The Portland Harbor Superfund Record of Decision (ROD) calls for dredging and capping contaminated sediment in portions of the lower Willamette River.
Many current and historic industrial sites adjacent to the Portland Harbor Superfund may pose a sediment recontamination risk if sources of pollutants are present and not adequately controlled. A mixed-use facility covering nearly 300 acres has been in operation since the early 20th century (Site). Source investigations at the Site have identified Polycyclic Aromatic Hydrocarbons (PAHs) in stormwater discharges as a potential concern for recontamination. Consequently, stormwater source controls are being aggressively implemented. Source control effectiveness has primarily focused on comparing discharge concentrations to screening level values (SLVs) developed by the Oregon Department of Environmental Quality (ODEQ) for the Portland Harbor, which are less than 0.02 µg/L for many PAH constituents of concern. Selecting effective source controls to achieve such low concentrations is challenging because Site PAHs are frequently associated with very fine sediment (< 5 µm) and limited performance data are available for potential stormwater treatment technologies that address PAHs.
Approach/Activities. In 2016, Site PAHs in stormwater discharges were characterized to provide critical information related to the potential fate and treatability of these persistent pollutants. The study design included the simultaneous collection of multi-event, flow-weighted composite water quality and stormwater solids samples. Water quality samples were analyzed for TSS and PAHs before and after laboratory filtration at three different filter sizes: 20, 5, and 0.45 micron. Stormwater solids samples were analyzed for grain size distribution and PAH solids concentrations within different grain size ranges. In 2018, a follow-up source control treatability pilot study was initiated to evaluate the effectiveness of potential passive filtration technologies that were anticipated to have relatively good performance and be implementable at the site. The testing system consisted of a stormwater diversion pump, a cartridge filter pretreatment tank, and a flow splitting manifold that distributed gravity flow to two proprietary treatment units and three engineered media columns. The treatability test was conducted onsite for 3 months during the 2017-2018 wet-season. Performance monitoring included device hydraulics, media clogging assessments, and long-term composite water quality sampling.
Results/Lessons Learned. The 2016 study showed that PAHs concentrations and particle sizes were distinct between the two adjacent basins. Most importantly high PAH concentrations and strong association with very fine sediment in one of the basins suggest that effective PAH treatment with the potential to meet the SLVs would require removal of most particulates larger than 0.45-micron in diameter. Results from the 2018 treatability study indicated a wide range in treatment effectiveness between the different treatment alternatives tested, with the most effective PAH removal resulting from the three engineered media columns and one of the proprietary filtration units. However, consistently achieving the SLVs is likely not possible without adding additional treatment processes or significantly increasing media contact times. System hydraulic data suggest that some of the treatment alternatives could require either advanced sediment pretreatment or excessive O&M to maintain flow rates. This presentation will describe the 2016 and 2018 monitoring study designs, equipment configurations, results, and implications related to treatability, O&M, and reductions in recontamination risks to the Portland Harbor. Potential application of the stormwater characterization and media filtration monitoring designs for other facilities and constituents will also be discussed.