PAH Source Investigation – San Diego, Closing the Knowledge Gap
Polycyclic aromatic hydrocarbons (PAHs) are an ongoing source of pollution in the environment. PAHs are released from petroleum products or the incomplete combustion of organic matter from both anthropogenic and natural sources. PAHs are semi-volatile organic compounds (SVOCs) consisting of fused aromatic (i.e., benzene-type) rings. PAHs are found in soil, sediment, ground water, surface water, air, and plant, animal, and human tissue as a result of past and present releases. The EPA has classified PAHs as “persistent, bioaccumulative, and toxic” (USEPA, 2012a; USEPA 2012c). Even in low doses, these pollutants are problematic as they are persistent and difficult to remediate. PAHs move between the atmosphere and land surfaces through volatilization and deposition processes. PAHs can become more stable when accumulated on airborne particulate matter or absorbed onto aquatic sediments (Irwin, 1997).
PAHs are continuously transported from the atmosphere into the watershed via wet and dry deposition, which presents a challenge for environmental managers because the sources of PAHs may be outside of their jurisdiction or from local sources. Atmospheric deposition accounts for a significant portion of PAH loading to waterbodies relative to other contaminants such as nutrients, trace metals, and semi-volatile organic contaminants which are typically dominated by sources on the watershed surface (Sabin et al., 2004).
PAHs are on the USEPA 303(d) list for causing toxicity in the San Diego Bay within the Downtown Anchorage, B Street/Broadway Piers, Chollas Creek, Switzer Creek and Paleta Creek watersheds. Currently, total maximum daily loads (TMDLs) are being developed to limit the amount of PAHs that can enter these waters while still meeting Water Quality Standards per the US EPA Clean Water Act. The TMDL is on hold since it was determined PAHs are ubiquitous and are poorly understood. Data gaps exists regarding the sources and contributions from each source, so it is not possible at this time to assign responsibility to any parties through a TMDL. One primary data gap is data characterizing the atmospheric contribution.
To better understand the contribution of aerially-deposited PAHs to local watersheds, this project was initiated by the City of San Diego Transportation and Stormwater Department as a special study prior to development and implementation of the applicable TMDLs. The State Water Resources Control Board has sponsored this project to collect data needed to better understand the sources of PAHs, relative contributions, and transport pathways as necessary for developing effective and defensible TMDLs.
To address the data gap, a monitoring program with wet and dry components was completed in January 2017. Data are being evaluated and the project report will be provided this summer. The project looks to provide a better understanding of the contribution of aerially-deposited PAHs to the project watersheds and bridge the gap between atmospheric sources and watershed sources. Findings will be summarized in the presentation.
Melissa is a Water Resources Control Engineer at the San Diego Regional Water Quality Control Board. Her current projects focus on total maximum daily load implementation and amendments to the Water Quality Control Plan for the San Diego Basin. She has 15 years of experience in the field of environmental protection, working in the private and public sectors and as part-time faculty for San Diego State University’s Department of Civil, Construction, and Environmental Engineering. Her areas of specialized experience include wastewater treatment, site remediation, human health risk assessment, and fate and transport analysis.
Vicki Kalkirtz is a Senior Planner in the City of San Diego’s Transportation & Storm Water Department, Policy & Enforcement section. She has been working on storm water policy issues for 7 years, five with the City. Vicki holds a Bachelor of Science in Environment and Natural Resources from the University of Minnesota, a Master of Urban Planning in Land Use and Environmental Planning and a Master of Science in Natural Resources with a focus on Environmental Justice from the University of Michigan.
Brenda Stevens is a Senior Scientist in the Water Resources Department at Amec Foster Wheeler. She has seven years of experience in environmental consulting, with focuses on watershed characterization studies, NPDES regulatory support, dry and wet weather water quality monitoring, WQIP development and implementation, and BMP effectiveness evaluations. She studied Earth Sciences at UC San Diego where she continues to volunteer with the Ultimate Frisbee team.