How much distance must there be between the high groundwater table and the bottom of the pit in a Class 2 system?

• A. 600 mm
• B. 900 mm
• C. 1200 mm
• D. 1500 mm

Answer: (B)

The distance being tested is about protecting groundwater and giving the system room to treat the effluent in soil. For a Class 2 system, the bottom of the pit must be at least 900 mm (about 3 feet) above the highest groundwater table. That vertical separation creates an unsaturated soil layer through which the effluent can infiltrate and be treated before it could reach groundwater, and it also helps prevent the pit from rising or floating if groundwater climbs. If the groundwater comes closer than 900 mm, the design wouldn’t meet Class 2 requirements, and a different system or adjustments would be necessary. So the required distance is 900 mm.