In Situ Pumping–Injection Remediation of Strong Acid–High Salt Groundwater: Displacement–Neutralization Mechanism and Influence of Pore Blocking

Abstract

Acid-polluted groundwater may cause many environmental problems due to its corrosivity. Pumping and injection technology is a commonly used remediation technology, and its main principles are displacement and neutralization. However, due to the high salinity in groundwater, blockage easily occurs and reduces the efficiency. The mechanism of pumping and remediation of strong acid–high salinity groundwater is unclear, and the mechanism and effect of pore blocking are unknown. In this paper, based on an actual polluted site, a field pumping test was carried out. Through groundwater monitoring and drilling core sampling, the process and mechanism of acid groundwater pumping–injection remediation were clarified, and the principle and impact of pore blockage are revealed. The results showed that increasing the injection pressure can effectively improve the repairing efficiency. When the pressure increased from 0.2 MPa to 0.3 MPa, the water injection efficiency per unit time was increased by more than 20%. The principle of pumping–injection remediation of acidic groundwater was mainly displacement, accounting for more than 93%, while neutralization only contributed less than 0.1%. Although the neutralization contribution was small, the neutralization interface of injected alkaline water and acidic groundwater was the main place for precipitation. The precipitation was mainly formed around the injection well, the amount of which decreases greatly with the increase in displacement distance. This was because the formation of precipitation required both an appropriate concentration of Fe and high pH (5.63). Affected by neutralization and dispersion, the pH of the acid–base water interface decreased and the necessary conditions for the formation of precipitation were not met. Therefore, in the actual pumping–injection restoration project, optimization can be carried out from two perspectives of appropriately increasing the injected water pressure and reducing the injected water pH. This study has important reference value for the control and remediation of such acid-polluted groundwater.