INFORMATION SHEET
Proposed Total Maximum Daily Load (TMDL) for Neshaminy Creek and Tributaries to Neshaminy Creek, Bucks and Montgomery Counties, Pennsylvania
What is being proposed? A TMDL plan to improve the quality of water in Neshaminy Creek and its tributaries.
Who is proposing the plan? To whom and why? The Pennsylvania Department of Environmental Protection (Pa. DEP) is proposing to submit the plan to the U.S. Environmental Protection Agency (U.S. EPA) for review and approval as required by federal regulation.
In 1995, U.S. EPA was sued for not developing TMDLs when Pennsylvania failed to do so. Pa. DEP has entered into an agreement with U.S.EPA to develop TMDLs for certain specified waters over the next several years. This TMDL has been developed in compliance with the state/U.S. EPA agreement.
What is a TMDL? A Total Maximum Daily Load (TMDL) sets a ceiling on the pollutant loads that can enter a water body so the water body will meet water quality standards. The Clean Water Act requires states to list all waters that do not meet their water quality standards even after pollution controls required by law are in place. For these waters, the state must calculate how much of a substance can be put in the water without violating the standard and distribute that quantity to all the sources of the pollutant on that water body. A TMDL plan includes waste load allocations for point sources, load allocations for nonpoint sources, and a margin of safety.
The Clean Water Act requires states to submit their TMDLs to U.S. EPA for approval. If a state does not develop the TMDL, the Clean Water Act states that U.S. EPA must do so.
What is a water quality standard? The Clean Water Act sets a national minimum goal that all waters be “fishable” and “swimmable.” To support this goal, states must adopt water quality standards.
Water quality standards are state regulations that have two components. The first component is a use, such as “warm water fishes” or “recreation.” States assign a protected use, or several uses, to each of their waters. The second component relates to the instream conditions necessary to protect the use(s). These conditions or “criteria” are physical, chemical, or biological characteristics, such as temperature and minimum levels of dissolved oxygen, and maximum concentrations of toxic pollutants.
It is the combination of the “use” and the “criteria” that make up a water quality standard. If any criteria are being exceeded, then the use is not being met and the water is said to be in violation of water quality standards or impaired.
What is the purpose of the plan? Neshaminy Creek is impaired due to high concentrations of phosphorus in the water column and silt covering the creek beds. The TMDL includes a plan for decreasing the instream phosphorus concentrations and for reducing the sediment loads delivered to the streams, in order to meet Pennsylvania water quality standards.
Why did we choose Neshaminy Creek? In 1996, Pa. DEP included Neshaminy Creek, two unnamed tributaries to Neshaminy Creek, Little Neshaminy Creek, Park Creek, Cooks Run, West Branch Neshaminy Creek and an unnamed tributary to West Branch Neshaminy Creek on the federal Clean Water Act, Section 303(d) List of Impaired Waters for aquatic life impairments due to nutrients, suspended solids and siltation.
What pollutants does this TMDL address? The proposed plan provides calculations of the stream’s total capacity to accept phosphorus and sediments. Algae growth in the water bodies is fueled by excess nutrients in the water column. It has been determined that phosphorus is the nutrient limiting productivity in Neshaminy Creek and its tributaries. Therefore, the TMDL will address phosphorus to remedy the nutrient impairments. Additionally, sediment loads delivered by stormwater runoff and streambank erosion are impairing the streams in the Neshaminy Creek watershed and will be addressed in the TMDL.
Where do the pollutants come from? At extreme low flows, the streamflow in Neshaminy Creek and its tributaries is predominantly made up of discharge effluents. Therefore, the phosphorus pollution at the critical low flow period in the Neshaminy Creek watershed comes from the point source dischargers.
Sediments carried to the stream in overland flow in wet weather periods are, in part, responsible for the siltation impairment in these water bodies. Streambank erosion caused primarily by increased flow volume and altered timing is also a major contributor of sediment to these streams.
How was the TMDL developed? Pa. DEP used a reference watershed approach to estimate the loading reduction of sediment that would be needed to restore a healthy aquatic community. The reference watershed approach is based on selecting a non-impaired watershed that has similar land use characteristics and determining the current loading rates for the pollutants of interest. This is done by modeling the loads that enter the stream, using precipitation and land use characteristic data. For this analysis we used the AVGWLF model (the Environmental Resources Research Institute of the Pennsylvania State University’s Arcview based version of the Generalized Watershed Loading Function model developed by Cornell University). This modeling process uses loading rates in the non-impaired watershed as a target for loading reductions in the impaired watershed. The impaired watershed is modeled to determine the current loading rates and determine what reductions are necessary to meet the loading rates of the non-impaired watershed.
The reference stream approach was used to set allowable loading rates for sediment in the affected watersheds because neither Pennsylvanian nor U.S. EPA has numeric water quality criteria for sediment.
The Department used the STREAMPLAN-PA instream water quality model to determine the phosphorus reductions necessary to lower water column concentrations in Neshaminy Creek and its tributaries.
How much pollution is too much? The allowable amount of pollution in a water body varies depending on several conditions. TMDLs are set to meet water quality standards at the critical flow condition. For a free flowing stream impacted by nonpoint source pollution loading of sediment, the TMDL is expressed as an annual loading. This accounts for pollution contributions over all streamflow conditions.
The critical period for a free flowing stream affected by point source nutrients is the extreme low flow condition. For this TMDL, in-stream phosphorus concentrations were evaluated at Q7-10 flow (10 year low flow for seven consecutive days). Phosphorus concentrations and primary production are highest during this period, leading to nuisance algae growth and possible dissolved oxygen depletion in the water column.
What is the TMDL for Neshaminy Creek?
How will these limits be met? Best Management Practices (BMPs) will be installed throughout the watershed to achieve the necessary sediment loading reductions. NPDES permits will be revised in the next renewal and will be consistent with the requirements of the TMDL for total phosphorus.
How can I get more information on the TMDL? The TMDL can be accessed through the DEP Website (http://www.dep.state.pa.us) by typing “TMDL” in the direct link field, and clicking GO. Choose ‘Neshaminy Creek’ from the pull-down menu with the heading ‘Select By TMDL Name’. The data and all supporting information used to develop the proposed TMDL are available from the Department. To request a copy of the proposed TMDL contact;
The Division of Water Quality Assessment and Standards Pennsylvania Department of Environmental Protection P.O. Box 8457 Harrisburg, PA 17120-8457 Phone: 717-783-2938, email: [email protected]
A public meeting to discuss the TMDL will be held in the Library at the Jamison Elementary School, 2090 Land Road in Jamison, Bucks County, PA on November 3, 2003 at 6:30 pm. Directions to the school can be obtained by contacting Lynda Rebarchak at 610-832-6219.
Persons with a disability may use the AT&T Relay Service by calling 1-800-654-5984 (TDD users) and request that the call be relayed.
How can I comment on the proposal? You may provide written comments on the TMDL to the above address. Comments must be received no later than November 17, 2003. Comments will not be accepted by facsimile or voice mail. The Department will consider all comments in developing the final TMDL.