Report again flags Taro dump liner’s leachate pool

For the third year in a row, an annual monitoring report on upper Stoney Creek’s Taro industrial dump is flagging the amount of leachate, or waste-contaminated water, sitting on the site’s double liner.

Consultant GHD Ltd. says there should be no more than half a metre of leachate on top of the site’s primary liner to minimize the potential for seepage into the layer below, but levels were up to eight times higher at times last year. The leachate’s depth ranged between two and four metres, and continues to be up to two metres, the June 29 report states, recommending owner Terrapure Environmental try to maintain a half-metre limit envisioned by the liner’s design.

The site’s 2015 and 2016 annual reports raised the same issue, and followed ones in 2013 and 2014 stating the liner’s leachate levels weren’t measured due to a failure of a monitoring device.

Terrapure communications director Greg Jones said the liner’s higher leachate levels are only at the dump’s lowest point and not indicative of the site as a whole.

He said increased pumping to the sewer system via a repaired discharge pipe is decreasing levels this year, and that sampling of water in a hydraulic layer below the primary liner continues to show leachate isn’t present there.

Terrapure is in the midst of an environmental assessment of its plan to boost the site’s capacity to 10 million cubic metres — up from 6.32 million — and raise its height by 2.5 metres. If approved by the province, the site’s volume of leachate is projected to grow to 186 million litres per year, up from 98 million.

Jones said the expansion’s proposed design changes should further reduce the overall amount of leachate on the liner, but to reach the groundwater it would have to penetrate both the hydraulic containment layer and a second clay liner below.

The dump’s surface water is contained by a groundwater collection system, but the annual report indicates a downstream monitor near the escarpment exceeded provincial objectives for some contaminants largely absent upstream. These include boron, cadmium and vanadium, all present in one or more monitors at the dump, although the report suggests other factors may be at play.

“Extensive subdivision development is taking place north of the site and it is expected some detections may be related to construction activities,” it states.

Paul Widmeyer of the Ministry of Environment’s Hamilton office said he couldn’t comment on the latest report because it has yet to be reviewed by technical support staff.