Environmental Monitoring

Monitoring wells are the most prevalent form of environmental monitoring for USTs. With environmental effects monitoring, it is difficult to determine which tank is leaking when there is more than one tank. These methods do not provide information on leakage rates or the size of the leak; however, once installed, a leak effects monitoring system enables more frequent checking for leaking tanks than the other methods. Table 11.20.5 presents the principal environmental monitoring methods.

An early warning monitoring technique of doublewalled tanks involves monitoring the space between the inner and outer walls of the tank, using either fluid sensors or pressure sensors. This is accurate and applicable with any double-walled tank.

Vapor wells may be used to detect hazardous gases or vapors released into the soil surrounding the UST. Gas detectors or portable gas sampling devices can be used to monitor for gaseous contaminants.

Groundwater monitoring wells may be used to detect or define the movement of leaked substances in a ground-water table. This typically entails drilling monitoring wells, installing monitoring casings, and performing chemical analyses. Table 11.20.6 presents a generalized groundwater sampling protocol.

Table 11.20.7 summarizes the advantages and disadvantages of the various leak monitoring techniques, including those presented in this section.

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