Water Infrastructure

NPDES Phase 1 MS4 Stormwater Management Program Assistance

Location: Tacoma, Washington

The Port of Tacoma selected DEA to support and assist with the analysis, planning, and programs that the port will develop and enact to achieve long-term compliance with its permits and provide stormwater management services to port facilities. The programming developed in this scope of work will apply to the next permit cycle, from 2013 through 2018. There are two pathways that will merge in this program: 1) the regulatory requirements imposed by the NPDES permit program or related to stormwater control policy and 2) the port’s need to control stormwater discharges and construct, operate, and manage the physical drainage infrastructure. Completed tasks include the Stormwater Characterization and BMP Selection Process Technical Memorandum.

Stormwater runoff quality from a site can be highly variable. For this reason, the frequency at which concentrations occur or exceed target values is critical in understanding the level of treatment performance needed to address the risk of exceeding or the probability of attaining a target level or permit compliance. Percent-exceedence/attainment curves characterizing and displaying water quality data for different stormwater pollutants were prepared to characterize influent or effluent for a specific site, a group of similar sites, an activity type, the port, an industry, etc. They can also be used to characterize effluent from a BMP or family of similar BMPs that will inform performance expectations and characterize the potential frequency of effluent concentrations. Using this characterization approach, the port is anticipating long-term permit and program needs and preparing a roadmap for future stormwater management activities, infrastructure, operations, maintenance, and permit compliance.