Reducing Inflow and Infiltration in Wastewater Systems

Stormwater flowing into a municipality’s sewer system through low gully traps, illegal connections, broken pipes, and unsealed manholes can cause overflows, system strains, and interruptions in your sewer operations. This is known as Inflow and Infiltration; aka I&I.

Why bother to fix Inflow & Infiltration?

By identifying I&I early and reducing their levels, municipalities can benefit from:

1. Reduced localized overflows: Through the management of overflows from manholes during rainfall, controlled overflow points, pump stations, and treatment plants.

2. Improve operational efficiencies: I&I reduces the sewer system capacity, limiting the potential for growth within a specific catchment.

3. Reduced ongoing costs: I&I results in clear water being pumped and treated along with wastewater, contributing to increased costs.

How to identify whether you have an I&I problem

Councils and water authorities can identify whether they have existing I&I issues within their system by looking for these indicators:

• Pumps run for hours and inflows increase significantly during storm events

• The hydraulic loading of wastewater treatment plants increases significantly after a rain event

• Localized overflows occur within a collection system during a heavy storm event

• An increase in inflow during dry weather conditions compared to previous months

Steps to reduce I&I within your wastewater system

First, identify the general vicinity of the issue through flow monitoring. Then identify the exact problem, locate the area(s) where it is occurring, and introduce measures to improve the situation.

The following steps provide a simple overview of an I&I reduction plan that can assist in identifying various stages associated with reducing I&I in a wastewater system:

1. Targeted monitoring – monitoring wastewater flows within the system

2. Identifying the problem – is it inflow or infiltration?

3. Source detection – where is it occurring within the system?

4. Rehabilitation – what can be done to reduce or eliminate the problem(s)?

Source detection

A few ways to detect the sources of I&I include:

Private Inspections – after receiving and documenting permission from property owners, inspecting private properties consists of visual assessments of the stormwater and wastewater networks within a property. Illegal connections could mean that a stormwater down pipe is directly connected to a wastewater gully trap.

Manhole Inspection – Manhole inspections can identify leaks from broken pipes, and joints due to tree root intrusion or design issues. Manholes can contribute to significant I&I through leaky covers as well.

Smoke Testing – Smoke testing locates I&I sources by identifying stormwater drain cross connections, broken pipes, and laterals, or unsealed manholes.

Dye Testing – Dye testing can be used to identify leaks and confirm smoke test results. The method uses water mixed with a non-toxic dye. The colored water Is pumped through the ground and storm water system and appears in the sanitary sewer collection system where leaks and illegal connections occur.

CCTV (closed circuit television) cameras – CCTV allows authorities to visualize the inside of pipes by using a small camera that travels down the length of a pipe to produce a visual representation of its condition. CCTV inspections can reveal the need for rehabilitating leaky pipes, facilitate grease or root removal, identify improper taps into the municipal lines, or find broken lateral connections.

Rehabilitation of Wastewater systems

Rehabilitation can include, but is not limited to, the following:

• Seal manholes and replace leaky covers

• Use cured-in-place piping (CIPP), trenchless rehabilitation or chemical grouting to seal leaks, and open cut replacement pipes

• Raise gully traps and disconnect stormwater downpipes from the gully trap and redirect into stormwater systems

• Fix broken laterals (reline or replace); fix any other private connections which might be improperly or illegally tapped into the municipal system

OMAG Risk Management Services wants to assist our municipalities in providing a safer and more efficient sanitary sewer system for their constituents. We offer several grants and programs to help you get started. Contact William Sheppard (wsheppard@omag.org) for more information if you are interested in improving your sanitary sewer system by reducing Inflow and Infiltration.

Preventing Waterjetting Injuries

You wouldn’t expect latex gloves to protect you from a gunshot. They won’t protect you from water-jetting accidents either. 

An OSHA article describing the dangers of high-pressure jetting notes, “High pressures can cause injuries similar to gunshot wounds, but have the added health hazard of involving contaminated water.” 

In pipeline-related industries, dangers are plentiful. Trenches, excavation, and confined spaces are often touted as the main concerns in risk management, but operators face another underestimated risk on a daily basis — cleaning with water under pressure. 

 “Injection injuries can happen at much lower pressures that are in use in drain and sewer applications. And that carries the risk of infection and tissue damage as well.  …Water injection injuries can appear minor but can cause serious health complications, even at pressures in the range of a consumer pressure washer or drain cleaner,”

says Peter Wright, association manager with the WaterJet Technology Association and Industrial & Municipal Cleaning Association. 

Despite being generally overlooked in terms of safety across the industry — due in part to a relatively low rate of injury when compared to working in trenches and the like — jetting is a concern simply because of how common it is. 

Lines are jetted for daily cleaning operations, inspections, and rehabilitation: With just about any work involving pipes, water jets are in play. 

 “Trying to get people to understand that you can get injured by a water jet strike is probably the most difficult bit to get across to people,” says Nick Woodhead, president of US Jetting. “We’ve got to start promoting safety.”

“I think people assume that hoses are not going to burst, and therefore, they are sort of immune. Or they’ve never seen a hose burst, or they’ve never seen a jet injury, so it doesn’t really register. People get complacent.” 

And it’s not just equipment malfunction that operators need to worry about. 

Case in point: Chad Unverzagt, the Indiana operator who was killed in 2012 during a routine sewer blockage. Unverzagt wasn’t killed by an exploding pipe or other malfunction — his hose got loose while the system was pressurized as he was attempting to retrieve it from the pipe. A momentary lapse in a job he’d done a thousand times before and for more than 30 years in the industry. 

With no protective gear, he didn’t stand a chance against the high-pressure water, which lacerated his neck, killing him before help could arrive. 

 “That’s more of an isolated incident, but it’s worth reminding people,” Woodhead says. “That’s why you’ve got to know what you’re working in.” 

A few months after that incident, Cleaner published another Safety First article, highlighting a new line of protective clothing from TST Sweden AB. Though the medium-pressure gear hadn’t reached enough awareness at the time to help Unverzagt, today, operators and their employers have fewer and fewer excuses for ignoring proper safety. 

“The safety gear is essential when you’re running a machine. So many people don’t wear anything,” Woodhead says. “We’ve got to try and get it across to people, it is worth investing in the kit to protect yourself. Even if you’re the operator and maybe the boss doesn’t want to spend the money; it’s worth investing in it, just as a precaution.” 

US Jetting has made it their practice to supply a pair of protective gloves to customers with the purchase of a jetting system, and it has encouraged other manufacturers to do the same. 

Other products like semiautomatic jetting systems give even more options for mitigating risk to operators. 

“OSHA says if there is safety gear available, the employers are bound to supply it,” Woodhead says. “Rather than have government regulation, we’d rather be self-regulated and have people understand (the dangers).” 

Beyond planning for the worst, simple common sense and following standard operating procedure goes a long way to ensuring safety. That includes checking the equipment before each job, performing the necessary maintenance, and assessing each job site before beginning any work. 

“It doesn’t take more than a couple of minutes to do the cursory checks,” Woodhead says. “Once you’ve gotten to your location, you’ve got to do your due diligence. … Just scope out the job for 15 or 20 minutes while your tank is filling up.” 

To get you started, Wright offers a few quick tips to keep in mind: 

“Use a skid that will not allow the nozzle to turn around in the pipe or mark the end of the hose a distance from the nozzle to help indicate the location of the nozzle within the pipe. Ensure the system is depressurized before conducting maintenance or repairs. Ensure the nozzle is well inside the pipe before bringing the system up to pressure,” Wright says. 

It’s easy to oversimplify pipe cleaning, but when the pressure is on, there’s a lot operators can do to prevent accidents — it’s just a matter of knowing how and promoting safety whenever possible. 

“It’s definitely important to have respect for the power and the force of high-pressure water streams,” Wright says.

MUNICIPAL WATER & WASTEWATER TREATMENT PLANT COVERAGE

Many of our Municipal Property Plan members own and operate their own Water and Wastewater Treatment Plants. Operating these plants can present challenges in providing routine plant maintenance, meeting growing population needs, staying in compliance with regulatory requirements and upgrading their outdated structures and equipment. Many have provided these upgrades and many more will soon need to do so. These upgrades can certainly impact values and leave your municipality exposed. Backup generators, upgraded or added pumps, electric control panels and SCADA systems are exposed to lightning and power outages. Buildings, fencing and lighting are exposed to hail and high winds and vandalism. 

 OMAG completed an appraisal project on all plants in 2020 through our partnership with a professional appraisal service. This was a five-year project targeted at appraising all of our members’ Water and Waste Water Treatment Plants. These professional appraisals were provided as a value-added service at no charge to members. Our purpose in performing these appraisals is to be certain that you are provided an accurate replacement value for these structures and equipment.

If you have any questions regarding your plants’ coverage or our professional appraisals of your plants, please contact Underwriting Director Chris Webb.   

Eliminate Water Hammer

WHAT IS WATER HAMMER?

Water hammer (or hydraulic shock) is the momentary increase in pressure inside a pipe caused by a sudden change of direction or velocity of the liquid in the pipe. Water hammer can be particularly dangerous because the increase in pressure can be severe enough to rupture a pipe or cause damage to equipment. 

CAUSES

It’s a simple fact that liquid flowing in a pipe contains two types of energy: potential energy and kinetic energy. Kinetic energy is attributed to its velocity and potential energy is represented by its pressure. Neglecting friction, the combination of kinetic and potential energy remains constant at all points throughout the length of the pipe. Changing the kinetic energy by changing the liquid velocity forces the pressure in the pipe to change. If the velocity of the liquid decreases (decrease in kinetic energy), the liquid pressure increases (increase in potential energy). 

Water hammer most commonly occurs when a valve is closed quickly and suddenly stops the flow of liquid in a pipeline. When this happens, shock waves travel back and forth through the piping system equal to the speed of sound in that liquid (for water at 70 degrees that is over 4800 ft/sec). These waves travel backward until encountering the next solid obstacle (frequently a pump or check valve), then forward, then back again until pressure is equalized.
Additionally, the sudden closure of a valve in a pipeline causes the momentum of the liquid column to exert a force on the valve’s shut-off element (disc, gate, or ball). This sudden separation of the water column causes two things to happen simultaneously: the pressure on the upstream side of the valve increases and pressure on the downstream side of the valve decreases. The liquid downstream of the valve will attempt to continue flowing, creating a vacuum that may cause the pipe to collapse or implode. This problem can be more serious if the pipe is on a downhill slope. 

To prevent a sudden change of pressure near the valve’s shut-off element, air and vacuum relief valves, or air vents, are installed just downstream of the valve to allow air to enter the line and prevent a vacuum from occurring.

Therefore, the proper opening and closing of valves is fundamental to safe pipeline operation. Closing a valve at the downstream end of a pipeline creates a pressure wave that moves in the upstream direction. Closing a valve in less time than it takes for the shock wave to travel to the end of the pipeline and back is called “sudden valve closure”. Sudden valve closure will change velocity quickly and can result in a pressure surge. 

OTHER CAUSES OF WATER HAMMER

• Rapid pump startup can induce the rapid collapse of a void space that exists downstream.
  Rapid pump shutdown can create a quick change in flow, which causes a pressure upsurge on the suction side and a pressure downsurge on the discharge side. Of the two, the downsurge is usually the major problem. The pressure on the discharge side reaches vapor pressure, resulting in vapor column separation.

• Check valve slam (Due to sudden deceleration, a check valve may slam shut rapidly.) 
  Movement of air pockets in a pipe. Air is compressible and if carried along in a pipeline, can act like a spring, being compressed at low spots in a line and expanding at high spots in the line. Compression and expansion produces pressure variations which, if great enough, could produce serious water hammer pressures. 

• Water-column separation can also result in serious water hammer pressure values when the separated column rejoins at high velocity. 

CONTROL

The following steps can be taken to reduce or eliminate water hammer:

• Proper education and training of personnel on the dangers of water hammer and how to mitigate them through proper opening and closing of valves.

• Use start-up and shut-down procedures for pumps that reduce the possibility of creating water hammer conditions.

• Reduce the velocity of the liquid in the pipe. To keep water hammer low, some references recommend keeping the flow velocity at or below 5 ft./s.

• Use slow-closing valves. Anything with a wheel, like a gate valve, is generally considered slow-closing. Valves with handles, like butterfly valves or ball valves, are considered fast-closing.

• Use pipe with a higher-pressure rating. For example, DR 26 HDPE pipe is rated for 65 psi, whereas DR 11 HDPE is rated for 160 psi.

• Air valves are often used to remediate low pressures at high points in the pipeline by admitting air into the line to reduce the possibility of partial vacuum and possible pipe collapse.

• Install pressure relief valves to prevent excessive pressure in the pipe.

• Use air chambers, surge vessels, accumulators or expansion tanks that are partially filled with air or gas and cushion possible shock.