Evaluating Urban and Naval Base Stormwater Impacts on Coastal Sediment Recontamination in San Diego Bay
Cleanup at contaminated sediment sites has often been initiated before land-based sources have been fully identified, quantified, or controlled. Under such conditions, sediment remediated sites have become recontaminated by continued inputs from off-site sources, including stormwater discharges, other permitted discharges, or transport of sediment from upstream areas. High levels of solids-associated contaminants of concern (COCs), particularly metals and hydrophobic organic compounds (HOCs), including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), are often present in urban and industrial stormwaters.
In 2013, a research team from Texas Tech University, the University of Michigan, the United States Navy Space and Naval Warfare Systems Command (SPAWAR), and Geosyntec Consultants were awarded grant funding through the Strategic Environmental Research and Development Program (SERDP) to study the role of urban stormwater in the potential recontamination of sediments and previously remediated sites. The role of Geosyntec Consultants and Dr. Robert Pitt from the University of Alabama is to provide stormwater technical services, including the characterization of stormwater pollutant loads and mass fractionation of settleable pollutants via data review, monitoring, and modeling. Stormwater loading of solids-associated COCs (i.e., recontamination) is particularly difficult to quantitatively evaluate due to the little-studied association between COCs and suspended sediment particle sizes (which govern their settling distance properties). Costs to control stormwater sources of COCs can also be very significant (particularly if the land-based sources are ubiquitous) relative to the anticipated recontamination risk reduction benefit.
The primary study objectives are as follows:
1) To develop a comprehensive dataset of new and existing stormwater monitoring data;
2) To characterize the role of urban stormwater in the potential contamination of sediments and remediated sites; and
3) To evaluate the magnitude and characteristics of episodic distributed source inputs.
A Source Loading and Management Model (WinSLAMM) is being calibrated to assess these objectives.
Existing data were incorporated into the model to the extent feasible, and new data were collected at Naval Base San Diego (NBSD), within the Paleta Creek Watershed. Monitoring locations at NBSD were selected on the basis of relevance to the Department of Defense, potential influence of ongoing event-driven background sources, and accessibility. The six selected locations, including two receiving water and four outfalls, represent a range of land use and discharge conditions.
Composite stormwater receiving water and runoff samples were collected using ISCO 6712 auto-samplers, which were triggered at each monitoring location by site-specific criteria, including real-time salinity (for tidally influenced locations), depth, flow, and/or rainfall. Composite samples were split by research partners at SPAWAR San Diego using a Dekaport splitter. Some splits were analyzed without being filtered, while the rest were filtered into operationally defined “dissolved” to “coarse sand” fractions to quantify pollutant concentrations associated with ranges of suspended sediment particle sizes. All sample analyses were performed by TTU.
This presentation will cover stormwater monitoring logistics using real-time controlled auto-samplers in an urban environment, analytical results including COC distribution by particle size category (which informs COC and suspended sediment transport distances), watershed model calibration and results, and the development of a decision making framework to better predict likelihood of bed sediment recontamination from continued stormwater discharges. Audience participation will be encouraged through multiple choice questions throughout the presentation, with answers indicated by a raise of hands.