Installed below grade when site constraints make above-ground impractical

Mercer designs below-ground oil-water separators for applications where elevations, space constraints, traffic loading, safety requirements, or existing infrastructure prevent above-ground installation. These systems are typically installed beneath paved areas or within vaults and become a permanent part of the facility.

From a separation standpoint, below-ground systems perform the same fundamental function as above-ground units. They use the same engineered internals, hydraulic control, and performance criteria. The difference is not separation capability — it is access, visibility, and long-term serviceability. Unlike above-ground systems, below-ground separators are often buried and forgotten, operating outside daily sight lines while compliance risk quietly accumulates.

That reality demands a higher standard of design, not a lower one. When a separator cannot be easily inspected or accessed, performance must be engineered in from day one. For that reason, Mercer treats below-ground systems as engineered process installations, not drop-in commodities. Much of the below-ground market is served by tank fabricators — steel spinners selling cylindrical vessels while moonlighting as wastewater treatment experts. Mercer is a process design company first. We refuse to trade long-term reliability, serviceability, or provable performance for an easier sale — especially when the system will be buried and expected to work for decades.

Because buried systems offer less forgiveness, Mercer emphasizes service access, internal visibility, and performance validation before and after installation — including free testing, site audits, and guaranteed results.