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disappearance. After 6 weeks, the rate of disappearance becomes low due to the decrease in concentration of TPH in soil. In Figure 1, treatments A and B, the activity is low for initial period and there is only slight loss of TPH during the initial 3 weeks. For treatment A, this may be due to the sterility of the environment inside the jar during the initial period. After 3 weeks, the rate of disappearance increases leading to TPH loss from the soil. The activity increases rapidly after 6 weeks for treatment A, which is duo to increased growth of microorganisms. The increased growth of microorganisms for treatment A can be due to the contamination of soil when the containers were opened to allow all COz to escape. In Figure 1 for treatment B (the initial concentration of TPH is same as treatment A but not sterile), the activity is low for the initial period, i.e. rate of disappearance of TPH is low for the first 3 weeks. Hereafter, there is a sharp increase in rate of disappeazance of TPH till 6 weeks. This may be due to an increase in number of microorganisms biodegrading TPH in the soil. After 6 weeks, a lower activity is displayed by the graph of treatment B. This may be due to the decrease in concentration of TPH in treatment B. It appeazs that a long time may be needed for the TPH to disappear from soil at this concentration of PAM and TPH in mixtures. In Figure 1 for treatment C, it is seen that at the end of 13 weeks, most of TPH has disappeared. Extrapolation of the graph for treatment C appears to suggest complete disappearance of TPH. In Figure I for treatment D, the rate of disappearance is low for the initial 3 weeks, and then the rate is slightly higher up [0 6 weeks. Overall the rate is lower for treatment D, which may be due to the absence of superfloc (solid crystal PAM) in treatment D. Superfloc was added in all other treatments. TPH Composition and Exposure Limits The identity of peaks was determined using GC/MS. A vast array of compounds was found to be contained in TPH. The four prominent peaks detected were for undecane, dodecane, tridecane and tetradecane. Mole fractions of the individual components are estimated as a ratio of individual component counts to total TPH counts. The values obtained for mole fractions of these four components are tabulated in Table 3. To confirm the mole fraction values obtained by ratio of counts, mote fraction of dodecane and tetradecane were also estimated by standard additions of the components to 10,000 ppm standard of TPH (from cydril) in acetone. The values of mole fractions obtained agreed well with those obtained by ratio method. Using Raoult's Law, and the vapor pressure data in Table 1, the concentration of each component in head space was calculated. The recommended exposure limit (REL) value for dodecane was obtained using MSDS data from Chevron Phillips and Mallinckrodt Baker, lnc. The estimated equilibrium concentration obtained is far less then the REL value as given in Table 4. Thus, the dodecane in TPH in the air is not expected to cause any health concern for the safety of human beings in the environment. The other components REL values were not found but their use is not expected to cause any concem as they fall in the same range as dodecane.