Description
Installation of EHC for VOCs Confidential Client Texas
Project: Installation of EHC for Treatment of Chlorinated
Volatile Organic Compounds, Site in Texas
Summary
Adventus installed 1 ton (909 kg) of EHC into a trench and 3 tons
(2,730 kg) of EHC into an open excavation at a site that has groundwater
contaminated with a mixture of chlorinated solvents.
The Challenge
Two areas of contamination were targeted for treatment. The first was a
dissolved plume migrating from a source zone through a thin permeable soil
unit overlying bedrock at approximately 12 ft (3.7 m) below ground
surface. The second was an open excavation containing groundwater, after
contaminated soil had been removed. The client's site was contaminated
with a large range of Contaminants of Concern (COCs) at the two locations
(Table 1).
The Solution
To treat these contaminants, EHC was selected for in situ treatment of
the contaminants. Adventus recently adapted its patented combination of
controlled-release solid carbon and zero valent iron (ZVI) particles to
yield EHC, a solid material for stimulating reductive dechlorination of
otherwise persistent organic compounds in groundwater.
Following placement of EHC into the subsurface, a number of physical,
chemical and microbiological processes combine to create strong reducing
conditions that stimulate rapid and complete dechlorination of organic
solvents and other persistent compounds. A permeable reactive barrier
(PRB) was constructed to intercept the dissolved groundwater plume
(Figure 1). The PRB was constructed with an excavator by
digging a 3 ft (0.9 m) wide trench down to the top of the bedrock,
followed by filling the bottom foot with a mixture of EHC and sand
(Figure 2). Only the bottom foot required filling because
the groundwater table was less than a foot above the bedrock, and the
permeable soil unit was also at this depth. The remainder of the PRB was
backfilled with pea gravel. The bottom 1 ft (0.3 m) of the excavation was
lined with sand and EHC (Figure 3), and the downgradient
wall of the excavation was lined with a 3 ft (0.9 m) high, 3 ft (0.9 m)
wide bench of sand and EHC.
The 3 ft (0.9 m) high bench would ensure that any water exiting the
excavation at the downgradient side would come into contact with the sand
and EHC mixture.
The Result
The installation was completed in early 2004. To monitor effectiveness
of the installation, wells were placed upgradient and downgradient of the
OPRB as well as within and downgradient of the excavation.
Figure 4 shows results at the excavation (shows
complete VOC removal from the source area). Two pairs of upgradient and
downgradient monitoring wells are being used to evaluate the effectiveness
of the PRB for treatment of the dissolved plume. The data for the first
upgradient-downgradient pair are provided in Figure 5,
with the upgradient data on the left-hand side, and the downgradient data
on the right-hand side.
Large reductions of all of the constituents present continue to be
observed after 21 months of field data. Data for the second well pairing
are shown in Figure 6, with lower overall reductions
potentially due to flow heterogeneity, but consistent performance over
time. Bench scale data for PCE and breakdown products were available from
two sites other than this one. Using these data, a model was prepared to
analyze the expected concentrations downgradient of the trench.
The modeled data were compared to observed concentrations in the field
(Figure 7). The results show that the field data, after
acclimatization, meet or exceed the concentrations drop expected based on
both sets of bench data.
Timeline
The installation was completed in less than 2 days. EHC performance was
observed quickly and for an extended period of time (approaching two years
at the time of writing).
Companies On This Project
ADVENTUS GROUP
