Which system feature is typically used when a gravity-fed drainfield is not feasible due to site constraints?

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When a gravity-fed drainfield isn’t feasible because of site constraints, the usual remedy is a mound system with engineered fill. Elevating the drainfield on a mound creates an infiltrative surface above the restrictive native soil—such as shallow soil, a high water table, or bedrock—so effluent has enough unsaturated depth to percolate and be treated. The engineered fill provides a stable, consistent substrate and lifts the bed to the right depth, while a dosing or pump system distributes effluent evenly across the raised bed. This setup doesn’t rely on gravity from the tank to a downhill trench, which is why it works when simple gravity-fed designs won’t. By contrast, a conventional trench still needs suitable soil depth and gravity flow, a tank-only system lacks a true drainfield, and surface irrigation isn’t typically a substitute in standard practice.