HYDROLOGIC ANALYSIS OF A POPLAR-BASED PHYTOREMEDIATION SYSTEM

An evaluation of the hydrologic performance of a poplar-based system for containing impacted groundwater was conducted over a five-year period at the Ischua Creek Habitat site in Machias, NY. An important parameter needed for the engineering design of poplar-based systems is the rate of groundwater uptake by the trees (evapotranspiration of groundwater = ET_G). Using field data from monitoring wells at the site, the method of White (1932) was applied to estimate the ET_G on a continuous daily basis. The White method estimates water consumed by trees based on diurnal fluctuations in groundwater elevations observed in well hydrographs. To perform the extensive five-year data analysis, an algorithm for automating the White method calculations was developed and refined. The statistical analysis of the results showed that the highest median ET_G values occurred in the third year of poplar growth (2014) for all the wells. However, the median ET_G values for the fifth year of poplar growth (2015) were similar to the first three years. Furthermore, the analysis demonstrated that for some years the wells with the highest median ET_G values were located distant (more than 15 meters away from the phytobarrier), in contrast to expected behavior. In general, robust relationships between ET_G, poplar growth and proximity to the phytobarrier could not be established for the five-year period of study. Therefore, it appears the White method may not be an appropriate technique for evaluating the performance of a phytobarrier. Possible reasons include the lack of complete areal coverage by the phytobarrier, the young age of the trees, data scatter in the observed hydrographs, and a variety of simplifying assumptions associated with the White method.