Treatment Processes
The Eagle River Water & Sanitation District (District) and the Upper Eagle Regional Water Authority (Authority) treat both groundwater and surface water sources to provide safe, reliable drinking water for our communities. Groundwater sources are of high quality in the Eagle River and Gore Creek watersheds and therefore require minimal treatment. Surface water typically requires more treatment in order to remove impurities introduced through atmospheric deposition and run-off from storm events and snowmelt. The District and Authority use a variety of drinking water treatment processes most effective for the type and quality of the source waters treated.
Conventional Treatment:
For surface water treatment, individual treatment processes are arranged in a "treatment train" (a series of treatment processes applied in sequence). Conventional treatment is the most commonly used treatment process for surface water. The individual treatment processes are described below.
-Pretreatment
Screening: Large debris such as sticks, leaves and trash are screened out and removed during this first step of the pretreatment process.
Ozone Treatment: Ozone is used to deactivate bacteria, viruses and other pathogens present in source water. It also increases the efficiency of the coagulation process and helps to reduce the concentration of metals and undesirable compounds that can form during the disinfection process.
-Coagulation, Flocculoation and Sedimentation
The coagulation, flocculation and sedimentation step of water treatment is a clarification process that works through the use of coagulants (chemicals which effectively bind small suspended particles to one another) to form larger particles, called floc, which can be settled and filtered out of the water. The joining of these particles to form larger settleable particles is called flocculation and occurs in the flocculation basin. The amount of coagulant needed for this process varies throughout the year and depends on the quality of the source water treated.
Water exiting the flocculation basin enters the sedimentation basin, also called a clarifier or settling basin. A layer of sediment, or sludge, is formed on the bottom of the basins as the particles settle out. The amount of sediment generated is often significant and can range from 1 to 3 percent of the total volume of water that is treated. The sediment layer is removed from the basin and sent to a wastewater treatment facility for treatment.
-Filtration
After separating and removing floc, the water is further treated to remove any remaining suspended particles and microorganisms. This is accomplished by filtering the water through gravel, sand and anthracite coal filters. This treatment step combines both physical and chemical processes to remove impurities.
-Water Reclamation
Backflushing, or backwashing, is a water reclamation process used to remove embedded particles in the filter. Reclaimed water containing backwash, or contaminated water, is returned to the beginning of the treatment process to be treated with raw source water. This reduces flows to the wastewater plant as only the settled sludge from this process is sent to the wastewater plant.
-Disinfection
Disinfection is the last step of the drinking water purification process. Chlorine, the disinfection agent, is added to the water to destroy any remaining pathogens. Bacterial re-growth is prevented by ensuring that a chlorine residual is maintained throughout the drinking water distribution system.
-Fluoridation
Fluoride is added to drinking water at various locations within the District and Authority service areas. Fluoridation is considered an effective means toward helping prevent tooth decay.
Microfiltration Water Treatment:
Microfiltration removes contaminants from water by filtering them through a microporous membrane. Microfiltration membranes were first introduced to the municipal water treatment market in 1987 and applied primarily to waters that were relatively low in turbidity (a measure of water cloudiness caused by the amount of suspended matter in the water). These were typically cold, clear source waters. Low pressure membranes were selected to remove turbidity spikes and pathogens without chemical conditioning. As low pressure membranes became more widely accepted, users began to apply this technology to water that contained more solids and higher levels of dissolved organic material. Recent developments in this technology have included both pre and post treatment to optimize the process.
Microfiltration effectively removes major pathogens and contaminants such as Giardia lamblia cysts, Cryptosporidium oocysts, and large bacteria. Membranes have a fixed pore size and remove particles by straining. These membrane units are compact and high in surface area, thereby reducing the overall footprint of treatment facilities. The Edwards Drinking Water Facility is a microfiltration plant that also uses coagulation to reduce the level of organics, taste and odor compounds and occasional color that can result from algal blooms in source water. The Gore Valley Drinking Water Facility (also a microfiltration plant) does not need coagulation for treating its source water.