Sanitation District No.1 Cost Effectively Reduces Overflows Into the Ohio River

Transcription

1 Sanitation District No. 1 of Northern Kentucky Sanitation District No.1 Cost Effectively Reduces Overflows Into the Ohio River Ohio WEA Collection Systems Workshop May 5, 2011

2 Sanitation District No. 1 of Northern Kentucky Created in 1946 Serves Boone, Kenton, and Campbell Counties in Northern Kentucky Serves approximately 350,000 people Greater Cincinnati / Northern Kentucky Airport

3 Sanitation District No. 1 of Northern Kentucky Total service area ~ 200 sq miles >1,600 miles of sewers >42,000 manholes 2 regional WWTP

4 Sanitation District No. 1 of Northern Kentucky Combined Service Area Combined service area ~ 12 sq miles Additional 21 sq miles of separate area tributary to combined interceptors 96 CSOs 15 flood pumping stations 3,302 catch basins Estimated annual overflow volume 1.5 BG

5 Watershed Consent Decree In October 2005 Sanitation District No. 1 negotiated a Watershed Consent Decree CSOs into compliance with CSO Policy by 2025 Public Outreach Regulatory Assistance Strategic Advisory Team Watershed Partners Eliminate sanitary sewer overflows by 2025 Improve water quality WATERSHED PLANNING PRIORITIZE CONTROLS INFRASTRUCTURE PLANNING and COMPLIANCE Develop Watershed Plans every five years that can address all sources of pollution Public Input Plans Regulatory Approval Outcome: affordable combination of gray, green, and watershed controls to improve water quality IMPLEMENT CONTROLS

6 River s Edge Project Background Proposed development along Ohio River in Dayton Kentucky, Northern Campbell County Would comprise 2,000 units of condominiums and single family residences along 1.5 miles of the Ohio River River s Edge Development McKinney St. CSO Main St. CSO

7 River s Edge Project Background Interceptor replacement was needed due to significant amount of fill (> 20 ) needed for development Developer proposed in-kind replacement The District decided that this was an opportunity to address two large CSOs (6 th and 7 th largest in terms of annual overflow volume) within the development boundaries Main St. Outfall McKinney Outfall Fill boundary

8 River s Edge Project Background Current Topography Flood Levee Ohio River 32 ft to levee top MH Depth 15 ft

9 River s Edge Project Background Post-Development Topography 10 ft to levee top Future Depth 37 ft

10 River s Edge Partnering Opportunity Addressing overflows now makes sense: Developer would have been responsible for in-kind replacement costs and construction which provides cost-sharing for any upsizing Design and Construction could go much quicker through partnership with the developer and their engineers and contractors using a modified designbuild There would be significant opportunity cost to come back later to do significant construction

11 River s Edge Existing Conditions Preliminary system-wide calibrated model was available as tool to assess current situation and to evaluate alternatives Model was developed in Infoworks Combined sewers 18-inches and larger Separate sewers 10-inches and larger

12 River s Edge Existing Conditions River's Edge Existing Conditions Location Length (ft) Size ORI Peak Flow Capacity (MGD) Peak Flow Needed For Conveyance (MGD) Beginning of Development to Main CSO " Main CSO to McKinney CSO " McKinney CSO to End of Development "

13 River s Edge Existing Conditions Existing System Model Results: Typical year overflow volume for Main St. is about 42 MG Typical year overflow volume for McKinney St. CSO is about 65 MG These two outfalls comprise almost 10% of the total CSO volume system-wide 72-inch McKinney St. Outfall 96-inch McKinney St. Outfall

14 River s Edge Alternatives Analysis Goal: Develop plan to address overflows in the near term while maintaining flexibility for long term planning Challenges: Watershed Planning not started yet Construction scheduled to begin within 6 months of notice Development is on upper end of combined sewer system Proximity to the Ohio River

15 River s Edge Alternatives Analysis Approach: Use typical year (1970) rainfall to develop preliminary sizes for a range of alternatives for comparison purposes to preview feasibility of various options. McKinney St. Outfall Initial Alternatives Evaluated: Local storage at each outfall with 0 overflows in typical year Conveyance to potential regional storage downstream at 0 overflows in typical year Potential Storage Locations Main St. Outfall Potential Storage Locations

16 Storage Sizing and Preliminary Construction Costs Local Storage (Typical Year Level of Control) Location Tank Volume (MG) Tank Pricing ($/gal) Tank Cost (M$) Main Street McKinney Street Interceptor Conveyance For Local Storage Option Location Peak Flow (MGD) Length (ft) Diameter (in) Pipe Pricing ($/in/ft) Pipe Cost (M$) Cumulative Cost (M$) Beginning of Development to Main CSO Main CSO to McKinney CSO McKinney CSO to Ward Total Estimated Construction Cost with 30% Cont: $44.3 million

17 Conveyance Sizing and Preliminary Construction Costs Typical Year Analysis - Wet Weather Options for Conveyance of All Peak Flows Does NOT account for additional downstream conveyance and/or storage River's Edge Conveyance Sizing (Typical Year Level of Control) Location Peak Flow (MGD) Length (ft) Diameter (in) Pipe Pricing ($/in/ft) Pipe Cost (M$) Cum Cost (M$) Beginning of Development to Main CSO Main CSO to McKinney CSO McKinney CSO to Ward Total Estimated Construction Cost with 30% Cont: $9.2 million

18 84-inch In-line Storage Alternative Additional option was added: Construct 84-inch replacement along entire length of development Provides conveyance sizing if Watershed Plan calls for conveyance but also provides 2.3 MG of in-line storage under current conditions for near-term benefit Provides flexibility in long-term Watershed Plan

19 Preliminary Alternatives Evaluation Advantage for local storage is that overflows are addressed on site and would achieve CSO compliance Disadvantage is that cost to store locally was prohibitively high and might not fit into Watershed Plan Potential sites for local storage were needed for development and was therefore not considered further Conveyance alternative only addressed moving peak flows downstream with no significant CSO reduction

20 84-inch In-line Storage Alternative Model Predicted Benefits: Scenario AREA CSO S TYPICAL YEAR VOLUME (MG) MODEL RESULTS MH Main St. CSO McKinney St. CSO Total Pre-Development With 84-inch Pipe Volume Reduction Percent Reduction 61% 87% 57% 68% Estimate downstream CSO volume increase is 3 MG Estimated Construction Cost with 40% Cont: $14.1 M

21 84-inch In-line Storage Alternative Analysis 84-inch sewer provides significant local reduction (68%) in overflow volume with minimal downstream increases Provides flexibility for conveyance option in future This option was selected for construction Developer agreed to pay for 31% of the total cost for a total savings of over $4.5 million! Final construction cost higher than earlier estimate due to local construction factors ($14.6 M) District cost was about $0.14 per gallon of CSO reduction

22 84-inch Sewer Design Design Challenges Joints leak resistant to 100-year flood elevation or up to 45-feet of water Corrosion resistant Withstand 35 of soil and groundwater loads Limit surge Prevent Ohio River intrusion 2 fps velocity during DWF Work within fixed upstream and downstream elevations Do not cause upstream flooding

23 84-inch Sewer Design Solutions Hobas CCFRPM pipe Watertight gasketed joint Corrosion resistant Fiberglass monolithic manhole risers Tideflex valves on outfalls Vents to discharge air when filling Surge Maintain inflow below conveyance capacity Surge model Upstream flooding Use model to evaluate backwater effects LF Manufacturing Hobas USA

24 84-inch Sewer Design Diversion Chambers New construction provided opportunity to construct new diversion structures to help meet Nine Minimum Control goals as part of the Consent Decree Design includes grit and floatables control in a single structure Hydraulic model used to assess hydraulics and performance of chambers an d to verify no flooding risk Inflow to interceptor had to be controlled to reduce chance for pocket surge Orifice into interceptor

25 84-inch Sewer Design Diversion Chambers

26 84-inch Sewer Construction Challenges Proximity to the Ohio River Groundwater rises and falls with the Ohio River Construction scheduled around river level probabilities using 36 years of level data Days per Year at or Above River Level Month Average Days above 30' Level (above 429.6) Groundwater problems at 30 January 15.0 February 17.0 March 23.0 April 19.0 May 13.0 June 6.0 July Days at or Above Level August 1.0 September 2.0 October 2.0 November 5.0 December 14.0

27 84-inch Sewer Construction Challenges Geotechnical Issues Pipe settlement due to additional load expected to be several inches which would significantly affect slope Much of the construction is in fill material which required over excavation in some places Slope stability problems concerns Long term Rapid drawdown Seismic Flexible pipe requires careful bedding and backfill to prevent excessive deflection

28 84-inch Sewer Construction Challenges Geotechnical Solutions Surcharge piles loaded 30 days before excavation to pre-load and force rapid settlement.

29 84-inch Sewer Construction Challenges Geotechnical Solutions Strict and careful installation procedures were put in place to ensure proper bedding and backfill Special bedding practices where over-excavated (burrito solution!)

30 84-inch Sewer Construction Challenges Ohio River Alignment within flood plain

31 Then Watershed Plans There are opportunities to utilize green infrastructure to reduce runoff to combined system. If implemented and effective, CSO volume would drop down to about 14.5 MG per year for an 87% reduction without additional gray controls based on model results With additional downstream controls, the overflow volume would drop to less than 1 MG per year or over 99% reduction

32 Overall Project Benefits Reduces overflow volume by 68% Saved over 30% in construction and more in design $0.14 per gallon of CSO removed Meets NMC for solids and floatables Grit removal protects downstream interceptor Prevents river intrusion and significant CSO overflow reduction Would meet presumptive level of control with implementation of green infrastructure Provides flexibility for future controls

33 Sean FitzGerald Brandon Vatter, Sanitation District No. 1 bvatter@sd1.org