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Westminster Blvd. Drinking Water Project

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What's Happening Now — Revised Draft Environmental Assessment Comment Period

Thank you to everyone who reviewed and provided comments on the revised draft environmental assessment (EA) report. The public comment period closed on February 28. The draft EAs can be found in the Documents section below.

Next, we will review all comments and incorporate them into the final EA where applicable. The final EA is anticipated to be published in the spring/summer of this year. Stay tuned for updates.

Project Summary

The City of Westminster is committed to providing affordable, high-quality water services. Semper and Northwest water treatment facilities currently supply more than nine billion gallons of clean and safe drinking water annually through over 500 miles of pipes to our residents and businesses.

The 54-year-old Semper Water Treatment Facility is nearing the end of its useful life and will soon need to be replaced. In 2015, the City began planning for a new water treatment facility to replace Semper.  Over the past two years, under City Council’s guidance, the City reevaluated the project and considered different options for the facility to better balance the community’s need for clean, safe, and affordable water after the community raised concerns about affordability.

The reevaluation focused on rightsizing the facility and associated infrastructure, which originally had an inflation-adjusted cost of over $300 million. As a thorough reevaluation, City Staff was able to reduce project cost by over $100 million, and City Council capped future rate adjustments to no more than 4.5% over the next decade. The approved Westminster Boulevard Drinking Water Project is a cost-effective, affordable solution with the flexibility to:

  • Replace aging infrastructure and expand if needed.
  • Respond to future state and federal clean water regulations.
  • Build additional treatment processes to respond to potential future wildfire contamination and emerging contaminants. 

Preliminary estimates for constructing the new facility are upwards of $200 million. This preliminary cost estimate ranges from -15% to +30%.  As design progresses, the estimate will become more certain and will be adjusted to market conditions and prevailing construction valuation.

The new facility will ensure the community continues to have clean, safe, and affordable drinking water for generations to come.

Map of Drinking Water Facility location

Click here for an ADA accessible PDF of the above photo

Graphic timeline

On April 24, 2023, City Council adopted Resolution 13, directing City staff to pursue the construction of a water treatment facility along Westminster Boulevard between 98th and 104th avenues. The project is currently in the planning, permitting, and design phase, with an expected 2028 completion date.

Associated Projects

The City is also working in conjunction with the following utility projects:

Water Supply Line 

A two-mile, 36-inch-wide waterline would transport untreated water from Standley Lake to the new treatment facility. The new water supply line would connect to the existing Standley Lake waterlines and would connect to the facility at the project site’s southern boundary.

Finished Waterline

A 30-inch-wide finished waterline would deliver clean, safe, and affordable drinking water from the facility to our community. The finished water pipeline would extend approximately one-third of a mile from the facility’s eastern boundary and connect to an existing water main.

Sewer Line

A sewer line would carry domestic wastewater from the facility to an existing sewer line located north of the project site. 


map of the future Westminster Boulevard Drinking Water Facility


Please do not hesitate to reach out to the project team, which can be reached by email at waterfacilityproject@westminsterco.gov or by phone at (720) 464-3435.

Thank you for your patience while we invest in our community!

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Community Advisory Team- Ongoing

Environmental Assessment — Fall 2023

What does a new treatment facility mean for my water rates? 

City Council incorporated the cost of the new water treatment plant when it approved the historic rate reductions last year. In order to provide immediate relief to rate payers, City Council adopted lower rates within the current three-tiered structure and increased the volumes allotted within each of those tiers in 2022. This significant rate reduction followed previous 10% water rate increases in both 2019 and 2020.  

City Council directed staff to better balance the need to maintain affordable water rates, while maintaining the City’s water system and ensuring the financial health of the water utility into the future.    

After extensive financial modeling, City Council adopted a 4.0% rate increase for 2023 and capped rate increases to no more than 4.5% for the next decade to balance the budget. These moderate rate increases over time support the defined 2023-2027 Capital Improvement Program including the right-sized water treatment plant while ensuring clean, safe, and affordable water for generations to come.



Westminster’s two drinking water treatment facilities, Semper and Northwest, provide water to the residents and businesses of Westminster, Federal Heights, and customers in unincorporated Jefferson and Adams counties. Semper provides drinking water for 75% of the City’s water demand and was built over 50 years ago, before current water treatment regulations were issued and modern technologies were developed. Northwest, built in 2001, has more modern water treatment technologies than Semper, and provides drinking water for 25% of the City’s water demand. 
The new water treatment facility will eventually replace Semper as it is phased out in the next two decades.
The facility site will have sufficient space to expand as water treatment processes and infrastructure are due for replacement. This phased approach is a financially responsible way to maintain and replace Westminster’s drinking water treatment infrastructure and will allow the City to keep the newer portions of Semper operational for the duration of its useable life. 

Over the past few years, under City Council’s guidance, the City reevaluated optionsfor Westminster’s new water treatment facility to better balance the need forclean, safe, and affordable water. This reevaluation focused on rightsizing thefacility and associated infrastructure, which originally had aninflation-adjusted cost of over $300 million. Reducing the size of the facilityand leaving room for future expansion reduces the projected cost, potentiallysaving ratepayers more than $100 million. The new facility will allow agingparts of Semper to be retired while continuing to use viable components as long as reasonable to maximize the value of thoseinvestments. This will allow a phased approach to replacing Semper.

The near- and long-term fiscal plan for the water utility currently includes up to 4.5% rate adjustments each year. These adjustments support the operations and maintenance of the system, debt service obligations, and the defined 2024-2028 Capital Improvement Plan. This plan includes a new water treatment facility and other important repair and replacement infrastructure projects to ensure clean, safe, and affordable drinking water for generations to come. 

We continue to explore what the new facility will look like. We will work closely with a community advisory team and provide the community with opportunities to share opinions during future online and in-person open houses.  

The project team is comprised of a few different consultants:

  • CDM Smith: Drinking Water Facility Design
  • Olsson: Environmental Assessment
  • Burns and McDonnell: Water Supply Line Design
  • HDR: Community Outreach and Communications, Site Selection, and Modeling
  • Hazen: Drinking Water Facility Process Design
  • McCarthy: Drinking Water Facility Construction Manager, Cost Estimating and Cost Efficiency

After the City identified the need for a new drinking water facility, a site selection alternatives analysis was conducted to evaluate sites suitable for construction of a new facility. The site selection process identified more than 50 sites for initial consideration. The initial site list was narrowed to nine using three categories of evaluation criteria: 

  1. Community
  2. Engineering
  3. Site characteristics

    The next phase of the process further reduced the list to three recommended sites. After further consideration, the site at 98th Avenue and Westminster Boulevard was selected. 

    The new facility is not anticipated to have any strong odors associated with it as it is an indoor facility dedicated to treating drinking water. It is not a wastewater facility. 
    The dewatering basins on the north side of the property are not expected to generate any sulfur odors during normal operations. The solids that accumulate in the basins will be periodically removed usually after a freeze/thaw, draining/drying cycle over the winter.

    Final design is not yet complete. The current draft design of the drinking water facility (60%) shows building heights ranging from 11.3 to 49.4 feet tall with an average height of 23.8 feet. The tallest building would be the two-story process building. The water tank is designed to be on the ground, not an elevated water tower.

    The finished waterline is sized to exceed the water treatment capacity for phase 1. An additional finished waterline will be built as new water treatment trains come online in the future. This will help create reliability in the water system and make the system more dependable in the event of water main breaks or other issues that can arise unexpectedly. 

    There will be dewatering basins on the northwest area of the property that will be filled and emptied on a cycle. Mosquito problems are not anticipated, but they will be mitigated if they occur.

    Common milestones for construction projects are 30%, 60%, and 90% design. These indicate the level of design that has been completed to that point and are often opportunities for public or community input.  
    • 30% design – Very high-level design with major project elements defined. The project team is determining any fatal flaws, defining the scope of the project, and refining the cost estimate.  
    • 60% design – Designs of major project components are completed and refined following input from the 30% milestone. The design team confirms that the plans and specifications will meet project objectives.  
    • 90% design – Details and concepts are refined following input from the 60% milestone. This is often considered final design and all that usually remains is ensuring permits are in place prior to construction beginning.