The length and width of the plume are affected by the groundwater velocity and the aquifer's hydraulic conductivity. The plume is more elongated in groundwater with high velocity than in groundwater with low velocity. The plume also tends to move slower in formations with low hydraulic conductivity than in formations with high hydraulic conductivity. A higher hydraulic conductivity can result in more rapid movement and a longer and narrower plume (Palmer 1992). The contaminant plume usually moves in the same direction as groundwater; however, this movement may not occur with a DNAPL that can sink to the bottom of the aquifer and flow by gravity in the opposite direction to groundwater flow.
Perched water is another important consideration in the effect of a groundwater flow regime on a contaminant plume. Perched water does not usually follow the regional groundwater flow direction but rather flows along an interface of hydraulic conductivity contrast. Therefore, a contaminant plume present in perched water can be moving in a different direction than the regional groundwater gradient. Groundwater fluctuations can move trapped contaminants from the vadose zone to the saturated zone.
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