Optimization Of Pump-and-Treat Systems At Groundwater Remediation Sites

Along with industrial development, groundwater, a significant source of drinking water and industrial water, has been seriously polluted in many places. Pump-and-treat technique is among the most widely used methods of groundwater remediation, for its promptness in altering the direction and velocity of groundwater and its easiness to control. However, long treating period, large amount of extracted groundwater, and high costs associated with pump-and-treat systems are the main limitation of its in-situ application.Only under optimal design could pump-and-treat technique be better applied at groundwater remediation sites. Some researchers have been working on its optimal design through mathematical methods, and have already developed some effective approaches. Visual Modflow 4.1 and 4.2 support Modular Groundwater Optimizer (MGO) (Wang and Zheng, 2002), which incorporates MODFLOW/MT3DMS with"global optimal algorithms", such as genetic algorithms, simulated annealing, tabu search, and facilitate the optimization of pump-and-treat systems.In this study, two-dimensional numerical models were developed based on a typical homogeneous VOCs contaminated site to study two categories of pump-and-treat systems: hydraulic containment systems and completely remove systems. Based on the optimal design via genetic algorithm, effects of several important factors on the optimization were identified to give general rules to guide field design. In hydraulic containment systems, the total pumping rate would increase linearly according to the increase of the hydraulic conductivity. However, the optimal locations of the pumping wells would keep the same. In multi-well strategies, the optimal locations of the pumping wells are along the transverse direction at the tail of the plume. For the plume studied in this research, 4% to 20% of the total pumping rate could be reduced due to the application of multi-well strategies.In completely removed systems, the influence of pumping well numbers, hydraulic conductivity, adsorption, treating period and the maximum concentration level of compliance on the pumping rates and optimal locations was studied. The amount of the total pumping rate would be larger at field sites with higher hydraulic conductivity, higher distribution coefficient, shorter treating period and lower maximum concentration level. Moreover, the optimal locations of the pumping wells would be different according to the difference of these parameters at field sites. In aquifers as mentioned, multi-well strategies are recommended with wells located along the longitudinal direction of the central line of the plume. For the plume studied, 4% to 30% of the total pumping rate could be reduced when multi-well strategies are applied.