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Vallecitos Water District Uses Flo-Dar for Better Management of Sewer System

In 1999, when the Engineering and Operations Department for the Vallecitos Water District (VWD) had a requirement to monitor wastewater flows at California State University-San Marcos, they chose two Marsh-McBirney (MMI) Flo-Dar Flowmeters. VWD had purchased MMI's Flo-Tote Open Channel Flowmeters (submerged type sensors) in the early '90's and was familiar with the quality engineered into MMI's flowmeter product line. The revolutionary Flo-Dar flowmeters had recently been introduced to the industry and the VWD felt that the unique features of the meter would be ideally suited for this billing application as well as for future I&I (Inflow and Infiltration) projects that were in the early development stages.

Two permanently installed Flo-Dar flowmeters would monitor the university's sewage flows to assess contracted capacity fees being paid to the district for sewage processing at the local wastewater treatment facility. Totalized sewage flow, as determined by the Flo-Dar meters, would be balanced with the university's water usage to determine capacity fees. A contract between the VWD and the university stipulated that the flowmeter selected for the billing application needed to have the ability to capture short duration flow peaks as well as flow totals, making the highly accurate Flo-Dar meter a perfect solution.

The Vallecitos Water District (VWD) is an independent district that provides water, wastewater and water recycling services to approximately 67,000 people in San Marcos, portions of Escondido and Carlsbad, and the surrounding unincorporated areas. The area encompasses over 200 miles of sewer lines ranging in size from 4" to 54". VWDâs facilities include 3 lift stations, a 2.5 mgd reclamation facility as well as a 7.54 mgd wastewater facility. The Engineering and Operations Department is responsible for the operation and maintenance of wastewater systems within the district as well as water systems, water reclamation and water quality.

The Flo-Dar Model 450's selected for the application were specifically designed for long-term monitoring projects where AC power is available. The product has a direct readout and two standard 4-20 mA outputs. The Flo-Dar flowmeter measures open channel without the need for a submerged sensor. The "above-the-flow" installation eliminates maintenance and lost data due to sensor fouling, essential criteria for this billing application. Flo-Dar's easy installation requires no manhole entry and the sensor can be installed and/or removed from street level. With Flo-Dar, on-going costs associated with confined space entry manpower and equipment are eliminated.

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. Level 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.

Chuck Reuck, VWD Capital Facilities Coordinator, comments, "The meters at the college are very reliable. Our sewer crew loves them because they can just walk up and get the readout from the meters and move on. The meters have reduced our man hours quite a bit and we donât have to babysit them. It is a very low maintenance item."

"With the Flo-Dar sensor we don't have to worry about the sensor and band becoming dislodged and losing our data ever again."

Due to the positive experience in the Cal State metering application, the VWD again contacted MMI about the purchase of additional Flo-Dar flowmeters for I&I work associated with their master plan as well as several capital improvement projects. The flowmeters needed to be compatible with the district's current telemetry systems. After an initial trial period with the Flo-Dar Model 464 flowmeter, VWD made the decision to purchase an additional 14 flowmeters. The trial meter was also installed in a billing application where it monitored wastewater flow at a local dairy. Submerged sensor type flowmeters had previously been installed at the site. Due to escalating maintenance costs and the loss of flow data that would commonly occur when the line flooded, the above-the-flow radar measurement technology of the Flo-Dar meter was ideally suited for the application. Reuck adds. "With the Flo-Dar sensor we don't have to worry about the sensor and band becoming dislodged and losing our data ever again."

The Model 464 transmitter is wired to a RTU where an analog radio transmits the flow signal to an existing site in the system that has the master PLC (programmable logical controller). Reuck comments, With the 4-20 outputs it is so easy to have that put into a radio system where it can be sent back to a central office. We don't have to go to the field and read the flow data. You can just sit at your computer and collect the data. With the spread-spectrum radios we use there is very little cost there." VWD also has a separate SCADA system for the sewer group. They receive their flow status at various points in the system and in the near future, simple algorithms will be built in to track the flows and alarm off any excessive flow or any significant, immediate drops in flow. According to Reuck, "This will give us an indication of line breaks that could cause significant infiltration. Currently we are trying to capture the data and alarm off of any drastic decreases that might indicate a line break. Due to the high profile incident in San Diego (30 million gallon wastewater spill in February 2000 resulting in $3.5 million dollar penalty), everybody in the San Diego and L.A. (Los Angeles) area is very keen on checking for leaks. It is a very high priority." Statistical analysis and graphical reporting of the flow data is performed using WonderWare software, developed by Invensys.

Prior to monitoring flow with the Flo-Dar meters, VWD utilized contracted turn-key services (flowmeter and data reporting services provided by another flowmeter manufacturer) for several different I&I studies. Reuck explains, "Meters with submerged style sensors were used for the studies. After reviewing the data, we felt that some of it was questionable. It just did not look right." Based on this experience, the district made the decision to purchase the Flo-Dar meters and perform their own flow monitoring studies.

Reuck looks forward to future I&I work and capital improvement projects where the Flo-Dar meters will be integrated. He adds, "These Flo-Dar's are such maintenance-free items that our operators can go on and worry about other things. Their accuracy is far better and more reliable. The installation was also a breeze - it only took about an hour. You just follow the provided directions and everything works perfect. The Flo-Dar may cost a little more but in the long run it really pays for itself."