Waterwater at ERWSDThe United States didn’t establish basic techniques of wastewater collection until the end of the 19th century.  The catalysts for centralized wastewater collection systems were significant population increases in urban areas and the emergence of diseases resulting from improper sewage disposal and management.  However, wastewater treatment was essentially absent at that time, so collection systems merely transferred the nuisances and public health risks of sewage to adjacent waterways and downstream riparian residents.  Wastewater treatment was in place, however, by the mid 1920s in conjunction with the Progressive Movement in the United States. This movement advocated the protection of natural resources, including water quality.

Presently, the Clean Water Act (CWA) addresses surface water quality protection in the United States.  The CWA employs a variety of regulatory and non-regulatory tools to minimize direct pollutant discharges into waterways. More broadly, the CWA aims to restore and maintain the chemical, physical, and biological integrity of the Nation’s waters so they can support “the protection and propagation of fish, shellfish, and wildlife and recreation in and on the water.”   The CWA authorizes the National Pollution Discharge Elimination System Permit Program, which controls water pollution by regulating point source dischargers, like wastewater treatment plants that discharge pollutants into U.S. waters.  Since its introduction in 1972, this Program has made significant improvements to our nation’s water quality.

Most homeowners are familiar with the in-home portion of the water cycle, which includes the plumbing fixtures and pipe networks.  However, many are unfamiliar with what happens to waste materials after they are flushed or washed down the drain.  Wastewater ultimately becomes part of the freshwater supply after a series of treatment steps. This water is eventually used downstream by people, aquatic life, and wildlife, so it must be treated before its release back into the receiving streams. Wastewater primarily originates from sinks, tubs, toilets, washing machines and dishwashers that are found in homes and businesses and is conveyed via a collection system.  Wastewater treatment facilities (WWTF) are designed to remove organic material, nutrients, and disease-causing organisms prior to effluent being released back into natural water bodies.

Wastewater treatment technology has improved greatly since the late 1800s. The District is dedicated to the design and implementation of the best treatment technologies to serve the community and protect water quality.   The District is aware that preventing water quality degradation is the most effective approach to water quality management.  The District operates three WWTFs. These facilities are located in Vail, Avon, and Edwards.  Each WWTF has unique features and treatment processes which are described in more detail on the wastewater treatment process tab below.

Treatment Process

The Eagle River Water and Sanitation District Wastewater Treatment Facilities (WWTFs) use four stages of treatment: Preliminary, Primary, Secondary and Disinfection. The final product of the wastewater treatment process is an effluent discharge that is typically cleaner than what is required by the Clean Water Act. The solids extracted during the treatment process are converted to biosolids which can be used as a soil amendment for certain land applications. Additionally, the District WWTFs have state-of-the-art odor control systems for treating odors produced during the treatment process. A brief summary of the wastewater, solids handling and odor control treatment processes follows.

Preliminary Treatment

Screening involves the removal of large objects from wastewater such as cans, bottles, sticks and plastics. These materials need to be removed because they can plug pipes, damage pumps and consume valuable treatment tank space. Screenings are hauled to the District’s Biosolids Containment Facility (BCF) for drying and final disposal at the Wolcott Landfill.

Grit Removal
Grit is the heavier inorganic material in wastewater that will not decompose or break down (i.e. sand, eggshells and gravel). It is removed in aerated grit tanks which are designed to keep the organics suspended while settling out the inorganic material.

Primary Treatment

Primary Sedimentation
Primary treatment involves the use of settling tanks, also known as sedimentation tanks, to remove the organic suspended and floating solids from the raw wastewater. The primary reason for removing organic material is to reduce the biochemical oxygen demand (a measure of the amount of oxygen needed to biochemically degrade the organic matter in the wastewater). Some Fats, (Oil and Grease) are also removed from treatment during this stage.

The District wastewater facilities cover the primary sedimentation basins to help protect them from the weather elements and to control odor.

Secondary Treatment

Secondary treatment consists of three steps: Aeration, Sedimentation in the secondary clarifiers, and Nitrification. These treatment stages are designed to remove the dissolved and colloidal organic material and nutrients not removed by primary treatment. Approximately 90 percent of biochemical oxygen demand, ammonia and suspended solids are removed from wastewater during secondary treatment.

Aeration or Activated Sludge
Activated sludge is a biological slurry, or active biomass, that is composed of bacteria, protozoa, amoebae and a range of other filter feeding microbes. These microbes are responsible for removing the majority of the remaining ammonia, phosphorus and soluble and fine suspended material in the wastewater. The activated sludge process, which takes place in the aeration basin, involves mixing air with the wastewater leaving the primary clarifiers. Here, the microorganisms, in the presence of oxygen, use the organic matter and nutrients in the wastewater to sustain their life processes. The resulting effluent leaves the aeration basins with suspended activated sludge that is then removed by the secondary clarifiers.

Secondary Clarifiers
The secondary clarifiers are responsible for settling out the activated sludge from the aeration basin effluent. The clear water resulting from this process is sent to the nitrification cells for further treatment. Most of the settled sludge, called return activated sludge, is sent back to the aeration process to replenish the active biomass. A portion of the remaining settled sludge, called waste activated sludge is wasted, or removed, and sent to the solids handling process.

The clear effluent leaving the secondary clarifiers is sent to the nitrification tanks for processing. Nitrification, simply put, is the biological oxidation of ammonia nitrogen (a compound toxic to aquatic life) to nitrate nitrogen. The nitrification process is carried out in an oxygen rich environment by two species of bacteria referred to as nitrifiers (Nitrosomonas and Nitrobacter). These bacteria work to remove the majority of remaining ammonia from the clarifier effluent water. This treated water is then sent to disinfection.


Ultraviolet Light Irradiation
Disinfection is the final treatment stage of wastewater before it is discharged to the receiving water. Ultra-violet (UV) irradiation is a non-chemical disinfection method. It works by destroying the reproductive capacity of pathogenic protozoa, bacteria and viruses in wastewater through the application of ultra-violet light. As of 2007, the Avon, Edwards and Vail facilities have been retrofitted with UV disinfection systems (replacing the more dangerous and toxic chlorine disinfection systems).

Solids Handling Process

Autothermal Thermophilic Aerobic Digestion, or ATAD, is a high temperature microbiological process that combines heat, air and thermophilic bacteria (bacteria that thrive under high temperature conditions) to convert wastewater solids into environmentally safe biosolids. The process begins by pumping the solids from the primary sedimentation tanks and secondary clarifiers to waste tanks. There they are mixed with polymers and thickened with the use of a belt press (equipment that separates the liquid from the solids). The solids are then sent to the ATAD digestion process where the thermophilic bacteria work to degrade the organic solids and reduce both sludge mass and volume. The heat released during the microbial degradation maintains thermophilic temperatures. Solids treated by the ATAD process result in Class A biosolids (solids that comply with the U.S. EPA 40 CFR Part 503 Class A biosolids regulations and can be used for land applications for beneficial re-use) which are a biologically stable product. The biosolids are held for up to 10 days at temperatures between 130°F to 140°F before being sent through a centrifuge which removes as much as 70% of the water. Biosolids are available for public landscaping use and stored at the District Biosolids Containment Facility.

Odor Control

Odorous gases are produced during the wastewater and solids handling treatment processes. Sulfur compounds including mercaptans, dimethlyl disulfide, and dimethyl sulfide, generated by ATAD are among the most offensive. Reducing sulfur compounds to acceptable or undetectable levels is challenging due to the fact that the human nose can detect these odors at extremely low concentrations. Because of the close proximity of treatment facilities to our communities, the District recognizes the importance of eliminating nuisance odors produced by the wastewater treatment processes. State-of-the-art odor control systems have been installed at each WWTF and are designed to eliminate or reduce odor compounds to levels that are undetectable to the surrounding communities.


The Eagle River Water & Sanitation District (District) owns and operates three wastewater treatment facilities located in Vail, Avon and Edwards. Combined, these facilities treat an average of 4.4 million gallons of wastewater per day (MGD). The current total design treatment capacity is 9.95 MGD. Each facility is staffed and operated 365 days a year by 14 full-time employees. A brief summary of each treatment facility follows.

Avon Wastewater Treatment Facility

This facility has a design capacity of 4.3 MGD and services the communities of Minturn, West Vail, Eagle Vail, Avon, Beaver Creek, Mountain Star, and some of Wildridge. The facility was built in 1966 and expanded in 1997 to include an ATAD solids handling process. The Avon WWTF, staffed by 5 full-time employees, uses a conventional plug flow activated sludge treatment process. Capital improvement projects were completed in 2005 and 2006 and included the installation and implementation of the following:

  • Supervisory Control and Data Acquisition system (SCADA)
  • UV disinfection system
  • ATAD aeration system upgrade
  • ATAD foam reducing pumps
  • In-line process monitoring equipment
  • Backup generator
  • Automated valves for SCADA

In 2012, upgrades were made to change the treatment process to a Modified Ludzack-Ettinger (MLE), which allows for greater nitrogen removal.

Vail Wastewater Treatment Facility

This facility has a design capacity of 2.7 MGD and services the communities of East Vail, Vail, and some of the facilities on Vail Mountains. Most of the current plant was constructed in 1982 and is staffed by 4 full-time employees. The Vail WWTF uses a conventional activated sludge process. At the Vail WWTF, ammonia is treated in separate tertiary nitrification reactors after secondary clarification. Solids are conveyed to the Edwards WWTF for further treatment and dewatering. Capital Improvement Projects are implemented to replace aging equipment, improve efficiency and safety, and comply with tightened regulations. Recent projects have included installation of a more efficient high-speed turbo blower, improvements to the nitrification aeration system, and the replacement of electrical switchgear.

Edwards Wastewater Treatment Facility

This facility has a design capacity of 2.95 MGD, is staffed by five full-time employees, and services the communities of Edwards, Cordillera, Homestead, Arrowhead, Singletree, Bachelor Gulch, Cordillera Valley Club, Wildridge, and Mountain Star. The facility was built in 1981 and expanded in 1986. It was upgraded in 2001 to include an autothermal thermophilic aerobic digestion (ATAD) process for solids treatment. Capital improvement projects were completed in 2001 and 2006 for the installation and implementation of the following: Supervisory Control and Data Acquisition system (SCADA), ATAD solids handling system, increased volume for odor control air handling system, UV disinfection system, and an efficient automated blower system for aeration. The system underwent another capital improvement in 2010 to improve ATAD to second generation ATAD. In 2013 the facility replaced the influent lift pumps. Currently the facility is undergoing construction to expand the ATAD solids treatment facility to treat all of the solids from the Vail, Avon, and Edwards WWTFs. This project will be completed in 2016. The Edwards WWTF uses a conventional activated sludge wastewater treatment process.

Biosolids Containment Facility (BCF)

The Biosolids Containment Facility was constructed in 1990 on District property in Wolcott to store and handle the Class A biosolids produced by the Avon and Edwards WWTFs. In 2005, the BCF was resurfaced to improve the storage and drying processes of solids treatment. On an annual basis, this facility handles approximately 1000 dry metric tons of 80% dry biosolids that can be used as a soil conditioner for certain applications. Please visit our biosolids page for more information.

Collection System

Wastewater is generated by residential, commercial, and industrial sources and collected by a system of sewer mains designed to deliver it to the wastewater treatment facilities located throughout the valley. In most cases, wastewater flow is moved through the sewer mains by gravity. However, there are situations where gravity is insufficient and the need for pump stations, or lift stations, is required. The District currently operates six lift stations. Some subdivisions and other system users operate private lift stations.

Lift stations are monitored with a lift station telemetry system. This system was initially constructed and put into service in 1982 and has been upgraded with newer technology over the years. The system monitors each station for various information including wet well levels, pumps status, station operation, and alarm status.

The Eagle River Water and Sanitation District Distribution and Collection Division is responsible for the operation and maintenance of seven lift stations, 5,137 manholes and 210 miles of sewer main.

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