7404 TMDLs for Zinc in the Red Clay Creek
1.0 Introduction and Background
1.1 Water quality monitoring performed by the Delaware Department of Natural Resources and Environmental Control (DNREC) and others has shown that the Red Clay Creek, adjacent to and downstream of Yorklyn, Delaware, does not meet applicable water quality standards for zinc. Although zinc is an essential element for both aquatic life and humans, excessive concentrations can adversely affect aquatic life and human health. Zinc concentrations in the Red Clay Creek are not high enough to adversely affect people who drink water that is withdrawn from the Red Clay Creek. Zinc concentrations do, however, frequently exceed water quality criteria designed to protect fish and other aquatic life from the toxic affects of the metal.
1.2 A reduction in the amount of zinc reaching the Red Clay Creek is necessary to assure that applicable water quality standards are met and beneficial stream uses are protected. Zinc enters the Red Clay Creek from point sources and nonpoint sources. The National Vulcanized Fiber (NVF) Company located in Yorklyn, Delaware, is the only permitted point source discharge of zinc to the Red Clay Creek in Delaware. Nonpoint sources of zinc in the Red Clay Creek include background loading from the area of the Red Clay Creek watershed upstream of Yorklyn, seepage of contaminated groundwater from beneath the NVF facility to the Red Clay Creek, and diffusive flux from Creek sediments to the overlying water column.
1.3 Section 303(d) of the Federal Clean Water Act (CWA) requires States to develop a list (303(d) List) of waterbodies for which existing pollution controls are not sufficient to attain applicable water quality standards. Section 303(d) also requires each state to develop Total Maximum Daily Loads (TMDLs) for those waterbodies and pollutants placed on the state’s 303(d) List. A TMDL sets a limit on the amount of a substance that can enter a water body while still assuring that applicable water quality standards are met and beneficial stream uses are protected. A TMDL is composed of three components, including a Waste Load Allocation (WLA) for point source discharges, a Load Allocation (LA) for nonpoint sources, and a Margin of Safety (MOS) to account for uncertainties.
1.4 DNREC listed the Red Clay Creek on Delaware’s 1996 and 1998 303(d) Lists because applicable water quality standards for zinc were, and continue to be, frequently exceeded. Therefore, DNREC is proposing the following Total Maximum Daily Load (TMDL) regulation for zinc in the Red Clay Creek.
2.0 Total Maximum Daily Load (TMDL) Regulation for Zinc in the Red Clay Creek, Delaware
Article 1. The TMDL for zinc in the Red Clay Creek shall be 1.81 pounds per day, measured as total zinc.
Article 2. The combined mass loading of zinc to the Red Clay Creek from NVF’s permitted discharge 002 (i.e., WLA002), plus the mass loading of zinc to the Red Clay Creek from contaminated groundwater beneath the NVF property (i.e., LAg..w.) shall not exceed 1.2 pounds of zinc per day, measured as total zinc.
Article 3 The load allocation of zinc from the area upstream of Yorklyn (i.e., LAup) shall be capped at 0.6 pounds per day, measured as total zinc.
Article 4. The margin of safety (MOS) for the TMDL listed in Article 1 has been set at 0.01 pounds of zinc per day. This small margin of safety (less than 1% of the TMDL) reflects the robust data set and the conservative approach used to establish the TMDL, while still accounting for the uncertainty associated with possible diffusion of zinc from Red Clay Creek sediments.
Article 5. DNREC has determined with a reasonable degree of scientific certainty that water quality standards for zinc will be met in the Red Clay Creek once the mass loading requirements of Articles 1 through 3 are met.
Article 6. Implementation of this TMDL Regulation shall be achieved through the development of a Pollution Control Strategy. The Strategy will be developed by DNREC in concert with affected parties, the interested public, and the Department’s ongoing Whole Basin Management Program. The manner in which the 1.2 pounds per day that is noted in Article 2 above is allocated between discharge 002 and the contaminated groundwater discharge shall be one particular area of focus as part of the Pollution Control Strategy. The Pollution Control Strategy will also consider how monitoring will be conducted to verify compliance with the TMDL.
Please note: The DNREC regulations provided on this web site are not a complete list DNREC’s regulations. The State Registrar of Regulations, working in conjunction with DNREC, is working toward populating this site over time with all of DNREC’s regulations, however this effort will not be complete until sometime in 2008. In the meantime, please refer to DNREC’s website for a more complete listing of DNREC’s regulations. DNREC’s website can be reached through the following link http://www.dnrec.state.de.us/DNREC2000/Rules.asp
