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Executive's Recommended Regional Infiltration and Inflow Control Program
Executive's Recommended Regional Infiltration and Inflow Control Program
The following recommendations make up the Executive’s recommended regional infiltration and inflow (I/I) control
program. The recommendations represent the consensus reached by the County and local
agencies throughout the 6-year program development process. Knowledge gained from flow
monitoring, modeling, pilot projects, and a benefit-cost analysis conducted during the I/I control
study served as the basis for consensus.
Recommendation Highlights
King County and the local agencies would select, implement, and evaluate two or three “initial” I/I reduction projects to test the effectiveness of I/I reduction on a larger scale than the pilot projects.
After completion of the initial projects, recommendations would be made to the King County Council regarding long-term I/I reduction and control, including applicable changes to policy or code. |
Recommendations are presented for both I/I reduction and long-term I/I control and for program
administration and policy. In addition to cost-effectively removing enough I/I from the collection
system to delay, reduce, or eliminate some
otherwise needed conveyance system
improvement (CSI) projects, measures must be in
place to maintain I/I reductions long-term and to
prevent future increases in I/I throughout the
regional system. Long-term I/I control includes
policy, administrative, financial, and technical
measures that promote an ongoing program of
review, maintenance, and repair of the collection
and conveyance system.
Recommendations for I/I Reduction:
- Identify cost-effective I/I reduction projects on a project-specific basis, rather than on a
regional basis or by the need to meet specific I/I reduction targets.
- Select two or three initial I/I reduction projects for implementation from the list of nine costeffective
projects identified in the benefit-cost analysis. King County and MWPAAC
(through the E&P Subcommittee) would work cooperatively to select these projects.
- In the next 3 to 5 years, construct the selected initial projects to test planning assumptions
and to gain more information about costs.
- Proceed with work on private property when a project calls for it. Experiences on initial
projects would be documented in terms of public involvement activities, private property
participation rates, costs, neighborhood impacts, groundwater effects, and special
construction issues that arise.
- Fund initial projects through King County wastewater revenue that is dedicated to funding
CSI projects in the regional conveyance system. For future I/I reduction projects, options to
supplement King County funding may be considered. For example, local agencies could
contribute funds to expand the project scope in order to take advantage of construction
efficiencies, as was done in some pilot projects, or to move a project into the cost-effective
category.
- Conduct pre- and post-project flow monitoring to test the ability of I/I reduction projects to
reduce enough flow to delay, downsize, or eliminate the need for CSI projects.
- Reconvene the E&P Subcommittee when initial projects and post-project flow monitoring
are completed to evaluate results of projects, adjust planning assumptions if appropriate, and
further refine private property protocols or best practices to ensure that successful approaches
are carried forward to future work.
- If the initial projects are deemed successful and future I/I reduction is approved, proceed
programmatically to apply I/I reduction planning to all CSI project planning. Wherever an I/I
reduction project is a cost-effective alternative to the planned CSI project, the County and
local agencies would implement the I/I reduction project provided that it is environmentally
and logistically feasible.
Recommendations for Long-Term I/I Control:
- Make use of existing local agency regulations to ensure that new development and
redevelopment within the regional wastewater service area meet up-to-date construction
standards for sewer conveyance lines and connections.
- Apply the standards, guidelines, procedures, and policies in final draft form to the initial I/I
reduction projects (included as Appendix A). Once they have been tested on large-scale
projects, the standards, guidelines, procedures, and policies would be reviewed and finalized
by the local agencies and translated into King County policy in the form of an ordinance.
- Conduct a system flow audit of the regional and local systems every 10 years to track I/I
levels. The County and local agencies would conduct the audits and use the information to
cooperatively make decisions about how to adjust I/I control measures as may be necessary.
- Do not implement a surcharge on local agencies for flows that exceed targeted I/I reduction
levels already established in the King County Code. The County and local agencies found
that implementing a surcharge, as contemplated in the King County Code, would be costly to
administer and would pose difficulties in verifying violations.
Recommendations for Program Administration and Policy:
- Authorize King County to centrally manage the I/I control program, to develop public
information materials for the overall program, and to serve as a central clearinghouse for
program inquiries and training.
- Conduct flow monitoring to assess effectiveness of I/I reduction over time.
- After completion of the initial I/I reduction projects, develop recommendations regarding
changes to local agency agreements and/or the King County Code.
For more information, please contact Erica Herrin at (206) 684-1138 or erica.herrin@kingcounty.gov.
Table of Contents
If you need a free copy of the Adobe Acrobat Reader to view these documents (.pdf), visit the King County Acrobat help page.
Transmittal Letter, December 29, 2005
Report and Appendices, issued December 2005 (4.6 MB)
Title Page, Acknowledgements (20 KB)
Contents (19 KB)
Chapter 1. Executive Summary (206 KB)
Chapter 2. Background (227 KB)
Chapter 3. Assessing I/I Levels and Reduction Technologies (964 KB)
Chapter 4. Benefit-Cost Analysis (668 KB)
Chapter 5. I/I Control Program Recommendation (361 KB)
Appendix A – Selected Legal Authorities Related to Implementing and Funding an Infiltration and Inflow Reduction Program (27 KB)
Appendix B – Final Draft Standards, Guidelines, Procedures, and Policies, Oct. 19, 2004
(located on separate Web page)
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