Numerical Simulation Of BTEX Contamination Remediation In Shallow Groundwater And Analysis Of Water Level Fluctuation

Using numerical simulation methods to study BTEX's pollution of the aquifer under the condition of oil leakage has become a hot spot.In this article,the injecting experiment of ethanol gasoline and regular gasoline was conducted by using a laboratory aquifer model(sand tank).By controlling the change of water level in the sand tank,the effect of mass flux on the natural attenuation of BTEX was studied.On the other hand,the effect of sulfate on the natural attenuation was studied by adding a high concentration of sulfate later in the experiment.Combining with the natural attenuation of BTEX in the aquifer and the effect of fluctuation of water level on the change of aquifer concentration,BTEX migration and transformation were simulated and corrected in the model by VISUAL MODFLOW software,and evaluated the experimental and simulation results.The results showed that:(1)The overall water level fluctuated 3 times.On the 77 th day when the water level suddenly increases,the average mass flux of BTEX on both sides rose from 35.5 mg/day on day 71 to 78.1 mg/day on day 103.After the second water rises slowly and after 129 th days,the pollutant concentration also increased.The average mass flux rose from 75.1 mg/d on the 128 th day to 110.7 mg/d on the 163 th day.The water gradually decreased after being stable for 20 days from 148 days to 167 days,and dropped to the initial water level on the 182 days.At this time,the BTEX concentration gradually decreased.Before the third water level fluctuation,the average mass flux was 12.7 mg/d on the 237 th day,and on the 285 th day after the fluctuation,the average mass flux was 50.4 mg/d.The effect of the water level fluctuation on the specific concentration of BTEX in the source area section was relatively Significant.By inverting the calibration parameters,the model finally determines the release of BTEX pollutants caused by the fluctuation of water level in laboratory aquifer model,that is,the point source continuous concentration boundary value.The simulation results of the dissolved amount of BTEX under fluctuating water level can provide data reference for the dissolved amount in real groundwater environment.(2)After the high-concentration sulfate ions were injected into the sand trough model in the later stage of the experiment,the concentration monitoring in the east trough was 334.6 mg/L.A total of 46 days of betting experiments took place.The injection sulfate mass was 1408.11 g.The observed sulfate output was calculated to be 1268.51 g using the grid subdivision method on the 604 th day.The simulated value used the black box method to calculate the sulfate.The mass is 1266.0 g.It can be seen that the input amount is significantly higher than the existing amount in the sand tank.The depleted sulfate mass may act as an electron acceptor to act on the redox reaction,accelerate the biodegradation process of BTEX,and promote its oxidation-reduction reaction.Immediately after the high concentration of sulfate was put into the aquifer,the concentration of BTEX showed an obvious decrease immediately.It was proved that sulfate was an efficient electron acceptor and accelerated the natural decay of BTEX and promoted its redox reaction.(3)The concentration of BTEX in the southern part of the experiment was significantly higher than that of the northern part in the fitting curve of the source region concentration and the time series.In the BTEX monitoring results on the 461 th day,the C2-45 monitoring result on the north side was 4.412 mg / L,South of C6-45 is 31.805 mg / L,this is because the southern side of the betting on the natural degradation of BTEX have a certain degree of inhibition.