They brave the depths of hundreds of miles of sewers beneath our cities. They may encounter rats, roaches, dark passages and can we talk about the smell? No, we’re not talking about a day in the life of the famous man who dons a rumpled brown fedora (a.k.a. the hat). We’re talking about a day in the life of SEH field expert Paul Kubesh and I/I technicians who setup flow monitoring instruments in your city’s sanitary sewer collection system.
One method used to identify inflow and infiltration (I/I) is to pinpoint where problems occur and isolate the areas that have the highest contribution of I/I and establish a flow monitoring program. The program should help to identify the presence, quantity and type of I/I issues which exist in the sewer system and provide information to assist cities with fulfilling the requirements of the federal and state Clean Water Act.
And the time of year matters according to Paul Kubesh, who is an expert at conducting flow monitoring programs. “Ideally cities should install the meters in February or March to get dry-winter weather flow and meltwater. Then summer brings rainfall events and hopefully you get a few big rainfall events to capture enough flow data—the more data the better.”
Inflow and infiltration are terms used to describe clear water, including stormwater and groundwater that enters sewer collection or wastewater system directly (inflow) or indirectly (infiltration):
I/I can result in negative environmental impacts, regulatory compliance issues, higher treatment costs, basement backups and excess wear and tear on the collection system. Additional water from I/I sources reduces the useful life, and the capacity of sewer systems and treatment facilities to transport and treat domestic and industrial wastewaters. Sewer flow monitoring helps communities determine whether their pipes are undersized in a certain location, what pipes need replacing and where leaks might cause problems, among other things.
Sanitary sewer flow monitoring generally involves placing equipment, usually a sensor, into the sewer flow—or above the sewer flow depending on the type of equipment. The sensor measures the depth and velocity and uses those parameters, along with pipe size and shape to calculate the flow rate. Sensors are placed in the sewer pipes, and a data collector is hung near the top of a manhole.
The goal of sewer flow monitoring is to gain knowledge and collect accurate and current information on the flow characteristics of the study area. The information provided by flow monitoring will help to locate those areas that have excessive I/I and determine if those areas need further investigation. This task should be conducted at the earliest possible stage to minimize the survey costs.
A meter installation consists of four components:
Whether your city has one district or 50, it’s important to map out the district location(s) before you begin. Geographic Information System (GIS) mapping of the sewer system includes sewer, water and storm drain system and provides the data necessary for analysis within each district.
A confined space is defined as any space that is large enough and so configured that a person can bodily enter and perform assigned work, has limited or restricted means for entry or exit and is not designed for continuous employee occupancy. In general, the atmosphere must be constantly monitored for sufficient levels of oxygen, and the presence of hydrogen sulfide gas, carbon monoxide gas and lower explosive limit levels.
“Everyone doing this work is confined space trained—safety is first so we don't have any issues,” says Kubesh. We don't want issues for ourselves or our clients.”
Traffic is another safety issue and SEH field experts manage traffic on most projects. “We may only be at one location for a half hour, or longer depending on the size of the pipe, so we take care of the traffic throughout the entire process,” says Kubesh. Because we are a moving system, we get traffic plans from the city and then manage the setup and tear down.”
When SEH field experts are ready to install flow meters, they make sure they have the essential field safety gear and equipment. Here’s a check-list of the recommended gear to help them do their job safely, or just make it easier:
Additional field gear includes, but is not limited to:
Now that they’re prepared with the recommended safety gear and a plan, they’re ready to venture to the project site and begin the meter installation. When they arrive at the first project site, what’s next? These are the field procedures followed:
At the job site, SEH field experts document existing and physical conditions of the collection system being evaluated. They identify and evaluate manhole(s) in the area and identify problem areas. Flow meter placement is similar to purchasing real estate—location is everything. The SEH field technicians select the manhole based on flow characteristics, identifying locations free of sediment and look for smooth linear flow conditions through the manhole.
In addition, each site is selected for ease of equipment installation and the physical characteristics of the manhole to determine if it is suitable for flow meter placement.
After a thorough site evaluation is complete, the manhole cover is opened and an air monitor device is lowered into the manhole to test the levels of oxygen, and the presence of hydrogen sulfide gas, carbon monoxide gas and lower explosive limit levels. Once completed, they set up the safety and non-safety equipment needed for installation which includes:
Communication is key between the field expert in the manhole and field experts above ground.
“Depending on the pipe size and I have everything at my disposal, one installation can take as little as 15 minutes if all goes well,” says Kubesh.
A GIS-based application is used to document the following installation information:
The data is downloaded over two weeks and uploaded to a server where it can be reviewed and analyzed for I/I contribution based on wet weather events. “If we know a significant rain event is forecasted, we will go out and download data before the event,” says Kubesh.
The flow data can be used to identify problem areas and establish additional investigation measures to target specific I/I sources.
When a flow metering program has been completed, additional steps cities can take to reduce or stop inflow and infiltration include: conducting manhole inspections, smoke testing, dye testing, closed circuit television (CCTV) inspections or private property inspection.
Inflow and infiltration (I/I) can result in negative environmental impacts, regulatory compliance issues, higher treatment costs, basement backups and excess wear and tear on the collection system. Sewer flow monitoring is the first step in identifying where problems are occurring and isolate the areas that have the highest contribution of I/I by establishing a flow monitoring program.
Paul Kubesh is a senior lead I/I technician with 16 years of helping cities find solutions for inflow and infiltration. Contact Paul