was developed to provide the framework for assessing downgradient risks to people and the

environment [ASTM, 2002].

 Recently several researchers have altered focus to the RBCA framework, studying the

effects of DNAPL source depletion on contaminant mass flux [Lemke et al., 2004; Annable et

al., 2005; Guilbeault et al., 2005; Jawitz et al., 2005; Wood et al., 2005; Fure et al., 2006;

Newman et al., 2006]. Because traditional plume control methods tend to be costly due to the

high insolubility of DNAPLs, leading to long term maintenance and operation expenses

[MacKay and Cherry, 1989; Mayer et al., 2002], aggressive source zone depletion measures are

attractive. While active remediation rarely achieves source zone clean up to regulatory limits,

the benefits of reduction in source mass have been predicted in models through decreases in

mass flux, source longevity, and associated maintenance costs [Rao et al., 2002; Falta et al.,

2005; Jawitz et al., 2005]. In 2-D heterogeneous physical models, aqueous dissolution

experiments determined that NAPL architecture was the primary control of the mass depletion,

flux response relationship [Fure et al., 2006]. Although simple uniform flow field models have

predicted that most of the mass needs to be removed to result in significant flux reduction, field

sites are not this simple [Sale andMc Whorter, 2001]. Even small natural heterogeneities in

media result in much greater heterogeneity in the groundwater velocity field [Kueper et al.,

1993]. Further Lagrangian steamtube modeling has demonstrated that as heterogeneity of

aquifer properties and the subsequent NAPL heterogenous architecture increase, more favorable

flux responses will follow source zone depletion [Jawitz et al., 2005]. This type of situation

better represents field conditions.