Harworth Colliery / Parcel 1 and Infrastructure

The Harworth Coking Works project involved:

• Chemical and geo-technical pre-classification of the soils with extensive site investigation on a grid system
• Removal of a large bund surrounding half of the site
• Break out of concrete hard standings followed by processing and crushing to produce useable product (Type 1 / 6F2) in the development
• Turnover and compaction of made ground to create an engineered development platform
• Targeted excavation of hotspots and treatment or offsite removal of hydrocarbon contamination within soils
• Decommissioning of a deep borehole
• Groundwater treatment of LNAPL at 28mbgl by in- situ pump and treat

The 7 Ha site was turned over to 2.5m with further excavation to 5m should contamination or foundations be present. Relic foundations were removed and reprocessed into 6F2 and Type 1 to be used in the earthworks platform and retained on site for use in the future development. Extensive hydrocarbon contamination was identified in soils across site with ex-situ bioremediation used to treat 5221m3 of contaminated soil. Upon completion of the bioremediation treated soils were validated to confirm compliance to site target levels and reused at depth within the soil platform.

Grossly contaminated soils that were unable to be treated on site were sent to offsite treatment centers or licensed landfill facilities. A 200mm low permeability cap was installed across the surface of the site following completion of the turnover for the purpose of reducing infiltration.

VHE completed the validation reports for the project for regulatory sign off.

Following the earthworks, infrastructure works was undertaken to serve the future housing developments.

The infrastructure works associated with the previously remediated Parcel 1 site were undertaken by VHE to enable the commencement of further development.

VHE constructed 0.5km of highway to adoptable standards under a Section 38 agreement, which was administered and overseen by Via EM on behalf of Nottinghamshire County Council. VHE also completed all the associated foul and storm water drainage installations to adoptable standards under Section 104 and Section 185 agreements with Severn Trent Water.

Key elements undertaken and completed include:

• Earthworks to form the highway and associated verges.
• Road and footway construction inclusive of asphalt layers, paving and decorative features.
• Storm water drainage system, inclusive of a large contractor designed headwall outfall to an existing water body under a Section 104 agreement.
• Foul drainage system, inclusive of the connection top and the diversion of the existing foul drainage services under a Section 185 agreement as described above and the installation of the developments new foul drainage including a pumping main and pumping station under the Section 104 agreement described previously
• Street lighting, traffic signs, street furniture and fencing installation.
• Soft landscaping and seeding works.
• Installation and coordination of multiple utility services and apparatus that will serve the future development including electric cables (both high and low voltage), gas main, water main, telecommunications ducting and chambers.
• Construction of the substation from the foundations up to and including the roof structure, installed on the periphery of the site on behalf of Northern Power Grid and GTC Utilities.

VHE faced challenges during the contract which saw us aid both the client and the designer to reach practical and viable solutions. These included locating existing HV cables where accurate historic plans did not exist, using vacuum excavation to enable the designer to finalise the position of the pumping station, the substation and drainage pipework alignments. In addition VHE met the challenge of coordinating and facilitating the works and requirements of the multiple utility companies to ensure timescales and key dates associated with the construction programme and the client’s contractual commitments to various house builders were met.

VHE continued to employ value engineering techniques and policy throughout the contract. Coal tar bound asphalt was temporarily stored on site which was associated with the remediation of the adjacent Coking Works. VHE proposed that this material could be cement stabilised and reused as sub-base material within a section of the permanent works, thus encapsulating any potential for contaminants to leach. This value engineering strategy made it a viable and cost effective product for re-use within the permanent works, prevented the material from being disposed of to landfill and reduced the import required to site.