When required by the department, owners and operators of an UST system must follow the procedures in WAC 173-360A-0720 to determine if the UST system is the source of off-facility impacts. These impacts include the discovery of regulated substances (such as the presence of free product or its constituents or vapors in soils, basements, sewer or utility lines, groundwater, or surface water) that has been observed by the department or brought to its attention by another person.