Bioretention Basin That Will Not Drain After Substantial Completion
A landscape architecture firm designed a 0.4-acre bioretention basin as the stormwater control measure for a 60-unit townhome development, assuming a field-verified infiltration rate of 1.5 inches per hour and a 48-hour drawdown requirement. During construction the firm made six monthly site visits and observed, but did not test, the basin subgrade. The contractor's own infiltration report, submitted with a pay application, shows 0.6 inches per hour at the borrow source; a post-construction test in the basin shows 0.2 inches per hour. After a 1.2-inch rain, standing water persists 96 hours and the county has issued a notice of violation. The contractor's letter demands that the landscape architect notify its professional liability insurer because of 'defective design.' The one-year warranty period has 11 months remaining, and $84,000 in retainage is held.
1. Distinguish the firm's construction-phase observation duties from supervision, and assess whether the standard of care was met.
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Construction observation is not supervision. The visits were to check general conformity with the drawings - not to direct means, methods, sequence, or safety, and not to warranty the contractor's work. The contractor is responsible for executing to the specified infiltration rate.
But the standard of care asks what a reasonable landscape architect would have done in the same circumstances. Here a report showing 0.6 inches per hour, against a design assumption of 1.5, arrived with a pay application. A reasonable practitioner reviewing that pay application had a duty to notice the discrepancy, ask whether the borrow material met specification, and document a response. Months of silence weaken the 'observation only' defense considerably.
Other facts matter: whether the specification required a field-verified rate at the borrow source, whether each site visit generated a field report noting the basin subgrade, and whether the contractor was ever directed in writing to stop and retest. If the file contains no written direction following the failing test, the firm's position is weaker than it appears.
Conclusion: liability is not automatic, but there is real exposure on the review failure. The firm should not answer the contractor's letter with 'observation only' and stop there.
2. Recommend an investigation and documentation sequence before the firm responds substantively to the contractor's letter.
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Sequence matters - the goal is to know the cause before anyone characterizes it.
First, preserve evidence. Send written notice to contractor and owner to preserve the basin as-is, including photographs, cores, and borrow-source data. Nothing is regraded until sampling is complete.
Second, commission an independent geotechnical investigation: double-ring infiltrometer tests at multiple locations, test pits to measure media depth and check for fines and sediment, sieve and organic content analysis, and a survey of the underdrain and outlet invert to confirm design ponding depth and discharge path.
Third, review records: the six field reports, contractor daily logs, material delivery tickets and gradation certificates, subgrade proof-rolling records, and every submittal touching the basin.
Fourth, cause analysis. The usual candidates are sediment-laden runoff entering the basin during construction and clogging the media, fines in the media, subgrade compaction during construction, a missing or blocked underdrain, an incorrect outlet elevation, and an optimistic original infiltration assumption. Each points to a different responsible party.
Fifth, notice. Notify the professional liability insurer now, and route any repeat of the contractor's letter through counsel. Do not admit or deny liability in writing; state that the firm is investigating and reserves all rights.
3. Should the owner release the $84,000 retainage and final payment? Advise the owner with reasoning.
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No. Retainage and final payment should wait for resolution, and the contract should be checked first - many standard forms let the owner withhold amounts sufficient to cover a bona fide dispute without regard to the warranty period.
The reasoning: final payment is not only about whether the work was finished but whether it conforms. A basin that ponds for 96 hours after 1.2 inches of rain and has triggered a county violation does not conform, and the warranty is not the owner's only remedy. Retainage is also the owner's only leverage once the contractor demobilizes.
Practical steps: issue written notice of nonconforming work and the county violation with a deadline for a remediation plan; withhold the $84,000 or the estimated cost of correction, whichever is less, rather than an arbitrary amount; confirm the warranty language and any statutory prompt-pay rules so the withholding is defensible; and do not certify the final application as full and complete - use a partial certification with a stated exception.
If investigation later shows the cause was construction practice, the owner can debit the correction from retainage. If it was design, the owner has a claim against the firm - which is precisely why the firm should not be advising release.