What actions must be taken to define the separation from effluent application points?

To properly define the separation from effluent application points, utilizing the maximum groundwater elevation as determined through monitoring is essential. This is because the elevation of groundwater directly influences the potential for effluent to contaminate nearby water supplies. Monitoring allows for accurate and updated information regarding groundwater levels, which is critical for ensuring that effluent is applied at a safe distance to prevent any adverse effects on regional water sources.

The other options, while they may pertain to different aspects of onsite wastewater management, do not specifically address the need for determining appropriate separation distances in relation to effluent application. For instance, measuring the distance from the water supply is important for setback requirements but does not focus on the groundwater's influence on the effluent's movement. Measuring the depth of the infiltration trench can be relevant for design considerations, but again, does not yield the necessary data regarding groundwater elevation. Lastly, assessing soil composition is crucial for understanding how effluent will be treated as it percolates but does not take groundwater levels into account, which is vital for separation definitions. Therefore, monitoring groundwater levels is the most relevant action in this context.