About CAST



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 a geographical area, and then select Best Management Practices (BMPs) to apply on that area. CAST builds the scenario and provides estimates of nitrogen, phosphorus, and sediment load reductions. The cost of a scenario is also provided so that users may select the most cost-effective practices to reduce pollutant loads.

For more technical details see the full documentation.

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Why use CAST?

CAST enables planners in the watershed to develop a plan for meeting a nitrogen, phosphorus, or sediment load allocation using the most cost-effective strategy. CAST provides “on-the-fly” estimates of load reductions. CAST allows users to understand which BMPs provide the greatest load reduction benefit, the extent to which these BMPs can be implemented, and the cost of these BMPs. Based on the scenario outputs, users can refine their BMP choices in their 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 2010 Chesapeake Bay TMDL. Since the Watershed Model is used to assess jurisdictions’ progress toward meeting the TMDL allocations, consistency with the Watershed Model is critical.

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Who benefits from using CAST?

CAST is has been used by multiple local jurisdictions and states for the Phase II WIPs, 2013 and 2015 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, Milestone and WIP. This allows involvement of the counties and other local planners in the Bay TMDL. CAST is easily accessible on-line with no need to install specific databases or software. All who request a login are granted one.

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What are CAST’s outputs?

CAST estimates of load reductions for point and nonpoint sources include: agriculture, urban, forest, and septic loading to the edge of a fourth-order stream and loads delivered to the Chesapeake Bay. CAST stores the geographic area, cost and implementation level 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.

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Why was CAST developed?

The first version of CAST was launched in 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.

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How is information entered into CAST?

CAST is designed to be useful to people with a general knowledge of BMPs. Knowledge of models or BMP load reduction calculations is not necessary. CAST is available on-line to users with a login and password, which may be requested from the website.

Data is entered into VAST in the following sequence:

  • The user selects a geographic area, such as a county.
  • CAST draws upon the same data sources as the Chesapeake Bay Program Partnership models to populate the parameters of the scenario based on user selections. The user can build a new scenario or import features of an existing scenario. The user may opt to share the scenario with other users on the system.
  • The user establishes costs of BMPs, or can use the defaults provided.
  • The user adds BMPs to the scenario using separate screens with options for urban, septic, forest, agriculture, animals, and manure transport. The user may edit the BMP selections at any time to modify the scenario.
  • The user selects calculate and the loads and costs are provided on screen and in downloadable tables.
  • The user also may compare scenarios.

Users may choose to enter BMPs as percent of land available or as actual acres or number of septic systems. The number of available acres changes depending on the other BMPs in the scenario. For example, the forest buffer BMP removes acres from one land use and converts it to forest. This means that there are fewer acres for other BMPs in the original land use. More information on the sequence of BMP application is found in the VAST technical manual file posted under documentation.

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How is CAST different from the other CAST family of tools?

VAST, MAST, and BayFAST are all based off of CAST. The load calculations performed by all tools are identical. VAST is the Virginia-specific version of CAST. VAST users may add their own land use. This land use is simply stored and may be useful to the Virginia Department of Environmental Quality as it works with the Chesapeake Bay Program to update the land use. MAST is the Maryland-specific version of CAST. MAST has some Maryland-specific geographies available through the interface and differences in the way that Processed Water facilities are displayed. MAST also has loads available for historical years to assist with local TMDL watershed planning. BayFAST allows users to define the boundaries of a parcel and the land use areas within that parcel, and then to build scenarios for those user-defined parcels.

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How do the load estimates produced by CAST agree with those produced by the Chesapeake Bay Program Partnership Watershed Model?

The developers of CAST regularly assess the fit between the load estimates and the Watershed Model. For a very large number of land-river segments under a range of BMPs, the fit is 95% or better. Download the latest, detailed report from the documentation page.

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Who develops and maintains CAST?

The Chesapeake Assessment Scenario Tool (CAST) was first developed in 2011 by Jessica R. Rigelman of J7 LLC and Olivia H. Devereux of Devereux Environmental Consulting, with funding provided by U.S. EPA. The immediate need was to provide local planners within the Chesapeake Bay Watershed with a tool to provide input into the TMDL Watershed Implementation Plan development process. With continued funding from the U.S. EPA, the functionality of the CAST family of tools has been expanded to serve multiple needs for environmental planning in the Chesapeake Bay Watershed. For more information about the developers visit the Contact Us page.

Future enhancements are developed with input from the states and local jurisdictions, the Chesapeake Bay Program Partnership, and the EPA. The tool will continue to evolve to meet the needs of users.

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