The Maryland 8-digit (MD 8-digit) Antietam Creek watershed (basin number 02140502) is located in the Potomac River basin within Washington County, Maryland. Antietam Creek is a free flowing stream that originates in Pennsylvania and empties into the Potomac River in Maryland. It is approximately 54 miles in length, with 37 miles in Maryland and 17 miles in Pennsylvania. The total watershed area covers 290 square miles, with approximately 185 square miles in Maryland and 106 square miles in Pennsylvania. Approximately 5% of the total watershed is covered by water (i.e. streams, ponds, etc.). The total population in the MD 8-digit Antietam Creek watershed is estimated to be approximately 82,000.
The Maryland Department of the Environment (MDE) has identified the waters of the MD 8-digit Antietam Creek watershed on the State’s 303(d) List as impaired by sediments (1996), nutrients (1996, 1998 – the Greenbrier Lake impoundment), dissolved oxygen (1996), bacteria (2002), and impacts to biological communities (2002). The designated use of the MD 8-digit Antietam Creek and its tributaries is Use IV-P (Recreational Trout Waters and Public Water Supply) except for Beaver Creek, Marsh Run, and Little Antietam Creek, which are classified as Use III-P (Nontidal Cold Water and Public Water Supply). The objective of the Total Maximum Daily Load (TMDL) established in the document below is to ensure that there will be no sediment impacts affecting aquatic health, thereby establishing a sediment load that supports Use III-P/IV-P designations for the MD 8-digit Antietam Creek watershed.
A TMDL for Carbonaceous Biochemical Oxygen Demand (CBOD) and Nitrogenous Biochemical Oxygen Demand (NBOD) to address the 1996 dissolved oxygen listing was approved by the U.S. Environmental Protection Agency (EPA) in 2002. A Water Quality Analysis (WQA) of Eutrophication to address the 1998 nutrients listing for the Greenbrier Lake impoundment was approved by the EPA in 2005, and a TMDL was submitted to the EPA in 2008 to address the 2002 bacteria listing. The listings for nutrients and impacts to biological communities will be addressed separately at a future date.
Note: Following the approval of the TMDL, it was discovered that the incorrect design flow was applied in the calculation of the Process Water Baseline Load for the Funkstown Wastewater Treatment Plant (WWTP). When the correct design flow of 0.2 million gallons per day (MGD) is used in the analysis, the individual Process Water Baseline Load for the facility increased by 2.2 ton/yr, and as a result, the total Process Water Baseline Load for the watershed also increased by 2.2 ton/year. Since the assimilative capacity of the watershed is fixed, and no reductions were applied to process water sources in the analysis, the individual Process Water wasteload allocation (WLA) for the facility and the total Process Water WLA for the watershed also increased by 2.2 ton/yr. Due to this increase, additional reductions, although minimal, were required from both the non-point source sector and regulated urban stormwater sector within the Maryland portion of the watershed.
In addition, an error in the original calculations was discovered during this process regarding the upstream load allocation (LA) assigned to Pennsylvania. When corrected, the upstream LA assigned to Pennsylvania increased by 6.7 ton/yr, and when added to the increase in the Process Water WLA, totals an 8.9 ton/yr increase. This increase is offset by the total 8.9 ton/yr decrease in the Maryland watershed area LA and NPDES Regulated Stormwater WLA to maintain the assimilative capacity of the watershed. The revised final version of the document containing these updated allocations is available for download below.
(Approved on December 18, 2008)
Additional Supporting Information
Please direct questions or comments concerning this project to Maryland's TMDL Program at (410) 537-3818.
1800 Washington Boulevard, Baltimore, MD 21230