sanitation district no. 1 of northern kentucky · sanitation district no. 1 of northern kentucky....
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Sanitation District No.1 Cost Effectively Reduces Overflows Into the Ohio River
Ohio WEA Collection Systems Workshop
May 5, 2011
Sanitation District No. 1 of Northern Kentucky
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
• Total service area ~ 200 sq miles
• >1,600 miles of sewers
• >42,000 manholes
• 2 regional WWTP
Sanitation District No. 1 of Northern Kentucky
Sanitation District No. 1 of Northern KentuckyCombined 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
Watershed Consent Decree•In October 2005 Sanitation District No. 1 negotiated a Watershed Consent Decree
– CSOs into compliance with CSO Policy by 2025
– Eliminate sanitary sewer overflows by 2025
– Improve water quality
•Develop Watershed Plans every five years that can address all sources of pollution
•Outcome: affordable combination of gray, green, and watershed controls to improve water quality
Watershed Partners
Regulatory Assistance
Public Outreach Strategic Advisory Team
PRIORITIZECONTROLS
IMPLEMENTCONTROLS
PlansRegulatory ApprovalPublic Input
WATERSHED PLANNING
INFRASTRUCTURE PLANNING and COMPLIANCE
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
Main St. CSOMcKinney
St. CSO
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 (6th and 7th largest in terms of annual overflow volume) within the development boundaries
Fill boundary
McKinney Outfall
Main St. Outfall
River’s Edge Project BackgroundCurrent Topography
MH Depth 15 ft
32 ft to levee top
Flood Levee
Ohio River
Future Depth 37 ft
10 ft to levee top
River’s Edge Project BackgroundPost-Development Topography
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 “design-build”
• There would be significant “opportunity cost” to come back later to do significant construction
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
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 2100 21" 2.8 15
Main CSO to McKinney CSO 3110 27" 6.5 48
McKinney CSO to End of Development 1900 27" 6.0 93
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
96-inch McKinney St. Outfall
72-inch McKinney St. Outfall
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
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.
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
McKinney St. Outfall
Main St. Outfall
Potential Storage Locations
Potential Storage Locations
Storage Sizing and Preliminary Construction Costs
Interceptor Conveyance For Local Storage Option
LocationPeak Flow
(MGD)
Length (ft)
Diameter (in)
Pipe Pricing ($/in/ft)
Pipe Cost (M$)
Cumulative Cost (M$)
Beginning of Development to Main CSO 15 2080 36 15 1.1 1.1
Main CSO to McKinney CSO 17 3010 42 15 1.9 3.0
McKinney CSO to Ward 19 2640 48 15 1.9 4.9
Local Storage (Typical Year Level of Control)
Location Tank Volume (MG) Tank Pricing ($/gal) Tank Cost (M$)
Main Street 3.1 5.4 16.7
McKinney Street 3.8 4.9 18.6
Total Estimated Construction Cost with 30% Cont: $44.3 million
• Typical Year Analysis - Wet Weather Options for Conveyance of All Peak Flows
• Does NOT account for additional downstream conveyance and/or storage
River's Edge Conveyance Sizing (Typical Year Level of Control)
Location Peak Flow (MGD)
Length (ft)
Diameter (in)
Pipe Pricing ($/in/ft)
Pipe Cost (M$)
Cum Cost (M$)
Beginning of Development to Main CSO 15 2080 36 15 1.1 1.1
Main CSO to McKinney CSO 48 3010 60 15 2.7 3.8
McKinney CSO to Ward 93 2640 84 15 3.3 7.1
Conveyance Sizing and Preliminary Construction Costs
Total Estimated Construction Cost with 30% Cont: $9.2 million
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
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
84-inch In-line Storage Alternative
Model Predicted Benefits:AREA CSO’S TYPICAL YEAR VOLUME
(MG) – MODEL RESULTS
Scenario MH 0360018 Main St. CSO McKinney St.
CSO Total
Pre-Development 7.9 41.7 64.8 114.4
With 84-inch Pipe 3.1 5.5 27.8 36.4
Volume Reduction 4.8 36.2 37.0 78
Percent Reduction 61% 87% 57% 68%
• Estimate downstream CSO volume increase is 3 MG• Estimated Construction Cost with 40% Cont: $14.1 M
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
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
84-inch Sewer DesignSolutions• 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
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
84-inch Sewer Design – Diversion Chambers
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 dataDays per Year at or Above River Level
202224262830323436384042444648505254565860
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300
Days at or Above Level
Leve
l (ab
ove
429.
6)
MonthAverage Days
above 30'
January 15.0
February 17.0
March 23.0
April 19.0
May 13.0
June 6.0
July 2.0
August 1.0
September 2.0
October 2.0
November 5.0
December 14.0
Groundwater problems at 30’
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
84-inch Sewer Construction Challenges
Geotechnical Solutions• Surcharge piles loaded 30 days before excavation to pre-load
and force rapid settlement.
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!)
84-inch Sewer Construction Challenges
Ohio River• Alignment within flood plain
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
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
Sean FitzGerald
Brandon Vatter, Sanitation District No. 1