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end of the idealized injection slug reached the Row 2 fence-line. The total volume crossing
the Row 2 fence-line from Day 54 to 74 consisted of a portion of injection slug with no
gasoline compounds while the remaining portion carried MGC concentrations consistent with
the pre-treatment conditions. Therefore, the increase in mass was near minimal from Day 54
to Day 74 after which the increase in cumulative mass was again consistent with the pre-
treatment loading conditions.
The CMC for MGCs demonstrated that the observed cumulative mass was significantly
lower than that from dilution-embedded CMC (Figure 5.8). By Day 135, the observed
cumulative mass was 24 to 53% lower than that expected after incorporating dilution (Table
5.2), which clearly indicates that persulfate oxidation led to a significant decrease in mass
load across the Row 2 fence-line. A larger decrease was observed for ethylbenzene, xylenes
and toluene (≥42%) than for TMBs, benzene and naphthalene (20 to 33%) which was
expected from the treatability study results (Sra et al., 2010). Overall, the relative decrease in
observed cumulative mass for MGCs was also synonymous with earlier observations related
to the inorganic data in which dilution was shown to play only a minor role. The slope of the
CMC at Day 135 can be assumed to provide a quantitative estimate of the source zone
strength since it represents the overall MGC dissolution rate. Slopes of the observed CMCs
were 22 to 62% lower than those for dilution-embedded CMCs at Day 135 (Table 5.2)
indicating that the source zone strength was depleted after persulfate treatment. Dissolution
rates for ethylbenzene and naphthalene decreased from 99.5 mg/day and 12.3 mg/day,
respectively, for dilution-embedded CMCs to 37.5 mg/day and 7.9 mg/day, respectively, for
observed CMCs.
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