By Steven Fann, P.E., William Naughton, PG, M.SAME, and Paul Treloar
In May 2016, a field demonstration project was performed on the Operations Area at Naval Air Station Lemoore, Calif., to demonstrate the efficacy of ice pigging to remove 50 years of biofilms and sediment buildup in the base’s drinking water distribution systems.
Excessive buildup of biofilm and sediment in water distribution systems can lead to loss of residual disinfectant as well as the generation of elevated levels of disinfection byproducts, such as nitrite/nitrate and trihalomethanes (THMs), which can trigger violations of the Safe Drinking Water Act. These concerns are commonly addressed by extensive hydrant flushing programs to discard water that no longer has adequate residual disinfectant and continue flushing until adequate residual disinfectant is restored.
Ice pigging involves pumping a slurry of ice into a main through a hydrant or other existing fitting and using system pressure to propel the pig downstream. It harnesses the characteristics of the semisolid ice slurry, which can be pumped like a liquid but behaves like a solid once the pig is formed in the pipe. As the pig travels downstream, the natural glacial effect of the ice scours the pipe and entrains, rather than bulldozes, accumulated sediment and biofilm. The ice pigging waste is collected through downstream hydrants for disposal.
Because the pig is semisolid, it cannot become stuck in the pipe like conventional hard, mechanical pigs or soft swabs. An ice pig can maneuver pipe bends, diameter changes, partially closed gate valves, and in-line butterfly valves without risking system blockage or damages. Any ice that remains behind simply melts. Ice pigging efficiently removes biofilms in water lines and improves the look and taste of drinking water. It reduces the need for treatment chemicals, uses approximately 50 percent less water than traditional hydraulic flushing techniques, and takes less time. Typically, the section of main being cleaned is out of service for no more than 30-min to 60-min.
Developed at the University of Bristol in the United Kingdom, and patented in 2005, ice pigging has been used in the United States since 2012 and is offered exclusively through SUEZ North America.
Located in the rich agricultural lands of the San Joaquin Valley in a semi-arid climate region, Naval Air Station Lemoore was deemed a good candidate for a field demonstration of ice pigging on a military installation because the base suffered from persistent and recurring issues in maintaining adequate chlorine residual levels in its potable water supply.
The study was performed by the Naval Facilities Engineering & Expeditionary Warfare Center at Port Hueneme, Calif., in collaboration with the U.S. Army Engineer Research & Development Center, SUEZ North America, and National Resources Consultants. It was sponsored by the Environmental Security Technology Certification Program.
The chlorine residual issues were partly due to pipe run dead ends, which result in low chlorine residuals and the need for increased chlorine dosage, and the low-flow velocities common in piping that is oversized to meet Department of Defense fire flow requirements. Due to poor water quality, Lemoore was cited for violating the Safe Drinking Water Act. In addition, California regulations and Executive Order 13514 require facilities, including military installations, to reduce water usage, including water used to flush potable water systems.
Because of its arid climate, Lemoore would obtain faster payback due to its location in an area prone to water scarcity that necessitates the implementation of aggressive water conservation measures. Another important factor was that the site has pipelines exceeding 3,000-ft in length to allow the demonstration of ice pigging’s ability to clean long pipes.
The demonstration at Lemoore cleaned 55,845-ft of pipes with diameters ranging from 8-in to 16-in. To evaluate the technology’s performance, benefits, and costs, the project monitored hydrant flushing frequency and volumes and system water quality, including a bacterial analysis pre- and post-pigging to validate improvements in system operations.
At Lemoore, the main was flushed briefly to note and record pre-flush readings. Public Works Department operators then isolated the main, and the required amount of ice was pumped in. At the same time, the outlet hydrant was opened to create a flow and allow water to be displaced as ice entered the main. The operators carefully controlled the flow between inlet and outlet to allow slightly more ice into the main than the amount of water being displaced. This allowed the ice to form a pig against a pressurized wall of water.
Once the required amount of ice was in the main, the delivery pump was turned off and the upstream valve opened to allow the system to flow and pressure to “push” the ice pig along the main toward the outlet hydrant. The flow rate was controlled by the outlet operator to maintain the line pressure above 20-psi. As the ice passed through the pipe, it removed and collected sediment, biofilm, and debris that had accumulated around the circumference of the pipes since 1961 and had not been removed by traditional flushing techniques.
Several performance objectives were established and validated through baseline monitoring prior to ice pigging, sampling and analysis during ice pigging operations, and after ice pigging monitoring. Performance categories included reduction of water used in hydrant flushing to cleaning effectiveness, residual chlorine, THM compliance, turbidity, chlorine consumption rate, system economics, impact to water system and facility operations, user satisfaction, and customer satisfaction.
Monitoring was performed through appropriate on-line monitors, collecting grab samples for laboratory analyses, and examination of operational log books and historical monitoring records. The collection data included amounts of sediment removed, residual chlorine, water used for hydrant flushing, chlorine consumption, bacterial testing, and bacterial community analysis.
Significant improvement in the operation of the system was demonstrated after ice pigging.
- Sediments removed by ice pigging ranged from 8.3-lb/mi to 81.8-lb/mi of pipe cleaned. Conversely, conventional hydraulic flushing did not remove any sediment.
- Residual chlorine did not change significantly before and after ice pigging and was steady at a level above 0-mg/l.
- Water used for hydraulic flushing was reduced 55 percent, from 5.5-million-gal/year before ice pigging to 3-million-gal/year after ice pigging.
- Annual water consumption was reduced by 6 percent, exceeding a federal goal of 2 percent.
- Sodium hypochlorite consumption for re-chlorination was reduced by 465.1-gal/year, and there was no THM violation after ice pigging. (Four violations were recorded the year prior when only conventional hydraulic flushing was performed.)
- Ice pigging effectively cleaned 9.3-mi of water mains in 12 days.
Results of the bacterial community analysis study in water distribution pipelines using 16S rRNA sequencing procedures showed that ice pigging removed entrenched biofilms and bacterial species highly resistant to the disinfectant. Conventional flushing only removed bacterial species closer to the surface of biofilms in contact with water. Also, in pipelines with extreme levels of chlorine, highly resistant bacilli predominated, whereas proteobacteria formed the predominant species under less extreme circumstances. Biofilms can exert chlorine demand and generate THMs. Therefore, the effective cleaning provided by ice pigging can help maintain distribution system water quality for a longer time horizon.
This successful project at Naval Air Station Lemoore demonstrates a cost-effective way to lower operational costs while improving the quality of drinking water for servicemembers and their families.
William Naughton, PG, M.SAME, is Director, Federal Markets, and Paul Treloar is Product Manager, SUEZ North America. They can be reached at email@example.com; and firstname.lastname@example.org.
Steven Fann, P.E., is Environmental Engineer, Naval Facilities Engineering & Expeditionary Warfare Center; email@example.com.
[This article first published in the January-February 2020 issue of The Military Engineer.]