Soil vapor extraction of wet gasoline-contaminated soil made possible by electroosmotic dewatering-lab simulations applied at a field site

PurposeSoil restoration is still mainly carried out ex situ by excavating and replacing the contaminated soil. In situ remediation would reduce the costs of soil transportation and this way, the problem is not merely transferred elsewhere. The present study introduces a field case where the aged, oil-contaminated soil in a former fuel station in Finland was treated in situ sequentially with different methods.Materials and methodsSeveral approaches, including soil vapor extraction and biostimulation with electrokinetic pumping, were performed in the field. After these treatments, the dense original portion of the soil beneath the gasoline pump location, ca 100m(3), was still contaminated with petroleum-derived volatile organic compounds (VOCs), with concentrations of nearly 10,000mgkg(-1) measured at some hotspots. After a period of electroosmotic water circulation, the electrical field (0.5Vcm(-1), DC) was kept connected for 6months without addition of water, leading to dewatering and warming of the soil.Results and discussionIn contrast to the situation with the original wet soil, VOCs, in lab conditions, were found to volatilize very efficiently from the dewatered soil. When the soil vapor extraction treatment was renewed using perforated tubing installed horizontally at ca 1m depth in the dewatered soil at the contaminated site, the treatment was efficient and the soil was decontaminated in 5months. The final VOC concentrations were on average 190mgkg(-1) (n=13) with the highest value of 700mgkg(-1) at one hotspot. After a risk evaluation, the site was concluded to be sufficiently clean for industrial use.ConclusionsSince with many former fuel stations, the contamination consists of both volatile fractions that are difficult to degrade by biological means and heavier compounds for which biostimulation is often suitable, a combination of different methods may be worth pursuing.Peer reviewe

In situ bioremediation of Fenton's reaction-treated oil spill site, with a soil inoculum, slow release additives, and methyl-beta-cyclodextrin

A residential lot impacted by spills from a leaking light heating oil tank was treated with a combination of chemical oxidation and bioremediation to avoid technically challenging excavation. The tank left emptied in the ground was used for slow infiltration of the remediation additives to the low permeability, clayey soil. First, hydrogen peroxide and citrate chelate was added for Fenton's reaction-based chemical oxidation, resulting in a ca. 50% reduction from the initial 25,000 mg/kg average oil concentration in the soil below the tank. Part of this was likely achieved through mobilization of oily soil into the tank, which was beneficial in regards to the following biological treatment. By first adding live bacteria in a soil inoculum, and then oxygen and nutrients in different forms, an approximately 90% average reduction was achieved. To further enhance the effect, methyl-beta-cyclodextrin surfactant (CD) was added, resulting finally in a 98% reduction from the initial average level. The applicability of the surfactant was based on laboratory-scale tests demonstrating that CD promoted oil degradation and, unlike pine soap, was not utilized by the bacteria as a carbon source, and thus inhibiting degradation of oils regardless of the positive effect on biological activity. The effect of CD on water solubility for different hydrocarbon fractions was tested to serve as the basis for risk assessment requirements for authorizing the use of the surfactant at the site.Peer reviewe

European achievements in soil remediation and brownfield redevelopment

With the aim of sharing best practices of soil restoration and management of contaminated sites among European countries and to raise awareness of the enormous efforts made to succeed in such difficult commitment, the experts of the EIONET Soil working group on contaminated sites and brownfields agreed to gather their country's interesting cases and successful stories of recovery of contaminated areas. This second edition of the monograph presents seventeen new cases from eight European countries and its Regions of how polluted sites and brownfields have been remediated like new methodologies of sustainable restoration of the subsoil, development of innovative technologies, and funding mechanisms etc. These stories have been compiled to present what national, regional or local governments are doing to improve the quality of the environment and the living conditions of their population. A second aim is the promotion of best practices among industry, consultancies and business operators.JRC.D.3-Land Resource