Existing uncontrolled fill on a site may indicate what kind of issue?

Existing uncontrolled fill on a site is significant because it suggests potential issues with the soil's bearing capacity. Uncontrolled fill refers to material that has been deposited without proper engineering practices, such as compaction or appropriate layer constructions. This haphazard placement can lead to variable densities and voids, which can greatly compromise the strength and stability of the soil underneath structures.

Low bearing capacity is a concern because if the fill is unstable or of inadequate strength, it may not support the loads imposed by buildings or other infrastructure safely. This could lead to differential settlement, structural damage, or even catastrophic failures. Hence, professionals need to assess and possibly remediate uncontrolled fill to ensure the soil can adequately support the proposed loads.

The other choices do not align with the implications of uncontrolled fill. A durable substrate and high load tolerance are unlikely characteristics of uncontrolled fill, which typically involves less reliable materials and construction methods. Likewise, uncontrolled fill does not inherently improve drainage management; in fact, it can potentially create problems such as poor drainage and increased erosion.