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TMDL Expertise |
The Clean Water Act requires the States to identify waters that do not meet water quality standards and to develop Total Maximum Daily Loads (TMDLs) considering point sources, nonpoint sources, and a margin of safety to account for uncertainty.The objective of a TMDL is to allocate allowable loads among different pollutant sources so that the appropriate control actions can be taken and water quality standards achieved. There are currently 20,000 waters listed as impaired that may require over 40,000 TMDLs. State agencies estimate that developing these TMDLs will cost States between $670 million and $1.17 billion annually over 15 years.
TMDL development requires a watershed-based approach to hydrology and water quality analysis. This same approach has been the fundamental service that AQUA TERRA Consultants has provided since its inception in 1985. AQUA TERRA has been at the forefront of developing and applying watershed simulation models for the past fifteen years, providing state-of-the-art modeling tools for the U.S. Environmental Agency and the U.S. Geological Survey through long term support contracts. Watershed simulation models provide a necessary tool for evaluating and developing TMDLs for moderately complex to complex settings. These tools enable source assessment, provide the means to establish the linkage between water quality targets and sources, and allow TMDL developers to represent and compare the consequences of alternative control options.
AQUA TERRA is strongly involved in the national TMDL effort. On an advisory level, we are participating in the refinement and review of the TMDL concept and development approaches. As a premier developer of software, we are producing new modeling tools targeted specifically for use in TMDL development efforts. Concurrently, we are involved in numerous TMDL development efforts, assuring the prudent use of models and providing feedback that will define needed enhancements to the current generation of modeling tools and techniques.
Concept Refinement and Review
Tony Donigian, the president of AQUA TERRA Consultants, served on the National Research Council Committee on Assessing the Scientific Basis of the Total Maximum Daily Load (TMDL) Approach to Water Pollution Reduction. The Committee was charged with the following tasks:
AQUA TERRA's participation in the Committee provided an excellent means of sharing our philosophies and experience with others involved in the TMDL process. At the same time our firm had a unique opportunity to benefit from first-hand exposure to the most current thoughts, approaches and tools that will guide TMDL efforts nation-wide.
In 1999, AQUA TERRA was funded by the U.S. EPA's Office of Research and Development, National Exposure Research Laboratory, Ecosystems Research Laboratory (ERD) to perform a detailed evaluation of existing models and recommend which ones are suitable for evaluating nutrient TMDLs. EPA has presented the results of this study to TMDL practitioners in regional meetings in Chicago, Illinois and San Diego, California. ERD and the EPA Office of Water staff are jointly developing an integrated training program for TMDL analyses that will further disseminate the information and recommendations that emanated from AQUA TERRA's model evaluation effort.
The final report is available.TMDL Tool Development
AQUA TERRA has distinguished itself in the area of TMDL modeling tool development. Over the past three years, our firm has taken the lead in developing Version 3.0 of the EPA Office of Water's BASINS modeling system, which has been specifically developed to aid States in performing TMDL activities. Concurrently, AQUA TERRA has continued to serve as the developer and maintainer of the EPA/USGS Hydrological Simulation Program - Fortran (HSPF), considered by many as the premier model for performing watershed-based analyses. Funding from EPA has enabled us to develop a tool useful for development of simpler sediment TMDLs, and funding from the Water Environment Research Foundation has resulted in a tool that enables its users to select from among 150 models that provide capabilities useful for making TMDL determinations.
The development activities that produced BASINS 3.0 have focused as much on ancillary software as on enhancement of the core modeling system itself. Accordingly, the BASINS 3.0 installation program not only includes the core system but also WinHSPF, GenScn, WDMUtil, and PLOAD, the first three of which were developed exclusively by AQUA TERRA Consultants. WinHSPF is a new interface to HSPF Version 12 that is replacing NPSM from BASINS 2.0. GenScn is a model post processing and scenario analysis tool that is used to analyze output from HSPF and SWAT. WDMUtil is used to manage and create the watershed data management files (WDMs) that contain the meteorological data and other time series data used by HSPF. PLOAD is a GIS and spreadsheet tool that offers an alternative method for calculating nonpoint sources of pollution in watersheds.
BASINS 3.0 includes several new data and functions including 1-degree DEM grids, an automatic delineation tool that creates watershed boundaries based on DEM grids, and new watershed report function for land use, topography, and hydrologic response units. In addition, a new watershed model, the Soil and Water Assessment Tool (SWAT) has been added. In its role as prime contractor for BASINS support and development for the past three years, AQUA TERRA has been closely involved in all the enhancements that were implemented within the core modeling system. With the firm's recent award of a 5-year continuation in its BASINS support contract, AQUA TERRA will continue to oversee the future of BASINS' development.
The HSPF watershed model has received strong endorsement as a tool for use in evaluating and developing TMDLs for moderately complex to complex systems. With the advent of the TMDL mandate, HSPF model application is proliferating. AQUA TERRA has maintained its role as the developer, enhancer and maintainer of HSPF for nearly two decades. Since 1981, AQUA TERRA personnel have supported or performed HSPF applications in 23 states, providing over $9 million of HSPF-related services to our clients. We have used HSPF to model watersheds ranging in size from small test watersheds to the entire Chesapeake Bay Basin. In addition, AQUA TERRA personnel have conducted HSPF workshops, in various changing formats and duration over the past 19 years.
Of the thousands of TMDLs that will be required by the Clean Water Act, one of the predominant pollutants of concern is sediment. One promising area of EPA assistance to the States is in refining, and making more usable, the simplified approaches for sediment TMDL development that are currently recommended. In many cases simplified methods are appropriate tools for developing TMDLs for watersheds that are not classified as heavily impacted. To support this objective, AQUA TERRA Consultants developed a Visual Basic spreadsheet tool named TMDL USLE. This spreadsheet is useful for estimating the expected relative magnitude of land surface sediment loadings (tons per year) from different land use types within a watershed. Applications of the spreadsheet vary from a very simple computation of the annual edge-of-field sediment loading from a single parcel of land to more complex applications designed to characterize grouped sediment sources throughout a watershed. Estimates of sediment loadings for grouped sources are particularly useful for TMDL analysis, since similar control measures can be considered for similar sources throughout the watershed. Currently the State of Louisiana is using TMDL USLE to conduct analyses for 300 watersheds, and EPA is planning a series of training sessions for the new software tool.
In order to assist its member subscribers in making the appropriate choice of water quality modeling tools for their specific problems (including TMDL concerns), the Water Environment Research Federation (WERF) provided funding for a study to assess the availability and use of hydrodynamic, runoff, and fate and transport models. AQUA TERRA Consultants teamed with HydroQual and Camp, Dresser and McKee to perform a comprehensive evaluation of currently available models. Upon completion of the model evaluation, AQUA TERRA developed a Visual Basic application called the WERF Model Selection Tool. The tool considers approximately 150 models; model capabilities are organized using model classes, with selection criteria varying somewhat from class to class. A "checkbox" approach to identifying appropriate models was implemented; as the checkbox designations are made, the tool continually updates a list of models that satisfy the requirements indicated by the user. By either tightening or loosening the model requirements, the user is able to identify an appropriate number of models for more detailed consideration. Model descriptions are available within the decision tool for all models; the model descriptions provide an initial source for additional information, and at the same time provide guidance on how to obtain technical assistance and/or more detailed documentation.
TMDL Development
AQUA TERRA has been, or is currently, involved in TMDL efforts in:
Our services have included training staff in model application; developing modeling approaches; assessing monitoring data and developing model databases; performing model applications; and evaluating our own model results and the results produced by other modelers.