NRCS, National Soil Survey Center 100 Centennial Mall North; Federal Building, Room 152

Lincoln, NE 68508-3866 Phone: 402-437-5499; Fax: 402-437-5336

An Equal Opportunity Provider and Employer

Subject: MGT -- Geophysical Field Assistance Date: August 29, 2016

To: Ann English File Code: 330-20-7 State Conservationist Natural Resources Conservation Service Columbia, South Carolina

Purpose: To provide technical assistance and training in the use of ground-penetrating radar (GPR) and electromagnetic induction (EMI) techniques with the soils staff located in Laurens County, South Carolina while assessing soil properties. Participants: Debbie Anderson, Soil Survey Regional Director (SSR-3), NRCS, Raleigh, NC Lance Brewington, MLRA Soil Survey Leader, NRCS, Laurens, SC Dennis DeFrancesco, Retired Soil Scientist, NRCS, SC Gary Hankins, Soil Scientist, NRCS, Laurens, SC Kamara Holmes, State Soil Scientist, NRCS, Columbia, SC Emory Holsonback, Area Resource Soil Scientist, NRCS, Laurens, SC Greg Taylor, Senior Regional Soil Scientist (SSR-3), NRCS, Raleigh, NC Wes Tuttle, Soil Scientist (Geophysical), NSSC, NRCS, Wilkesboro, NC Activities: All field activities were completed on March 8-11, 2016. Summary: 1. The MLRA soils office located in Laurens, SC has a newly acquired conductivity meter

(Profiler EMP-400 manufactured by Geophysical Survey Systems, Inc., Nashua, NH). Apparent conductivity surveys were completed at multiple sites as associations were made between changes in apparent conductivity (ECa) and changes in soil properties including depth to bedrock and changes in clay and moisture. Deeper soils and soils with more clay and moisture resulted in higher ECa measurements. Ground-penetrating radar surveys were also completed to assess changes in depth to bedrock and associated changes in apparent conductivity. The NRCS staff were very receptive to new methods of soils investigations and minimally invasive procedures resulting from the use of ground-penetrating radar (GPR) and electromagnetic induction (EMI). The NRCS staff demonstrated the ability and an eagerness to conduct EMI investigations independently while yielding meaningful interpretations. Follow-up training is recommended in the use of EMI techniques to help reinforce operational techniques and data processing.

Ann English Page 2 2. Geophysical interpretations are considered preliminary estimates of site conditions. The

results of all geophysical investigations are interpretive and do not substitute for direct soil borings. The use of geophysical methods can reduce the number of soil observations, direct their placement, and supplement their interpretations. Interpretations should be verified by ground-truth observations.

It was a pleasure for Wes Tuttle to work in South Carolina with members of your fine staff. DAVID HOOVER Acting Director National Soil Survey Center Attachment: Technical Report cc: Debbie Anderson, Soil Survey Regional Director (SSR-3), NRCS, Raleigh, NC Lance Brewington, MLRA Soil Survey Leader, NRCS, Laurens, SC Kamara Holmes, State Soil Scientist, NRCS, Columbia, SC Zamir Libohova, Research Soil Scientist (NSSC Liaison), NSSC, MS 41, NRCS, Lincoln, NE Michael Robotham, National Leader, Technical Soil Services, SSD, NRCS, Lincoln, NE John “Wes” Tuttle, Soil Scientist (Geophysical), NSSC, NRCS, Wilkesboro, NC Doug Wysocki, National Leader, Soil Survey Research and Laboratory, NSSC, MS 41, NRCS,

Lincoln, NE

1

This technical report was prepared by Wes Tuttle Geophysical Soil Scientist, USDA-NRCS-NSSC, Wilkesboro, North Carolina

Equipment The radar unit is the TerraSIRch SIR (Subsurface Interface Radar) System-3000, manufactured by Geophysical Survey Systems, Inc.1 Morey (1974), Doolittle (1987), and Daniels (1996) have discussed the use and operation of GPR. The SIR System-3000 consists of a digital control unit (DC-3000) with keypad, color SVGA video screen, and connector panel. A 10.8-volt Lithium-Ion rechargeable battery powers the system. This unit is backpack portable and, with an antenna, requires two people to operate. The antenna used in this study has a center frequency of 200 MHz. The RADAN for Windows (version 7.0) software program was used to process the radar records (Geophysical Survey Systems, Inc, 2008).1 Processing included color transformation, surface normalization, time-zero adjustment and range gain adjustments. The Profiler EMP-400 sensor (hereafter referred to as the Profiler) is manufactured by Geophysical Survey Systems, Inc. (Nashua, NH) (see Photo 1). 1 Operating procedures for the Profiler are described by Geophysical Survey Systems, Inc. (2008). The Profiler has a 1.22 m (4.0 ft) intercoil spacing and operates at frequencies ranging from 1 to 16 kHz. It weighs about 4.5 kg (9.9lbs). The Profiler is a multifrequency EMI meter that can simultaneously record data in as many as three discrete frequencies. For each frequency, both in-phase (susceptibility) and quadrature phase (apparent conductivity, EC3) data are recorded. The calibration of the Profiler is optimized for 15 kHz and, as a consequence, ECa is most accurately measured at this frequency (Dan Delea, GSSI, personal communication). Surveys can be conducted with the sensor held in the shallower-sensing HDO or the deeper-sensing VDO orientations. The sensor's electronics are controlled via Bluetooth communications with a Trimble TDS RECON-400 or a Trimble Nomad Personal Data Assistant (PDA). 1 To collect geo-referenced data, the PDA is configured with an integral l2-channel WAAS (Wide Area Augmentation System) GPS. Geonics Limited manufactures the EM38 meter. This meter is portable and requires only one person to operate. No ground contact is required with this meter. McNeill (1980) and Geonics Limited (1998) have described principles of operation for the EM38 meter. Lateral resolution is approximately equal to its intercoil spacing. The EM38 meter has a 1 m intercoil spacing and operates at a frequency of 14,600 Hz. When placed on the soil surface, this instrument has a theoretical penetration depth of about 0.75 and 1.5 m in the horizontal and vertical dipole orientations, respectively (Geonics Limited, 1998). Values of apparent conductivity are expressed in millisiemens per meter (mS/m). To help summarize the results of this study, the SURFER for Windows (version 8.0 and version 11.0) developed by Golden Software, Inc. was used to construct two-dimensional simulations. Grids were created using kriging methods with an octant search. Ground-Penetrating Radar: Ground-penetrating radar is a time scaled system. The system measures the time it takes electromagnetic energy to travel from an antenna to an interface (i.e., soil horizon, stratigraphic layer) and back. To convert travel time into a depth scale requires knowledge of the velocity of pulse propagation. Several methods are available to determine the velocity of propagation. These methods include use of table values,

1 Manufacturer's names are provided for specific information; use does not constitute endorsement.

2

common midpoint calibration, and calibration over a target of known depth. The last method is considered the most direct and accurate method to estimate propagation velocity (Conyers and Goodman, 1997). The procedure involves measuring the two-way travel time to a known reflector that appears on a radar record and calculating the propagation velocity by using the following equation (after Morey, 1974):

V = 2D/T [1] Equation [1] describes the relationship between the propagation velocity (V), depth (D), and two-way pulse travel time (T) to a subsurface reflector. During this study, the two-way radar pulse travel time was compared with measured depths to known subsurface interfaces within each study site. Computed propagation velocities were used to scale the radar records. Electromagnetic Induction: Electromagnetic induction is a noninvasive geophysical tool that can be used for soil and site investigations. Advantages of EMI are its portability, speed of operation, flexible observation depths, and moderate resolution of subsurface features. Results of EMI surveys are interpretable in the field. This geophysical method can provide in a relatively short time the large number of observations that are needed to comprehensively cover sites. Maps prepared from correctly interpreted EMI data provide the basis for assessing site conditions, planning further investigations, and locating sampling or monitoring sites. Electromagnetic induction uses electromagnetic energy to measure the apparent conductivity of earthen materials. Apparent conductivity is a weighted, average conductivity measurement for a column of earthen materials to a specific depth (Greenhouse and Slaine, 1983). Variations in apparent conductivity are caused by changes in the electrical conductivity of earthen materials. The electrical conductivity of soils is influenced by the type and concentration of ions in solution, volumetric water content, temperature and phase of the soil water, and amount and type of clays in the soil matrix (McNeill, 1980). The apparent conductivity of soils increases with increases in soluble salts, water, and clay contents (Kachanoski et al., 1988; Rhoades et al., 1976). Electromagnetic induction measures vertical and lateral variations in apparent electrical conductivity. Values of apparent conductivity are seldom diagnostic in themselves. However, relative values and lateral and vertical variations in apparent conductivity can be used to infer changes in soils and soil properties. Interpretations are based on the identification of spatial patterns within data sets. To assist interpretations, computer simulations of EMI data are normally used. To verify interpretations, ground-truth measurements are required. Discussion The MLRA soils office located in Laurens, SC has a newly acquired conductivity meter (Profiler EMP-400 manufactured by Geophysical Survey Systems, Inc., Nashua, NH). Apparent conductivity surveys were completed at multiple sites as associations were made between changes in apparent conductivity (ECa) and changes in soil properties including depth to bedrock and changes in clay and moisture. Ground-penetrating radar surveys were also completed to assess changes in depth to bedrock and associated changes in apparent conductivity. Site 1 EMI Survey – Dairy Site (Laurens County) Soils The site is located approximately 3 miles northeast of the small town of Gray Court, SC. The site was in an area mapped Appling loamy sand, 2 to 6 percent slopes and Appling loamy sand, 6 to 10 percent slopes

3

(USDA/NRCS, Web Soil Survey). Field 2 was mapped Cecil sandy loam, 2 to 6 percent slopes and Cecil sandy loam, 6 to 10 percent slopes, eroded. The very deep, well drained Appling and Cecil soils formed on ridges and side slopes of the Piedmont uplands in residuum weathered from felsic igneous and metamorphic rocks. These soils are deep to saprolite and very deep to bedrock. Soil Classification - Site 1 (Laurens County) and Site 2 (Chester/York Counties) Appling - fine, kaolinitic, thermic Typic Kanhapludults Cecil - fine, kaolinitic, thermic Typic Kanhapludults Thomson - coarse-loamy, mixed, semiactive, thermic Ultic Hapludalfs Molena - mixed, thermic Psammentic Hapludults Brewback - fine, mixed, active, thermic Aquertic Hapludalfs Wynott - fine, mixed, active, thermic Typic Hapludalfs Winnsboro - fine, mixed, active, thermic Typic Hapludalfs Chewacla - fine-loamy, mixed, active, thermic Fluvaquentic Dystrudepts Survey Design: Two individual surveys were completed to assess the survey site (Figure 1). The grid area was approximately 200 meters x 130 meters. Survey procedures were simplified to expedite fieldwork. Two parallel lines defined the upper and lower boundaries of each survey grid area. EMI surveys were completed by walking at a fairly uniform pace in a back and forth pattern. Survey transect lines were spaced apart at a distance of 20 meters. The Profiler was carried at a height of approximately 8 inches (20 cm) above the surface and was operated in the continuous mode with measurements recorded at a 1 sec interval. The meter was carried in the vertical and the horizontal dipole orientations during data collection in two separate surveys. Depth of penetration (geometrical) was approximately 0 - 1.8 meters in the vertical orientation and 0.9 meters in the horizontal dipole orientation.

4

Photo 1. EMI survey completed with the Profiler EMP-400 sensor, manufactured by Geophysical Survey Systems, Inc., Nashua, NH. Measurements of apparent conductivity are measured in milliSiemens per meter (mS/m). The soils staff located in Laurens, SC did an excellent job operating and processing the ECa data resulting from the EMI surveys.

5

-82.0795 -82.079 -82.0785 -82.078 -82.0775

34.641

34.6415

34.642

34.6425

Dairy SiteVertical Dipole Orientation

(0 - 1.8 m)

-82.0795 -82.079 -82.0785 -82.078 -82.0775

34.641

34.6415

34.642

34.6425

-82.0795 -82.079 -82.0785 -82.078 -82.0775

34.641

34.6415

34.642

34.6425

-82.0795 -82.079 -82.0785 -82.078 -82.0775

34.641

34.6415

34.642

34.6425

-82.0795 -82.079 -82.0785 -82.078 -82.0775

34.641

34.6415

34.642

34.6425

-55-51-47-43-39-35-31-27-23-19-15-11-7-315913172125293337

Latit

ude

Longitude

mS/m

-82.0795 -82.079 -82.0785 -82.078 -82.0775

34.641

34.6415

34.642

34.6425

Dairy SiteHorizontal Dipole Orientation

(0 - 0.9 m)

0246810121416182022242628303234363840

-82.0795 -82.079 -82.0785 -82.078 -82.0775

34.641

34.6415

34.642

34.6425

-82.0795 -82.079 -82.0785 -82.078 -82.0775

34.641

34.6415

34.642

34.6425

Longitude

Latit

ude

mS/m

B

A

C

C

C

C

C

C

CC

C

6

Figure 1. Spatial pattern of apparent conductivity (ECa) measured with the GSSI Profiler conductivity meter in an area mapped Appling loamy sand, 2 to 6 percent slopes and Appling loamy sand, 6 to 10 percent slopes. The anomalous spikes in apparent conductivity (locations C) are thought to be attributed to discarded metal debris. Results Figure 1. A total of 1011 measurements were recorded with the GSSI Profiler meter in the horizontal dipole orientation (HDO). Apparent conductivity averaged 5.4 mS/m and ranged from 0.2 to 41.6 mS/m. One-half of the observations had an apparent conductivity between 3.9 and 5.9 mS/m. A total of 983 measurements were recorded with the GSSI Profiler meter in the vertical dipole orientation (VDO). Apparent conductivity averaged 4.0 mS/m and ranged from -79.1 to 15.2 mS/m. One-half of the observations had an apparent conductivity between 3.5 and 6.2 mS/m.

Figure 2. Spatial pattern of apparent conductivity (ECa) measured with the GSSI Profiler conductivity meter in an area mapped Cecil sandy loam, 2 to 6 percent slopes and Cecil sandy loam, 6 to 10 percent slopes, eroded.

-82.083 -82.0825 -82.082 -82.0815 -82.081 -82.0805

34.6395

34.64

34.6405

34.641

-82.083 -82.0825 -82.082 -82.0815 -82.081 -82.0805

34.6395

34.64

34.6405

34.641

1.5

3.5

5.5

7.5

9.5

11.5

Field 2 - Dairy SiteVertical Dipole Orientation

(0 - 1.8 m)mS/m

-82.083 -82.0825 -82.082 -82.0815 -82.081 -82.0805

34.6395

34.64

34.6405

34.641

Latit

ude

Longitude

A

B

7

Results Figure 2. A total of 1697 measurements were recorded with the GSSI Profiler meter in the vertical dipole orientation (VDO). Apparent conductivity averaged 8.3 mS/m and ranged from -2.1 to 13.0 mS/m. One-half of the observations had an apparent conductivity between 7.6 and 9.1 mS/m.

Photo 2. Soil borings are being taken after an EMI survey with the Profiler to verify changes in apparent conductivity and associated changes in soil properties. In Figures 1 and 2, changes in spatial patterns of apparent conductivity were thought to be associated with changes in soil characteristics. Areas containing higher apparent conductivity were thought to contain more clay/moisture and/or deeper soil profiles. In Figure 1, the soil/bedrock interface was observed in soil borings at 73 cm (29 in.) at location “A” and 33 cm (13in.) at location “B”. In Figure 2, soil borings at location “A” revealed a more developed soil profile with a thicker clay subsoil horizon - 95 cm (38 in) and no soil/bedrock interface was observed within 1.5 m (60 in.). Soil borings at location “B” revealed a thinner clay subsoil horizon thickness - 50 cm (20 in.) and a soil/bedrock interface observed at 115 cm (46 in.). More contrasting anomalous features (spikes in apparent conductivity – areas “C”) were thought to be associated with discarded metallic objects (Figure 1). Metal debris was observed across the survey area at various locations.

8

Soils across the survey area (Figure 1) were mapped Appling loamy sand, 2 to 6 percent slopes and Appling loamy sand, 6 to 10 percent slopes and are classified as very deep to bedrock. Soil borings and observations at various locations across the survey area suggest that shallower soils dominate the site. Moderately deep (50 -100 cm) and shallow soils (

9

Figure 3. File 13. Radar record collected with the SIR-3000 radar unit and a 200 MHz antenna across an area of Cecil sandy loam, 6 to 10 percent slopes, eroded. A white line approximates the soil/bedrock interface. Scale is in meters.

Figure 4. File 14. Radar record collected with the SIR-3000 radar unit and a 200 MHz antenna across an area of Cecil sandy loam, 2 to 6 percent slopes. A black line approximates the soil/bedrock interface. Scale is in meters.

10

Radar records obtained with the 200 MHz antenna was generally of good to excellent interpretative quality. Observation depths were greater than 2.0 meters. After review of the radar records and associated ground-truthing (soil borings), soils across the survey transect area ranged from shallow to moderately deep to very deep and were quite variable with respect to depth to bedrock. The soils across the survey site were mapped very deep. Interpretative results suggest a complex of soils with respect to soil depth. Additional investigations need to be completed to more fully assess map unit composition. Site 2 - Chester/York Counties EMI Surveys Soils The sites are located approximately 3 miles (Figure 5) and 3.5 miles (Figure 6) north of the community of Lockhart, SC near the Chester and York County line. Site 2A was in an area mapped Thomson sandy loam, 0 to 4 percent slopes and Molena.variant sand, 1 to 4 percent slopes. Site 2B was in an area mapped Brewback fine sandy loam, 2 to 6 percent slopes, Cecil sandy clay loam, 2 to 6 percent slopes, moderately eroded, Wynott-Winnsboro complex, 6 to 10 percent slopes, moderately eroded and Chewacla loam, 0 to 2 percent slopes, frequently flooded (USDA/NRCS, Web Soil Survey). The very deep, well drained Thomson soils formed in loamy and sandy fluvial sediments on Piedmont stream terraces and flood plains. The moderately deep, somewhat poorly drained Brewback soils formed in residuum from basic rocks or mixed acid and basic rocks on Piedmont uplands. The very deep, somewhat excessively drained Molena soils formed on stream terraces of the Piedmont and have reddish brown sand A horizons, and yellowish red loamy fine sand Bt horizons. The moderately deep, well drained Wynott soils formed in residuum from gabbro, diorite, and other dark colored mafic rocks on uplands in the Piedmont. The deep, well drained fine Winnsboro soils that formed in material mostly weathered from dark colored basic rocks of the Piedmont. The very deep, somewhat poorly drained Chewacla soils formed on alluvial flood plains in the Piedmont and Coastal Plain regions. Survey Design: Surveys were completed to assess the survey sites (Figures 5 and 6). The survey areas were irregular in size and shape. Survey procedures were simplified to expedite fieldwork. Two semi-parallel lines defined the eastern and western boundaries of each survey grid area. EMI surveys were completed by walking at a fairly uniform pace in a back and forth pattern while methodically traversing the sites while collecting apparent conductivity measurements. The Profiler was carried at a height of approximately 8 inches (20 cm) above the surface and was operated in the continuous mode with measurements recorded at a 1 sec interval. The meter was carried in the vertical dipole orientation (VDO) during data collection at the two separate sites. Depth of penetration (geometrical) was approximately 0 - 1.8 meters in the vertical dipole orientation.

11

Figure 5. Spatial pattern of apparent conductivity (ECa) measured with the GSSI Profiler conductivity meter in an area of Thomson sandy loam, 0 to 4 percent slopes and Molena.variant sand, 1 to 4 percent slopes. Site 2A - Results – Figure 5 A total of 2570 measurements were recorded with the GSSI Profiler meter in the vertical dipole orientation (VDO). Apparent conductivity averaged 5.9 mS/m and ranged from -86.8 to 255.0 mS/m. One-half of the observations had an apparent conductivity between 3.6 and 7.0 mS/m. In Figure 5, changes in spatial patterns of apparent conductivity were thought to be associated with changes in soil characteristics as observed in soil borings at locations A, B and C. Areas containing higher apparent conductivity (B) contained more clay/moisture as compared to soil profiles observed at locations A and C. Anomalous spikes in apparent conductivity (locations D) were thought to be associated with discarded metal debris. The elevated spike in apparent conductivity at location E was thought to be attributed to the close proximity to the metal wire fence line.

-81.4565 -81.456 -81.4555 -81.455 -81.4545 -81.454

34.822

34.8225

34.823

34.8235

Field 1Profiler - Vertical Dipole Orientation

(0 - 1.8 m)

-81.4565 -81.456 -81.4555 -81.455 -81.4545 -81.454

34.822

34.8225

34.823

34.8235

0

4

8

12

16

20

24

28

-81.4565 -81.456 -81.4555 -81.455 -81.4545 -81.454

34.822

34.8225

34.823

34.8235mS/m

Latit

ude

Longitude

A

BC

E

D

D

D

12

Site 2B – Field 2 (back side of farm) Results – Figure 6 A total of 975 measurements were recorded with the GSSI Profiler meter in the vertical dipole orientation (VDO). Apparent conductivity averaged 19.8 mS/m and ranged from 5.5 to 43.9 mS/m. One-half of the observations had an apparent conductivity between 14.0 and 24.8 mS/m. In Figure 6, changes in spatial patterns of apparent conductivity were thought to be associated with changes in soil characteristics as observed in soil borings. This was also reflected in soils mapping at the site. The higher activity clays with higher expansive properties observed in the Brewback soils attributed to higher apparent conductivity as compared to the lower activity clays observed in the adjacent Cecil soils. Geophysical interpretations are considered preliminary estimates of site conditions. The results of all geophysical investigations are interpretive and do not substitute for direct soil borings. The use of geophysical methods can reduce the number of soil observations, direct their placement, and supplement their interpretations. Interpretations should be verified by ground-truth observations.

13

-81.4494 -81.449 -81.4486

34.833

34.8332

34.8334

34.8336

34.8338

34.834

34.8342

34.8344

34.8346

34.8348

34.835

34.8352

Field 2 - (backside of farm)Profiler - Vertical Dipole Orientation

(0 - 1.8 m)mS/m

-81.4494 -81.449 -81.4486

34.833

34.8332

34.8334

34.8336

34.8338

34.834

34.8342

34.8344

34.8346

34.8348

34.835

34.8352

-81.4494 -81.449 -81.4486

34.833

34.8332

34.8334

34.8336

34.8338

34.834

34.8342

34.8344

34.8346

34.8348

34.835

34.8352

4

9

14

19

24

29

34

39

44

Latit

ude

Longitude

Brewback fsl, 2-6%

Cecil scl, 2-6 %,mod. eroded

Wynott-Winnsboro complex, 6-10%, mod. eroded

Chewacla loam, 0-2%, freq. flooded

14

Figure 6. Spatial pattern of apparent conductivity (ECa) measured with the GSSI Profiler conductivity meter in an area of Brewback fine sandy loam, 2 to 6 percent slopes, Cecil sandy clay loam, 2 to 6 percent slopes, moderately eroded, Wynott-Winnsboro complex, 6 to 10 percent slopes, moderately eroded and Chewacla loam, 0 to 2 percent slopes, frequently flooded. References: Conyers, L. B., and D. Goodman. 1997. Ground-penetrating Radar; an introduction for archaeologists. AltaMira Press, Walnut Creek, CA. 232 pp. Daniels, D. J. 1996. Surface-Penetrating Radar. The Institute of Electrical Engineers, London, United Kingdom. Doolittle, J. A. 1987. Using ground-penetrating radar to increase the quality and efficiency of soil surveys. 11-32 pp. In: Reybold, W. U. and G. W. Peterson (eds.) Soil Survey Techniques, Soil Science Society of America. Special Publication No. 20. Geonics Limited. 1998. EM38 ground conductivity meter operating manual. Geonics Ltd., Mississauga, Ontario. Greenhouse, J. P., and D. D. Slaine. 1983. The use of reconnaissance electromagnetic methods to map contaminant migration. Ground Water Monitoring Review 3(2): 47-59. Kachanoski, R. G., E. G. Gregorich, and I. J. van Wesenbeeck. 1988. Estimating spatial variations of soil water content using noncontacting electromagnetic inductive methods. Can. J. Soil Sci. 68:715-722. McNeill, J. D. 1980. Electromagnetic terrain conductivity measurement at low induction numbers. Technical Note TN-6. Geonics Ltd., Mississauga, Ontario. Morey, R. M. 1974. Continuous subsurface profiling by impulse radar. p. 212-232. IN: Proceedings, ASCE Engineering Foundation Conference on Subsurface Exploration for Underground Excavations and Heavy Construction, held at Henniker, New Hampshire. Aug. 11-16, 1974. Rhoades, J. D., P. A. Raats, and R. J. Prather. 1976. Effects of liquid-phase electrical conductivity, water content, and surface conductivity on bulk soil electrical conductivity. Soil Sci. Soc. Am. J. 40:651-655. USDA/NRCS, Web Soil Survey (http://websoilsurvey.nrcs.usda.gov/app

Geonics Limited. 1998. EM38 ground conductivity meter operating manual. Geonics Ltd., Mississauga, Ontario.

2016-08-29T16:52:04-0500DAVID HOOVER