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U.S. County is First in Flow Also

New Castle County, Delaware, the U.S.'s first county in the first state, is located in the northern most part of the state. New Castle County is the state's primary economic center, representing a major portion of the state's taxable base and population, and serves as its leading business, service, and industrial center. The County has a strong industrial base, and is one of the chief chemical manufacturing centers of the world. This densely populated area represents one-third of the entire state's population.

The Environmental Operations division of the Special Services Group is responsible for 1,700 miles of sewer lines that include over 40,000 manholes. The Special Services Group is responsible for flow monitoring of these lines in addition to many other related tasks. In order to better serve its residents and comply with federal mandates, a substantial financial commitment was made by the county to resolve the sewage overflows and backups experienced by their residents. This long-term commitment would take years for the Environmental Operations Group to accomplish with some phases requiring the use of contracted consulting services.

System rehabilitation work required for the project as well as post-modification effectiveness are evaluated using Marsh-McBirney flowmeters. Prior to utilizing Marsh-McBirney flowmeters, level-only meters including Manning dippers were used by the county, as well as smoke and dye tests that are still performed today to verify some county flows. The Special Services Group purchased their first Flo-Tote Area/Velocity open channel meters in the early 90's for the project.

The Flo-Tote (pictured at right), introduced in the 1980's, was the world's first computerized "data-logging" flowmeter and revolutionized the way open channel flow monitoring had been performed for decades. At the time of the initial purchase, the county was working with a consulting firm that used Marsh-McBirney flowmeters however due to escalating fees and data reporting errors, an investigation ensued into the requirements necessary for the county to perform their own flow studies. A year prior to the initial purchase, Lynn Gillespie, Sr. Sanitary Maintenance Technician, attended Marsh-McBirney's 3-day Flo-Tote Training class and was impressed with what he had learned. Lynn reported his findings back to the county and a decision was made to allow the county to purchase their flowmeters directly from Marsh-McBirney and provide their own data collection services. Today, New Castle County relies on a fleet of over 50 Marsh-McBirney flowmeters to accomplish the tasks at hand.

In addition to the purchase of the Flo-Totes, several Marsh-McBirney Flo-Mate hand held portable velocity flowmeters were purchased for spot-check velocity measurements where an instantaneous readout is required. Gillespie states that "...a snapshot of the flow can easily be accomplished from the surface with Flo-Mate. We also use the meter to verify in-line flowmeter accuracy or determine by-pass pump sizes. With the Flo-Mate I can give an answer in 5 minutes versus hours of long-hand work that the process previously required."

When Marsh-McBirney introduced their newest generation of open channel flowmeter, the Flo-Dar non-contact velocity/area meter, Gillespie was intrigued that a product was finally available that did not require a submerged sensor. Flo-Dar provides the user with highly accurate flow measurements under a wide range of flows and site conditions. By measuring the velocity of the fluid from above, Flo-Dar eliminates accuracy problems inherent with submerged sensors including sensor disturbances, high solids content and distribution of reflectors. Flo-Dar transmits a digital Doppler radar beam that interacts with the fluid and reflects back signals at a different frequency than that which was transmitted. These reflected signals are compared with the transmitted frequency. The resulting frequency shift provides an accurate measure of the velocity and the direction of the flow. Depth is detected by ultrasonic pulse echo. Flow is then calculated based on the Continuity Equation:

Q = V x A, Where Q = Flow, V = Average Velocity and A = Area.

In February 2000, five Model 460 Portable Flo-Dar meters were ordered by the County. The county relies on the Flo-Dar meters primarily for monitoring applications that are difficult to measure with submerged sensor type meters either due to metering location (physical size/depth), low flows or heavily debris-laden flows. After the initial sensor installation, confined space entry is not necessary by data collection personnel since the Flo-Dar sensor can be easily removed from street level by means of a retrieval tool. Gillespie feels that the real benefit of confined space entry elimination for him lies in the time-savings, an important asset when there are just two people performing the work.

Flo-Tote and Flo-Dar flowmeters both utilize Flo-Ware software designed by Savannah Environmental. The Flo-Ware for Windows Model T-200 communications program allows for viewing of real time data, site instrument adjustment and data retrieval. Lynn states that "The Flo-Ware software support I have received from Savannah Environmental is the best I have gotten from any company,"

As New Castle County's commitment to eliminate CSO's and maintain a reliable wastewater system continues through the years, Lynn looks forward to Marsh-McBirney's customer commitment to continuously design and develop innovative problem-solving flow instrumentation.