In a residential development composed of large lots, which soil investigation should the architect request for on-site sewage disposal?

The correct choice is based on the need to evaluate the soil's capacity to absorb water, which is crucial for on-site sewage disposal systems. A percolation test measures the rate at which water seeps into the soil, providing essential information about its drainage capabilities. This is vital for determining if the soil can effectively handle the effluent from a septic system and ensures that sewage is properly treated before it reaches groundwater.

In residential developments, particularly those with large lots and potential for individual septic systems, understanding the soil's percolation rates informs design decisions for septic systems and their sizing. Without this test, there could be risks of groundwater contamination or system failure, leading to public health concerns and environmental issues.

Other tests mentioned are less relevant to the specific needs of evaluating sewage disposal. An evaporation test assesses water loss through evaporation and does not provide information on soil absorption capacities. Tests for soil alkalinity relate to the chemical composition of the soil rather than its physical properties affecting percolation. A test for soil density measures how compacted the soil is but does not determine its ability to absorb and filter water effectively, which is crucial for on-site sewage disposal.