The Portland Bureau of Environmental Services (BES) is responsible for operating and maintaining the city’s sewer system and managing stormwater.
Portland’s sewer system conveys and treats both sanitary sewage and storm runoff via two treatment plants. The larger facility, the 140 acre Columbia Boulevard Treatment Plant (CBTP) in north Portland, was completed in the 1950s and has been expanded and upgraded repeatedly since then, most recently in 2000. The plant is a secondary treatment plant which uses an activated sludge process. Some solids from secondary treatment are processed in anaerobic digesters; biosolids produced by the digesters are applied to farmland. Methane gas is also produced by the treatment process. This gas is used on-site for heating needs and the excess is sold to nearby industrial facilities or burned on-site.12 BES also operates a smaller secondary treatment facility to the south of the city.
The CBTP treats an average of 70 million gallons per day (26.6 billion gallons annually), but during wet weather events daily flows can be four times as high. The plant only has sufficient secondary treatment capacity for 100 – 110 MGD, so during wet weather events any flows above this level receive primary treatment only. USEPA would prefer that BES have a larger secondary treatment capacity, on the order of 120 – 160 MGD; BES has argued that wet weather sewage flows are sufficiently diluted that BES can meet EPA’s discharge requirements with enhanced primary treatment and disinfection. EPA is currently (July 2010) reviewing information provided by BES as a part of the Columbia Boulevard plant’s permit review.
Using data from Metro, BES has estimated that flows to the treatment plant could increase by 0.8% per year. However, dry weather flows have not increased over the past
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BES recently constructed an $8 million biogas facility to generate electricity from methane gas created from various treatment processes. Rather than flaring, the gas will be used to generate electricity for use on-site within the treatment plant. The plant was already using microturbines to generate some electricity but expansion of the microturbine installation was not considered feasible due to space constraints and maintenance costs. Instead, BES installed two reciprocating engines with 1.7 MWe combined capacity. The engines generate 40% of the plant’s power and also provide heat to the digesters. All heat is being recovered from the engines, which are operating at about 82% efficiency, with 37% electrical efficiency. The plant is producing 40 – 45 million cubic feet of gas per month at 50 – 55% methane content. BES underestimated the amount of gas being produced at the plant when sizing the equipment, and approximately 25% of the gas (equivalent to 1,500 MWh per month) is still being flared. BES expects to recover the cost through reduced electricity purchases (~$500k/year in savings) and the sale of Business Energy Tax Credits. The microturbines are currently offline but BES is attempting to get them back online using gas produced by the reciprocating engines’ treatment system. The plant also has a fuel cell system which was decommissioned in 2005 due to high operating costs, and required upgrades were not considered economic. Electricity generated at the plant is sold to PGE through their net metering system; there is a 2 MWe cap on net metering generation sites.
10 years, likely due to conservation measures and decreased industrial activity. Presumably conservation measures will eventually yield declining returns and dry weather flows will begin escalating, but forecasting when this will occur is difficult. Wet weather flows have steadily increased as the Big Pipe projects have been connected, bringing more stormwater into the system. Before 1995, peak wet weather flows were often roughly 250 MGD; once the East Side Big Pipe is connected in late 2011, storm flows will regularly be 450 MGD, which is the current hydraulic capacity of the system13. Current operating and maintenance costs for the Columbia Boulevard plant are $500 per million gallons. However, there are additional operating costs for the 90+ pump stations which move sewage to the treatment plants; information on these facilities was not available.
As discussed previously, BES recently held a workshop on decentralized natural
wastewater treatment and the issues associated with designing and implementing these facilities. Several case studies were discussed at the workshop, including local ones such as the OHSU Center for Health and Healing, the planned Oregon Sustainability Center, and the Port of Portland. 14
Portland receives an annual average precipitation of 37 inches, which generates billions of gallons of stormwater runoff. Stormwater washes over roofs, streets, driveways, sidewalks, parking lots, and land surfaces. Many older neighborhoods in Portland have a sewer system that mixes untreated sewage and storm runoff in a single pipe, which can overflow during storm events. Stormwater can carry pollutants to waterways and can also cause flooding and erosion, destroy natural habitat, and contribute to combined sewer overflows (CSOs). The clay soils commonly found west of the Willamette are not good for infiltration, contributing to high run off. Sandy soils east of the Willamette River allow stormwater to soak into the ground. In east Portland, about 9,000
underground injection control (UIC) systems collect stormwater runoff from streets and infiltrate it. For many areas east of the Willamette, UICs are the only available form of stormwater management.
The federal Clean Water Act, Safe Drinking Water Act, and Endangered Species Act require the city to manage stormwater runoff to protect water quality in rivers and streams, protect watershed health, and protect groundwater as a drinking water resource. The city’s federal stormwater permit requires Portland to reduce stormwater pollution, and manage other programs that respond to water quality requirements. In 2005, the Oregon Department of Environmental Quality (DEQ) also issued the state’s first Water Pollution Control Facilities (WPCF) permit to the City of Portland, authorizing
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Peak storm flows can be as high as 1 billion gallons per day, with all flows in excess of 450 MGD discharged as overflows to the river.
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Workshop materials are available here:
stormwater discharges into city-owned public UICs. The permit establishes construction, operation, and maintenance requirements for UICs to ensure that UICs in Portland protect groundwater as a drinking water resource.
For much of the 20th century, Portland’s sewer system has not had sufficient capacity to handle large stormwater flows, resulting in the sewer system overflowing during wet weather events and discharging untreated sewage directly into the Willamette River. Since the 1990s, Portland has been working to reduce the incidence of CSOs, largely by finding ways to slow the flow of stormwater runoff into the sewer system or divert it entirely.
Storm flows have been diverted through projects such as encouraging homeowners to disconnect downspouts, constructing separate storm sewers, and diverting streams in the West Hills from the sewer system. BES has also invested in several Big Pipe projects, which are large diameter pipes which collect stormwater and bring it to the Columbia Boulevard plant. The third and final of these projects, the East Side Big Pipe, is currently under construction and is expected to be completed in 2011. These projects have already reduced the incidence of CSOs in Portland by 94 to 99%.
These large infrastructure projects have been complemented by smaller-scale projects to reduce stormwater flows and increase infiltration to groundwater. The Tabor to the River project, on Portland’s east side, is the largest such project. BES has also identified several locations as potential Green Streets, and has designed and installed swales and other features to capture and filter stormwater runoff.
BES has also developed the Stormwater Water Management Manual. Projects that develop or redevelop over 500 square feet of impervious surface or that propose new offsite discharges or new connections to the public system are required to comply with the Manual‘s stormwater management requirements for the impervious area draining to the discharge point. Typically, stormwater that is generated from private property has been managed on private property, in privately maintained facilities. Stormwater that is generated from public property has been managed on public property, in publicly maintained facilities.15
In 2006, the City of Portland adopted a Watershed Management Plan. The Watershed Plan is a framework for evaluating the condition of the City's urban watersheds and for implementing projects to improve watershed health. The Plan will be implemented through the Watershed Services Group, River Renaissance, other City bureaus, agencies, and citizens' groups. An overarching theme of the Plan is to achieve improved
watershed health through watershed-friendly development, installation of new stormwater infrastructure, and the repair and maintenance of existing infrastructure in
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There is precedent for systems that integrate public and private lands. Shared public-private stormwater management facilities have recently been installed in the Central District of South Waterfront.
new ways that will improve watershed health. The Plan suggests a management system to track City progress toward well-defined watershed health goals. Another major component of the Plan is an integrated City response to local, state and federal environmental requirements.
The City is divided into five watersheds within the Plan. All three Pilot EcoDistricts considered in this screening are part of the Willamette Watershed, which includes Forest Park, downtown's commercial core, industrial districts on both sides of the river, and Portland's most densely populated residential neighborhoods. The Willamette Plan Area is divided into 27 subwatersheds, drainage areas of only a few square miles or less, to facilitate map and assessment of restoration potential. Most Pilot EcoDistricts are located within a single subwatershed, although the Pilot EcoDistrict boundaries do not necessarily follow the subwatershed boundaries.
Gray water use is a strategy to reduce portable water consumption and wastewater flows, and to support local water balance. In Oregon, gray water is regulated by the Oregon Department of Environmental Quality. In 2009, Oregon passed House Bill 2080, which legalizes the use of gray water for beneficial uses. The bill establishes that a person may not construct, install, or operate a gray water reuse and disposal system without a permit from the Oregon Department of Environmental Quality (DEQ). The bill further directs the Environmental Quality Commission (EQC) to adopt rules for gray water permitting. Under the law, gray water means shower and bath wastewater, bathroom sink water, kitchen sink wastewater, and laundry wastewater. Gray water does not mean toilet or garbage wastes, or wastewater contaminated by soiled diapers. Water from toilet flushing, kitchen dishwashers and sinks, which contain human waste, potentially toxic soap and food residue, are considered black water.
HB 2080 directs the EQC to adopt rules on gray water permitting. DEQ is working with an Advisory Committee to develop these rules. In developing rules, the EQC has been directed to minimize the burden of permit requirements on property owners; and to prescribe requirements that allow for the treatment, disposal, or reuse of gray water. DEQ expects the rulemaking process to take about 2 years.
Portland's sewer system is financed largely through user fees. For most customers, sewage fees are based on metered water usage. For industrial customers and other "extra strength" users, additional fees apply. Portland finances stormwater
management services primarily by collecting public utility fees on developed property. Additional revenue for sewer and storm system expansion also comes from System Development Charges (SDCs) on new development or large redevelopments. SDCs have multiple components and are challenging to estimate in advance. Stormwater SDCs are mostly based on impervious area. A building with 20,000 sq ft of impervious area would have a stormwater SDC of approximately $5,000. Sanitary sewer SDCs are $4,000 per dwelling unit (or equivalent number of fixtures), plus an additional $5,000 - $10,000 per building depending on site size and any branch lines required. A 100-unit residential building's sanitary sewer SDCs would be roughly $400,000 - $500,000.
No information was available on the GHG emissions associated with operating Portland’s sewer system. The biogas used at the CBTP produces GHG emissions but these have a lower contribution to global warming than if methane from decomposition were discharged directly to the atmosphere. Emissions associated with pumping and other energy use in excess of the energy produced from biogas were not available.