To: Members of the Castle Rock Water Commission
From:
Mark Marlowe, P.E., Director of Castle Rock Water
Title
Resolution Approving a Construction Contract between the Town of Castle Rock and C&L Water Solutions for Woodlands Sewer Interceptor Manhole Rehabilitation
Town Council Agenda Date: March 3, 2020
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.
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 at the upstream end of the Woodlands Interceptor has been detained in the sanitary 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 resistive 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 fully 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 and ranged from $189,950 to $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. The specific FRP insert product in the proposal carries a 50-year manufacturer’s warranty. 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.
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.
Public Outreach
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.
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 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 recommend to Town Council approval of the above Resolution as presented”
Attachments
Attachment A: Resolution
Exhibit 1: Construction Contract
Attachment B: Site Location Map