posted on Feb. 13: McMaster geologists aid municipalities in their search for future drinking water


[img_inline align=”right” src=”” caption=”C. Eyles and P. Meyer”]The recent Walkerton, Ontario crisis involving serious
contamination of the town's drinking wells has focussed attention
on the issue of the potability of ground water. Research by
McMaster geologists in the Milton-Georgetown area cannot
guarantee the quality of underground water. But it will greatly
help municipalities make decisions about whether or not to
supply their areas with well water for drinking.

“You cannot take cleanliness and potability for granted (where
ground water is concerned),” says Carolyn Eyles, a professor in the School of Geography & Geology. Frequent testing
and chlorinating are just as important with municipal well water as with lake water sources.

Eyles and M.Sc. geology student Patricia Meyer are in the
process of completing analysis of sediments recovered from a number of boreholes drilled near the towns of Milton and Georgetown last summer.

Because the Halton area is growing so rapidly, additional sources of water are needed. While Milton elected to pipe water from Lake
Ontario, Georgetown decided to try and rely on well water.

Meyer is participating in a project to drill a series of boreholes to
determine the depth of the bedrock, the type of sediment layers overlying the bedrock,
and the existence of possible aquifers – layers of porous rock or
sand containing water. The project is being funded by the regional municipality of Halton and was developed
by Steven Holysh, a hydrogeologist employed by the region.

This drilling project provided an excellent opportunity to map the sediment layers, Meyer
explains. A total of 11 holes were drilled, some up to 240 feet
deep. The boreholes identified the presence of sand layers above the bedrock which
could be good potential aquifers. She is now writing up the
findings and will create a model of the area to assist
municipal planners in deciding where future wells should be drilled.

“This is the most detailed subsurface information ever obtained for
this area,” Eyles says. “The results have important implications
for areas in the whole Great Lakes basin.”

Establishing aquifer
characteristics not only helps in the search for future drinking
water supplies but it also permits delineation of potential
contaminant migration pathways in industrialized urban areas,
she notes.

As part of her thesis, Meyer has also conducted a limited
number of shallow reflection seismic surveys in the area.
However, the large amount of sand near the surface made it difficult for seismic signals to penetrate to significant depths below the surface. This made it very difficult to produce a reliable picture of the subsurface layering of the buried valley.

According to the Canadian Ground water Association, 25 per cent
of Canadians rely on ground water for their drinking supply. The
term ground water could be misleading; in fact, it refers to water
held underground in porous soil or rock, much like water is held
in a sponge. Ground water supplies are replenished by rain and
snow melt, and can be polluted in much the same way as
surface water – by landfill seepage, septic tanks, and leaky
underground gas tanks, and as a result of overuse of pesticides
and fertilizers.

In searching for possible areas of ground water supplies,
geologists target the bedrock valley where rivers flowed many thousands of years ago, depositing coarse sediment which forms the most productive aquifers. Aquifers that are deeply buried below the ground surface in such bedrock valleys are more likely to produce “clean” water than aquifers that lie close to the surface.

Another factor to consider is the type of sediments existing just
above the ground water area and how they are layered, Eyles
says. Also, the aquifer needs to have sufficient volume of water
so that it will not affect the level of water table. For example, it makes no
sense to drill a well in an area that will drain a nearby wetland. Finally,
one should consider land use practices in areas where wells
will be located.

In response to the Walkerton disaster, Ontario's Ministry of the
Environment conducted a six-month inspection blitz of the
municipal water treatment plants in the province. In December,
almost half of the 645 plants were ordered by the ministry to
improve testing, disinfecting and training procedures. Twenty-five
plants did not even meet minimum sampling requirements,
including those in Guelph, Waterloo and Orillia.

The Walkerton events have heightened awareness among the
public about the benefits of water treatment and the importance
of protecting ground water, Eyles says. More research such as that conducted by Eyles and Meyer, will help in making more informed decisions on the management and protection of Ontario's ground water.

Editor's note: This file was amended on Thursday, Feb. 22 to correct some inaccuracies.