Site module: high-yield pitfalls and confusions

One-line orientation

A roll-up of small, high-frequency Site traps that don’t each merit a full card — paired confusions the exam reuses across PA/PPD/PDD.

Key points

• Macro vs micro (climate/wind): macro = regional/prevailing patterns; micro = site-specific conditions that locally modify them. Compare regional data against the actual site.
• USGS = planning, not design: great for early feasibility (topography, hydrology, land use), not precise enough for detailed design/construction — hire a licensed surveyor for that.
• Zoning before design: the ordinance fixes use, density, and the buildable envelope; confirm it first or risk redesigning.
• Cohesive vs granular soil: clay is the clearest cohesive soil. Silt may be nonplastic and behave more like granular soil; its bearing and moisture behavior depend on its classification and condition. Sand and gravel are granular.
• Cofferdam vs check dam: cofferdam keeps water out (pumped dry to build below water); check dam slows channel flow for erosion control.
• Detention vs retention: detention dry + slow release; retention permanent pool. (Full card exists — this is the one-line reminder.)

Confusions / comparison

Confusion	One side	The other side
Macro vs micro (wind/climate)	Macro = regional/prevailing	Micro = site-specific local modifiers
USGS map	Planning / feasibility only	Not design-precise — needs a surveyor
Zoning timing	Confirm zoning first	Designing first risks non-permitted scheme
Soil type	Clay — characteristically cohesive and plastic	Sand/gravel — granular; silt varies with classification
Dam type	Cofferdam — keeps water out (pumped dry)	Check dam — slows channel flow (erosion)
Pond type	Detention — dry, slow release	Retention — permanent pool

Related

→ Detention vs retention (this module) · Runoff strategies (this module): check dam vs cofferdam in context · Site slopes (this module): grading thresholds · Swales vs berms (this module).