Total Maximum Daily Load (TMDL) Development Methodology for Waterbodies in New York State Closed to Shellfish Harvesting

Srinivasan Rangarajan, Ph.D., P.E., Haiyi Lu, Charles L. Dujardin, P.E., and T. Gulbransen

The U.S. Environmental Protection Agency (EPA), Region 2 is sponsoring this technical work to assist the New York State Department of Environmental Conservation (NYSDEC) in exploring mechanisms for implementing water quality control strategies. The goal is to design a flexible yet technically sound Total Maximum Daily Load (TMDL) development methodology for waterbodies listed in New York State's (NYS) Clean Water Act Section 303(d) list as closed for shellfish harvesting, and build the state's program development capabilities by providing NYSDEC with an expertise to submit TMDLs of this nature. The study objectives include:

• Identification of water quality target(s) for pathogens based on the designated use, shellfish harvesting,
• Assessment of point and non-point sources of pollution that contribute pathogen load to the waterbody,
• Establishment of linkage between water quality target(s) and sources, thereby, the baseline scenario of pollution loading from point and non-point sources, and
• Development of load allocations to achieve water quality target(s).

HydroQual, Inc., through a subcontract agreement with Battelle Memorial Institute for this project, has been working with EPA Region 2 and NYSDEC. The NYS has recommended Oyster Bay Harbor and Flanders Bay in Long Island (New York) for pilot application of the methodology developed here. This methodology will provide guidance for development of TMDLs for the remaining waterbodies in the 303(d) list.

As guidance documents, two technical memorandums have been prepared and submitted to EPA for review. The first one provides detailed information on over 150 public domain and commercial models that were identified and evaluated for their suitability for pathogen TMDL development. The second memorandum provides guidance for data analysis, a decision-tree of modeling frameworks and TMDL allocation procedures suitable for waterbodies with shellfish harvesting based on the following considerations:

• Critical tidal conditions
• Background pollutant contributions
• Types and sources of point and non-point sources of pollution·
• Soil characteristics and current and projected landuses
• Seasonal variations
• Current TMDL requirements
• Water quality target(s) and margin of safety
• Weather (precipitation and wind) conditions selected for TMDL development
• Data availability, accuracy and its reliability
• Model's predictive capabilities
• Ease of transferability
• Methods for allocation of loadings and their soundness, and
• Potential controls to achieve allocated loadings for the point and non-point pollution sources.

The methodology proposed in the second memorandum will be used to develop TMDLs for the two waterbodies recommended by NYSDEC. Technical support documents will be assembled in Spring 2002 to demonstrate the application of this methodology to the two waterbodies, and develop additional guidance for addressing the remaining listed waterbodies closed for shellfish harvesting. These documents will include an explanation of the data used, all assumptions and itemized TMDL calculations describing individual waste load allocations (WLA), load allocations (LA), seasonal variations, margin of safety (MOS) and future load allocations for pathogens and pollutant source combinations affecting the waterbodies under investigation. Additional recommendations, as appropriate, will be provided to NYS for developing water quality control methodologies.

In the Oyster Bay Harbor and Flanders Bay pilot projects, the assessment of the sources of pollution was achieved from analysis of existing flow and water quality data and/or collection of additional data from NYSDEC, USGS and other sources. Water quality target(s) have been identified by considering, in addition to the State's water quality standards for pathogens, an MOS to account for unidentified sources of pollution and increases in pollutant loads associated with future growth in the watershed. The most suitable modeling frameworks using a combination of load generation and pathogen transport models have been identified to define the linkage between the target and sources.

To be Presented at:

November 13-16, 2002
National TMDL Science and Policy Conference
Hosted by the Water Environment Federation
Phoenix, Arizona