Designing industrial sites as one system
On an industrial site the grading, containment, drainage and access elements constrain each other. Resolved in sequence they conflict; resolved together they do not. What has to be decided early, and why.
Industrial sites — processing facilities, compressor stations, tank farms, logistics terminals — have a property that ordinary commercial development does not: the civil elements are tightly coupled. The grading determines where the containment can go, the containment determines how the drainage works, the drainage determines where the access roads can run, and the access roads constrain the grading.
Designed in sequence, each decision removes options from the next one. Designed together, they usually resolve.
Separating clean and potentially contaminated drainage
The organising decision on most industrial sites is the drainage split.
Runoff from process areas, containment areas and loading areas is potentially contaminated and cannot simply be discharged. It has to be collected, contained, and managed — treated, tested before release, or removed. Runoff from roofs, landscaped areas and non-process paving is clean and can go to the conventional stormwater system.
Keeping these separate is a grading problem before it is a piping problem. The two systems need distinct catchments, and the boundary between them has to be a real grade break that holds in the built surface, not a line on a plan. Where the split is not enforced by the grading, clean water enters the contained system — which means paying to manage clean water, and sizing the containment for volume that should never have arrived.
Getting this wrong is expensive for the life of the facility, not just during construction.
Containment
Secondary containment holds the contents of a tank or vessel if it fails, plus an allowance for precipitation, for long enough to respond.
Three things about containment design are consistently underestimated:
The floor is a graded surface. A containment area drains to a controlled point so that accumulated precipitation can be tested and removed. That means it is a design surface with its own grading, tying into the berm and the tank foundations.
The volume is not a prism. The retained volume is the space inside the berm below the design level, minus what the tank foundations, plinths and internal structures displace. Computing it from the design surface accounts for this. Computing it as area times depth does not, and overstates the capacity.
Berms constrain everything around them. A containment berm is a physical obstruction to surface drainage, to vehicle movement and to the grading beyond it. Its footprint at the toe is considerably wider than the crest, and that footprint has to be reserved during site layout.
Access and loading
Industrial access roads carry loaded heavy vehicles, and the design vehicle is larger than for commercial development. Design that on the actual vehicle:
- Turning paths. Swept path analysis for the largest vehicle that will use the route, at every turn, intersection and dock approach. A turn that a design vehicle cannot make without mounting the shoulder destroys the shoulder repeatedly.
- Grades. Loaded vehicles are grade-limited, and steep grades at intersections and approaches cause problems in winter conditions.
- Loading areas close to flat. Trailers dock and couple on these surfaces.
- Pavement structure for actual loading. Industrial traffic is heavy and repetitive. Under-designed pavement fails early, and it fails where the traffic concentrates.
Access also has a drainage dimension: roads intercept surface flow, so cross drainage has to be provided where they cut across a flow path, and the road itself has to drain.
Utilities in a crowded corridor
Industrial sites carry more buried services than commercial ones — process piping, firewater, power, instrumentation, drainage — often in shared corridors, and often with separation requirements between them.
Coordinating this in three dimensions during design, rather than resolving it in the field, is the difference between a clash found on a screen and a clash found by an excavator. The crossings are where the conflicts concentrate, and they are also where the cover requirements and the grading interact.
What this means for sequencing
The elements above cannot be optimised independently, which argues for a different order of work than the conventional one:
- Establish the drainage split and the containment areas first, because they are the hardest constraints and they consume the most land.
- Set the access and circulation around them, with the real design vehicle.
- Grade to serve all three, rather than grading first and fitting the rest in.
- Coordinate the utilities against the resulting surface.
The cost of the alternative is not usually a design failure. It is a series of compromises, each individually reasonable, that accumulate into a site that is more expensive to build and more awkward to operate than it needed to be.
