News 10-28-98

Bulletin Board

How Your Drinking Water Is Treated To Guard Against New Health Threats

October 28, 1998

Where Does Your Drinking Water Come From?

All of Salt Lake City's surface waters are treated in modern water treatment plants. City Creek, Parleys and Big Cottonwood streams are treated in Salt Lake City owned water treatment plants. Little Cottonwood stream is treated in the Metropolitan Water District's Little Cottonwood Water Treatment Plant located in Sandy City, along with water from Deer Creek Reservoir. The Jordan Valley Water Treatment Plant located in Buffdale also treats Deer Creek water that is delivered to Salt Lake City at 2100 South and 3800 West.

All of these treatment facilities treat water to water quality levels that exceed federal standards.

Nearly 85 percent of Salt Lake City's water comes from surface water treatment plants. The remaining 15 percent is ground water from springs and deep wells.

The Treatment Process

Chlorine is added as a disinfectant at the beginning and if necessary at the end of the treatment process. Chlorine has been found to be effective in destroying harmful bacteria that can cause diseases in humans.

Coagulation and sedimentation is a dual process. The process is aided by adding chemicals such as alum and lime to the raw water. These chemicals, when rapidly mixed and stirred in the coagulation basin, form a white snowflake-appearing substance call "floc." In the coagulation basin the floc grows in size and collects bacteria and dirt. As the floc-treated water passes through the sedimentation basin, the floc settles to the bottom of the basin. Other chemicals such as activated carbon or potassium permanganate may be added to help remove color, bad tastes and odors.

Filtration is the final step in the treatment process. Chemicals added to the process are virtually gone by now, and the water flows through beds of sand and anthracite coal that trap the last few particles. Treated water emerges at the bottom of the filter beds and is piped to the end of the plant and into the distribution system. A small amount of chlorine is added to keep the water safe in its journey to the customer's tap.

The filter beds are cleaned by back washing, or reversing the flow of water, flushing the trapped matter off the filter beds into the sludge basins.

The treatment residuals are collected in drying beds, where the liquid water is evaporated from the solids. Once dry, the solids (sludge) are hauled by trucks to the landfill.

Optimizing Treatment Processes to Combat Emerging Health Threats

In 1993, Milwaukee experienced a water borne disease outbreak as a result of Cryptosporidium, a relatively unknown parasite. Over 400,000 people were infected with cryptosoporidiosis. This outbreak, the worst recorded in modern U.S history, acted as a wake-up call for the regulatory agencies and the water suppliers across the county. The presence of this organism is found in surface water and some ground water. In a precautionary measure, the water suppliers through their professional organizations voluntarily began operating water treatment plants at standards more stringent than federal requirements in order to insure their customers’ water free of the organism. Likewise, in November 1994 a finished water turbidity standard of 0.1 NTU was set for all water treated in Salt Lake City treatment facilities. The federal drinking water standard is 0.5 NTUs.

Salt Lake City joined with its other suppliers during the same year to ensure that all the water delivered into Salt Lake City’s distribution system met the same voluntary standard. This group ultimately reached out to other surface water entities within the state of Utah. Known as the Utah Quality Alliance, on February 12, 1997, this group was accepted into the EPA Partnership for Safe Water program. Today 75 percent of the state's population is served drinking water from water treatment plants that are in the Partnership program.

Under the Partnership program, Salt Lake City and its suppliers have optimized all of the treatment processes to increase maximum treatment efficiency. Salt Lake City and its suppliers, the Metropolitan Water District of Salt Lake City and the Salt Lake County Water Conservancy District continue to operate their water treatment facilities at voluntary 0.1 NTUs. Operators at Salt Lake City owned plants are authorized to shutdown the facilities if they feel that they are not producing water of the highest quality.

Linda Moss, Process Control Analyst, explains the progress made in water treatment; "Water quality today has greatly improved over the past ten years, particularly in finished water turbidity." She adds, "In the past we were interested in meeting regulations, now the approach is to optimize for the best water quality possible." Ms. Moss’s job is to pursue an ongoing optimization program in each of Salt Lake City’s water treatment plants, and as a member of the Utah Water Quality Alliance, other treatment facilities that provide water to the City. "The main element in the program is to look at each unit process in the water treatment plant and optimize each one sequentially." This begins from the head works of the treatment plant to the water leaving the treatment facility.

New technology is aiding in the measurement of finished water turbidity. Particle counters determine the size of particles passing through the filter bed media. "This is an important new tool in ensuring that the water after treatment is of the highest quality possible," comments Ms. Moss.

Linda Moss can be reached at 801-583-5915


	Home \| Info Center \| Contact Us \| What's New \| Links \| Privacy Statement \| Site Info \| Text Version \| Accessibility Copyright © 2005 Salt Lake City Corporation. All Rights Reserved.