MACKAY’S CROSSING UXO SURVEY AND INVESTIGATIONS

SARAH HALLIDAY AECOM CONTAMINATED LAND ADVISOR TO LHJV FOR TRANSMISSION GULLY

MIKE SKIFFINGTON MIExpE MILSEARCH

• Sarah Halliday (AECOM) & Mike Skiffington (Milsearch)

• UXO Survey and Removal, MacKay’s Crossing,

Paekakariki, March 2015

• Sarah: Context, requirements to do the work etc,

• Mike: Methodology, execution, findings

INTRODUCTION

The Site is at the northern extent of the alignment for the

Transmission Gully alignment, adjacent to the current SH1

– the area as a whole is referred to as MacKay’s Crossing

SETTING

Paekakariki

The Site is located between the former Camps MacKay

and Russell – WW2 US Marine training camps.

SETTING

Paekakariki

Camp MacKay (landward of SH1)

Camp Russell (seaward of NIMT)

• PSI completed in 2011 (Aurecon), including an initial

geophysical survey identifying potential anomalies

• No soil sampling completed

• PSI (incl geophysical survey report) used to support

application for NES consent for soil disturbance during

construction in 2013 (Golder)

• NES consent granted with following conditions:

PREVIOUS WORKS

‘Prior to work commencing, a clean up operation shall be undertaken for the

removal of unexploded ordinance (UXO) at the site. A comprehensive UXO

detection shall be made by a suitable qualified UXO professional(s) to identify

specific targets for excavation and flag them in the site for subsequent

removal. The suitably qualified UXO professional shall sign-off the area when it

is free from UXO’

Note: Removal and disposal of UXO shall be carried out in coordination with

NZ Police and NZDF.

‘A Detailed Site Investigation shall take place after the area is signed off as

free from UXO and before any soil disturbance has taken place. The DSI and

reporting must be in accordance with Clause 3 of the NES. The investigation

shall include site sampling and lab analysis appropriate to the historical

activities identified in the [Aurecon PSI report]’. (abridged).

NES CONSENT CONDITIONS

• Approached Milsearch and asked them to review the

consent condition requiring the UXO clearance and

advise if workable – Yes……with limitations.

• Decision to proceed with UXO detection and removal as

specified by consent condition.

• This is where Mike comes in……

ENTER MILSEARCH

SITE

• 5 hectare site

• Adjacent to

SH1

• Divided into 3

areas for

survey and

investigation

AREA 1

• Former State Highway 1

• Tarsealed

• Bounded by

• Swamp

• Current SH 1

AREA 2

• Mown grass with some

sealed area

• Underground Services

• High Pressure Gas line

• Fibre Optic Cable

• Close to Former Camp

MacKay Site

AREA 2

• Substantially disturbed

during 2006 SH 1

construction works

• Used for stockpiling

roading material

• Evidence of re-levelling

on completion of those

works

AREA 3

• Paddocks

• Underlying peat soil

• Eastern edge disturbed

during 2006 works

SELECTION OF TARGET

• EO within this Site most

likely to have been

dropped or discarded

• Minimum Targets:

• Grenade Hand

Fragmentation Mk 2

• Projectile 37mm

• Target Depth: 0.3m BGL

SELECTION OF SURVEY TECHNOLOGY

ELECTROMAGNETIC SURVEY

• Areas 1 & 2

• Selected due to;

• Less susceptible to

influence from

services/fences

• Potentially magnetic metal

chip seal

• Geonics EM61 Mk 2 High

Power

MAGNETIC SURVEY

• Area 3

• Underlying peat potentially

conductive reducing

effectiveness of EM

• Geometrics G858

Magentometer

• Dual Sensor

SITE PREPARATION

• Vegetation Slashing

• Tree Removal

• Fence Removal

EQUIPMENT CALIBRATION

• Targets

buried at

0.3m BGL

• Tests equipment

function

• Interpretation

threshold

• GPS offset

INTERPRETATION

• Area 1 – 376 anomalies

• Area 2 – 649 anomalies

• Area 3 – 569 anomalies

INTERPRETATION REPORTS

• Site divided in to

Blocks

• Documentation

• Geophysical

Plots

• Interpretation/

Investigation

Report (Dig-

Sheet)

• GPS file

INVESTIGATION

• Area 1 – 20%

Assessment

• Area 2 – 100%

Remediation & 20%

Assessment

• Area 3 – 20%

Assessment

INVESTIGATION METHOD

• Anomalies relocated with

HPGPS

• Each anomaly

investigated with metal

detector or magnetometer

• Mechanical Plant used for

large and deep anomalies

AREA 1 FINDS

• Primarily related to

road infrastructure

and refuse 31%

12%

7% 7%

6%

3%

34% Wire

Road Infrastructure

Star Picket

Refuse

Bolts

Car Parts

Other Scrap

AREA 3 FINDS

• Mixture of

agricultural and rail

waste

2%

40%

9% 4% 3%

9%

7%

26% Geology

Wire

Rail RelatedScrapHand Tools

Star Pickets

Pipe

Bolts

Other Scrap

AREA 2 FINDS

• Mixture of;

• Recent refuse

from 2006 works

near surface

• Historic

infrastructure @ >

0.3m BGL

0.19% 1%

26%

1%

10%

2% 5%

3% 8% 2%

42%

EO

SAA

Wire

Site Infrastructure

Pipe - old

Star Picket

Rail related scrap

Construction relatedanomaliesNail

Bolt

Other Scrap

AREA 2 EO FIND

• Grenade Fragmentation

• Found amongst road chip

remnant from 2006 works

• Likely to have been moved

within the area during the 2006

works

AREA 2 EO & SAA FINDS

AREA 2 FINDS

• Potential ACM lined pipe

• Set aside and reported to

URS

• Tested and found to be

negative

CONCLUSION • UXO Survey and Investigation Operations require;

• Understanding the site history

• Identifying the target ordnance

• Determining its source/delivery – dropped, buried, fired

• Identifying the site conditions

• Selecting the appropriate technology for the target and the site

• A contaminated site remains contaminated until

assessed or remediated