City of LaPorte Chooses Flo-Dar Flowmeter for Difficult CSO Application

Sewer systems built before the mid-20th century disposed of their sewage by allowing it to be directly discharged into rivers and streams. These sewer lines also carried storm water runoff to the river. Concern for water quality and public health led cities to build sewage treatment plants whose wastewater was treated before discharge. New sewer lines were constructed to carry wastes to these treatment plants. Diversion dams were built in the old sewer lines to divert sewage into the new system and to prevent sewage from discharging into the river, except during rainstorms. 

The old river discharge openings, or outfalls, were left in place to act as "relief valves" to prevent sewage from backing up into people's homes during storms. Since combined sewers also carry storm water, rain increases the volume of water in the system, which then overflows the diversion dams allowing raw sewage into the rivers. These overflows are referred to as Combined Sewer Overflows, or CSOs. 

In 1989, the U.S. Environmental Protection Agency (EPA) adopted a Combined Sewer Overflow Strategy designed to reduce and eliminate the more than 1,000 nationwide combined sewer overflows. At that time, more than 1,000 cities had CSO's. States were required to develop strategies to reduce pollution from combined sewers and bring dischargers into compliance with the federal Clean Water Act. 

Today the number of cities with CSO's has been reduced to approximately 772. One of the 772 cities with a CSO is the City of LaPorte, Indiana. The reduction of CSO flows is a major concern to this picturesque community dotted with sizeable lakes that provide various types of water sports. For decades, LaPorte has been known as a manufacturing center and today is home to nearly 100 manufacturing firms.

For the City of LaPorte, IN, the measurement of flow in a large CSO application was critical for the CSO reduction phase of their long term control plan (LTCP). Jerry Jackson, Superintendent for the City of LaPorte's Wastewater Department, had the responsibility to purchase a flowmeter that would provide accurate flow readings for this "difficult to instrument" channel. The application has a diverter that includes a holding basin positioned at the head of the wastewater treatment plant. In the past, this application had proven difficult to measure. A level only device was originally installed in the basin but due to large solids content, only rough estimates were available. The installation of a weir or flume was also considered and ultimately ruled out as a means of measuring flow due to purchase/construction expense and inefficiency due to the high flow levels and solids content.

A trade journal advertisement for the Marsh-McBirney Flo-Dar Flowmeter caught Jerry's attention and he was referred to the local sales representative, Chesley Associates. An attractive feature of the Flo-Dar for this application was that the sensor was installed above the flow and there was no need for a submerged sensor that could get fouled by debris. Also, the flow channel being instrumented had side walls that created an odd shaped channel making it difficult for most flowmeters to measure. The large size of this CSO application required the extended level feature of the Flo-Dar flowmeter that allows for the measurement of high levels ranging from 60 to 240 inches. This feature was ideal for LaPorte's CSO application where previous flow measuring devices had failed due to high levels.

The city has conducted several comparison tests between the known volume of the holding basin with that of the flow data from the Flo-Dar flowmeter. Jerry was quite impressed with the Flo-Dar accuracy, which indicated flow readings within 2-3% of the known basin volume. Decisions on future infrastructure improvements, including a screening and solids facility, will be determined utilizing the Flo-Dar flow data.