Remediation And Transport Modeling Of Organic Contamination And Heavy Metal In Groundwater

Groundwater contamination has led to environmental health risk andecological safety. This problem has been more and more attention togovernment and environmental scientists. In October10,2011, the Chinesegovernment passed the “National Groundwater Contamination Prevention andRemediation Plan （2011-2020）”. The plan is the first programmatic documentof groundwater contamination prevention and remediation in China. Itindicates that groundwater contamination prevention and remediation havebeen included in decision-making at national level. As far as the current stateof groundwater contamination is concerned, there are the following threetypes of contamination: Dense non-aqueous phase liquids （DNAPLs）, Lightnon-aqueous phase liquids （LNAPLs） and heavy metals. They have becomethe top priority of groundwater contamination prevention and remediation.Thereby, perchloroethylene （PCE）, benzene and hexavalent chromium (Cr⁶⁺)are chosed as target contaminants in the paper. In addition, with the rapiddevelopment of computer technology, numerical simulation has become animportant tool to study transport and remediation process of contaminant ingroundwater. Therefore, it is a very meaningful work about researchingtransport and remediation law of the three pollutants by numerical simulationtechnique.Based on some groundwater remediation tests performed by our researchgroup in the past few years, we adhere to combination of self-developmentand introduction for groundwater numerical simulation software, and developprogram codes that can perform the following functions: multispecies mother-daughter kinetic reactions, Monod kinetics reactions, adsorption andchemical clogging of heavy metals. The program codes are on the basis ofMODFLOW-2005developed by USGS and MT3DMS developed by Prof.Chunmiao Zheng in University of Alabama. The main results can be writtenas follows.For PCE-contaminated aquifer repaired by multi-PRB using iron andmicrobial community （FeMB） as reactive media, it built the multispeciesmother-daughter kinetic reactions model and developed its program codes.The results showed that （1） the bulk mass transfer coefficient was veryimportant for PCE transfering from non-aqueous phase to aqueous phase, andaffected the dissolution time and concentration peak,（2） thebiological/chemical reaction of PRB using FeMB as reactive media wasdominant in remediation process,（3） the concentration peak of two-stagePRB had a37%decrease comparing with that of one-stage, the value ofthree-stage had also a36%decrease comparing with that of two-stage,therefore multi-PRB could be a preferred option for intermediate products inremediation process,（4） the losses of reaction rate and hydraulic conductivitycan cause a decline of remediation effect.For benzene-contaminzted aquifer repaired by slow-release oxygensource （SOS） technique and PRB with oxygen-releasing compounds （ORC）,it built the Monod kinetics reactions model including benzene, DO andmicrobial species, and developed its program codes. The results showed that（1） placing the release oxygen well closer to source was more efficient,enough DO maybe accelerate the growth of microbial species which couldconsume more benzene,（2） the vertical velocity of gasoline in unsaturatedzone was dominates by its saturation, the most of gasoline was trapped byunsaturated zone after gasoline spills, it would cause potential risk of soilecological environment,（3） the scenario of oxygen-releasing rate15mg/Lcould have a80%decrease of benzene concentration in treated groundwater,the contaminant plume of benzene in saturated zone was near groundwatertable, it should be considered for PRB design,（4） the SOS and PRB with ORC were potential methods that can provide oxygen for groundwater.For a column test of hexavalent chromium (Cr⁶⁺), it developed aparameter estimation model for adsorption using genetic algorthms, thendesigned the PRB’s optimal size using modified chitosan （PEG-CTS#5） asreactive media. The results showed that （1） using MODFLOW/MT3DMS astool, the design method was appropriate on the based of the contaminantplume of0.1mg/L for Cr⁶⁺,（2） PEG-CTS#5may be a potential adsorptionmedium to restore Cr⁶⁺-contaminated groundwater, but it would bulge ingroundwater and clog the flow,（3） the increase of horizontal and verticaltransverse dispersivity would decrease the PRB’s width and increase thelength and height, the heterogeneity was very important for PRB’s design.For chemical clogging in groundwater remediation, it built a modelconsidering the chemical clogging around radial collector well, and developedits program codes. The results showed that （1） the model computing the waterdischarge of radial collector well was reasonable, the water discharge inbottom of horizontal screen lateral was bigger than that near the center of well,（2） the water discharge of radial collector well after45days declined by10-15%due to the chemical clogging, the groundwater table would raise andfinally influence engineering safety.