To: Honorable Mayor and Members of Town Council
From: Mark Marlowe, P.E., Director of Castle Rock Water
Title
Resolution Approving a Construction Contract with C&L Water Solutions, Inc. for the Woodlands Sewer Interceptor Manhole Rehabilitation Project
Body
________________________________________________________________________________
Executive Summary
Castle Rock Water is seeking Town Council approval of a resolution (Attachment A) approving a construction contract (Exhibit 1) in the amount of $403,370.50 with C&L Water Solutions (C&L), along with $40,400 (10%) staff-managed contingency, for a total authorization of $443,770.50 for the Woodlands Sewer Interceptor Manhole Rehabilitation.
Castle Rock Water Staff identified 7 corroded concrete manholes on the Woodlands Sewer Interceptor for rehabilitation in 2020. A request for proposals was published on the Rocky Mountain E-Purchasing System in December 2019. Three proposals for manhole rehabilitation were received in response to the advertisement. Staff rated C&L’s proposal the highest, and the rehabilitation technique and products proposed will meet the project’s objectives. C&L’s proposal represents the best long-term value to the Town. Construction is anticipated for the summer of 2020.
Notification and Outreach Efforts
The Woodlands Sewer Interceptor manholes selected for rehabilitation are in close proximity to
residential properties in the Woodlands Development. There has been a history of sewer odor related complaints from adjacent residents. Castle Rock Water will notify adjacent property owners with information about the project and conduct an open house to discuss the project in greater detail.
Performing this rehabilitation work will result in some odors during construction. By diverting flow around the manholes being rehabilitated, the source of the odor will be removed from the immediate area and the existing odor control facility will continue to operate during construction. This project will be an inconvenience to the immediate neighbors as well as to residents who use the path that parallels the sewer. The path will be closed during construction and CR Water will coordinate with the Parks Department for the closure. Communication with the neighborhood will be an ongoing program before and during the project. We expect there will be odor complaints during construction and we will do our best to address those on a case-by-case basis.
History of Past Town Council, Boards & Commissions, or Other Discussions
Castle Rock Water staff presented this resolution to the Castle Rock Water Commission at their February 26, 2020 meeting, and the Commission voted unanimously at a vote of 5 to 0 to recommend approval of the resolution to Town Council.
Discussion
The Woodlands Sewer Interceptor is a 2.5-mile gravity pipeline installed in 1987 that conveys
wastewater flows from development areas east of Founders Parkway/Ridge Road (Founders Village, Castle Oaks/Terrain, Castlewood Ranch, Bella Mesa), as well as the Woodlands development, back to the Plum Creek Interceptor. A significant portion of the Town’s wastewater flows through the interceptor pipeline. The interceptor is a critical component of the Town’s wastewater collection system.
Wastewater from areas east of Founders Parkway/Ridge Road are pumped uphill to the Woodlands Interceptor through long pressurized force main pipelines from various lift stations operated by Castle Rock Water. The two primary force mains (Castle Oaks and Mitchell Creek) are both greater than 2 miles in length. Some of the wastewater conveyed through these force mains has been previously conveyed by other smaller force mains. Wastewater flows by gravity to lift station wet wells where it is detained before being pumped through force mains. Thus, the majority of wastewater arriving has been in the collection system for a significant period of time. As wastewater is detained in a sanitary collection system and when it is pumped through long force mains, oxygen levels are depleted and anaerobic bacteria are proliferated. The increase in anaerobic bacteria ultimately leads to the production of hydrogen sulfide gas in the collection system. Hydrogen sulfide gas is the most common cause of odor complaints related to wastewater collection systems and is also responsible for 99 percent of all sewer corrosion. Both of these have historically been issues for the Woodlands Sewer Interceptor.
The Woodlands Interceptor pipeline itself is constructed of polyvinyl chloride (PVC) which is highly resistant to the corrosive effects of sulfuric acid produced by hydrogen sulfide consuming bacteria in the system. Thus the interceptor pipeline itself is in good shape. However, the concrete manholes between pipe sections have not been as fortunate. Concrete and many metals are extremely susceptible to the corrosive effects of sulfuric acid. The high levels of hydrogen sulfide present in the Woodlands interceptor have led to severe corrosion of the concrete manholes. Recent inspections by Castle Rock Water staff have discovered deterioration of several inches of concrete from the manhole wall sections. This degrades the overall strength of the manhole structure and can lead to an eventual collapse of the manhole. There are seven manholes in the upper portion of the Woodlands Interceptor that appear to have high levels of concrete degradation. These manholes were selected as the most critical and targeted by Castle Rock Water for rehabilitation in 2020.
There are many different products and techniques employed in the rehabilitation of concrete manholes. Because of the high level of concrete degradation, Castle Rock Water decided to pursue full structural rehabilitation methods for the manholes selected. A request for proposals (RFP) for rehabilitation of the 7 Woodlands Interceptor manholes was published on the Rocky Mountain E- Purchasing System in December of 2019. Because of the variety of rehabilitation techniques available, a bid schedule with unit quantities was not included with the RFP. Instead, respondents were asked to provide proposed rehabilitation techniques and products along with a corresponding schedule of values that would be evaluated by Town staff on a value basis in meeting the project’s objectives.
Proposals were received from three contractors with prices of $189,950, $221,397.50 and $403,370.50. Staff rated the three proposals independently of proposed costs. The proposal from C&L Water Solutions was unanimously rated higher than proposals from the other vendors and was the only proposal that fully met the Town’s objectives for the project. C&L’s proposed rehabilitation method involves installation of fiberglass reinforced polymer (FRP) manhole “inserts” that are placed within the existing degraded sewer manhole. The advantage of this rehabilitation method is that the majority of the existing concrete manhole is replaced with an FRP manhole in its existing location with minimal removal of the existing degraded manhole. This minimizes the amount of overall excavation and corresponding construction footprint. The base of the existing manhole must be reconstructed and the top cone section removed before the FRP manhole with integral cone section is inserted within the existing failed manhole. The end result is a new FRP manhole constructed within the existing manhole. The FRP manhole is structurally rated to withstand all anticipated loads (independent of the remaining existing manhole) and has the advantage of being impervious to corrosion from sulfuric acid resulting from hydrogen sulfide. C&L has successfully installed over 150 manhole inserts for other major entities in the Denver/Metro area. C&L’s proposal represents the highest initial capital cost but staff is of the opinion that the inserts will provide the best long-term solution resulting in the lowest life cycle cost for this critical infrastructure.
The lowest cost proposal approach would involve demolition and removal of existing failing manhole liners and build back of the existing manhole concrete structure with cementitious materials before placement of a cured-in-place manhole liner. This manhole build back approach requires significant preparation including high pressure water blasting to remove the corroded concrete from the existing manhole walls. Due to the extreme levels of existing concrete degradation observed in these manholes, staff is of the opinion that this approach could involve a significant level of construction risk as well as unknown long term life expectancy. The median cost proposal approach recommended the installation of manhole inserts. However, the proposal did not include specific details or product recommendations for the manhole inserts. The contractor’s total experience in this type of manhole rehabilitation is installation of 3 manhole inserts. These inserts appear to have been installed on a sample/demonstration basis for potential future projects. The lack of contractor experience in the proposed rehabilitation method as well as the lack of product information and details presented in the proposal did not give staff confidence to pursue this proposal further.
C&L will begin the work in March with more detailed “manned entry” inspections of the 7 manholes.
This will provide specific measurements needed for fabrication of the FRP inserts as well as any adjustments to the scope of work that could be needed due to findings. Construction duration is approximately 2 months and anticipated for summer 2020. Rehabilitation of the manholes must occur with the line under service and Caste Rock Water staff is working with C&L on a plan to manage wastewater flows during construction.
Budget Impact
Funding for this project will come from the Sewer Line Rehab budget. A first quarter budget amendment of $475,000 has been requested to accommodate other anticipated 2020 projects.
|
Project |
Account Number |
2020 Budget |
2020 Amended Budget |
This Authorization |
|
Sewer Line Rehab |
213-4575-445.75-62 |
$500,000 |
$ 975,000 |
$443,770.50 |
Staff Recommendation
Staff requests Council approval of a construction contract in the amount of $403,370.50 with C&L
Water Solutions, along with contingency of $40,400, resulting in a total project authorization of
$443,770.50 for the Woodlands Sewer Interceptor Manhole Rehabilitation Project.
Proposed Motion
“I move to approve the Resolution as introduced by title.”
Attachments
Attachment A: Resolution
Exhibit 1: Construction Contract
Attachment B: Site Location Map