8
Setting Ecosystem
Loading Limits
Introduction
This chapter describes a step-by-step procedure I developed to set Total
Maximum Daily Load (TMDL) limits for selenium. The need for this procedure in the United States stems from actions taken by the US Environmental Protection Agency (USEPA) that require TMDL limits on impaired
water bodies. For many years, water-quality regulations in the United
States have been implemented through point-source control programs
such as the NPDES (National Pollution Discharge Elimination System)
permit system. Recently, the USEPA has placed more emphasis on characterizing and reducing non-point sources of pollution in order to provide
watershed-level improvement of water quality. This approach, know as
Total Maximum Daily Loads, sets a limit on the total aggregate amount of
a contaminant allowed in an aquatic system. The objective of TMDLs is to
identify all pollution sources and then allocate/regulate discharges to meet
the water-quality needs of aquatic life within a watershed. The states are
required to identify impaired water bodies in order to comply with Section 303(d) of the Clean Water Act. The USEPA is working with states and
implementing the TMDL program as a way to gauge point and non-point
sources of pollution, to control/reduce discharges, and to improve overall
water quality pursuant to the requirements of Section 303 (d). The USEPA
has requested that state and federal biologists provide input for this process for substances ranging from nutrients and sediments to pesticides
and trace elements such as selenium. Every substance identified as a
priority must be given a separate TMDL assessment, and this must be
done individually for each impaired water body. The biologist's role may
range from a simple review and recommendation, based on available
information, to coordination/conduct of field work to assess contaminant
cycling and fate, fish and wildlife exposure, toxicity, and other factors,
involving considerable time and resources.
The magnitude of this effort becomes apparent when one considers
that each state may have dozens to even hundreds of impaired water
134
Setting Ecosystem
Loading Limits
Introduction
This chapter describes a step-by-step procedure I developed to set Total
Maximum Daily Load (TMDL) limits for selenium. The need for this procedure in the United States stems from actions taken by the US Environmental Protection Agency (USEPA) that require TMDL limits on impaired
water bodies. For many years, water-quality regulations in the United
States have been implemented through point-source control programs
such as the NPDES (National Pollution Discharge Elimination System)
permit system. Recently, the USEPA has placed more emphasis on characterizing and reducing non-point sources of pollution in order to provide
watershed-level improvement of water quality. This approach, know as
Total Maximum Daily Loads, sets a limit on the total aggregate amount of
a contaminant allowed in an aquatic system. The objective of TMDLs is to
identify all pollution sources and then allocate/regulate discharges to meet
the water-quality needs of aquatic life within a watershed. The states are
required to identify impaired water bodies in order to comply with Section 303(d) of the Clean Water Act. The USEPA is working with states and
implementing the TMDL program as a way to gauge point and non-point
sources of pollution, to control/reduce discharges, and to improve overall
water quality pursuant to the requirements of Section 303 (d). The USEPA
has requested that state and federal biologists provide input for this process for substances ranging from nutrients and sediments to pesticides
and trace elements such as selenium. Every substance identified as a
priority must be given a separate TMDL assessment, and this must be
done individually for each impaired water body. The biologist's role may
range from a simple review and recommendation, based on available
information, to coordination/conduct of field work to assess contaminant
cycling and fate, fish and wildlife exposure, toxicity, and other factors,
involving considerable time and resources.
The magnitude of this effort becomes apparent when one considers
that each state may have dozens to even hundreds of impaired water
134