Theme: 08. Metals

Topic Area: 8c. Precipitation and Stabilization of Metals

Formatted Title:

Aligning Site Remediation for Arsenic with Site Development Needs

Background/Objectives:

Arsenic impacts were identified at a site intended to undergo development. Arsenic levels exceeding the impact to groundwater soil standards and groundwater quality criteria were observed at the site. Site development plans were being considered, but plans were uncertain. The exact extent of soil excavation for construction activities was unknown. As a result, both vadose zone and groundwater remediation to address arsenic impacts was tested through a treatability study to verify the effectiveness of the remedial reagents and to develop recommendations for field implementations. Two proprietary reagents, GeoForm™ and MetaFix^®, were tested to reduce soil leachate and groundwater arsenic concentrations.

Approach/Activities:

Bulk soil and groundwater samples were recovered from the site. Groundwater analytical samples were collected in the field and homogenized soil samples were collected in the treatability laboratory. These data served as a baseline. Thereafter, the homogenized vadose zone soils were mixed with reagents and wetted with site groundwater and incubated at room temperature for a period of two weeks. Following this treatment period, analytical soil samples were collected form the test and control jars. In a separate experiment, the vadose zone soils were solidified with different doses of Portland cement to identify dosage of cement that would be needed to achieve a minimum strength of 50 pounds per square inch (psi). In parallel, homogenized saturated soil and groundwater were treated with a combination of remedial reagents and the soil slurry was incubated for a period of over seven weeks. Sacrificial treatments and controls were sampled over three sampling events. A solidification test was also set up for the saturated soil for a period of 14 days.

Results/Lessons Learned:

Results of the vadose zone soil testing helped identify reagent doses that significantly decreased the arsenic levels in treated soil leachate as compared with the untreated soil leachate. An effective dose of Portland cement to solidify the soil was also identified. Treatment of saturated soil and groundwater revealed that aqueous phase levels of dissolved arsenic decreased in time in treatments, however arsenic levels in the control were far less to begin with. The aqueous phase water quality and geochemical data along with the dissolved arsenic data were used to interpret the efficacy of the treatment. Treatability test data and lessons learned as a part of the testing will be presented.

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Smita Day