December 12, 2012

Soil problems will add costs to Solmar project

As published in The Erin Advocate

Soil problems will make it more expensive for Solmar to build its proposed subdivision, and require strict inspection by the Town, according to Water Superintendent Frank Smedley.

In a report to council, he highlighted initial concerns about reports submitted by the developer, as part of a plan to build a new commercial-industrial area and 1,240 homes, over 30 years, on 300 acres in the north end of Erin village. These include soil analysis reports paid for by Solmar, available on the Town website ( Smedley's full report is also on the site, in the Nov. 20 council agenda.

Since the current Erin Water System has no capacity to supply these homes, a new pump house will be needed. It would be fed by two closely-spaced wells, plus two more wells, outside the capture zone of the first ones.

The Bel-Erin well, just south of County Road 124 on the Ninth Line, is not currently in use, but may need to be put back into service, said Smedley. A new filter system would be needed.

He also questioned the proposed water supply projections, and said that the developer should be required to pay for financial plans for both the water and sewage systems. He said the Town should update its Servicing Standards to deal with this development.

As of Monday, Solmar's Functional Servicing report was still not available on the Town website. Smedley noted that Solmar has a good location for its proposed sewage treatment plant (Tenth Line at County Road 52), but that it is outside the village urban area.

"It is in the Green Belt," he said. "Getting approval to put it in that area may be a problem."

He also suggested that since the Town has no Waste Water Department, council could consider using "a company like the Ontario Clean Water Agency to operate the sewage system under a contract that requires them to train Town staff to take the facility over after five years."

Soil tests show that the area between Dundas Street and County Road 124 does not drain well because of silty clay, glacial deposits of till and boulders, and layers of sand. Smedley said this is a "big problem" and that sandy areas could have ground water issues.

The engineering reports says, "The topsoil contains appreciable amounts of organic matter; it is unsuitable for supporting structures and must be stripped." The water level is already very high in some areas, and removing the topsoil means it will be even closer to the surface.

Some of the topsoil could be used for landscaping, but the high content of roots and humus "will generate an offensive odour and may produce volatile gases under anaerobic conditions."

The tests were done with 35 boreholes, about six metres deep, in 2011 and 2012. Test pits and more laboratory analysis may be needed.

Smedley said rigourous inspection is essential, because "if foundations, driveways, parking lots, roads, sewers and water mains are not installed properly" a series of difficulties could ensue.

Excavation must be deep enough, and compacting of trenches done according to detailed procedures, to avoid future ground settlement, which could lead to leaks in water lines, and infiltration of ground water into sewer lines. Sewer connections may need to be wrapped or waterproofed. There are many large boulders, which must be removed.

"Future sewer and water main repairs will be more expensive due to soil instability issues that may require dewatering," said Smedley. Improper construction could lead to "uneven road, driveway and parking lot surfaces", "basement settling and cracking with some leaking issues" and "higher infrastructure life cycle costs due to shorter life cycles".

Road sub-drains are recommended by the soil engineers. Sub grades must be "proof-rolled" to test for soft or watery areas – these must be sub-excavated and filled with solid material. Smedley suggests that the final coat of asphalt not be applied until the base asphalt has been in place for three years.

The construction of house foundations may require extra precautions, including digging extra-deep trenches and immediately filling them with concrete up to the normal level of the footings, and reinforcing the foundations with steel rods. After construction, perimeter sub-drains, damp-proofing and polyethylene slip membranes may be needed to reduce the risk of water or frost damage.

"The last thing the Town needs is a large number of foundation failures on buildings that the Town of Erin Building Department approved," said Smedley. "The Town needs to act proactively to ensure these foundations are completed properly and documented as such. Settling, cracking foundations are not easy to repair."

Solmar's inspection of the site revealed no visible signs of excavated pits, but Smedley said gravel was being removed from the south-west corner of the property up until the late 1980s. That is the area where Solmar plans to collect some of the subdivision storm water.

Because of the high groundwater and low permeability of the soils in the area, Smedley recommends against the use of Low Impact Development (LID) storm water devices. Such a strategy attempts to detain runoff close to its source, allowing it to evaporate or filter into the ground instead of going to large ponds and into the river.

"Standard storm water ponds should be used," said Smedley. "Structures like storm ceptors should not be used unless there are no other options."

Stormceptor is the brand name for a product that slows stormwater in a large container, allowing oil to rise and be held back, and sediment to settle. It requires regular inspection and maintenance, including removal of the oil and sediment by a waste management company.

Smedley said the current plan to allow some storm water to flow east into Core Greenlands, without a stormwater pond, may not be allowed by Credit Valley Conservation.