Define the reason for the arrangement
The objective may be gravity feed, integration with existing equipment or use of limited above-ground space. Quantify the inlet head benefit and compare it with the civil work required. Do not assume that a vessel described as suitable for below-grade installation can simply be buried in direct contact with soil.
Plan inspection and removal
Provide access to valves, instruments, manways, supports and identification plates. Consider how equipment will be lifted out or inspected over its service life. Pressure-equipment inspection requirements and the plant maintenance strategy should influence the layout before the civil design is fixed.
Address the environment
Review flood risk, drainage, groundwater, corrosion exposure, ventilation and any confined-space implications with the responsible site designers. Electrical and instrument equipment must suit the installation environment. The pit or chamber design should not allow routine leaks or washdown water to collect around critical components.
Keep operational interfaces visible
Product lines, air supply, venting and drains still need a coherent route and safe access. Confirm where personnel will observe the equipment and respond to alarms. An above-ground skid may sometimes be the more maintainable option even if it needs a different feed arrangement. Select the configuration through a documented site review, not only a footprint comparison.
General engineering guidance. Numerical examples are illustrative; project specifications and acceptance criteria are agreed for the actual duty.