While property owners often confuse the two, a Perc Test and a Geotechnical Report serve entirely different purposes and cannot be used interchangeably for structural work.

### Perc Test (Percolation Test)

• Primary Purpose: Used solely for septic system design.
• Key Data: It measures the soil’s absorption rate in minutes per inch to determine the size of a leach field.
• Structural Relevance: It provides no data on whether soil can support a building. Building departments will not accept a perc test for foundation permits.
• Typical Cost: $100 – $300 per test hole.

### Geotechnical Report

• Primary Purpose: Evaluates soil bearing capacity for structural foundation design and repair.
• Key Data: Provides comprehensive technical details including soil type classification, density, groundwater depth, shear strength, and shrink/swell potential.
• Structural Relevance: Essential for calculating foundation dimensions and determining the depth and spacing of helical piers.
• Typical Cost: $800 – $3,500 depending on the project scope and site access.

In the Denver metro area, geotechnical reports must be prepared by a licensed geotechnical engineer and follow ASTM standards to ensure the long-term stability of the structure.