Description
Project: Enhanced Reductive Dechlorination (ERD) and In Situ Chemical Reduction (ISCR) using EHCR
CH2M Hill United States Marine Corps Site, North Carolina
Summary
Site groundwater was impacted with chlorinated volatile organic
compounds (CVOCs) at concentrations as high as 80,000 ppb. A total of
24,100 lbs of EHC was injected into areas of elevated CVOC concentration
to yield enhanced in situ chemical reduction (ISCR). Six months after the
EHC injection, TCA levels had decreased by 94% and TCE levels had
decreased by 84 to 90% at the targeted areas, without generation of
problematic catabolites.
The Challenge
The surficial aquifer consists of unconsolidated, inter-fingering beds
of fine sand, silt, clay, shell, and peat beds with scattered deposits of
coarser grained material as part of relic beach ridges and alluvium. The
aquifer averages about 40 feet thick and has an estimated average
hydraulic conductivity of 10 ft/day. Site groundwater under a sensitive
operational facility was impacted by TCE, cis 1,2-DCE, 1,1,1-TCA and
1,1-DCA with maximum detected concentrations of 73,000, 6,600, 24,000 and
4,800 ppb, respectively. These impacts extended from about 10 ft bgs to a
depth of approximately 20 ft bgs.
The goal was to reduce the CVOCs mass in a timely and effective
manner.
The Solution
There were two hot spot areas on site targeted for remediation; these
were located under Buildings "A" and "B". In January 2005, a total of
24,100 lbs of EHC were injected into the two hot spot areas. Approximately
13,400 lbs of EHC were injected at Building A into an area measuring
approximately 110 ft long x 150 ft wide x 10 ft deep, giving an EHC
application rate of approximately 0.07% to soil mass. Approximately 10,700
lbs of EHC were injected at Building B into an area measuring
approximately 100 ft long x 150 ft wide x 10 ft deep, giving an EHC
application rate of approximately 0.06% to soil mass. The EHC was supplied
as a dry powder in 50-lb bags and mixed with water on site into
slurry.
The EHC slurry was injected into a total of 47 injection locations from
10 to 20 ft bgs. The injections were conducted using a direct injection
technique and the injection points were spaced approximately 25 ft apart.
Figures 1 and 2 show the injection
layout at Buildings A and B, respectively.
The Result
Figure 3 shows the concentration of CVOC in
groundwater at the hottest well at Building A and Figure 4 shows the
concentration of CVOC in groundwater at the hottest well at Building B
before and after the EHC injection. As summarized below, EHC treatment
effectively removed CVOCs without the accumulation of catabolic
intermediates.
TCA: Six months following the EHC injection, rigorous performance
monitoring showed that TCA levels decreased by 94% (from 24,000 to 1,400
ppb) at the hottest area at Building B, without accumulation of
problematic catabolites. TCA levels remained non-detect at Building A.
TCE: Six months following the EHC injection, TCE levels decreased by
91% (from 49,000 to 4,400 ppb) at Building A, with a slight increase in
DCE levels (from 3,027 to 5,819 ppb). TCE levels decreased by 84% (from
7,400 to 1,200) and total DCE levels decreased by 72% (from 5,300 to 1,488
ppb) at Building B.
The Cost
The material cost of using EHC was $3.90/yd3 ($5.00/m3) at Building A
and $3.40/yd3 ($4.40/m3) at Building B.
With an estimated life of >36 months, continued monitoring is
expected to show that in situ chemical reduction (ISCR) using the EHC
technology offers a safe, effective and cost-efficient remedial solution
for similarly impacted environments.
Companies On This Project
ADVENTUS GROUP
