By Carl Smith
A significant risk to public health exists when potable water distribution systems are exposed to the inflow of contaminated water or toxins at air valve locations along drinking water pipelines. Although routinely protected from contamination at the point of service with backflow prevention devices, little attention has been directed to air valve inflow locations in water pipeline vaults, or exposed air valves in low lying areas located throughout the system.
Air valves are crucial in maintaining pipeline efficiency and to provide protection from transients and other potentially destructive phenomenon such as filling, draining, surges and or line breaks. American Water Works Standard (AWWA) C512 suggests water pipelines and distribution systems require air valves be placed at all high points and regular intervals (i.e. every half mile) to exhaust and admit air during system operation to insure efficiency and protection. AWWA Manual 51 also provides recommendations for use and installation of air valves.
Post 911 water distribution systems were recognized by the EPA as one of our nation's most vulnerable infrastructure assets.
In colder climates and urban areas, water pipelines are typically buried and the air valve is installed in below-ground vaults. If the vault becomes flooded and a vacuum occurs in the pipeline due to a power failure or negative pressure transient, the contaminated flood water can be sucked through the air valve. The EPA has published several white papers summarizing the work in this area. In fact, the 2001 EPA study on "Accessing and Reducing Risks," identified one of the causes of loss of physical integrity to be "appurtenances in a flooded meter or valve pit". Valve vaults are rarely monitored and the contamination may be routinely repeated and go undetected.
Inflow prevention is important because air valves and reservoir vents are vulnerable to cross connection as well as malicious tampering. Air valve vaults are typically vented by means of a "J" Pipe connected to the air valve, or are un-piped. Unfortunately, all have the potential for flooding or malicious tampering.
The above concerns led to the study, evolution, and introduction of inflow prevention systems. An inflow preventer is a mechanical device mounted to the outlet of an air valve or vent pipe to allow the normal exchange of air in and out of a water system and to prevent the inflow of contaminated water into a potable water system and/or malicious tampering.
When flood water enters the device it raises a float that seals tightly against a resilient seat. With the vault flooded and the valve closed the device can still release air from the pipeline to maintain efficiency. However, when a vacuum occurs in the pipeline contaminated water will not be allowed to enter the pipeline.
The American Society of Sanitary Engineers (ASSE), which has developed product standards on many cross connection devices, was requested to publish an inflow prevention standard. An ASSE working group was established in 2005 and a standard was written in accordance with procedures developed by the American Standards institute (ANSI), ASSE Standard #1063-2008, "Air Valve Inflow Preventer".
Given the elevated concerns for security and safe drinking water, inflow prevention is important because air valves and reservoir vents are vulnerable to flood contamination as well as malicious tampering. Inflow preventers can be installed in new or existing air valves or reservoir vents to mitigate these threats and conditions.
About the author: Carl Smith is the VP Sales/Marketing for Val-Matic Valve and Mfg. Corp., a manufacturer of valves for water/waste water treatment plants, pipeline transmission and distribution systems.