September 29, 2026
This week’s photo is courtesy of- Arizona Beeman Drilling - Gold Canyon, AZ, USA.
Safety Focus
Part 2 of 4: Electrical Safety Near Water: Spot It
Yesterday: water plus temporary power. Today: how to spot trouble before someone grabs it. Walk it in the order the power flows: start at the source, follow the cord, finish at the pump or tool.
At the source. Look at the generator first. OSHA's portable generator guidance is direct: "Keep a generator dry; do not use it in the rain or wet conditions." If discharge water is pooling under the frame, or the generator sits downhill of the discharge line, that is your first hazard. Check that the grounding connections are tight.
Along the cord. 1926.416(e)(1) is clear: "Worn or frayed electric cords or cables shall not be used." 1926.416(e)(2) adds that extension cords "shall not be fastened with staples, hung from nails, or suspended by wire." Extension cords for portable tools must be "of three-wire type" and "designed for hard or extra-hard usage" (1926.405(a)(2)(ii)(J)). A missing ground prong turns a three-wire cord into a two-wire cord. Look for cut jackets, tape repairs, spots crushed under a tire, and plug connections sitting in water.
At the outlet. On a construction site, every 120-volt, single-phase, 15- and 20-amp receptacle that is not part of the permanent building wiring and is in use by employees needs GFCI protection, unless the employer runs an assured equipment grounding conductor program instead (1926.404(b)(1)). A GFCI, or ground-fault circuit interrupter, is the device that cuts power when current leaks where it should not. No GFCI and no grounding program you can see on paper means nobody plugs in.
At the pump or tool. Check where the cord enters the housing. OSHA requires flexible cords to be connected with strain relief that prevents "pull from being directly transmitted to joints or terminal screws" (1926.405(g)(2)(iv)). A cord yanked loose at the housing is a shock waiting for wet hands.
Key Takeaways:
• Walk the power path: source, cord, outlet, tool.
• Worn or frayed cords come out of service. No exceptions.
• No GFCI and no grounding program means no plug-in.
Sources:
• OSHA: Using Portable Generators Safely
Knowledge Share
Part 2 of 4: Recovery and Boundaries: Understand It
Yesterday: why recovery data is worth collecting. Today: how to turn it into a number.
Two clocks. Recovery uses two clocks. t is the time since pumping started. t' ("t prime") is the time since pumping stopped. Residual drawdown, s' ("s prime"), is how far the water level still sits below its static level at any moment during recovery.
Formula Spotlight: Theis Recovery Method
s' = (264 Q / T) log (t / t')
T = 264 Q / Δs'
T = transmissivity, in gallons per day per foot (gpd/ft)
Q = pumping rate during the test, in gallons per minute (gpm)
Δs' = change in residual drawdown over one log cycle of t/t', in feet
264 is a unit-conversion constant, the same one you met in Cooper-Jacob in Week 5.
How to plot it. USGS lays out the method: plot residual drawdown "on the arithmetic scale and t/t' on the logarithmic scale." Then: "After the value of t' becomes sufficiently large, the observed data should fall on a straight line." Read the change in s' across one log cycle of t/t' (say, from 100 down to 10). That is Δs'.
Worked example. A well pumped at 250 gpm. On the recovery plot, residual drawdown changes 3.3 feet across one log cycle. T = 264 × 250 ÷ 3.3 = 20,000 gpd/ft, or about 250 square meters per day.
The catch. The first minutes after shutdown will not sit on the line. The straight line only shows up once t' is large enough, so do not fit the early points. Then compare: if recovery T and drawdown T land close together, you can lean on both. If they are far apart, find out why before anyone sizes a pump.
Tomorrow: what the plot looks like when the cone of depression hits a boundary.
What this means for your next design: Get T from recovery as well as drawdown. Two answers that agree are worth more than one.
Sources:
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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