J, =q,C, (1-13)

Both the water flux and mass flux require a cross sectional area (i), or control plane. This is best

illustrated in Figure 1-2.





 qi

 AzJi





Figure 1-2. Water flux (q;) and contaminant flux (J,) across a control plane. AX
 and AZ are the cross sectional distances and the cross sectional area A, is the
 product of these two lengths.

 In the field, there have been a number of new technologies developed recently for

assessing in-situ mass flux. One of these is the University of Florida passive flux meter (PFM)

[Hatfield et al., 2004; Annable et al., 2005; Basu et al., 2006]. This downhole device allows the

simultaneous measurement of groundwater flux and contaminant flux across a control plane of

wells. Another new method for flux measurement is the integral groundwater investigation

method (IGIM) or integral pump test [Bockelmann et al, 2001; Bockelmann et al, 2003; Bauer et

al., 2004; Jarso et al., 2005]. A modification of this method has been utilized by Guilbeault et

al. [2005] at several sites to simultaneously pump a control plane of wells continuously,

capturing the entire contaminant plume, and affording an estimation of mass flux.

 Finally, we can determine the mass discharge for the source area, a full measure of the

source zone strength. This is the mass leaving the source area per unit time. The product of the

total cross sectional area with the contaminant mass flux (J,) is the mass discharge (Md) [USEPA,

2003].