FRTR Field Sampling and Analysis Technologies Reference Guide

6 SAMPLE ANALYSIS TOOLS for VOCs, SVOCS, and PESTICIDES

6.2 EX-SITU ANALYSIS

6.2.29 Ground Penetrating Radar

Use:

Ground penetration radar (GPR) is most commonly used for locating buried objects (such as tanks, pipes, and drums); mapping the depth of the shallow water table; identifying soil horizons and bedrock subsurface; mapping of trench boundaries; delineating karst features and the physical integrity of manmade earthen structures; and selecting locations for installation of suction samplers in the vadose zone.

Description:

GPR utilizes a transmitting and a receiving antenna, which are dragged along the ground surface. The small transmitting antenna radiates short pulses of high-frequency radio waves (ranging from 10 to 1,000 MHz) into the ground, and the receiving antenna records variations in the reflected return signal. The principles involved are similar to reflection seismology, except that electromagnetic energy is used instead of acoustic energy, and the resulting image is relatively easy to interpret. Continuous microwave technologies are similar to GPR except that a range of frequencies is continuously emitted resulting in interference patterns between the emitted and reflected wave. The spacing (in frequency) between interference maxima or minima as the emitting frequency changes measures the depth of the reflecting surface. Best penetration is achieved in dry sandy soils or massive dry materials such as granite, limestone, and concrete. GPR provides the greatest resolution of currently available surface geophysical methods and is the only reliable method for detecting buried plastic containers.

Analytes:

11. TPH

Media:

Soil/Sediment	Water	Gas/Air
ADEQUATE	SERVICEABLE	Not Applicable

Selectivity:	Technique measures a part of the compound.
Susceptibility to Interference:	High.
Detection Limits :	500+ ppm (soil); 100+ ppm (water).
Turnaround Time per Sample:	More than a day. The depth of the buried layer or object being analyzed determines the time it takes the radar pulses to travel from the surface antenna to the target and back to the receiving antenna. Generally, moisture content of the media being examined will have the greatest effect on time requirements. The greater the amount of water saturation, the lower the radar velocity and the lower the object will appear in the radar profile.

Applicable To:

Screen/Identify	Characterize Concentration/Extent	Cleanup Performance	Long-Term Monitoring
ADEQUATE	BETTER	ADEQUATE	ADEQUATE

Quantitative Data Capability:	Data become quantitative with additional effort.
Technology Status:	Commercially available technology with limited field experience.
Certification/Verification:	Technology has not participated in CalEPA certification and/or CSCT verification program.
Relative Cost per Analysis:	Mid-range expense.

Limitations:

Depth of penetration (typically 1 to 15 meters) is less than direct current (DC) resistivity and electromagnetic (EM) methods, and is further reduced in moist and/or clayey soils and soils with high electrical conductivity.
Trade off between resolution and depth of penetration.
Bulkiness of equipment can limit use in rough terrain.
FM radio transmissions might interfere with signals depending on the frequency.
Unshielded antennas are susceptible to interference by metallic materials.
Bouldery till might scatter signal, masking underlying bedrock.
Unprocessed images require processing as they provide only approximate shapes and depths (continuous microwave methods are still in developmental stages).

ASTM Standards/EPA Methods:

No applicable ASTM standards or EPA methods are cited for this technology.

Sample Access/Collection Matrix

Sample Analysis Matrix

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