Experimental Study On The Remediation Of Existing Underground Saltwater

Excessive pumping destroyed the balance between fresh water and salt water,resulting in serious saltwater intrusion and large area of underground saltwater.Some measures are adopted in order to effectively control seawater intrusion, suchas undercurrent barriers and ‘fresh water curtain’, which may Lead to salt waterretention in coastal aquifer. The existence of underground saltwater may lead tobad effect in environment. Therefore, how to repair the existing undergroundsaltwater turns to be a important study, and laboratory test, as a kind of effectivemeans of research can be used to solve this problem.The effect of different ways to remediate underground saltwater was studiedthrough sand tank experiment. The effect of different forms of supply (atmosphericprecipitation infiltration, surface water infiltration, fresh water reinjection) wasanalyzed and the interface of salt-fresh water was also recorded during theexperiments. At the mean time, the influence of different hydraulic conditions onthe repair effects during extraction of underground saltwater was studied. Inaddition, based on all the test results, the reasonable, reliable and effective way torecover saltwater is gained. The main conclusions are as follows:⑴The infiltration water from surface water body expanded in a ’sector’ shapein aquifer, which can remediate underground saltwater. The large the water level is,the good effect the remediation is owing to the large amount of infiltration water.Because of inlet of water in aquifer boundary, the infiltration water from surfacewater body tends to escape the aquifer, which decreasing the remediation effect. Theinfiltration water seems to be messed up in the shallow part of aquifer, whiledistributes in layers in the deep.⑵Atmospheric precipitation infiltration reaches into underground saltwaterthrough vadose zone, restore saltwater in form of planar propulsion, which influenced bythe hydraulic gradient of aquifer, leading to the slope of salt-fresh water interface. The large the rainfall intensity is, the farther distance the precipitation infiltration canreaches, which is good to saltwater remediation. While precipitation intensity was4.89and7.18cm/h, the salinity of sampling point7was still6g/L. However, thesalinity of sampling point7has fallen while precipitation was10.16cm/h in50min.Rainfall patterns can affect recovery process.⑶With the increase of injection intensity, freshwater injected into aquifer wasincreased, which increase move speed, expand influence scope, and do good to theremediation. The interface formed between saltwater and fresh water is moresmooth, and the effect of remediation is more stable. Under the same injectionintensity, water injected into well stay away from recharge boundary can increase theinlet water, which increased modestly, and the outlet water will increased too, whichincreased dramatic. Difference of inlet and outlet in aquifer increases with wellposition is closer to the recharge boundary (1#:0.99L,2#,0.99L,3#:0.41L). Inthis chapter,4#well was noneffective in removing saltwater.⑷The remediate range of underground saltwater by surface water body andatmospheric precipitation infiltration is large than in injection well. Fresh waterinjected into aquifer through well can be setted in any position, while infiltrationwater from surface water body and atmospheric precipitation can only restoresaltwater from shallow to deep. Because of capillary force in vadose zone, the inletwater can be stored in vadose zone, which changes the underground water level.⑸Pumping out water through wells can accelerate the moving speed of inletof water from recharge boundary, leading to remediation area laid between theboundary and well. The large the pumping intensity is, the large amount of watergoes into aquifer, which is helpful in reducing the salinity of saltwater. The mostimportant factor in install a well is to improve efficiency. Compared with theincomplete well, complete well can make water flow in the aquifer evenly, so as toremediate saltwater in a vertical profile evenly. The whole existing undergroundsaltwater can be remediated effectively by optimized pumping ways.