Collection System

The collection system conveys wastewater from Metro’s connectors for treatment.

The collection system conveys raw wastewater for treatment. An interceptor sewer carries wastewater directly to the treatment facility or to another interceptor. Individual connectors maintain their systems and Metro Water Recovery typically takes ownership of the collection system when an interceptor segment carries more than one connector’s flow. The flow and loadings are metered at the transition of each connector’s systems to Metro’s system. The majority of Metro’s service area and collection system are serviced by gravity flow interceptors with lift station facilities where gravity flow is not possible. There is no treatment associated with the collection system, but there are opportunities to utilize the fairly stable temperatures within the collection system for heat recovery and heat rejection.

Metro Water Recovery’s service area

Metro’s service area covers approximately 715-square miles including Denver, Arvada, Aurora, Brighton, Lakewood, Thornton, Westminster and portions of Adams, Weld, Arapahoe, Douglas, and Jefferson counties. The service area is divided into seven drainage basins summarized in the table below.

Drainage BasinsTributary Treatment Facility
Central Denver NorthRWHTF
Central Denver SouthRWHTF
Cherry CreekRWHTF
Clear CreekRWHTF
Lower South PlatteRWHTF
Sand CreekRWHTF
South PlatteNTP

The South Platte basin

Prior to construction and startup of the NTP, the South Platte basin was formerly part of the Lower South Platte basin. The northern portion of the Lower South Platte basin was redefined when the South Platte Interceptor was created, which now sends flows to the NTP. The South Platte basin will be expanded following the construction of the Second Creek Interceptor. All of the flow from the Second Creek Interceptor will be treated at the NTP.

The facilities comprising the Metro Water Recovery Transmission System include:
  • 43 Interceptors
  • 234 miles of gravity pipe (8-inch to 90-inch diameter)
  • 30 siphon structures
  • 106 metering facilities
  • 111 diversion structures
  • 3,708 manholes
  • Three lift stations and three miles of force mains
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Diversion Structures

The diversion structures located throughout Metro’s Collection System are used for two purposes:

  1. Temporary flow diversions to perform line cleaning, physical and closed-circuit television inspections, maintenance, and construction
  2. Flow control between parallel or relief interceptors

All of the 111 diversion structures in the Transmission System use stop logs to regulate flow. Stop log height is varied to achieve the desired flow split between pipes.

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Flow Metering Facilities

Metro uses flow metering facilities throughout the Transmission System to support the Annual Charge program and monitor interceptor flows, perform capacity evaluations, and support operations and maintenance needs. The data from these flow meters is also used to calibrate Metro’s Transmission System hydraulic model. Flow meters record flow on a short-term or continuous basis. Metro typically uses flumes (Parshall, Cutthroat, or Palmer Bowlus) to meter flow for gravity interceptors. Magnetic meters are used for pressurized pipes (force mains).

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Annual Charge Program

Metro is considered to be a wholesale wastewater treatment provider. This means Metro does not directly bill residents or businesses. Instead, as defined by section 4 of Metro Water Recovery’s Rules and Regulations, Metro bills its connectors based on how much flow they send to the two plants and the contents of the flow (loadings). Annual charges are assessed annually to all of Metro’s connectors to cover the operating costs, debt service, and capital needs of Metro. Annual charges account for 75% of Metro’s total revenue in any given year.

The Environmental Services Sampling Team (EST) within the Environmental Services Department is responsible for collecting Annual Charge (AC) wastewater samples, for measuring flow, and for maintaining the associated equipment. The AC sampling schedule is developed annually to assure representative flow metering and sample collection. 

Frequency of the sampling is based on the customer category established in R&R Section 4. Customer categories with higher flow and/or more variable pollutant loadings are monitored more frequently than categories with lesser contributions. The AC Sampling is conducted during the work week, throughout the weekends, and on holidays.

There are approximately 100 annual charge stations throughout the collection system. Each station is classified into a group (A-E) based on the amount of flow and loadings that are expected. The loadings are categorized by analytical data of TSS (Total Suspended Solids), BOD (Biological Oxygen Demand), and TKN (Total Kjeldahl Nitrogen).

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Capital Investments

PAR 1232 – Second Creek Interceptor

2014-2024 Investment: $194.3M

Construction of a new 17-mile interceptor to serve a new service area and portions of the Sand Creek basin, conveying flows to the NTP.

PAR 1312 – Thornton North Washington Fixed Asset Replacement

2017-2025 Investment: $41.7M

Construction of a new lift station serving the South Thornton and North Washington interceptors prior to treatment at the RWHTF to replace the existing Thornton-North Washington Lift Station that has reached the end of useful life.

PAR 1325 – Diversions and Metering Facilities Grating Condition Assessment and Improvements

2017-2022 Investment: $4M

Evaluate the condition of grating in Transmission System structures and recommend a replacement schedule.

PAR 1340 – Force Main and Siphon Condition Assessment and Cleaning

2018-2023 Investment: $6.9M

Evaluate the condition of force mains and inverted siphons in the Transmission System and provide cleaning and rehabilitation.

PAR 1343 – National Western Center (NWC) Delgany Interceptor Relocation

2018-2022 Investment: $9.2M

Relocate the Delgany and Delgany Common interceptors below grade to connect the redeveloped National Western Center (NWC) with the South Platte River and provide connections for a heat recovery/rejection system operated by the NWC.

PAR 1363 – Interceptor Rehabilitation 2020-2022

2020-2023 Investment: $35.8M

Rehabilitate segments of Transmission System interceptors and manholes and underground conduits at the RWHTF identified as high priority.

Innovations

Corrosion resistant materials (piping, manholes and covers, concrete products, etc.)
Resource Recovery

During the Delgany Interceptor relocation which occurred at the National Western Center (NWC) under PAR 1343, the development included a system designed to extract the thermal energy of the wastewater to provide heating to the development in the winter months. This reduces thermal pollution while offering a sustainable heat source. During summer months, the wastewater is used as a heat sink, reducing the carbon footprint for HVAC.

Capital Investments (15 years)

Projects are based on the current anticipated regulatory requirements but are subject to change without notice. Projects are planned and are subject to change without notice including the cost estimates.

Fort Lupton Connection

No cost 2022-2027

Oversight of the Fort Lupton force main connection to the NTP.

Delgany Interceptor System Odor Control Facility

2023-2024 Investment: $1.7M

Construction of an odor control facility at the National Western Center (NWC) heat recovery/rejection system.

Future Structure Rehabilitation

2024-2025 Investment: $2.5M

Rehabilitate structures within the Transmission identified as high priority.

Future Interceptor Rehabilitation

2024-2037 Investment: $61.3M

Rehabilitate segments of Transmission System interceptors and manholes identified as high priority.

Transmission System Odor Control Facilities

2028-2029 Investment: $4.3M

Construct new odor control facilities in the Transmission System.

Sand Creek Interceptor System Improvements

2033-2037 Investment: $55M

Rehabilitate the Sand Creek and Sand Creek Parallel interceptors and manholes connecting to the RWHTF.

Innovations

Resource Recovery

Metro is working to expand the use of wastewater thermal energy as a sustainable part of development in the region while reducing thermal pollution.

Treatment Process Map