High-Resolution Site Characterisation (HRSC) using the Membrane-Interface & Hydraulic Profiling Tool (MiHPT) - Webinar with Geoprobe

Direct sensing technology for contaminated land investigation in sites impacted with petroleum hydrocarbons or chlorinated solvents

The webinar organised by Legion Drilling, featuring Dan Pipp from Geoprobe as the presenter, focused on High-Resolution Site Characterization (HRSC) using the Membrane Interface & Hydraulic Profiling Tool (MiHPT) for investigating contaminated soil and groundwater. The MiHPT system combines two popular direct sensing tools, the Membrane-Interface Probe (MIP) and the Hydraulic Profiling Tool (HPT), to provide simultaneous logging of contaminant and hydrogeological properties.

Contaminated Land Investigation, Direct Sensing, High-Resolution Site Characterisation (HRSC), Mobile Laboratory, Soil Sampling

What is Membrane-Interface & Hydraulic Profiling Tool (MiHPT)?

MiHPT is particularly valuable for remedial design characterisation, helping to elucidate the interaction between geological features and contaminant fate and transport. The system enables cost savings in the investigation phase due to reduced laboratory analyses, fewer field campaigns, and minimal investigation-derived waste.

The major benefits of MiHPT include the combination of the mature MIP and HPT logging techniques, real-time data visualization capabilities, minimal waste production, and enhanced insights through collating multiple logs in cross-sections or creating 3D models. The tool's typical production rate is 3-5 MIP locations per day (or 5-7+ HPT locations per day), and it complements more costly and lengthy characterisation and remediation methods (e.g., soil sampling, monitoring well installation, chemical injection, activated carbon injection), leading to cost-effective and sustainable solutions.

The MIP component of MiHPT incorporates a heating block for enhancing volatilisation of volatile organic compounds (VOCs). The VOCs go to a mobile gas chromatography (GC) unit housing three chemical detectors, typically photoionisation detector (PID), flame ionisation detector (FID), and halogen-specific detector (XSD), for delineation of VOCs.

The HPT system, used for groundwater investigations, involves an electrical conductivity sensor and a continuous direct-push injection logging system. Interpretation of HPT logs involves analysing flow rate, injection-induced pressure, and electrical conductivity values.

MiHPT Capabilities

During the technical webinar, Dan Pipp covered various aspects, including the capabilities of MiHPT for detection of organic contaminants and high electrical conductivity fluids, and its applicability in different subsurface conditions. The presentation highlighted Legion Drilling's expertise as pioneers in delivering HRSC services in Australia.

The webinar commenced with a fundamental introduction to direct push technology, emphasizing its application in unconsolidated soils and its limitations in dense materials and bedrock formations. The drilling process was explained, highlighting the need for direct contact with the soil for accurate measurements.

MiHPT Functionalities

The webinar featured detailed explanations of the MiHPT probe's functionalities, such as the electrical connectivity dipole, which provided data on caly content and other subsurface characteristics based on conductivity levels. The hydraulic profiling tool's operation and interpretation were elucidated, emphasizing its role in estimating the formation permeability (water-saturated hydraulic conductivity) by injecting water and recording the induced pressure.

The MiHPT's application was showcased through field examples, emphasising its capability to map VOC contaminants in real-time. The presentation covered scenarios with varying soil compositions and discussed the challenges posed by high concentrations or NAPL levels. The webinar emphasised the need for adaptation and optimization of field plans based on direct sensing data and the importance of an elevation survey for accurate interpretation of logs.

Dan Pipp explained the MIP chemical detector capabilities in detecting various VOCs (including chlorinated and petroleum hydrocarbons) and highlighted the importance of understanding MIP detection limits and response levels through quality control measures, such as response tests and log reviews, ensuring the reliability of the collected data. A detailed breakdown of the MiHPT's data channels, including electrical connectivity, HPT pressure, and gas chromatograph readings, was provided.

The presentation followed with guidance on choosing suitable compounds for MIP quality control based on their chemical properties, such as boiling point, vapor pressure, water solubility, and molecular weight. Dan Pipp offered valuable resources, including a list of compounds with compatible properties for MIP analysis, accessible on the Legion Drilling website.

Log Interpretation Examples

Pipp provided log interpretation examples beginning with a log where he emphasised the importance of the scales used in the logs, especially for interpreting patterns. He identified a likely double-bonded chlorinated solvent, potentially trichloroethane or perchloroethylene, based on patterns observed on the logs. Additionally, he highlighted the significance of methane responses in detecting breakdown products of hydrocarbons.

The logs demonstrated correlations between electrical connectivity (EC) and HPT pressure, aiding in identifying different soil types. Pipp suggested that higher EC and HPT pressure indicated the presence of clayey materials. He also discussed logs indicating non-chlorinated petroleum hydrocarbons and presented a low-level MiHPT log, illustrating the versatility of the tool for a wide range of contaminant concentrations, from ppb to NAPL levels, although always being aware of the challenges involved.

Moving to specific site examples, Pipp showcased an old petrol station. The MiHPT logs indicated the presence of contaminants, prompting further soil core sampling. Concentration analysis of soil cores revealed varying contamination levels at different depths, emphasizing the need for comprehensive testing.

Pipp also shared data from a site in Denmark. The MiHPT logs showcased electrical connectivity, HPT pressure, and MIP detector responses. By correlating MiHPT data with utility information, the team identified sewer line connections contributing to contamination hotspots.

The webinar concluded with Pipp highlighting the importance of combining EC and HPT data to understand lithology and migration pathways. The presentation stressed the utility of MiHPT in developing effective remediation strategies.

In summary, the Legion Drilling webinar provided valuable insights into HRSC using MiHPT for investigating contaminated soil and groundwater. Pipp demonstrated the interpretative capabilities of MiHPT logs, showcasing their applications in diverse environmental settings and emphasizing their significance in site assessment and remediation design, offering valuable insights for professionals in the field and equipping attendees with insights into its applications for HRSC in contaminated site investigations.

Check out other webinars organised by Legion Drilling here.