The 8-Foot Sewer Trench and the Trash Pump in the Arroyo
A 60-lot subdivision in Bernalillo County is under construction. A utility crew is installing 8-foot-deep sanitary sewer in sandy clay with caliche layers. At 9:00 a.m. the county inspector observes: spoil piled about 18 inches from the trench edge; a 24-inch water line crossing the trench with no support; no ladder anywhere along a 60-foot open cut; two laborers hand-grading the bottom while the excavator bucket is parked directly over the trench. The foreman says the crew's "competent person" is the excavator operator, who is currently running the machine. Groundwater is seeping into the trench, and a 3-inch trash pump is discharging directly into an arroyo that runs to the Rio Grande. The site has 22 acres of disturbed area; the SWPPP is in the trailer but the last inspection entry is 11 days old. Two laborers are dry-cutting rebar and concrete with a gas-powered saw.
1. List the stop-work conditions in the trench and state what must be true before anyone re-enters.
Read the worked answer
Stop work immediately and remove all personnel from the excavation.
- No protective system at 8 feet. Excavations 5 feet or deeper require a protective system - sloping, benching, shoring, or a trench box - designed for the soil type, unless a competent person documents stable rock. Sandy clay with caliche layers is not stable rock.
- Spoil at 18 inches. Spoil and equipment must be kept at least 2 feet back from the edge; the surcharge from the spoil pile is loading the trench wall that is already unprotected.
- Unsupported water line crossing. A utility crossing an excavation must be supported and protected; if it fails, the trench floods and the walls collapse.
- No ladder in a 60-foot cut. A means of egress must be within 25 feet of lateral travel for every worker at 4 feet or deeper.
- Bucket parked over personnel. Struck-by hazard; the excavator must be shut down or moved before anyone works beneath it.
- No competent person. The operator running the machine cannot simultaneously perform the competent person's duties: classifying soil, selecting the protective system, and conducting inspections at the start of each shift and after rain or any change in conditions. A competent person must be designated by name, trained, and given authority to stop work.
Re-entry requires: a designated competent person's inspection and written log entry, a correctly installed protective system matched to the soil classification, spoil and equipment relocated, egress installed, the water line supported, and dewatering in place.
2. Evaluate the dewatering and stormwater practices. What is required before the pump runs again?
Read the worked answer
Both the discharge and the site inspections are out of compliance.
Stormwater: 22 acres of disturbance is far above the 1-acre threshold, so the site needs NPDES Construction General Permit coverage and a SWPPP implemented on the ground, not stored in a trailer. Weekly inspections and inspections after every storm event are required, and the file shows an 11-day gap. That gap alone is a permit violation and is the first thing a state inspector will document.
Dewatering: pumping sediment-laden groundwater straight into an arroyo that drains to the Rio Grande is an unauthorized discharge. Construction dewatering is not automatically covered by the site's stormwater permit, and the water is carrying fines from the trench. Before the pump restarts:
- Confirm with NMED whether the discharge needs coverage under the construction permit or a separate discharge authorization, and meet any turbidity or visual-plume limits.
- Route the water through a sediment basin, filter bag, or weir tank; discharge to a stabilized vegetated area rather than directly to the arroyo.
- Inspect and log the discharge point daily during pumping and stop pumping if a plume is visible.
- Never pump to a storm drain or arroyo without authorization, and never pump concrete washout or bentonite slurry at all.
The judgment being tested: a trash pump in an arroyo is a permit violation with federal exposure, not a housekeeping detail.
3. Address the dry-cutting operation and describe the documentation that should exist by the end of the day.
Read the worked answer
Silica: dry-cutting rebar and concrete with a gas saw generates respirable crystalline silica. Handheld saws require either integrated water delivery at the blade or a vacuum dust-collection system with a filter - one of the two, every time. Dry cutting with neither is prohibited. Add the appropriate respirator for the task and duration, restrict the area, and train the operators. The dust also drifts across the site, so nearby workers need to be considered.
Documentation that should exist by the end of the day:
- A stop-work notice and a written corrective-action log with time stamps, photographs, and the name of the person who authorized re-entry.
- The competent person's excavation inspection record: date, soil classification, protective system used, and the inspector's signature.
- The daily site safety briefing (tailgate talk) covering excavation hazards, struck-by, and silica, signed by the crew.
- The silica exposure control method selected for each tool and the training record for the saw operators.
- A SWPPP inspection entry for today, correction of the discharge, and a note of any NMED notification.
- Notice to the utility owner about the water line and to the general contractor's insurer if a citation is likely.
The examiner is looking for the reflex: violative condition → stop work → correct → document → re-inspect before re-entry. The paperwork is what turns a citation into a manageable event instead of a willful violation.