Site Event/Activity record ECH6160 - North Dee 2D Seismic Survey Area, Cheshire: Appraisal Study of Heritage Assets of Archaeological Interest

Report summarising the results of an appraisal of heritage assets of archaeological interest within the North Dee area of 2D seismic survey, undertaken for TESLA International Exploration Ltd on behalf of Igas Energy plc. The study was primarilly undertaken during September and October 2014 and the data acquisition in October and November 2014. The survey area, which totals approximately 140km², is located within the Department of Energy and Climate Change licence areas PL189 and PL190 to the south of the River Mersey and Runcorn. It includes Ellesmere Port to the north-west and Chester and the River Dee to the south-west (although Chester itself was largely excluded from the survey area). The purpose of the study was to identify the presence of recorded heritage assets of archaeological interest and to advise on mitigation measures necessary to ensure that no damage was caused as a result of the survey, in particular damage from vehicles, drilling of boreholes for shot points, the affect of vibroseis tractors on structures (especially the low frequency start of a vibration sweep), the detonation of shot points and the effect of low frequency or blast shock waves. As part of the mitigation strategy no source points were located within the extent, or close to, any scheduled monuments. Data acquisition was largely achieved using up to two vibrator tractor units (vibroseis) operating in convoy along road, track or cross country source traverses with individual source point locations being a theorectical distance of 20m apart. Where this was not possible, source generation was based on using an explosive seismic charge which required individual shot points drilled to a depth of some 6m. Drilling of shot points was undertaken using ar rotary drill mounted on a small agricultural tractor or an auger unit mounted on an all-terrain vehicle for areas with restricted access. Receiver stations were also positioned at 20m intervals along the survey lines, with each station consisting of a temporary surface positioned stand-alone Hawk recording node with attached external battery linked to a string of conventional seismic geophones lightly healed into the ground to a depth of circa 6cm. (1)