Florida Utility Realizes Collection System Optimization, I&I Control with Flow Monitoring

The utility’s sanitary sewer system serves around 90,000 customers​ through a collection of almost 900 miles of gravity main pipes and 300 miles of force main. Around 35,000 maintenance holes and 400 lift stations are also managed by ECUA. Much of the city’s infrastructure was built in the late 1800s, and some of the original vitrified clay pipes are still in use today.

In recent years, the area’s high rainfall and aging infrastructure led to inflow and infiltration (I&I) problems and costly Sanitary Sewer Overflow (SSO) events for the utility staff to manage.

“Tracing rainfall inflow is very important for us, because we're in the top three rainiest cities in the lower 48,” said Mark Evan Robertson, Manager, Wastewater Infrastructure with ECUA. “Because we have a high groundwater table, the infiltration is pretty consistent. But during a rain event, monitoring the inflow can help us to narrow down [areas in the system that may be leaking and] we need to investigate.”

To help map and generate flow reporting for I&I investigations, ECUA outsourced lift station monitoring and control at an annual cost of about $320,000 for hardware equipment rental and software licenses.

Typically, level sensors are installed for about 3-4 months to gather data and trends and then relocated to another area of interest.

“When I joined ECUA, the utility was paying service fees for every device relocation, so many of the existing devices had been in the same spot since installation. The data being collected was no longer useful to the team,” Robertson recalled.

To lower service costs and to gain more insight by redeploying flow monitoring devices as needed, ECUA worked with Badger Meter to bring collection system monitoring in-house. With open channel flow monitoring devices, ECUA hopes to prevent rainfall inflow and costly overflow events in its system.

Raven-Eye 2 units identify I&I rates for future rehabilitation projects.

Initial Deployment Details

ECUA’s SCADA system provides lift station health data, including runtime reports and alarms for high water levels. This information is used to identify areas within the sewer network that may likely have a leak so that field crews can be assigned to investigate specific sites for sewer rehabilitation work.

The utility’s initial installation included eight Raven-Eye 2 flow meters with ultrasonic level sensors for operational awareness to monitor sewer levels and prevent overflows and leaks in the network.

The Raven-Eye 2 is an advanced, non-contact radar area and velocity flow meter that provides accurate and reliable flow data for monitoring and I&I detection while reducing the need for field maintenance.

“A lot of our basins are really tiny, and therefore a pressure or area velocity meter that sits in the flow line wouldn't be the best choice for these sites,” said Robertson. “The Raven-Eye 2 and RU-35 data logger can pick up such minuscule flow amounts that it's better for our operation here.”

In addition, several RG-32A Rain Gauge Recorders are installed at locations with rain tipping buckets. The wireless, battery-powered, single-channel rain gauge recorder is used to confirm rainfall data along with the lift station data for greater insight. Flow monitoring data is sent to the Remote Monitoring software from Badger Meter, allowing operators to view rainfall data and site-specific data together in a simple system.

“Data from the rain gauges is used in conjunction with lift station data,” Robertson explained. “If there is a runtime difference between a dry spell and a rain event, this may indicate the need for a closer look by our field staff.”

In some larger trunk mains, ECUA is installing Beluga Submersible Area Velocity flow meters. Both the Raven-Eye 2 and Beluga devices are used in conjunction with the RU-35 data logger, delivering a powerful solution for open channel flow monitoring, CSO and sanitary system overflow (SSO) monitoring, RDII analysis, surcharge monitoring and custody transfer billing.

Level monitoring units provide operational awareness, monitoring sewer levels so ECUA staff can prevent overflows and leaks in the network.

Putting the System to the Test

Recently, during a four-inch rain event, five lift stations reported high water level alarms. Robertson immediately deployed the level monitors in these locations to monitor water rates for about a month.

Typically, the utility would have performed smoke testing to find and repair a leak, but by positioning the devices to isolate several mains, ECUA was able to test a couple hundred feet in a sample versus a few miles of pipe.

“We just don't want to go smoke test an entire basin, because it’s just not cost-effective to just have our employees out there, spinning their wheels trying to find [a leak],” Robertson said. “[Deploying these devices] is like having another employee there, collecting data [so that we can be precise in our response].”

In one area, the utility was able to identify 6-8 lateral breaks where water was coming directly into the sewer system via a stormwater ditch, without the time and drain on utility departments associated with smoke testing an entire basin.

Building a Collection System Action Plan

As part of the requirements of the utility’s Consent Decree, staff are currently developing a collection system action plan to meet flow monitoring requirements.

“Part of our consent decree requirements includes pipe inspection, so we can use these devices to cover that requirement,” Robertson said. “We can continue to add devices to the system and expand the coverage area for complete monitoring of all areas [in the future].”

With trend reporting, users can see when results fall outside of typical values and investigate the highest change rates first for early response. The data helps operators and field staff focus their efforts and decreases response time for I&I events.

“Instead of level indication, the ultimate goal would be to fix all your inflow problems and monitor your flow and then see if a new inflow problem arises,” Robertson said.

Next Steps

With these level indicators in place, Robertson is working on tracing rainfall inflow data for a neighborhood previously identified for a sewer rehabilitation project. This pre-basin rehab data set will be compared against the post-rehab data to confirm the effectiveness of the system.

Using open channel flow monitoring devices from Badger Meter, ECUA is well on its way to eliminating incidents of rainfall inflow and preventing sanitary sewer overflows from impacting its network.