Release of dense nonaqueous phase liquids (DNAPLs) into fractured media has resulted in a lot of groundwater contamination even though their fate and migration in fractured rocks are not well understood. In this paper, the groundwater contamination by DNAPLs is generalized as a series of phase transformation among immiscible phase (IP), dissolved phase(DP) and phase of diffused into and adsorbed onto rock matrix (DAP). The equations for calculating the lifetime of IP and the mass of IP available for DP (M,) were derived. The impact of IP on groundwater contamination was represented by taking the M, as the load on the groundwater system. An example is given to illustrate the application of the theory and the sensitivity analysis was carried out. For the case considered in this paper, it seems that the diffusion into the matrix from IP can reduce the value of M,. The impact of the DNAPLs on groundwater quality mainly depends on M, groundwater velocity and fracture spacing, but is nearly independent of the fracture aperture and fracture porosity. The rate of contaminant migration in fractures can be substantially retarded due to the matrix diffusion.
Dens at article, la contamination des caux sonterrainnes par les DNAPLs est generalisee comne serie de chagenert de phase entre la phase immiscible (IP), la phase dissolute (DP), et le phase de le mutrice rochause dans lequelle il ya diffusion et surlaquelle se proluit l' adsorption (DAP). Les cqeation servant a calculer le cluree de vie de IP ct la mosse de IP dispmible pour DP (M) ont ete dirivees. L'impact de la sur le contaminàtion des caux souterraines a ete ∼epresentee en prerant sour M, la charge sur le systeme des eaux souterrains. Un example est dorre pour illuatrer l'application de la theorie et ure analyse de sensibilite a ete fait.
Dense nonaqueous phase liquids (DNAPLs) such as chlorinated solvents, creosote and PCB oils are common groundwater contaminants. They may have three phases in fractured rocks, i.e. Immiscible Phase (IP), Dissolved Phase (DP) and phase of Diffused into and Adsorbed onto rock matrix (DAP), as shown in Figure 1. It is obvious that contamination by DNAPLs is actually a series of phase transformation such as from IP to DP; from IP to DAP to DP and from DP to DAP to DP. The remaining mounds and columns located in fractured networks (Zhou et al, 1992) will be removed very slowly by groundwater dissolution flowing around them and finally transformed to the DP. Until now, the experiments examining the dissolution process of the IP has been restricted to the sand columns (Schwille's, 1988). Some other investigators simulated the dissolution process of mounds (pools) in porous media using mathematical models (Hunt et al, 198B; Johnson and Pankow, 1992). In their research, it was usually assumed that the matrix of the porous aquifers has a negligible effective porosity and all of the IP was transformed to DP. But, in the fractured aquifers, the rock matrix has a significant effective porosity, matrix diffusion process will play an important role in removing the IP. Some of the IP will diffuse into and adsorb onto the rock matrix and thus becomes DAP. This can occur either when the IP penetrates into the matrix pores beneath it (Longstaff et al, 1992) or when the molecular diffusion carries the dissolved solvent into the pore water beneath it.