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Update of the Rationale for the Derivation of EC & SAR Standards

Update of the Rationale for the Derivation of EC & SAR Standards. Montana Board of Environmental Review May 13, 2011. Tongue River at State Line Station. Powder River near Moorehead, MT.

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Update of the Rationale for the Derivation of EC & SAR Standards

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  1. Update of the Rationale for the Derivation of EC & SAR Standards Montana Board of Environmental Review May 13, 2011

  2. Tongue River at State Line Station

  3. Powder River near Moorehead, MT

  4. Administrative and Legal ProceedingsDEQ began investigating need for standards in late 1990’sBER petitioned to establish EC & SAR standards in 2002 MT used a narrative standard at the timeDEQ completed an exhaustive review and administrative record, including many public meetings,a collaborative group, and hired a technical expertBER adopted numeric standards in 2003BER left the narrative standard in place for antidegradationsignificance threshold, but asked the department to consider alternative approaches

  5. BER petitioned in 2005 to establish numeric antidegradation threshold,require reinjection of produced water, and other administrative adjustments Following thorough review and development of another administrative record, BER adopted numeric antidegradation criteria, but did not adopt the requirement for reinjection WY filed suit against the Board in state district court in MT WY producers filed suit in federal district court in WY against EPA for not disapproving the MT standards MT won in state district court in MT; upheld by Montana Supreme Court WY producers won in federal district in WY

  6. Federal judge remanded approval to EPA and found that EPA: • failed to consider the entire administrative record from the state rulemaking • Failed to articulate a thorough analysis for its decision • Failed to determine whether the MT standards are based on appropriate technical and scientific data, and • Failed to provide proper notice and comment DEQ solicited specific input on EC & SAR standards as an element of the 2010 Triennial Review • Compiled about 40 studies & research projects conducted between 2003-2010 • 60 day public comment period ending June 2010 • 70 comments containing 48 issues received • Comments & responses in Appendix II of Rationale

  7. Salinity v. Sodium • Salinity • Typically measured as TDS or Electrical Conductivity (EC) • Harmful to plants • Sodicity, typically measured in terms of proportion of Na+ relative to Ca++ & Mg++ • SAR = [Na] / ( [Ca] + [Mg] )-2 • Harmful to soils with clay content

  8. EC effects depend on: • Crop • For example, field beans can tolerate about half the soil water salinity that alfalfa can tolerate • Irrigation practices • Soil water EC tends > irrigation water EC due to evapotranspiration • “leaching fraction”, the percentage of irrigation applied in excess of crop need to carry excess salts beyond root zone • Proportion of rainfall to irrigation water (dilutes salt concentration)

  9. Soil Water EC vs Irrigation Water ECwith lines for different leaching fractions (Univ. Calif. Water Management pub. 3375)

  10. Setting EC Criterion for Crop • Identify: • Most sensitive crop • Soil water EC threshold, above which crop production starts to decline • Typically more concentrated than irrigation water • Leaching fraction necessary to protect soil from excess salt buildup • Determine relative proportion of irrigation water & precipitation to meet crop needs, if those needs can be fully met (Tongue)

  11. Correction Factor on Tongue • Effective Infiltration = (Annual Precip)(Infiltration Factor) • Effective Infiltration = (14.44”)0.8 = 11.5” • Agronomic need = (crop need)(leaching fraction) = (30”)1.15 = 34.5” • Irrigation water = Agron need – effective infiltration = 34.5” – 11.5” = 23” • Correction Factor = (Precip + Irrig)/Irrig = (11.5 + 23)/23 = 1.5

  12. Calculating the EC Criterion - Tongue • Target crop: Field Beans • To maintain soil water < 1,000 us/cm • Irrigation Water needs to be < 667 (from Ayers & Westcott, 1985) • Apply Correction Factor (1.5) • Criterion = (667)1.5 = 1000

  13. Calculating the EC Criterion - Powder • Target crop: alfalfa • Soil water must be < 2000 us/cm • Irrigation water must by < 2000 us/cm (Ayers & Westcott, 1985) • Insufficient water available to fully meet agronomic need • Correction factor cannot be calculated • Criterion = 2000 us/cm

  14. SAR effect depends on: • Soil type • Sensitivity of individual soils variable • e.g. related to amount & type of clay • MT standards drawn from published literature & independent of soil type • Salinity of water • EC moderates SAR effect • However, precipitation decreases EC, but has little effect on SAR in soil water (rainfall effect)

  15. SAR Criterion • Threshold of harm depends on salinity in the soil water • higher the salinity the higher the SAR can be without adverse dispersive effect on the soil • however, salinity limited by crop tolerance • Relationship published (Hanson) • Rainfall effect must be considered

  16. Relationship between EC and SAR

  17. Relationship between EC and SAR (considering precipitation effects)

  18. Tributaries Leaching only occurs once in 8 to 10 years Calculations/approach drawn from: Agricultural Drainage, 1999 deMooy & Franklin, 1977 Ayers & Westcott, 1976 Assumptions made for Initial soil salinity Water holding capacity of soil Standard of 500 us/cm results in soil salinity of 2300 to 2800 us/cm & alfalfa yield decrease of 2 to 5%

  19. Montana ElectricalConductivity (EC) and Sodium Adsorption Ratio (SAR) Standards • Tongue River – Irrigation season – 1000 EC 3 SAR Nonirrigation season – 1500 EC 4.5 SAR Powder River - Irrigation Season - 2000 EC 5 SAR - Nonirrigation season – 2500 EC 7.5 SAR Tributaries - 500 EC 3 SAR

  20. Recommendations  Department finds that the great majority of the literature published since 2003 supports • the need for protective numeric standards • the manner in which they were developed • the ultimate values that the Board adopted. • Department has not identified any basis through these recent studies, nor through the public comments received, that argue revisitation of the general approach, the numbers themselves, or the manner in which they are implemented.  Department therefore recommends that the Board not initiate further rulemaking on the EC & SAR standards at this time  Department intends to submit this Rationale to EPA, and request approval of the numeric standards submitted in 2003 and 2006

  21. Nondegradation • State Policy to protect high quality water • Significance determination • Carcinogens • Toxics • Harmful • Narrative • If significant change to water quality, then need authorization to degrade • Includes alternatives analysis

  22. Nondegradation Impaired waters Standard 100 High Quality Ambient 10 0

  23. Significance Thresholds Standard Narrative standard: measurable x effect on use or measurable change in aquatic life or ecological integrity) 10%, if ambient < 40% of Standard (harmful) Increasing Change 15% of Standard (toxics) Existing water quality: Carcinogen: any change 0

  24. Harmful Nondegradation Approach Exceeds standard, No authorization to degrade allowed Standard Requires authoriz. to degrade 50 % 40 % Allow 10% 0

  25. Montana Electrical Conductivity (EC) and Sodium Adsorption Ratio (SAR) Standards

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