Groundwater Treatment
Pump and Treat
Water treatment plants are capable of removing free product, dissolved phase organic compounds and certain inorganic materials.
HBR is able to design, fabricate and maintain treatment plants capable of remediating perched water or groundwater to standards suitable for disposal to foul or surface water sewer by incorporating a variety of filters and oxygenation systems.
Groundwater remediation can be carried out via an ex-situ arrangement within a pump and treat system or in-situ by the introduction of injection and extraction pipe work to promote biodegradation.
The design of the system incorporates telemetry to allow routine maintenance and efficiency to be monitored from off site.
Soil Vapour Extraction (SVE)
An
in situ technique designed to physically remove volatile and semi-volatile organic contaminants (VOC's, SVOC's) from the unsaturated sub-soils, by applying a vacuum to a system of wells across the impacted zone. Air is drawn through the soil enhancing volatilisation of contaminants from the soil pores, with vapour treatment carried out at the surface with granulated activated carbon (GAC) units. A low permeability membrane can be placed across the area to prevent short circuiting.
HBR often combine SVE with other techniques such as dual phase extraction (multiphase extraction), air sparging and bioventing. The volatilisation of substance from aqueous solution is governed by its Henry's Law constant, therefore, we are able to assess the suitability of the approach for specific contaminants. Generally, however, most VOC's and SVOC's can be removed and treated including:
- Benzene, Toluene, Ethyl Benzene, Xylenes (BTEX)
- Petroleum and diesel range hydrocarbons
- Chlorinated solvents
Air Sparging (AS)
This approach involves the injection of compressed air into the saturated zone below the groundwater table, in order to promote volatilisation of dissolved contaminants into the unsaturated zone. Volatiles are also stripped in the immediate area of the sparge point. SVE can then be used, as detailed above, to remove the contaminants. The increased oxygen content also enhances natural aerobic biodegradation and chemical oxidation.
Multiphase Extraction (MPE)
This is a well used common approach, combining the removal of dissolved phase contaminants in groundwater in the saturated zone, together with vapour in the unsaturated zone by vacuum (slurping) also known as vacuum enhanced recovery (VER) and non-aqueous phase liquid (NAPL) or free phase product, from recovery well points. The associated drawdown of the water table towards the well by dewatering creates a cone of depression, which enhances recovery of vapours by from the originally saturated smear zone.
The application of high vacuum can also aid the recovery of NAPL and water from fine grained soils, with induced air flow through the contaminated zone helping to promote aerobic biodegradation.
LNAPL is recovered by skimmer units as it flows towards the recovery point, with oil/water separators used at the surface to separate out the water. Product removal is important when considering remedial design, as it can act as a secondary source of contamination on a site and its recovery can account for a significant amount of contaminant mass reduction. Product recovery can be enhanced by Sufactant / cosolvent flushing. This method involves the injection and subsequent extraction of either biodegradable detergent or solvent into the saturated zone, within target areas to solubilise and/or mobilise DNAPLs. This would provide greater recovery than would be achieved using abstraction wells and excavation sumps. Extracted DNAPL can then be disposed off site or can go for recycling at special facilities.
The vapour extracted is generally treated by stripping GAC units, with dissolved phased contaminants in water treated on site using a variety of physical, chemical and biological techniques, prior to disposal to foul sewer or recirculation into the site via infiltration trenching, depending on the quality required.
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