Ex Situ Chemical Oxidation of Soils at a Fuel Storage Depot, Sweden

Estimated Reading Time: 3 minutes

With RGS Nordic

Summary

An area of impacted soils was discovered at an oil-distribution depot at a Swedish harbour. This was thought to have occurred due to historic spillages and leaks from industrial land use on the site. Remediation of the soils was required to MKM levels (Swedens generic industrial land use clean-up criteria).

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As the contaminated soil was quite shallow (1.0-2.5m BGL) it was determined that excavation would be easily achieved. Treatment of the soils through biopiling or windrows was not deemed appropriate due to limited space. Therefore ex situ mixing of the soils with a chemical oxidant, PersulfOx, was chosen in order to provide rapid reduction of the contaminant mass. This would be followed by a short period of enhanced biological degradation in the treated soils, stimulated by the increased redox in the soil moisture following the chemical oxidation process. Partial chemical oxidation of the hydrocarbons into more bioavailable and biodegradable compounds would also accelerate biodegradation of a proportion of the residual contaminant mass.


PersulfOx was added into the soils at a dosage rate of 17kg per 1m3 of soils. This was then mixed thoroughly using an Allu hydraulic bucket, during which the soils were wetted. This would increase the soil moisture in order to facilitate the chemical reaction. Care was taken to avoid adding too much water and risk damaging the geotechnical properties of the soils.

The sides and base of the excavations were validated to delineate the vertical and lateral extent of the impacted zone and ensure that all of the contaminated soil had been removed. Following application of the PersulfOx, the treated soils were then placed back into the excavations and validated. Following successful validation, the soils were compacted to the required capacity in order to allow site traffic to pass over the treated areas.

Results

Sampling of the soils three months after treatment, showed that the target concentrations had been reduced to below the target guideline values, see Figure 1 and 2.

Fig. 1: Combined results from both areas, Aliphatic C5-C16

  • The impacted soils were successfully remediated in a short period of time.
  • Due to its built-in catalyst, the use of PersulfOx avoided the need for dangerous activators such as hydrogen peroxide or caustic soda, making the remediation process much safer.
  • The treatment area was minimised, making the remediation of the soils practical and avoiding greater disruption to the site operator.

Fig. 2: Combined results from both areas, Total Petroleum Hydrocarbons

Protection of a river using an activated carbon barrier in North Italy

Estimated Reading Time: 3 minutes

Summary

On a 6 hectare site in northern Italy, an extensive enhanced reductive dechlorination process had been previously been carried out by REGENESIS using a combination of proprietary electron donors (3-D Microemulsion and HRCs). This resulted in successfully reducing TCE contamination and its daughter products from high levels (suggesting the presence of some DNAPL) to low dissolved phase concentrations. The concentrations were suitably low to allow regulatory closure of the internal part of the site. This was achieved within 2 years from a single injection. Immediately beyond the downgradient site boundary, a river presents a sensitive receptor. This, plus legislative rules, determine that the site boundary targets are very stringent (<1 μg/L). Although the previous electron-donor application has reduced the contaminant influx dramatically, at such low concentrations, biodegradation alone may not reach these low targets.

Therefore, a second phase treatment has been implemented in order to enhance the biodegradation process further using PlumeStop, a Liquid Activated Carbon. This application will adsorb the contamination and provide a biomatrix on which the dehalogenating bacteria will come into contact with the chlorinated solvents. This combination of sorption and biodegradation will provide an enhanced reduction in contaminant concentrations, which will then be sustained and further contaminant influx is adsorbed and degraded.

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Treatment

PlumeStop was applied in a double pilot test performed in two areas of the site, where different contaminant concentrations were observed. This was useful for demonstrating technology’s efficacy and to design and accurate dose for the full scale treatment. A larger PlumeStop barrier application is now being implemented along the site boundary. This will create a subsurface activated carbon filter along the length of the downgradient boundary. This consists of approx. 150 direct push injection points, performed using two Geoprobe rigs, in parallel. The dosage has been tailored for each sub-area depending on the contamination concentration and heterogeneity of the alluvial subsurface.

What’s Special

  • Unique in situ process allows for fast depletion of residual organic contaminants in order to reach very stringent values using only a single application.
  • Bioregeneration of the injected carbon filter is achieved through biodegradation of the sorbed chlorinated compounds: this provides long term treatment (years – decades) from a single application.
  • The system will replace a costly Pump & Treat barrier that has worked to hydraulically confine the site for 10 years. This will allow the owner to finally cease all site remediation activities and allow regulatory site closure.

In Situ Treatment of Chrome(VI) Plume in Fast Flowing Aquifer, NW Italy

Estimated Reading Time: 5 minutes

Summary

A former chemical manufacturing plant in northwest Italy was due for demolition to allow redevelopment into residential properties. Site investigations showed elevated concentrations of Cr(VI) in the groundwater, which were above the stringent National Standards of 5μg/L, requiring remedial works to be completed. The groundwater under the site is aerobic and fast-flowing, causing the contaminant plume to migrate beyond the site boundary. It was decided that an in situ approach was required to remediate the Cr(VI) prior to sale of the site.

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Site plan showing treatment areas, injection wells (pink) and monitoring well (blue) locations

Remedial Approach

Two areas within the plume were identified as being above the site remediation target of 100μg/L. These were targeted with an injection of 3D Microemulsion (3DMe) and MRC in order to reduce the soluble Cr(VI) to non-toxic solid Cr(III) and stabilise it within the aquifer matrix.

The dose of MRC was tailored to match the vertical distribution of the contamination in order to provide the most accurate and cost effective treatment. 3DMe relies upon micellar transportation following injection in order to provide a wide radius of influence from each injection location. This was important on this deep site, in order to minimize the number of injection points required on the site.

Fixed injection points were installed and a single application of the reagents was completed. The injectable substrates were combined at a central mixing location and then pumped into several injection points simultaneously. The process was repeated until the all of the target areas were treated.

Reagent mixing and injection into fixed wells

3-D Microemulsion (3DMe)®

3DMe provides an immediate, mid-range and long-term, controlled release supply of hydrogen (electron donor) to rapidly create and then sustain anaerobic conditions. This will reduce the Cr(VI) to Cr(III), which will then settle out as a solid. Reversion to natural conditions following the 3DMe treatment (in perhaps five years or more) will not cause this process to reverse.

3DMe is also designed to distribute over very wide areas from each injection point. This is achieved through the molecule having hydrophilic and oliophilic properties hence upon mixing with water, 3DMe forms a microemulsion made of tiny micelles, which propagate through and coat the aquifer. This micelles are also able to transport MRC molecules within them, creating a wide and effective treatment zone, which is then sustained for many years.

Metals Remediation Compound (MRC)®

MRC is a controlled release remediation product designed specifically for the treatment of hexavalent chromium (Cr(VI)) in groundwater. MRC’s active compound is an ester of cysteine (a sulfur-containing amino acid) on a carbon backbone molecule of glycerol and sorbitol. A cysteine-based product such as MRC is well suited for in situ Cr(VI) immobilisation, since it has a strong affinity for metal contaminants and does not alter the properties of the subsurface. The active compound in MRC (sorbitol hexacysteinate) is embedded in a polylactate matrix that provides a carbon source and electron donor for subsurface bacteria. This combination of materials makes MRC a viscous but injectable material that slowly releases the cysteine ester to a contaminated aquifer via hydrolysis by water or enzymatic action by microbes. MRC’s slow release property allows for a longevity of 12 to 18 months in an aquifer, allowing for an effective approach to metals immobilisation.

Chromium VI concentrations in groundwater before and after treatment.
Area 1 and 2 need to reach the site remediation target, Area 3 needs to reach CSC

Results

Validation monitoring shows very good substrate distribution at all but one out of thirteen monitoring points. The reduction of the Oxidation- Reduction Potential (ORP) and dissolved oxygen with the simultaneous increase of the Total Organic Carbon (TOC), as well as an increase in iron and manganese, clearly showed the desired trend. The analytical results showed a rapid and significant reduction of CrVI targeting values often below the 5 μg/l limit, with a removal efficiency of 90% on average.

Downgradient Chromium VI concentrations at 25m (red), 75m (green) and 80m (blue) from the site

What’s Special?

  • The ability of 3DMe to self-distribute over a wide radius of influence from each injection point allowed the injection grid to be widely spaced. This minimised the number of application wells, which, given the depth of the treatment, greatly reduced the remedial costs.
  • Treatment of Cr(VI) was very rapid and sustained despite the aquifer being very aerobic and fast flowing.
  • Even though the aquifer was very fast-flowing, the products have not suffered from wash-out and continue to successfully treat the target areas over an extended period of time.
  • The seasonal variation in groundwater level at the site has the potential 
to mobilise contaminants into the groundwater during periods of high precipitation. The longevity of the reagents allows this contaminant influx to be addressed and avoid rebound.
  • The injection technology selected saved money by avoiding the use of clustered-wells. The injection rate was high, saving time on site.
  • The results of the remediation can be seen over 20m downgradient, through a significant reduction of Cr(VI) in offsite monitoring wells, providing rapid benefit to the environment on and off the site.

Historic Site On Track To Reach Remediation Goals

Estimated Reading Time: < 1 minute

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Case study highlights:

  • Creative combined remedy approach addressed accumulated contaminants from over 100 years of manufacturing operations
  • Innovative application approach using 1.5” diameter wells effectively accommodated low ceiling and tight spaces, allowing for successful reagent injection
  • 180 days post-injection, all VOCs were measured at greatly reduced concentrations and geochemical conditions remain ideal for biodegradation

This case study reviews a site in the Ohio River Valley where historic industrial operations over the last 100 years at a manufacturing facility have resulted in PCE and TCE impacts to 7,500 square feet of shallow groundwater. To move the redevelopment of this site forward, groundwater VOC sample results must meet the U.S. Environmental Protection Agency maximum contaminant levels (MCLs) for four consecutive quarters. Download the case study to learn about the combined remedy using PlumeStop, HRC, and BDI+ to address the contaminants.

Combined Remedy Leads to Site Closure

Estimated Reading Time: < 1 minute

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Case study highlights:

  • Significant contaminant reductions achieved in both the source area and core plume
  • 8-10 weeks of time saved compared to alternative approaches
  • $500,000 saved in project costs compared to alternative Electrical Resistance Heating (ERH) approach being considered

This case study reviews an active Underground Storage Tank (UST) case with the Arizona Department of Environmental Quality (ADEQ), where the site needed to meet ADEQ closure levels quickly in order to seek risk-based closure as part of a property transaction. After performing remedial assessment activities, the consulting firm Antea Group selected a combined remedy approach from REGENESIS, which included soil mixing using RegenOx® and H2O2 in the source zone and ISCO injections using PersulfOx® in the core plume. The solution from REGENESIS achieved ADEQ Closure levels for the site and now Antea Group is seeking a risk-based closure.

Successful 12-Month Pilot Trial of Enhanced Reductive Dechlorination

Estimated Reading Time: 4 minutes

With RGS Nordic and Nordic Envicon

Introduction

REGENESIS were approached by RGS Nordic and Nordic Envicon to form part of a specialist team to design a remedial scheme for a former aerospace factory in Finland.

An area of over 100,000m2 is impacted by a chlorinated solvent plume in the groundwater, comprising predominantly cis-1,2-dichloroethylene (DCE) contamination. The first phase of these works comprised a pilot trial, to demonstrate the applicability and efficacy of the suggested treatment method ahead of full-scale deployment.

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Remediation Approach

The site had many challenges that needed to be overcome in order to deliver a cost-effective scheme of works:

  • Complex heterogeneous formation, comprising sands, gravels, silts and crystalline bedrock;
  • Extremely large plume (>100,000m2 of which 60,000m2 requires treatment);
  • Conflicting seasonal groundwater flow directions;
  • Full-scale works will be required to deliver a fully remediated site within two years.

After completing an in-situ remediation option appraisal the team agreed that the full-scale strategy should comprise a series of ‘barriers’ (treatment zones through which groundwater would continue to flow, but in which the contamination would be degraded) perpendicular to groundwater flow.

This configuration would minimize the number of injection points, reducing application costs, without compromising treatment efficiency. The electron donor which was suggested was 3-D Microemulsion® (3DMe).

Fig. 1 – The molecular structure of 3-D Microemulsion

Fig. 2 – The 3 Stage Release profile of 3DMe

3DMe provides three stages of electron donor release from a single concentrate of specially designed polar molecules. When mixed with water on site, 3DMe forms a high-volume microemulsion, without the requirement of emulsifiers.

Upon injection into the groundwater, 3DMe initially moves out into the formation and adsorbs to the soil particles. As the molecule is designed to be appropriately soluble, it then gradually dissolves back into the groundwater, where it ferments to drive enhanced reductive dechlorination (ERD), but also reaches its critical micelle concentration (300 ppm), reforms as a microemulsion and moves further out from the injection point.

This process repeats to ‘self-distribute’ the 3DMe over large distances within the subsurface, without it washing away. This mechanism allows for wider injection spacing which reduced the number of injection locations.

Fig. 3 – 3DMe micelle representation

Fig. 4 – Injection configuration

Pilot Trial Application

Prior to a full-scale application being completed, it was determined that a pilot test should be completed. The intention was to determine how well the heterogeneous formation would accept the application, verify the injection spacing and confirm the efficacy of the treatment. A 20m wide barrier was installed perpendicular to groundwater flow. This consists of 5 injection points, forming two rows with 10m spacing within the rows and 4.5m in between rows (see fig. 4) This created an effective injection spacing of 5m perpendicular to groundwater flow.

Direct push injection was used, with the requisite dose of 3DMe injected at each location from 4m BGL (groundwater level) to 10m BGL (top of the competent bedrock).

Fig. 5 – Injection works on site

Fig. 6 – Injection works on site

Results

Validation was completed over 12 months following application. During this period the small amounts of PCE and TCE were reduced in the groundwater to below detection limit. The main cis-1,2-DCE contamination was reduced by 99% to 13μg/L, well below the remedial target of 500μg/L. Sequential production and degradation of daughter products showed that full reductive dechlorination was achieved, with vinyl chloride (VC) concentrations peaking at 280μg/L, but then quickly decreasing to 12μg/L by the end of the validation period. Full reductive dechlorination was also evidenced by the production of ethene throughout the treatment.

Fig. 7 – Contaminant concentrations plots in target area over time

Fig. 8 – Total CHC concentrations over time

Conclusion

  • The pilot trial demonstrated the ability to apply 3DMe on a wide grid in a heterogeneous formation.
  • The treatment successfully reduced the contaminant of concern by 98%, well below the remedial target values.
  • Full reductive dechlorination of the contaminant was achieved.
  • The pilot trial allows for the full scale treatment to be accurately 
designed and programmed.

Treatment of mixed chlorinated ethenes and ethanes at an active site, UK

Estimated Reading Time: 4 minutes

Introduction

REGENESIS was approached to offer an in situ remedial solution to address high levels of mixed chlorinated solvent (TCA and TCE) contamination of the groundwater at a site in northeast Scotland. At the time, an ongoing DPVE system was operating, but was unable to achieve the remediation goal of a 75% reduction in chlorinated solvent mass. Furthermore, a supplementary MIP investigation showed that there was more contamination at depth (>6m) which the DVPE system was not able to reach.

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Fig. 1 REGENESIS Remediation Services applying 3DMe and BDI Plus on site

The initial design was based on treatment between 3 – 9m BGL of the aquifer across a 1,200m2 using 3DME and BDI with the preferred method of application being direct push injection. However, during the MIP investigation progression of the rods deeper than 6mBGL was found to be difficult. This raised concerns that (1) direct push injection would not be able to reach 9m BGL and (2) injection of the required dose of 3DMe may not be possible. REGENESIS were therefore asked to undertake a pilot study over a limited area to demonstrate that the works were possible. This was completed successfully and also showed excellent dose response and demonstrated to the site owners that the works (which were completed at night) would not have a deleterious effect on their operations.

Full Scale Application

The pilot trial was conducted over two days (see figure 1) during which the direct push injection rig had no problems getting the injection rod to the required depth of 9m BGL (unlike the MIP). Furthermore, the required volume of 3DMe was accepted by the aquifer with minimal daylighting/surfacing.

Following the MIP and pilot, the fullscale design was tailored to provide the most cost effective approach for the site. 60 direct push injection points were completed over 10 nights, with no disturbance to the site operations.

The direct push injection points were centred on BH 11, a pre-existing well, to ensure we had good baseline data. Both BH11 and the surrounding wells were monitored over 8 months to assess the effect and distribution of 3DMe.

Results

Following the injection works, quarterly validation monitoring was completed. Post injection monitoring showed no inhibition of parent compound degradation due to the mixed halogenated compound plume. 98% and 99% reduction in mean concentration of TCA and TCE respectively.

Full reductive dechlorination was achieved with no build up in daughter products (see fig 2 and 3). The validation curves suggest that both biotic and abiotic degradation occurred.

Fig. 2 Mean concentrations of Chlorinated Ethanes over time

Fig. 3 Mean concentrations of Chlorinated Ethenes over time

Abiotic degradation occurred through the production of reduced iron species by the production of low redox conditions created by the 3DMe.

What’s Special

  • A limited pilot study was used to prove the practicality and efficacy of the proposed approach. This area did not require further injection, so added little extra cost to the remediation of the site.
  • Bioaugmentation using BDI+ avoided any inhibition of either chlorinated ethenes and ethanes by ensuring that the microbial consortia contained viable counts of dehalogenating bacteria specialising in either contaminant group.
  • Very high levels of contamination, suggestive of DNAPL, were reduced to very low concentrations within 18 months.
  • No build up of degradation products occurred, showing full reductive dechlorination was achieved and sustained.
  • No disturbance of the onsite operations occurred during the limited injection time onsite, with the remediation occurring under the site as it continued to function normally.
  • Remediation goals were achieved.

Fig. 4 REGENESIS’s team onsite

Advanced Remedial Technologies Restore Neighborhood

Estimated Reading Time: < 1 minute

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Case study highlights:

  • Application of combined REGENESIS technologies to biodegrade contaminants, prevent further plume migration, and protect occupants from the threat of vapor intrusion.
  • Reduction of the total cVOC plume extent by 95% and reduced mass by 99.8%.
  • Positive results indicating the degradation process is ongoing and processing.

This case study reviews a former plating facility in southwest Michigan that had released chlorinated volatile organic compounds (cVOCs) into shallow groundwater, resulting in a ¼-mile long contaminant plume. In response, the Michigan Department of Environmental Quality (MDEQ) and the environmental firm, DLZ, implemented a combined remedy which included mitigating vapor intrusion in the residential basements and treating the groundwater plume with a novel, multi-phase in situ bioremediation approach.

Galligu and TPH Contaminated Site Remediation in Runcorn, UK

Estimated Reading Time: 5 minutes

Summary

Wildgoose Construction’s redevelopment of a former bus depot into commercial/retail, including a new public house for Marston’s, posed unique and complex challenges. Geotechnical and Environmental Associates Ltd (GEA) identified that each step in the solution process would have a follow-on effect, so a well thought-out, integrated approach was crucial for the project’s success.

BB Award and GE Award finalist logos

Fig. 1 – PlumeStop barrier injection near site boundary

The site comprised a hillside covered by industrial waste from the Leblanc process comprising several metres of galligu above a black ash layer which was underlain by cohesive glacial till. Two geoenvironmental issues needed addressing:

  1. Stability: the galligu had a weak structure, with a ‘toothpaste’ consistency in parts;
  2. TPH contamination; leaking underground storage tanks (UST)s onsite resulted in fuel infiltrating the subsurface and moving offsite via perched water in an ash layer beneath the galligu.
The downgradient boundary comprises a steep slope to the canal where the contaminated groundwater egressed at ground-level, polluting the waterway.
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An integrated solution: Soil/cement mixed panels were used to support structures, with a soil/cement mixed mattress covering the entire site, as a load transfer platform. Installation of these panels altered the groundwater flow, which therefore needed modelling to ensure the contaminant treatment could be targeted accurately.

Modelling groundwater flow through anthropogenic waste and man-made installations presented a challenge, as models are designed for more homogeneous and isotropic conditions. However, it was shown that groundwater would be raised and channelled towards the panel ‘wall’ at the boundary. Here the groundwater would funnel through gaps at a higher velocity.

An innovative Liquid Activated Carbon substrate was used to integrate with the panels, which required no maintenance and provided effective treatment in the extremely bio-toxic environment created by galligu. This subsurface carbon-filter entirely prevented contaminant egress from the site.

Integrated Geoenvironmental Solution

The structure of galligu varied across the site: from fused crystalline ‘rock’ in upper areas, to a weak ‘toothpaste’ consistency at depth – unsuitable to build on. Previous settlement caused hydrocarbon leaks from broken pipes, resulting in the bus depot closure. Potential settlement prevented the use of a raft foundations. In addition, the presence of a high pressure gas main prevented the use of a piling solution. Therefore a soil/cement panel solution was piloted and then installed full scale by Deep Soil Mixing Ltd, using in situ mixing equipment (see figure 5 and 6).

Fig. 2 – Conceptual Site Model in Section

Fig. 3 – Remedial Strategy in Section

The geotechnical solution created a new challenge: to understand how the cement stabilised columns would alter the groundwater flow pattern across the site. This was crucial to know, in order to determine where contaminant egress may occur at the site boundary.

Galligu creates strongly alklaline, arsenic rich, reduced conditions in the subsurface. This inhibits biological degradation, resulting in ongoing persistence of TPH. This chemistry prevents typical remedial approaches to be taken as the remedial solution would have to: not react with the cement, galligu or ash; capture the hydrocarbons in the toxic conditions produced by the galligu; work for decades, until the residual secondary source is depleted, without power, pumping or further action.

When PlumeStop Liquid Activated Carbon (LAC) was chosen, the placement of this underground filter needed to be carefully considered. At the boundary, the groundwater flow was extremely fast through the gaps. Hence, by moving the barrier into the site, the slower groundwater allowed for a longer treatment time in the PlumeStop. The PlumeStop barrier length was guided by the modelling, to transect the entire contaminant plume. REGENESIS provided bespoke design work to match the predicted groundwater flow and contaminant levels (i.e. the contaminant flux).

Application

REGENESIS worked with GEA and their client to ensure the design matched their requirements. REGENESIS also managed and completed the injection works onsite using direct push injection, and then provided a completion report and warranty.

All work was completed on a busy construction site, with a high-pressure gas main and large easement.

Results

Following injection of the PlumeStop across the width of the predicted contaminant plume, the TPH concentrations at the site boundary were dramatically reduced by 98%. Although not the main focus of the treatment, low levels of PAH were also reduced to non-detect.

Fig. 14 – TPH concentrations at site boundary before and after PlumeStop barrier treatment

Conclusion

This integrated geoenvironmental solution was highly successful, delivering a number of key achievements:

  • Galligu is often treated ex-situ, which was not practical in this situation. The soil/cement stabilisation approach provided an economical solution to the geotechnical problems presented by Galligu, whilst encapsulating the contaminants within it and minimising future leaching. Being a low disturbance technique, it also permitted treatment alongside a high-pressure gas main where piling was not permitted. Groundwater modelling of the altered flow pattern was required to allow the design of the remedial scheme. Due to the inevitable uncertainties associated with groundwater flow through the ash layer this modelling was carried out using a low cost electrical analogue modelling technique.
    • The remedial scheme allowed the project to proceed within budget and was delivered on time.
    • Treatment of petroleum hydrocarbon contamination in the presence of galligu has not been completed previously to our knowledge.
    • This was the fourth use of PlumeStop in the UK and represents an imaginative and fully thought-through application that allowed highly effective remediation, protection of a public waterway and cost-effective geoenvironmental treatment of a busy and difficult site.

This project has won in the category ‘Best Conceptual Design’ in the Brownfield Briefing Awards 2018, and was shortlisted in the GE Awards 2018.