Detailed Unexploded Ordnance (UXO) Risk Assessment Project Name Bridle Lane, Downham Market Client RSK Site Address Bridle Lane, Downham Market, PE38 9QY Report Reference DA11353-00 Date 16/06/2020 Originator CJ Find us on Twitter and Facebook st 1 Line Defence Limited Company No: 7717863 VAT No: 128 8833 79 Unit 3, Maple Park, Essex Road, Hoddesdon, Herts. EN11 0EX www.1stlinedefence.co.uk Tel: +44 (0)1992 245 020 [email protected] Detailed Unexploded Ordnance Risk Assessment Bridle Lane, Downham Market RSK Executive Summary Site Location The site is located on the outskirts of Downham Market, in the west of the county of Norfolk, East Anglia. The site is comprised entirely of undeveloped agricultural land. The site is bordered to the north by undeveloped agricultural land, to the east by a small hard-ground pathway, to the south by foliage adjacent to agricultural land, and Bridle Lane and residential property, and to the west by Low Road The site is approximately centred on the OS grid reference: TF 62293 04235 Proposed Works The proposed project is understood to comprise the development of a new housing estate and associated infrastructure, such as roadways and access ways. At the time of writing no imminent works are understood to be planned. Geology and Bomb Penetration Depth Site specific geotechnical information was not available to 1st Line Defence at the time of the production of this report. An assessment of maximum bomb penetration depth can be made once such data becomes available, or by a UXO specialist during on-site support. It should be noted that the maximum depth that a bomb could reach may vary across a site and will be largely dependent on the specific underlying geological strata and its density. UXO Risk Assessment Taking into consideration the findings of this study, based on factors such as potential UXO contamination, the likelihood of UXO remaining, the risk of encountering UXO during the proposed works, and the UXO that UXO may be initiated, 1st Line Defence has assessed that there is a Medium Risk from Allied military ordnance at the site of proposed works. The risk from German aerial-delivered ordnance (including both larger HE bombs and S.D.2 anti-personal ‘butterfly bombs’) has been assessed as Low-Medium The Risk from Allied Ordnance At the outbreak of WWII, the entire site comprised undeveloped agricultural land. However, in 1942, during the mid- war period, the eastern area of the site was requisitioned for the development of airfield structures, as part of the development of RAF Downham Market. RAF Downham Market was opened in the summer of 1942, and was utilised extensively by bomber aircraft. First occupied by the No.218 Squadrons, and later by the No.635 and No.68 squadrons of Pathfinder Force, numerous bombing missions operated out of the Downham Market airfield across the remaining period of the war. A WWII-era Air Ministry Site Plan shows the proposed site boundary encompassed a section of the western part of RAF Downham. Within this section were two T2 hangar structures, one dispersal pan and another dispersal pan partially included within the north-east of the site. The presence of these structures within the site boundary raises the risk of on-site UXO contamination. This is because temporary ordnance stores were frequently located at the sites of structures such as dispersal pans to rearm and resupply aircraft. This plan also shows the airfield perimeter to intersect the middle of the site and for the western section of the site to have remained occupied by open agricultural land. The position of the site area on and next to the former airfield is also considered to elevate the risk of UXO contamination, due to the potential for training and defence exercises to have taken place within the area. Details of such activities are however limited due to the current restriction of availability of RAF Log Books. At least one major aircraft crash involving a Stirling heavy bomber is recorded to have occurred within close proximity to, if not within, the site boundary. Evidence of this crash is documented in two Operational Record Books (See 11.6). Corroborating this evidence is information obtained from the Norfolk Heritage Explorer web tool, which details that in 2010 a “large amount of aircraft debris” was recovered from an area of land within which the eastern section of the site boundary is included within. Although efforts would have been made by military personal to clear this crash site, including any ordnance previously stored on board, such efforts were note always comprehensive and the risk of UXO contamination in the surrounding area as a result of this incident cannot be discounted. In summary, no evidence could be found to suggest that any former airfield features specially designated for the storage or usage of ordnance, such as the bomb stores or firing ranges were situated within the site boundary. However the risk from Allied UXO is still considered to be elevated on site in comparison to the ‘background level’ for the region, as Report Reference: D11353-00 II © 1st Line Defence Limited www.1stlinedefence.co.uk Detailed Unexploded Ordnance Risk Assessment Bridle Lane, Downham Market RSK UXO Risk Assessment result of the conditions outlined above; including its position within the airfield, the presence of dispersal pans, the presence of a historic bomber crash site and the potential for live training to have occurred in the area. Furthermore, no clear perimeter fence could be identified on site within the available WWII-era imagery, so it has not been possible to discount that such activities would have equally effected the western section of the site, situated outside the airfield’s official boundary. The Risk from German Aerial Delivered Ordnance • During WWII, the site was located within the Rural District of Downham. According to Home Office statistics Downham sustained an overall low density of bombing, with an average of 5.2 items of ordnance recorded per 1,000 acres of land. Despite this low density bombing campaign, it is likely that a high proportion of the ordnance deployed in the district was targeted at airfields. Although RAF Downham was built after the main period of bombing in the region. • At least one air raid is documented at RAF Downham, although this appears to have resulted in relatively little damage to the operation of the airfield. Local Air Raid Damage Files record one 250kg and two 50kg HE bomb strikes within “Downham Market Aerodrome”, as well as the dropping of five canisters of S.D.2’s (anti-personal ‘butterfly bombs’) . The locations of these bomb strikes are recorded as in the vicinity of the control tower and west of “No.4 runway”, the exact proximity from the site of which is unknown. In any case, the associated written report suggests the vast majority of these bomb strikes were account for and dealt with. • Post-war aerial photography of a low quality shows a potentially damaged area in the form of clearance located in the eastern section of the site. However, this cleared hanger is considered more likely to result from the demolition of the airfield following its closure, as no evidence could be found to support the presence of bomb damage at this structure. • The remainder of the site comprises undeveloped open ground, on which no obvious signs of bomb damage such as craters and disturbed ground can be observed—although the low quality of the image inhibits an accurate analysis. • Ground cover across much of the site also varied across time, and in condition. Before the construction of RAF Downham Market, the ground cover was broadly not considered to have been favourable to the detection of UXO. • Following the construction of RAF Downham Market, the ground cover is not considered to have been homogenous across the site. The western section of the site—comprising undeveloped open ground—is considered to still have ground cover unconducive to the detection of UXO. Although the risk is considered to be reduced by the low density of bombing in the region. a Signs of UXO are more likely to be noticed near the hangers and access ways. Subsequently as RAF Downham Market is known to have been targeted by German bombing on at least one occasion but no specific reference could be found to the site, the risk from German UXO has been slightly elevated to low- medium. Post-War Redevelopment The site has sustained limited redevelopment post-war. In 1952, RAF Downham Market was closed and the land sold off for farming use. Virtually all structures within the perimeter of the airfield—including the two hangar and two dispersal pan structures within the site boundary—were cleared and replaced by agricultural land. Current satellite imagery indicates that the site has remained agricultural land since. The risk of UXO remaining, especially shallow buried items such as German S.D.2 bombs, German incendiary bombs and Allied LSA/SAA, is considered to be mitigated at the location of post-war excavations and developments. This mitigation of risk will apply at the location of and down to the depths of such post-war developments. The risk from deep-buried unexploded bombs is only considered mitigated at locations where post war piling or deep foundations have taken place. Recommended Risk Mitigation Measures The following risk mitigation measures are recommended to support the proposed works at the Bridle Lane, Downham Market site: All Works UXO Risk Management Plan Site Specific UXO Awareness Briefings to all personnel conducting intrusive works. Open Intrusive Works (trial pits, service pits, open excavations, shallow foundations etc.) Non-Intrusive UXO Magnetometer Survey and Target Investigation.