A precaster in Ontario provided a complete residential onsite wastewater solution that installs quickly, reduces the overall footprint and provides the homeowners with peace of mind for many decades to come.
By Kirk Stelsel, CAE
Concrete’s primary components are coarse and fine aggregates, cement and water. While there are other elements added to modern mix designs such as admixtures, fibers and sometimes even color, the four primary ingredients can be found in every batch of concrete. It’s only fitting, then, that an engineer and homebuilder are using precast concrete tanks with advanced filtration systems to meet stringent effluent requirements for a new subdivision being built around a lake that was once an aggregate mine.
From mine to mansions
Driving through Heritage Lake Estates in Puslinch, Ontario, it’s hard to imagine it was previously home to a steady stream of heavy equipment and dump trucks. Today, well-manicured lawns, picturesque greenspaces and homes torn straight from the pages of magazines dot the shoreline and area surrounding a lake that is now ready for fishing, boating and swimming.
Not that long ago, though, the lake was a quarry, and those lawns were roads for heavy equipment coming and going. Once mining operations subsided, the pit became the lake that now serves as the heart of the development. Natural ecosystems and wildlife have reclaimed the spaces not occupied by homes, creating a scenic, natural allure that has drawn in homeowners.
A housing development, however, is much more than just homes. The infrastructure needed to supply water, power and treat waste must be designed to meet the demands of future homeowners and the needs of the land while complying with all applicable codes.
Residents of Heritage Lake Estates are relying on Timberworx Custom Homes to turn their dream homes into reality. Timberworx, in turn, relies on Van Harten Surveying, a professional land surveying and engineering company, to take the architectural house plans and site them on the properties to ensure they comply with the zoning requirements and determine the drainage characteristics of the soil.
This important work leads to a critical consideration for the homes being built for the development – how they handle wastewater. The houses are not connected to a sanitary sewer line, so each property is privately serviced. As part of Van Harten’s engineering work for the development, it designs and specifies the wastewater system for each house. Many factors come into play, including the fact that the houses are taking up the maximum 20% of each lot space, leaving limited room for the wastewater disposal bed. Van Harten also takes into account a potential future pool or amenity area on the property. Finally, the system must meet a requirement for an extraordinarily high level of sewage treatment.
“We’re putting together a complete detailed site-grading, site-sewage-design drawing and a report that our client uses to get a permit to start building the house,” said John Duffy, a consulting engineer with Van Harten. “With septic systems, it’s traditionally a septic tank and a leaching bed. In most of the subdivisions that we do work in, as part hydrogeological work that is done, the calculations tell the developer that instead of a standard septic tank system they have to install an advanced sewage treatment system.”
Nitrate is a concern due to Heritage Lakes being a rural development, and Ontario has a 10 mg/L limit for nitrate in groundwater. As the effluent seeps into the ground in the subsurface disposal bed, it enters groundwater and could impact drinking water in surrounding neighborhoods. The result of the hydrogeological study for Heritage Lakes set the target effluent nitrate concentration at 14 mg/L, which dictates the need for an advanced treatment system.
The soils in the Heritage Lakes development vary greatly as well, from native gravel that was not mined and allows for a small filter bed to much less permeable native soil that requires an area bed or a shallow buried trench bed. As a result, each lot’s system is unique.
Beyond the basics
While it was clear the residents of Heritage Lakes Estates would need more than a standard wastewater system, the needs of this development exceed what most advanced systems provide. Duffy said most systems typically achieve a 30-50% nitrate reduction. In this particular development, however, the engineering identified that the system needed a 65% reduction of nitrate concentration in the effluent. As homebuilding got underway, Van Harten turned to Unit Precast in Breslau, Ontario, thanks to a longstanding relationship. Unit Precast is able to supply the homes with the high quality precast concrete tanks paired with an advanced filtration system that would meeting the required treatment requirements.
In January 2017, the development was thrown a curveball when the Ontario Building Code was changed, which meant the treatment systems needed to meet the new CAN/BNQ 3680-600 reference standard. Unit Precast prides itself on meeting the customer’s needs from start to finish and was able to pivot quickly in order to continue its work in the development.
“Unit Precast’s way of doing business has always been to provide installers with a complete solution so they can focus on excavation and disposal and not on the technology standpoint,” said Scott Robinson, managing director of Unit Precast. “We provide a complete, full package including the precast concrete tanks, all components fully plumbed and wired and ready for backfill, along with full startup and commissioning services and after sales support and service. That’s a differentiator and another way that a precaster can add value to their products in order to differentiate themselves from the crowd.”
Each system is comprised of three precast tanks, which are installed in tight locations. Unit Precast was able to reduce the footprint of the tanks by approximately 40% by pouring the tanks upright, a first for the company, in a new form custom made for the job. Prior to that, Unit Precast had always poured tanks upside down and flipped them. The tank capacities range from 500 to 3,000 gallons.
Inside the tanks is an advanced treatment system from Waterloo Biofilter. The system features an anerobic digester with a long tube, either 12 inches or 15 inches, that runs the extent from the inlet to the outlet back around to the inlet. This tube hangs inside of the tank and works like a digester rather than a traditional septic tank. The concept is based on the laminar flow principle, which means all of the particles are flowing at the exact same speed and the overall movement of the fluid is calm.
Next, the effluent is transferred to the basket tank which contains foam cubes. The foam cubes are the home for the microorganisms. The wastewater is pumped from the digester tank and is sprayed onto the foam cubes. There’s a pump in bottom of the basket tank which then transfers the effluent to the last tank with two compartments for denitrification and discharging the wastewater to the disposal bed. Denitrification occurs through Waterloo Biofilters WaterNOX-LS, which is an upflow filter that uses autotrophic bacteria to dentrify effluent in a proprietary blend of agricultural minerals. The system is designed to remove 95% of total nitrogen.
Off and running
The new systems have been installed at eight properties so far, and Robinson said Unit Precast will install another eight later this year as new houses are built. The tanks in place are performing well and have met the stringent requirements set forth by the province. Unit Precast has had such success pairing its tanks with the advanced treatment system that it has another 92 unit development for the same system opening this year.
By using precast concrete tanks in combination with the advanced wastewater system, homeowners can rest easy knowing the system in place will meet local requirements and also stand the test of time thanks to the durability and resilience of precast concrete.
Kirk Stelsel, CAE, is NPCA’s vice president of communications and public affairs.