In situ remediation of chlorinated solvents in clay till can be highly challenging because reagent delivery is constrained by low-permeability and the rate of treatment is limited due to inadequate contact with solvents that have diffused into the clay matrix. Conventional direct-push technology (DPT) and enhanced fracturing techniques can improve delivery of treatment agents; however, the radius of influence (ROI) of these methods in clay till is limited and often controlled by natural fracture networks. Here we present a novel method for relatively rapid emplacement of reactive treatment agents in clay till and other unconsolidated low-permeability matrices using DPT high-pressure jet injection. The method uses a custom-fabricated DPT injection tip possessing multiple injection ports, and combines jetting for emplacement of reagent-filled conduits, followed by emplacement of reagents into hydraulic fractures propagated into notches cut into the geologic matrix by jetting. The performance of the method was demonstrated in a full-scale application at a site Nivå, Denmark (the Site) where zero valent iron (ZVI) powder was injected for treatment of a chlorinated solvent source area in clay till and silt.
The target treatment zone (TTZ) at the Site occurs in a variable sequence of clay till and silt deposits between depths of 6 to 12 meters below ground surface (mbgs). Chlorinated solvent concentrations within the TTZ, pre-treatment, typically ranged from 40 to 80 mg/Kg. The area and volume of the TTZ is approximately 705 m2 and 3,900 m3, respectively. High-pressure (700 bar) DPT jet injection was used to deliver ZVI powder (Hepure), guar gel slurry, and sand into 19 injection borings with a grid spacing of approximately 6 meters. Between 4 to 7 injections were performed in each boring, with depth spacing of approximately 1 m apart. Overall, 123 injections were performed, with a target 400 kg ZVI, 200 kg sand, and 570L guar gel slurry emplaced into each injection interval. A total of 49 tonnes of ZVI powder was injected into the TTZ. To enable effective determination of radius of injection (ROI), as well as separation of injection intervals, in three co-located injection borings, a different combination of colored sands (white, red, or green) or dyes (rhodamine WT or brilliant blue) was used. Over 67 coreholes were advance to map the ROI throughout the TTZ. Cores were logged at 1cm resolution with depth for presence of injected ZVI using a field portable magnetic susceptometer.
The injection effort required 19 days to complete 123 injections. Results indicate that the DPT jet injection method consistently created subhorizontal ZVI/sand fractures with a ROI from 3 to 4 meters; in some cases the ROI extends to more than 5 meters. Within individual injection borings, distinct fractures were emplaced effectively with depth separations of 0.5 to 1 meter. The method also achieved emplacement of ZVI-filled conduits with ROIs of 0.5 to 1 meter from the injection point. The findings of this work indicate that high-pressure DPT jet injection is capable of achieving rapid, controlled emplacement of treatment agents in clay till with ROIs as great as 5 meters, and therefore represents a substantial improvement over the injection capabilities of conventional DPT injection and hydraulic fracturing in clay till.
Background
In Denmark we have very low threshold values for chlorinated solvents in indoor climate and at many polluted sites remediation is being conducted to lower the indoor concentration. Many of the solutions applied are based on ventilation of the capillary break layer under the buildings.
Ventilation systems in the capillary break layer can be provided with electrically driven blowers (active ventilation) or with passive ventilation systems based on e.g. pressure drop across a building created by wind or by applying wind cowls on the roof.
To apply ventilation systems in the capillary break layer successfully, a range of design parameters must be described in details. The right choice of blowers is of crucial importance and the amount of energy needed to run the ventilation system should be assessed. For passive ventilation systems documentation must be provided in order to ensure that the solution applied meets the requirements for driving forces created by wind.
At many sites the exceeding of the threshold value is quite small and often a passive ventilation system is chosen. But often this solution is made without sufficient knowledge about the design parameters, and the lack of effect identified at many passive ventilation systems indicates that the systems applied are insufficient.
Lack of knowledge about the applications and the limitations of the use of passive ventilation can be part of the explanation why insufficient passive ventilation systems are still applied at many sites. The demand for solutions independent of electrical power can be a part of the explanation as well.
Active ventilation systems require energy and the use of renewable energy will result in more environmentally correct solutions and hence a better carbon footprint by lowering greenhouse gas emission. In addition, the use of renewable energy possibly lowers the operation costs.
Aim of the project
The aim of the project is to collect knowledge to be used for a catalogue with a review of when the use of renewable energy for active ventilation remediation is cost effective. The renewable energy could be based on solar cells, wind energy, geothermic energy or hybrid systems which combine different renewable energy sources.
Another aim of the project is to describe applications and limitations of passive ventilation systems and gain a better knowledge of the influence of wind on buildings.
Approach and Results
The project consists of four phases: 1) a literature study of different kinds of renewable energy (solar, wind, soil, geothermic) in order to identify energy sources and equipment for different kinds of remediation systems, 2) design and conduct laboratory experiments with wind cowls, 3) modelling the passive ventilation effect of wind on buildings using Computational Fluid Dynamics – CFD at a site in the city of Vejen, Denmark, and 4) field test of selected renewable energy sources.
Phase 1, 2, and 3 of the project will be completed in March 2015 and the results will be presented at the conference. Phase 4 covering field test of renewable energy sources will be initiated in the spring of 2015.
Surfactant Enhanced Aquifer Restoration at a Former Chemical Weapons Manufacturing Site
Taylor-King C., Thomas J., Hopkins N., Holmes M.
Celtic Technologies Ltd, Columbus House, Greenmeadow Springs, Tongwynlais, Cardiff, CF15 7NE. Tel: 02920 368636, Fax: 02920 368637, Louis.Pang@celtic-ltd,.com
Abstract
This site was previously one of the most contaminated sites in South-West England and has a long industrial history as a munitions and chemical warfare plant during World War One, followed by zinc and lead smelting with sulphuric acid production until 1972, and then production of pharmaceuticals, agrochemicals and refrigerants until 2008, when the site was closed. In order to allow redevelopment Celtic were appointed to tackle the remediation works. The most complex and technically challenging element of the works was the in-situ remediation of a contaminant plume, comprising a cocktail of chlorinated compounds, the principal contaminants by mass being chloroform and trichlorofluoromethane (Freon-11) within the deep aquifer, known as the Fluvio Glacial Sands (FGS). The remedial objective was to recover the maximum possible contaminant mass from the FGS within the project timescale. Conventional recovery methods alone were not expected to achieve significant recovery within the programme allowed, therefore enhancement was proposed using surfactant injection to aid conventional pumping.
The remediation works comprised three phases; 1) Drilling, delineation and hydraulic recovery, 2) Surfactant injection and 3) A second phase of hydraulic recovery, to recover the additional mass liberated by surfactant injection.
PHASE 1: In total, 59 new wells were drilled and installed as either recovery and re-injection wells as all groundwater had to be re-injected back into the aquifer following treatment. The first phase of pumping recovered over 1,000 kg of contaminant mass from over 5,000 m3 of groundwater in 6 weeks of operation. In addition, valuable data on groundwater concentrations was gathered during the pumping phase, delineating mobile contaminant mass and aiding the effective design of the Phase 2 surfactant injection works.
PHASE 2: The second phase of the in-situ works, comprising surfactant injection, involved surfactant injection into 8 wells within an area of circa 1,360 m2. Over one effective pore volume of surfactant solution was injected into the aquifer over a two week period, prior to subsequent extraction in Phase 3. Prior to full-scale implementation, comprehensive in-house laboratory trials involving vial tests and soil column tests were carried out, with the aim of selecting the most suitable surfactant for both the contaminants of concern and the aquifer geology.
PHASE 3: The post surfactant injection hydraulic recovery yielded a significant increase in mass recovery, recovering a conservative estimate of 550 kg of contaminant mass over a two day period. Mass recovery gradually decreased in the 6 weeks of pumping following surfactant injection, following which there was sufficient confidence that the additional mass liberated by surfactant injection had been recovered, and the programme of treatment was completed. Post works groundwater monitoring indicated significantly reduced concentrations in the aquifer, particularly in areas where pre-works concentrations were indicative of the presence of free phase contaminant mass. At the end of the remediation programme, over 11,690 m3 of groundwater had been treated, removing over 2,500 kg of VOCs in just over 3 months of active recovery.
CONCLUSION: Surfactant Enhanced Aquifer Remediation (SEAR) was successfully deployed at the Avonmouth site, resulting in the liberation and recovery of additional residual contaminant mass from the aquifer. The detailed in-house laboratory trials carried out by Celtic contributed significantly to the success of full-scale field application. Remediation works were completed and verified in a timely manner, allowing the development works to continue on budget and on programme.
Background
Surfactants offer two mechanisms for recovering NAPLs: 1) to mobilize NAPL by reducing NAPL/ water interfacial tension, and; 2) to increase the NAPL’s aqueous solubility–called ‘solubilization’–as an enhancement to pump & treat. The second approach has been well-studied and applied successfully in several pilot-scale and a few full-scale tests within the last 15 years, known as Surfactant Enhanced Aquifer Remediation (SEAR). In cases where improved sweep efficiency is desired, the endpoint mobility ratio M° can be reduced using a viscosifier such as foam as was employed successfully at the Hill AFB site in the late 1990s. A useful source of information for this second approach is the “Surfactant–enhanced aquifer remediation (SEAR) design manual” from the U.S. Navy Facilities Engineering Command. Few attempts, however, have been made at recovering NAPLs using the mobilization approach presented in this paper. This approach has the potential to recover NAPLs using less surfactant, less pore volumes (PV) of throughput, with lower overall cost.
Objective
Our goal is the design and implementation of a surfactant flood that will recover an LNAPL, Jet A fuel, from a surficial sand aquifer located in Denmark, using a smaller amount of surfactant solution and as few PV of throughput as possible as compared to the SEAR approach. The approach will rely on mobilizing the LNAPL and will include the use of foam as a means of directing the injected solution to the LNAPL contaminated zone. Hydraulic control wells will be incorporated in the design of the project to ensure capture.
Conclusion
This paper will review the laboratory work that has been performed as part of the design for a full-scale implementation of a micellar flood that will include mobility control using foam. Completed lab work includes phase behavior screening of surfactants and detailed salinity scans of the most promising formulations and generating a ternary diagram to be used for the numerical simulations of the field application. We will also present results of two 1-D column tests and in situ foam generation tests. These results will be used in numerical simulations of the 1-D column experiments, followed by three-dimensional simulations of the site in order to design the implementation and optimize performance. In addition, the site owners and regulators were able to make crucial decisions such as the anticipated field results based on this work.
In recent years remediation practitioners within the contaminated land sector have responded to the continued growth and development of sustainable initiatives within the environmental industry by bringing to market remedial solutions and concepts that score highly in social, economic and environmental criteria. One such remedial technology is Trap and Trap™ (T&T), a patented US-based technology that has been applied at a small number of sites around Europe in recent years.
T&T relies upon high-pressure sub-surface top down injections of proprietary water-based formulas of granular activated carbon (GAC), impregnated with amendments to trap and chemically degrade contaminants. BOS100® is a prepared formulation of GAC impregnated with metallic iron to support the continued trapping and complete chemical reduction of CHC contaminants on the GAC surface. BOS200® is a prepared formulation of GAC inoculated with a selected blend of naturally occurring micro-organisms and gypsum (calcium sulphate) to support the continued trapping and biodegradation of petroleum hydrocarbons on the GAC surface.
T&T does not typically require follow up injection events (as is common place with ISCO for example) to provide continued protection from an upgradient source, making it a high-value option with a low carbon footprint and financial burden, especially where upgradient contaminant sources are inaccessible for direct treatment or removal. As is the case with other injection-based technologies such as chemical oxidation, T&T injection recipes can be amended in response to ground conditions and contaminant load to meet a given set of performance objectives. However, where T&T differs is that once installed the technology needs little to no on-going maintenance to provide continued capture and treatment, with the GAC surface regenerating via secondary treatment mechanisms (chemical and/or biological degradation), thus allowing continued trapping to occur. Furthermore, T&T does not generate solid or liquid wastes for above ground treatment; it does not rely on hydraulic control of the groundwater to provide containment or treatment of the plume and it requires no active systems, power, or the installation of engineering measures or pipework to run.
The treatment mechanisms of the technology will be discussed, followed by a presentation of the first implementation of T&T within the United Kingdom, where pilot trials were scheduled to demonstrate the efficacy of the technology (ahead of full-scale implementation) in mitigating the impacts of chlorinated solvents and petroleum hydrocarbons within two discrete areas of an operational bulk storage terminal, near London.
Project design and implementation was bespoke to each contaminant plume; the first being a dissolved phase chlorinated solvent plume (TCE, DCE, VC) and the second, a highly impacted LNAPL plume (some 700mm thick) with both areas lying below operational infrastructure such as tanks, gantries and process pipework.
The case study will highlight the various characterisation steps used to confirm the conceptual site model and develop trial design (incorporating the use of soil cores, Membrane Interface Probe work and field testing/monitoring). An overview of the resultant post treatment results will be provided before a discussion of the merits of the technology is presented with a particular focus on sustainability metrics contrasted at full-scale with competing technologies at the site to examine the relative sustainability of the technology using semi-quantitative scoring methods. The analysis will show that T&T was considered the most suitable approach for full-scale treatment because it provided the most effective and robust means of reducing the contaminant burden, whilst minimising site disruption during installation and operational periods.
This project was recently awarded ‘Best In-situ Design’ at the UK Brownfield Briefing Remediation Awards, October 2014.