Underground Storage Tank Investigation
Although underground storage tanks can be used to keep a variety of fluids, a common use is for holding
petroleum products (e.g., gasoline, diesel, aviation fuels, used oil, allied petroleum products etc.). This
type of storage facility is used by service stations, taxi companies, bus lines, trucking companies,
industry, government and a range of other organizations. It is estimated that there are more than 15,000
underground tank systems in Alberta at the present time.
Leaking storage tank systems are an increasing environmental and safety concern. During a thirty year
period beginning in the 1950’s, thousands of underground storage tanks were installed in Alberta, most of
which were made of painted and unprotected steel, making them susceptible to corrosion and in may
cases, eventually penetrating the tank and causing a leak.
More recently, many of these tanks are being removed and, in some cases, are replaced for continued
operations. Indication of subsurface contamination is required to be monitored by regulatory authorities
and, where applicable, clean-up of contaminated soil and groundwater are necessary before the site is
reused for other purposes or replacement tanks are installed.
AN-GEO has been involved in many of these underground storage tank investigations at commercial and
industrial sites. Typically, contaminated soils are removed to reduce the risk of contaminant migration
and hazardous vapour emission. AN-GEO will assist the client in determining the nature and extent of the
subsurface contamination and recommend appropriate methods for site rehabilitation.
In most cases, contaminated soil with vapour emission above threshold values for fire, explosion and
health hazards must be removed. Hydrocarbon vapour emission is measured in the field with a portable
hydrocarbon vapour detector; other specific chemical vapour emission such as gasoline is generally tested
with target sensitive detection tubes.
When the exposed soil in the excavation reaches an acceptable vapour emission level, soil samples are
collected and submitted to an analytical chemical laboratory to determine the concentration of regulated
hydrocarbon contaminants like benzene, toluene, ethyl benzene and xylene remaining in the ground.
These concentrations are compared to available permissible levels (designated by regulatory authorities)
and, if acceptable, the excavations are then backfilled with a “clean” fill material. In some cases where
all the contaminated soil cannot be removed because of physical restrains, other contingent measures may
be required after further consultation with the regulatory authorities.
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