Remediation Period Research Articles

The Feasibility on Application of Enzyme-Linked Immunosorbent Assay for Screening Dioxin Soil on Contaminated Site

Enzyme-Linked ImmunoSorbant Assay (ELISA) is a dioxin screening test method, which has several advantages such like low setup cost, low analysis cost, low technical barriers, simple operation, and short analysis time. The case study of this study is a dioxin contaminated site. ELISA was applied in this site due to its widely contaminated range, numerous surveys, and short remediation period. The experience earned in this case study could be the reference for similar pollution site in the future.

Multi-objective optimization for free-phase LNAPL recovery using evolutionary computation algorithms

A nonlinear, multi-objective optimization methodology is presented that seeks to maximize free product recovery of light non-aqueous phase liquids (LNAPLs) while minimizing operation cost, by introducing the novel concept of optimal alternating pumping and resting periods. This process allows more oil to flow towards the extraction wells, ensuring maximum free product removal at the end of the remediation period with minimum groundwater extraction. The methodology presented here combines FEHM (Finite Element Heat and Mass transfer code), a multiphase groundwater model that simulates LNAPL transport, with three evolutionary algorithms: the genetic algorithm (GA), the differential evolution (DE) algorithm and the particle swarm optimization (PSO) algorithm. The proposed optimal free-phase recovery strategy was tested using data from a field site, located near Athens, Greece. The PSO and DE solutions were very similar, while that provided by the GA was inferior, although the computation time was roughly the same for all algorithms. One of the most efficient algorithms (PSO) was chosen to approximate the optimal Pareto front, a method that provides multiple options to decision makers. When the optimal strategy is implemented, although a significant amount of LNAPL free product is captured, a spreading of the LNAPL plume occurs. Editor Z.W. Kundzewicz; Associate editor L. See Citation Dokou, Z. and Karatzas, G.P., 2013. Multi-objective optimization for free-phase LNAPL recovery using evolutionary computation algorithms. Hydrological Sciences Journal, 58 (3), 671–685.

Hybrid algorithm performance with varying population size for multi-objective optimisation of in-situ bioremediation of groundwater

In-situ bioremediation of groundwater is one of the remediation technique applied for cleaning groundwater at its site. Cost of remediation and remaining concentration of contaminant are the main conflicting objectives to be decided during remediation period of groundwater. Multi objective optimisation is one of the best techniques to obtain Paretos for the conflicting objectives. In this study metaheuristic hybrid algorithm has been used to obtain Paretos for in-situ bioremediation of groundwater. Further, the performance of Paretos obtained with varying population size has been evaluated. The results indicate that too small or too large population size does not give well spaced Paretos. Only the population size in specific range shows better performance in the present study for groundwater remediation. The cost analysis of in-situ bioremediation based on the Paretos obtained from proposed hybrid algorithm shows that percentage increase in cost increases as the clean up standard of groundwater increases.

Kinetic Modelling and Half-Life Study on Enhanced Soil Bioremediation of Bonny Light Crude Oil Amended with Crop and Animal-Derived Organic Wastes

In this study, the potential effects of crop and animal-derived organic wastes as nutrient supplements to biostimulate autochthonous microflora for hydrocarbon biodegradation were investigated. Microcosms containing soil were spiked with weathered Bonny light crude oil (WBLCO) (10 % w/w) and amended with various amounts of groundnut shell, beans shell, melon shell, cassava peels, cow dung and pig dung alone or in combinations. The rates of biodegradation of the crude oil were studied for a remediation period of 42 days under laboratory conditions. The results showed that there was a positive relationship between the rate of petroleum hydrocarbons biodegradation and presence of the crop and animal-derived organic wastes alone or in combination in soil microcosms contaminated with crude oil. The WBLCO biodegradation data fitted well to the first-order kinetic model. The model revealed that WBLCO contaminated-soil microcosms amended with crop and animal-derived organic wastes had higher biodegradation rate constants (k) as well as lower half-life times (t1/2) than soil microcosms amended with NPK fertilizer and unamended soil (natural attenuation) remediation system. The biodegradation rate constant and estimated biostimulation efficiency values showed that among the crop and animal-derived organic wastes used alone and in combinations, pig dung suggest to offer the best biostimulation performance, which was closely followed by the combination of pig dung and cassava peels. The system proposed here is inexpensive, efficient, and environmentally friendly and may thus offer a viable choice for petroleum hydrocarbons-contaminated soil remediation.

Biodegradation of 2,6-Dichlorophenol Wastewater in Soil Column Reactor in the Presence of Pineapple Peels-Derived Activated Carbon, Palm Kernel Oil and Inorganic Fertilizer

In this study, the potential effects of palm kernel oil (PKO), pineapple peels derived-activated carbon (PPAC) and NPK fertilizer (20:10:10) as amendment agents on the natural bioattenuation of 2,6-dichlorophenol (2,6-DCP) in tropical agricultural soil were investigated. The effect of PPAC dosage on 2,6-DCP biodegradation was also studied. Column reactors containing soil were spiked with 2,6-dichlorophenol (2,6-DCP) wastewater (300 mg/l) and amended with PKO, NPK fertilizer and PPAC alone or in combinations. The rates of 2,6-DCP biodegradation were studied for a remediation period of 42 days under laboratory conditions. The results showed that there was a positive relationship between the rate of 2,6-DCP biodegradation, bacterial growth rate and presence of NPK fertilizer and PPAC (alone or in combination) in soil column microcosms contaminated with 2,6-DCP. The 2,6-DCP biodegradation data fitted well to the first-order kinetic model. The model revealed that 2,6-DCP contaminated-soil microcosms amended with NPK fertilizer and PPAC (alone or in combination) had higher biodegradation rate constants (k) as well as lower half-life times (t1/2) than soil column microcosms amended with PKO and unamended soil (natural attenuation) remediation system. Thus, the use of combined NPK fertilizer and activated carbon (NPK + PPAC) to enhance 2,6-DCP degradation in the soil could be one of the severally sought bioremediation strategies of remediating natural ecosystem (environment) contaminated with organic chemicals.

Remediation of Residents in Difficulty

To determine, through a 10-year review, (1) the prevalence of residents in difficulty, (2) characteristics of these residents, (3) areas of residents' weakness, and (4) outcomes of residents who undergo remediation. A retrospective review of resident records for the University of Toronto Faculty of Medicine's (UT-FOM) Board of Examiners for Postgraduate Programs (BOE-PG) was done from July 1, 1999 to June 30, 2009 using predetermined data elements entered into a standardized form and analyzed for trends and significance. Outcomes for residents in difficulty were tracked through university registration systems and licensure databases. During 10 years, 103 UT-FOM residents were referred to the BOE-PG, representing 3% of all residents enrolled. The annual prevalence of residents referred to the BOE-PG ranged from 0.2% to 1.5%. The CanMEDS framework was used to classify areas of residents' weaknesses and organize remediation plans. All 100 residents studied had either medical expertise (85%) or professionalism (15%) weaknesses or both. Residents had difficulties with an average of 2.6 CanMEDS Roles, with highest frequencies of Medical Expert (85%) Professional (51%), Communicator (49%), Manager (43%), and Collaborator (20%). Often, there were multiple remediation periods, with an average of six months' duration. Usually, remediation was successful; 78% completed residency education, 17% were unsuccessful, and 5% remained in training. Residents in difficulty have multiple areas of weakness. The CanMEDS framework is an effective approach to classifying problems and designing remediation plans. Successful completion of residency education after remediation is the most common outcome.

Remediation of sandy soils contaminated with hydrocarbons and halogenated hydrocarbons by soil vapour extraction

This paper presents the study of the remediation of sandy soils containing six of the most common contaminants (benzene, toluene, ethylbenzene, xylene, trichloroethylene and perchloroethylene) using soil vapour extraction (SVE). The influence of soil water content on the process efficiency was evaluated considering the soil type and the contaminant. For artificially contaminated soils with negligible clay contents and natural organic matter it was concluded that: (i) all the remediation processes presented efficiencies above 92%; (ii) an increase of the soil water content led to a more time-consuming remediation; (iii) longer remediation periods were observed for contaminants with lower vapour pressures and lower water solubilities due to mass transfer limitations. Based on these results an easy and relatively fast procedure was developed for the prediction of the remediation times of real soils; 83% of the remediation times were predicted with relative deviations below 14%.

Blood dioxin biomonitoring to assess local residents’ exposure from a large urban remediation project

BackgroundA total of 265000m3 of dioxin contaminated soil and sediments from past industrial activity was treated on site in an urban setting in Sydney, Australia. To respond to local community concerns about potential dioxin exposure from fugitive emissions a human biomonitoring study was undertaken. ObjectiveTo determine whether local residents were exposed to significant amounts of dioxin from the remediation process.Methods: Blood samples were collected from local residents around the site and a representative metropolitan control group. They were pooled within age and sex strata and the change in dioxin concentrations over the remediation period and a summary of the mid point and post remediation dioxin concentrations were compared between groups. Information on dietary intake was collected to look for possible confounding. ResultsThe mean dioxin Toxic Equivalent concentrations (TeQ) decreased among both the local resident and control groups over the remediation period by 1.9 and 2.1pggm−1 lipid respectively. Modelled blood concentrations adjusting for age and sex did not detect a significant difference between groups for changes in either TeQ or 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8 TCDD). The summary measure approach did however demonstrate that the 2,3,7,8 TCDD concentrations among the local resident group was approximately 0.7pgg−1 lipid higher compared to the control group post remediation. There were no significant changes in dietary intake sources of dioxin. ConclusionBiomonitoring demonstrated that local residents were not exposed to significant quantities of dioxin. Large scale remediation of dioxin contaminated land can be safely undertaken in an urban setting.

Factorial Designs Application to Study Enhanced Bioremediation of Soil Artificially Contaminated with Weathered Bonny Light Crude Oil through Biostimulation and Bioaugmentation Strategy

The objective of this study was designed to evaluate the effects of biostimulation and bioaugmentation amendment agents (NPK fertilizer, Tween 80 and mixed culture) on the bioremediation of tropical soil samples artificially contaminated with Weathered Bonny Light Crude Oil (WBLCO). Response Surface Methodology (RSM) with Box Behnken Design (BBD) was used with three levels and three factors of NPK fertilizer (2 - 6 g), Tween 80 (5 - 15 mg/l) and mixed culture (0.5 - 1.5 g/l) as independent variables and WBLCO removal as dependent variable (response) in a six weeks remediation period. The results showed that the rate of WBLCO removal generally increased with increase in the amount of NPK fertilizer, Tween 80 and mixed culture (biomass), respectively. A statistically significant (P < 0.0001) second-order quadratic regression model for WBLCO removal (using design-expert statistical program (v. 6.0.8)) with a coefficient of determination, R (=0.9996) was obtained. Numerical optimization technique based on desirability function was carried out to optimize the bioremediation process. The optimum values for biostimulation and bioaugmentation amendment agents to achieve a predicted maximum WBLCO removal of 84.88 percent were found to be: NPK fertilizer, 4.25 g; Tween 80, 10.22 mg/l and mixed culture, 0.46 g/l. At this optimum point, the observed WBLCO removal was found to be 83.79 percent. The statistical analyses and the closeness of the experimental results and model predictions show the reliability of the regression model and thus, biostimulation and bioaugmentation of indigenous microbial density and activity can reduce remediation period of petroleum hydrocarbon contaminated environment and subsequently the cost of remediation.

Box-Behnken design application to study enhanced bioremediation of soil artificially contaminated with spent engine oil using biostimulation strategy

This work studies the biodegradation of spent engine oil in soil using Box-Behnken design under response surface methodology. NPK fertilizer (inorganic nutrient), Tween 80 (nonionic surfactant), and pig manure (organic nutrient) concentrations were used as independent biostimulant variables, while total petroleum hydrocarbon (TPH) and hexavalent chromium (Cr (VI)) reductions as dependent variables (response) in a 42-day remediation period. A statistically significant second-order quadratic regression model for TPH and Cr (VI) removal was obtained. The coefficient of determination (R2 = 0.9995 for TPH and 0.9988 for Cr (VI)) and probability value (P < 0.0001) demonstrated significance for the regression model. Numerical optimization technique based on desirability function was carried out for initial spent engine oil concentration of 10% w/w to optimize the biodegradation process. The optimum values for biostimulation agents to achieve a predicted maximum TPH and Cr (VI) removal of 67.20% and 53.20%, respectively, were found to be as follows: NPK fertilizer, 4.22 g; Tween 80, 10.69 mg/l; and pig manure, 47.76 g. At this optimum point, the observed TPH and Cr (VI) reductions were found to be 66.47% and 52.33%, respectively. The statistical analyses and the closeness of the experimental results and model predictions show the reliability of the regression model, and thus, biostimulation of indigenous microbial density and activity can reduce remediation period of petroleum hydrocarbon and heavy metal-contaminated environment and subsequently the cost of remediation.

Enhanced Bioremediation of Soil Artificially Contaminated with Kerosene: Optimization of Biostimulation Agents through Statistical Experimental Design

The main goals of this work were to study the enhanced bioremediation of soil artificially contaminated with kerosene via biostimulation strategy, evaluate the influence of biostimulating agents on the rate of degradation and to optimize the biostimulating agents for maximum kerosene removal. The study was carried out by artificially contaminating an un-impacted tropical soil with 10% (w/w) kerosene oil in earthen pots and various concentrations of NPK fertilizer, Tween 80 and hydrogen peroxide were added and then incubated for six weeks remediation period. To optimize the range of experimentation, Response Surface Methodology (RSM) with Box Behnken Design (BBD) was used with three factors and three levels of NPK fertilizer, Tween 80 and hydrogen peroxide as independent variables and kerosene oil (total petroleum hydrocarbon) removal as dependent variable (response). The results showed that there were significant variations in the kerosene oil biodegradation pattern with respect to NPK fertilizer, Tween 80 and hydrogen peroxide. A statistically significant (P < 0.0001) second-order quadratic regression model for kerosene oil removal (using Design-Expert Statistical program (v. 6.0.8) with a coefficient of determination, R (= 0.9992) was obtained. Numerical optimization technique based on desirability function was carried out to optimize the bioremediation process. The optimum values for biostimulating agents to achieve a predicted maximum kerosene removal of 75.06% were found to be: NPK fertilizer, 4.30 g (equivalent to 0.0215 μg/kg); Tween 80, 10.03 mg/l and hydrogen peroxide, 1.13 g/l. At this optimum point, the observed kerosene oil removal was found to be 73.95%. Thus, biostimulation of indigenous microbial density and activity can reduce the period for remediation of contaminated environment and subsequently the cost of remediation. Response Surface Methodology (RSM) is a reliable and powerful tool for modeling and optimizing of kerosene oil bioremediation processes.

Mycoremediation of polycyclic aromatic hydrocarbons (PAH)-contaminated oil-based drill-cuttings

Spent white-rot fungi (Pleurotus ostreatus) substrate has been used to biotreat Nigerian oil-based drill cuttings containing polycyclic aromatic hydrocarbons (PAHs) under laboratory conditions. The Latin square (LS) experimental design was adopted in which four options of different treatment levels were tested in 10 L plastic reactors containing fixed masses of the drill cuttings and fresh top-soil inoculated with varying masses of the spent P. ostreatus substrate. Each option was replicated three times and watered every 3 days under ambient conditions for a period of 56 days. Microcosm analysis with a series II model 5890 AGILENT Hp ® GC-FID showed that, the PAHs in the drill cuttings were mainly composed of 2 to 5 fused rings with molecular-mass ranging from 128 to 278 g/mol, while the total initial PAHs concentration of the drill cuttings was 806.31 mg/kg. After 56 days of composting, the total amount of residual PAHs in the drill cuttings decreased to between 19.75 and 7.62%, while the overall degradation of PAHs increased to between 80.25 and 92.38% with increasing substrate addition. Individual PAH degradation ranged from 97.98% in acenaphthene to 100% in fluorene, phenanthrene and anthracene. Statistical analysis, using the 2-factor analysis of variance (ANOVA), showed that there were no significant differences (p < 0.05) in the biodegradation of the PAHs due to the substrate levels applied and remediation period, as well as a nonsignificant (p < 0.05) interaction between substrate levels applied and remediation period. These results showed that spent white-rot fungi (P. ostreatus) substrate may be suitable for biotreating PAH-contaminated Nigerian oil-based drill cuttings.

An experimental study on the bio-surfactant-assisted remediation of crude oil and salt contaminated soils

The effect of bio-surfactant (rhamnolipid) on the remediation of crude oil and salt contaminated soil was investigated in this study. The experimental results indicated that there was a distinct decline of total petroleum hydrocarbon (TPH) concentration within the soil when using rhamnolipid during a remediation period of 30 days, with maximum TPH reduction of 86.97%. The most effective remediation that was observed was with rhamnolipid at a concentration of 2 CMC in soil solution, and a first-order TPH degradation rate constant of 0.0866 d−1. The results also illustrated that salts in soil had a negative impact on TPH reduction, and the degradation rate was negatively correlated with NaCl concentration in soil solution. The analysis of soil TPH fractions indicated that there was a significant reduction of C13-C30 during the remediation process when using bio-surfactant.

Characterisation of the rhizoremediation of petroleum-contaminated soil: effect of different influencing factors

Abstract. Pilot experiments were conducted to analyse the effect of different environmental factors on the rhizoremediation of petroleum-contaminated soil. Different plant species (cotton, ryegrass, tall fescue and alfalfa), the addition of fertilizer, different concentrations of total petroleum hydrocarbons (TPH) in the soil, bioaugmentation with effective microbial agents (EMA) and plant growth-promoting rhizobacteria (PGPR) and remediation time were tested as influencing factors during the bioremediation process of TPH. The results show that the remediation process can be enhanced by different plant species. The order of effectiveness of the plants was the following: tall fescue &gt; ryegrass &gt; alfalfa &gt; cotton. The degradation rate of TPH increased with increased fertilizer addition, and a moderate urea level of 20 g N (Nitrogen)/m2 was best for both plant growth and TPH remediation. A high TPH content is toxic to plant growth and inhibits the degradation of petroleum hydrocarbons. The results showed that a 5% TPH content gave the best degradation in soil planted with ryegrass. Bioaugmentation with different bacteria and PGPR yielded the following results for TPH degradation: cotton+EMA+PGPR &gt; cotton+EMA &gt; cotton+PGPR &gt; cotton &gt; control. Rapid degradation of TPH was found at the initial period of remediation caused by the activity of microorganisms. A continuous increase of degradation rate was found during the 30–90 days period followed by a slow increase during the 90–150 days period. These results suggest that rhizoremediation can be enhanced with the proper control of different influencing factors that affect both plant growth and microbial activity in the rhizosphere environment.

Rhizoremediation of diesel-contaminated soil using the plant growth-promoting rhizobacterium Gordonia sp. S2RP-17

A plant growth-promoting rhizobacterium (PGPR) was isolated and identified as Gordonia sp. S2RP-17, which showed ACC deaminase and siderophore synthesizing activities. Its maximum specific growth rate was 0.54 ± 0.12 d(-1) at 5,000 mg L(-1) of total petroleum hydrocarbon (TPH), and its maximum diesel degradation rate was 2,434.0 ± 124.4 mg L(-1) d(-1) at 20,000 mg L(-1) of TPH. The growth of Zea mays was significantly promoted by the inoculation of Gordonia sp. S2RP-17 in the diesel-contaminated soil. Measured TPH removal efficiencies by various means were 13% by natural attenuation, 84.5% by planting Zea mays, and 95.8% by the combination of Zea mays and Gordonia sp. S2RP-17. The S2RP-17 cell counts were maintained at 1 × 10(6) CFU g-soil(-1) during the remediation period, although they slightly decreased from their initial numbers (2.94 × 10(7) CFU g-soil(-1)). These results indicate that rhizoremediation using both Zea mays and Gordonia sp. S2RP-17 is a promising strategy for enhancing remediation efficiency of diesel-contaminated soils.

Variation in time-to-compliance for pump-and-treat remediation of mass transfer-limited aquifers with hydraulic conductivity heterogeneity

In this study, the impact of correlation length (λ) of hydraulic conductivity (K) heterogeneity on pump-and-treat (P&T) remediation period (time-to-compliance) for a mass transfer-limited aquifer is evaluated. Additionally, impacts of variance (σ 2), different distributions of high and low K zones and different initial contaminant masses are explored. Two different P&T policies including different number of wells pumping at different rates are employed for the investigation. Simulation–optimization approach in which a genetic algorithm (GA) is linked with a groundwater flow and contaminant transport model is used. Results show that K heterogeneity, in terms of λ ln K , $$ \sigma_{\ln \,K}^{2} $$ and respective locations of low and high K zones, significantly impacts the time-to-compliance. Contaminant presence at low K zones can increase the time required to clean up the aquifer. Lower variation is observed in time-to-compliance for the remediation design utilizing higher number of wells pumping at slower rates compared to the design with a single well pumping at a higher rate. Higher number of wells increases the robustness of P&T remediation system when aquifer is heterogeneous in K.

Numerical simulation of surfactant-enhanced remediation of heterogeneous aquifer contaminated with nonaqueous phase liquids

A three-dimensional, multiphase, multicomponent compositional simulator was employed to simulate nonaqueous phase liquid (NAPL) migration during surfactant-enhanced aquifer remediation (SEAR) in spatially correlated heterogeneous fields. Aquifer heterogeneity was accounted for by considering the permeability to be a spatially random variable, and a geostatistical method was used to generate random distributions of the permeability. Spatial distributions of saturations in the NAPL and temporal changes of organic recovery, effluent concentrations of organics and surfactant, and pressure drop at the injection well for heterogeneous aquifers were compared with those in a homogeneous aquifer to examine the effects of different levels of heterogeneity. Variations in permeability fields have a pronounced effect on the organic recovery efficiency due to the long-term persistence of nonaqueous phase liquid and additional dispersion. Permeability heterogeneity also leads to the tailing off of effluent organic concentrations and significant loss in injectivity over the remediation period. For a small slug of surfactant, surfactant-enhanced remediation resulted in a relatively small improvement in the recovery of NAPL, especially in highly heterogeneous aquifers. Migration of high-concentration organic plumes to other layers by crossflow was also found to have a significant influence on SEAR behavior.

Vertical Electrokinetic-Flushing Remediation

An optimum reagent was selected to decontaminate the radioactive soil near nuclear facilities by using the developed vertical electrokinetic-flushing equipment, and the optimum remediation conditions were established to obtain a higher remediation efficiency and a minimum waste-solution volume. Namely, the acetic acid was selected as an optimum reagent due to its higher remediation efficiency. The average removal efficiency by a vertical electrokinetic-flushing remediation was 4.6% more than that by a vertical electrokinetic remediation. The optimum remediation conditions were suggested to be when the acetic concentration is 0.01 M, the injection rate of the reagent is 2.4 ml/g and the remediation period is 20 days for the vertical electrokinetic-flushing equipment of a 8.3 L volume. In these conditions, the removal efficiencies of Co2+ and Cs+ were 98.3% and 88.8%.

Health-Risk-Based Groundwater Remediation System Optimization through Clusterwise Linear Regression

This study develops a health-risk-based groundwater management (HRGM) model. The model incorporates the considerations of environmental quality and human health risks into a general framework. To solve the model, a proxy-based optimization approach is proposed, where a semiparametric statistical method (i.e., clusterwise linear regression) is used to create a set of rapid-response and easy-to-use proxy modules for capturing the relations between remediation policies and the resulting human health risks. Through replacing the simulation and health risk assessment modules with the proxy ones, many orders of magnitude of computational cost can be saved. The model solutions reveal that (i) a long remediation period corresponds to a low total pumping rate, (ii) a stringent risk standard implies a high total pumping rate, and (iii) the human health risk associated with benzene would be significantly reduced if it is regarded as constraints of the model. These implications would assist decision makers in understanding the effects of remediation duration and human-health risk level on optimal remediation policies and in designing a robust groundwater remediation system. Results from postoptimization simulation show that the carcinogenic risk would decrease to satisfy the regulated risk standard under the given remediation policies.

Optimal In-Situ Biormediation System Design Using Simulated Annealing

The presented procedure combines continuous simulated annealing (CSA) heuristic optimization with BIOPLUME II simulation for optimizing in-situ bioremediation system design. The design goal is to minimize the total cost of facility installation and operation needed to achieve contaminant plume containment and cleanup. System design elements include pumping rates and well locations. During optimization, pumping rates are treated as continuous variables, differing from previously reported simulated annealing combinatorial optimization for groundwater management. To improve computation efficiency, CSA annealing schedules employing four different temperature update functions (TUF) are contrasted. Each yields somewhat different optimal designs and requires different computation effort. An adaptive TUF used almost 4,000 simulations to develop the lowest-cost design. A geometric TUF used 5% fewer simulations to create a design costing about 3% more. Site characteristics significantly affect optimal system design features. For a specific design, bioremediation improves with increasing hydraulic conductivity, longitudinal dispersivity, and remediation period and with decreasing retardation factor.