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The Impact of Drilling and Production Operations 121

produced water could not be correlated with total volatile organic
carbon, total organic carbon, oil and grease, or salinity.
Field studies around offshore platforms have shown that the impact
of produced water discharge depends on the volume of water dis-
charged and the water depth. Except for shallow waters, little effect
on the benthic community has been observed at distances greater than
about 100 meters from the platform (American Petroleum Institute,
1989d; Rabalais et al., 1990).
Onshore discharges of produced water may be allowed if the water
has a "beneficial use" in agriculture and wildlife propagation, even if
it is not suited for human use. In Wyoming, for example, acceptable
water quality is determined if more than 50% of water fleas and
fathead minnows can survive in the produced water for 48 and 96
hours, respectively (Mancini and Stilwell, 1992).

3.8 NUCLEAR RADIATION

Humans are constantly exposed to a background level of nuclear
radiation, from both natural and man-made sources. At most petroleum
drilling and production facilities, there is no incremental radiation
exposure from associated activities. At a few areas, however, naturally
occurring radioactive materials (NORM) can accumulate to levels
where a significant incremental exposure above background is possible,

3.8,1 Radioactive Decay

Radioactive decay occurs when the nucleus of an atom is in an
unstable energy state. It is the process used by the nucleus to reach a
more stable energy state. The three major types of radioactive decay
are alpha, beta, and gamma decay. Other types of decay, such as
spontaneous fission and spontaneous neutron emission, are possible but
occur very infrequently. Induced neutron emission and induced fission
can also occur when the nucleus has absorbed another particle, such
as an alpha particle or a neutron.
Alpha decay is the emission of a helium nucleus (doubly ionized
helium atom) from the nucleus of an unstable atom. Beta decay is the
transformation of a neutron in the nucleus into a proton and an
electron. The proton remains in the nucleus and the electron is emitted.
In some cases of beta decay, a proton is transformed into a neutron