Unexploded Ordnance on Auckland s Doorstep. WasteMINZ November 2017

Transcription

1 Unexploded Ordnance on Auckland s Doorstep WasteMINZ November 2017

2 Scope Site Background. Site Assessment. Geophysical Survey. Investigation. Findings. Challenges. Key Points.

3 Weiti Bay Site Access Road leading to subdivision site. Will form part of the Penlink Designation. Currently active beef farmland. Transected by an existing farm access road. Sloping hillsides with swamps and streams in low lying areas. East Coast Road at the western end of the site.

4 Site History Used by NZ and US forces as a live fire training area between Used on a permission basis, i.e. not Defence Land. Records indicate use as a Grenade and Mortar Range. Also possibly aerial bombing.

5 Site History Defence attempted some clearance works in Compensation was paid to the then land owner. NZDF responded to UXO in UXO listed as a site hazard on the farm Health and Safety Plan. NZDF response to OIA request stated they had no record of the site, other than the 2006 UXO response.

6 Initial Works Provide UXO Awareness Induction. UXO Safeguarding of Geotechnical Investigations. UXO Contamination Assessment.

7 UXO Contamination Assessment 10% Assessment of 18ha. Completed by 1 man over 4 days. Equipped with metal detector, digging tool and Garmin GPS. All items of interest were logged on GPS.

8 UXO Contamination Assessment Grenade Components; No. 36M. Mortar Components; 2inch. 81mm. Small Arms Ammunition.

9 UXO Contamination Assessment Located 126 items of Explosive Ordnance Waste and Small Arms Ammunition. Delineated 10ha requiring UXO Remediation Works.

10 Site Preparation Survey and Clear new boundary fence alignment. Removal of internal farm fences. Removal of all livestock. Felling and removal of trees. Erection of new boundary fence.

11 Geophysical Survey Selection of Technology; Electro-Magnetic. Magnetic.

12 Geophysical Survey - Selection of Technology Technology Advantages Disadvantages Electromagnetic systems Metal Detectors; Detect both ferrous and nonferrous metals Less sensitive than magnetometer to naturally occurring geological influences Provides very good definition of anomalies Detection is less affected by large metallic features adjacent to survey areas e.g. fences Lesser detection depth than magnetometer though can be more sensitive to shallow targets depth penetration being dependent on coil size. Relatively heavy requires larger power output therefore necessitating large batteries Quantitative data such as depth of the anomaly is difficult to determine without extremely expensive multi-channel multi component equipment. Slower survey rate generally leading to higher cost

13 Geophysical Survey - Selection of Technology Technology Advantages Disadvantages Magnetic systems Magnetometers; Relatively lightweight Can detect small ferrous items at greater depths than metal detection in benign conditions Faster survey rate, easier to configure with multiple sensors therefore covering a greater swathe each pass. Survey data will provide indicative anomaly depths. Affected by naturally occurring geology which can preclude its use in areas with naturally occurring magnetic influences e.g. volcanic rock or laterite. The magnetic influence from adjacent metallic feature will be detected at greater distances than that of metal detector. These features can potentially obscure adjacent subsurface anomalies. Adjacent items will interfere making the depth and mass calculations less useful in more contaminated sites Tends to be more affected by electrical interference like fences and power lines

14 Geophysical Survey - Specification Specification determined by calculated penetration depth, based on; ordnance weight, muzzle velocity, soil characteristics. Locate metal objects with the magnetic characteristics of; 81mm 1m. 2in 0.3m. Grenade 0.3m. Test samples obtained and a calibration survey completed.

15 Geophysical Survey - Execution Site was divided into 50 m grid system. Completed using a quad sensor magnetometer integrated with RTK GPS. Initial survey works were completed by a 3 man team in 4 days. Additional 3 days of follow-up works for additional areas and resurvey.

16 Geophysical Data Interpretation Coverage of 11.36ha anomalies identified for investigation. Road areas were unable to be interpreted due to magnetic road gravel. Road areas were scraped in a follow up mobilization and resurveyed.

17 Geophysical Anomaly Investigation Completed by 2-3 man team over 12 days. Anomalies positioned with HPGPS. Investigation team utilized magnetometer to detect anomaly. Confirmed identification entered on Dig Sheet.

18 Quality Control Geophysicist Data Review during survey Gaps in Data. Data quality; GPS and magnetometer. Review of Investigation Reports Identify anomalies inconsistent with interpreted amplitude. Review geophysical data to identify additional anomalies for investigation.

19 Investigation Results

20 Unexploded Ordnance Finds 3 x 81mm Mortar Bombs. 3 x 60mm Mortar Bombs. 5 x 2inch Mortar Bombs. 1 x No36M Hand Grenade. All were destroyed by NZDF in situ

21 Unexploded Ordnance Distribution

22 UXO/EOW Density Modelling 10% Assessment 100% Investigation

23 White Phosphorus EOW from 81mm WP mortar bombs had remnant White Phosphorus attached. Spontaneously combusted on being exposed (after 75 years in the ground).

24 Challenges Weather. Working on operational farm land. Active roads. Road seal. Phasing of works. Understanding of the site. Land use subsequent to range closure.

25 Postscript Mortar UXO found by construction workers outside the area assessed or remediated. Adjacent to East Coast Road. Additional 0.25ha surveyed and investigated - no finds of EOW or UXO. Potentially moved to that location during previous road works or farming activities.

26 Key Elements Understanding of the site history and conditions. Selection of appropriate methodology and technology. Communication and coordination.

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28 Map 1940 s

29 Map 1940 s 2016 works area overlain

30 Current Aerial 1940 s boundaries overlain

31 81mm Mortar M m Munitions Maximum Ranges from find locations Rifle Grenade 180m 60mm Mortar M m 2inch Mortar 600m

32 18 Pounder Gun 8.5km Munitions Maximum Ranges 81mm Mortar 60mm Mortar 2inch Mortar Rifle Grenade