To: Members of the Castle Rock Water Commission
From: Mark Marlowe, P.E., Director of Castle Rock Water
Josh Hansen, CIP Project Manager/ Engineering
Title
Tank 18 Project Update [Liberty Village Subdivision]
Town Council Agenda Date: December 21, 2021
Body
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Executive Summary
The purpose of this memo is to summarize historical info and recent progress on the Tank 18 Project (also known as Liberty Village Yellow Zone Tank). Tank 18 was previously designed in 2013 and bid for construction in 2014. Bid prices were significantly over budget at the time and construction of the project was deferred. Since that time the majority of homes in the Liberty Village/Cobblestone Ranch Development have been constructed and the tank project has been fully funded by tap fees. The tank is needed for water supply for the development and to help buffer high pressure events in the distribution system. Castle Rock Water included construction funds in the 2021 budget and has been working on updating construction documents and regulatory approvals for the project. Staff anticipates bidding construction of the project in December 2021.
Discussion
The Liberty Village/Cobblestone Ranch Development on the far northeastern edge of Town, is zoned for 1,245 single family equivalents (SFEs), although the development agreement (DA) discusses 1,500 SFEs. Per the DA, the Town, “in order to fully integrate the water system constructed by the Owner with the Town’s municipal water system”, intended to construct a storage tank and related infrastructure to serve the property at full buildout. The tank project was to be financed and constructed by the Town by reliance on the Owner to purchase water system development fees. The DA further stipulated that should the Town determine that equivalent water services may be provided in lieu of development of the Water Tank the Town could apply revenues received to construct such alternate infrastructure.
Water system development fees are currently $4,030 per SFE. The development is rapidly approaching construction build-out of the 1,245 zoned SFE’s which means that roughly $4 to $5 Million has been collected in water system tap fees which has fully funded the new tank. The area is currently served by a single 16-inch pipeline from the Castle Oaks area (See Attachment A), with stored water from two existing red zone tanks. The water is fed down into the area through a series of pressure reducing valves (PRVs) that reduce the red zone supply pressure down to blue pressure then to yellow zone pressure to service the area. The two red zone tanks have a combined operational storage volume of 5.1 million gallons and sufficient existing storage capacity to meet operational storage needs of Liberty Village. However, the storage from these tanks is delivered to the development by the single 16-inch pipeline. The single feed connection through multiple pressure zones is the primary reason a storage tank is needed.
Several years ago one of the PRVs serving the area failed and the resultant high pressure caused a rupture in the pipeline. This resulted in a temporary loss of water service for the entire development. Subsequently, Castle Rock Water installed pressure relief devices on the PRVs so that in the case of a high pressure event, the PRVs would dump water to relieve downstream pressure. Staff also completed an emergency interconnect waterline to the Pinery Water and Sanitation District system. This provided an immediate interim solution for a second source of water in an emergency situation.
The long term solution to a secondary supply of water is a storage tank serving the development. An advantage of a storage tank in the area is that the tank can act as a “damper” in high pressure events to mitigate pipeline rupture risks. Shortly after the high pressure pipeline event, staff started planning the Tank 18 project.
In 2013, Castle Rock Water engaged Bates Engineering to design a new 2 million-gallon potable water tank to support the Liberty Village Development. Staff subsequently bid construction of the project in early 2014. Bid pricing came in significantly higher than what was budgeted for the project and staff elected to defer construction of the tank. The primary reasons for deferring tank construction at that time included;
• Insufficient project funding - limited number of water system tap fees had been collected
• Water quality concerns due to low demand from limited number of homes constructed
• Redundant storage and supply available to meet existing development demands at the time
As of 2021, a significant portion of Liberty Village has been built out which has increased water demand from the area. Sufficient funding has been collected from tap fees and redundant supply from the tank is now needed to mitigate risk from the single waterline serving the development. As such, staff has been working with Bates Engineering to update contract documents to the latest standards. Staff has submitted design documents to the Colorado Department of Public Health and Environment for approval and is working through final review comments with the department.
A request for contractor qualifications was published on the Rocky Mountain E-Purchasing System in late October and statements of qualifications were received from 9 contractors. Staff has evaluated qualifications and reduced the list to approximately 5 that will receive bid documents. Final bid documents are being drafted and staff anticipates bidding the project in December with construction in 2022.
Staff is also working on design of a new 16-inch waterline that will connect the tank to the existing 16-inch pipeline in Castle Oaks Drive. This project will be constructed in 2022 prior to completion of Tank 18 so the tank can be filled and tested upon completion. Per the DA agreement, the Liberty Village Developer is responsible for construction of a 16-inch yellow zone waterline that will connect Tank 18 to the Liberty Village distribution system to put the tank into service. This project will be constructed in a similar timeframe.
Budget Impact
Recent construction costs for post-tensioned concrete water tanks in the Denver Metro area have trended towards $2 per gallon. Construction costs for Tank 18 are anticipated to be in the range of $3.5 to $4 Million. $3.85 Million was included in the 2021 budget for the project.
Attachments
Attachment A: Site Location Map