ANTIDEGRADATON and NITROGEN IN GREAT BAY Paul Currier, P.E., P.G. New Hampshire Department of Environmental Services NHEP Technical Advisory Committee December 7, 2007

WATER QUALITY STANDARDS Clean Water Act PL92-500, sections 303, Essential elements –Designated Uses –Criteria to support the uses –ANTIDEGRADATION POLICY CFR title 40, Sec Env-Ws 1708 Antidegradation

ANTIDEGRADATION Three Tiers –TIER 1: Maintain existing uses, support designated uses –TIER 2: High Quality Waters High quality shall be maintained and protected unless there is social and economic justification –TIER 3: Outstanding Resource Waters Administrative tier – not based on existing WQ Quality shall be maintained and protected Short term, temporary degradation allowed in specific cases

Tier 2 High Quality Waters Water quality shall be maintained and protected (except for insignificant degradation) unless there is social and economic justification. Tier 1 Degradation of water quality is not allowed to provide for “buffer.” Impaired Degradation of water quality not allowed. (Separate requirement for TMDL study) Worse Better Water Quality WQ Standard

OUTSTANDING RESOURCE WATER (TIER 3) Administrative tier DES can adopt by rule Applies to all parameters, not just nutrient- related May be too restrictive for a large watershed (3) Where high quality waters constitute an outstanding National resource, such as waters of National and State parks and wildlife refuges and waters of exceptional recreational or ecological significance, that water quality shall be maintained and protected.

POSSIBLE TIER 1 DETERMINATION FOR GREAT BAY Antidegradation status may be a moot issue if an interim N standard is adopted soon Use a “Weight of Evidence” approach Ask the question “has 90% or more of the assimilative capacity been used” for N or a parameter that is a function of N