Posts Tagged ‘Drinking water quality’

Helpful USEPA Papers and Links

Here are three very helpful USEPA papers written by the Office of Ground Water and Drinking Water between 2002 and 2006.
Finished Water Storage Facilities August 15, 2002
Page 2
2.1.1 Sediment
Sediment accumulation occurs within storage facilities due to quiescent conditions which promote particle settling. Potential water quality problems associated with sediment accumulation include increased disinfectant demand, microbial growth, disinfection by-product formation, and increased turbidity within the bulk water. Instances of microbial contamination and disinfection by-product formation due to storage facility sediments are described in the Pathogen Contamination and Microbial Growth section and the Disinfection By-Product formation section, respectively.
Page 11
Comprehensive inspections are performed to evaluate the current condition of storage facility components. These inspections often require the facility to be removed from service and drained unless robotic devices or divers are used. The need for comprehensive inspections is generally recognized by the water industry. AWWA Manual M42 (1998) recommends that tanks be drained and inspected at least once every 3 years or as required by state regulatory agencies. Most states do not recommend inspection frequencies thereby leaving it to the discretion of the utility. States that do have recommendations are Alabama (5 years), Arkansas (2 years), Missouri (5 years), New Hampshire (5 years), Ohio (5 years), Rhode Island (external once per year; internal, every five years), Texas (annually), and Wisconsin (5 years). Kirmeyer et al. (1999) recommend that comprehensive inspections be conducted every 3 to 5 years for structural condition and possibly more often for water quality purposes.
Page 12
Kirmeyer et al. (1999) recommended that covered facilities be cleaned every three to five years, or more often based on inspections and water quality monitoring, and that uncovered storage Prepared by AWWA with assistance from Economic and Engineering Services, Inc. 12facilities be cleaned once or twice per year. Commercial diving contractors can be used to clean and inspect storage facilities that cannot be removed from service. AWWA Standard C652-92 provides guidelines for disinfection of all equipment used to clean storage facilities.
On December 2006 Office of Ground Water and Drinking Water. Total Coliform Rule Issue Paper. Inorganic Contaminant Accumulation in Potable Water Distribution Systems.
Health Risks from Microbial Growth and Biofilms in Drinking Water Distribution Systems June 17, 2002
Page 26
G. Sediment Accumulation
Significant microbial activity may occur in accumulated sediment (USEPA, 1992b). Organic and inorganic sediments can also accumulate in low-flow areas of the distribution system, and enhance microbial activity by providing protection and nutrients (USEPA, 1992b). Biofilms that slough can accumulate in the periphery of distribution systems leading to sediment accumulation and the proliferation of some microorganisms (van der Kooij, 2000). Sediments may be an important source of nutrients in open finished water reservoirs, by accumulating slowly biodegrading materials which are then broken down and released into the water column (LeChevallier, 1999b). The opportunities for biofilm development may be more abundant in storage tanks than in distribution system piping. Frequently, water is drawn from storage tanks only when water demand is high, such as during drought, fire flow, and flushing operations. This intermittent use results in prolonged storage times that may lead to increased sediment accumulation and lack of a disinfectant residual in the finished water storage vessel. Biological and aesthetic effects can be observed following the release of accumulated sediments from low flow areas of the distribution system (Geldreich, 1990).
Many studies have identified microbes in accumulated sediments, including both pathogens and non-pathogens. These include bacteria, viruses, protozoa, algae, fungi and invertebrates. Opportunistic pathogens that have been detected, and can multiply in sediments, include Legionella andmycobacteria (van der Kooij, 2000). Some primary pathogens can also survive for some time in sediments. Hepatitis A virus survived more than four months in sediments at both 5/C and 25/C (Sobsey et al., 1986). Other opportunistic pathogens found in sediments include Pseudomonas fluorescens and Flavobacterium spp. (Berger et al., 1993). Sediments can also release nutrients into the water which stimulate biofilm growth downstream (LeChevallier, 1999b).
Page 34
I. Proper Storage Vessel Management and Alteration
Proper storage vessel management and alteration, when necessary, can prevent contamination of the distribution system. Following TCR violations in 1996 in Washington D.C., one measure that proved effective in bringing the system back into compliance was the cleaning, inspection and disinfection of storage tanks and reservoirs (Clark, et al., 1999). To reduce pathogen presence and biofilm development, systems should have a scheduled program to rehabilitate all water storage facilities (USEPA, 1997). Proper operation and maintenance of storage tanks and reservoirs is listed as a BAT in the TCR (USEPA, 1992b). Storage tanks and standpipes should be pressure flushed or steam cleaned, then disinfected before returned to service (USEPA, 1992b), preferably with a disinfectant solution. This may not only remove microbial contamination from the vessel’s inner surface, but also nutrients that may be present. Proper operation of storage vessels can also reduce excessive residence times, which can lead to microbial survival and growth, and biofilm formation. Properly designed inlets and outlets, and the overall system design can improve problems caused by dead ends (Trussell, 1999). Pathogen contamination due to air introduction can be reduced by installing air filters to guard against pollution entering covered water reservoirs (USEPA, 1992b). Covering finished water reservoirs can protect against contamination from airborne sources, surface runoff, accidental spills and animals, such as insects and birds (USEPA, 1992b). EPA’s Uncovered Finished Water Reservoirs Guidance Manual describes recommended contamination control measures related to birds and other animals, human activity, algal growth and insects and fish (USEPA, 1999b). An understanding of the storage hydraulics and operation is important in reducing contamination of the finished water.

17 - 1

If you need assistance inspecting or cleaning water storage tanks or towers call
Ron Perrin Water Technologies toll free at 1-888-481-1768.
For a fast quote Fax your tank information to 817-246-1740.
Or e-mail your tank information:
Out of Texas contact Robert at
Texas Water Utilities please contact Debi Wheelan at

The Importance of Cleaning Water Storage Tanks

July 24, 2008 Leave a comment

Safe municipal drinking water has been with us so long that it is easy to forget that even today the World Health Organization estimates that over a billion people do not have access to clean drinking water.  Administrators who manage water systems know that the luxury of having safe drinkable water comes at a cost.  It is a constant struggle to maintain the aging infrastructure and keep up with the most effective water treatment options.

Although water treatment chemicals and treatment methods have taken great leaps forward over the years there is still a basic element of sanitation in our water systems that is often overlooked.  Simple sediment build up in the bottom of a water storage tank can undermine the best plans and most advanced chemical treatments. In a municipal water system sediment builds up over time.  With 10 years of inspecting water storage tanks behind us and thousands of tanks inspected, we have found that three inches of sediment or less is common across Texas, but we have found some tanks with many times that and even multiple feet of sediment.

Keeping your water storage tanks clean may be one of the most overlooked maintenance procedures in the drinking water industry.  Out of sight and out of mind, sediment in the bottom of your water storage tanks is never seen and rarely thought of.   The sediment that builds up in almost all potable water tanks can be a habitat for bacteria and other contaminates like cryptosporidium that devastated the city of Milwaukee in the spring of 1993.

Read the full article here:

See a video of a tank being cleaned by a dive crew here: