CSO Pollutant Loading
The Willamette Plan Area is served by both combined sewers and separate sanitary sewers. Figure 4 shows the locations of separate and combined sewer basins in the Willamette planning area.
Estimates of CSO and stormwater loads for the City’s combined and separate sanitary sewer areas within the Willamette planning area were developed in 1996-1997 during the CSO Predesign Project. As part of this project, BES modified an existing SWMM model of the collection system and ran the model for a six-year simulation period. A six-year simulation period (1982 to 1987) was chosen for the project because this period includes a representative annual mean precipitation and the range of rainfall conditions experienced in the Portland area (BES, 1999). Overflows predicted from combined and separate areas with the SWMM model were input into a SIMPTM model developed by Kurahashi & Associates under contract with BES to estimate pollutant loading. SIMPTM predicts pollutant loads using landuse-specific event mean concentrations for stormwater and constant concentrations for municipal sewage. The SIMPTM model was calibrated to monitoring data during the CSO Characterization Study BES, 1997a).
Table 7 summarizes predicted annual CSO loads for total copper, total lead, total zinc, TSS, E. coli, and BOD5 for subwatersheds within the Willamette planning area. The table also presents ranks of CSO loads among the subwatersheds by parameter, as well as by overall CSO loading. Overall ranks were calculated as the average of the six parameter ranks for each subwatershed.
The Systems Analysis Group at BES developed a GIS-based pollutant loading model for the Willamette Plan Area to illustrate the relative potential for pollutant loading from different land uses. It is important to note that this model was not designed to generate absolute loading values. Rather, it serves as a tool to identify hot spots that may be responsible for generating proportionally more pollutants than other areas within a watershed. These areas may be prioritized for pollutant reduction in future watershed planning efforts. Alternatively, areas of low pollutant loading could be targeted for protection.
The model incorporates information on land use, impervious area, pervious area, and vegetation; it employs standard equations to estimate pollutant loading from each 100 by 100 foot grid section. Mean pollutant loading from various types of land use were obtained from water quality sampling data collected by the City of Portland and the Association of Clean Water Agencies (ACWA). Four pollutants were explored: total phosphorus (TP), total suspended solids (TSS), E. coli, and biological oxygen demand (BOD). The results for TP, E. coli, and BOD are still under development. The results for TSS loading are described below.
Illicit Discharges Elimination Program (IDEP)
The Illicit Discharges Elimination Program (IDEP) addresses the issue of pollutants discharged into Portland’s stormwater system as a result of illicit connections and improper disposal. This is required under the City’s NPDES permit for stormwater as part of the stormwater management program. It is the mission of IDEP to prevent, search for, detect, and control illicit discharges in the City of Portland (Portland, et al., 2002).
IDEP is managed by the Spill and Protection and Citizen Response Section within BES’s Environmental Compliance Division and the Industrial Source Control Division (Portland, et al., 2002). The Investigations and Monitoring Division of the Systems Management Group responds to complaints or reports of illicit connections (Woodward-Clyde, 1996). Both divisions have investigation and enforcement authority.
Currently, grab samples are obtained at 101 locations along the Willamette River and Columbia Slough. These locations are sampled approximately three times during the dry season from June to September, twice per event. IDEP has maintained this level of monitoring each year since 1994. The parameters analyzed in the IDEP Program are conductivity, pH, temperature, copper, iron, zinc, fecal coliform, and residual chlorine (Portland, et al., 2002).
Industrial NPDES Permits
The Clean Water Act requires that stormwater and wastewater discharges from certain industrial and commercial activities be regulated through the use of NPDES permits. There are two types of industrial NPDES permits used by ODEQ: general and individual permits. General permits allow facilities with activities of a similar nature to be covered under a single permit that applies to all facilities in that category. Permit requirements, including monitoring requirements, are the same for all facilities covered under a particular general permit. Individual permits are issued for a single facility and have requirements that are specific to that facility. Individual permits can cover both wastewater discharges and stormwater discharges from a facility. Both individual and general permits are required to be renewed and reissued every 5 years.
Information on NPDES discharges in the Willamette watershed planning area is available through the ODEQ Wastewater Permits Database (ODEQ, 2003) and the USEPA Permit Compliance System Database (USEPA, 2003). Table 2 provides information on each of the industrial discharge and industrial stormwater permits in the planning area, including permit issuance and expiration dates, and monitoring requirements obtained from these databases. In general, monitoring requirements for individual stormwater permits include parameters most likely to be present in stormwater from that specific facility. Figure 2 indicates the locations of the permitted facilities in the planning area.
The City of Portland has a Memorandum of Agreement (MOA) with DEQ that authorizes the City to administer the Industrial Stormwater permits for those facilities located within the City of Portland. The City is responsible for informing the regulated community about the regulations; determining whether facilities are required to obtain a permit; determining whether a facility is exempt from the program; stiving to conduct annual inspections of each permitted facility; reviewing the Stormwater Pollution Control Plan (SWPCP) and determining compliance with the permit; responding to complaints; taking appropriate action to enforce applicable requirements of the City Code; soliciting voluntary compliance and referring to DEQ when the City does not have authority and compliance is not obtained.
Stormwater Pollutant Loading
The Willamette Plan Area is served by both combined sewerss and separate sanitary sewers. Figure 4 shows the locations of separate and combined sewer basins in the Willamette planning area.
Estimates of CSO and stormwater loads for the City’s combined and separately sewered areas within the Willamette planning area were developed in 1996-1997 during the CSO Predesign Project. As part of this project, BES modified an existing Storm Water Management Model (SWMM) model of the collection system and ran the model for a six-year simulation period. A six-year simulation period (1982 to 1987) was chosen for the project because this period includes a representative annual mean precipitation and the range of rainfall conditions experienced in the Portland area (BES, 1999). Overflows predicted from combined and separate areas with the SWMM model were input into a Simplified Pollutant Transport Model (SIMPTN) model developed by Kurahashi & Associates under contract with BES to estimate pollutant loading. SIMPTN predicts pollutant loads using landuse-specific event mean concentrations for stormwater and constant concentrations for municipal sewage. The SIMPTN model was calibrated to monitoring data during the CSO Characterization Study (BES, 1997a).
Table 8 summarizes predicted annual stormwater loads for total copper, total lead, total zinc, TSS, E. coli, and BOD5 for subwatersheds within the Willamette planning area. Table 8 also presents ranks of stormwater loads among the subwatersheds by parameter, as well as by overall stormwater loading. Overall ranks were calculated as the average of the six parameter ranks for each subwatershed. Stormwater load estimates are given for all of the subwatersheds in the planning area with the exception of the Outer East subwatershed, which is served by stormwater sumps (UICs).
Underground Injection Controls (UICs)
On June 1, 2005, the Oregon Department of Environmental Quality issued a Water Pollution Control Facilities (WPCF) permit to the City of Portland for its Class V stormwater underground injection control (UIC) systems, more commonly referred to as sumps. The permit expires in 2015.
The DEQ defines a UIC as any system, structure, or activity that discharges fluid below the ground or subsurface. Class V UICs are stormwater systems such as sumps, drywells, and French drains. Portland currently has an estimated 8,500 active UICs that collect runoff from public streets.
In areas served by combined sewers the sumps divert runoff that might otherwise contribute to combined sewer overflows. In areas served by separate sanitary sewers, the sumps are used to manage street runoff. Sedimentation manholes adjacent to the sumps trap sediments and pollutants.
Most of the sumps are located east of the Willamette River in deposits of gravelly sandy soils, which generally have sufficient capacity to manage runoff from a 10-year storm event. Estimates indicate that a majority of UICs are located above the highest groundwater level and do not directly discharge to groundwater (BES, 2002).
Most City owned UICs are generally 3 to 4 feet in diameter and range in depth from a minimum of 2 feet up to 40 feet. Current construction standards require that new UICs be approximately 30 feet deep and have a sedimentation manhole (10 feet depth) to capture pollutants(BES, 2002).
Recent estimates indicate that UICs drain a total area of 17, 010 acres, of which 7,831 acres (48 percent) is impervious. The average area drained by each UIC is 2.5 acres, of which 1.2 acres is impervious. Overall, 3.9 million cubic feet of stormwater per day on average is estimated to flow to all UICs; about 430 cubic feet of stormwater per UIC per day (BES, 2002).
Eighty-five percent of the land use drained by UICs is residential; 12 percent is commercial and industrial, and 3 percent is parks and open space. A 1997 study sponsored by the Oregon Association of Clean Water Agencies (ACWA) and performed by Woodward-Clyde summarized data collected from land use based stormwater monitoring conducted in Oregon. This data analysis is considered to be a statistically valid representation of pollutant loading from different land uses. The results demonstrated that open space sampling stations generally had significantly lower pollutant discharge levels than other land uses, and that industrial stations generally had higher pollutant discharge levels than other land uses. Residential land use also showed lower pollutant concentrations than the other developed land uses, but was higher than open space. Transportation and commercial land uses generally showed higher pollutant concentrations than residential land uses (Woodward - Clyde, 1997).