Delhi water treatment plant build a "balancing act"

A ‘fine balancing act’ is perhaps the best description to summarize the delivery of a new $13-million wastewater treatment plant in the community of Delhi in Norfolk County, Ont.

Designed to “post disaster” standards which will allow it to resist a (once in) 50-year earthquake without damage, the plant is one of the county’s most expensive infrastructure projects in decades, says David Evans, associate director, R.V. Anderson Associates Limited. (Those standards include reinforcing steel in the masonry block walls.)

Comprised of six tanks, a headworks building with odour control, a primary pump house building, a blower/electrical/chemical building, and a pipe access tunnel, the conventional activated sludge plant is being built immediately south of the existing 1947 plant.

The old plant has to remain operating during the construction which started last November and won’t wrap up until well into late 2015, he says.

For general contractor Stone Town Construction Ltd. of St. Mary’s, Ont., that means working in very tight constrained quarters. But the planning and design process leading up to the construction was also a balancing act and just as daunting, says Evans.

In 2012, Norfolk County asked the consulting firm for a feasibility study on a potential upgrade of the plant which is located in downtown Delhi in a residential area. Not only were there operational and maintenance problems, “there was a heightened perception about odours.”

The consultant ultimately concluded the plant “wasn’t really worth saving” and that was the candid assessment presented to county council — which had to make some tough choices, says Evans.

A number of options were considered including building a new plant on a different site. But property would have to be purchased and there was another stumbling block as well.

Besides a new plant, a pumping station would also have to be built.

“Sewage plants are usually placed in the lowest elevations possible and for good reason. It allows for gravity sewage pipes. Ultimately the decision was to stay on the same site.”

Of course, that has presented a number of logistical challenges for Stone Work Construction. An access road for equipment had to be built and a chlorine chamber tank had to be demolished before construction could even begin.

And considerable dewatering of the site is required which, Evans points out, is one of the drawbacks of placing plants in a low-elevation area. It was one of the many factors the county and the consultant had to consider during the ‘building new or staying on the same site’ evaluation.

The high water table influenced the design and construction of the six steel-reinforced concrete tanks which comprise the bulk of the facility. In high ground water areas a sewage tank has the potential to float if it’s empty, as can be the case for repairs or maintenance.

“It becomes a boat.”

To prevent that floatation, the Delhi tanks have extra thick 600-mm-thick slabs which are attached to 12-metre-deep steel piles. They also have oversized toes which provide lateral support to hold them down, says Evans.

To cope with the tight constraints, Stone Work Construction has divided the plant footprint into three sections. Currently, the contractor is concurrently erecting the west and east halves with the use of two cranes in an approximately 15-metre-wide space where the centre section will be built. “There’s not a lot of room.”

Once the west and east halves are finished, the contractor will shift its machines slightly to the north and build the centre segment.

“They (the contractor) have made really good progress,” says Evans, noting that while Delhi usually experiences very mild winters, that wasn’t the case this past winter.

While the new plant is scheduled to open in 2015, that won’t be the end of the project. The old facility will still have to be demolished, he says.

This is the second project where Norfolk County, the contractor, and R.V. Anderson have worked together. The first was the Port Rowan Wastewater Treatment Plant which uses a membrane filtration technology to reduce the environmental impact on the county’s Long Point region. It was the recipient of an Ontario Public Works Association technical innovation award.