MULTIPLE SPLITS OF THE PLUME
By the earthDr!
Multiple splits of the same plume can be used to influence clean outer ground-water flowpaths to flush contaminants from soil or consolidated rock but at differing locations along the long axis of the ground-water plume. Splitting a plume of contaminated ground water into multiple portions is not limited to just influencing clean ground water to flow beneath a single structure to curtail seeps of contaminated ground water.
Multiple splits of a plume can be used to influence clean ground water to flow beneath more than a single home as depicted in the first figure on this page. When multiple splitting of a plume is practiced, in each subsequent downgradient split, the clean ground water used to flush the soil or consolidated rock is taken at increasing distances from the pumped well. In other words, the next downgradient capture zone is bigger than the preceding one. The transverse-lateral extent of capture increases in the downgradient direction when multiple splitting of the plume is practiced. In multiple splits of a plume, such as depicted by this first figure, the second capture zone totally envelopes the first capture zone.

Multiple splitting of the plume can be used to excise the source-recharge area from contributing contaminant mass to the downgradient extent of the plume.
Plume splitting is often done to curtail the mass transport of contamination beyond the source-recharge area. This can be done in conjunction with splitting the plume at some downgradient point in order to influence clean ground water to flow beneath the affected home as indicated by this second figure. When plume splitting is done at the source-recharge area, the duration of time necessary to split the plume at some downgradient point is decreased due to hydraulic control preventing continued mass transport from the source-recharge area. The necessary duration of time for splitting the plume at the affected home is defined by the amount of time needed for the entirety of the plumelet to flow from just downgradient of the source-recharge area to the secondary, more distant recovery well located upgradient of the receptor basement. When this plumelet has been entirely recovered by the secondary recovery well, this secondary well can be placed offline and recovery limited to the primary well at the source-recharge area. This primary well can be placed offline sooner, if the higher concentrations of contaminant mass in the soils have been remediated by such means as excavation or soil venting at the source-recharge area.

Obviously, an alternative to hydraulic control of the source-recharge area is that the entire source-recharge area is excavated to remove all contaminant mass. However, it should be noted that there are several advantages to hydraulically controlling the source-recharge area even if this area is to be excavated. It is not likely that all the contaminant mass, both as produsols and solusols, will be removed since contaminated soil is difficult to fully delineate to mark it for removal. Therefore, hydraulic control is an insurance policy to capture any contaminant mass that is migrating in the ground water, that wasn't excavated and removed. Hydraulic control is easier to implement and upgrade than is soil excavation and removal at the source-recharge area; therefore, it can be implemented fairly expeditiously at the source-recharge area as it equally can at downgradient points in order to influence the flow of clean ground-water beneath a home.

Splitting the plume at the source-recharge area should be a temporary measure until a more definitive method to remedy these highly contaminated soils has been achieved. Ground-water quality should be the measure of performance used to determine when to terminate hydraulic control at the source-recharge area.

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