Final TMDLs Approved By EPA: Triadelphia Reservoir and Rocky Gorge Reservoir

Both Triadelphia Reservoir and Rocky Gorge Reservoir (also referred to as the Patuxent Reservoirs) lie in the Patuxent River watershed.  The Patuxent River drains into Chesapeake Bay between Washington, DC and Annapolis, MD.  The portion of the watershed draining to the reservoirs lies primarily in Howard and Montgomery Counties, but also includes a small portion of Prince George’s County.  Both reservoirs are part of the Washington Suburban Sanitary Commission’s (WSSC) water supply system for Montgomery and Prince George’s Counties.  Water supply intakes in Rocky Gorge Reservoir feed WSSC’s Patuxent Water Filtration Plant near Burtonsville, MD.  Triadelphia Reservoir, which is upstream of Rocky Gorge Reservoir, is used to maintain capacity in Rocky Gorge Reservoir.

Triadelphia Reservoir and Rocky Gorge Reservoir have been designated as Use IV-P and Use I-P waterbodies, respectively, in the Code of Maryland Regulations (COMAR and COMAR  Both reservoirs were identified on the 303(d) list submitted to EPA by the Maryland Department of the Environment (MDE) as impaired by the following (years listed in parentheses):  nutrients (1998) and impacts to biological communities (2002 and 2004).  In addition, Triadelphia Reservoir was listed as impaired by sediment in 1998.  The document, available below, establishes TMDLs for the nutrient and sediment impairments.  Biological impairments within these watersheds will be addressed separately at a future date. 

Total Maximum Daily Loads of Phosphorus and Sediments for Triadelphia Reservoir and Total Maximum Daily Loads of Phosphorus for Rocky Gorge Reservoir, Howard, Montgomery and Prince George's Counties, Maryland
EPA's Decision Letter EPA's Decision Letter
Main Report TMDL Patuxent Reservoirs.pdf  (996KB)
 Appendix A Appendix_A.pdf  (2791KB)
 Appendix B Appendix_B.pdf (158KB)
 Appendix C Appendix_C.pdf (522KB)
 Appendix D Appendix_D.pdf (12KB)
Appendix E Appendix E.pdf (21KB)
Nonpoint Source Tech Memo NPS_Tech_memo.pdf (11KB)
Point Source
Tech Memo
PS_Tech_memo.pdf (11KB)
Comment Response Document CRD_Patuxent_Reservoirs.pdf (60KB)

Additional Supporting Information

Modeling Report (MR) Pax_Modeling_report.pdf (1905KB)
MR Appendix A Pax_Modeling_report_Appndix_A.pdf  (376KB)  
MR Appendix B Pax_Modeling_report_Appndix_B.pdf (2106KB)
MR Appendix C Pax_Modeling_report_Appndix_C.pdf (556KB)
MR Appendix D Pax_Modeling_report_Appndix_D.pdf (192KB)

Contact Information

Please direct questions or comments concerning this project to Maryland's TMDL Program at (410) 537-3818.