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Today’s I/I Infrastructure Challenges

As we discussed in the previous post in this series, the increasing failure of America’s aging infrastructure has forced municipalities of all sizes to deal with the problem. The challenge is to do so as quickly and cost-effectively as possible. In this post, we review a sampling of the ways our cities and towns are addressing the most visible and pressing element of this issue: inflow and infiltration (I/I).

As wastewater collection systems deteriorate, I/I pours in, overwhelming collection systems. Sanitary sewer overflows (SSOs) have become a huge issue. So much so, that the federal Environmental Protection Agency (EPA) has recognized that many cities need help dealing with this scourge.

Helpful I/I Resources

The Agency has created a Wastewater Collection System Toolbox. It is intended to guide municipalities to better inspect, maintain and replace their collection system components and help avoid overflows. A large part of this maintenance involves finding and eliminating sources of I/I.

Within the elements of this toolbox, the EPA:

  • encourages the use of newer technology such as GIS and other location-based information systems to survey, assess and track system condition
  • advocates thorough planning to manage ongoing maintenance work and improvement of system capacity (CMOM)
  • supports communication with end users of the infrastructure, about ways they can contribute to a healthy system

As part of a U.S. EPA initiative, “Water Infrastructure Outreach,” several new tools are posted here for downloading to help manage infrastructure renewal, including:

How Some Municipalities Are Handling I/I

Many municipalities in California have posted their Sewer System Management Plans online, which could serve as a starting place for others who don’t have the resources to reinvent the wheel. You can find them by using the search string “Sewer System Management Plans.”

Speaking of what municipalities are already doing, let’s look at some concrete strategies they’re using to deal with I/I:

Baltimore, Maryland entered a modified consent decree in October of 2017. The MCD requires the city to do some additional rehabilitation on top of that it performed under the initial consent decree of 2002. It has initiated a two-phase, four part program to address these requirements:

  • Expedited Reimbursement Program – This is for sewage backups caused by wet weather. The program offers up to $2,500 per dwelling unit, per event, for reasonable, documented clean-up and disinfection costs.
  • SSO Notifications – The city maintains a database of ongoing sanitary sewer overflow (SSO) reports. These are collected on a monthly basis and reported quarterly to the U.S. Environmental Protection Agency (EPA) and the Maryland Department of the Environment (MDE).
  • Clean Drain Campaign – This initiative from the city’s Department of Public Works raises the awareness of Baltimore residents about proper disposal practices for cooking fats, oils, grease, wet wipes, and other household waste. This is intended to reduce clogs in public sewer mains
  • Headworks Project – Keys to the project are a well to receive incoming sewage, and a series of very powerful pumps that will improve sewage flow. Essentially, it will act as a giant sump pump. This project at the Back River Wastewater Treatment Plant will cost about $430 million, and go into operation by the end of 2020. Construction will continue into 2021. Ultimately, it will eliminate more than 80 percent of the volume of sewage overflowing the city’s aged sanitary sewer system, and keep the streams, harbor, and Chesapeake Bay cleaner.

The city also holds annual public meetings to update all stakeholders on the project’s progress.

Portions of Chattanooga, Tennessee’s wastewater infrastructure system are reaching the end of their useful life. This is causing failures in the wastewater system, mostly during heavy rain events when wastewater system capacity is overwhelmed by a high volume of stormwater. This, many times, results in sanitary sewer overflows (SSOs).

The city has embarked on a multi-phase, multi-year project that includes major upgrades and revisions to several sections of the wastewater system. These include:

  • pipe rehabilitation
  • pump station improvements
  • upgrades to the Moccasin Bend Wastewater treatment plant
  • comprehensive operational audits

How We Can Help

If your municipality is currently facing similar challenges, TrioVision wants to help. We are proud to offer some of the most technologically advanced, hardest-working CCTV inspection equipment available for the televising and recording of underground structures. Call or click today to get in touch with one of our sales specialists who can get you what you need to keep your systems flowing below ground, where they belong.

Second in a series

The I/I Issue: What’s The Big Deal?

In our first post of this series, we defined inflow and infiltration, or I/I. In this post, we’ll explore the reasons it’s a huge problem in wastewater management.

The reason I/I presents huge challenges for municipalities stems from four basic issues:

  • Upstream – Pipeline Capacity: Conveyance system pipeline capacities being overwhelmed and causing sanitary sewer overflows (SSOs) during significant rain events
  • Upstream – Overflow Costs: Imposition of fines, consent decrees, and loss of funding opportunities dues to frequent SSOs
  • Downstream – Treatment Capacity: Huge amounts of clear water overwhelming the treatment capacity of wastewater treatment plants (WWTPs) and increasing pumping costs
  • Downstream – Treatment Costs: Dilution of sewage directly increasing costs of chlorination, ozonation, or ultraviolet disinfection

Let’s take a more detailed look at each of these problems.

Upstream Issues: Pipeline Capacity

As discussed in our previous post, I/I flows are referred to as “clear water.” This distinguishes it from sanitary sewage flows. This clear water gets treated right along with the sanitary flows, resulting in unnecessary costs for municipalities. The clear water also eats up valuable capacity inside a collection system. These systems are built and rated to accept only so much total flow. Most American cities’ collection systems are at least 75 years old. They were built to service far smaller populations than they must now accommodate. These systems are already working at maximum capacity.

Many communities are likely to experience some SSOs. However, older communities located downstream from overloaded city sewer systems will experience them most, due to their lower elevation in the watershed. The sanitary sewer systems in these older communities carry nor just their own wastewater and I/I; they also receive flows from their upstream neighbors’ sewer systems. When they experience higher volume created by stormwater leaking in from rain events, they must either divert flows into holding tanks, if available. If not, they suffer SSOs.

Upstream Issues: Overflow Costs

These SSOs are a health hazard. They can create serious flooding events that cause unsanitary water to back up into buildings. They can also create a situation in which the federal Environmental Protection Agency (EPA) issues a Consent Decree. This is an order for the city to fix the problem, at huge public cost. The city or agency may fail to meet federal or state guidelines for the integrity of its system. Excessive I/I can be an indicator of such failing systems. This situation can cause these municipalities to become ineligible for low-interest loans from grant or revolving fund opportunities. That makes this a significant and circular problem.

There are other costs associated with I/I overflows, including:

  • road and waterway cleanup
  • the potential for fines if the overflow problem is not corrected
  • litigation and potential liabilities for the responsible city or agency, resulting from sewer system backups into basements or households

Downstream Issues: Treatment Capacity

Clear water also takes up valuable capacity at WWTPs. According to Kirby Van Note, a water resources practice center leader at SEH (an engineering, architectural, environmental and planning company), a single leak from a joint in a manhole or pipe can generate 7,200 gallons of water daily. The cost of its treatment at the wastewater plant can translate into an annual cost of $6,500 for a city. Multiply this cost by the number of leaks across the sanitary sewer system, and you can imagine its hefty price tag for a municipality.

To accommodate massive flow influx from I/I, overwhelmed wastewater treatment plants must speed up their processes. As a result, poorly treated domestic and industrial wastewater is often discharged to the environment. Unremoved organics may be converted to disinfection byproducts through chemical disinfection prior to discharge, but not every plant has this capacity.

Downstream Issues: Treatment Costs

I/I costs water treatment facilities (and, indirectly, consumers) vast amounts of money in treatment operating expenses. All water entering a WWTP must be treated as wastewater. Dilution of sewage by clear water directly increases the cost of pumping the flows. Physical structures, including screens and pumps, must be enlarged to handle the peak flow. Primary clarifiers must also be enlarged to treat average flows, though primary treatment of peak flows may be accomplished in detention basins.

I/I also increases actual treatment costs. This includes chlorination, ozonation, or ultraviolet disinfection, depending on the type of treatment used by the plant.

What About Secondary Treatment?

Biological secondary treatment can only be effective while the concentration of soluble and colloidal pollutants remains high enough to sustain enough microorganisms to digest those pollutants. These pollutants are typically measured as biochemical oxygen demand, or BOD. Secondary treatment is expected to remove 85 percent of soluble and colloidal organic pollutants from sewage containing 200 mg/L BOD. But BOD removal by conventional biological secondary treatment becomes less effective with clear water dilution. It practically ceases when BOD concentrations entering the facility are diluted below about 20 mg/L.

In cases where this capacity overwhelm is happening, cities must often face difficult decisions. Do they invest dollars to reduce I/I, or limit new residential or economic development? New development can strain collection systems already operating at capacity. They sometimes even lead to the need for repairs. However, limiting residential or economic development opportunities stifles a city’s growth. It also sacrifices opportunities to capture tax revenue. Both can create a financial burden for the city.

You can easily see now why inflow and infiltration have become such enormous issues in any municipality’s wastewater management and public works operations and infrastructure budget. In our next post, we’ll take a look at how we arrived at this point, and how sources of I/I can be detected.