BACKUPS! Solving the Problem in a Seattle Neighborhood

Transcription

1 BACKUPS! Solving the Problem in a Seattle Neighborhood MARTHA BURKE SEATTLE PUBLIC UTILITIES A ND A NDY BEHNKE HERRERA ENVIRONMENTAL CONSULTANTS PNCWA BOISE, IDAHO

2 Broadview Area

3 Project Study Area

4 Informal Drainage in Broadview Area

5

6 Broadview Green Grid

7 Backup from December 2007 Storm

8 Backup in House from December 2007 Storm

9 Pipe Defects Identified in Broadview Area Area Total 1822 Number of Occurrences Percentage Description % Alignment % Radial Crack 0 0.0% Longitudinal Crack % Inflow/Infiltration 2 0.1% Broken Joint % Misaligned Joint % Lateral % Roots % Debris 2 0.1% Structural - Ovality 4 0.2% Structural - Collapse % Structural - Deterioration 6 0.3% Broken Pipe % Deposits - Attached % Deposits - Settled % Fracture % Tap Break % Miscellaneous

10 Cleaning and Maintenance Activity for Broadview from 1997 through 2008 Area Number of Occurrenc es Percentage Description % Manual Inspection % Jet Clean % Machine Rod Mainline % Sewer Backup Inspection % Sewer Mainline TV % CCTV Demand/Response % Hydrocut Mainline 9 0.4% Jet and Hydrocut % Chemical Foam for Roots 1 0.0% Maintenance Hole Inspection Total % Other Maintenance

11 Maintenance Frequency

12 Broadview Community Council Newsletter

13 Problem Areas and Monitor Locations

14 Initial Results of Investigation Infrastructure Condition Sewers generally good some sags, few breaks, some lateral intrusion Maintenance Root intrusion from laterals; moderate debris Ditches and culverts in need of cleaning clogged with debris

15 Pipe Condition Generally Good

16 Lateral Problems Root Intrusion from Lateral Lines

17 Root Intrusion Problems at Joints

18 Broadview Smoke Testing Summary June Summary Total Number of Connections to Sanitary Sewer Percent By Type of Connection Percent of Total Residences Downspouts 95 41% 7% Ground/Other 66 29% 5% Drain/Catch Basin 52 23% 4% Faulty Cleanout 17 7% 1% Total % Number of connections 230 Total residences 1,434 Test area (acre) 406

19 Downspout Connections Identified from Smoke testing

20 Modeling Approach Objective: Evaluate alternatives for reducing sewer backups. Model Platform: EPA-SWMM 5 Data: 12 ADS Flow Monitors Two rain gauges, RG1 and RG7 Smoke testing results Other studies

21 Model Scenarios Baseline Scenario status quo of existing system Alternative 1 Pipe Replacement 1 st Ave. NW and NW 115 th St. NW 105 th St. Alternative 2 Inflow Reduction Disconnecting 20% of downspouts (scenario 1) Disconnecting 50% of downspouts (scenario 2) Disconnecting 100% of all connected impervious area (scenario 3) Alternative 3 Infiltration Reduction 20% infiltration reduction (scenario 1) 40% infiltration reduction (scenario 2) 80% infiltration reduction (scenario 3)

22 Model Results for 105 th Street NW 105 th Street. Pipe Segment Location Capacity 1 (CFS) 1/7/2009 OBS Discharge (CFS) 100-Year MOD Discharge (CFS) 100-Year MOD Discharge as Percent of Capacity 1 (%) to to to to NW 105 th Street between Palentine Avenue and 1 st Avenue NW NW 105 th Street between 1 st and 2 nd Avenue NW NW 105 th Street between 2 nd Avenue NW and alley to the west NW 105 th Street between 3rd Avenue NW and alley to the east n/a n/a

23 Model Results for Pipe on 115 th Street NW 115 th Street and 1 st Avenue NW. Pipe Segment Location Capacity 1 (CFS) 1/7/2009 OBS Discharge (CFS) 100-Year MOD Discharge (CFS) 100-Year MOD Discharge as Percent of Capacity 1 (%) to (Inflow to Manhole) to (Inflow to manhole) to (Outflow from manhole) Along NW 115 th Street to the west of 1 st Avenue NW Along 1 st Avenue NW to the north of NW 115 th Street Along NW 115 th Street to the east of 1 st Avenue NW

24 Assessing Costs Using the Triple Bottom Line Initial Capital Cost: Include costs borne by others as well as SPU. Future Costs: O&M, periodic rehab, decommissioning, etc. Incurred by SPU and others. Life of Investment: How long it will function before replacement is needed. Effectiveness: Change in annual likelihood of bad consequences such as number of backups. Ancillary Benefits (or costs): Significant nonmonetary considerations such as regulatory, habitat benefits, interagency cooperation. Quantify where possible.

25 Business Case for Alternative 1 Avoided Cost of Backups Estimated: Annual: $21,000-$38,000 Total over 100 years: $420,000-$750,000 Project cost: Must be less than $750,000 to be worth doing Non-monitized costs/benefits include: Regulatory: State and feds want to see basement backups reduced Health: Avoids exposure to pathogens from sewage Community Relations: Improves perception of City by community

26 Pipe Replacement Construction Cost with Contingency &WSST $399,537 Indirect Cost PM, Design Engineering $10,389 Contracts $34,000 Construction Engineering and Admin (10%) $40,000 Project Cost incl. Construction and Indirect Cost $483,926 Project Contingent at 5% $ 24,196 TOTAL ESTIMATED PROJECT COST $508,122

27 Early Actions Pipe replacement Proactive cleaning

28 Pipe Replacement Locations

29 Pro-Active Maintenance Maintenance Program has following components: Reactive: Crews respond to calls to remove obstructions Conditional: Adjunct to other work; clean and TV pipe to assess condition Preventive: Pipes are on a schedule for regular cleaning, but can be as long as 10 years Proactive: Cleaning of pipes in an area where there is the potential for backups. Evaluate how much material removed. If large amount, may also TV.

30 Additional Programs to Control I&I Implement in target sub-basins: Roof Drain Disconnect Program Side Sewer Repair and Replace

31 I & I Control Voluntary Disconnect Program Pilot Project will be done for Ballard basin starting spring 2010 Utilizes voluntary incentive program and on-line interactive process If successful, can apply the same approach in Broadview starting 2011.

32 Rain Wise Web Site

33 I & I Controls Side Sewer Repair/Replacement Use King County Pilot Project as a model If effective will apply to selected Broadview subbasins Would probably not implement until 2011/12

34 Role of the Property Owner Under current City law home owners are responsible for their side sewers need to maintain and clean regularly Some locations with basements at low elevations may need to install backflow preventers

35 Capacity Citywide Broadview is only one of several areas in the City of Seattle with capacity needs. SPU is working to identify, cost out, and prioritize those needs. The City will be updating its Comprehensive Plan over the next 18 months and this information will be folded into that effort.

36 Locations Where Sewer Capacity is Limited

37 A Dose of Reality Can t project against all storms 2007 storm was ranked as greater than 130 year storm. May not be able to protect all homeowners if houses are at a low elevation compared to sewers. Can reduce the frequency and extent of problem through proactive maintenance and improving capacity of the system. Need to consider what is an acceptable level of service and how do we measure that.