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.

E-mail: angeo@sprynet.com