Upper Occoquan Sewage Authority Replaces Ultrasonic Flowmeters with Marsh-McBirney Flo-System

The Occoquan watershed lies just southeast of Washington, D.C. and serves as a major water source for over a million citizens in the northern Virginia area. Prior to the 1960âs the area was primarily rural until infrastructure improvements led to rapid population increases of approximately 500 people per week. The dammed water from the watershed formed the Occoquan Reservoir which supplies water for residents, however the dramatic population increase adversely affected water quality. Once adequate local treatment plants treatment plants were operating at or over capacity in this now thriving suburban area. Plans were quickly set in motion to make management of the watershed a top priority for the sustenance of the region.

A comprehensive plan was adopted to build an advanced treatment plant with high treatment standards that could successfully discharge into the reservoir. The alternative plan to divert discharge out of the Occoquan watershed was denied. The construction of the Upper Occoquan Sewage Authorityâs (UOSA) Regional Water Reclamation Plant was completed in 1978 resulting in plant capacity of 54 MGD. The UOSA plant services Prince William, Manassas, Manassas Park and portions of Fairfax counties.

The world-renowned plant is comprised of sophisticated water reclamation systems that meet the highest treatment standards in the world. For over 20 years, the UOSA facility has produced water by a method known as indirect potable reuse water. The water is highly treated recycled water that is returned to the natural environment and mixes with other waters for an extended period of time. The blended water is diverted to the treatment plant for sedimentation, filtration and disinfection before it is distributed. The mixing and travel time of the water through the natural environment provides the benefit of sufficient time to assure that the treatment system has performed as designed and the opportunity for additional treatment through natural processes such as sunlight and soil filtration. Most importantly, this method provides increased public confidence that the water source is safe. Today, unplanned indirect potable reuse is occurring in also every major river system in the United States.

An integral factor in the efficient operation of the UOSA plant is the accurate monitoring of wastewater flows throughout the facility. When problematic ultrasonic flowmeters failed to provide accurate and reliable flow readings, plant personnel began their search for replacement meters. Don Thompson, Industrial Controls Manager at UOSA, states, 'We had some strap-on ultrasonic meters and some time interval type meters that did not work well in these applications.ä Marsh-McBirneyâs local representative, Butch Blanton of Coastal Products, regularly stopped by the plant to see if there were any problems that he may be able to assist us with in the plants equipment needs."  Thompson adds, 'Butch usually asks me what kinds of things Iâm having problems with. It just so happened that I was having problems with one of the ultrasonic meters on that day he stopped by and he said he had the solution!ä Thompson accepted Blantonâs recommendation to try Marsh-McBirneyâs Model 282 Insertable Full Pipe Flowmeter on a trial basis. The Model 282âs electromagnetic sensor can be used for pressurized line applications from 2 to 96 inches. Because price is independent of pipe size, the Model 282 offers a cost-effective alternative to traditional flowmeters whose costs go up as pipe size increases.

The Flo-System Model 282 is used to measure water and wastewater as well as any type of industrial flow processes involving conductive fluids such as potable water, slurries, sludge, cooling water, and pulp stock. Velocity and pipe diameter information are utilized by the Model 282 to accurately determine flow over wide flow ranges. The Model 282 sensor has provided unsurpassed performance for nearly two decades.

Pleased with the exceptional performance of the trial meter, Thompson placed an order for an additional 10 meters. The analog output from the flowmeters is fed into the plants distributed control system where it is used to adjust the influent valves. Additionally, Thompson states, 'We are measuring the influent flow into our selectors and the return activated sludge. Daily flows are also tracked through the basins.ä

'We like the ease of installation and the ease of setting the meters up.ä, he adds. The Model 282âs electromagnetic sensor is installed through a standard hot-tap without the need to divert or interrupt plant flows. The sensor is installed and operating within minutes. The meterâs electronics utilize easy-to-use menu-driven software for ease of instrument set-up and monitoring.

'The 11 meters are working great which is why we are ordering an additional five meters, making it a total of 16 meters at the plant.ä, Thompson adds. Once concerned with unreliable flow instrumentation, the Mode 282 flowmeters have provided the perfect solution for the UOSAâs state-of-the-art facility as it continues to produce high quality water for the region.