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CSO Control Program-- |
Source: Section 1.4 from 2006-2007 Annual Report.
Supervisory Control and Data Acquisition (SCADA)—formerly called CATAD (Computer Augmented Treatment and Disposal System) when it was an in-house developed system— controls the West Point Treatment Plant collection system
Projects to enhance the use of storage capacity in existing sewers are part of ongoing improvements to the SCADA system. In 1992, storage levels behind regulator stations were raised to improve capture of CSO. Currently, a modified CSO drawdown strategy is being employed at the Interbay Pump Station. This strategy will provide storage capacity in the upper portion of the Elliott Bay interceptor (EBI) for as long as possible. The available storage will be used when flow exceeds the allowed flow through the pump station.
SCADA computer hardware and software at West Point was replaced with a new system in May 2004 to bolster the reliability of monitoring and control of offsite regulator and pump stations. The system will continue to be tested and refined as necessary. The new hardware includes enough capacity to install and run an optimization program (predictive control) to monitor rainfall and conditions in the major trunks and interceptors, predict inflows to the sewer system, and optimize the regulation of flow through the regulators to minimize CSOs. Predictive control model development and calibration is taking place in 2005–2008; a new updated control program is targeted for 2008–2010.
These improvements to the SCADA system could reduce CSO volumes by as much as 150 MG per year. Additional improvements will be explored as information becomes available.
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The King County Department of Natural Resources and Parks, Public Health–Seattle & King County, and Seattle Public Utilities jointly developed and are implementing a CSO Notification and Posting Program. Ecology approved the program as meeting state and federal requirements for public notification and providing information to the community regarding the possible health impacts of CSOs. Public notification is one of EPA’s Nine Minimum Controls. The County’s program has evolved to integrate with other public information and involvement programs. The current program includes the following elements
The recently modified NPDES permit for West Point required the County to conduct a study to determine the feasibility of providing more immediate notification of overflows, including the feasibility of providing a Web-based system. Technology upgrades to the West Point SCADA system may have allowed for provision of “real time” overflow information on the Internet. Such a system is being piloted internally. Having determined the technical possibilities of providing “real time” information King County has been meeting with interested public groups and has been participating in public events such as fairs and farmers markets to discuss the potential of a Web site and to gather information on public preferences. This information and the results of the internal pilot will be evaluated and a decision will be made in early 2008. More detail on this program, the alternatives considered, other agency approaches, and public involvement is provided in the Final Public Notification Feasibility Study, submitted to Ecology on July 1, 2007. The report can be accessed on the County’s CSO control program Web site (http://dnr.metrokc.gov/wtd/cso/library.htm).
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King County and the City of Seattle jointly manage stormwater discharges in the Lander and Densmore drainage basins that occur as the result of County sewer separation projects. This ongoing management program includes Densmore-specific requirements under the NPDES municipal stormwater permit. Program elements include source control, baseline sampling of stormwater discharges, and inspections. As specified in a local agreement between the City and County, the City maintains the stormwater system and manages any necessary source control enforcement actions.
The Lander stormwater system was built in 1992 to reduce CSOs at the Lander Regulator Station. A new wastewater sewer was built, and the original pipeline was cleaned and converted to a storm drain. A low-flow diversion of stormwater to the new sewer was included to capture any first flush of pollutants during rain. The stormwater and remaining Lander Regulator CSO discharge share the same City-owned outfall to the Duwamish River East Waterway.
The Densmore stormwater system was built in 1994 to reduce CSOs at the University Regulator Station. It collects stormwater from the Haller Lake area and Green Lake drainage, as well as outflow from Green Lake, which had previously entered the combined sewer system. The Densmore system runs from Green Lake to Lake Union. A pump station located to the north of Lake Union discharges to Lake Union just west of the I-5 bridge. In the event of pump failure, high-level weirs allow stormwater to discharge to the combined sewer to prevent damage to the pump station or to Green Lake park facilities.
The Densmore stormwater system has experienced hydraulic, mechanical, and electrical problems since it began operation. An upgrade to the system has just been completed (see Section 1.3.2).
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A 10-year post-control sediment sampling program began in 2006 near the outfall for the new Elliott West CSO Treatment Facility. Surface sediment samples from 16 stations are being collected and analyzed for sediment chemistry and benthic infauna. Monitoring the sediment near the new outfall was part of the requirements for the Section 7 consultation for the U.S. Army Corps of Engineer permit.
In mid 2007, design was completed for cleanup of contaminated sediments in front of the old Denny Way CSO site off of Myrtle Edwards Park. An Agreed Order and the interim action work plan were finalized by Ecology in early October 2007. Dredging will occur November 2007– February 2008. A ten-year monitoring program will start in 2008 to evaluate additional areas further offshore with sediments exceeding sediment management standards. After five years of monitoring, alternatives for cleaning up additional areas will be evaluated with Ecology and other stakeholders.
In 2000, the U.S. Environmental Protection Agency (EPA) declared an area of the Duwamish Waterway from the south end of Harbor Island to the Turning Basin as a Superfund site. King County, City of Seattle, Port of Seattle, and The Boeing Company formed a working group to complete early action cleanups at several locations in the area and complete the work necessary to determine the final Superfund clean up of the waterway. The site risk assessments are complete and the draft remedial investigation will be out for public review in November 2007. King County has completed two early action cleanups in front of King County CSOs (Norfolk and Duwamish/Diagonal). Monitoring programs are under way at both locations. Design is complete for the cleanup of Slip 4 (in cooperation with the City of Seattle). Cleanup of Slip 4 is on hold while Ecology completes source control actions at North Boeing Field that threaten recontamination of the cleanup site.
In 2006, King County, City of Seattle, and Port of Seattle formed a working group to complete the work necessary to determine the final Superfund cleanup of the East Waterway of the Duwamish River. EPA approved the scope of the remedial investigation/feasibility study spring 2007, and work has started. The Hanford/Lander CSOs are part of the East Waterway cleanup. Cleanup of approximately 20,000 cubic yards of sediment in front of the Lander CSO will occur in winter 2008–2009.
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View the most recent Annual Report.
Return to:
> CSO Program Page
> CSO Introduction Page
> CSO Control Program Library Page
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For questions about the CSO Program, contact Karen Huber.
Department of Natural Resources Updated: Nov. 9, 2007
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