PRESENTED TO: ENGINEERING AND PLANNING SUBCOMMITTEE OF THE METROPOLITAN WATER POLLUTION ABATEMENT ADVISORY COMMITTEE DECEMBER 5, 2013 Regional Wastewater Services Plan and Conveyance System Improvement Program Planning Assumptions 1

Schedule for Briefings with E&P DatePlanned Topic May 2, 2013 COMPLETED Overview of process to update planning assumptions June 6, 2013 COMPLETED Future population, planning horizon, and water conservation assumptions August 1, 2013 COMPLETED Sewered area growth rate and average wet-weather I/I degradation rate September 5, 2013 COMPLETED Follow-up from June 6 and August 1 discussions October 3, 2013 COMPLETED New system I/I and Peak I/I degradation rate -- procedures November 7, 2013 COMPLETED New system I/I and Peak I/I degradation rate Follow-up from previous meetings as needed December 5, 2013Peak I/I degradation rate Summary of planning assumptions 2

Today’s Presentation Planning Assumption Background Peak I/I degradation rate proposed assumption Review planning assumptions for use in CSI Update and RWSP Comprehensive Review Next Steps 3

Regional Conveyance System Needs Assessment Prioritize Projects and Update Cost Estimates 2015 Update Update of Planning Assumptions Treatment Plant Flow Projections Review of RWSP Programs & Policies Conveyance System Improvement Project Identification Review of Asset Management Assumptions Review of Technology & Regulatory Trends 2014 Review 2015 Update 4

additional future I/I = I/I degradation + additional sewered area current I/I water conservation reduction future population and employment current sewage flow Components of Future Flows 5

I/I Degradation Rate Concept:  Collection system becomes leakier over time due to physical changes (settling, tree roots, impacts) and corrosion Approach:  Identify basins that had minimal change over the last decade  Initially done by comparing sewered area  Compare predicted peak I/I flows between 2000 and 2010 Difficulties:  I/I degradation rate has not been measured previously  Increase in I/I flow is small relative to other factors 6

7 Initial Basins for I/I Degradation Rate

Ongoing Work: Refinement of Basin Selection Comparing 2000 and 2010 sewer collection systems  Were there changes in the collection system? Comparing base sewage flow to population based estimate  Do changes in base sewage flow match how population and water use have changed? Verifying meter placement and model flows  Was flow meter location changed?  Is flow meter data of high quality?  Are any upstream basins removed from model predictions?  Do changes in calibration procedure affect results? 8

Refinement of Basin Selection Comparing 2000 and 2010 sewer collection systems  No significant changes were found Comparing base sewage flow to population based estimate  Identified several basins where upstream basin flows were not subtracted out. Verifying meter placement and model flows  Identified a couple of basins with noisy data or data gaps  Recalibrated 17 basins to 2001 data, the calibration procedure had a noticeable impact in some basins. 9

Example BEL100: 2000 vs Model 2001 Meter Data 2001 Model 2010 Meter Data Rain Increase in Flow 2010 Diurnal Pattern

Example FACT004: Model 2001 Meter Data 2001 Model 2010 Meter Data Rain Decrease in Flow 2010 Diurnal Pattern

Summary 32 basins in comparison Added basins with Pump Station data Calculated change in I/I over the decade remained widely variable  maximum decrease of 58%  maximum increase of 110% Limited base flow in data set reduces model confidence Variability in results is too great to have high confidence in average value 12

Assumption: I/I Degradation Previous Assumption: WTD assumes that I/I degradation starting in 2000 would be 7 percent per decade, with a limit of 28 percent over a 40-year period. Proposed Assumption: Assume an I/I degradation rate of 7 percent per decade, to the planning horizon (50 years). 13

Planning Assumptions Update Summary AssumptionPreviousNew Extent of Service AreaSewerable areas within UGA Same Design Flow (Separated Conveyance) 20-year peak flowSame Future Population2003 PSRC Forecast2013 PSRC Forecast Planning Horizon Water Use (gpcd or gped)Year 2000 values: Seattle Residential: 55 Other Residential: 66 Commercial: 33 Industrial: 55 Year 2010 values: Water ConservationA 10% reduction in per day water consumption between 2000 and 2010, with no additional reduction after 2010 A 10% reduction in indoor per capita and per employee water consumption between 2010 and 2030, with no additional reduction after Inside Seattle Outside Seattle Residential (gpcd)4654 Commercial (gped)3019 Industrial (gped)

AssumptionPreviousNew Sewered Area Growth Rate90% of unsewered sewerable area sewered by 2030, 100% sewered by Additional unsewered (but sewerable) area will continue to grow at the rate until service area is fully sewered in 2060 (approx. 20% per decade) AWW I/I Degradation (Treatment Plants) Increase of 7% per decade up to a maximum of 28%. No AWW I/I degradation. New System I/I (Separated Conveyance) Initial rate of 1,500 gpad with degradation applied starting one decade after construction. Initial rate of 2,000 gpad with degradation applied starting one decade after construction Peak I/I Degradation (Separated Conveyance) Increase of 7% per decade up to a maximum of 28%. December 15 Planning Assumptions Update Summary

Contacts For questions on RWSP Comprehensive Review contact: Debra Ross, or For questions on CSI Program Update contact: Steve Tolzman,

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18 King County Wastewater System with Sewer Flow Scheme

Assumption: Water Conservation Updated Assumption: A 10 percent reduction in indoor per capita and per employee water consumption between 2010 and 2030, with no additional reduction after

Water Conservation Assumption Applied Future water consumption = (current water consumption) X (cumulative water conservation factor) Previous Proposed 2010 Proposed 2020 Proposed 2030 Proposed 2040 Seattle residential (gpcd) other residential (gpcd) commercial (gped) industrial (gped)