CVMS: The latest innovation in UST safety
By Peter Cochefski
Company:
OPW Fuel Management Systems
Title:
Marketing Product Manager
Years in the industry:
23 years
First job:
Draftsman for a small contract engineering company
Family:
Wife Cathy, daughters Sarah, Courtney and Tori
Hobbies and/or Activities:
Scuba diving and golf
How long
have you been reading NPN?
23 years |
By September 2005, there were 452,041 confirmed leaks in underground storage tank systems across the United States. This was a significant increase from April 1995 when there were more than 287,000 reported and confirmed leaks.
At sites without any kind of leak-detection equipment installed, leaks were discovered late, after contamination had already spread, polluting the environment. These leaks resulted in costly cleanups to the owners of the sites. In response, UST owners across the United States initiated cleanups at approximately 422,000 sites, while completing cleanups at approximately 332,799 locations. Additionally, cleanups are still in process but not yet completed at 119,242 sites.
In December 1988, the U.S. Environmental Protection Agency issued regulations to protect the environment and public health from the effects of leaking USTs. These regulations required UST systems installed after December 1988 to have leak, spill, overfill and corrosion protection in an effort to reduce spills, leaks and protect the environment. The regulations also stipulated that UST systems installed prior to December 1988 would be given until Dec. 22, 1998 to comply (upgrade) with the requirements.
Advancements in Technology
Leak detection technology for USTs has progressed from a wooden gauging stick to a complex system of probes and sensors centrally wired into a control console. Sticking the tank gave the owner a manual reading of the amount of product in the UST, but didn’t provide up-to-the-minute information on the status of the liquid inventory in their tanks.
Advancements in this technology not only provide the ability to monitor possible leaks, but also give UST owners and operators enhanced fuel-management capabilities. Today’s technology has the ability to gather data from peripheral systems, such as point-of-sale, fuel control, dispensers and other related fueling devices.
Today, leak detection for USTs and piping is a must for tank owners. Federal, state and local regulations mandate that measures be taken to provide early warning of leaking tanks or pipes to prevent contamination of soil, drinking water supplies and air. However, as of September 2005 roughly 66 percent of the UST facilities in the United States were in significant operational compliance with both the release-detection and release-prevention requirements.
Focusing on Vapor Releases
After regulations were in place that specifically dealt with liquid leaks in USTs, the state of California began to investigate the potential problems associated with vapor releases. In 2002, in response to widespread vapor releases from USTs in the state, California’s Legislature passed Assembly Bill 2481. This new bill required significant improvement in the continuous monitoring methods for newly installed USTs, specifically that of the interstitial space of tanks, sumps and product lines.
This assembly bill required that the interstitial space be maintained under a vacuum or pressure and outlined a performance standard where a breach in the primary or the secondary wall must be detected before the liquid or vapor phase of the hazardous substance stored in the UST is released into the environment. Additionally, the bill provided for the use of an interstitial liquid level measurement method to satisfy the requirement that the interstitial space of newly installed UST systems be maintained under constant pressure.
At the time AB 2481 was introduced, an established method for monitoring tanks was already available in California. This consisted of a hydrostatic or brine monitoring method, which is also referred to as the “interstitial liquid level measurement” method.
Tanks utilizing this method of filling the interstitial area with a brine solution rely on a positive head pressure within the interstitial space that is greater than the stored substance under operating conditions within the primary containment. This positive head pressure is maintained through the use of a liquid reservoir mounted on the top of the tank and is monitored by a sensor in the reservoir to determine whether or not the fluid in the interstice increases or decreases. The sensor triggers an alarm in the monitoring system if the brine level in the reservoir increases or decreases significantly. Depending on the level of groundwater surrounding the tank, the liquid level within the interstice could move up or down in the event of a leak. Any breach in the primary or secondary containment will be detected before the hazardous substance is released to the environment.
It should be noted that hydrostatic or brine monitoring is not necessarily perfect. In fact, this method is susceptible to changing environmental conditions around a tank that could result in system failures and/or false alarms. In addition, because these systems use fluids to detect leaks, precautions must be taken in warm weather to ensure that evaporation does not cause false alarms and prevent it from detecting leaks.
California now stipulates that the interstitial space of USTs, containment sumps and product piping installed on or after July 1, 2004, must be maintained under a constant vacuum or pressure, and any breach in the primary or secondary containment must be detected before the stored product is released to the environment.
The Latest Innovation
The latest monitoring method and technology available today is “Continuous Vacuum Monitoring”, commonly referred to by its acronym CVMS. The CVMS establishes a standard vacuum of 20 inches of water column within the interstices to monitor the integrity of the primary and secondary containment barriers. By drawing a small vacuum on the interstitial space of tanks, sumps and product lines, the entire primary and secondary containment system is continuously monitored.
Even the slightest loss of vacuum or the detection of liquid (hydrocarbon or water) will signify the possibility of a leak and put the system into an alarm condition. The system may also initiate positive submersible turbine pump shutdown as a result of a vacuum of liquid alarm condition.
This type of system is highly accurate and offers real-world advantages over other technologies. For starters, vacuum and pressure monitoring systems do not maintain a head pressure within the interstitial space that is greater than operating conditions within the primary containment. Brine tanks do maintain a higher head pressure and may weaken the containment.
Further, because the CVMS replenishes itself with air, supplied via the STP siphon port, the system automatically maintains the correct vacuum levels at all times to ensure accurate monitoring at all times.
A CVMS typically consists of four main components:
- A Control Unit housed inside the building and used to identify any alarm conditions. The system can monitor interstitial spaces separately or together depending on site-specific options.
- Vacuum Lines are attached to a sump unit and to the piping interstices with all product, vent and vapor piping terminating into the turbine sumps for easy access. On certain configurations, a “Vacuum Bridge” between the interstice of the piping located in separate sumps will be used.
- The Sump Unit is mounted inside the tank sump and includes a liquid float switch, turbine siphon and pressure switch, and is the point where all vacuum input lines originate for connection to tank, sump and primary pipe interstices and penetration fittings.
- Vacuum Indicator Gauges are used to pinpoint the precise location of leaks in the event of an alarm.
Vacuum systems are considered to be so accurate and reliable that they are even used to assure the integrity of new tank secondary containment from the time of production to the time the tank is backfilled. Any significant loss of vacuum is an indication that the system requires further investigation before the product is put into use.
The success of CVMS in California is catching the attention of other states as it is now viewed as the most effective means of leak detection. In fact, Florida is already considering following California’s lead of requiring continuous monitoring of secondary containment piping by vacuum, pressure or brine systems. In Florida, this is being driven by an increased emphasis on environmental protection against hydrocarbon discharges after more than 175 polyethylene piping incidents had occurred there over the past several years. Of these incidents, 12 percent resulted in hydrocarbon discharges into the environment. Although the majority of the leaks were contained in the piping interstice, the Florida Department of Environmental Protection states that more stringent monitoring is warranted.
Conclusion
Even without regulatory mandates, tank owners are increasingly concerned about protecting the environment and are deciding on the use of secondary containment monitoring because it offers substantial benefits. The environmental advantages of secondary containment monitoring would include the ability to provide additional insurance against product releases into the soil or groundwater. The financial and operational advantages would include simple and cost-effective leak-detection monitoring and an added level of protection against improperly installed or maintained tanks. From a financial standpoint it is a small expense to pay when compared to the potential costs that could be incurred from fines, cleanup, report writing, lawsuits and business interruption in the event of a release.
Continuous vacuum monitoring’s ability to deliver a higher level of monitoring capability than ever before attainable will undoubtedly pay environmental dividends we can all appreciate.
