Cr. O’Fallon Cr.

Transitional Zone Stream – Elk Creek

Most Streams Already Meet the Criteria Based on probabilistic stream survey: About 70-80% of stream miles statewide currently meet the TP criteria About 70-80% of stream miles statewide currently meet the TP criteria About 85-90% of stream miles statewide currently meet the TN criteria About 85-90% of stream miles statewide currently meet the TN criteria

Reach Specific Criteria used where naturally elevated nutrients (e.g., due to geology) from a level IV ecoregion affect reaches downstream in another ecoregion. Acceptable downstream concentrations are estimated from relative contribution of sources in the two ecoregions.

1.Criteria are not “no sample shall exceed” 2.EPA recommends 10-25% exceedence rate for most types of criteria (303(d) listing guidance) 3.A 9-year dataset on MT’s Clark Fork River shows Sites with consistent nuisance algae –Sites with consistent nuisance algae – 54% of N and P samples exceed criteria 54% of N and P samples exceed criteria Sites without nuisance algae –Sites without nuisance algae – only 6% of N and P samples exceed criteria only 6% of N and P samples exceed criteria 25% exceedence appears to be a threshold.25% exceedence appears to be a threshold. Above that, nuisance algae very likely. Above that, nuisance algae very likely. Recommend: 20% allowable exceedence rate Allowable Exceedence Rate for Criteria

MT draft numeric nutrient standards were out for public comment until April 1 st. See Circular DEQ-12A Recent hearing before MT BER

Application of Proposed Nutrient Standards Examples: discharge from existing permitted source where: A. Discharge is directly to stream, stream is on the 303(d) list for nutrients B. Discharge is directly to stream, stream is not on the 303(d) list for nutrients and C. Discharge of effluent is to groundwater with hydrologic connection to surface water C. Discharge of effluent is to groundwater with hydrologic connection to surface water (if no connection, only groundwater standards apply) (if no connection, only groundwater standards apply)

A. Stream is on the 303(d) list for nutrients Stream already exceeds nutrient standards so standards are to be met at end-of-pipe (July-Oct) Stream already exceeds nutrient standards so standards are to be met at end-of-pipe (July-Oct) – If cost prohibitive/technologically infeasible, permittee can apply for a variance: > 1 MGD: 1 mg TP/L, 10 mg TN/L > 1 MGD: 1 mg TP/L, 10 mg TN/L < 1 MGD: 2 mg TP/L, 15 mg TN/L < 1 MGD: 2 mg TP/L, 15 mg TN/L Lagoons: Maintain performance/monitor Lagoons: Maintain performance/monitor Variance applies for up to 20 years, but stricter treatment requirements over that period are likely Variance applies for up to 20 years, but stricter treatment requirements over that period are likely Other, case-specific variances also available Other, case-specific variances also available

B. Stream is not on the 303(d) list for nutrients Dilution in mixing zone based on stream’s ambient nutrient concentrations and the seasonal 14Q5 flow from July to Oct Dilution in mixing zone based on stream’s ambient nutrient concentrations and the seasonal 14Q5 flow from July to Oct – Seasonal 14Q5 flow = lowest average 14 consecutive day low-flow (July-Oct) occurring once every 5 years, on average occurring once every 5 years, on average – Nutrient standards met end-of-mixing zone Variance can be requested if calculated limit is still cost prohibitive Variance can be requested if calculated limit is still cost prohibitive

C. Discharge to groundwater with hydrologic link to surface water Discharge permit written to meet surface water nutrient standards at the 14Q5 flow, after mixing Discharge permit written to meet surface water nutrient standards at the 14Q5 flow, after mixing – Volume of discharge and post-mixed groundwater concentration are mixed in with 14Q5 flow – Monitoring occurs end-of-pipe even though discharge is to groundwater – Likely to be written for year-round application Nutrient variance can be requested (if limits are still cost prohibitive) because nutrient surface-water standards are being applied Nutrient variance can be requested (if limits are still cost prohibitive) because nutrient surface-water standards are being applied

Thanks. Questions? (406) (406)