Flat ground, tight soil, and where the water goes
Deerfield's soils are silt loams and silty clay loams on zero to four percent slopes, most of them classified in Hydrologic Soil Group C or D, with wet depressional soils in the lower pockets. Flat ground and slow-draining soil is the least forgiving combination there is for hardscape: water has no gradient to leave by and no profile to sink into, so it sits.
That is why a Deerfield project spends real money below grade. Excavation to depth, compacted aggregate base in lifts, drain tile and dry wells where the water actually collects, downspouts routed away from the house, and grading that pitches to somewhere legal. The Village takes the same view: a drainage plan sealed by a licensed engineer and approved by the Village Engineer is required with most building permits, and grading or recontouring on its own still requires a permit. Work that does not change the footprint, add impervious surface or alter stormwater flow is exempt.
The 100-year floodplain follows the Middle Fork of the North Branch of the Chicago River on the east side of the village and the West Fork on the west side. On a lot near either corridor, floodplain status can decide where hardscape goes before anything is drawn.

