City Meter, Inc.

It is common occurrence in the United States for wastewater treatment and collection systems to experience large spikes in wet weather sewage flow volumes. Some wastewater treatment systems experience wet weather flow spikes as large as ten times their average dry weather flows. Wet weather flows are caused primarily by infiltration and inflow into the sewer system.

Infiltration and Inflow - Problem Defined

Infiltration is ground water which enters the sewer system through defects in sewer system piping. Inflow is ground or rain water which enters the sewer system through direct connections to ground and rain water sources. Collectively these ground and rainwater sources are called infiltration/inflow (I/I).

Examples of Infiltration/Inflow sources sewer service meters will find include:

• cracked or mechanically damaged sewer service laterals
• damaged or missing sewer service lateral cleanouts
• improperly installed sewer service laterals (such as sewer service piping with no glue in pipe joints)
• yard drains connected to sewer service
• roof gutters and downspouts connected to sewer service piping
• building foundation drains connected to sewer service piping
• basement sump pumps connected to sewer service piping
• private wells used for potable water connected to sewer service piping
• leaks caused by root intrusion

Infiltration/inflow occurs primarily during wet weather time periods and can hydraulically overload central sewer collection system piping, lift stations and wastewater treatment plants. Sanitary Sewer Overflows (SSO's) are often caused by hydraulically overloaded sewer system infrastructure caused by infiltration/inflow. Hydraulic overload occurs when there is more wastewater to transport than the pipes and lift stations have the ability to carry. Ultimately, hydraulic overload can cause the sewage to overflow from manholes and lift stations. These SSO events pollute streets, ditches, rivers and streams with potentially harmful disease causing bacteria and other pathogens present in untreated wastewater.

To date, infiltration/inflow has been handled by building oversized sewer system infrastructure - pipes, lift stations and wastewater treatment plants - to transport and treat the peak wet weather and normal flows. Building oversized infrastructure to handle peak wet weather flows requires large capital investments, high ongoing maintenance and high ongoing operating expenses. Oversized sewer infrastructure treats the symptoms of infiltration/inflow rather than the cause of the infiltration/inflow and does not remove the infiltration/inflow sources or associated flows.

The efficient solution to the infiltration/inflow problem requires the removal of the defects and illegal connections which allow ground and rain water to enter the wastewater collection system. While this is the obvious solution to the infiltration/inflow problem, history has proven it an extremely difficult task to quickly and efficiently find and quantify the sources of infiltration/inflow on an ongoing basis. Most programs to date focus on rotating inspection crews searching for infiltration/inflow sources on a continuous basis.

Infiltration and Inflow - Existing Inspection Methods

Many methods have been used in an attempt to find and eliminate sources of infiltration/inflow in centralized sewer systems. Infiltration/inflow studies commonly use smoke testing, dye testing and camera inspection of sewer system lines to find suspected infiltration/inflow sources. There are several problems with existing infiltration/inflow study methods:

• Existing inspection methods provide a "snapshot in time" of sewer infrastructure condition.
• Existing inspection methods often fail to find direct intentional inflow connections due to the use of hydraulic traps or pump systems.
• Existing inspection methods often fail to find infiltration unless wet weather is active during inspection program time frame.
  • Inspection crews often do not work during wet weather periods.
• Existing inspection methods require constant repetition of inspection services if new defects are to be found as they occur in the system.
• Existing inspection methods require extensive time periods to inspect the entire sewer system.
• Existing methods are man power intensive and costly to maintain inspection crews, equipment and supplies.
• Existing inspection data is subjective and qualitative. This data may have limited value in court enforcement proceedings.
  • Flow reduction is not quantified and at best is only estimated.
• Defects identified on private property may require court enforcement proceedings to cause owners to repair.
• Existing inspection programs focus primarily on public or utility sewer system assets.
• 60 - 80% of infiltration/inflow comes form private property per US EPA and other sewer industry publications.

The City Meter Solution to Infiltration and Inflow - Indentify Customers Producing the I/I & Provide Motive For Repair

City Meter, Inc. recognized the necessity of metering each individual sewer service connection and the advantages that metering would provide. The City Meter sewer service meter allows sewer utility operators to easily identify infiltration/inflow producing private properties by comparing the water sold to each sewer service customer to the water returned through the sewer service meter over a finite period of time. Customers who return more volume of sewer than water purchased are clearly allowing ground water or rain water to enter into the sewer service connection on their property. A penalty sewer service billing rate multiplier applied to each customer who discharges more sewer volume than water volume purchased during a billing period can generate added system revenue and provides direct economic motivation for the customer to repair their portion of the collection system. Once the customer provides certification from a licensed plumber that his or her system has been inspected and repaired, the customer can be returned to the standard billing rate structure. If the same property is identified as producing infiltration/inflow at a later time, the process is repeated. The purpose of the penalty billing multiplier is to give the sewer customer economic incentive to disconnect illegal connections and maintain their portion of the sewer service. Alternatively, sewer utilities may choose to bill customers based on the actual volume of sewage returned to the sewer collection system.

City Meter's Sewer Service Meters offer the following advantages over conventional inspection methods:

• Identification of private properties producing infiltration/inflow without physical inspection programs.
• Quantification of infiltration/inflow flow from private properties.
  • Existing methods cannot easily quantify infiltration/inflow amounts.
• Real time identification of all private property defects using water meter, sewer service meter readings and simple data analysis.
  • Meter data can be used to identify new infiltration/inflow sources as they are introduced into the system.
  • Private property inspection programs can be eliminated. (Significant cost savings)
• Real time identification of utility piping defects using sewer lift station and manhole meters in conjunction with sewer service meters and data analysis methods.
  • Meter data can be used to identify areas where infiltration/inflow sources exist in the utility owned portion of the system.
  • Roving inspection programs can be eliminated. (Significant cost savings)
  • Meter data can be used to quantify the amount of infiltration/inflow in each problem area identified in the utility owned portion of the system.
  • Meter data can be used to allocate inspection and repair crews to highest I/I producing areas in the utility owned portion of the system.
    • This method allocates work crews most efficiently.
    • Provides the highest ROI for utility funded inspection and repair programs.
• Sewer Service Meters can be used to bill based on actual flow volume returned to sewer system.

Conclusions:

Just as the U.S. Environmental Protection Agency required all wastewater treatment facilities to install flow monitoring and recording equipment as an enforcement tool; sewer service meters give the system operator a tool to pass along the responsibility for the flow volume discharged by each customer connection to the sewer collection system. The installation and implementation of sewer service meters provides each sewer service customer the direct economic motivation to operate and maintain their portion of the collection system or to directly bear the increased service cost should they choose not to do so.

Sewer service meters can be used as a tool to economically identify sources of infiltration/inflow in both private property and utility owned assets. Efficiently identifying the location and quantifying infiltration/inflows sources is the essential first step towards removal of the system defects. The City Meter sewer metering system finds the sources of the infiltration/inflow problem so the utility operator can concentrate on repairing the infiltration/inflow producing defects in the utility owned portion of their collection system. Once the identified system defects have been repaired the sewer collection and wastewater treatment system will experience lower variations in peak wet weather flows. Lower peak wet weather flows will:

• allow utilities to continue to use existing collection system and treatment plant infrastructure for longer periods of time before upgraded facilities are required.
• allow wastewater treatment plant to operate more easily within permitted capacity and effluent treatment parameters.
  • less treatment process upsets due to high variations in flow.
• allow operation at maximum efficiency.
  • less chemicals
  • less electricity
  • less wear and tear on lift stations, pumps and other mechanical equipment.

City Meter's sewer service meters are the long term continuous and permanent solution to infiltration/inflow problems.

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