Experimental Study On Hydraulic Control And Remediation Of Trichloroethylene Pollution In Single Well Pumping And Infiltration Groundwater

In order to achieve effective control of contaminated groundwater and efficient groundwater remediation for petrochemical site groundwater contamination,the single-well pump-out-return infiltration synchronous cycle groundwater hydraulic control and contamination remediation technology is innovatively studied.In this paper,a laboratory-scale pore aquifer physical sand column model is constructed and a MODFLOW groundwater flow numerical model is built based on this physical model,based on which a laboratory-scale contaminated aquifer is constructed and remediated.The feasibility of single-well pumping-retrieval synchronous cycle to achieve hydraulic control,the relationship between the main parameters(hydrogeological conditions,hydrodynamic conditions,and artificial intervention conditions),the influence of parameters on hydraulic control and the removal effect of trichloroethylene in the laboratory physical sand column are investigated.The research results include the following three main aspects:(1)Laboratory-scale physical model constructionThe laboratory physical sand column model was constructed,and the movement change pattern of groundwater flow can be clearly described by setting monitoring points at multiple distances in multiple directions.The hydraulic properties of the aquifer in the laboratory physical sand column model were investigated through infiltration experiments and recharge-drainage experiments,and the hydrogeological parameters of the laboratory physical sand column model were obtained,including the permeability coefficient of 0.01 cm/s,the porosity value of 0.4,the feedwater value of 0.09,and the water-holding value of 0.31.The laboratory device with pumping-return infiltration can control the groundwater within a certain area to form a Capture zone(capture radius close to 32 cm).The laboratory physical sand column model built can better provide the parameter basis for the construction of the numerical model.(2)Study of key factors for groundwater hydraulic control in single-well extraction-return infiltration systemThe numerical model based on the laboratory physical sand column model calibrated with measured water levels at different locations can better portray the actual groundwater flow field in the physical model when achieving hydraulic control.The variation of the pumping-return seepage flow rate has little effect on the range of water level landing funnel in the numerical model,but has a greater effect on its depth of descent,and the maximum depth of descent reaches 1.76,4.55,9.75,and 18.65 cm when the pumping-return seepage flow rate is 1,2.5,5,and 10 cm~3/s,respectively.Based on Dupuit formula,different scenarios of pumping-return seepage and aquifer permeability based on 16 The numerical simulation results were fitted and a linear relationship was found between Q/K and(h~2-h_w~2)/(lgr-lgr_w)with a fitting coefficient R~2=0.99.Under different withdrawal-return seepage volumes(1,2.5,5,and 10 cm~3/s),the degree of hydraulic control reaches95.63%,97.69%,97.93%,and 98.17%,respectively.The key factors affecting the degree of hydraulic control include hydrodynamic conditions and hydrogeological conditions,and the corresponding parameters are permeability coefficient,pumping-return seepage flow volume,and percolation range.When the re-infiltration range and aquifer permeability coefficient are certain,the capture range and capture rate both increase with the increase of the extraction-infiltration volume;when the re-infiltration range and extraction-infiltration volume are certain,the capture range and capture rate both decrease with the increase of the aquifer permeability coefficient;when the aquifer permeability coefficient and extraction-infiltration volume are certain,the capture range and capture rate both decrease with the increase of the re-infiltration range.There is a quantitative relationship between the degree of hydraulic control and the strength of aquifer permeability,the size of pump-out-return infiltration volume and the radius of retrieval,and the expression of the quantitative relationship can be used to guide the design of key parameters for achieving hydraulic control at actual contaminated sites under different scenarios and conditions.(3)Study on the remediation effect of single-well extraction-infiltration system on trichloroethyleneThe filler conditions were screened by column experiments,and a filler layer was constructed in the laboratory physical model to remove trichloroethylene.The device was poisoned by adding trichloroethylene solution to the entire simulated aquifer,and a simulated contaminated aquifer was constructed,with the overall trend of increasing and then decreasing contaminant concentrations from top to bottom.After 80 cycles,the average removal rate reached 92.44%and the trichloroethylene removal amount was about 1871.4 mg.