Artificial Remediation Tests And Demonstration On Existing Underground Saltwater Aquifer

As the main population distribution area, the industrial and agricultural of coastalareas developed rapidly, freshwater resources were highly demanded. Excessivepumping destroyed the balance between fresh water and salt water, resulting insaltwater intrusion. At present, the saltwater intrusion has harmed dozens of countriesand regions in the world, has caused huge economic loss, affected production and lifeof local residents seriously. Against the universal saltwater intrusion, further study ondistribution and remediation of existing underground saltwater can provide theorybasis, at the same time, the theory application has obvious practical value in rationaldevelopment, utilization and protection of groundwater resources.Based on the hydrogeological conditions of research area, this paper conductsand tank experiment using representative medium of this area, the experimentreflects characteristics of research area adequately. First, the dynamic distributioncharacters of saltwater are surveyed through analyzing impact of river and rainfallsupplies to the groundwater. And then, artificial remediation through single wellpumping is simulated, paper analysis the factors on remediation effect, and based onthis, the remediation process optimized by increasing injection well. Finally, studyrepair existing saltwater using pumping-injection in the demonstration. Through theabove research, several conclusions have been obtained as follows:⑴River supplies can remediate existing saltwater partly, and the remediationeffect of saltwater near river is much more better. The head difference between riverand groundwater can influence remediation effect. When the head difference increasefrom2cm to4cm, the recharge in unit time adds21%, the range of remediationexpanded, and remediation degree increase, the reducing degree of D point is4.18times of preceding.⑵Influence depth of the rainfall recharge process is10cm, the response ofshallow aquifer is immediate, its salinity reduce in different degree, but the deeper aquifer has a delayed response, its salinity appear to increase. The changes of salinityare much smoother in continuous rainfall process than in intermittent rain process, theminimum salinity of point A is3.93‰. But, in intermittent rain process, degree ofsalinity decrease of shallow aquifer is much bigger; point A can decrease to2.73‰.⑶In the pumping remediation process existing river recharge, river displacesaltwater in frontal form. Mode of operation and arrangement of well would influencethe remediation effect. The pumping flux increase from80to160or240mL/min,remediation time can shorten47.6%and65.1%; When the pumping duration of115minutes under the experimental conditions, though the pumped water salinity is2.74‰at the end of pumping, it still meet the drinking water standards throughnatural recovery process, and also shorten30.3%compared with the duration ofpumped water salinity was1.0‰. When the pumping well was located near by theimpermeable boundary, the pumping well could extract high concentration salinewater effectively, it improve the overall remediation effect significantly; Theremediation time would extend only9.1%using partially penetrating well, so,partially penetrating well can replace complete penetrating well in remediation.⑷Artificial recharge can raise groundwater level, improving the remediation ratebetween pumping and injection well. In the pumping-injection process with two wells,injection flux can influence remediation effect clearly. When the injection flux issmall, remediation efficiency is not good, larger injection flux can improveremediation efficiency. In this paper, when injection flux is100mL/min, theremediation time is90.9%of the single pumping process.⑸In different operation mode, remediation result of pumping-injection withthree wells process is different. Remediation time optimization in continuousoperation process is not obvious, but it can reduce the risk of land subsidence. Underthe discontinuous operation mode, the difficult remediation area can be repair easilythrough increasing pumping flux. Compare with single pumping process,pumping-injection with two wells, and continuous operation mode with three wells,operation time shorten17.2%,20%and27.3%, so, discontinuous operation process isthe best remediation scheme. ⑹Pumping process reduce the groundwater level, which can cause migrationof saltwater. Artificial recharge can hinder the movement of concentration saltwater,more importantly, it can displace and dilute saltwater. With pumping-injection processin23days, all salinity reduces below1‰, which achieve drinking water standard.