2.10 SPILL SITES


        EPA's (1988, 1990) model for computing volatilization rates from "new spill sites" is implemented in the user-interface (AG-VCASE = 3) of MEPAS 3.n versions. Spills occur when wastes are accidently released from a containment system. When the spilled material is a liquid waste containing volatile organics, volatilization will occur until the organics are depleted; the volatilization rate may be time-dependent. If the spill occurred on soil, the liquid material will soak into the bulk of the soil while the volatilization process progresses. The duration and the extent of the soaking process will depend upon the characteristics of the soil and the waste. The model used for estimating emission rates from spill sites in MEPAS assumes that a finite but sufficient amount of the original liquid spill remains on the surface of the elements of the soil or pavement. Most emissions are attributable to the liquid above the surface of the spilled object. The equations for estimating emission rates are the same as the equations used for a surface impoundment (Equations 29 and 30). Thus, the emission rate averaged over time, T, from a spill site is
 

(34)


 
 
where
          The overall mass-transfer coefficient to be used in Equation 34 can be obtained from Equations 31, 32, and 33 as described previously.

        If a spill is left for some time without cleanup, the spilled volatile materials may no longer be pooled on the surface and the spill model will no longer be appropriate. The spill materials that have not been lost by volatilization (or other processes), will generally be soaked into the underlying surface. The resultant situation will often more closely resemble one of the models for contaminated soil.