Negative Pressure Event: Localized Low Water Pressure in Water Main Can Temporarily Threaten Safe Water Supply

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Recently several neighborhoods in the Washington D.C. area were affected by an advisory to boil and cool water that is used for drinking or cooking. The reason for the advisory was the result of low pressure in water mains in neighborhoods caused by a failed valve in the water distribution system. The original boil advisory, issued Friday, July 13, 2018 at 4:30 a.m. came after a valve malfunction at the Bryant Street pumping station near Howard University Thursday evening about 8:30 p.m., which caused an unexpected drop in water pressure for about 66 minutes (elapsed time until water pressure was restored). Some criticized officials for taking about eight hours to alert the public about the low pressure or negative pressure event.

When the water boil precautions ended, only one test resulted in discovery of contamination. DC Water officials said water from a fire hydrant at one of 13 test sites tested positive for coliform bacteria. The finding, did not indicate the presence of imminent causes of threat to health, but it did indicate the possibility of presence of other pathogens. In other words, the presence of coliform bacteria is used to indicate that other pathogenic organisms of fecal origin may be present — and is a cause for alarm. Consider hepatitis pathogens, etc.

The Washington Post reported that some residents were angered that officials botched the job of conveying something as vital as the safety of drinking water, and that residents were confused about the possible dangers, and were frustrated that Washington D.C. officials had not clearly communicated the risks.

Officials in any community have a responsibility to provide safe water. Each year the Village of Arlington Heights provides a water report to water customers that is required by The 1996 Safe Drinking Water Act. The report is available on The format of the water quality report is regulated by the United States Environmental Protection Agency (USEPA). USEPA requires certain mandatory language and data in this report. These informational items must be published every year in the Village’s Water Quality Report. Arlington Heights has a good record of water quality in normal situations. However, extraordinary incidents can jeopardize water health and safety at a local level.

Low Water Pressure Concerns?
The incident in Washington D.C. brings many concerns about low pressure incidents locally in Arlington Heights and Chicagoland. Cardinal News found that many water main breaks can temporarily threaten safe tap water, and that most communities do not issue water boil advisories when pressure drops. Cardinal News also discovered that while a water boil may remedy microbial contamination of drinking water, a water boil treatment does not necessarily rid the water of other contaminants — such as pesticides, petroleum products, fertilizers, etc. — that may be in the soil adjacent to a broken water main. In other words, we tend to focus on microbes that might make us sick in a few hours or days. But what about contamination by chemicals that might make us sick in years or decades?

What causes low water pressure?
The most common cause of low water pressure is a broken water main, which is localized to the affected neighborhood. Another cause can be extensive water flow from firefighting operations, which can affect a local neighborhood when heavy water flow is used to extinguish a major fire. Another cause can be some type of failure in the water distribution system, such as the valve failure in Washington D.C. That valve failure in Washington D.C. is believed to have been caused by human error.

The biggest concern in Arlington Heights — and most common occurrence — would be a water main break. When water is flowing in the street and buckling pavement, pushing up sod, and throwing silt into the street; the pressure in the water main is dropped, and the pressure delivered to residents is lower. The potential for a negative pressure event exists. That means stuff outside the pipes might get inside the broken pipes, and into your drinking water.

Why Is Low Pressure a Concern?
Simply put, contaminants will flow from a relatively higher pressure to a lower pressure. If contaminants are in the soil — next to a broken water main that no longer has the pressure or integrity to keep chemicals and microbes out — those contaminants can enter the water distribution system. According to the EPA, any contaminant exterior to the distribution system may enter potable water supplies during a negative pressure event. Chemical contaminants could include pesticides, petroleum products, fertilizers, solvents, detergents, pharmaceuticals, and other compounds. Predominant pesticides in urban areas include atrazine, simazine, prometon, and diazinon (Patterson and Focazio 2001). According to the EPA, other studies have detected insect repellants, fire retardants, and other industrial chemicals (Koplin et al. 2002). If chemical compounds intrude in sufficient concentration or volume, they might result in acute toxicity. Microbial contaminants are a concern because even with dilution, some microbes (e.g., viruses) could cause an infection with a single organism, according to the EPA.

Only microbial contaminants would be 100 percent eliminated by a water boil order. Many chemical contaminants could maintain their chemical structure or be converted to other chemicals in boiled water. Additionally, the chemical contaminants with boiling points at or below the boiling point of water (212°F) could be vaporized into the air in your kitchen. The chemical contaminants with boiling points higher than water could be concentrated in your remaining volume of boiled drinking water. The boiling point of the pesticide Atrazine is 392°F.

Karim et al. (2001) reported on a study that examined 66 soil and water samples collected from eight utilities in six states. The samples were collected immediately adjacent to the drinking water pipelines. The purpose of the study was to determine the presence of microbial contaminants in the soil immediately external to the distribution system. Whenever a water main was excavated, samples were collected of either the water or the undisturbed soil next to the pipe. Total coliform and fecal coliform bacteria were detected in water and soil in about half of the samples, indicating the presence of fecal contamination. Bacillus was found in almost all the samples, which is not a surprise since it is a normal soil organism. Viruses were detected using culturable methods in 12 percent of the soil and water samples, and by molecular methods in 19 percent of the soil samples and 47 percent of the water samples. When these data are combined, 56 percent of the samples were positive for viruses either in the water or the soil. Sequence analysis showed that these viruses were predominantly enteroviruses (the vaccine strain of Poliovirus), but Norwalk and Hepatitis A viruses were also detected, providing clear evidence of human fecal contamination immediately exterior to the pipe.

In the same study an analysis of the levels of organisms detected showed that they could be quite high; for example, total fecal coliform levels were as high as 104 bacteria per 100 grams of soil. This may not be surprising considering that sewer lines are often located only a few feet away from water mains and service lines. Engineering standards call for a minimum separation of 10 ft between drinking water and sewer pipelines, although separations can be as little as 18 inches if the drinking water pipe is located at a higher elevation than the sewer pipe (Recommended Standards for Water Works 1997). Also, many older constructions may persist that involve close positions of water service pipes and sewer lines. In saturated soil conditions, microbes can move several meters in short periods of time (Abu-Ashour et al, 1994). This microbial transport could be aided by water flowing out of the sewer (exfiltration).

How do water authorities test for low water pressure?
There really is no reliable way to test water pressure in an open broken pipe in the ground. The Village of Arlington Heights Standard Operating Procedures (SOP) for a Water Main Break defines that a precautionary boil order needs to be issued if water pressure falls below 20 PSI. But how do they confirm the specific 20 PSI critical figure?

How transparent are community authorities regarding extraordinary water pressure circumstances, and how timely are important notifications and alerts?

Currently Arlington Heights doesn’t usually provide alerts (via Facebook, Twitter, etc) when a water main break occurs, unless it affects heavy vehicle traffic. According to Village of Arlington Heights Water Main Break SOP, notices are to be hand-delivered to residential and commercial water customers with a Red Notice: “Precautionary Boil Order.” The notices must be hand-delivered to every door where water service has fallen below 20 PSI or where service has been completely shut off. A copy of a notice for the hazardous element Lead (Pb) must also be delivered. The SOP also requires that a map be annotated, with the addresses included, for the affected locations; but the SOP does not clarify whether the map and address information is to be delivered to water customers.

Arlington Heights has very competent and effective public works crews that repair water main breaks in all kinds of physical locations and weather conditions, including brutally cold weather. Are the Village of Arlington Heights communications standards held to the high standards delivered by the dedicated public works department staff on the streets and in the trenches?

While there are no known incidents of a water main break causing an immediate illness from microbes in Arlington Heights, the possibility of chemical contamination in addition to microbial contamination should cause concern about illnesses, such as cancer, developing years later, following exposure to water contaminated by pesticides, fertilizers and other chemicals in the ground next to water main pipes.

The safest way to reduce risks of possible exposure to contaminated drinking water would be to alert residents as soon as a water main break is detected. Many times police on patrol discover water main breaks. An all-village alert could advise people to use their own judgement about consuming tap water if they live or work near a water main break. The alerts could be posted on Facebook and Twitter. The water main breaks usually affect small areas of a block or two. Once the specific location of the water main break shut-off area, including a map identifying residents and business affected is understood, a second all-village alert could advise residents of the limited locations of residents and business affected. The alerts should include a map and specific street addresses or blocks of street addresses.

Trinity Washington University in Northeast Washington complained in a tweet to D.C. Water that its revised map of the reduced affected area did not include street names, making it impossible for the university to properly update students.

— Washington Post

The Village of Arlington Heights should also introduce a campaign to urge residents to notify the village as soon as they see water on the ground that could be caused by a water main break. Not only are water main breaks potential health threats, but they cost the village money as gallons of Lake Michigan water spills out onto the ground.

Safe water professionals are concerned about clean water, but are village officials doing all that is necessary to identify a low pressure or negative pressure event when a water main break occurs? And are village officials notifying residents with the best means possible.

More coming soon … in a series.

See also …

The Potential for Health Risks from Intrusion of Contaminants into the Distribution System from Pressure Transients

Abu-Ashour, J. et al, 1994. Transport of microorganisms through soil. Water, Air and Soil
Pollution. 75:141-158.

Karim, M, M. Abbaszadegan, and M.W. LeChevallier. 2001. Potential for pathogen intrusion during pressure transients. JAWWA submitted.

Kolpin, D. W., E. T. Furlong, M. T. Meyer, E. M. Thurman, S. D. Zuagg, L. B. Barber, and H. T. Buxton. 2002. Pharmaceuticals, hormones, and other organic wastewater contaminants in US
streams, 1999-2000: a national reconnaissance. Environ. Sci. Technol. 36: 1202-2111.

Patterson, G.G. and M. J. Focazio. 2001. Contaminants and drinking water sources in 2001: recent findings of the U.S. Geological Survey. Open File Report 00-510. USGS, Denver, CO.

Recommended Standards for Water Works, 1997. Great Lakes Upper Mississippi River Board of State Public Health & Environmental Managers. Health Education Services, Albany, New York.

For most of D.C., tap water is safe. But communication problems abound

Areas of Washington DC Affected by Water Boil Advisory After Drop in Pressure in Water Main
Fri July 13 2018 4:35 pm

Village of Arlington Heights 2017 Water Quality Report [PDF]


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