How many percolation tests must be carried out if this procedure is used?

• A. Two
• B. Three
• C. Four
• D. Five

Answer: (B)

Percolation tests measure how quickly soil in the proposed absorption area can accept effluent. Because soil properties can vary noticeably over short distances, a single test may not reflect what the whole field will do. Running multiple tests in different spots within the area gives a more reliable picture of the site's infiltration rate and helps identify any slower, limiting patches. The typical practice uses three tests to balance getting representative data with reasonable field effort. The results are used to size the drain field, usually by applying the rate from those tests to determine the required area; using three tests helps ensure the design isn’t overly optimistic about soil performance.