October 7, 2026
This week’s photo is courtesy of- GeoLog, LLC, Cottonwood, AZ, USA.
Safety Focus
Part 3 of 4: Overhead Power Lines and Mast Raising: Control It
Start with jurisdiction, because it trips people up. OSHA's crane standard (Subpart CC) is where the well-known 20-foot rule lives, but 1926.1400(c)(11) says plainly that Subpart CC does not cover "dedicated drilling rigs." For a drill rig on construction work, the clearance numbers come from the equipment rule, 1926.600(a)(6), on top of the general electrical rule at 1926.416(a). In general industry, they come from 1910.333(c)(3).
The legal minimums. For lines rated 50 kV (50,000 volts) or below, 1926.600(a)(6) requires at least 10 feet (about 3 meters) between the line and any part of the equipment or load. Above 50 kV, add 0.4 inch for every kV over 50. A 200 kV line works out to 10 feet plus 60 inches, or 15 feet. General industry sets the same 10-foot clearance for vehicles and mechanical equipment at 50 kV and below.
Moving the rig. In transit with no load and the mast lowered, 1926.600(a)(6)(iii) requires 4 feet for voltages less than 50 kV, 10 feet for voltages over 50 kV up to and including 345 kV, and 16 feet for voltages up to and including 750 kV.
Train to the stricter number. NIOSH's 2026 guidance says to keep machinery, equipment, and loads "20 feet or more" from energized, uncovered lines. The Alaska investigators recommended a 20-foot safety zone. Ten feet is the OSHA minimum for lines up to 50 kV. A crew standard of 20 feet (about 6 meters) or more is a recommended practice, not a rule, and a better one, because it is often tough to correctly judge the distance to the wire. On high-voltage lines the legal distance can exceed 20 feet (about 21 feet 8 inches at 400 kV), so always use whichever number is larger.
Put a spotter on it. 1926.600(a)(6)(iv) requires a designated person to watch clearance "where it is difficult for the operator to maintain the desired clearance by visual means." That person watches the line and nothing else. NIOSH also says to run machines slower than normal near lines.
Best control: eliminate the energy from the equation. Ask the utility to de-energize and ground it. Insulating links and proximity alarms help, but 1926.600(a)(6)(v) says those devices do not change any other requirement.
Key Takeaways:
• Dedicated drill rigs fall outside the crane standard; on construction work, look to 1926.600(a)(6) and 1926.416(a).
• Minimum: 10 feet for lines up to 50 kV, more as voltage rises.
• Make 20 feet or more your crew standard (more where the voltage requires it), with a dedicated spotter.
• The surest control is a line the utility has de-energized and grounded.
Sources:
• OSHA: 29 CFR 1926.1400, Scope
• OSHA: 29 CFR 1926.600, Equipment
Knowledge Share
Part 3 of 4: Subsurface Geology Analysis: Apply It
A cross-section is a side view of the ground, built by lining up logs from several wells. It turns separate holes into one picture. Here is how to build one.
1. Convert depth to elevation. Wells sit on different ground. Subtract each depth from that well's surface elevation so the logs line up on the same datum. Example: Well A sits at 1,250 feet elevation and hits clay at 80 feet, so the clay top is at 1,170 feet. Well B sits at 1,238 feet and hits clay at 68 feet. That is also 1,170 feet (about 357 meters). If the logs confirm it is the same clay (step 3), the bed is lying flat. By depth alone, the two contacts look 12 feet apart.
2. Line the logs up in map order along the line of the section.
3. Match signatures, not just words. One driller's "sandy clay" is another's "clayey sand." A gamma spike with low resistivity in Well A should show up as the same pattern in Well B. The USGS manual on borehole geophysics notes that even where resistivity logs are hard to read for lithology, "stratigraphic units still can be correlated between the wells using these logs."
4. Connect only what you can defend. Clay lenses pinch out between holes. Draw a dashed line where you are inferring and a solid line where the logs agree.
5. Pick the screen zones. Look for intervals where low gamma, higher resistivity, an SP shift, and coarse cuttings all agree. Then sample those intervals for grain-size analysis (that topic arrives later in this series). Watch for resistivity falling with depth; at Jamesport, the USGS used a conductivity log to trace water turning brackish and then salty toward the bottom of the well.
What this means for your next design:
• Correlate by elevation, never by depth.
• A good field rule: screen where several lines of evidence agree, and keep screen out of zones the logs flag as poor water quality.
Sources:
• USGS (Keys, TWRI 2-E2): Borehole Geophysics Applied to Ground-Water Investigations, Electric Logging
Recommended Print References:
• Hydraulics of Wells: American Society of Civil Engineers
• Handbook of Ground Water Development- Roscoe Moss Company
• Groundwater & Wells, Third Edition- Edited by Robert J. Sterrett, Johnson Screens
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