4.3 Water, adjacent structures and surface encumbrances

1 The rule on accumulated water

1926.651(h)(1): "Employees shall not work in excavations in which there is accumulated water, or in excavations in which water is accumulating, unless adequate precautions have been taken to protect employees against the hazards posed by water accumulation. The precautions necessary to protect employees adequately vary with each situation, but could include special support or shield systems to protect from cave-ins, water removal to control the level of accumulating water, or use of a safety harness and lifeline."

Read the two conditions: water that has accumulated, and water that is accumulating. The second is the one crews talk themselves past — the bottom is only damp now, and the work will only take an hour. The standard treats a rising level as the hazard, because it is.

The precautions are named as examples, and they are structural: a support or shield system, water removal to control the level, a harness and lifeline. "We'll be careful" is not on the list.

2 Pumps, drainage and the competent person

1926.651(h)(2): "If water is controlled or prevented from accumulating by the use of water removal equipment, the water removal equipment and operations shall be monitored by a competent person to ensure proper operation."

Both the equipment and the operations, monitored by a competent person. A pump that quits at lunch, loses suction, or cannot keep up with an inflow is a trench filling up while the crew works in it, and the standard puts a named person on watching for that.

1926.651(h)(3) covers surface water: "If excavation work interrupts the natural drainage of surface water (such as streams), diversion ditches, dikes, or other suitable means shall be used to prevent surface water from entering the excavation and to provide adequate drainage of the area adjacent to the excavation. Excavations subject to runoff from heavy rains will require an inspection by a competent person and compliance with paragraphs (h)(1) and (h)(2) of this section."

Two duties there, and the second is the one that gets missed on Monday morning: an excavation subject to runoff from heavy rain requires an inspection by a competent person and compliance with (h)(1) and (h)(2) — before anyone works in it again.

3 What water does to the soil class

This is the link back to Part 2, and it is why water is a structural issue rather than a comfort issue. Under Appendix A (b):

• Submerged soil is soil which is underwater or is free seeping. Type C.
• Soil from which water is freely seeping — Type C (iii), explicitly.
• Submerged rock that is not stable — also Type C.
• Wet soil holds significantly more moisture than moist soil, in a range where cohesive material will slump or begin to flow when vibrated.
• Wet granular material that showed apparent cohesion when moist loses those properties when wet.
• And the thumb penetration paragraph, (d)(2)(iii), says outright: if the excavation is later exposed to wetting influences such as rain or flooding, the classification must be changed accordingly.

So a trench cut to a Type B slope on a dry Tuesday is out of compliance on a wet Wednesday, not because anyone re-cut it, but because the ground it was cut in is now a different class. That is what Appendix A (c)(5) — reclassification — is for.

4 Adjacent structures: 1926.651(i)

Water is not the only thing pushing on your wall. (i)(1): where the stability of adjoining buildings, walls or other structures is endangered by excavation operations, support systems such as shoring, bracing or underpinning shall be provided to ensure their stability for the protection of employees.

(i)(2) is a prohibition with four exceptions. Excavation below the level of the base or footing of any foundation or retaining wall that could reasonably be expected to pose a hazard to employees shall not be permitted except when:

1. 1
   A support system such as underpinning is provided to ensure the safety of employees and the stability of the structure; or
2. 2
   The excavation is in stable rock; or
3. 3
   A registered professional engineer has approved the determination that the structure is sufficiently removed from the excavation so as to be unaffected by the excavation activity; or
4. 4
   A registered professional engineer has approved the determination that such excavation work will not pose a hazard to employees.

Note that two of the four exceptions require a registered professional engineer to approve a determination. "It looks far enough away" is not one of the four. And (i)(3): sidewalks, pavements and appurtenant structures shall not be undermined unless a support system or another method of protection is provided.

That last sentence describes MIFACE 05MI084 exactly: a trench dug tight against a garage and a sidewalk, sides close to vertical, spoil on both lips because the yard was too small. The wall and part of the sidewalk came in together and killed a 24-year-old worker.

5 Surface encumbrances: 1926.651(a)

The first paragraph of 1926.651 is the one nobody quotes: "All surface encumbrances that are located so as to create a hazard to employees shall be removed or supported, as necessary, to safeguard employees."

In plain terms: everything at the surface that could come into the hole. Trees and stumps at the lip, boulders, light poles and sign posts, a fence line, a stack of pallets, an old slab, the curb. If it creates a hazard, it gets removed or supported before the excavation exposes it.

Surface encumbrances are also a classification question. A tree at the edge means roots and old disturbed ground; a pole means a buried footing; a slab means fill underneath. Each one is a reason to look harder at the soil on that side.

6 The wet-trench checklist

• Is there water in the bottom, or is it coming in? Then (h)(1) applies and work stops until precautions are in place.
• Is the pump running, and who is the competent person monitoring it and the operation?
• Has this excavation seen runoff from heavy rain? Then an inspection by a competent person is required before re-entry — (h)(3) and (k)(1).
• Has the soil class been revisited? Freely seeping or submerged soil is Type C.
• Is the protective system still rated for that class at that depth?
• Is there anything at the surface — a structure, pavement, a tree, a pole — that needs support or removal under (a), (i)(1) or (i)(3)?

The last chapter of this course covers the rest of the surface: buried utilities, spoil, traffic and mobile equipment, and the daily inspection that puts all of it on one record.