Remediation efforts have concluded at a former fertilizer-manufacturing site near Charleston, SC. Significant concentration reductions for the primary metals of concern (arsenic and lead) in soil and groundwater were achieved through stabilization involving excavation of contaminated soil, mechanical mixing with EnviroBlend C, and backfilling with treated soil.
The Ashepoo site is underlain by 1-8 feet of low-strength fill and debris above 14-28 ft of loose permeable sand resting on low-permeability clay; the water table is approximately 4 ft below ground surface. The fertilizer manufacturing process used at Ashepoo between the mid-1800s and the 1960s involved dissolution of phosphate rock (containing trace levels of naturally occurring arsenic) with sulfuric acid in lead-lined vats. Dissolved lead and arsenic were found at concentrations up to 18mg/L and 220 mg/L, respectively. Additionally, the pH of groundwater was as low as 0.4 standard units.
In 1999, a PRB was selected as the preferred remedy for the site. Pre-design investigations, however, found the remedy was not appropriate due to unfavorable hydrogeologic conditions. The amendment selected for use at Ashepoo (EnviroBlend®) was based on pH neutralization and buffering, reduction/oxidation, lead-complexation, and arsenic adsorption/co-precipitation. Excess acid neutralization capacity was added to the process to provide for long-term pH control of the treated soil mass.
Successful treatment results were achieved through the excavation of unsaturated soil and direct mechanical mixing with dry chemicals using a specialized Lang rotary mixer. Full-scale application of this technology began in February 2002 and was completed nine months later.
Quality control of the aquifer soil treatment was monitored through a porewater screening process followed by groundwater sampling from 20 temporary wells. Post-treatment median arsenic and lead concentrations in ground water from the six wells were 92 and 98% lower, respectively than pre-treatment median concentrations. The maximum post-treatment lead concentration was 0.028 mg/L, with approximately 70% of the samples meeting the lead concentration target. The maximum post-treatment arsenic concentration was 0.68 mg/L, with about 25% of the samples meeting the arsenic target.
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These case studies are examples of the extensive work EnviroBlend has completed across the United States. For more information on our project experience please contact us.
