Conversely, it may be provident to build a deeper storage to accommodate gravity flow of the manure from a barn that is built at grade.
If the in-situ soils are found to have sufficiently low permeability, generally in the order of 1E-9 m/s or less, a cut and fill style design is usually selected.
If in-situ soils are not of the quality needed for a "Cut and Fill" design, the next most desirable construction is that of a Compacted Clay Liner.
A properly managed EMS is usually much safer than an above ground concrete or steel manure storage which can suffer from catastrophic failure due to the large head pressure encountered.
Forced ventilation/positive pressure for 5-15 minutes is recommended to flush the toxic gases and replace them with oxygen so someone can enter the storage area safely.