Mr. Einarson also reminded the committee that plume maps only tell half the story, a NAPL plume is 3-dimensional and the vertical direction must be considered too. Changes in groundwater levels can cause relatively thick zones of residual NAPLs above and below the current water table. Myth 5 - MTBE plumes always plunge as they travel downgradient . Once they have migrated away from the release site, plumes of recalcitrant solutes travel with the regional groundwater flow. Therefore, plume depth is controlled by the regional flow system.
Plumes can rise in groundwater discharge areas.
Groundwater pumping from deep municipal wells often causes plumes to plunge as the pumping creates a strong downward hydraulic gradient. Conduits such as stratigraphic windows and improperly abandoned wells can cause dissolved plumes to flow strongly downward. Myth 6 - Once residual NAPL is removed MTBE plumes can always be quickly remediated . Mr. Einarson explained that in general this is true, especially in coarse grained units. This is because MtBE does not sorb significantly to soil particles.