Communication is Key to Successful Outfall Relocation and NPDES Permitting

In 2014-2015, RMC worked with both the Novato Sanitary District and the State Coastal Conservancy to obtain Regional Water Quality Control Board approval to relocate the District’s outfall about 1.2 miles inland to a restored marsh adjacent to the Hamilton Wetlands Restoration Project. The outfall’s new location provides year-round freshwater flows to help sustain the brackish marsh habitat. We also provided full regulatory assistance for reissuance of the 2015 National Pollutant Discharge Elimination System (NPDES) permit for the District’s 7.0-MGD secondary wastewater treatment plant.

hamiltonwetlandsv2RMC began the work by leading coordination activities with Regional Water Quality Control Board staff to verify the regulatory approach for supporting the outfall relocation. We then completed four important water quality studies:

  1. Dilution Analysis of the Proposed Discharge. The District’s previous NPDES permit included dilution credits for specific water quality parameters. RMC investigated the applicability of these dilution credits with the new outfall. Through modeling, conducted with the assistance of modeling subconsultant RMA of Davis, California, we analyzed hydrodynamics and water quality in the San Pablo Bay to evaluate potential dilution of the proposed discharge. We performed tracer analyses to define site contours for varying dilution factors.
  2. Mixing Zone Analysis. For the Regional Water Quality Control Board to allow dilution credits, the State Implementation Policy (SIP) dictates that certain mixing zone conditions be met. RMC prepared a detailed mixing zone analysis by evaluating effluent and receiving water data to determine the relevant parameters, using the effluent data to determine the smallest practicable mixing zones, and analyzing the SIP mixing zone conditions.
  3. Antidegradation Analysis. The relocated outfall must comply with federal and state antidegradation policies, which define different “tiers” according to water quality and/or impairment. To demonstrate compliance, RMC collected, analyzed, and compiled extensive water quality data. We then quantitatively evaluated the incremental water quality impacts of a year-round discharge from the treatment plant to the marsh by studying effluent and receiving water concentrations for numerous pollutants, as well as estimating pollutant loads from wastewater treatment plants throughout the Bay Area. RMC also identified specific environmental and socioeconomic benefits of the project, and used the tiers to determine compliance with the antidegradation policy. Our analysis showed that the receiving water is expected to continue to meet water quality objectives and protect beneficial uses after the outfall is relocated.
  4. Justification for Shallow Water Discharge. The San Francisco Bay Basin Plan specifically prohibits point source discharges that achieve an initial dilution of less than 10:1 with few exceptions. To justify continued exception to this prohibition for the new outfall, RMC developed a document that shows how achieving a dilution greater than 10:1 would be an inordinate burden, describes the District’s active water recycling program, and presents the specific net environmental benefits of the proposed marsh.

As these four water quality studies were being performed, RMC was also intricately engaged in the District’s NPDES permit reissuance process. We completed multiple federal and state forms, maps, and schematics and documented District improvements. RMC collected, compiled, and reviewed several years of plant influent, effluent, biosolids, and receiving water monitoring data to complete the 2014 permit renewal application—also known as the Report of Waste Discharge (ROWD). Using this data, our team performed a reasonable potential analysis (RPA) for the District’s effluent to identify constituents needing effluent limits and calculated anticipated final effluent limits. Because there are different ways to interpret language in state and regional regulations, we conducted sensitivity analyses with the RPA to determine the most appropriate regulatory scenario for the District.

Throughout the efforts, RMC kept the communication lines open among the District, the State Coastal Conservancy, and the Regional Water Quality Control Board. We also kept a close eye on upcoming regulatory initiatives (e.g., statewide toxicity policy) and several other NPDES permit renewals that could set precedent for new permit requirements.

After submittal of the ROWD with the water quality studies in September 2014, RMC continued to assist the District with NPDES permit negotiations. Our staff performed in-depth reviews of both the administrative draft permit and public draft permit (i.e., tentative order), prepared detailed comments in both instances to submit to the Regional Water Quality Control Board, and actively engaged in discussions with the three entities about the permit. RMC’s proactive communication and thorough analysis and documentation led to a successful permit adoption in July 2015.

Jennie Pang – Environmental Engineer