What is CAST?

Chesapeake Assessment Scenario Tool (CAST) is a web-based nitrogen, phosphorus and sediment load estimator tool that streamlines environmental planning. Users specify the Best Management Practices (BMPs) and their location. CAST builds the scenario and provides estimates of nitrogen, phosphorus, and sediment load reductions.

For more technical details see the full documentation.



Why use CAST?

CAST enables each local Bay jurisdiction to develop a plan for meeting a load allocation. CAST provides the jurisdictions with opportunities for “on-the-fly” estimates of load reductions.

CAST allows users to understand which BMPs provide the greatest load reduction benefit and the extent to which these BMPs can be implemented. Based on the scenario outputs, users can refine their BMP choices in their WIP planning.

CAST facilitates an iterative process to determine if Total Maximum Daily Load (TMDL) allocations are met. Scenarios may be compared to each other, TMDL allocations, or the amount of nitrogen, phosphorus, and sediment from the Watershed Implementation Plan (WIP) or a current annual progress scenario.

CAST scenarios closely replicate the results of the Chesapeake Bay Program’s (CBP) Watershed Model. Other available tools have assumptions that may be different from those used in the Watershed Model for developing the current TMDL. Since the Watershed Model is used to assess the jurisdictions’ progress toward meeting the TMDL allocations, consistency with the Watershed Model is critical.

  • Uses CBP-approved BMPs and efficiencies
  • Consistent with the CBP Phase 5.3.2 Watershed Model and updates
  • Provides a consistent input scale – users have the opportunity to use their No Action, most recent Progress, and/or WIPs scenarios


Who benefits from using CAST?

CAST has been used by multiple local jurisdictions and states for the Phase I and II WIPs, 2012 Milestones and even local TMDLs. Any user may see the source of the data that was used in developing the TMDL and the state’s most recent annual progress scenario and WIP. This allows involvement of the counties and other local planners in the state WIP. CAST is easily accessible on-line with no need to install specific databases or software. All who request a login are granted one.



What are CAST’s outputs?

CAST estimates of load reductions for point and nonpoint sources include: agriculture, urban, waste water, forest, and septic loading to the land (edge-of-stream) and loads delivered to the Chesapeake Bay. CAST stores data associated with each BMP as well as the load for each sector and land use. With these data tables, CAST also serves as a data management system. Thus, users may quantify the impacts of various management actions while improving local management decisions.

In addition, CAST creates data files for direct input to the CBP’s Scenario Builder, avoiding the need to transform or transpose such data and eliminating a potential source of error. CAST and other Chesapeake Bay modeling tools complement each another.



Why was CAST developed?

The first version of CAST was launched in June 2011 to provide local jurisdictions, such as counties, with a tool to provide input into the TMDL WIP process. The U.S. Environmental Protection Agency (EPA) issued a TMDL in 2010 for the Chesapeake Bay based on allocations established by the states. The jurisdictions that drain to the Chesapeake Bay include New York, Pennsylvania, West Virginia, Maryland, Delaware, District of Columbia, and Virginia. The states agreed that it would be more efficient for states to allocate responsibility within their respective political boundaries, and for EPA to issue one overall TMDL that reflected each state’s allocation. Since planning happens at a more local scale, such as county, some states downscaled the allocation to the county level.



What's next for CAST?

The tool will continue to evolve to meet the needs of users. Future plans for CAST include adding new features relating to the costs and benefits of each scenario, user interface improvements, and continued improvement of the agreement with the Watershed Model. Data and BMPs are updated to match those accepted by the Chesapeake Bay Program on an ongoing basis. All of these future enhancements are planned with input from the states and local jurisdictions, the CBP, and the EPA.