Commercial & Specialized
Sand Trap (Carwash)
A car wash sand trap — also called a grit chamber, sand interceptor, or automotive waste separator — is an underground tank or chamber installed in the drain system of a car wash facility to capture sand, grit, silt, and heavy debris before wastewater enters the sanitary sewer. Sand and abrasive particles washed from vehicles are extremely damaging to sewer infrastructure and are prohibited from discharge in most jurisdictions.
Car wash sand traps work through gravity settling — water flows slowly through the chamber, allowing dense particles to settle to the bottom while cleaner water exits the outlet. Sand traps often include an oil chamber as well to capture automotive fluids and petroleum residues (creating an oil/water separator function). Minnesota car washes face particularly heavy loading during late winter and spring when road sand applied over the winter is washed from vehicles in concentrated amounts.
What This Means for You
If you operate a car wash in Minnesota, your sand trap is a regulatory requirement. Overflow or blockage from a full sand trap can shut your operation down immediately and trigger MPCA enforcement for oil discharge. Schedule cleanings before the trap reaches 50% capacity; increase frequency during March–May when spring sediment loads are highest.