Our senior staff has conducted soil assessments and remediation in more than 20 states in accordance with differing state and federal regulatory requirements. The geology and soil included sediment in the coastal plain, saprolite in the piedmont and mountain provinces, competent igneous and metamorphic rocks, marine-deposited limestone, and shale and sandstone including basin and range sediments. Contaminants remediated include nutrients, metals, petroleum hydrocarbons, chlorinated and non-chlorinated volatile organic compounds (VOCs), and semi-volatile compounds.
Duncklee & Dunham has designed, built, and installed soil-remediation systems that include air-sparge and soil-vapor-extraction systems, multi-phase extraction for soil components of petroleum hydrocarbons and VOC’s, injection and soil blending of chemical oxidants (hydrogen peroxide, Fenton’s Reagent, potassium and sodium permanganate, sodium persulfate, and slow-release oxygen compounds), and biological enhancers (carbon sources such as molasses, sodium lactate, or emulsified vegetable oils) for in-situ remediation, and fixation of contaminants in soil.
Prior to remediation-system design, Duncklee & Dunham conducts geochemical evaluations to determine the ability of soil to absorb and decelerate migration of contaminants with respect to target compounds in the soil. We conduct treatability bench tests to select the best remediation product based on soil characteristics and contaminate properties. We use small-scale field pilot studies to evaluate delivery methods and dosage rates. When the regulatory cleanup standard is more strict than site-specific conditions require, we may use the Synthetic Precipitation Leaching Procedure (SPLP) to determine the actual level necessary to be protective of the groundwater utilizing the soil’s ability to absorb and curtail contaminants
Duncklee & Dunham also uses conventional methods and innovative methods such as field test kits and cone penetrometer testing (CPT), and testing in mobile analytical laboratories. Sample-collection devices include many varieties of direct-push equipment, drilling rigs, and manual sampling equipment. We have used field-screening methods with immunoassay kits for releases of pesticides, PCBs, chlorinated compounds, and petroleum hydrocarbons to provide real-time information to field teams while equipment is in the field. This results in better targeting of contaminated areas with drilling rigs, soil borings, and sampling crews, which results in lowered assessment costs. More effective remediation at a lower cost is also a benefit of this approach.
Duncklee & Dunham conducted an extensive soil assessment in the Coastal Plain of North Carolina to delineate heavy metals in the unsaturated zone. The assessment consisted of over 180 borings that extended to just above the water table (~20 feet below ground surface). After delineating the extent of the contaminants, we conducted an extensive treatability study to determine the following:
1) to what degree the soil beneath the impacted areas can attenuate the contaminant before it reaches the water table, and
2) to what degree the prescribed reagent would reduce leachable concentrations of the contaminant.
The results of the treatability study showed the underlying soil can adsorb significant amounts of the contaminant and the adsorption capacities were a function of soil type, depth and pH. These results allowed us to prescribe the lowest effective dosage of reagent only to areas of the site that required remediation, which reduced leachate concentrations to below detection limits and kept costs to a minimum. We oversaw the blending of the reagent to depths of over 20 feet below ground surface, covered the treated soil with a geotextile warning fabric and capped the treated area with clean backfill from on-site.