The City of Idaho Falls has many car washes available to citizens to keep their cars clean. It is up to the owners and operators of those facilities to help keep the discharges from these operations clean. Each car wash is required to have a sand-oil separator in each bay. These sand-oil and water separators must not be allowed to accumulate sufficient solids to hinder their clarifying performance. When the volume of solids in a sand-oil water separator exceeds 25%, efficiency begins to decrease significantly.

Sand-oil separators are pre-treatment devices commonly used in vehicle related facilities as a method to separate sand and oil from wastewater discharges. They are typically installed in a maintenance shop area and receive oily wastewater generated during processes such as vehicle maintenance and washing.