Chesapeake Assessment Scenario Tool


The new model version includes updates to the data and methods that change loads in the scenarios and years. This includes your own scenarios, scenarios shared with you, and public scenarios. Public scenarios and the shared scenarios owned by CBP Admin are recalculated for you. However, you will need to transition and run your own scenarios from CAST-19 to CAST-23 using the "Migrate Scenarios" button on the Scenarios page. Once you move your scenarios, run the scenarios to see the new loads. Once CAST-23 is live, users will no longer have access to CAST-19, including those that had been granted access to the draft version of CAST-23.

The official Phase III WIPs are those loads from the CAST version in which they were developed. The loads change in all scenarios, including the WIPs, in this new version. The BMPs from the Phase III WIPs are available in the scenario "WIP 3 CAST-2023 Version." The loads from the original version of the WIPs are available in the scenario "WIP 3 Official." The 2025 Phase III Planning Targets do not change. The milestone goals do change. The 2009 progress changes since the entire history of BMP implementation is re-run with each new version of CAST. With the 2009 starting point adjustment, the trajectory to the 2025 planning target endpoint shifts. As we get closer to 2025, the effect of the shift is less than earlier years since we are closer to the anchored 2025 target. The milestone goal steps up with each cycle (80% in 2021, 90% in 2023). The unaccounted additional loads are not in the CAST scenario results and are loads that EPA will not hold jurisdictions accountable for in 2025. Use the CAST Planning Targets tool to compare planning targets to public scenarios.

The detailed changes between CAST versions are documented in the About menu under Model Documentation. The list of changes that will occur is as follows.

The changes that impact loads include:

  • BMPs submitted, including the TMDL critical period, are updated. This update impacts multiple estimates including the BMPs credited through 2017 land use (except for forest buffers, tree and forest planting, which is 2002), the amount of nutrients applied to meet crop needs, and the historic manure transport of total phosphorus through 2016.
  • The agricultural land use total acres are now determined by the Land Data Team's change product from 2013 rather than the USDA Agricultural Census total acres.
  • Agricultural and urban fertilizer sales data are updated to include data reported to American Plant Food Control Officials (AAPFCO) through 2016. The missing fertilizer for 2013 and 2014 was corrected. State-supplied fertilizer data is utilized for 2017-2020.
  • New fertilizer sales data results in new urban fertilizer application rates for the years 2013 through 2025.
  • The 2013-2025 land use acres, septic systems, and sewer service areas are updated.¬†Base conditions are newly available through 2030.¬†
  • Maryland biosolids are updated. The amount for other jurisdictions is simply carried forward for all future years.
  • Pennsylvania updated their combined sewer overflow reductions.
  • Virginia's insignificant facilities wastewater data was updated for 2014-2020.
  • West Virginia found errors in their 2009 wastewater data and corrected those, leading to an increase in loads.
  • Virginia and West Virginia's harvested forest acres are updated for 2021. Maryland's 2013 to 2021 harvested forest acres are updated.
  • Construction acres are updated for 2021 in all states except Maryland. New York updated construction acres for 2016-2021.
  • The split between Pennsylvania's permitted and nonpermitted feeding space has been updated.
  • The amount credited for tree BMPs that are credited in the land use rather than credited in the submitted BMPs is changed. The tree BMPs are now credited 15 years prior to the date of the aerial imagery in the land use. These BMPs include forest buffers, tree planting, and forest planting.
  • The credit duration of RI-9: Forest Nutrient Exclusion Area and RI-10: Forest Buffer on Watercourse is extended from 10 to 15 years.
  • Changes to nutrient application eligibility in Phase 6 CAST. This change allows all crop nutrient applications to be both manure and fertilizer eligible if that crop/land use allows it.
  • Virginia's regulated/unregulated developed acreage in CAST is corrected.
  • Updated BMP history (as of February 2024)

BMPs previously approved for planning will become available for annual reporting:

  • The urban stream restoration protocol #5 is available.
  • The urban stream restoration default value is not available for annual reporting after 6/30/2022.
  • The credit duration for tree planting, forest planting, and forest buffers was changed from 10 to 15 years. The credit duration indicates the time frame that a BMP is considered valid without inspection. With inspection, a BMP is credited indefinitely.
  • The impervious disconnection BMP was corrected so that it can be applied only on impervious land. Previously it was available on pervious land.
  • The abandoned mine reclamation BMP is now credited as a land use change to forest.
  • The wetland BMPs creation and rehabilitation are updated per the expert panel report. The wetland enhancement BMP is removed.
  • The grey infrastructure nutrient discharge elimination BMP was added to CAST-23.
  • Wetland BMPs have no credit duration.
  • Animal mortality BMPs are available.
  • Newly approved oyster restoration BMPs are available.
  • The agricultural ditch BMPs are available for annual reporting. The water control structures BMP efficiency is updated to be zero now that the ditch BMPs are available.

The tools available from the homepage are updated. These include:

CAST-23 will be the last model update to the Phase 6 suite of models. This follows the decision to update the CAST schedule, which was approved by the Water Quality Goal Implementation Team, Management Board, and Principals' Staff Committee. The decision can be found in the September 26, 2023 PSC meeting minutes.