Geology Reference
In-Depth Information
prior to excretion, but these may be cleaved in wastewater treatment
plants, releasing active pharmaceuticals.
177
Similarly, the disposal of
contaminated sludge on land as a fertilizer should be viewed with
concern.
177
The use of veterinary medicines may also cause environmental
risks.
186
3.3.5.2.5 Industrial solvents. Six are widely used in the UK - di-
chloromethane (DCM), trichloromethane, 1,1,1-trichloroethane (TCA),
tetrachloromethane trichloroethene (TCE), tetrachloroethene or per-
chloroethylene (PCE).
157
Although there has been a steady decrease in
use over the past 20 years, four (TCE, PCE, TCA, and DCM) are
frequently found in drinking water. The major pollution threat is when
solvents are discharged directly into or onto the ground, due to illegal
disposal or accidental spillage. Since groundwater is not exposed directly
to the atmosphere, the solvents are not able to escape by evaporation, so
it is the aquifers that are most at risk from these chemicals. Pollution of
groundwater by industrial solvents is a very widespread problem (e.g.
Netherlands, Italy, USA, UK
187
), with aquifers underlying urbanized
areas such as Milan, Birmingham, London, or New Jersey containing
high concentrations of all solvents. The stability of TCE in particular
and the inability of these solvents to readily evaporate mean that such
contamination will last for many decades.
157
A typical example of groundwater contaminated by synthetic organic
chemicals from jet fuel and degreasing solvents (e.g. halogenated
methanes, ethanes, and ethenes, including trichloroethylene, perchlor-
oethylene, and vinyl chloride) can be found at Otis Air Force Base on
Cape Cod, Massachusetts, USA, where the Cape's sole-source aquifer
has been affected. The groundwater plumes, some in excess of 5 km in
length, moving at
B
0.5 m per day, contaminate 30 million litres of the
Cape's drinking water every day. Reactive wall (Ni-Fe) technology is
being employed to try to reduce concentrations of 5-150 mgL
1
TCE
and tetrachloroethylene below the local drinking water limits of 0.5 mg
L
1
.
188
The chlorinated ethenes are degraded in the presence of zero-
valent iron by an abiotic reduction process.
3.3.5.2.6 MTBE. Methyl tert-butyl ether (MTBE), an oxygen-con-
taining compound used as a fuel additive since the 1970s, moves quickly
through soil, is highly soluble and does not biodegrade easily. It has
been found in shallow groundwater in Denver, New England,
189
and
elsewhere in the USA, most notably in Santa Monica, California, where
a 1996 spill of MTBE-containing gasoline resulted in the contamination
of wells at concentrations as high as 610 mgL
1
, well above the state's
advisory limit of 35 mgL
1
.
190
In a preliminary assessment of the
