NGA 21 Locating And Marking Of Facilities Practice Test

Transmission of an impressed signal through the ground is governed by how conductive the soil is. Soil conditions—especially moisture content, salt content, and texture—determine the ground’s resistivity. When soil is moist or saline, ions carry the current more readily, so the signal travels farther with less attenuation. Dry, sandy, or rocky soils raise resistance and dampen the signal quickly, limiting how far you can detect it. Temperature can shift resistivity, but the dominant factor is the soil’s ability to conduct. Weather, humidity, and wind speed can influence surface moisture a bit, yet they don’t set subsurface transmission as strongly as the soil’s composition and moisture do. Because this controls the strength and reach of the impressed signal underground, soil conditions are the primary determinant.