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Planning / Comprehensive Master Plan / Water Resources Element / Stormwater RunOff / Non-Point Pollution Prevention

The 2009 Sustainability Plan also identifies pollution prevention as a major goal for a more sustainable Baltimore. The air we breathe, the water we use, and the environments which surround us directly affect Baltimore’s health and quality of life. Historically, we have made decisions without consideration for where the materials or inputs we use come from or what will become of the outputs, for instance in the form of pollution. To be sustainable, we need to change our way of thinking and begin to view all “waste” in new ways through reducing, reusing and recycling.

Pollution Prevention Goal #3: Ensure that Baltimore water bodies are fishable and swimmable

In accordance with the federal Clean Water Act, Baltimore is striving to restore our water quality to fishable and swimmable levels by 2020, a very aggressive goal given the challenges we are facing. Baltimore has thousands of stormwater outfall pipes that drain our streets and private land. Many contain sewer leakage and other pollutants and chemicals. Trash also washes from streets into these stormwater pipes, ultimately reaching Baltimore streams and our harbor. Baltimore Harbor is the ‘bottom of the bowl,’ where most regional stream systems empty into. To reach our goal, we must employ a variety of creative strategies that include the watershed land in both Baltimore City and surrounding jurisdictions.

Strategy A: Implement recommendations in the City County Watershed Agreement
The Watershed Agreement emphasizes the importance of interjurisdictional cooperation and identifies 11 distinct strategy areas with specific recommendations for water quality improvements.

Strategy B: Study creation of a stormwater utility or other new funding sources
A stormwater utility would function similiarly to Baltimore’s existing water and wastewater utilities and would fund maintenance and improvements to Baltimore’s water quality system. The utility would assess a fee related to stormwater pollution and use those fees to support new water quality improvements and to maintain existing structures and systems. A draft technical report was commissioned and written by a private consultant. It provides a partial discussion on the analysis and development of rate and revenue projections.

Strategy C: Reduce amount of impervious surfaces and increase on-site stormwater treatment Ensure that the Maryland Department of the Environment’s stormwater permit requirements are met by requiring the reduction or treatment of at least 50% of redevelopment sites’ existing impervious area. Identify and implement targeted technologies to reduce existing impervious surfaces. Impervious surfaces increase the volume of rain water and pollutants that enter stream systems during storms, causing stream bank erosion and sediment and pollutant discharge into the harbor and bay. Examples of ways to treat stormwater on-site include green medians in streets, green roofs, and ‘green’ alleys made of porous asphalt that allows rainwater to seep through, thus not adding to stormwater volume that flows off-site.

Strategy D: Protect and restore Baltimore’s stream corridors
Restore and stabilize Baltimore’s streams to prevent erosion and restore habitat. Baltimore’s streams have been severely eroded and degraded by changes in drainage patterns caused by development in the surrounding watersheds. Stream restoration projects manage stormwater flow and restore stream channels by widening and greening them, adding rock weirs, or changing their configuration. These changes allow for replanting of vegetation and creation of ‘pooling’ areas for fish and other wildlife.

Strategy E: Create watershed-based natural resource management plans
Create and implement watershed specific plans to more effectively organize environmental and planning efforts for system-wide improvements. Study and document existing conditions and opportunities for environmental improvements within Baltimore watersheds to identify more environmentally-sensitive development plans that concentrate restoration efforts in areas that will provide the most benefit.

Strategy F: Increase actions by individual property owners to treat stormwater
Educate residents and businesses about small-scale storm water management. The majority of land in Baltimore that is part of our stormwater drainage patterns is privately owned, yet only a very small percentage of this land is improved for stormwater treatment. Small scale improvements such as rain barrels, rain gardens, tree planting, downspout disconnections, and trash management would help improve water quality significantly.

Water Resources Planning Assessment

Nutrient loadings

Impervious cover is one of the key determinants for estimating nutrient loadings from urban areas and is the basis for prescribing restoration measures under the National Pollutant Discharge Elimination System Permit (NPDES) for stormwater. Under the City’s permit the Department of Public Works determined the City’s impervious cover to be 23,373 acres which is 45.1 percent of the total 51,790 acreage of the City. A copy of the methodology is attached. Over the past two permit cycles, the City has been required to provide some degree of restoration or “treatment” for 20 percent of the impervious cover or 4674.6 acres. The City will be issued a new 5-year NPDES permit in January 2010 that will include a requirement to restore an additional 20 percent of the impervious area for a total of 9349.2 acres.

The Center for Watershed Protection’s Short-cut Method is one of the most widely accepted methods in the country for estimating contaminant loading rates from urban areas. This method has been incorporated into spreadsheet format and is referred to as the watershed treatment model. The computations and loading estimates for total nitrogen and phosphorus for the entire city are also provided in the attached file and summarized below.

The total nutrient loadings for the City are:

  • TN Load = 640,335 pounds per year
  • TP Load = 55,520.5 pounds per year

Nutrient reductions via retrofitting:

While there are no guidelines for the definition of restoration or “treatment”, the City assumes this to mean the equivalent nutrient load reduction that would occur if 100 percent of the runoff from the impervious area drain to state-of-the-art best management practices.

Based on estimates of BMP efficiencies from several documents including the Maryland Stormwater Design Manual and Center for Watershed Protection, we assume that typical nutrient reduction efficiencies for urban BMP’s are 30 percent for total nitrogen (TN) and 40 percent for total phosphorus (TP).

The projected load reduction as a result of projects implemented under the NPDES permit through 2009 is 31,245 pounds per year for total nitrogen and 3,666 pounds per year for total phosphorus which equates to 4.9 percent and 6.5 percent of the total nitrogen and phosphorus loadings. Several projects are under design and the City has committed to meet the full 20 percent under the existing NPDES permit in addition to another 20 percent reduction over the next five year permit cycle for a total load reduction by 2015 of:

  • Total TN reduction = 76,840 # per year (12 percent of total)
  • Total TP reduction = 9016 # per year (16 percent of total)

Note as of this point in time, the nutrient TMDL reductions projected for NPS’s for the City and County are 15 percent. This will undoubtedly increase when the load allocations for the Chesapeake Bay nutrient TMDL are developed. While the next NPDES (2010) Permit for stormwater will most likely require a schedule for meeting the load allocations, it is unlikely that the City and County will meet the targeted reductions by 2015.

Nutrient reductions via redevelopment:

Unfortunately, the City’s Stormwater Management Program did not keep track of the amount of development that occurred during the 10 year permit period corresponding to when the restoration began under the NPDES Program. The existing stormwater management requirement is that redevelopment sites have to reduce runoff or provide treatment for 20 percent of the site’s impervious area. This requirement was initiated in October, 2000 and was recently modified under the Stormwater Management act of 2007. The new regulations increase the amount of impervious area that has to be treated to 50 percent and will go into effect in May 2010 when local ordinances are required to be adopted.

Therefore, for the sake of this assessment it is safe to say that any projected growth over the 6 year comprehensive planning period (or next 5 year permit cycle) will have to control 50 percent of the existing impervious cover. We also assume that BMP efficiencies will remain at 30 percent for TN and 40 percent for TP however the new regulations specify that environmental site design be used to meet the requirements which could substantially increase these efficiencies.

The 6 year comprehensive plan makes the following assumptions regarding additional growth.

  • approximately 10,000 additional households are planned
  • an average lot size would be 0.025 acres
  • the average impervious cover is 45 percen
  • the additional 10,000 households would equate to approximately 112.5 acres of impervious cover
  • since these are redevelopment projects no additional nutrient loadings are anticipated

Using the CWP’s short cut method described above, 112.5 acres of impervious cover generates the following loadings from the expected redevelopment over the planning period:

  • TN= 3068 #/yr
  • TP= 271.3 #/yr.

Given the new stormwater requirement of treating 50 percent of this amount and assuming the reduction efficiencies of state-of- the- art practices to be approximately 30 percent for TN and 40 percent for TP.

  • TN load reductions from redevelopment = 920.4 #/yr
  • TP load reductions from redevelopment = 108.5 #/yr

Therefore the combined 6 year projected load reductions from the NPDES Permit and Stormwater Management regulations are:

  • TN= 77,760 #/yr
  • TP= 9,287 #/yr

In addition, Baltimore City is spending considerable resources to monitor nutrient loading from our 3 stream systems. In subsequent analyses, we will attempt to apply the watershed treatment model to the watersheds draining these streams. We will then compare the modeling results to the monitoring data to determine the accuracy of the model.

Also, we have a monitoring program to determine the effectiveness of urban BMP's. In the future, rather than using gross assumptions on BMP's efficiencies, we hope to provide more accurate estimates for stream restoration



Department of Planning
Thomas J. Stosur, Director
417 E. Fayette Street
8th Floor
Baltimore, MD 21202
(410) 396-7526 (PLAN)
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