Procedure
135
bodies that will need TMDLs, many of which could involve selenium,
because of its widespread concern as a water quality issue (Lemly et
al. 1993; Lemly 1999). Although the USEPA has published an overview
document that explains principles underlying the development and
implementation of TMDLs (EPA 1999), no procedures specific to selenium are given. This leaves biologists and environmental contaminant specialists without the assessment framework necessary to
effectively address the TMDL issue for selenium. Due to selenium's
propensity to bioaccumulate, to cause reproductive impairment in fish
and wildlife, and to persist in the environment, selenium-specific
methods are needed. It is critical to have a technically sound approach
for evaluating selenium, because it is considered a priority contaminant by natural resource managers and the USEPA. This chapter provides guidance by laying out an assessment method that links the basic
components of the USEPA's TMDL program to the contaminant-specific
information necessary for selenium.
Procedure
This method is structured to answer 2 basic questions: (1) Is selenium
impairing the water body based on biological criteria? and (2) If so, what
amount of selenium load reduction is necessary to correct the problem? A
7-step procedure (Fig. 8.1) can be used to answer these questions and
develop environmentally safe TMDL limits for selenium. The basic premise
in this approach is that selenium concentrations should be kept below
levels that threaten the reproduction of fish and aquatic birds.
Step 1: Delineate and Characterize
the Hydrological Unit
TMDLs for selenium should be based on an assessment of the degree of
toxicological hazard to fish and wildlife. This assessment is influenced
by the hydrology of the site under consideration. The physical area
from which measurements are taken to evaluate selenium concentrations and biological threats/effects, that is, the database for setting
TMDLs, must encompass more than an isolated segment of a river, a
tributary stream, or other limited area. Because of hydrological connections between the various aquatic habitats that may be present in a
watershed basin-wetlands, rivers, streams, lakes, and impoundmentsthe toxic threat from selenium contamination is also connected. For
example, a TMDL limit that is set for a stream or river where low
bioaccumulation occurs may result in seemingly harmless concentrations becoming a problem in downstream impoundments or in offchannel bays and wetlands where bioaccumulation is greater.
135
bodies that will need TMDLs, many of which could involve selenium,
because of its widespread concern as a water quality issue (Lemly et
al. 1993; Lemly 1999). Although the USEPA has published an overview
document that explains principles underlying the development and
implementation of TMDLs (EPA 1999), no procedures specific to selenium are given. This leaves biologists and environmental contaminant specialists without the assessment framework necessary to
effectively address the TMDL issue for selenium. Due to selenium's
propensity to bioaccumulate, to cause reproductive impairment in fish
and wildlife, and to persist in the environment, selenium-specific
methods are needed. It is critical to have a technically sound approach
for evaluating selenium, because it is considered a priority contaminant by natural resource managers and the USEPA. This chapter provides guidance by laying out an assessment method that links the basic
components of the USEPA's TMDL program to the contaminant-specific
information necessary for selenium.
Procedure
This method is structured to answer 2 basic questions: (1) Is selenium
impairing the water body based on biological criteria? and (2) If so, what
amount of selenium load reduction is necessary to correct the problem? A
7-step procedure (Fig. 8.1) can be used to answer these questions and
develop environmentally safe TMDL limits for selenium. The basic premise
in this approach is that selenium concentrations should be kept below
levels that threaten the reproduction of fish and aquatic birds.
Step 1: Delineate and Characterize
the Hydrological Unit
TMDLs for selenium should be based on an assessment of the degree of
toxicological hazard to fish and wildlife. This assessment is influenced
by the hydrology of the site under consideration. The physical area
from which measurements are taken to evaluate selenium concentrations and biological threats/effects, that is, the database for setting
TMDLs, must encompass more than an isolated segment of a river, a
tributary stream, or other limited area. Because of hydrological connections between the various aquatic habitats that may be present in a
watershed basin-wetlands, rivers, streams, lakes, and impoundmentsthe toxic threat from selenium contamination is also connected. For
example, a TMDL limit that is set for a stream or river where low
bioaccumulation occurs may result in seemingly harmless concentrations becoming a problem in downstream impoundments or in offchannel bays and wetlands where bioaccumulation is greater.