DEVELOPMENT OF A MODEL SEDIMENT TMDL PROTOCOL TO EXPLICITLY CONSIDER CONSTRUCTION SOURCES

Construction stormwater sources have traditionally been considered as part of the load allocation portion (LA) of the Total Maximum Daily Load (TMDL), and have not been targeted for pollutant loading reductions in most TMDLs. Recent EPA policy requires all National Pollutant Discharge Elimination System (NPDES)-regulated stormwater discharges to be addressed by the wasteload allocation (WLA) component of the TMDL. This new emphasis on including stormwater sources in WLAs will result in a greater regulatory focus on construction activity in watersheds on the 303(d) list. In response to this situation, the National Association of Home Builders (NAHB) developed a model sediment TMDL protocol to serve as a resource for NAHB and its members to demonstrate to the states and to EPA how sediment in stormwater runoff from construction and land development activities can be reasonably regulated within the context of the TMDL program. The specific intent of the model sediment TMDL protocol is to establish a scientifically-defensible and practical approach to setting sediment WLAs for these activities where warranted by the waterbody impairment.The project included the compilation and review of 71 sediment TMDLs. These TMDLs were reviewed with respect to determination of impairment; selection of TMDL targets; identification of existing sources; calculation of assimilative capacity; allocation between WLA/LA; and consideration of stormwater sources. In addition, a literature search was conducted to find and evaluate alternative and/or innovative approaches for developing sediment TMDLs, beyond those methods identified in the review of existing TMDLs. A total of ten additional documents were obtained and reviewed.Based upon the documents reviewed, a model sediment TMDL protocol was developed. The model sediment TMDL protocol is designed to meet all regulatory requirements and be scientifically defensible. The protocol is divided into separate sections and provides preferred methodologies for the individual steps of the TMDL development processproblem identification, setting a TMDL strategy, defining TMDL targets, source assessment, determining assimilative capacity, and defining allocations.This project demonstrates the work of a stakeholder group to help shape an emerging aspect of the national TMDL program into a form that is scientifically valid and allows the construction industry to continue doing business while complying with all regulatory requirements.