Procedure
137
purpose of setting TMDL limits. Importantly, TMDLs derived is this manner will reflect the transport and bioaccumulation of selenium within the
entire HU, rather than simply focusing on a small, artificially designated
segment of the system. Failure to use a HU approach can set the stage for
significant biological problems and undermine the intended outcome of
the TMDL process. Consult Chapter 6 for more information on the rationale and justification for using HUs.
In order to properly delineate the HU, some information on waterborne selenium concentrations is needed. This can be obtained from
monitoring data or from new measurements taken to provide a screening-level assessment. Use the entire HU as a "mixing zone" for the
purpose of evaluating potential selenium transport and bioaccumulation. Characterize and map the aquatic system of the HU using available information in combination with field reconnaissance to identify/
verify hydrological connections. Identify all aquatic habitats within
the HU: wetlands, streams, rivers, off-channel bays, lakes, reservoirs,
other impoundments. Map their spatial and gradient/hydrological relationships, determining what flows where and what flows int%ut of
what. Obtain information on trophic status, prevailing sediment type
(organic, inorganic, mixed), and volume replacement times or flushing rates for lakes, reservoirs, and other impoundments, bays off mainstem rivers, and wetlands. Describe the general level of primary
productivity (low-oligotrophic, moderate-mesotrophic, high-eutrophic),
predominant flow regime (slow, moderate, swift), and dominant sediment characteristics (depositional, erosional, particle size, organic,
inorganic, mixed) of flowing-water habitats. Large rivers merit special
attention in order to identify, map, and describe the variety of habitats
that may be present, for example, main-stem, off-channel bays, seepage or floodplain wetlands. Characterize fish and wildlife uses (feeding, spawning, nesting, migration, etc.) and identify biota of special
concern, for example, endangered or threatened species, management
priorities, and selenium-sensitive species (eg, centrarchid fishes,
Lepomis sp., Micropterus sp.; waterbirds such as stilts, Recurvirostra sp.;
and ducks, Anas sp.). Also, identify habitats where bioaccumulation
would likely be greatest (eg, wetlands, lakes, reservoirs and other impoundments, and off-channel backwater areas of rivers).
Step 2: Determine if Hazardous
Levels of Selenium are Present
Gather information on selenium concentrations. If there is no recent
monitoring data (within the past 2 years), or if the data do not satisfy
the following requirements, then it will be necessary to collect and
analyze new samples. Selenium concentrations are needed for 5 ecosystem components: water, sediments, benthic macroinvertebrates, fish
137
purpose of setting TMDL limits. Importantly, TMDLs derived is this manner will reflect the transport and bioaccumulation of selenium within the
entire HU, rather than simply focusing on a small, artificially designated
segment of the system. Failure to use a HU approach can set the stage for
significant biological problems and undermine the intended outcome of
the TMDL process. Consult Chapter 6 for more information on the rationale and justification for using HUs.
In order to properly delineate the HU, some information on waterborne selenium concentrations is needed. This can be obtained from
monitoring data or from new measurements taken to provide a screening-level assessment. Use the entire HU as a "mixing zone" for the
purpose of evaluating potential selenium transport and bioaccumulation. Characterize and map the aquatic system of the HU using available information in combination with field reconnaissance to identify/
verify hydrological connections. Identify all aquatic habitats within
the HU: wetlands, streams, rivers, off-channel bays, lakes, reservoirs,
other impoundments. Map their spatial and gradient/hydrological relationships, determining what flows where and what flows int%ut of
what. Obtain information on trophic status, prevailing sediment type
(organic, inorganic, mixed), and volume replacement times or flushing rates for lakes, reservoirs, and other impoundments, bays off mainstem rivers, and wetlands. Describe the general level of primary
productivity (low-oligotrophic, moderate-mesotrophic, high-eutrophic),
predominant flow regime (slow, moderate, swift), and dominant sediment characteristics (depositional, erosional, particle size, organic,
inorganic, mixed) of flowing-water habitats. Large rivers merit special
attention in order to identify, map, and describe the variety of habitats
that may be present, for example, main-stem, off-channel bays, seepage or floodplain wetlands. Characterize fish and wildlife uses (feeding, spawning, nesting, migration, etc.) and identify biota of special
concern, for example, endangered or threatened species, management
priorities, and selenium-sensitive species (eg, centrarchid fishes,
Lepomis sp., Micropterus sp.; waterbirds such as stilts, Recurvirostra sp.;
and ducks, Anas sp.). Also, identify habitats where bioaccumulation
would likely be greatest (eg, wetlands, lakes, reservoirs and other impoundments, and off-channel backwater areas of rivers).
Step 2: Determine if Hazardous
Levels of Selenium are Present
Gather information on selenium concentrations. If there is no recent
monitoring data (within the past 2 years), or if the data do not satisfy
the following requirements, then it will be necessary to collect and
analyze new samples. Selenium concentrations are needed for 5 ecosystem components: water, sediments, benthic macroinvertebrates, fish