In 2014 Exelon Generation Company, LLC (Exelon), in cooperation with the Maryland Department of Natural Resources (MDNR), Maryland Department of the Environment (MDE), University of Maryland Center for Environmental Science (UMCES), U.S. Geological Survey (USGS), U.S. Army Corps of Engineers (the Corps), and the U.S. Environmental Protection Agency (USEPA) Chesapeake Bay Program, initiated the multi-year Lower Susquehanna River Integrated Sediment and Nutrient Monitoring Program (Integrated Monitoring Program), with the following primary goals:
The original study was to target up to six storm events with flows equaling or exceeding 100,000 cfs. At the conclusion of all field efforts, the results of the Integrated Monitoring Program were to be used to update the suite of Chesapeake Bay (the Bay) Watershed and Water Quality models for use in the 2017 TMDL Midpoint Assessment. As of June 2016, two official sampling events have occurred, both of which had peak flows less than 182,000 cfs.
In late 2015, due to a lack of storm events in the target flow range and the lack of available corresponding empirical data, Program partners began discussing alternative approaches that could be implemented in early 2016 to supplement the modeling efforts associated with the Midpoint Assessment.
From these conversations, Exelon developed a two phased-modeling approach that would enhance and complement the existing Phase 6 HSPF Watershed Model (HSPF) as well as the simulation of inputs to the Bay Water Quality and Sediment Transport Model (WQSTM). The two phased modeling approach includes developing:
As part of this modeling effort, the Exelon team agreed to work closely with the Chesapeake Bay Program (CBP) Modeling Workgroup and Corps modelers throughout this process to ensure that all parties are in agreement on the methods used, deliverables provided, and implementation of results into the suite of CBP models (specifically Phase 6 CBP Watershed Model and WQSTM). In addition, Exelon agreed that all modeling efforts and reports will be subject to two independent reviews, including (1) interim review and guidance from an independent modeling evaluation group to be contracted and coordinated by the Chesapeake Research Consortium (CRC) and (2) additional review as part of a larger review of the CBP’s Phase 6 Watershed Model that is already scheduled for 2016 as part of the activities of the CBP’s Scientific and Technical Advisory Committee (STAC). The Evaluation/Review Team comprises four independent evaluators/reviewers. The Scope of Work (which includes this same background information as preamble) was agreed upon by all parties at the beginning of the review process. The evaluation group will review the modeling methods, results, and reports and provide feedback and comments as appropriate. Comments provided by the evaluators/reviewers will be taken under advisement by the Exelon team.
1 Sampling Event No. 1 occurred April 6-14, 2015 with peak flows of 146,000 and 182,000 cfs. Sampling Event No. 2 occurred April 22-25, 2015 with a peak flow of 125,000 cfs.
2 In addition, supplemental data were collected at Marietta, Holtwood, and Conowingo during a February 2016 high flow event (peak flows ~180,000 cfs). Although data were collected, this was not considered an official sampling event.