Two Feet of Silt and a Disclaimer
On a 100 ft × 60 ft retail pad, footing excavation for a one-story masonry building exposes 3 to 6 ft of organic silt below the bearing elevation shown on the drawings. The geotechnical report, incorporated by reference, was based on two borings at opposite corners and described “stiff to very stiff clay.” The contract states that the contractor is responsible for verifying subsurface conditions and that all excavation is included in the lump sum. The structural engineer issues a written directive: undercut 24 in. below bearing, place filter fabric, and backfill with No. 57 stone up to bearing elevation. The affected area is 6,000 sq ft. Costs: extra excavation and haul-off $30/cy; No. 57 stone delivered and placed $48/cy; filter fabric $0.65/sf. The contract has a Type I differing site condition clause requiring notice within 7 days. The owner's representative calls the directive a “no-cost clarification.” It is raining.
1. Is this an actionable differing site condition, and how far does the “contractor responsible for subsurface conditions” clause actually reach?
Read the worked answer
Yes, this is a Type I differing site condition, and the disclaimer does not dispose of it.
- Type I means the actual conditions differ materially from what the contract documents indicated. The documents indicated stiff clay to bearing; the site has 3–6 ft of organic silt that cannot carry a footing. That is not a judgment call - the engineer's own directive to undercut 24 in. is the admission.
- The disclaimer is not absolute. A contractor is generally held to have inspected the site and to have drawn reasonable inferences from the data furnished; a clause allocating subsurface risk to the contractor is enforceable as to what the contractor should reasonably have anticipated from the available data. It does not license the owner to furnish a report describing a condition that does not exist. Two borings at opposite corners of a 100 × 60 ft pad is a thin basis for a
2. Price the change order. Show the quantity derivation and identify what else belongs in it.
Read the worked answer
Quantity: 6,000 sf × 2.0 ft = 12,000 cf ÷ 27 = 444.4 cy (the full volume is extra - the contract lump sum already covered excavation to the bearing elevation on the drawings).
| Item | Quantity | Rate | Amount |
|---|---|---|---|
| Extra excavation and haul-off of unsuitable silt | 444.4 cy | $30/cy | $13,333 |
| No. 57 stone, delivered and placed | 444.4 cy | $48/cy | $21,333 |
| Filter fabric | 6,000 sf | $0.65/sf | $3,900 |
| Direct subtotal | $38,566 | ||
| Field overhead and profit (assume 15%, per contract) | $5,785 | ||
| Change order | ≈ $44,351 |
Also belongs in it (do not leave on the table):
- Side-slope over-excavation. Stone backfill at 1:1 or steeper flanks adds volume beyond the plan area; measure the actual excavated prism, not the footing footprint, or you will eat that waste.
- Dewatering. Organic silt plus rain plus an open pit equals pumping; keep a daily log of pump hours and crew time, because it is only recoverable if it is documented contemporaneously.
- Testing and retesting. Compaction tests on the stone, third-party observation required by the geotech - bill them as owner-directed.
- Time. If the undercut is on the critical path, price the field overhead for those days separately.
What not to claim: a credit for the clay excavation that was replaced - the engineer chose the method; you are pricing the extra depth, not the substitution.
3. What do you do in the next week, in order, given the 7-day notice clause and a representative calling this “no-cost”?
Read the worked answer
Day 1 - written notice. Deliver a differing site condition notice within the 7 days, referencing the clause, the geotech report, the engineer's written directive, and the date of discovery. State that cost and time impact is being determined and that the contractor reserves all rights. Verbal objections do not preserve anything; the notice does.
Day 1–2 - document the physical condition before it is buried. Photograph the exposed silt with a scale or survey rod, record elevations and the depth of organics at multiple points against the plan bearing elevation, and get the geotech and the engineer to confirm in writing that the material is unsuitable. Once the stone goes in, the evidence is gone. A short signed field memo from the engineer is worth more than a hundred photographs.
Day 2–3 - joint measurement. Ask the owner's representative to walk the undercut prism and sign a field quantity sheet - length, width, depth, and the stone tickets. If they decline, measure it yourself with the surveyor and send the measurement in writing the same day. Stone tickets are the strongest cost evidence you will ever have.
Day 3–5 - priced change order, with the unit rates above, submitted formally rather than discussed.
Day 5–7 - schedule impact and escalation. If the representative continues to call it a no-cost clarification in writing, respond in writing that the work is being performed under protest, that the directive is a change, and that the contractor expects payment; do not stop work over it, and do not sign a release or a “no additional cost” daily ticket.
Rain: document it as a separate, concurrent delay event on the daily reports so that any weather time is not absorbed into the undercut claim.