Background Where did CSO systems begin? Combined Overflow (CSO) Control Eric Bergstrom HDR Engineering Background System Development Before About 196 House Background System Development After 196 Building Downspout Downspout Catch Basin Manhole Cover Manhole Catch Combined Basin Interceptor CSO Overflow Structure Background System Development After 196 Combined Overflow Structure City of Seattle 47B Overflow Structure Combined Overflow (CSO) 1
CSO Overflow Structure Bremerton OF2 Overflow Structure Bremerton OF6 CSO Overflow Structure Everett - PSO5 How Frequently Do CSOs Occur? Washington State CSO Reduction Requirements Revised Code of Washington (RCW 9.48.48) 1987: the greatest reasonable reduction of combined sewer overflows at the earliest possible date Washington Administrative Code (WAC 173-245) 1987: control of each CSO such that an average of one untreated discharge may occur per year One CSO Event? Overflow Rate 12 1 8 6 4 2 Simple CSO System Inter-event Period 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 Hour 24-Hour Interevent Period Establishes Independent CSO Events 2
Development of CSO Control Program Characterize the CSO System Document Existing System, Impervious Area Measure Frequency and Overflow Rate Develop and Select Control Alternatives Implement Improvements Design Secure Funding Construction Monitor Performance Characterize Overflows CSO Structure Bremerton OF1 Characterize System - Flow Monitoring Characterize Flows Mount Vernon - 27-inch Palmer Bowlus Flume Develop CSO Control Alternatives Separation Increase Conveyance and In-line or Off-line Storage At-Site Alternatives: 1. Separate Inflow Sources Construct New Storm Drain 3
Alternatives: 2. Build Larger to the Alternatives: 3. Storage or Interceptor Storage/ What works? Just separate, right? Bremerton - Key Features Population 37, City Began in 1891 with U. S. Navy Purchase of Naval Shipyard Former Home of U.S.S. Missouri 1 Mile Bremerton Service Area 23 square miles Bremerton CSO Basin 8 Overflows Port Washington East Bremerton Narrows West Bremerton Combined Separated Sinclair Inlet Pump Station 5 gpm To WWTP 11 Acres, ~3 homes 5 gpm Dry Weather Flow 4 Catch Basins 44 House Roof Drains t c 3 minutes 4
Overflow Structure Bremerton OF8 1,25 Bremerton CSO Basin 8 Only 25% of Flow from Known Inflow Sources.45 Overflow Rate, gpm 1, 75 5.4.35.3 25.25-25 -5-75 3.7 inches of rain 18 hours.2.15.1.5 Rainfall, inches/15 min. -1, Wednesday Thursday Friday Saturday Date and Time. Clear Understanding of Impact of Rainfall It s a Combined System - Disconnect the Inflow Sources Right? System Wide Approach is Required Overflow Rate, gpm 1,25 1, 75 5.45.4 Infiltration That Would Remain After Separation.35.3 25.25.2-25 -5-75.15.1.5 Rainfall, inches/15 min. Separation -1, Wednesday Thursday Friday Saturday. Pump Station Conveyance Date and Time Annual Overflows, million gallons Bremerton CSO Control Program HDR 2 174 177 174 188 18 162 166 171 16 126 14 165 124 152 17 12 15 143 111 1 83 8 8 81 69 6 Predicted 4 Overflow Without CSO Control 19 18 Annual 2 Measured Overflow 3 8.2.4 2.1 1994 1995 1996 1997 1998 1999 2 21 22 23 24 25 26 In-line Storage Mount Vernon, WA 7 feet of 6-inch Pipe 1 million Gallons of Storage 5
Mount Vernon CSO Control Performance Washington State CSO Reduction Requirements 14 12 1 8 6 125 12 Before Past Year CSO Requires means any process which removes at least 5% of the total suspended solids Washington State Deparatment of Ecology Accepts Interpretation of 5% Removal of TSS on Average Annual Basis 4 2 6 Frequency, Events per Year 5.9 Volume, Million Gallons per Year 5% Removal of Solids for CSO? Conventional Interpretation 5% Removal of Solids for CSO? Conventional Interpretation Flow 25 mg/l TSS CSOs may only have 5 mg/l TSS Solids Treated 125 mg/l TSS Flow 25 mg/l TSS Solids Interpretation for CSO Combined Flow 1, pounds per year TSS Solids Treated 125 mg/l TSS Treated CSO 5, pounds per year TSS CSO Example of CSO Assumes 85% of Solids Removal at WWTP or NPDES Permit Efficiency Off-line Storage/ Sized to Capture Minimum 59% of Annual CSO Volume Small CSO Events may not Result in Discharge Large CSO Events may Result in Discharge with Effluent Conc. the Same as Influent Disinfection of Discharges Typically Required 1 st Storm 5, gal of CSO 1 lbs of TSS 1, gal 5, gal & 1 lbs of Solids to WWTP No Discharge Storm Total Solids Solids Solids to WWTP Removed 1 st 1 lbs 1 lbs 85 lbs 6
Example of CSO 2nd Storm 2, gal of CSO 4 lbs of TSS 1, gal Disinfection 1, gal & 2 lbs of Solids to WWTP 1, gal 2 lbs of TSS Storm Total Solids Solids Solids to WWTP Removed 1 st 1 lbs 1 lbs 85 lbs 2 nd 4 lbs 2 lbs 17 lbs Percent Removal: (255 lbs / 5 lbs) = 51% King County - Henderson CSO Project 1. Henderson Pump Station, 2 mgd 2. Forcemain 3. Storage and Tunnel 4. Overflow Pipe Project Cost $77M Service Area 4,6 Ac King County - Henderson CSO Storage and Tunnel 3,1 feet 14-8 Tunnel 4 million gallons 2 Treated Discharges/yr Henderson CSO Tunnel Current HDR Projects City of Everett, Bond Street CSO Facility City of Seattle, Henderson, Genesee CSO Basins Questions 7