Quarterly Report 2: Casey Fork Watershed

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Quarterly Report 2: Casey Fork Watershed
Introduction
This is second in a series of quarterly reports to provide an update of Total Maximum Daily
Load (TMDL) development in the Casey Fork Watershed. The Illinois Environmental Protection
Agency (Illinois EPA) is responsible for TMDL development and has contracted with Camp
Dresser & McKee (CDM) to complete TMDLs within this watershed. Illinois EPA plans to
complete the TMDLs for this watershed within the next eight months. This quarterly report
provides a brief description of how models and methodologies will be utilized in conducting
TMDLs in the watershed.
Overview of Methodologies and Models
Methodologies and models will be utilized to assess TMDL endpoints for the Casey Fork
Watershed. Some physical settings, such as suspended solids in a lake or stream, habitat
alteration, or existence of noxious plants, do not lend themselves to typical water quality
modeling. In these situations, where only limited or qualitative data exist to characterize
physical impairments, methodologies will be used to develop TMDLs and implementation
plans as appropriate.
In addition to methodologies, watershed and receiving water computer models are available for
TMDL development. Most models have similar overall capabilities but operate at different time
and spatial scales and were developed for varying conditions. The available models range
between empirical and physically based. However, all existing watershed and receiving water
computer models simplify processes and often include obviously empirical components that
omit the general physical laws. They are, in reality, a representation of data.
Each model has its own set of limitations on its use, applicability, and predictive capabilities.
For example, watershed models may be designed to project loads within annual, seasonal,
monthly, or storm event time scales with spatial scales ranging from large watersheds to small
sub-basins to individual parcels such as construction sites. With regard to time, receiving water
models can be steady state, quasi-dynamic, or fully dynamic. As the level of temporal and
spatial detail increases, the data requirements and level of modeling effort increase.
The models to be utilized in this watershed include the Watershed Management Model,
Generalized Watershed Loading Functions model, Environmental Protection Agency Screening
Procedures and STREAMDO.
Methodology and Modeling Approach for Streams
For the Casey Fork Watershed, TMDLs for the following constituents will be completed using a
watershed/receiving water model combination:
n DO
n Manganese
n Salinity/TDS/chlorides