The need to reduce inflow and infiltration (I/I) (surface water runoff and groundwater) into sanitary sewage collection systems is becoming an increasing priority to many cities, municipalities and wastewater agencies across the United States. Problems associated with I/I often include the following: uncontrolled overflows and bypasses (sewage to the creek); basement backups (damage to personal property); and water impacts to treatment facilities (costly capital improvements required). Since the 1970’s, the USEPA has required sewer operators to eliminate all sanitary sewer overflows. Assessing
the problem is the first step. An assessment has three objectives: 1) quantify the I/I problem, 2) identify the I/I sources, and 3) evaluate cost-effective correction plans.
“Smoke Testing is, perhaps, the most effective and economical method of locating major sources of I/I such as storm drainage connections, curb inlets, and area drains. In addition to I/I sources within public infrastructure, smoke testing will also locate I/I connections on residential properties. This includes all possible ways that rainfall runoff and ground water can enter into the municipal sewer system from private property (downspouts and sump pumps). These connections violate plumbing codes.”
The above is from “Controlling Inflow and Infiltration In Wastewater Collection Systems” by Mark G. Wade, P.E.; Wade & Associates, an American Society of Civil Engineers (ASCE) Technical Paper.
From the O’Fallon
Code of Ordinances:
City § 51.035 Connections to Downspouts and the Like Prohibited - No person shall make connection of roof downspouts, exterior foundation drains, area-way drains or other sources of surface runoff or groundwater to a building sewer or building drain which, in turn, is connected directly or indirectly to a public sanitary sewer.
§ 51.050 Storm Water, Uncontaminated Water, and the Like - (A) Prohibition. No person shall discharge or cause to be discharged any storm water, surface water, ground water, roof runoff, subsurface drainage...
(B) Discharge of unpolluted drainage. Storm water and all other unpolluted drainage shall be discharged to such sewers as are specifically designated as combined sewers or storm sewers, or to a natural outlet approved by the City Engineer…
Sanitary sewer systems are simply not designed to take storm water or sump pump waters. These waters overload the system’s capacity and cause sewer backups into basements. If the waters get to the sewage treatment plant, they cause problems by overloading the plant and generally reeking havoc. Overtime, utility and equipment maintenance costs all skyrocket.
For example, suppose roof drains on a house are connected to the sanitary sewer, and we have a one-inch rainfall. A 1,200 square foot roof would produce nearly 750 gallons of runoff in a short period. The same rainfall producing groundwater would likely cause a standard sump pump connected to our sanitary system to remove nearly 1,000 gallons of groundwater over a period of six hours. Now, compare that to the fact that engineers for sanitary systems only plan for a household of 4 people to discharge 400 gallons into the system over a 24-hour period.
Carrying the above example further, imagine if 10% of the roof drains and basement sump drains in O’Fallon are attached to the sanitary system. That would mean that on days that it rained about an inch, the sewage treatment plant would see nearly one million gallons of additional water to pump and treat. This causes chaos at the plant and lift stations, which take the flow to the plant, and costs about $5,000 a day more than an average daily cost to accommodate that flow. Additional costs include the cost of cleaning up the homes flooded by sanitary sewers that were surcharged due to the extra flow.
The City is in the process of evaluating the integrity of all its sanitary sewer mains and will be smoke testing areas of the City’s mains to determine the extent of illicit connections this summer and likely every summer for a while. Individual residents will be notified of the testing. Standby for news.
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