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pollutant mobility and improves handling characteristics. Two types
of solidification have been used: adding materials to absorb free liquids
and adding materials to chemically bind and encapsulate the contami-
nants. Most off-site disposal sites use solidification to treat the wastes
for final disposal by burial (Jones, 1990; Roberts and Johnson, 1990),
Absorbants are typically used to dewater reserves pits in areas where
the evaporation rate is low. Materials that have been added to the pits
to absorb free water include straw, dirt, fly ash, clays, kiln dust, fly
ash, and polymers.
The best solidification methods, however, are those that chemically
bind the contaminants. These methods are based primarily on portland
cement, calcium silicate, or alumino-silicate reactions (Carter, 1989;
Nahm et al., 1993). These materials, unlike fly ash or kiln dust, can
reduce the leachability of toxic heavy metals, asbestos, oils, and salts.
The mobility of metals from such solidification can be reduced by 80-
90%, while that of organics can be reduced by 60-99% (U.S. Environ-
mental Protection Agency, 1990).
Vitrification by heating the solids to a high enough temperature to
melt silica has also been proposed (Buelt and Farnsworth, 1991), but
is likely to be too expensive for applications in the petroleum industry.

6.3 TREATMENT OF AIR EMISSIONS

During drilling and production activities, a substantial volume of
air pollutants can be generated and emitted. These pollutants include
hydrocarbons, sulfur oxides, nitrogen oxides, and particulates. A
variety of treatment methods are available, but their effectiveness
varies considerably with the pollutant being treated.

6.3.1 Hydrocarbons

The primary source of hydrocarbon emissions is from the exhaust
of internal combustion engines. Unfortunately, there is little that can
be done to treat these emissions other than to operate the engines
within their design specifications.
The vapor space in production tanks can collect volatile hydro-
carbon vapors. These vapors can be collected and treated with vapor
recovery systems (Webb, 1993). Casing gas from thermal enhanced
oil recovery operations may also contain high levels of hydrocarbon