Sustainable Water Management - Sustainable Practices in Geoenvironmental Engineering - page 81

found to be highly susceptible to nitrate contamination from agricultural sources (Burkart
and Stoner, 2002).
Another major class of contaminants is microorganisms from agricultural runoff, and
septic and sewage systems. Microorganisms contribute turbidity, odors, and elevated lev-
els of oxygen demand. Drinking contaminated water can lead to severe gastrointestinal ill-
nesses and even death. The case of Walkerton, Ontario, a small town 200 km northwest of
Toronto, is an example of this. In May 2000, heavy rain washed manure into swampy land,
which subsequently contaminated drinking well water. More than 2300 people became ill
and 7 died as a result of drinking the contaminated well water. This is discussed further
in Chapter 9.
Numerous organic compounds are potentially mutagenic and carcinogenic to humans,
animals and plants. We have previously seen from Figures 1.4 and 1.5 in Chapter 1 how
industrial, agricultural, and urban discharges can contaminate aquifers and surface
waters. As indicated previously, the sources of these contaminants can be traced to waste
streams and discharges from industrial plants, households, resource exploitation facilities,
and from farms. Oil spills, are a major cause of devastation to marine and land ecosystems.
Some examples of contaminant groups include pesticides and herbicides such as dichloro-
diphenyltrichloroethane (DDT), aldrin, chlordane, diazonin and partinon, volatile organic
compounds (VOCs) such as vinyl chloride, carbon tetrachloride and trichloroethylene
(TCE), and heavy metals (e.g., chromium, cobalt, copper, iron, mercury, molybdenum,
strontium, vanadium, zinc). VOCs enter the water systems as industrial and municipal
discharges. Owing to their higher volatility, they are less persistent than herbicides and
pesticides. Metals originate from industrial processing, runoff from mining operations
and atmospheric disposition from incinerator emissions and other processes.
All the other sources of contaminants shown—i.e., discharges and waste streams—
are most likely contained in storage dumps, landills, holding ponds, tailings ponds, or
other similar systems. All of these containment systems have the potential to deliver
contaminants to the receiving waters (groundwater and surface waters) because of
eventual leaks, discharges, and failures. Some of these will be discussed in detail in
Chapter 5.
In urban regions, leakage of sewers and other wastewater sources can signiicantly con-
tribute to recharge and contamination of aquifers. It was estimated in 2013 that more than
985 million m 3 /year of wastewater (2.6 trillion gal/year) was lost due to broken sewers
in the United States (Uni-Bell PVC Pipe Association, 2011). Aquifers under cities can be
highly polluted, making them unsuitable for drinking water. This is particularly signii-
cant in regions where (a) wastewater is untreated; (b) source contaminants such nitrates,
ammonia, fecal coliforms, and dissolved organic carbon abound; and (c) urbanization is
rapid and essentially uncontrolled.
Contamination of the surface waters and groundwater can occur as a result of industrial
or municipal discharges or runoff from agricultural land, mining operations, or construc-
tion. Industrial contaminants in the groundwater such as benzene, toluene, xylene, and
petroleum products originate from (a) leakage of underground storage tanks, (b) chemical
spills, and (c) discharges of organic chemicals and heavy metals such as cadmium, zinc,
mercury, and chromium. The numbers of affected sites in the United States have been
reported to be at least 5 or more orders of magnitude (Gleick, 1993). Runoff and seepage
from mining operations can contribute signiicant levels of heavy metals, for example, in
the illustration shown in Figure 3.4 of runoff of iron from a coal mine.