Buried Tank, Substitute Paver, and a 14-Day Request on a Civic Plaza
A 1.2-acre civic plaza is 40% complete under a $3.1 million lump-sum contract with a 210-calendar-day schedule. Scope includes 18,000 sf of set-on-sand concrete pavers over a 6-in aggregate base, an 8-ft seat wall, and 14 shade trees. On day 96, excavation for the seat wall footing exposes a buried 6,000-gallon steel tank and two abandoned 2-in fuel lines, none shown on the drawings. The geotechnical report, which the contract incorporates and describes as information only, noted possible fill of unknown origin in that area. The contractor submits an RFI asking for a directive to have the owner remove the tank, plus a 14-day time extension and $68,000. A second RFI asks whether a 2-in-thick paver from another manufacturer is equivalent to the specified 2-3/8-in paver. The seat wall is on the critical path; the pavers are not. The owner's representative wants to deny both requests outright.
1. Is the tank a differing site condition? What is your recommendation, and what documentation do you require?
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Treat this as a probable differing site condition, not a contractor risk, and act quickly rather than debating. The contract's own geotechnical language - possible fill of unknown origin - puts the owner on notice that the subsurface was uncertain, and a 6,000-gallon tank with fuel lines is not a condition a bidder can reasonably be expected to have discovered by site visit or by reviewing a report that described fill generically. The information-only disclaimer weakens but does not erase the owner's exposure.
Process matters more than the label. Acknowledge the RFI in writing within the contract's notice period, direct the contractor to stop work in that footprint only, and preserve both parties' rights. If urgency demands it, issue a written directive to proceed on a force-account or time-and-materials basis with a not-to-exceed cap, so no one later argues about entitlement to the work itself.
Documentation to require: dated photographs with scale and GPS, survey tie to the drawings, tank capacity and condition, evidence of whether product remains, soil sampling and lab results for petroleum hydrocarbons and metals from the excavation and stockpile, disposal manifests, and a daily record of equipment and labor. Get the tank's regulatory status checked - many jurisdictions require notification when an abandoned tank is discovered, which can add a review period you must build into the schedule.
2. How do you evaluate the paver substitution, and what is your answer?
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Run a substitution through a defined process rather than a thumb on the scale. Require the contractor to submit, in writing and within the contract's substitution window: product data and test reports for compressive strength, water absorption, freeze-thaw durability, dimensional tolerance, and slip resistance; a sample for color and finish; the manufacturer's warranty; and an explicit statement of every other change the substitution forces, including setting bed, base course, edge restraint, and joint sand.
The decisive question is loading, not appearance. A 2-in paver is roughly 16% thinner than 2-3/8 in, which reduces its stiffness and its ability to distribute wheel loads. If any part of the plaza is a designated fire apparatus access lane, a delivery route, or a maintenance vehicle path, the thinner unit almost certainly fails the required loading and must be denied there. If the area is strictly pedestrian, the substitution may be acceptable - but only if the base course is increased to compensate, the edge restraint is re-detailed, and the contractor absorbs any cost and schedule effect.
A workable answer is a split decision: deny in vehicular and emergency-access areas, approve for pedestrian-only panels with a compensating base detail and no change in contract price or time. Say so in writing, state the technical basis, and note that approval in one area does not set a precedent elsewhere.
3. The contractor asks for 14 days and $68,000. How do you evaluate entitlement, duration, and cost?
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Separate the three questions - entitlement, time, and money - because they are decided on different evidence.
Entitlement follows from the differing-site determination. If the tank is compensable, the contractor is entitled to the reasonable direct cost of removal, disposal, permits, and testing plus the contract's markup. Ask for a cost breakdown by labor, equipment, material, disposal, and subcontractor, with backup for each, and compare the disposal quote against the manifest tonnage. Disallow home-office overhead unless the contract provides for it, and check whether any portion is already covered by a unit price or allowance.
Duration is proved, not asserted. The seat wall is on the critical path, so the delay is real in principle, but 14 days is a claim, not a finding. Ask for a fragnet or an updated CPM showing the actual added sequence: expose, notify, characterize, obtain approval, remove, dispose, backfill, test, and resume. Tank removal plus soil confirmation commonly runs 3–6 working days once approved; the regulatory notification period may extend it. Look for concurrency and for work the contractor could have resequenced into the affected window.
A defensible outcome is often a partial approval: direct costs substantiated, a time extension of 4–6 days supported by the schedule analysis, and a written reservation of rights on the balance pending final documentation.