For higher velocity zones, it is likely that PCE experiences greater groundwater flow,

resulting in greater removal by natural gradient dissolution. This is evidence of site aging, the

reduction of DNAPL saturation in higher conductivity regions. Furthermore, flow bypass has

been documented in DNAPL distributions with higher saturations and pools. This behavior is

detected in MLS-4 and MLS-6.

2.5 PCE Aqueous Concentration Scaling

 Since the process of ethanol flushing enhances the solubility of PCE by cosolvency, any

groundwater samples that contain ethanol will be artificially high in PCE. Thus, all samples

need to be scaled to the maximum possible PCE concentration, Cmax. In the absence of ethanol,

Cmax is simply the aqueous solubility limit, 156 mg/L. The maximum PCE solubility as a function

of the fraction of ethanol in water was measured by Van Valkenberg [1999] (Figure 2-6)



 6






 y = -6.591x3 + 10.098x2 + 0.087x + 2.181 Log C-PCE
 SS R2 = 0.998 Poly. (Log C-PCE)

 0 -

 3



 Log 156 mg/L (
 2
 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1


 CET (Fraction of Ethanol in Water)

 Figure 2-6. Solubility of PCE in ethanol/water mixtures. The data was fit with a
 polynomial equation.