Optimization Of Hydraulic Control Programs For Groundwater Contaminated Sites

The Pump-and-treat technique is among the most widely used methods of groundwater remediation, also the typical of ectopic approach. The pump-and-treat technique optimization could help the layout of the wells and single well pump rates more reasonable, and shorten the pumping time, improve efficiency. Therefore, the optimization study is the key of Pump-and-treat. In this paper, contaminated sites in typical hydrogeological conditions of pore water were studied. Groundwater flow and solute transport coupled model for these sites were set up with Visual MODFLOW, and the optimization of the Pump-and-treat plans was carried out. The parameter Sensitivity analyze were also performed and the affection of there parameters were discussed. Moreover, researches on the influence of pumping time when adding the wall were studied. The main conclusions are as follows:According to the typical aquifer thickness, permeability, Hydraulic gradient, 16 typical hydrological conditions of unconfined aquifer and confined aquifer were set up. The results shows that when the aquifer thickness less than 50m, permeability less than 1m/d, because the single rates too small, lead to the Pump-and-treat can not be used as an technology in emergency treatment of groundwater contaminated sites. In addition, whether it is unconfined aquifer or confined aquifer, the key factors to pumping time is aquifer thickness and permeability. Both directly determines the single pump rates, and further determines the pumping time. However, the impact of Hydraulic gradient to pump-and-treat is not big. For the same thickness of aquifer, the total required amount of groundwater pumping is almost unchanged.The parameter sensitivity analyzes shows: for the unconfined aquifer, descending order of influence was aquifer thickness> permeability>single rates. For the confined aquifer, change the aquifer and single pump rates could save the pumping time, but without much change in permeability. The efficiency of the Pump-and-treat shows: high efficient were achieved for the early stage, when half of total optimized pumping time past, the residual pollutant concentration field has dropped to 25% to 33%. However, the efficiency would decline sharply over time. The combination of the wall and Pump-and-treat shows: If the initial concentration is not too high, the location of pumping well has major impact on adding wall. When the pumping well installed in the downstream to the plume, adding the wall on the downstream have the best effect, adding the wall on the upstream could extend the pumping time, adding the wall on the above or below of the plume have the same effect. For the single well, when the plume is 40m, adding the wall has the best effect. For the same aquifer, the influence of permeability to total pumping time is not very big.