City of Alton, Illinois

Located 25 miles north of St. Louis, Missouri, the City of Alton, Illinois is home to 30,000 residents. Alton sits at a historically important point of the American Midwest, near the confluence of the Illinois, Missouri and Mississippi Rivers.

Responsible for streets and wastewater treatment/maintenance is Alton’s Public Works Department. Alton’s collection system consists of sanitary, storm and combined sewers that include 205 miles of main lines, 3,680 manholes, 1,026 catch basins, 858 inlets and 13 pump stations. The regional treatment system for Alton and six neighboring communities has an average daily flow of 8 MGD with a capacity of 10.5 MGD design flow and 26.25 MGD peak flow.

Alton, like many older communities throughout the United States, has some outdated infrastructure that includes combined sewers that collected both stormwater runoff and sanitary sewage in the same pipe. A portion of Alton's sewer lines date to the 1800’s with the last combined system constructed in the 1920’s. In the 1960’s Alton began the separation of their systems. During dry weather, "combined sewer systems" transported wastewater directly to the sewage treatment plant. In periods of rainfall or snowmelt, however, the wastewater volume in a combined sewer system can exceed the capacity of the sewer system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess wastewater and storm water directly to nearby streams, rivers, lakes, or estuaries.

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. 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. Alton is currently working with an outside engineering firm to investigate the use of a natural wetlands treatment process for two of their CSO’s that is pending EPA approval. The wetlands approach has the capability of saving taxpayer dollars versus the traditional method of installing piping separations and system rerouting.

According to Bob Roth, Wastewater Treatment Superintendent, City of Alton, “We use the Sigma flow meters primarily to monitor (3) CSO’s known as Shields & Central, Piasa and Turner Track. We also use Sigma meters throughout collection system to monitor flow at times. Sigma meters have been used at the city since the early 90’s, about 17 years now. In conjunction with flow monitoring we also use Sigma samplers.” The City of Alton currently utilizes three Sigma meter models to monitor flows including (3) Model 920’s, (2) Model 910’s, and (2) Model 950’s in their open channels in pipes. Typical line sizes monitored are between 8" to 42” lines.

Integral to the reduction of CSO flows at Alton is the accurate measurement of flow provided by the Sigma 920 meters. Roth adds, “We do utilize multiple sensors. We have enjoyed working with the software, Insight, and do all of our own reporting. The DTU’s (Data Transfer Units) are great for the field crews because it allows them to download the data versus using a computer in the field.”

The Sigma Model 920 Area Velocity Flow Meter can be used in portable or permanent applications and is available with up to two independent level/velocity channels. You can measure level and velocity in two channels or velocity in one and level in another. The meter is housed in a rugged yet ergonomic watertight enclosure (NEMA 6P) measuring only 7 x 18
inches. Available with submerged pressure transducer/velocity sensor or in-pipe ultrasonic depth sensor combined with a “waferthin” velocity sensor that provides greater accuracy in shallow flows such as those seen in Alton’s Shields CSO location.

In closing, Roth states, “The Sigma flow meters are rugged and their longterm stability has been great too. That’s why we’ve stayed with them for so long.” Going forward, Roth notes that the City of Alton may consider Hach’s Flow Meter Trade-Up Program to allow them to upgrade to the ‘latest and greatest’ Hach flow meter offerings.