Jul 8 2024

Cut Development Costs with Pressure Sewer Systems

Across North America, housing development continues to boom. With an investment in residential building construction projected to exceed $700 billion by the end of 2024, infrastructure expansion, including water and wastewater planning, must keep pace to support this growth.

Two grinder pumps sitting side-by-side. Blue new grinder pump improves residential development.

As development spreads to rural areas with minimal existing infrastructure, the costs for builders increase. Typically, builders use gravity sewer systems to collect wastewater. This traditional method, although effective in many contexts, encounters challenges in rugged terrain or low population density areas, often requiring extensive excavation and costly installations.

Given the financial implications, alternative sewer solutions offer more economical options for infrastructure expansion.

Equipment Cost

A pressure sewer system employs a network of grinder pumps to transport wastewater through small-diameter pipes under pressure to a collection or treatment system. Each home is equipped with a grinder pump station consisting of four main components: a basin, a 1-2 HP grinder pump, a level control, and a control panel. Lateral piping from the basin ranges from 32 mm to 50 mm in diameter, while the main sewer line typically ranges from 200 mm to 300 mm. The pipe size varies depending on the number of homes connected to the system. Hydraulic design considerations aim for sufficient scouring velocity to prevent solid settlement.

In contrast, a gravity sewer uses larger diameter pipes, typically ranging from 400 mm to 900 mm. Similar to pressure sewers, gravity sewers require sufficient scouring velocity to prevent solid settlement. Therefore, pipes must be installed at consistent downward slopes, and lift stations are required to transport wastewater to higher elevations.

Lift station equipment can be very costly. It includes pumps, level controls, a control panel, variable frequency drives, telemetry systems, valves, and pressure gauges. Depending on capacity, lift station pumps may start around 20 HP for small stations and can go up to 150 HP or beyond. The equipment found in one lift station alone can exceed $100,000. Many municipalities have several lift stations, depending on the distance homes are located from the force main or treatment facilities.

While a single development utilizing a pressure sewer might require hundreds of grinder pump stations, the overall cost of this equipment is relatively small compared to the cost of several lift stations. The equipment cost can be easily added to the price per lot when selling the development.

Installation Cost

Gravity sewer systems require large diameter pipes installed at a consistent downward slope, necessitating significant excavation. If existing infrastructure, such as roads, is already in place, it must be torn up during sewer installation.

Installing lift stations also requires significant excavation, often several stories below ground level. Each lift station site may need a control building, often protected with fencing and gates to prevent unauthorized access.

In contrast, pressure sewer systems install pipes directly below the frost line via directional boring, eliminating the need for deep excavation and preventing disruption of existing infrastructure. Piping follows the land’s contour, allowing installation in various terrains, including rocky, hilly, and high water table areas. Consequently, developers can use land that might have been considered too costly with traditional infrastructure. Minimal excavation is needed to install basins on each lot.

Deferring Upfront Cost

It’s important to remember that the infrastructure in existing homes had to be established before construction. All equipment and installation expenses are incurred long before owners occupy a new home. For a single new development project, the entire sewer system must be planned and installed before breaking ground on homes.

In phased developments built over several years, infrastructure, including piping and lift stations, must be developed to accommodate the system’s full capacity, even if that is many years away.

With a pressure sewer system, developers can defer a significant amount of their equipment cost until the sale of a home. They need only install the piping network upfront, while basins, pumps, and controls can be installed immediately before occupancy. This allows income from the home sale to finance the equipment, notably reducing upfront development costs.

Operational Cost

If gravity systems operated without lift stations, operational costs would be minimal. However, lift stations come with large and complex equipment, requiring significant capital. Large horsepower pumps can cost thousands per year in electricity alone. Incorporating telemetry and monitoring features adds additional monthly communication fees. Municipalities or service utilities must also employ operators and electricians to keep equipment functioning as expected.

While pressure sewer systems do not eliminate operator jobs, the homeowner covers the electrical cost of the grinder pump. Grinder pumps use very little electricity compared to lift station equipment, costing similar to other small household appliances.

Maintenance Costs

Municipalities or service utilities familiar with lift station maintenance may feel overwhelmed at the prospect of maintaining hundreds to thousands of grinder pump stations. The key difference is the frequency of service required. Most operators visit their lift stations for basic maintenance daily or weekly.

In contrast, grinder pumps typically require service calls every 7 to 10 years. While nuisance calls for problems such as float issues or clogging can occur, they are easily fixed, and new parts are far less expensive.

Many municipalities or utilities charge a monthly sewer fee to residents, providing funding for standard service calls. Other solutions include charging homeowners for grinder pump service on a case-by-case basis. In some cases, homeowners own and maintain their grinder pump stations.

The article was first published in ES&E Magazine’s June 2024 issue.