Page 300 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

264 part II The Water, Weather, and Climate Systems
groundwater that underlies agricultural land in Canada. The levels are below the guidelines for Canadian drinking water quality but, while historical data suggest that nitrate levels have not changed in the last 50 years, the incidence of bacteria in well water has almost doubled in the same time period. The 1996 State of Canada’s Environment Re- port noted that, in some areas, nitrate levels were more than four times greater than the Canadian drinking water guidelines. The Canadian Environmental Sustainability Indicators website reports that there has been no change at monitoring sites in nitrate levels for 60% of the sites between 1990 and 2006 (www.ec.gc.ca/indicateurs-indicators/ default.asp?lang=En&n=2102636F-1). Regardless of the spatial nature of the source, pollution can spread over a great distance.
As discussed in GeoReport 9.3, scientists are using satellite data to estimate the overall volume of the groundwater resource. Assessing groundwater quality re- mains problematic, however, since aquifers are generally inaccessible to measurement and analysis.
Fracking Shale plays are areas that are deemed by geo- scientists to contain economically viable quantities of oil or gas. In much of North America, methane lies deeply buried in shale deposits as a significant reservoir of natural gas (Figure 9.17). Canadian shale plays are rec- ognized in the Maritime Provinces, Québec and Ontario,
the Prairie Provinces, and British Columbia. Prospective plays underlie much of Alberta.
Over the past 20 years, advances in horizontal drill- ing techniques, combined with the process of hydraulic fracturing, or “fracking,” opened access to large amounts of natural gas previously deemed too expensive or diffi- cult to tap. A typical shale gas well descends vertically, then turns and drills horizontally into the rock strata. Horizontal drilling exposes a greater area of the rock, al- lowing more of it to be broken up and more gas to be re- leased. Then a pressurized fluid is pumped into the well to break up the rock—90% water, 9% sand or glass beads to prop open the fissures, and 1% chemical additives as lubricants. The specific chemicals used are as yet undis- closed by the industry. This use of an injected fluid to fracture the shale is the process of fracking, derived from hydraulic fracturing, or hydrofracking. Gas then flows up the well to be collected at the surface.
Fracking uses massive quantities of water: approxi- mately 15 million litres for each well system, flowing at a rate of 16000 L per minute. As with other resource- extraction techniques, fracking leaves hazardous by- products. It produces large amounts of toxic wastewater, often held in wells or containment ponds. Any leak or fail- ure of pond retaining walls spills pollutants into surface water supplies and groundwater. Methane gas leaks around well casings, which tend to crack during the fracking
▶Figure 9.17 North American shale plays. Current plays are producing oil or gas while prospec- tive plays are the focus of exploration activities. Updates from the industry can be found at www.shalemarkets .com/about-us/fracking101/north- american-shale-plays-map/.
[U.S. energy information adminis- tration based on data from various published studies. Canada and Mexico plays from ari. Updated: May 9, 2011.]
140oW
130oW
Lower Besa River
Montney
Doig Phosphate
Hilliard- Baxter- Mancos-Niobrara
Mancos Hermosa
50oN
50oN
40oN
40oN
30oN
30oN
20oN
120oW
110oW
100oW
90oW
80o 70o
0
150
300 KILOMETRES
Monterey- Temblor
Monterey
Gammon Niobrara*
Excello- Mulky
Woodford
Bend Barnett
Eagle Ford
Antrim
New Albany
Utica
120oW
Muskwa- Otter Park
Niobrara* Cody
110oW
Colorado Group
100oW
90oW
80oW
70oW
60oW
50oW 40oW
Horton Bluff
Heath**
Mowry
Lewis Avalon
Barnett- Woodford
Eagle Ford, La Casita
Pierre- Niobrara
Fayetteville
Floyd- Neal
Chattanooga Conasauga
Bakken ***
Utica
Frederick Brook
Devonian (Ohio) Marcellus
Eagle Ford, Tithonian
Pimienta
Maltrata
Stacked plays
Shallowest / youngest
Intermediate depth / age
Deepest / oldest
* Mixed shale & chalk play
** Mixed shale & limestone play *** Mixed shale & tight dolostone- siltstone-sandstone play Prospective shale plays
Basins / Under water
Haynesville- Bossier
Pimienta, Tamaulipas
Current shale plays
Tuscaloosa