Inspecting and cleaning your water storage tanks and towers is critical to keeping your drinking water safe.

On June 17th 2002 the USEPA Office of Ground Water and Drinking Water  published a white paper titled: “Health Risks from Microbial Growth and Biofilms in Drinking Water Distribution Systems”.  In section 4 the paper list the types of microbes that may contaminate drinking water tanks.  I have selected this section along with several others for your review.  I also included excerpts from another white paper published on August 15, 2002 “Finished Water Storage Facilities” also reviews contaminants that may be in tank sediment and the importance of tank inspection and cleaning.

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Health Risks from Microbial Growth and Biofilms in Drinking Water Distribution System

IV. Microbes that May Present a Public Health Risk in the Distribution System

This section of the paper will discuss the potential public health concern that arises when certain microbes and their products become a component of the distribution system biofilm. While some potential health effects are listed in the tables herein, additional health effects are provided in tables on the EPA Office of Ground Water and Drinking Water website. The organisms and toxins discussed are:

 Bacteria, Viruses, Protozoa, Invertebrates, Microbial toxins, Algae and algal toxins 

A number of technical reviews of the literature have been published on biofilm organisms in the water distribution system and factors that influence their survival and growth (Geldreich and LeChevallier, 1999; Geldreich, 1996; van der Wende and Characklis, 1990; LeChevallier, 1989a; LeChevallier et al., 1990a; 1990b; 1999b; Costerton and Lappin-Scott, 1989; Marshall, 1992; Mittelman, 1991; USEPA, 1992b; NRC, 1982).

Any microbe (including some pathogens) present in water may attach, or become enmeshed, in the biofilm. Primary pathogens, which cause disease in healthy humans, may survive for a time in the biofilm. However, the survival time for many pathogens in biofilms is uncertain and likely varies depending on the organism For some pathogens, the distribution system is a physical, chemical, and biological environment unsuited for their growth. However, pathogens may accumulate in the biofilm, and the biofilm may extend the survival of primary pathogens by protecting them from disinfectants. These pathogens may be sloughed from the biofilm into the water column due to changes in the flow rate. The persistence of waterborne disease, or of microbial contamination in a distribution system, long after the cause of the distribution system problem has apparently been corrected suggests that there may be an isolated pocket of static or slow-flowing water or biofilm erosion or sloughing is occurring (i.e. the slow-release mechanism).

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D. Entry through contamination of finished water storage vessels

Both covered and uncovered finished water reservoirs provide opportunities for microbial contamination of the distribution system, and the subsequent inclusion in distribution system biofilms. Contaminated stored water can enter water distribution pipes when the water is drawn from the

vessels for distribution. Contamination introduced through earlier points in the distribution system may be amplified during storage (e.g., biofilm growth). Storage vessels may accumulate sediment, enhancing the ability of microbes to thrive during storage.

Microbial contaminants can enter open storage reservoirs by natural phenomena, animals or humans. Birds and other animals can introduce microbial contaminants through their feces, or through general contact with the finished water. Some open finished water reservoirs may also be subject to surface runoff which may be contaminated. The Interim Enhanced Surface Water Treatment Rule (IESWTR) requires that all newly constructed finished water reservoirs, holding tanks and other facilities constructed for surface water systems or ground water systems under the direct influence of surface water serving 10,000 or more people, be covered (Federal Register, December 16, 1998). The Long Term 1 Enhanced Surface Water Treatment Rule (LT1) extended this requirement to surface water systems or ground water systems under the direct influence of surface water serving fewer than 10,000 people (Federal Register, April 10, 2000).

Inadequately secured covered finished water storage vessels may allow microbial contamination to enter the distribution system. When air is drawn through air vents to replace water leaving the vessel, contamination in the air can enter (USEPA, 1992b). Humans and animals can enter inadequately protected covered finished water vessels and introduce contamination. Underground basins are susceptible to bird, animal and human contamination (USEPA, 1992b), while ground level and elevated finished water storage tanks can also become contaminated by humans and birds. A S. typhimurium outbreak in Gideon, Missouri, which caused over 400 cases of illness and seven deaths, was likely caused by bird feces contaminating an elevated storage tank (Clark et al., 1996). More information on contamination of storage vessels is addressed in a separate paper on covered storage.

E. Entry through Improper Treatment of Materials, Equipment or Personnel in Contact with Finished Water

Materials, equipment and personnel introduced to the distribution system also provide pathways for microbial contaminants to enter biofilms. The materials can include filter materials, piping, sealing vials and others (Schaule and Fleming, 1997). Personnel in contact with the water can provide a pathway for contaminant introduction (Schaule and Fleming, 1997) by introducing contaminants during maintenance or repairs of the distribution system or storage vessels. Equipment placed inside water distribution systems, such as tank cleaning equipment or video equipment used to inspect pipelines, can introduce contaminants if not decontaminated prior to use.

F. Entry through inadequate distribution system security

Lack of proper security may result in microbe entry, followed by incorporation of the microbial contaminants into the distribution system biofilm. This may result from intentional security breaches, such as vandalism or terrorism. Also, unintentional contamination can result from unauthorized users tapping into the distribution system and swimmers using storage vessels or reservoirs. Distribution systems can have many

miles of pipe, and many storage tanks and interconnections. Because of this, systems can be susceptible to tampering, allowing contamination

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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 and mycobacteria (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).

VIII. Suitable Measures for Controlling Biofilm Development

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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.

Proper turnover of the water in finished water storage facilities eliminates what amounts to dead ends and can reduce the extent to which biofilms develop, minimize nutrient availability and prevent the accumulation of sediments. To accomplish this systems can exercise valves to reduce stagnation, and eliminate excess storage (Crozes and Cushing, 2000).

Systems can exercise additional control over biofilm accumulation and microbial growth in finished water storage vessels by preventing sediment accumulation. This can be accomplished through periodic flushing (Crozes and Cushing, 2000) and cleaning.

__________________________________________________________

EPA White Paper #2

Office of Water (4601M)

Office of Ground Water and Drinking Water

Distribution System Issue Paper

Finished Water Storage Facilities   August 15, 2002   

Additional Information

The paper is available at the TCR web site at:

http://www.epa.gov/safewater/disinfection/tcr/regulation_revisions.html

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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.

2.1.2 Pathogen Contamination and Microbial Growth

Prepared by AWWA with assistance from Economic and Engineering Services, Inc. 3

Microbial contamination from birds or insects is a major water quality problem in storage tanks. One tank inspection firm that inspects 60 to 75 tanks each year in Missouri and southern Illinois reports that 20 to 25 percent of tanks inspected have serious sanitary defects, and eighty to ninety percent of these tanks have various minor flaws that could lead to sanitary problems (Zelch 2002). Most of these sanitary defects stem from design problems with roof hatch systems and vents that do not provide a watertight seal. Older cathodic protection systems of the hanging type also did not provide a tight seal. When standing inside the tank, daylight can be seen around these fixtures. The gaps allow spiders, bird droppings and other contaminants to enter the tank. Zelch (2002) reports a trend of positive total coliform bacteria occurrences in the fall due to water turnover in tanks. Colder water enters a tank containing warm water, causing the water in the tank to turn over. The warm water that has aged in the tank all summer is discharged to the system and is often suspected as the cause of total coliform occurrences. Storage facilities have been implicated in several waterborne disease outbreaks in the United States and Europe. In December 1993, a Salmonella typhimurium outbreak in Gideon, Missouri resulted from bird contamination in a covered municipal water storage tank (Clark et al. 1996). Pigeon dropping on the tank roof were carried into the tank by wind and rain through a gap in the roof hatch frame (Zelch 2002). Poor distribution system flushing practices led to the complete draining of the tank’s contaminated water into the distribution system. As of January 8, 1994, 31cases of laboratory confirmed salmonellosis had been identified. Seven nursing home residents exhibiting diarrheal illness died, four of whom were confirmed by culture. It was estimated that almost 600 people or 44% of the city’s residents were affected by diarrhea in this time period. A 1993 outbreak of Campylobacter jejuni was traced to untreated well water that was likely contaminated in a storage facility that had been cleaned the previous month (Kramer et al. 1996). Fecal coliform bacteria were also detected in the stored water. In 2000, a City in Massachusetts detected total coliform bacteria in several samples at one of their six finished water storage facilities (Correia, 2002). The tank inspector discovered an open access hatch and other signs of vandalism. This tank was drained and cleaned to remove several inches of accumulated sediment. Three other finished water storage facilities were cleaned in 2001 without being drained and removed from service. The tank closest to the filtration plant was found to contain two to three inches of accumulated sediment and the tanks in outlying areas contained four to six inches of sediment. Shortly after the tanks were returned to service, the City experienced widespread total coliform occurrences in the distribution system (Correia, 2002). The City’s immediate response was to boost the free chlorine residual in the distribution system to 4.0 mg/L (including at tank outlets). Also, the distribution system was flushed continuously for two days to remove the contaminated water. These measures resolved the coliform bacteria problem. A boil water order was not required. To prevent the problem from recurring, the City has instituted a tank cleaning program in which all tanks are cleaned on a three year cycle. City engineers are planning to improve water turnover rates by separating the tank inlet and outlet piping.

In 1995, a water district in Maine traced a total coliform bacteria occurrence in the distribution system to two old steel tanks with wooden roofs (Hunt 2002). Upon inspection, many roof shingles were missing and large gaps were present in the tank roofs. After the tanks were Prepared by AWWA with assistance from Economic and Engineering Services, Inc. 4 drained, an interior inspection found two feet of accumulated sediment, widespread coating failure on the tank sidewalls, and evidence of human entry. The tanks were cleaned and the distribution system was flushed and disinfected. A boil water order was in place until system water quality was restored. The tanks have since been replaced with a modern preload concrete tank.

3.3 Tank Inspections  Page 10

Like water quality monitoring, tank inspections provide information used to identify and evaluate current and potential water quality problems. Both interior and exterior inspections are employed to assure the tank’s physical integrity, security, and high water quality. Inspection type and frequency are driven by many factors specific to each storage facility, including its type (i.e. standpipe, ground tank, etc), vandalism potential, age, condition, cleaning program or maintenance history, water quality history, funding, staffing, and other utility criteria. AWWA Manual M42, Steel Water Storage Tanks (1998) provides information regarding inspection during tank construction and periodic operator inspection of existing steel tanks. Specific guidance on the inspection of concrete tanks was not found in the literature. However, the former AWWA Standard D101 document may be used as a guide to inspect all appurtenances on concrete tanks. Concrete condition assessments should be performed with guidance from the tank manufacturer. Soft, low alkalinity, low pH waters may dissolve the cementitious materials in a concrete reservoir causing a rough surface and exposing the sand and gravel. The concern is that in extreme cases, the integrity of reinforcing bars may be compromised. Sand may collect on the bottom of the storage facility during this process. Routine inspections typically monitor the exterior of the storage facility and grounds for evidence of intrusion, vandalism, coating failures, security, and operational readiness. Based on a literature review and project survey, Kirmeyer et al. (1999) suggested that routine inspections Prepared by AWWA with assistance from Economic and Engineering Services, Inc. 11 be conducted on a daily to weekly basis. Where SCADA systems include electronic surveillance systems, alarm conditions may substitute for physical inspection.

Periodic inspections are designed to review areas of the storage facility not normally accessible from the ground and hence not evaluated by the routine inspections. These inspections usually require climbing the tank. Periodic inspections, like routine inspections, are principally a visual inspection of tank integrity and operational readiness. Based on a literature review and project survey, Kirmeyer et al. (1999) suggested that periodic inspections be conducted every 1 to 4 months.

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.

Uncovered finished water reservoirs have unique problems. Consequently, water utilities have ceased constructing such facilities. As noted previously, the IESWTR prohibits construction of new uncovered finished water reservoirs in the U.S. Under the LT2ESWTR, existing uncovered finished water reservoirs will be managed in accordance with a state approved plan, if the facility is not covered subsequent to the rule’s implementation. Flexible membrane covers are one means of enclosing uncovered reservoirs and these types of facilities also require specific routine, periodic, and comprehensive inspections to ensure the cover’s integrity.

3.4 Maintenance Activities  Page 11

Storage facility maintenance activities include cleaning, painting, and repair to structures to maintain serviceability. Based on a utility survey conducted by Kirmeyer et al. (1999), it appears that most utilities that have regular tank cleaning programs employ a cleaning interval of 2 to 5 years. This survey also showed that most tanks are painted (exterior coating) on an interval of 10 to 15 years.

4.0 Summary

Microbiological, chemical, and physical water quality problems can occur in finished water reservoirs that are under-utilized or poorly mixed. Poor mixing can be a result of design and/or operational practices. Several guidance manuals have been developed to address design, operations, and maintenance of finished water reservoirs. Water quality issues that have the potential for impacting public health include DBP formation, nitrification, pathogen contamination, and increases in VOC/SOC concentrations. Elevated DBP levels within storage facilities could result in an MCL violation under the proposed Stage 2 Disinfectants and Disinfection Byproduct Rule, based on a locational running annual average approach. A separate White Paper on Nitrification indicates that nitrite and/or nitrate levels are unlikely to approach MCL concentrations within the distribution system due to nitrification unless finished water nitrate/nitrite levels are near their respective MCLs. Pathogen contamination from floating covers or unprotected hatches is possible. Recommended tank cleaning and inspection procedures have been developed by AWWA and AWWARF to address these issues.

Inspecting and cleaning your water storage tanks and towers is critical to keeping your drinking water safe.  For a free inspection or cleaning quote call 817-377-4899.

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