Taking THMs Out of the Mix

Monterey, Calif., is a seaside town that enjoys cool weather, picturesque beaches and, for the most part, excellent water quality. However, over the last few years, trihalomethane (THM) levels in the Ryan Ranch part of its system have risen dramatically. Despite aggressively flushing this part of the system and periodically boosting chlorine at the tank to improve residual levels, Monterey was on track to breach its total trihalomethane (TTHM) levels in the summer of 2011.

Taking Aim at Thermal Stratification in Water Tanks

The City of Rifle, Colo., knows painfully well that during summertime in the Colorado desert, the daytime heat loading on drinking water tanks can be intense. When exposed to long hours of sunlight, the water inside these tanks is heated and rises to the top of the tank, forming a layer of isolated, high-temperature water that can be up to 10°C (22°F) warmer than the fresh, cool water delivered during the tank’s daily fill cycles. This warmer layer floats up and down like a piston on top of the cooler bottom water and is never refreshed.

Improving Disinfectant Retention and Stabilizing Water Quality

Maintaining disinfectant residual levels in drinking water reticulation systems is a challenge, even under normal conditions. Water must travel through several kilometers of pipes and is often stored in water tanks and basins before reaching customers. However, when the distance between the treatment plant and customer is extensive, maintaining adequate disinfectant levels becomes even harder. Further challenges become apparent during times of low water usage as the age of water within the water reticulation system increases.

The Problem

A Proactive Approach

San Jose Water Co., located in the heart of Silicon Valley in California, is used to being on the forefront of innovation. As one of the largest and most technologically sophisticated investor-owned utilities in the U.S., it has taken a proactive approach to improving drinking water quality and lowering operating costs. 

Stopping Standpipe Stratification

Thermal stratification is often an invisible problem inside water storage tanks. Without taking water temperature measurements at different depths, a municipality may be unaware that warm water is trapped and aging for days or even weeks in the top
of their tank. Typically, the only warning signs of thermal stratification are sudden changes in disinfectant residual levels and taste and odor complaints, usually during warm summer months.

Under the California Sun

The City of Covina, Calif., faces water quality challenges that are typical for many urban and suburban water systems across the southern United States. Nestled in the heart of the greater Los Angeles area, Covina receives water from several sources and distributes finished water through multiple pressure zones. With large variations in seasonal demand, operators must balance maintaining supply and reducing water age with requirements for emergency preparedness. 

The problem

Thermally Homogenous but Chemically Stratified Tanks

Pinellas County, Fla., has a distribution system that is typical of many major metropolitan water systems, with over 700,000 customers, 2,000 miles of piping and several large water storage facilities. The Pinellas County Department of Environment and Infrastructure (DEI) has seen a decline in water usage over the last decade, due to both active water conservation programs and downturns in the regional economy. This decrease in water usage, combined with warm southern temperatures, has increased water age and incidences of nitrification in parts of its chloraminated system.

Aeration Cuts THMs in Oversized Maryland Tank

The City of Rockville, Md., located just outside of Washington, has taken a proactive approach to meeting water quality regulatory compliance for its drinking water system. However, an unexpected notice of violation for exceeding the maximum contaminant level (MCL) of total trihalomethanes (TTHMs) in 2008 caused the city to critically examine water quality in its water distribution system. TTHMs are chemicals that form when chlorine reacts with naturally occurring organic matter found in drinking water, such as Rockville’s drinking water source—the Potomac River.

Water Storage Tank Stays Ice-Free Despite "Polar Vortex" Storm

January 2014 brought a major weather event to the northern United States and Canada, and many challenges to water utilities in the region. An ultracold mass of air descended out of Canada into the United States, and temperatures fell to record levels. Water utilities struggled with dangerous work conditions, water main breaks and ice formation in water storage tanks. The City of Atwater, Minn.—situated 100 miles west of St. Paul—has seen its share of cold winter weather, but January 2014 set new records.

Mixing Technology Eliminates Ice in Wyoming Mountain District Tank

South of Laramie Water and Sewer District (SLWSD) is a consecutive system that purchases water from the city of Laramie, Wyo. Since SLWSD was formed in 1996, managing icy conditions and maintaining water quality in their only tank—a 300,000 gal pedisphere—has been a concern.

Mixing in Large Underground Water Storage Tanks

Large underground water storage tanks are a common feature of many water distribution systems in the United States and Europe. These basins are typically rectangular, shallow and concrete and feature numerous columns that support a thick roof. Unlike aboveground storage tanks, which are often visible for miles, underground storage tanks are hidden from view. In many cases, municipalities utilize the land above the storage reservoir for recreation or parking.

Active Mixer Eliminates Stratification in Standpipe

The Spanaway Water Co. in Washington discovered thermal stratification in its standpipe after noticing heavy condensation on the outside wall of the steel tank. The operator expected that the cold water inside the tank was causing the condensation, but was alarmed that the condensation was only visible 20 ft up the side of the 127-ft standpipe. To test his theory that the tank was thermally stratified, the operator installed a series of submersible temperature probes at 20-ft intervals inside the tank.

Active Mixing Keeps Tanks Ice Free

While most people enjoy a little ice in their water glass, a large ice plug inside a water storage tank can spell disaster. Unfortunately, ice damage is difficult to avoid in northern climates. Depending on the air temperature, inlet water temperature, amount of turnover, and presence of tank insulation and heaters, ice formation can range from a thin skin to a several-ton ice cap.

Active Mixing Tames Nitrification

Redwood City, Calif., is one of 24 municipalities in the San Francisco Bay Area that receives its water from the San Francisco Public Utility Commission (SFPUC). 

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