Geophysical Magnetometry Survey at Wantage Clean Water Growth Project, Oxfordshire

The survey was undertaken using four Bartington Grad601 sensors mounted at 1m intervals onto a rigid carrying frame. The system was programmed to take readings at a frequency of 10Hz on roaming traverses (swaths) 1m apart. These readings were stored on an external weatherproof laptop and later downloaded for processing and interpretation. The system was linked to a Trimble R12 Real Time Kinetic (RTK) differential Global Positioning System (dGPS) outputting in NMEA mode to ensure a high positional accuracy for each data point. MLGrad601 and MultiGrad601 (Geomar Software Inc.) software was used to collect and export the data. Anomaly GeoSurvey v1.12.3 (Lichenstone Geoscience) and QGIS v.3.34.6 software was used to process and present the data respectively. Survey was successfully undertaken across all parts of the proposed pipeline route options. The data has recorded a focus of archaeological activity east of Letcombe Brook and three ditch-like anomalies of possible archaeological potential east of Cow Lane, both areas that were previously highlighted for their archaeological potential by earlier trial trench evaluations and from cropmarks. The survey has therefore corroborated and also expanded upon the understanding of the nature and extent of the archaeology revealed during the previous evaluations. Those evaluations recorded several small settlement clusters surrounded by paddocks and enclosures, dated to the Romano-British period. The survey has confirmed that these features extend east to Letcombe Brook and that there was a regular enclosure pattern aligned broadly north-northeast to south-southwest that spans the area covered by both Route Option corridors. Though the magnetic responses are less clear in the northern part of the survey area east of Letcombe Brook (Route Option 2), a concentration of discrete responses, at least two of which are indicative of localised burning, strongly indicate the presence of further archaeological activity in line with the findings of the previous trenching evaluation. The survey has not recorded any clear continuation of these features west of Letcombe Brook and no anomalies of clear archaeological potential have been recorded further east of this focus of activity towards the A338, a former Roman road, despite multiple pits and gullies containing medieval pottery being recorded here in previous trench evaluations (Route Option 1). Three linear ditch-like anomalies are recorded in the north-west part of the survey corridor, immediately east of Cow Lane in the vicinity of pits, gulleys and a possible field system visible as cropmarks and also recorded during previous trial trench evaluations. Outside of these two areas the survey findings are limited to a vague linear arrangement of discrete responses, likely recording an infilled watercourse or leat linked to a Mill Pond north of the survey area that is depicted on historic mapping, and two discrete responses of uncertain origin located adjacent to the former Roman road. The detection of a range of anomalies, including those of probable and possible archaeological origin in locations previously highlighted as having archaeological potential, indicates that there was sufficient magnetic contrast, for the detection of sub-surface archaeological features, notwithstanding the limitations of magnetometer survey to identify certain types, size and period of archaeological features, particularly over the generally unresponsive prevailing mudstone and clayey geology. To that end, past excavation results east of Letcombe Brook indicate that archaeological activity in this area was likely more concentrated than revealed by the magnetometer survey.