Abstract
Leaking underground fuel storage tanks are a major public health concern of the 1980s. The discovery of these leaking tanks and the potential for groundwater contamination prompted legislation which requires monitoring of existing tanks and removal of those tanks found leaking. In San Diego County, the removal of an underground storage tank is witnessed by a Hazardous Materials Specialist (HMS). The HMS and the tank contractor (TC) who actually conducts the tank removal are both subject to exposure to organic vapors during this work activity. To investigate the organic vapors at gasoline tank removal sites, breathing zone and general air samples are collected on large (400/200 mg) charcoal tubes. Breathing zone samples were collected for both HMSs and TCs. General air samples were collected upwind and downwind from the site, three meters deep in the excavation and directly above the excavation at grade. Five gasoline tank removal sites were sampled. The samples were analyzed for pentane, n-hexane, heptane, octane, nonane, benzene, toluene, xylene, trimethylbenzene, and total hydrocarbons (an estimate of gasoline).
The mean personal exposure levels of HMSs to benzene, n-hexane, and total hydrocarbons were 0.1, 0.5, and 2.3 ppm, respectively. The mean personal exposure levels of TCs to the same air contaminants were much higher, i.e. 3.6, 15, and 105 ppm. Mean concentrations of benzene, n-hexane, and total hydrocarbons in the excavation were 14, 41, and 395 ppm, respectively; mean concentrations of the same air contaminants at grade were 0.2, 1.9, and 9.7 ppm. The exposure levels of the monitored personnel did not exceed the organic vapor eight-hour Threshold Limit Values. However, the exposure levels of TCs to benzene and other organic vapors were 10 to 53 times higher than those of HMSs, and thus the TC may be monitored as the maximum risk employee. Upwind concentrations were one to six times less than those downwind. Area concentrations in excavations were 22 to 68 times greater than the concentrations found directly above the excavation at grade. The use of extended vents during the inerting procedure (putting dry ice into the tank) seemed to reduce the extent of air contamination by a factor of 4 to 86. The inerting step seemed to be the major contributor to the overall exposure of employees to organic vapors and, therefore, is the prime step of the tank removal procedure at which the industrial hygienist's attention should be focused.
