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r <br /> make up less than one percent of gasoline. The most abundant <br /> cycloalkane is cyclopentane (0. 3.9-0. 58 percent by weight) (SWRCB <br /> 1987) . Their water solubilities and vapor pressures are both <br /> moderate-to-high. Cycloalkanes have low human toxicities and <br /> effects generally occur only at high levels of exposures. There <br /> are no reports of adverse effects resulting from exposures to <br /> environmental concentrations resulting from gasoline release <br /> (Sandmeyer 1981b) , so they will not be examined in detail . <br /> Aromatic compounds contain one or more benzene rings (a benzene <br /> zing has six carbon atoms in a ring with alternating double and <br /> single bonds between carbons) . Aromatics are significant <br /> constituents of gasoline: by weight, the major aromatics are <br /> benzene (0. 12-3. 5%) , toluene (2 .73-21. 80%) , and xylene (3.22- <br /> 8.31%) (SWRCB 1987) . The aromatics have relatively high vapor <br /> pressures and water solubilities, so they may migrate from a site <br /> by transport either in ground water or soil vapor. Because of <br /> the mobilities, environmental properties, and concentrations of <br /> • the aromatic compounds, the RA will evaluate these compounds, <br /> especially benzene. <br /> Table 6 summarizes the potential appropriate or relevant and <br /> applicable regulations for soil and water. The U.S. Maximum <br /> Contaminant Level (MCL) is an enforceable drinking water <br /> standard. The U.S. recommended MCL (MCL goal) and the California <br /> OHS Action Level are intended as guidelines and are not enforce- <br /> able. The National Ambient Air. Quality Standard is an enforce- <br /> able standard for outdoor air. The U.S . Occupational Safety and <br /> Health Administration (OSHA) Permissible Exposure Limit __s an <br /> enforceable standard for air in a workplace. Recommendations for <br /> exposure have been made by the American Conference of Govern- <br /> mental Industrial Hygienis-s (AC-31H) and the U.S. National <br /> Institute of occupational Safety and Health (NIOSH) . The ACGIH <br /> Threshold Limit Value and NIOSH Criterion are nonenforceable. <br /> guideline values for the workplace. <br /> 15 <br />