Guest Commentary: Water Quality Success Through Tank Maintenance

July 24, 2014

The Safe Water Drinking Act (SWDA) of 1974 directed EPA to ensure public water systems meet minimum standards for protecting public health. Public water supplies are tested and regulated to ensure water remains free from unsafe levels of contamination, but acceptable contaminant levels vary widely among people and population groups (NCSU BAE 1996). Therefore, the SWDA also gives individual states the opportunity to set and enforce their own drinking water standards if the standards are at least as strong as EPA’s national standard, and most of these states and territories directly oversee the water systems within their borders (USEPA, “Regulating Public Water Systems and Contaminants under the Safe Drinking Water Act). Many also follow the National Secondary Drinking Water Regulations (NSDWR) or secondary standards which regulate contaminants such as: aluminum, copper, iron, manganese, silver, zinc, chloride, fluoride, foaming agents, sulfate, color, corrosives, odor, pH, and total dissolved solids (TDS). Water systems must also test for certain contaminants for which there are no current standards to help determine which contaminants should be regulated by new standards, and the levels of those standards (USEPA, “Drinking Water Contaminants).

Responsibilities
Water operators are often assigned the important task of maintaining water storage tanks and the water quality within. Water system operators must be certified to ensure that systems are operated safely, and all states are currently implementing EPA-approved operator certification programs. National drinking water standards are legally enforceable, which means that both EPA and states can take enforcement actions against water systems not meeting safety standards. Water operators can also lose their license to operate a water system if unhealthy water is found in their system. However, most operators often take great pride in providing excellent water quality; and therefore, monitor the water often for chemical and physical changes that could indicate contamination. Under Source Water Assessment Programs, every state must conduct an assessment of its sources of drinking water (river, lakes, reservoirs, springs, and ground water wells) to identify significant potential sources of contamination and to determine how susceptible the sources are to threats (USEPA, “Understanding the Safe Drinking Water Act”). Onsite monitoring with direct contact to the water source is preferable, but other evaluations offsite in laboratories may also be required for more extensive testing.

Water Properties
When water properties such as temperature, pH, level of dissolved metals, and turbidity change over an extended period of time, the water tank is often a good place for operators to begin their investigation. For example, temperature is an important indicator of water quality because temperature can affect water’s ability to hold oxygen (US DOI 2014). Oxygen depletion occurs most often in the summer and fall when water temperature is highest. Bacteria consume oxygen as organic matter decays, and stratified or stationary water can become stagnant during this time. Mixing systems, over-the-top fill pipes or separate inlet and outlet pipes can be installed to help maintain a constant temperature and level of oxygen in the water throughout the tank. Tanks properly sized to meet domestic and fire flow demands with good turnover can also help maintain water quality by preventing stratification, freezing, and water age.

The PH Scale

An important indicator of chemical changes in water is pH, because it determines the solubility of chemical constituents such as nutrients and heavy metals. Metals tend to be more toxic at lower pH because they are more soluble. TDS can create too high or too low pH levels depending on the type of dissolved solid, and water quality problems often occur in both extremes. High pH causes a bitter taste; water pipes and water-using appliances become encrusted with deposits and it depresses the effectiveness of the disinfection of chlorine. Low-pH water will corrode or dissolve metals and other substances at a faster rate (US DOI 2014). The ideal pH range for water is between 7.2 and 7.6, and it’s best to have water tanks inspected and cleaned if pH levels begin to vary outside this range.

Turbidity is a measure of the cloudiness of water, and it is used to indicate water-quality and filtration effectiveness. Higher turbidity levels are often associated with higher levels of Total Suspended Solids (TSS) and disease-causing microorganisms such as viruses, parasites and some bacteria, because microscopic organisms use the suspended solids as food and shelter (USEPA, “Drinking Water Contaminants”). After a period of slow water movement, the suspended solids will begin to accumulate on the bottom of the tank as sediment or mud. The water and sedimentation must be removed periodically to minimize corrosion and microbial growths. Tanks should be washed out and inspected at least once every three years, and where water supplies have sediment problems, annual washouts are recommended (AWWA 2013). Ideally, tanks should be cleaned in the late winter/early spring and again in the fall, when the water temperature is likely to change; or when other chemical or physical changes are noticed in the water.

Qualified Inspections
A technical bulletin, “Microbial Contamination of Water Storage Tanks” (pub 172), was issued in September 1995, because too many occurrences of microbial contamination of water storage were found due to tank inspection failure or inadequate inspections. Today, the occurrence of microbial contamination is lower because more tanks are inspected, but the quality of inspections varies widely. Too many inspection services look only at the condition of the paint and ignore other important issues. These inspections fail to reveal major sanitary defects (MO DNR 2004). A knowledgeable and reputable company with proper equipment and insurance should be contacted to perform these services. All aspects of the tank should be inspected for not only structural repairs and coating system updates, but also for sanitary issues in accordance with EPA, AWWA, NFPA, and any other state standards that may apply. All sanitary defects should be reported to the tank operator and addressed immediately. A written report with a detailed account of defects, photographs and recommendations should also be provided.

Sanitary defects often overlooked include damaged vent, overflow pipe screens and other tank openings. All openings should be properly sealed to prevent precipitation, airborne containments, birds, insects, and other animals from gaining access to the drinking water. Security measures to prevent trespassing should also be considered when protecting the water quality. No trespassing signs, surveillance, and a fenced in area with locks should be installed, and exterior ladders that terminate 8 feet above the ground with a locking ladder guard can help prevent water contamination from trespassers.

Sanitizing Equipment & Disinfection
Today, Remotely Operated Vehicles are becoming popular methods for inspecting and cleaning water storage tanks. However, all equipment entering the storage tank must be properly sanitized by the inspection/cleaning crew before entering the tank. All reputable inspection and cleaning firms should follow the AWWA guidelines for disinfecting their equipment and cleaning tanks (AWWA 2011). Tanks must be cleaned and disinfected regularly to destroy disease-producing organisms, and close monitoring of water properties can help determine the most effective method that will produce the least amount of disinfectant by-products. Disinfectant by-products (DBP) are also contaminants that chemically change water, and DBP formation is largely dependent on reaction time, and it can continue for several days within the distribution system. At the same time, disinfectant residual must be maintained throughout the most remote components of the system to ensure pathogen-free water.

Drinking Water Programs for Water Quality Success
EPA has set standards for 90 contaminants: microorganisms, disinfectants, disinfection by-products, inorganic chemicals, organic chemicals, and radionuclides. Monitoring water properties can help detect these contaminants, but monitoring alone is not enough. Water tanks must be frequently inspected and cleaned by qualified individuals to limit water contamination and maintain water quality. Public water systems in financial distress can look into the Drinking Water State Revolving Fund and other drinking water programs for water system improvement grants that are provided by EPA.

References
American Water Works Association (AWWA). 2011. AWWA C652-11 Disinfection of Water-Storage Facilities.

AWWA. 2013. Manual of Water Supply Practices–M42, Revised Edition. Pp. 58, 88.

Missouri Department of Natural Resources (MO DNR). 2004. “Inspection of Water Storage Facilities.” Water Protection Program technical bulletin, April 2004.

North Carolina State University Extension at Bio&Ag Engineering (NCSU BAE). 1996. “Water Quality & Waste Management: Health Effects of Drinking Water Contaminants.” March 1996. www.bae.ncsu.edu/extension/ext-publications.

US Department of the Interior (US DOI). 2014. The US Geological Survey (USGS) Water Science School. Accessed April 2014. Last modified May 2, 2014. http://water.usgs.gov/edu/waterquality.html.

USEPA. “Drinking Water Contaminants.” Last modified June 3, 2013. http://water.epa.gov/drink/contaminants.

USEPA. “Regulating Public Water Systems and Contaminants under the Safe Drinking Water Act.” Last modified April, 7, 2014. http://water.epa.gov/drink.

USEPA. “Understanding the Safe Drinking Water Act.” Last modified April 7, 2014. http://epa.gov/safewater. 

About the Author

Erika Henderson

Erika Henderson is director of research for Pittsburgh Tank and Storage.

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