EM Spectrum

EM Wave Theory

Simplifications: Conductors:   Dielectrics: 

Conductors and Dielectrics Skin depth = SQRT (2/  ) Wave speed = SQRT (2  /  ) Wavelength = 2  SQRT (2/  ) Note -  are together Skin depth = 2 SQRT (  /  ) /  Wave speed = 1 / SQRT (  ) Wavelength = 2  /  SQRT (  ) Note -  appears here

EM Spectrum GPR frequencies –Lowest ~80 MHz sees deepest— ~30m but poor rez. –Highest ~1200 MHz Shallow— ~10 cm High rez

Monitoring Remediation: GPR

GPR

GPR Antennas 100 Mhz – ( air = 300 cm) 200MHz – ( 150 cm) 500 Mhz – ( 60 cm) 900 Mhz – ( 33 cm)

Dielectric constant, K permittivity  = K  o where  o = 1/36  x sec/ohm-m K = 1 air V = 30 cm/ns = 4 gasoline = 15 = 6 dry sand = = 20 wet sand = 6.7 = 81 water = 3.33

GPR Catalog Summary of GPR signatures found by the Netherlands Institute of Applied Geoscience R.A. van Overmeeren, 1998, Radar facies of unconsolidated sediments in The Netherlands: a radar stratigraphy method for hydrogeology, Journal of Applied Geoscience, v. 40, p.1-18.

GPR Fluvial Catalog

GPR Glacial Catalog

GPR Aeolian Catalog

GPR Marine Catalog

GPR Catalog, Summary

Gasoline Spill at OGI

OGI Test Tank

OGI Line E6: hours 0-48 Pre-spill 12 hrs 24 hrs 36 hrs 48 hrs

OGI Line E6: Hours hrs 60 hrs 72 hrs 84 hrs 96 hrs

OGI Line E6: Hours hrs 120 hrs 132 hrs 144 hrs 158 hrs

Things to notice Gasoline spreads in fingers, maybe reflecting microtextures in the sand. The fingers wax (and wane?) as heads build up at the source. They pulse outward. (Not shown) A repeat survey done the following spring showed bright spots (gas pockets) scattered at different depths.

Problem: Why bright spots? Jeff Daniels and his students at Ohio State have studied many LNAPL spills in the Midwest. They find that GPR reflections are almost always dim or absent over gasoline spills. Why was my result (in Oregon) different from his (in Illinois, Indiana, and Ohio)?

DaveC at Coeur d’Alene

Borehole GPR in a boat

CDA GPR - profile

CDA GPR - Interp

GPR Characteristics MHz Uses true EM reflections Textures, petro- chemicals, UXO... High rez (~10 cm) Fast ( km/hr) Can work near cultural noise Maximum depth penetration <~30m Can’t penetrate conductive ground (>~30 mS/m) –clays –brackish porewaters Realistic sections