PROCESS BASED REMEDIATION
Contaminated groundwater is a concern at many brownfield sites. When hydrocarbons compounds such as fuels, solvents or lubricants are the key contaminants, ‘free product’ or Non-aqueous Phase Liquids (NAPL) will sometimes still be present in the ground and may be long lasting sources of contamination to the groundwater. Vapours associated with fuels/solvents may also be present in the pore space and pose unacceptable risks.
Process based remediation covers a number of mechanical remediation techniques which are used to extract vapour, contaminated groundwater or NAPL from the ground so they can be treated. Common methods include:
PUMP AND TREAT
Contaminated groundwater is pumped via strategically placed extraction wells and transferred to a water treatment system. The treated water is then either disposed of to the sewer, recycled on site or sometimes re-injected into the ground.
NAPL is often separated from groundwater using a particular type of pump and treat scheme. Sometimes NAPL can be recovered directly from the ground without the requirement to pump groundwater when quantities are significant. Heat or surfactants can also be applied to enhance the recovery of NAPL. Recovered NAPL is then stored onsite before recycling at a licensed facility.
SOIL VAPOUR EXTRACTION (SVE)
Hydrocarbon vapours are extracted from the vadose zone using a vacuum system connected to extraction wells. The extracted air containing the hydrocarbon vapours is treated before being safely discharged to atmosphere.
DUAL / MULTI PHASE EXTRACTION (DPE/MPE)
This involves the combined extraction of liquids (groundwater and NAPL) and vapour, a combination of the above three techniques. Vapour and liquid can either be extracted together under a vacuum (DPE) or separately using submersible pumps for the liquids and vacuum for the vapours (MPE).
AIR SPARGING / BIO VENTING
Pressurised air or oxygen is injected into the groundwater. Air enhances partitioning of volatile contaminants out of the groundwater for collection via SVE, whilst oxygen stimulates the native soil micro-organisms which break down contaminants into harmless compounds via bioremediation.
The choice and design of a process based remediation system will depend largely on the site conditions, the contaminants, and the remediation objectives. As part of the design process, our multidisciplinary team will factor in relevant aspects: from the hydrogeology, borehole drilling and well design, to the choice of pump, the size of oil separation vessels, the health and safety aspects, or the type chemical treatment. Once in place, our systems are designed to run around the clock, in a largely automated manner and require only minimal supervision.
ERS has designed and operated process remediation systems at all scales. Our experience ranges from low-budget, single well, pump on demand skimmer systems for localised oil spills, to complex automated systems with the addition of bacteria and nutrients in re-circulated groundwater to promote bioremediation of residual contamination.
If you’d like to find out whether a process based remediation scheme may be suitable for your site, contact us today to speak to one of our experts.