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Implementing Advanced Site Characterization Tools

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About ITRC
Navigating this Website
1 Introduction
1 Introduction Overview
1.1 Purpose and Scope
1.2 Technologies
1.3 How to Use this Document
2 ASCT Implementation
2 ASCT Implementation Overview
2.1 Tool Selection
2.2 Tool Application
3 Direct Sensing
3 Direct Sensing Overview
3.1 How to Select and Apply Direct Sensing Tools Using this Document
3.2 Membrane Interface Probe
3.3 Optical Image Profiler
3.4 Laser-Induced Fluorescence
3.5 Cone Penetrometer Testing
3.6 Hydraulic and Groundwater Profiling Tools
3.7 Electrical Conductivity (EC) Probe
3.8 Flexible Liners
4 Borehole Geophysics
4 Borehole Geophysics Overview
4.1 How to Select and Apply Borehole Geophysical Tools Using this Document
4.2 Fluid Temperature
4.3 Fluid Resistivity
4.4 Mechanical Caliper
4.5 Optical Televiewer
4.6 Acoustic Televiewer
4.7 Natural Gamma Logging
4.8 Borehole Flow Meters
4.9 Advanced Borehole Logging Tools
5 Surface Geophysics
5 Surface Geophysics Overview
5.1 How to Select and Apply Surface Geophysical Tools Using this Document
5.2 Electrical Resistivity Imaging
5.3 Ground Penetrating Radar
5.4 Seismic Methods
5.5 Electromagnetic Surveys
6 Remote Sensing
6 Remote Sensing Overview
6.1 How to Select and Apply Remote Sensing Tools Using this Document
6.2 Drones
6.3 Visible Spectrum Camera
6.4 Camera Features
6.5 Photogrammetry
6.6 Sample Collection and Monitoring using Drones
6.7 Cost Considerations
6.8 Case Studies
7 Stakeholder and Tribal Perspectives
8 Regulatory Perspective
8 Regulatory Perspective Overview
8.1 Challenges and Solutions
9 Case Studies
9 Case Studies Overview
9.1 MIP Boring Data Allow On-Site Decisions to Fill Data Gaps and Reduce Uncertainty during Triad Approach Evaluation at Five South Dakota Sites
9.2 MIP Allows Real-Time Identification and Delineation of DNAPL Plume at a Former Naval Air Station in California
9.3 OIP-Green Probe Delineates Extent of Coal Tar NAPL at a Former Gas Manufacturing Plant in Kansas
9.4 LIF Survey with UOVOST® Provides More Accurate Representation of LNAPL Plume at a Former Bulk Petroleum Storage Facility in New Hampshire
9.5 UVOST Differentiates LNAPL Types to Allocate Financial Liabilities at a Retail Petroleum Facility in Tennessee
9.6 TarGOST Determines DNAPL Extent and HPT Confirms Site Lithology at a Former Creosote Facility in Louisiana
9.7 CPT Borings and Hydropunch Sampler Optimize Site Characterization at an Aviation Industrial Complex in California
9.8 Waterloo APS, CPT, and LIF Data Update CSM and Help Optimize Selected Remedy at a Former Refinery in Oklahoma
9.9 Conceptual Site Model Development Using Borehole Geophysics at the Savage Municipal Water Supply Superfund Site in New Hampshire
9.10 ERI Provides Data to Improve Groundwater Flow and Contaminant Transport Models at Hanford 300 Facility in Washington
9.11 Surface and Borehole Geophysical Technologies Provide Data to Pinpoint and Characterize Karst Features at a Former Retail Petroleum Facility in Kentucky
9.12 GPR Data Show Location of Buried Debris and Piping Associated with a Former Gas Holder in Minnesota
9.13 Resistivity, Seismic Exploration, and GPR Provide Data to Evaluate Clay Reserves at a Commercially Mined Pit
9.14 Seismic Refraction, Electric Resistivity, and Multichannel Analysis of Seismic Waves Provide Data to Locate Monitoring Well Locations in a Mixed-Use Area in Northern Virginia
9.15 Surface Geophysical Methods Provide Data to Identify Prospective Utility Waste Landfill Sites in Karst Terrain in Missouri
9.16 Airborne Time-Domain Electromagnetic Method Maps Sand Distribution along the Illinois Lake Michigan Shore
9.17 Drone Technology Expedites and Streamlines Site Characterization at a Former Golf Course in Missouri
9.18 High-Resolution and Thermal Aerial Images Identify Mine Openings at an Abandoned Colorado Mine
9.19 RPAS Collects Water Samples to Avoid Safety Concerns at Montana Tunnels Mine
Additional Information
Appendix A. Tool Tables and Checklists
Glossary
References
Acronyms
Acknowledgments
Team Contacts
Document Feedback

 

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9.14 Seismic Refraction, Electric Resistivity, and Multichannel Analysis of Seismic Waves Provide Data to Locate Monitoring Well Locations in a Mixed-Use Area in Northern Virginia

Nathan Stevens, PG
Kleinfelder, Inc. (Maine)
Westborough, MA
[email protected]

At a site in a mixed commercial and residential area in northern Virginia, a recent assessment identified MTBE in bedrock groundwater at locations cross gradient to groundwater flow. Based on these results, additional bedrock monitoring wells were needed. Area mapping and local reconnaissance, in combination with borehole geophysical and aquifer testing, indicated that relatively discrete, steeply dipping fractures were potentially responsible for both movement of contaminated groundwater from the overburden to bedrock and transport of MTBE away from the site. Surficial geophysical technologies were selected to allow the determination of appropriate and feasible monitoring well locations and because the methods overcame the following site-specific challenges: density of development in the area; the proximity of potential receptors (private potable wells)’ and properly identifying top of bedrock, potential fractures, and feasible drilling locations. In addition, the methods needed to be acceptable to the regulatory authority, understandable to the public, readily available, and cost effective.

Seismic refraction (SR), ER, and MASW were used to identify potential monitoring well locations. A total of 550 linear ft of ER survey, 1,500 linear ft of MASW, and 2,100 linear ft of SR were performed over three days along roadways or through commercial parking lots.

Based on the initial data described above, two ER lines were conducted south of the site using an Advanced Geosciences SuperSting™ R8 earth-resistivity meter and Swift automatic electrode system in dipole-dipole arrangement (see Figure 9‑51). Approximately 3,000 soundings were collected. The electrode spacing (dipole size) was 6.6 ft to 10 ft and used 32 and 35 electrodes. ER data, when analyzed, identifies contrasts in the conductivity (inverse of resistivity) of the subsurface. Patterns in the contrast of conductivities are a line of evidence to the location of clays, bedrock, and potentially saturated fractures. The end result is an illustration of basic stratigraphy of the study area.

Figure 9‑51. ER lines conducted on the site

Seven SR lines were conducted using a 24-channel Geode Seismograph with 10-Hz geophones and a 10-pound manual hammer. Two of the SR lines were conducted in a roll-along setup to maintain vehicle traffic in the public roads. Each line used 10-foot geophone spacing and five source locations. SR ER data, when analyzed (see Figure 9‑52 for an example), identifies differences in seismic velocity due to the bending of seismic waves as identified by the time required for the signal to travel from the source (hammer) though the subsurface and to the receiver (geophones). Patterns in the contrasts of seismic velocities can indicate the depths and locations of weathered and competent rock as opposed to overburden unconsolidated materials. The end result is an illustration of the stratigraphy of the study area.

Figure 9‑52. Seismic refraction profile along line 1

Five MASW lines were conducted. Data collection was performed using a 24-channel Geode Seismograph with 10-Hz geophones and a 12-pound hammer. Sources were placed at each end and on 10-foot centers. MASW uses the surface wave component of the seismic signal, in conjunction with the body-wave component used by SR, within a frequency/velocity model to identify anomalies in the stratigraphic model developed using SR. These anomalies can represent fractures or fracture zones, especially those that intersect the top of the competent bedrock as determined by SR and ER (see Figure 9‑53 for an example).

Figure 9‑53. MASW profile along line 1

Surficial geophysical results allowed the identification of a trend of anomalies categorized as a fracture zone and the subsequent determination of monitoring well locations. The justification for these locations was easily understood by the regulator and public because of the developed figures. The figures provided documentation of the various lines of evidence offered by each technique, profiles of the interpreted subsurface, and plan shown on an aerial photo base. This approach became the basis for installing sentinel monitoring wells between the site and potential receptors and served as an important component when presenting the CSM subsequent meetings.

The cost of the geophysical survey was approximately $15,000, which was less than one-half the cost of a single well and provided important assurances to all stakeholders that the selected monitoring well locations were appropriate.

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