seven corners tank replacement
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Seven Corners Tank
Replacement
Council Work Session
City of Falls Church
January 17, 2017
Seven Corners Tank Replacement
Why is a new tank needed?
What alternatives have been
considered?
What are the benefits of a
new tank?
Next steps
Seven Corners TankWillston Tank
Seven Corners Area Water Service
Willston Pumping Station
Former City of Falls Church Water Service Area
Water Pressure in Seven Corners Area
History of low pressures
History of insufficient storage
Some areas of low fire flow
Some small projects implemented in effort to improve pressure to some areas
Prior recommendations consistently recommended higher hydraulic gradeline (and by definition taller tank)
Replace Seven Corners Tank to match Willston (approx. 50 feet taller)
Expand the Willston zone and construct a new tank
Water Quality in Seven Corners Area
Recurring issues with maintaining a chlorine residual in distribution system
Several operational changes implemented to mitigate but problems persist
Issues a direct result of water age in Seven Corners tank
Water age is a direct result of hydraulic limitations of the Seven Corners tank
Additional Challenges
Insufficient storage in Willston zone for current
demands
Identified in 1997 Master Plan and subsequent
studies
Previous CIP’s planned to address
Challenges with land acquisition for new tank site
Storage, fire flow and pressure issues will be
exacerbated with proposed redevelopment
Seven Corners Tank
Redevelopment in Seven Corners Area
What has changed?
Able to more comprehensively address pressure and water quality issues in Seven Corners area
Review issues/challenges in perspective of larger system integration
Eliminate large “dead end” configuration of Seven Corners area
Raise the target service pressure for high ground areas
Larger customer base to support needed system improvements
Fairfax Water’s Recommendation
Replace Seven Corners tank with a taller tank on existing site
Create new, higher pressure zone to encompass existing Seven Corners and Willston
Construct a pumping station in base of tank
Eliminate Willston Tank and Pumping Station
Reduce long term maintenance expenses through consolidation of facilities
Eliminate “dead-end” configuration of Seven Corners area distribution system
Seven Corners Tank Replacement
1.25 MG of storage
Pumping station within tank
base
Est. cost: $10.75 Million
Increase service pressures by 10
to 25+ psi
Improve fire flows
Address water quality concerns
Support redevelopment of area
Seven Corners Tank Replacement
Fairfax Water owns the land
Site has been used for water storage since 1961
Site is centrally located within area it will serve
Minimizes improvements to transmission system
to supply the tank
Required easements for construction are
temporary in nature
Alternatives Considered
Conversion of Seven Corners tank to pumped
storage
Replacement of Willston tank
Construct new tank on Fire Station property
Construct new tank on School property
Conversion of Seven Corners to
Pumped Storage Cannot be accomplished on
existing site
Requires acquisition of additional land resulting in permanent impacts to adjacent property(ies)
Eden Center, Cemetery, Koons
Requires additional transmission mains
Creates operational/water quality issues elsewhere in the system
Excluding land acquisition, estimated cost of $14.4 Million
Existing Seven Corners Tank Site
Required Water Main
Construct New Willston Tank
Requires land acquisition (cost unknown) Existing site unable to accommodate a larger tank
No available vacant parcels
Requires construction of new tank ($8.5 Million)
Requires new pumping station ($5.2 Million) Located on existing Seven Corners site
Existing Willston PS and easement too small
Requires additional transmission ($2.3 Million)
Excluding land acquisition estimated cost of $15.9 Million
Existing tank Site
Site previously Identified for new tank
Willston Tank Alternative
Additional Required Transmission for Willston
New Pumping Station4,500 linear feet of 24-inch water main
New Willston Tank
County School and Fire Station Sites
Seven Corners Fire Station
Bailey’s Upper Elementary School
County Sites
Not owned by Fairfax Water
Fully utilized or plans to expand
– no room for a tank
Tank at Fire Station would have
to be 25 feet taller than Seven
Corners
Sites would require additional
transmission mains
Seven Corners Fire Station
Baileys Upper Elementary
Fairfax Water’s Proposed
Replacement of Seven Corners Tank Least cost alternative at $10.75 Million
Improves service for existing customers in Seven Corners and Willston areas Addresses long-standing pressure issues in Seven Corners area
Addresses long-standing storage deficiency in Willston pressure zone
Addresses water quality issues
Provides storage capacity and pressure to support contemplated redevelopment
Least construction disturbance to community
Consolidates number of water facilities required to provide service – improves operational efficiency
Only alternative that does not require permanent land acquisition on private property
Customers Benefitting from Proposed Tank
Hydrant Fire Flow Improvements with New Tank
Proposed Seven Corners Tank
Tysons TankProposed Seven Corners Tank
Tysons Central Development
KOONS
EDEN CENTER
Temporary Construction Easement
Pedestal
Bowl
OAKWOOD CEMETERY
COW
Existing Tank
Next Steps
City consideration of zoning code amendment to allow for consideration of Seven Corners tank replacement
Continue discussions with adjacent property owners
Easement negotiation/acquisition
Continue discussions with City staff regarding temporary arrangements for City radio
Develop preliminary design drawings for applications to City and conduct community meetings
Questions?
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