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FAQs - Construction Activities

Article Index

Page 4 of 6

DoWCoP FAQs - Construction Activities

Does placing of material beneath cover layers amount to discarding of waste?
Material placed beneath buildings and hard standing such as car parks and roads within the land being developed is not waste, if the material is demonstrated to be non-waste by evidence of suitability for use and the works are carried out in accordance with the requirements of the CoP. Where there is any dispute regarding the use of material in this way then readers are referred to the Environment Agency guidance “Defining Waste Recovery: Permanent Deposit of Waste on Land”.
Is material a waste if it is placed in or on the ground and has to be contained to prevent harm to human health or the environment?
Where excavated material is not suitable for the proposed use it will be waste and hence the CoP will not be applicable. For example if the material has to be placed in an engineered cell and managed to prevent harm to human health or pollution of the environment then this would be viewed as having been discarded as waste. This will be a landfill and require an environmental permit. There is a distinction between this scenario and that relating to cover layers above.
Why does the Code of Practice make no distinction between contaminated and uncontaminated material?
The need to distinguish between “contaminated” and “uncontaminated” soils is no longer considered necessary. These are self-defining terms on a site specific basis having regard to the risk assessment, e.g. some soil may not be considered contaminated for a given land use, but would be for a more sensitive land use, on the same site.
Is recovered aggregate a waste if it is produced in accordance with the WRAP "Quality Protocol for the production of aggregates from inert waste"?
No it is not likely to be waste. Typical uses of recovered aggregate include pipe bedding and selected backfill to sewer excavations; carriageway sub-base construction; and the construction of vertical, granular filled drains to aid consolidation of compressible clays.
Is the installation of a barrier to prevent groundwater movement or contain contaminants a waste activity?
Bentonite slurry cut-off walls: Bentonite / cement slurries are used to construct vertical barriers in the ground to prevent groundwater movement or to contain contaminants. Depending upon the site-specific circumstances, this would either not require an Environmental permit or may comply with the EA Enforcement Prosecution Policy Functional Guidelines. Reference should be made to the EA Remediation Position Statement Guidance for details.
Are soil improvement techniques treatment activities and do they require a permit?

Construction activities carried out on uncontaminated soils solely for the purpose of improving geotechnical properties are not generally regarded as waste treatment operations and do not require a permit. These include:

  • Lime/Cement Stabilisation: Stabilisation of soils with high moisture content to improve their compaction characteristics by mixing with lime cement or cement only. If the lime is considered to be a waste material, or if the treatment is required specifically to recover a discarded material this may need to be reconsidered.
  • Vibro Compaction: Vibratory techniques to improve the bearing capacity of weak soils (often made ground). These techniques use a vibratory poker that is lowered into the ground under its own weight. In most cases, stone is introduced into the ground either down the centre of the poker or into the hole when the poker is removed. The poker applies further compactive effort until adequate resistance is achieved. The combined effects of the vibration and the introduction of the stone result in an increase in the density of the soil and a consequent improvement in bearing capacity. This activity must be carried out in accordance with requirements of the EA published guidance "Piling and Penetrative Ground Improvement Methods on Land Affected by contamination: Guidance on Pollution Prevention. NC/99/73".
  • Dynamic Compaction: This technique involves dropping a heavy weight from considerable height to compact weak soils (often made ground). A series of ‘footprints’ are formed which are subsequently filled with granular fill. This may either be a primary aggregate or a recycled material. Dynamic compaction is not a waste treatment activity (unless it is being done on a landfill site for example) and any risk to controlled waters must be addressed during the assessment of the Planning permission.
  • Surcharging: This technique involves placing soils in a mound to compress weak soils thus reducing future settlement potential. If the material used for the surcharging is generated and then reused (in line with the CoP) on the site it should not require a WFD permit or Exemption. However, if the material is to be imported or exported from the site after use there may be requirements for waste permitting.
  • Piling: There are various forms of piling which are used to transfer structural loads through weak soils to more competent materials at depth. These range from driven displacement, bored and continuous flight auger bored piles. A WFD permit will not be required for this activity. The piling activity must be carried out in accordance with requirements of the EA published guidance "Piling and Penetrative ground Improvement Methods on Land Affected by contamination: Guidance on Pollution Prevention. NC/99/73".
  • Soil Reinforcement: This technique involves the introduction of geotextiles or ‘geogrids’ to layers of soil (often made ground) to improve load distribution and bearing capacity. This technique is also often applied to improve the slope stability of soils to facilitate construction of steep sided embankments. A variation, to improve the stability of cuttings, is the use of ‘soil nailing’ whereby rods are ‘fired’ into the ground at regular intervals.
  • Reinforced Concrete Raft Foundations: This is a common foundation solution used on weak or potentially expansive soils. Certain ground conditions, in particular expansive clay soils require the foundation to be constructed on a bed of compacted granular material made from primary aggregate.

Does de-watering of an excavation require a permit?

The removal of more than or equal to 20m3 /day water may require the granting of an Abstraction Licence under the Water Resources Act 1990. However, the current Environment Agency position is not to require a permit for pumping water that has gathered in an excavation if the water is to be disposed of solely to prevent interference with building operations. Any changes to this position will be publicized via the EA or DEFRA websites.

Dewatering of excavations: Where extractions have to penetrate below standing groundwater levels, dewatering will be required. A number of techniques ranging from sump pumping, to the use of external well points or deep wells can be used. Discharge of the pumped water may require a permit but the activity does not fall within the remit of the WFD.

Infiltration Drainage: Sustainable urban drainage solutions (SUDS) often call for infiltration of collected surface water to maintain surface water discharges from a developed site as closely as possible to the rates prior to development. This can occur on greenfield and brownfield sites, although we would not encourage this on contaminated sites. Discharge consents may be required but these activities do not fall within the WFD.