KIRTLAND AIR FORCE BASE ALBUQUERQUE, NEW MEXICO ...

APPENDIX B
Magnetic Surveys
useful for determining this contact if the transmitter/receiver separation is greater than the
width of the landfill (i.e., it is not the best method to employ if most of the waste materials
are confined within ―thin‖ trenches).
― The Geonics Limited EM-34 has the ability to utilize 3 frequencies from 0.4 Khz to 6.4
Khz and coil separations of 10, 20, and 40 meters. By varying the frequency and/or coil
orientation at a constant coil separation, the system is sensitive to variations in
conductivity at different depths. The maximum depth sensitivity of the EM-34 system is
approximately 200 ft. The Max-Min EMI sounding system manufactured by Apex
Parametrics has the ability to utilize 10 frequencies from 220 Hz to 56 Khz and coil
separations of 25 to several hundred ft. Again, by varying the frequency at a user-defined
constant coil separation, the system is sensitive to variations in conductivity at different
depths.
― EMI sounding techniques are generally more cost effective than direct current resistivity
techniques, however, the methodology used should be carefully selected by experienced
personnel after a thorough review of the program objectives and site specific variables.
Time Domain Measurements-Geonics EM-61:
― The EM-61 time domain EMI technique is a geophysical method primarily designed for
detecting metallic objects. Numerous primary electromagnetic pulses (150 per second)
are directed into the ground with a coil, and the secondary magnetic field generated within
the subsurface is measured during the time between pulses. For metallic targets, the
secondary magnetic field exists for longer periods of time when compared to the
secondary magnetic field response from natural earth materials. By measuring the
secondary magnetic field at a specific time, the relative response between metallic and
natural earth materials is at a maximum.
― The EM-61 system consists of various geometries of coils, coil sizes and time gates of
measurement. The utilization of 2 coils permits the EM-61 to discriminate between
shallow and deep targets, much like a vertical magnetic gradiometer. The EM-61 has the
ability to detect a single 55-gallon drum at a depth approaching 10 ft in optimum
conditions.
There are a variety of different types of magnetometers designed for specific situations. In general,
magnetometers detect man-made items and features that are ferrous (i.e., contain iron). Natural features
that have different amounts of magnetite and other magnetic minerals (e.g., fault contact between
intrusive gabbro and limestone) can also be identified using magnetometry.
Magnetic measurements are generally made in a series of parallel lines across the survey area. The
desired resolution and the size and depth of the objects of interest determine the location and spacing of
measurement stations or survey lines. Data are digitally recorded, and the resulting magnetic intensities
at locations across the survey area are used to infer the presence of magnetic anomalies. Because of the
phenomenon of temporal magnetic drift (usually diurnal), a magnetic survey should include a base station
at which magnetic measurements are made at regular intervals. The base station is later used to correct
all field survey data for the earth‘s natural diurnal magnetic field changes. At a minimum, the following
information should be recorded during the survey.
Kirtland AFB
SOPs for Field Investigations B-69 April 2004