This method is considered an ecological approach to decontamination. In the case of poplar trees, the unaltered trees themselves exude a suite of enzymes that change the chemical structure of many petroleum products and volatilize them in situ. Phytoremediation requires water to work. In fact, the techniques outlined above have been used to decontaminate not just the plant's immediate soil environment but also the water passing through the soil. Hyperaccumulators and other phytoremediants are commonly planted as crops.
Crop plants pump large amounts of water from the soil.
This enables some phytoremediation techniques to cleanse water above and below the water table. One drawback in the realm of ground water decontamination is the plant's effective rooting depth. As in the case of poplar trees, tree pits are excavated to a depth of 100 feet. The pit is then backfilled with a controlled soil particle size to draw groundwater above the local water table via capillary action. The poplar will then send its roots to a depth of almost 60 feet to meet the water.