Most homeowners never think about their sump pump until a problem occurs, let alone how their discharge could be affecting the community. A sump pump is a mechanical device typically located in a sump pit in a basement or crawl space. Its purpose is to pump accumulated clear water (i.e., groundwater or stormwater) from building foundation drains and downspouts to the stormwater system.
Unfortunately, many sump pumps are improperly plumbed into the sanitary sewer system, putting an additional burden on the sanitary sewer collection system and the wastewater treatment plant.
Why is clear water a problem?
Clear water consumes capacity in the sanitary sewer system, causing sewer back-ups which release raw sewage into homes and the environment. This, in turn, creates health and safety issues that can be costly to resolve. Additionally, clear water that reaches the wastewater treatment plant (WWTP) is treated unnecessarily. This increases the cost of treatment, reduces the life of the equipment, and may necessitate a WWTP expansion.
How much clear water is being added to the sanitary sewer system?
The amount of water pumped into your system illicitly will depend on several factors:
The number of improper connections that exist in your community.
The amount of water being pumped from each home, which depends on:
Precipitation duration (how long) and intensity (how hard);
The ground water elevation relative to the home’s basement or crawlspace;
The soil types around a given home’s basement or crawlspace; and,
The ability for groundwater and precipitation to enter the home.
You can use the following example to estimate the flow being added to your own community; just substitute in information you know to be more relative to your community:
Assuming the average house in an average water table requires a 1/3 Horsepower sump pump. The top selling 1/3 Horsepower sump pumps discharge approximately 1,800 gallons per hour at 10 ft. of discharge lift. 1
Keeping in mind that some home’s sump pumps may run constantly during wet weather or high ground water and some home’s experience very little infiltration into the home except during the heaviest precipitation events; assume that the average sump pump in your community runs 6 hours per wet day, or 15- minuets every hour (for an entire day).
Assume that 2 homes in 100 have sump pumps illicitly connected in your community and that there are 2.3 people per average home. This gives us a sump pump per capita factor of 0.9% (2/100/2.3).
If your community has a population of 10,000:
(10,000 people) x (0.009 pumps/capita) x (1,800 gal/hr/pump) x (6 hr/day) = 972,000 gallons per average wet day from sump pumps
How much could these sump pump discharges be costing my community?
The operational cost to treat wastewater varies significantly from community to community; from as low as $0.30 to nearly $8.00 per 1,000 gallons. 2 To calculate your communities Cost to Treat: Divide your wastewater utilities annual operating budget in dollars (labor, power, chemicals, contract services, etc.) by your total annual flow (as MGD) divided by the number of days per year (365) multiplied by 1,000 to get your cost to treat in $/1,000gal. Continuing the example above:
Your community treated an average of 4.2 MGD in 2015 and met its annual operating budget of $2,000,000; you calculate your cost to treat as:
[($2.0 Mil/yr) / (4.2 Mgal/day)] / [(365 day/yr) x (1000)] = $1.30 / 1,000 gallons
The estimated cost to treat sump pump water is then:
($1.30 / 1,000 gal) x (est. 972,000 gallons/wet day) = $1,300 / wet day
The Midwest experiences approximately 120 days with precipitation per day:
($1,300 / wet day) x (120 days/yr) = $150,000 annually or 7.5% of your annual budget
What is the solution?
Due to high wastewater flows in the sanitary sewer system during wet weather periods, communities should consider conducting house-to-house inspections to identify and subsequently remove sump pumps from the sanitary sewer system. This process often includes the following steps:
- Ensure your saniary sewer use ordinance prohibits the connection of sump pumps to the sanitary sewer system
Send a letter to residents informing them of the plan and rationale for conducting inspections. This letter should also provide directions for residents to call the Utility or consultant to choose an available time slot for inspection.
Conduct the inspection, usually ranging in time from 5-20 minutes, depending on the configuration of the house’s plumbing.
Document identified sump pump connections to the sanitary sewer system and notify the property owner that the connection will need to be removed and repaired. This can be accomplished a variety of ways, ranging from enforcement penalties to providing financial incentives.
Why act now?
Removing clear water from the sanitary sewers will:
Reduce the cost of operating the WWTP;
Protect your investment in the public infrastructure;
Reduce the potential for backups and property damage;
Help to increase customer satisfaction; and
Help to ensure that future residential, commercial and industrial developments will have capacity to use the sanitary sewers.
To learn more about conducting sump pump inspections in your community, contact Wessler Engineering for more information.
1 Based upon a survey of the top-selling sump pumps on Amazon, Home Depot, and Lowes’s websites
2 Based on a 2015 survey of approximately 80 communities in Indiana. Operational Costs per 1,000 gallons do not include capital costs associated with the construction of sewers or treatment plants, only the operational and maintenance costs.