Duncklee & Dunham has conducted hundreds of groundwater assessments in over 30 states in accordance with differing state and federal regulatory requirements. Obtaining a sufficient number of data points to overcome site and plume heterogeneity is a priority for those projects where remediation to low regulatory standards is needed.
Our staff also has extensive experience in different hydrogeological environments in assessing plumes of chlorinated solvents (including 1,4-dioxane), nutrients, petroleum hydrocarbons, MTBE, and inorganic compounds. These differing hydrogeologic environments include fractured bedrock, Coastal Plain sediments, and karst.
For routine and simple groundwater assessment projects, we use standard assessment methods such as auger or air-rotary and direct-push drilling rigs. Other methods commonly used include soil-gas surveys, geophysical surveys, and the collection of samples for testing for monitored natural attenuation parameters.
When we need more advanced methods to help determine site and plume heterogeneity, we have used methods such as membrane interface probe (MIP), laser-induced fluorescence, TarGOST®, Waterloo APS™, the hydraulic-profiling tool, or a mobile analytical laboratory to obtain high-density data. High-density data are needed in these instances so that we can determine the true horizontal and vertical delineation of the contaminant plume and to identify preferential pathways for contaminant migration in the saturated zone. These data are especially helpful when targeted injections of chemical oxidants or bioaugmentation substrates are planned.
Groundwater Assessment Projects
Duncklee & Dunham has a high level of experience in the design and installation of groundwater-treatment systems that include in-situ chemical oxidation (ISCO), monitored natural attenuation (MNA), microbiological augmentation, other injection approaches, air sparging, soil-vapor extraction, pump-and-treat with aeration, granular activated carbon, stripping towers and ion exchange. The following paragraphs describe a few recent groundwater assessment projects in more detail.
- A recent project involved the collection of aquifer matrix data for input to the PHREEQC geochemistry model at a metals site in central North Carolina. Geochemical input data included clay mineralogy, iron and manganese hydroxides, and total organic carbon. The model output predicted the amount of the metal that can be adsorbed by the aquifer matrix.
- Duncklee & Dunham conducted an extensive groundwater assessment in the Coastal Plain of North Carolina that identified paleochannels in the subsurface that act as preferential pathways for inorganic contaminants to migrate much further from the source area than originally expected by others. Duncklee & Dunham implemented the use of sonic drilling and soil-sampling techniques, a hydraulic profiling tool equipped with a groundwater sampling system, and a Waterloo Advanced Profiling System (APS)™ to identify these paleochannels, define the plume, and develop a robust conceptual site model. We used these data to design and implement a Remedial Action Plan to remediate the groundwater plume and protect a nearby municipal water-supply well. The groundwater-remediation system consisted of a network of carefully placed extraction-well screens to effectively remove the contaminants from the saturated zone, while targeting these preferential pathways and maintaining hydraulic control of the plume.
- Duncklee & Dunham assessed the subsurface of a major oil terminal and adjacent property on the Ohio River in Kentucky under the National Contingency Plan. Unique challenges of this project included the reversal of typical hydraulic gradients due to river flood stages along with complex clay and sand stratigraphy. We are using in unison a MIP assessment, air sparging, soil-vapor extraction, a dewatering system combined with ex-situ chemical oxidation, bioaugmentation and infiltration, and a 2 MGD pump-and-treat system to protect a nearby municipal well field.