a brownfield site contains a plume of tce-contaminated groundwater. the highest observed tce concentration is 1 mg/l and the plume extends approximately 150 meters in the transverse horizontal direction (perpendicular to the groundwater flow). the regional hydraulic gradient is 0.005, the aquifer porosity is 0.3, the vertical saturated thickness is approximately 3 meters, the mean aquifer hydraulic conductivity is 10-3 cm/s, and the aquifer organic content is negligible. specify the longitudinal dimension (l) of an iron-based permeable reactive barrier (prb) system that will result in groundwater leaving the site at the drinking water standard or below. assume a tce decay rate of 0.20 day-1 within the prb and include the effect of dispersion. state any assumptions and comment on the feasibility of your designed system, including a brief description of the vertical and transverse horizontal prb extent