Contact Us

HBR Head Office
7 Appleton Court, Calder Park,
Wakefield, WF2 7AR

Telephone: 01924 250 132

Fax: 01924 251 394


Blackwell Southern Regional Office

Coggeshall Road, Earls Colne
Essex, CO6 2JX

Telephone: 01787 222768

Fax: 01787 224391

Blackwell Midlands and South West Regional Office
4 Bredon Court, Brockeridge Park,
Twyning, Gloucestershire
GL20 6FF

Telephone: 0844 482 9685

Blackwell Scottish Regional Office
Broken Cross,
Douglas Water,
ML11 9PB

Telephone: 01324 483713

HBR Certificates

In-situ Processes

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 surfactant / 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.

Chemical Oxidation

Oxidation processes can be used to transform organic contaminants into less toxic and less mobile forms, with complete reactions producing carbon dioxide and water. They are referred to as 'redox reactions',  as the oxidising agent gains electrons (reduced valence state-reduction) while the contaminant loses electrons (increased valence state-oxidation).  This electron exchange breaks carbon bonds creating new smaller compounds.  Oxidants can also be used for iron and chromium precipitation and the destruction of cyanides and sulphides.

The most commonly used oxidising agents are hydrogen peroxide (H2O2), sodium persulphate (S2O8) and potassium permanganate (KMnO4).  Many redox reactions require chemical additions, such as pH alterations, or the presence of catalysts (Fentons Reagent combines iron with hydrogen peroxide) to economically facilitate the required reaction. Therefore, for successful applications of oxidation techniques, an understanding of chemical kinetics and the thermodynamic potential of the reactions is essential.

A number of parameters can effect the redox reactions, such as soil organic matter, pH, existing redox conditions, nature and extent of contamination, and carbonate/bicarbonate concentrations.  Therefore, as an important part of the design process, HBR undertake laboratory treatability studies to establish optimum conditions the reactions to take place and the existing oxidant demand of the soils and groundwater.

HBR apply the process either in-situ, by introducing oxidants into the subsurface with gravity wells or injection methods or ex-situ by soil mixing or groundwater circulation systems.  For ex-situ soil applications, HBR's mixing plants incorporate feed systems, which are suitably resistant to the corrosive nature of oxidizing agents and capable of the control and collection of off-gasses produced during reactions.

Contaminants that can be typically treated include:

- petroleum, diesel, MTBE, BTEX

- chlorinated solvents

- pesticides and herbicides

- carbon disulphide

- polychlorinated byphenyls (PCB's)

- cyanides and sulphides