Water Pollution - The Drinking Water - page 175

of groundwater contamination are cause for concern for the drinking water
practitioner. Why? Consider the importance of groundwater. People depend
upon groundwater in every state, and its usage accounts for approximately
one-fourth of all water used. This consumption includes about 35% of water
withdrawn for municipal water supplies.
underground Storage Tanks
If we could look at a map of the United States indicating the exact location of
every underground storage tank (UST), most of us would be surprised at the
large number of tanks buried underground. With so many buried tanks, it
should come as no surprise that structural failures arising from a wide vari-
ety of causes have occurred over the years. Subsequent leaking has become a
huge source of contamination that affects the quality of local groundwaters.
Note: A UST is any tank, including any underground piping connected to
the tank, that has at least 10% of its volume below ground (USEPA, 1987).
The fact is, leakage of petroleum and its products from USTs occurs more
often than we generally realize. This widespread problem has been and con-
tinues to be a major concern and priority in the United States. In 1987, the
USEPA promulgated regulations for many of the nation's USTs, and much
progress has been made in mitigating this problem to date.
When a UST leak or past leak is discovered, the contaminants released to
the soil and thus to groundwater, it would seem to be a rather straightfor-
ward process to identify the contaminant, which in many cases would be
fuel oil, diesel, or gasoline. Other contaminants, however, also present prob-
lems; for example, in the following section, we discuss one such contaminate,
a byproduct of gasoline, to help illustrate the magnitude of leaking USTs.
Mtbe
In 1997, the USEPA issued a drinking water advisory, Consumer Acceptability
Advice and Health Effects Analysis on Methyl Tertiary-Butyl Ether (MtBE) , to
provide guidance to communities exposed to drinking water contaminated
with MtBE. MtBE is a volatile organic chemical. Since the late 1970s, MtBE
has been used as an octane enhancer in gasoline. Because it promotes more
complete burning of gasoline (thereby reducing carbon monoxide and ozone
levels), it is commonly used as a gasoline additive in localities that do not
meet the National Ambient Air Quality Standards.
Note: A USEPA Advisory is usually initiated to provide information and
guidance to individuals or agencies concerned with potential risk from
drinking water contaminants for which no national regulations cur-
rently exist. Advisories are not mandatory standards for action and are