La Verne, Calif., situated in the eastern Los Angeles basin, has seen its fair share of growth and change since it was incorporated as a quiet agricultural town in 1887. Now part of the greater mega-metropolis of Los Angeles, La Verne has a population of more than 33,000 and relies on water both from its own system of wells and from wholesaler Three Valleys Municipal Water District (TVMWD), part of the massive Metropolitan Water District of Southern California.
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.
La Verne, Calif., situated in the eastern Los Angeles basin, has seen its fair share of growth and change since it was incorporated as a quiet agricultural town in 1887. Now part of the greater mega-metropolis of Los Angeles, La Verne has a population of more than 33,000 and relies on water both from its own system of wells and from wholesaler Three Valley Municipal Water District (TVMWD), a part of the massive Metropolitan Water District of Southern California.
In the summer of 2014, Placer County Water Agency (PCWA) in California was facing a trihalomethane (THM) crisis. Drought across the western United States had led to increased levels of organic matter in the source water, and water conservation measures had resulted in lower water usage, resulting in higher water age in distribution systems. Higher organic levels required higher levels of chlorine disinfectant, which increased THM levels during treatment. Higher water age allowed THM formation to grow further in the distribution system.
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.
Scotland is blessed with a wealth of resources, including spectacular natural landscapes, a rich history and abundant fresh water. Because of the strategic and economic importance of its water resources, the “Hydro Nation” considers drinking water quality to be a national priority. As climate change and land use increasingly affect Scotland’s water resources, Scottish Water continues to invest in promising technologies to ensure that drinking water quality remains at the required standards for its customers.
Standpipes are among the most problematic tank geometries to mix. Inlet velocities are typically small in magnitude and horizontal in direction. The substantial majority of water in the standpipe must remain in the tank to produce and maintain pressure in the distribution system, so there is often a hard limit (typically 70% to 90% of capacity) below which the operators cannot draw. This takes away the default (yet energy- and labor-intensive) method of mixing—the forced drawdown and refilling of tanks.
Redwood City, Calif., operates a 500,000-gal ground-level steel tank with a single inlet/outlet. Located in the Bay Area of Northern California, Redwood City purchases chloraminated water from a regional wholesale supplier. During the summer, the total chlorine residual of samples taken near the bottom of the tank typically remained at the target level of 2.0 mg/L, but residual levels in samples taken from the top few feet of the water inside the tank would drop significantly, sometimes to undetectable levels.
Stanly County, in central North Carolina, is typical of many smaller rural water utilities in the U.S. Due to excess capacity in the city water system that supplies the surrounding county, Stanly County receives finished water that is often at or above the maximum contaminant level (MCL) for total trihalomethanes (TTHMs). Without a treatment plant of its own, Stanly County is limited to few options for bringing its water into compliance.
A rectangular, in-ground concrete tank in Ontario, Calif., had poor circulation and low turnover, and it suffered from excessive water age. During the winter, this tank showed good water quality. But because of thermal loading on the roof in the summer, stratification between top and bottom would build to almost 16°F, which would isolate the top water from the rest of the reservoir, leading to complete residual loss and acceleration of bacterial and biofilm growth.
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.
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.
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.
Powerful mixing is an essential tool for eliminating thermal and chemical stratification inside water storage tanks and maintaining consistent water quality. While underground tanks tend to be better insulated and less prone to thermal stratification than aboveground tanks, they face significant disadvantages when it comes to water quality.
When it comes to selecting the right trihalomethane (THM) removal system for a tank, custom design is key. Optimizing system design is critical for predicting and achieving THM removal rates, minimizing energy requirements and calculating long-term operating costs.
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.
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.
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.
With the Stage 2 Disinfectants and Disinfection Byproduct Rule in place, operators are increasingly adopting in-tank aeration to lower trihalomethanes (THMs) in the distribution system. Operators have many technologies to choose from, but each aeration technology comes with its own set of challenges. When it comes to selecting the right THM removal system for a tank, custom design is key. Optimizing system design is critical for predicting and achieving THM removal rates, minimizing energy requirements and calculating long-term operating costs.
Richmond, Calif.-based PAX Water Technologies and Sunnyvale, Calif.-based Aqua Metrology Systems unveiled the installation of an in-tank aeration system at San Jose Water Co. The system, installed by Utility Service Group, is being deployed in a 12 million-gal water storage tank to maintain high water quality during the drought.