Introduction to Soil & Groundwater Remediation Techniques for Inland Oil Spills

Inland oil spill incidents can have a devastating effect on the environment resulting in fish kills, contamination of surface and groundwater resulting in the closure of water supplies and damage to aquatic ecosystems. They can also result in impacts to human health, building structures and third-party property. Oracle Environmental Experts utilise a wide range of remediation techniques to address the effects and impacts of inland oil spills on soil and groundwater which we explore briefly in this article.

Excavation and Removal

Excavation and removal of oil contaminated soils remains a common remediation technique for addressing contaminated soils, quickly removing contaminated materials, preventing risk of further impacts, and reducing ongoing liabilities. Typically, a site assessment is undertaken first to determine the nature and extent of contamination, and to establish the scope of the excavation works. Excavation can then either be undertaken manually by hand, by heavy equipment such as excavators, or by vacuum excavation equipment around sensitive services or protected trees. The contaminated soils are loaded into skips or trucks and transported off site to a suitably permitted facility for subsequent treatment or disposal. Clean soil is then brought in and appropriately compacted to replace the removed soil, and ground surfaces are then reinstated to match the original condition.

Soil Vapour Extraction

This in-situ remediation technique can be used to remediate permeable soils and structures that can otherwise not be removed, for example through the base of excavations or beneath sensitive building structures. Perforated steel lances are installed into the contaminated area and connected to a vacuum pump that creates a negative pressure zone within the soil, pulling the contaminated vapours toward the extraction points. The technology provides two treatment elements, removal of the more volatile hydrocarbon components coupled with increased airflow providing increased quantities of oxygen for microbial degradation. The vacuum pump pulls the air and vapour from the soil into the treatment system, which consists of a moisture knock-out pot and granular activated carbon, which filters the volatile organic compounds and outputs to air. Oracle Environmental Experts monitor the flow through the system and the concentrations of contaminants in the extracted vapours to measure the effectiveness of the treatment process.

In-Situ Chemical Oxidation

Another option for the in-situ treatment of oil contaminated soils and groundwater is chemical oxidation.  This technique involves the injection of a chemical oxidant (e.g., hydrogen peroxide or a proprietary ‘off-the-shelf’ product) into the contaminated area, typically though perforated steel lances or boreholes. The oxidant can be applied under gravity or under pressure. Once the chemical oxidant comes into contact with the contaminants, it initiates a chemical reaction known as oxidation which breaks down the organic contaminants, ultimately transforming them to carbon dioxide and water. Oracle Environmental Experts monitor the injections to measure the progress of the oxidation reactions and to ensure that the desired treatment goals are being met.

Chemical oxidation should only be completed by experienced contractors with sufficient knowledge of the chemicals being applied, the soil conditions into which the oxidants are being injected, the presence and location of any buried services and the health and safety impacts associated with the treatment. It can be an aggressive treatment process but can also be very successful and fast-acting when applied appropriately.

The oxidation process can also be used in combination with other remediation techniques such as SVE in soils and pump and treat in groundwater to enhance remediation processes and timescales.

Pump and Treat

Pump and treat is an established approach to the recovery of oil contaminated water and light non-aqueous phase liquid or (LNAPL) or free phase oils from water. This method involves the installation of sumps into shallow groundwater or boreholes into deeper groundwater and the placing of pumps to draw the groundwater and oil to surface for subsequent treatment and recovery. The choice of pump is of key importance and will be dictated by several factors including depth to groundwater, groundwater recharge, and the type and quantity of oil present. The initial focus is likely to be on recovering as much of the LNAPL or free phase oil as possible, and diaphragm pumps and air-driven top-loading pumps are often the best option to achieve good separation of the oil and water.

The pumps draw in the oil and groundwater creating a cone of depression which encourages further oil into the sump or borehole, and the recovered oil and water is passed through an oil-water separator to enable recovery of the oil in its free phase. Dissolved phase hydrocarbons in the water are then passed through granular activated carbon filters to remove all traces of hydrocarbons from the water prior to discharge to ground or sewer under the appropriate consents or permits.

Throughout the treatment process, the quality of the treated water is closely monitored to ensure that it meets the required standards for discharge.

This approach can be used to intercept oil contaminated groundwater from contaminating surface waters, building structures or third-party boreholes and water supplies.  Other remediation techniques can be used in combination with pump and treat to achieve improved levels of clean-up and to speed up treatment timescales. For example, it can be used in combination with chemical oxidation, air sparging or bioremediation for additional polishing and to enhance treatment.

Bioremediation

Bioremediation is a remediation technique that uses micro-organisms to reduce pollution through the biological degradation of pollutants into non-toxic substances. This can be used to remediate organic contaminants in soils and waters and involves either aerobic or anaerobic micro-organisms which often use the breakdown of the target contaminants as an energy source. For bioremediation to be effective, the right temperature, nutrients, and food/energy source must also be present. The right conditions allow the right microbes to grow and multiply and reduce more contaminants. The process can be carried out in-situ or ex-situ and can be completed through the addition of oxygen and nutrients to enhance the natural bacteria preset in the soil and groundwater or can involved the addition of bacteria that have been cultured to preferentially remove certain contaminants.

When carried out in-situ nutrients, oxygen enhancers or bioremediation products are typically injected into soils and groundwater through lances or applied through wells. The progress of the bioremediation can be monitored through the measurement of contaminant reduction and through the increase in concentration of by-products such as carbon dioxide.

Ex-situ treatment of soils and groundwater can also be completed where site logistics allows. Soils are typically treated in bio piles or windrows (arranged in a long line) after the addition of nutrients and temperature and moisture content have been optimised. After completion of treatment, soils may be able to be re-used on site subject to the appropriate permissions. Ex-situ treatment of groundwater can be carried out in treatment vessels or bioreactors These are tanks in which groundwater is mixed with microbes and nutrient amendments for treatment. Depending on the site, the treated water may be pumped back to the ground or discharged to surface water or to sewer.

The process can take from a few months to several years to complete depending on factors such as contaminant concentration, environmental conditions such as temperature and moisture content. Bioremediation has the advantage of using natural processes to clean up sites and as it may not require as much equipment, labour, or energy as some other clean up methods, it can also be cheaper.  

Closing Comments

Oracle Environmental Experts excel in delivering rapid response to emergencies, handling spills and pollution incidents with efficiency. We are dedicated to pioneering innovative methods for tackling soil and groundwater contamination challenges and it is important to note that we have no vested interest in any particular technique or technology. We consider the available remedial options and assess the relevant constraints to develop the most appropriate solutions assessing the carbon footprint of our works prior to implementation and on completion.

Reach out to Oracle Environmental Experts at 01684 252858 to explore all of our soil and groundwater remediation solutions.