EPA’s Final Total Nitrogen General Permit for Great Bay Addresses Key NACWA Comments
(December 9, 2020) – On November 24, EPA Region 1 issued the final Great Bay Total Nitrogen General Permit (GP) for 13 eligible wastewater treatment facilities (WWTFs) that discharge nitrogen within the Great Bay watershed in New Hampshire.
NACWA is pleased that several concerns raised in the Association’s May 7 comments on the draft permit were addressed. The final permit contains an adaptive management structure that will provide municipalities with greater flexibility to maximize recent investments in wastewater treatment facilities and to leverage non-point source (NPS) and stormwater measures that have the ability to reduce nitrogen entering the Great Bay estuary.
Coverage under the permit is no longer mandatory. The municipalities can choose whether to be regulated by the GP or to have nitrogen limits imposed by EPA through the renewal process of their individual permits. Under the GP, the municipalities can prioritize funds for local nonpoint source reductions in a manner and on a schedule according to plans they will propose rather than additional WWTF improvements.
The draft permit set WWTF effluent total nitrogen (TN) mass load limits based on 2012-2016 flow data and required WWTFs to meet annual average effluent limits. In its comments, NACWA recommended that EPA modify the loading requirements in a manner that appropriately accounts for seasonal variability. The final permit is still based on historical flow data but has been updated to more recent (and higher) 2015-2019 flows.
More significantly, the 8 mg/L concentration basis for the load limits has been revised from an annual average to a rolling 7-month seasonal average associated with the growing season. To meet the draft permit’s annual average, utilities would have been required to achieve extreme reductions in warmer months to meet annual averages that assume effective nutrient removal in the winter. The discharge of all pollutants other than nitrogen from the 13 WWTFs will continue to be authorized by each facility’s respective individual NPDES permit.
The draft permit attempted to establish an adaptive management framework to give the WWTFs some flexibility to address nonpoint source contributions of nitrogen. But the draft permit had a one-size-fits-all (OSFA) approach that would have set in stone an aggressive 20-year program target in the initial five-year permit. The final permit adopts an approach that will further the intended objectives. It smartly abandons the OSFA 20-year approach and instead gives the communities the option to submit their own proposals for nonpoint source reductions over a five-year term that can be better tailored to address local needs and opportunities.
The final permit retains as its basis the problematic literature-based 100 kg/hectare/year watershed loading rate but allows permittees to submit a proposal to EPA within 180 days of the effective date of the permit (February 1, 2021) that outlines an inclusive and transparent process for “comprehensively evaluating any significant scientific and methodological issues relating to the permit, including the choice of a load-based threshold of 100 kg ha-1 yr-1 versus any other proposed threshold, including a concentration-based threshold of 0.32 mg/L.” If the New Hampshire Department of Environmental Services concurs with the permittee’s findings, they will be included in the administrative record for permit renewal.
EPA also removed a requirement to develop and implement nutrient optimization plans and eliminated a required ambient monitoring program, the scale of which would have put an enormous burden on the WWTFs while providing little flexibility to make changes to the initial program design.