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Nine Minimum Controls

How King County complies with the EPA's CSO control standards.

King County has implemented a number of programs to satisfy the requirements of the Nine Minimum Controls, which are a part of U.S. Environmental Protection Agency's (EPA's) codified CSO Control Policy. The definitions for the controls in the renewed NPDES permit for the West Point Treatment Plant differ slightly from EPA's definitions (refer to table below).

King County's programs and activities in regard to each of the Nine Minimum Controls is described in the Annual Report (refer to the section "Programs to Meet EPA's Nine Minimum Controls").

 King County's compliance with EPA's Nine Minimum Controls

    EPA's Nine Minimum Controls  How King County complies, as listed in the West Point Treatment Plant NPDES Permit
1 Proper operation and regular maintenance programs for the sewer system and CSOs

Control 1—Reducing CSOs Through Operation and Maintenance

Implement proper operation and maintenance programs for the sewer system and all CSO outfalls to reduce the magnitude, frequency, and duration of CSOs. The program must consider regular sewer inspections; sewer, catch basin, and regulator cleaning; equipment and sewer collection system repair or replacement, where necessary; and disconnection of illegal connections.

2 Maximize use of collection system for storage

Control 2—Storing CSOs in Collection System

Implement procedures that will maximize use of the collection system for wastewater storage that can be accommodated by the storage capacity of the collection system in order to reduce the magnitude, frequency, and duration of CSOs.

3 Review and modification of pretreatment requirements to ensure that CSO impacts are minimized

Control 3—Optimizing Pretreatment Program

Review and modify, as appropriate, its existing pretreatment program to minimize CSO impacts from the discharges from nondomestic users.

Maximization of flow to secondary treatment plant for treatment
Control 4—Maximizing Flow to Treatment Plant
Operate the POTW treatment plant at maximum treatable flow during all wet weather flow conditions to reduce the magnitude, frequency, and duration of CSOs. The Permittee must deliver all flows to the treatment plant within the constraints of the treatment capacity of the publicly owned treatment works (POTW).
5 Elimination of CSOs during dry weather

Control 5—Preventing Dry-Weather Overflows

Dry weather overflows from CSO outfalls are prohibited. The Permittee must report each dry weather overflow to the permitting authority as soon as it becomes aware of the overflow. When it detects a dry weather overflow, the Permittee must begin corrective action immediately and inspect the dry weather overflow each subsequent day until it has eliminated the overflow.

6 Control of solid and floatable materials in CSOs

Control 6—Controlling Solids and Floatables

Implement measures to control solid and floatable materials in CSOs.

7 Pollution prevention programs to reduce contaminants in CSOs

Control 7—Preventing Pollution

Implement a pollution prevention program focused on reducing the impact of CSOs on receiving waters.

8 Public notification program to ensure that public receives adequate notice of CSO events and impacts

Control 8—Notifying the Public

Implement a public notification process to inform the citizens of when and where CSOs occur. The process must include (a) mechanism to alert persons of the occurrence of CSOs and (b) a system to determine the nature and duration of conditions that are potentially harmful for users of receiving waters due to CSOs.

9 Monitoring to effectively characterize CSO impacts and the efficacy of CSO controls

Control 9—Monitoring CSO Outfalls

Monitor CSO outfalls to characterize CSO impacts and the efficacy of CSO controls. This must include collection of data that it will use to document the existing baseline conditions, evaluate the efficacy of the technology-based controls, and determine the baseline conditions upon which it will base the long-term control plan. This data must include:

  • Characteristics of the combined sewer system including the population served by the combined portion of the system and locations of all CSO outfalls in the CSS.
  • Total number of CSO events and the frequency and duration of CSOs for a representative number of events.
  • Locations and designated uses of receiving water bodies.
  • Water quality data for receiving water bodies.
  • Water quality impacts directly related to CSO (for example, beach closing, floatables, wash-up episodes, fish kills).