When is sampling of free product and groundwater beneath free product appropriate?
While not required at all facilities, DEQ may require sampling of free product and groundwater beneath free product under certain site-specific circumstances as sampling of free product and groundwater beneath free product can provide useful information. DEQ may require this sampling to: assist in development of a more complete site conceptual model; determine the nature and extent of contamination at a facility; identify chemical composition in free product and dissolved-phase contamination; assist in development of site clean-up methods; and assist in identifying natural attenuation factors, among other things. This sampling may also be appropriate during initial investigations, if the history of the facility is unknown or uncertain or if there are neighboring properties that have used potential contaminants (e.g. industrial sites or gas stations) that may result in multiple contaminant sources. Collection of groundwater samples beneath free product should be planned carefully, as pa
