A Comprehensive Review for Groundwater Contamination and Remediation: Occurrence, Migration and Adsorption Modelling

The provision of safe water for people is a human right; historically, a major number of people depend on groundwater as a source of water for their needs, such as agricultural, industrial or human activities. Water resources have recently been affected by organic and/or inorganic contaminants as a result of population growth and increased anthropogenic activity, soil leaching and pollution. Water resource remediation has become a serious environmental concern, since it has a direct impact on many aspects of people’s lives. For decades, the pump-and-treat method has been considered the predominant treatment process for the remediation of contaminated groundwater with organic and inorganic contaminants. On the other side, this technique missed sustainability and the new concept of using renewable energy. Permeable reactive barriers (PRBs) have been implemented as an alternative to conventional pump-and-treat systems for remediating polluted groundwater because of their effectiveness and ease of implementation. In this paper, a review of the importance of groundwater, contamination and biological, physical as well as chemical remediation techniques have been discussed. In this review, the principles of the permeable reactive barrier’s use as a remediation technique have been introduced along with commonly used reactive materials and the recent applications of the permeable reactive barrier in the remediation of different contaminants, such as heavy metals, chlorinated solvents and pesticides. This paper also discusses the characteristics of reactive media and contaminants’ uptake mechanisms. Finally, remediation isotherms, the breakthrough curves and kinetic sorption models are also being presented. It has been found that groundwater could be contaminated by different pollutants and must be remediated to fit human, agricultural and industrial needs. The PRB technique is an efficient treatment process that is an inexpensive alternative for the pump-and-treat procedure and represents a promising technique to treat groundwater pollution.

The Effect of Heterogeneity on the Distribution and Treatment of PFAS in a Complex Geologic Environment

Per-and polyfluoroalkyl substances (PFAS) have been identified as emerging contaminants of concern in the environment in a wide variety of media including groundwater. Typically, PFAS-impacted groundwater is extracted by pump and treat systems and treated using sorptive media such as activated carbon and ion exchange resin. Pump and treat systems are generally considered ineffective for the remediation of dissolved phase contaminants including PFAS but instead are considered applicable for plume containment. An alternative to pump and treat is in-situ treatment. The demonstrated use of in-situ treatment for PFAS-impacted groundwater is limited with only colloidal activated carbon (CAC) being shown to effectively attenuate PFAS over short and moderate time periods. Active research topics for the in-situ treatment of PFAS include the effect of heterogeneity on the distribution of the CAC, the lifespan of the CAC itself, the effect of competitive adsorption/absorption, and the effect of other geochemical conditions on the removal process. This study looked at the effect of heterogeneity on the distribution of CAC and subsequent treatment of PFAS at a site with a multiple aquifer system. The site’s geology varied from a silty sand to sand to fractured bedrock with all three units being impacted by PFAS and benzene (B), toluene (T), ethylbenzene (E), and xylene (X). Parameters evaluated included the distribution of the CAC as well as the subsequent treatment of the PFAS and BTEX. Results of groundwater sampling indicated that the PFAS detected within the groundwater were treated effectively to below their respective reporting limits for the duration of the 1-year test in both the silty sand and sand aquifers. The PFAS in the fractured rock aquifer showed a different treatment profile with longer carbon chained PFAS being attenuated preferentially compared to the shorter carbon chained PFAS. These results suggest that competitive sorptive reactions were occurring on the CAC within the fractured rock. Analysis of the unconsolidated aquifer materials determined that direct push injection of the CAC was effective at delivering the CAC to the target injection zones with post-injection total organic carbon (TOC) concentrations increasing by up to three orders of magnitude compared to pre-injection TOC concentrations. Heterogeneity did have an impact on the CAC distribution with higher hydraulic conductivity zones receiving more CAC mass than lower hydraulic conductivity zones.

A field-scale remediation of residual light non-aqueous phase liquid (LNAPL): chemical enhancers for pump and treat

The remediation of petroleum-contaminated soil and groundwater is a challenging task. The petroleum hydrocarbons have a long persistence in both the vadose zone and in the aquifer and potentially represent secondary and residual sources of contamination. This is particularly evident in the presence of residual free-phase. Pump-and-treat is the most common hydrocarbon decontamination strategy. Besides, it acts primarily on the water dissolved phase and reduces concentrations of contaminants to an asymptotic trend. This study presents a case of enhanced light non-aqueous phase liquid (LNAPL) remediation monitored using noninvasive techniques. A pilot-scale field experiment was conducted through the injection of reagents into the subsoil to stimulate the desorption and the oxidation of residual hydrocarbons. Geophysical and groundwater monitoring during pilot testing controlled the effectiveness of the intervention, both in terms of product diffusion capacity and in terms of effective reduction of pollutant concentrations. In particular, non-invasive monitoring of the reagent migration and its capability to reach the target areas is a major add-on to the remediation technique. Most of the organic contaminants were decomposed, mobilized, and subsequently removed using physical recovery techniques. A considerable mass of contaminant was recovered resulting in the reduction of concentrations in the intervention areas.

Decontamination of dense nonaqueous-phase liquids in groundwater using pump-and-treat and in situ chemical oxidation processes: a field test

The combination of pump-and-treat and in situ chemical oxidation processes can effectively accelerate the remediation of DNAPL pollutant in groundwater.

Analytical and Numerical Methods for a Preliminary Assessment of the Remediation Time of Pump and Treat Systems

Several remediation technologies are currently used to address groundwater pollution. “Pump and treat” (P&T) is probably one of the most widely applied, being a process where contaminated groundwater is extracted from the subsurface by pumping and then treated before it is discharged or reinjected into the aquifer. Despite being a very adaptable technology, groundwater remediation is often achieved in long and unsustainable times because of limitations due to the hydrogeological setting and contaminant properties. Therefore, the cost–benefit analysis over time results in an inefficient system and a preliminary evaluation of the clean-up time is crucial. The aim of the paper is to compare, in an integrated manner, the application of some models to estimate the time to compliance of a P&T system in relation to the specific hydrogeological condition. Analytical solutions are analyzed and applied to an industrial site and to a synthetic case. For both cases, batch flushing and the advection-dispersion-retardation (ADR) model underestimate remediation times comparing the results to real or simulated monitoring data, whereas the Square Root model provided more reliable remediation times. Finally, for the synthetic case, the reliability of analytical approaches and the effects of matrix diffusion are tested on the basis of a numerical groundwater transport model specifically implemented, which confirm the results of the analytical methods and the strong influence of the matrix diffusion on the results.

Use of a Novel Biopellet to Treat Total Petroleum Hydrocarbon Contaminated Groundwater

Conventional pump-and-treat strategies for dealing with groundwater contamination are both energy- and time-consuming. Potential passive biological techniques are of interest to remedy the massive volume of total petroleum hydrocarbon (TPH)-contaminated groundwater worldwide. In this study, novel biopellets made of TPH-acclimated microbes, fermented fruit peel materials, and CaO2 recycled from eggshells were manufactured to treat TPH-contaminated groundwater. The biopellets provided 56 mg of oxygen and achieved a C:N:P ratio by weight of 10:4:1. Moreover, each biopellet was capped with alginate to prolong its floating time in water to 25 days. The mimicked groundwater spiked with 500 mg/L diesel TPHs (TPHd) was treated using our novelly manufactured biopellets. After 8 days of treatment, results showed a 98.8% removal of spiked TPHd at a rate of 64.1 mg/L per day, with a microbial count that increased from nearly zero to 1.0 × 107 CFU/mL. The residual TPHd constituents were mainly C13–C18. Furthermore, microbial consumption of N, P, and oxygen was noted during the 8-day period of TPHd removal. As the TPHd level increased to 1500 mg/L, the removal rate reached 45 mg/L per day, and all TPHd had been removed after 22 days.