Charles County Watershed Implementation Plan

Maryland has published a Watershed Implementation Plan (WIP) that describes its strategy for meeting statewide targets for reducing discharge of nitrogen, phosphorus, and sediments to the Chesapeake Bay. These targets were established by the USEPA as part of the Chesapeake Bay TMDL.

The Maryland state agencies that developed the WIP in turn assigned targets to local entities, including Charles County, broken down by “source sector.” The Charles County Phase II Watershed Implementation Strategy (February 2013) presents scenarios and recommends two-year milestones for reducing loads from the source sectors for which the County is responsible:

  • Wastewater
  • Urban stormwater
  • Septic systems
  • Forest

(The County is not responsible for loads from the Towns of Indian Head and La Plata, both of which are separate municipalities with jurisdiction over their own land area.) The strategy discusses integration of the Bay TMDL requirements with those of other county programs and requirements, including the Municipal Separate Storm Sewer System (MS4) Discharge Permit.

While the County has been assigned target loads as part of the Bay TMDL, these target loads are not directly enforceable. The only enforceable aspects of the TMDL are requirements incorporated into NPDES permits, such as a permit issued to a wastewater treatment plant or the County’s MS4 permit.

Maryland, along with other states in the Chesapeake Bay Watershed, is currently developing its Phase III WIP. These plans will build on the success of the Phase II process and develop methods and strategies for achieving the pollution reduction required by the Bay TMDL by 2025.


The County’s responsibility for total nitrogen and total phosphorus loads from this source sector includes the Mattawoman and Swan Point major municipal wastewater treatment plants (WWTPs) as well as minor municipal WWTPs. The County does not have to reduce loads in this sector to meet targets — in fact, the loads are allowed to increase over time.

Maryland’s Phase II WIP strategy includes a higher target for wastewater than what is currently being discharged by the WWTPs in the County. This is because the Mattawoman WWTP, the County’s largest, is operating below its maximum flow capacity (it operated at 57 percent of its maximum capacity as of 2012), and because water re-use and water conservation projects reduce the overall volume of wastewater going to the County’s WWTPs. The County expects the Mattawoman WWTP to have excess loading capacity through 2025, which could be used to offset the need to reduce loads in other sectors.

Urban Stormwater

The County’s responsibility for total nitrogen and total phosphorus loads from this source sector includes stormwater loads from the County’s Phase I MS4 area and from non-regulated loads from areas not served by stormwater systems owned and operated by an MS4 jurisdiction. To meet the its targets for this sector, the County will have to reduce total nitrogen loads by 20.3 percent and total phosphorous loads by 38.2 percent. There is no sediment target for this sector.

Stormwater loads generated from active construction sites are expected to be controlled according to current Stormwater Management Ordinance and are not addressed in the WIP.

The County has identified potential restoration activities and best management practices (BMP) retrofits for reducing nutrient loads, taking into account cost effectiveness, implementability, ease of maintenance, life expectancy, and public acceptance.

  • Urban nutrient management. Runoff of fertilizer from turf in urban areas is thought to play an importnat role in causing nutrient pollution to the Chesapeake Bay. Urban nutrient management practices include restructing the types of nutrients allowed in fertilizer, regulating the timing of nutrient application, requiring certification of lawn care professionals, and establishing best practices for application of fertilizer.
  • Stream restoration. Stream restoration is an increasingly common approach in the Chesapeake Bay watershed and elsewhere to restore stream systems that have been degraded by urban development. Stream restoration techniques include a number of different approaches that attempt to re-establish the dynamic equilibrium between a stream and its watershed. These techniques include physical grading to re-establish a stable channel pattern and reconnect the stream with the floodplain, introducing habitat features such as step-pools and woody debris, and estabishing or enhancing riparian vegetation.
  • Pond retrofits. Many ponds designed for water quantity management are not efficient at removing pollutants. These ponds can be retrofitted to meet criteria adopted in 2002 to slow and filter drainage area runoff.
  • Environmental Site Design (ESD) retrofits. ESD retrofits are small-scale treatment practices installed to address impacts associated with development, such as permeable pavement, bioretention, green roofs, vegetated swales, or other landscape infiltration to capture and treat runoff from impervious surfaces.
  • Shoreline stabilization.  Shoreline stabilization and erosion control practices protect shoreline from excessive wave action by creating a marsh or an offshore structure such as a sill, breakwater, or sand containment structure.
  • Buffer restoration. Intact natural vegetated stream buffers provide important terrestrial habitat and shading and also serve to dampen runoff velocities and filter runoff pollutants before they enter a stream. These functions are lost or significantly diminished when stream buffers are removed or compromised by land management decisions. This strategy considers restoring deficient stream buffers via reforestation.

Septic Systems

To meet its total nitrogen load reduction target, the County will have to reduce nitrogen loads by 32 percent. Because septic systems do not remove phosphorus or sediment, no targets for these constituents are assigned to this sector.

Three different BMPs can be implemented to reduce load from septic systems:

  • Septic system pump-out. Regular pumping of septics not only reduces nitrogen discharge, but also increases the life of the septic system. It is one of the least expensive ways to to achieve nitrogen reductions in the septic sector. The County has developed a septic pump-out reimbursement program to encourage County residents to pump out their septic systems every 3 to 5 years.
  • Septic system upgrade to best available technology (BAT). Grants are available through the Bay Restoration Fund for State-approved BAT nitrogen removal upgrades to existing residential septic systems. Priority is given to failing septic systems in the Critical Area (land within 1,000 feet of the mean high water line of tidal waters or the landward edge of tidal wetlands).
  • Septic system connection to a WWTP. Connecting a septic system to a WWTP can reduce its nitrogen load by 90 percent or more. The County is considering several scenarios for reducing its load from the septic sector, such as connecting all the septic systems in the Development District to or a Priority Funding Area to a WWTP. Another option is to focus on septic systems in the County that are in the Critical Area, as these systems contribute the highest loads.


The Phase II WIP assigned forests their current loading, and no reduction is required from this sector. Forests have the lowest loading rates of any land use type in the Chesapeake Bay watershed, and local governments can actually reduce loads from other sectors by converting different land use types to forest.

Relationship to NPDES MS4 Permit

There are a number of overlaps between the requirements in the County’s MS4 permit and the load reductions needed to meet targets for the Bay TMDL. For more information, go to the Charles County MS4 Permit web page.