How it works
Customers can specify a composite rubber or cast iron lid that features bolted lugs to minimize theft and indented rather than through-and-through pickholes that let in water.
Virtually all other components are made from EPDM rubber that the company describes as “almost as hard as a hockey puck.” In addition to being corrosionproof and non-conductive, the material’s chief advantage is its weight: The frame weighs 55 pounds; tapered adjustment risers, 22 pounds each.
Installation doesn’t require heavy equipment, a benefit in difficult-to-access locations or where equipment isn’t allowed. Once the manhole chimney is excavated and exposed, a one- or two-man crew can set the new frame and lid in less than an hour, using the tapered adjustment risers to match slope in street installations or raise the lid above the original surface in off-road applications.
All components are bolted together, and to the original manhole structure; and all components are sealed together with butyl sealant. The result is a watertight seal from the chimney up. The rubber components perform well in freeze/thaw cycles compared to concrete and iron. They don’t heave, crack, or oxidize and the rubber-to-rubber, butyl-catalyzed seals eliminate joint leaks for decades.
Before installing the new covers, the department used to set off-road frames and covers 1.5 feet aboveground. This reduced surface inflow, but left unsightly manhole tops in residential neighborhoods that conflicted with landscaping and were obstacles for lawn mowing.
Moncton is also using the product to minimize I&I as development occurs.
When streets are built, sanitary sewers are placed in the middle of the street, high on the crown, which minimizes the likelihood of stormwater runoff entering manholes. But sewer extensions often precede street construction as density increases in once-rural areas; when the street is eventually paved, the sewer is located down in the curb and gutter.
A watertight seal also has provided an unforeseen benefit: odor reduction. Manhole vents in rear yard easements can give off unwanted odors, and Bonhower has found that the new frames and lids are gas tight as well. By concentrating on manhole renewal, his team is also literally putting themselves in ‘better odor’ with the citizens they serve.
Angus Stocking is a licensed land surveyor who has been writing about infrastructure since 2002; e-mail email@example.com. E-mail Darryl Bonhower at Darryl.Bonhower@moncton.ca.