If the bund on the current plot is also the pond, which volume is it serving? Detention, water quality, or retention? The civil basis already answered before the plot is drawn: none of them. Bund area counts towards no other use and may not serve as stormwater detention volume [FACT]. A fuel bund and a coolant containment may not share one. That is the seventeenth registered discipline of the civil basis, graded there as a regulation-driven fact, and it removes an overlap the space model's own iteration assumes is available. Set beside the space model's stormwater term, its effect turns out not to be confined to the bund. A land trial the space model had checked against three conditions now carries six, and the stormwater term was already the weakest subject in that model.
Bunds Need a Controlled-Discharge Class, Not Detention Volume
Stormwater area comes out of an implicit loop: impervious area sets facility area, facility area adds half of itself back into impervious area, and the loop runs once more. The coefficient carrying that loop has three tiers, 0.08, 0.15 and 0.25, and moving between the outer two changes the stormwater subject elevenfold [SENSITIVITY]. A note in the space model calls this the one subject whose upper envelope cannot be guaranteed, because rainfall intensity, return period, discharge standard and receiving water are all absent from the project.
Hardened bund and containment surfaces do shed water, and the civil review uses that to raise a structural objection to the same equation. Their runoff is controlled discharge and is barred from the stormwater system. So they cannot enter impervious area, where they would wrongly enlarge the detention volume, and they cannot be dropped either, because they need their own valves, collection and ground. A third class is created for them, a controlled-discharge area, and the separation between that class and the drainage system has to be drawn as a physical object, a valve or a kerb. The reasoning given is that a ground slope can be altered silently during construction while a valve cannot.
Wetland and other waters inside the boundary are not a fourth pond. They are not natural detention, and they are not a design outfall, until the environmental and survey questions that would make them so have been closed in writing.
A Continuous Coefficient Cannot Envelope the Three Pond Volumes
Three volumes drive the pond: detention, water quality and retention. Whether they add, partly overlap, or collapse to the largest of the three is a discrete ruling made by the authority and the record engineer together, and the civil basis states that a designer may not choose the largest in order to save land. Against one unchanged set of unclosed inputs the two ends of that choice differ by a multiple, and pond area moves in proportion to volume. A continuous coefficient with three tiers cannot represent a discrete jump, so the three tiers do not envelope the answer they were assumed to bracket.
Both arrangements that would have saved land are gone already, for reasons that are not hydrological. Infiltration is excluded here because it drives water towards a possible cable trench, two medium-voltage routes, the communications routes and foundations that may carry an uplift case. Underground storage collides with the services corridor and with the bearing route for heavy transport. What survives is the surface form, the most land-hungry of the four branches the civil basis sets out. The civil basis does not select a form. Selection belongs to the record engineer and the authority.
A fire tank is not that pond either. The same non-overlap set that keeps bunds out of detention keeps fire storage out of the stormwater volume.
The Land Trial Now Carries Six Unruled Conditions
None of it has been calculated, and the file that would calculate it is empty. Four return periods sit in the delivered stormwater parameter model, the two-year, ten-year, twenty-five-year and hundred-year events, and all four rows say the same thing [TARGET]:
- duration, rainfall depth and distribution: to be confirmed;
- pre-development and post-development flow: not calculated;
- detention volume: not calculated;
- outfall limit: to be confirmed.
Each row carries a hold on its own storm and a second hold on the outfall, each verdict cell reads blocked, and each method cell names the authority. Those three coefficient tiers are therefore placeholder values standing in for a calculation nobody has begun, and the elevenfold spread between them measures how wide the ruling could be rather than how uncertain the hydrology is.
Three conditions are added to the trial by the civil basis: no wetland, floodplain intrusion or building prohibition inside the boundary; gravity drainage with a discharge point that is available and able to accept the design flow; and construction-period disturbance solved inside the boundary. Each is ruled by a party that has supplied nothing so far. Any one of them failing moves an area in the hundreds to thousands of square metres, against a trial margin the space model put at 2.5 per cent [MODELED]. The civil basis does not recompute the trial. It does not declare the trial infeasible. It records that the condition count went from three to six.
If the authority and the record engineer rule that the three volumes may overlap, and the survey returns a discharge point able to accept the design flow, the stormwater subject stops being the binding term and the condition count falls back towards three. No such ruling exists, and no survey has been ordered.
One figure in this chain has no claimant at all. The hardening rate of the inspection and corridor strip is treated as zero by the space model and named by the civil review as a quantity that must be filled in, and it multiplies straight into the same loop.
Limits and open items
Confirmed: bund area counts towards no other use and may not serve as stormwater detention volume; a fuel bund and a coolant containment may not share one. [FACT]
Study values, not a pond: the 0.08 / 0.15 / 0.25 coefficient tiers and the elevenfold spread between the outer two; the 2.5 per cent trial margin; the four uncomputed return periods; the three volumes behind one pond; and the three-to-six condition count. [SENSITIVITY] [MODELED] [TARGET]
Open: the merge rule; the controlled-discharge area; the corridor hardening fraction; every hydrological input on the four storm rows; gravity drainage and a capable outfall; wetland and floodplain intrusion; construction-period disturbance. No survey has been ordered. Nothing here selects a stormwater form. Nothing releases an acreage. [HOLD]
Ask which surface is doing two jobs
The useful test is not whether the trial still closes. Point at the current plot and name the surface that is serving two purposes. If the answer is the bund, the seventeenth discipline has not reached the drawing.
© 2026 K&K Data Service Inc. All rights reserved. Reproduction or republication is permitted only with clear attribution to K&K Data Service Inc. and a working hyperlink to the canonical URL of this article. Excerpts must preserve the technical context, maturity labels, assumptions, and limitations. No excerpt may imply project approval, field validation, certification, or endorsement that the original article does not state.
Source: K&K Data Service Inc., “Fuel and Coolant Bunds Cannot Be Counted as Stormwater Detention,” https://www.kkdatasvc.com/lab/fire-structure-site-and-compliance/bunds-are-not-detention-the-acreage-trial-got-tighter/.
Request the Public Calculation Note. If your project record shows a different result, or the same failure domain under another name, we want to see it. Email inquiry@kkdatasvc.com or use the contact page.