Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015" ELECTROCOAGULATION (EC) AND CHITOSAN ENHANCED SAND FILTRATION (CESF) TREATMENT TECHNOLOGIES FOR DREDGE RETURN WATER: TWO CASE STUDIES ON THE LOWER DUWAMISH WATERWAY IN SEATTLE, WASHINGTON L.M. Doty1 ABSTRACT Thirteen years ago, the Lower Duwamish Waterway in Seattle, Washington was designated as a superfund site due to contamination with heavy metals, PCBs/cPAHs, and dioxins/furans, the result of heavy industrial use in the area over the last century. Comprehensive clean-up is still a few years out, however the Environmental Protection Agency (EPA) designated 29 acres of “hot spots” that posed enough threat to human and environmental health to warrant Early Action. Two specific Early Action Areas (EAA) conducted environmental dredging activities from 2013 to 2014. Due to contamination levels, specifically heavy metals and PCBs, traditional methods of on-barge dewatering were not allowed. Site 1 had limited upland real estate and implemented an Electrocoagulation (EC) treatment train. Geotubes with polymers, an established dewatering technique, was considered for Site 1, however potential toxicity of the polymers and lack of sufficient real estate made this option unfeasible. Site 2 had no upland real estate and deployed a barge mounted Chitosan Enhanced Sand Filtration (CESF) system. Both the EC and CESF treatment technologies carry a General Use Level Designation (GULD) granted by the Washington State Department of Ecology for turbidity removal on construction sites. The GULD status of these technologies helped streamline the permitting approval process. Site 1 operated for 48 days without any water violations, discharging 6,300,000 gallons of treated water back to the Duwamish River. Site 2 operated for 45 days without any water quality violations, discharging over 5,000,000 gallons of treated water back to the Duwamish River. The laydown areas required were approximately 5000sf and required no ground disturbance, as all treatment train components were mobile. For Site 1, this equates to a nine- fold reduction is land use compared to the Geotube approach. No land was available for Site 2, so temporary equipment on flexi-floats was the only alternative. As presented and discussed in the Site 1 and Site 2 case studies, EC and CESF provide reduced footprint options for treating contaminated return water for direct discharge to surface waters. Both technologies produced effluent with water quality levels well below discharge limits. In addition both technologies have GULD approvals and are considered non-toxic which eliminates the need for ongoing toxicity screening and streamlines the approval process. Keywords: dredge return water, contamination, remediation, superfund, water treatment, chitosan enhanced sand filtration, electro-coagulation, CESF, EC, PCBs 1 CPSWQ/CPESC, Regulatory & National Construction Manager, Water Tectonics, Inc, 6900 Merrill Creek Parkway, Suite C, Everett, Washington 98203, USA, T: 425-349-4200, Fax: 425-349-4890, Email: [email protected]. 176 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015" INTRODUCTION The Lower Duwamish Waterway (LDW) Superfund Site is the last five mile stretch of the Duwamish River before it empties into Elliot Bay at Harbor Island in Seattle, Washington. Both sides of the LDW are heavily industrialized/commercial areas interspersed with the Georgetown and South Park neighborhoods of south Seattle. Heavy industrial and maritime use over the last 100 years have left area soils, groundwater and river sediments contaminated with polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), dioxins/furans, arsenic and other heavy metals. In addition to commercial use, the Duwamish/Green river system is a traditional fishing ground for the Suquamish and Muckleshoot tribes and is also home to numerous fish hatcheries that release approximately 10 million juvenile salmon per year1. In 2001 the Environmental Protection Agency (EPA) placed the LDW on the Nation Priority List to protect and restore benthic organisms, resident fish populations and protect those who rely on these species as a food source. Following EPA’s listing, the Washington State Department of Ecology (WADOE) added the LDW to the Washington Hazardous Sites List in 2002. Due to the size and complexity of the LDW, the final Record of Decision (ROD) for clean-up of the entire site was only recently finalized (November 2014). The ROD details the clean-up of approximately 177 acres and will involve dredging, capping and natural sedimentation with an estimated cost of $342 million2. Prior to the issuance of the ROD, EPA identified six specific areas within the LDW site that posed immediate threats to the environment and human health. These are called Early Action Areas (EAAs). These EAAs had “hot spots” of contamination that in some cases were orders of magnitude higher than the surrounding LDW. Starting in 2011 EPA and WADOE entered into agreements with the owners and/or responsible parties to perform remedial actions. This paper discusses the remedial actions taken at the Boeing Plant 2 and Jorgensen EEAs, specifically dredge water return treatment during dredging activities. Locations are shown in Figure 1. Lower Duwamish Waterway superfund site and EEAs.Figure 1 below. 177 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015" Figure 1. Lower Duwamish Waterway superfund site and EEAs. 178 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015" DREDGE RETURN WATER TREATMENT Dredge return water management is highly variable from site to site and is largely dependent on the type of dredge project. Maintenance dredging will be less treatment intensive than a remediation project. Simple dewatering through the scuppers may be allowed on a maintenance project where extensive treatment with Geotubes® and coagulants may be required on environmental remediation projects. In some cases the water returned is not allowed to be discharged to the receiving water and must be discharged to the sanitary sewer. The pros and cons of these traditional methods are presented below in Table 1. Table 1. Pros and cons of traditional dewatering processes. Method Pros Cons Sufficient treatment for Environmental/Remediation? Scuppers Easy, no additional cost Provides no treatment or No as barges come equipped only minimal treatment when filter fabric place over scuppers (large diameter soil particles). Geotube® Solids dewatering and Dewatering fluids may YES provided dewatering water treatment in a need further treatment fluids are properly treated. single step. If dewatered before discharge to material is clean, filled surface waters or sanitary bags can be used for sewer. Inconsistent bank stabilization or effluent water quality. other landscape feature. Large staging area High flow rate capacity. required for laydown and dewatering capture. Tubes are difficult to move once full. Sanitary Sewer For non-contaminated Not all jurisdictions YES provided dewatering sites minimal treatment is allow discharge. fluids are properly treated. typically required. Discharge may be subject to a per gallon fee. Some treatment likely required. Flow rates limited. As remediation projects become more complex and space limited alternatives to traditional methods will be needed. Some alternatives can be borrowed from the upland construction industry where, particularly in Washington State, Active Treatment has been common for over a decade. Active Treatment Technologies Active Treatment involves pumping water, adding coagulants and filters to remove sediment and dissolved contaminants from a waste stream. In Washington State active treatment technologies have been extensively refined to treat turbid and pH impacted stormwater and groundwater in the construction industry. The practice became so prevalent that WADOE created a targeted assessment protocol, Chemical Technology Assessment Protocol – Ecology or CTAPE. The CTAPE process uses engineering evaluation as well as water quality performance and toxicity data to develop a General Use Level Designation (GULD) for a proposed technology. These approvals dictate how a coagulant or technology may be applied, what filtration must be used and how the system will be operated. The two GULD approved technologies used on the LDW EEA case studies are discussed in detail below. Chitosan Enhanced Sand Filtration (CESF) Chitosan is a natural coagulant that promotes flocculation and facilitates the removal of particulate and colloidal solids (including clay and fine silt) from stormwater when used in conjunction with sand filtration. Chitosan is the only known naturally-occurring cationic (positively-charged) polysaccharide biopolymer. Chitosan Acetate is 179 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015" soluble at pH less than 7. When the pH increases above 8.0 the chitosan will precipitate out of solution & becomes inactive. Figure 2. Molecular representation of chitosan acetate. Chitosan promotes coagulation and flocculation of solids in storm/ground water waste stream. Coagulation is the process of destabilizing the predominately negative charge of particulate and