S EIMP.06.00.06M ANAGEMENT PLAN

ENVI

RONM

ENTA

L MAN

AGEM

ENT

SYST

EM

EIMP.06.00.06 SUBSIDENCE MANAGEMENT

PLAN ENVIRONMENTAL IMPACT MANAGEMENT PLAN

(EIMP)

APPROVAL Name Position Signature Date

Document Owner Dave Meyers Manager HSECT

SSE Andy Mifflin GM Operations

Revision 1

03/08/2021

03/08/2021

EIMP. SUBSIDENCE MANAGEMENT PLAN

Document Uncontrolled when Printed. Refer to SHMS Intranet for Controlled Version. Page 2 of 33

Contents Introduction .................................................................................................................................... 4

Scope ....................................................................................................................................... 4

Ensham Mine Overview .................................................................................................................. 6

Mining Activities...................................................................................................................... 6

Topography and Drainage ....................................................................................................... 6

Soils ......................................................................................................................................... 6

Geology ................................................................................................................................. 12

Groundwater Regime ............................................................................................................ 13

Land Use ................................................................................................................................ 13

Predicted Subsidence .................................................................................................................... 16

Introduction .......................................................................................................................... 16

Pillar Design ........................................................................................................................... 16

Compression Analysis ........................................................................................................... 17

Predicted Subsidence ............................................................................................................ 18

Surface and Subsurface Cracking .......................................................................................... 18

Subsidence Impacts .............................................................................................................. 18

Subsidence Monitoring ................................................................................................................. 18

Lidar Monitoring ................................................................................................................... 19

Real Time Monitoring ........................................................................................................... 23

Monitoring Surveys ............................................................................................................... 25

Underground Surveying ........................................................................................................ 27

Surface Inspections ............................................................................................................... 27

Groundwater Monitoring ...................................................................................................... 27

Monitoring Schedule and trigger levels ................................................................................ 30

Subsidence Management Measures ..................................................................................... 31

Legal Compliance and References ................................................................................................ 31

Terms and Abbreviations .............................................................................................................. 31

Abbreviation and Description ............................................................................................... 31

Review History .............................................................................................................................. 32



ROLES AND RESPONSIBILITIES ...................................................................................................... 32

Figures Figure 1-1. Mine Layout ......................................................................................................................... 5

Figure 2-1. Surface Topography and drainage ....................................................................................... 7

Figure 2-2. Soil Types ............................................................................................................................. 8

Figure 2-3. Conceptual Hydrogeological Model Cross Section (EIS Submission, 2021). ...................... 13

Figure 2-4. Land Uses at Ensham Mine (2021)..................................................................................... 15

Figure 3-1. Maximum Mining Height for a FoS of 1.6 .......................................................................... 17

Figure 4-1. Lidar transect across an area of unmined soil type 6.2. .................................................... 20

Figure 4-2. Lidar transect along an area of 502 panel with soil type 6.2 ............................................. 21

Figure 4-3. Lidar transect along an area of 114 panel with soil types 2.3, 4.2 & 5.2 ........................... 22

Figure 4-4. Expanded Lidar transect along an area of 114 panel ........................................................ 22

Figure 4-5. Fixed Monitoring Station. .................................................................................................. 23

Figure 4-6. Location of Remote Subsidence Monitoring – Ensham Underground Area. ..................... 24

Figure 4-7. Subsidence Monitoring above 500 Mains, 502 and 503 Panels. ....................................... 25

Figure 4-8. Monitoring Data – 500 Mains and 502 Panel Stations. ..................................................... 26

Figure 4-9. Monitoring Data – 114 Panel Stations (No mining as of July 2021). ................................. 26

Figure 4-10. Groundwater Monitoring Bores ...................................................................................... 29

Tables Table 2-1. Terrain Units and Soil Types .................................................................................................. 9

Table 2-2. Stratigraphy ......................................................................................................................... 12

Table 4-1. Monitoring Schedule ........................................................................................................... 30

Table 5-1. References ........................................................................................................................... 31

Table 6-1. Terms ................................................................................................................................... 31

Table 7-1. Review History .................................................................................................................... 32



INTRODUCTION Ensham Mine (EM) is an opencut / underground bord and pillar coal mine located approximately 35 km east of Emerald along the Nogoa River in Central Queensland. The mine is operated by Ensham Resources Pty Ltd (Ensham), a wholly owned subsidiary of Idemitsu Australia Resources Pty Ltd (Idemitsu), on behalf of the Ensham Mine joint venture (JV) partners. The JV partners, and holders of the Environmental Authority, are Bligh Coal Limited, Idemitsu Australia Resources Pty Ltd, and Bowen Investment (Australia) Pty Ltd. EA EPML00732813 (the EA), dated 3 September 2020, is the relevant environmental authority under which Ensham operates the mine (DES, 2020).

Ensham currently undertakes underground mining using continuous miner operations, while utilising the existing access and supporting infrastructure located within the current Mining Leases. The mine also produces coal from open cut pits using both dragline, and truck and shovel operations. Mining extracts a portion of the combined Aries/Castor seam plies, typically leaving the higher ash, uppermost plies in the roof the underground roadways.

It is proposed to extend the life of the existing underground bord and pillar operation into areas north, west and south of existing operations into existing granted mining leases (zones 2 and 3) and into ML 700061 (zone 1) when granted (refer Figure 1-1):

SCOPE This Plan addresses the monitoring and management of subsidence impacts from Ensham’s bord and pillar underground mining operation. This includes the triggers for investigation of potential subsidence impacts, guidance on surface inspections, groundwater monitoring, mitigation and management measures are also included, as well as guidelines for landowner consultation if required.

The Department of Environment and Science draft guideline – Watercourse Subsidence – Central Queensland Mining Industry, version 7 has also been referenced for guidance in the compilation of this Subsidence Management Plan (SMP).



FIGURE 1-1. MINE LAYOUT



ENSHAM MINE OVERVIEW

MINING ACTIVITIES The Ensham mine has been operating since 2011. The mine will continue to produce around 4.5million tonnes per annum of thermal coal with the addition of zones 1,2 and 3.

Coal from the underground mine is mined by five production units and transferred to the surface via the Ramp 4 drift conveyor.

TOPOGRAPHY AND DRAINAGE The terrain in the Ensham area is generally low-lying, and the few hills within the area are capped by a hard layer formed on the surface known as duricrusts (Figure 2-1). The main drainage of the area is via the Nogoa River, which flows in an easterly and south-easterly direction through the Ensham mining leases before joining the Comet River to form the Mackenzie River near the town of Comet (Figure 2-1).

In the Ensham area, the elevation of the Nogoa River banks average 150 metres above Australian Height Datum. The Nogoa River is used for irrigation, drinking water and stock water supply, with flow maintained by releases from Fairbairn Dam, located south of Emerald. Due to the supply of water from the Fairbairn Dam to downstream users, the Nogoa River flows essentially all year round. The anabranch however is ephemeral and flows generally following a significant rain event.

The low-lying area includes floodplains and riparian zones along the Nogoa River and an anabranch, which runs to the north of the Nogoa River.

SOILS The soils over the underground mine plan were mapped in 2006 and partially updated in 2021 (Figure 2-2 and described in more detail in Table 2-1). The different soils react differently to climatic conditions, which will affect the ability to detect any subsidence.



FIGURE 2-1. SURFACE TOPOGRAPHY AND DRAINAGE



FIGURE 2-2. SOIL TYPES

TABL

E 2-

1. T

ERRA

IN U

NIT

S AN

D S

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TYP

ES

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logi

cal R

egim

e La

ndfo

rm

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Fo

rmat

ion

/ Lith

olog

y N

o.

Des

crip

tion

- (Su

rfac

e Fo

rm a

nd

Slop

e R

ange

) G

roup

N

o.

Maj

or S

oil G

roup

So

il Ty

pe

Soil

Des

crip

tion

Qa

Qua

tern

ary

Allu

vium

; Riv

er a

nd

Floo

dpla

in D

epos

its -

clay,

silt,

sa

nd, g

rave

l

0 Ch

anne

l flo

ors,

low

floo

d te

rrac

es

and

bank

s of m

ajor

stre

ams a

nd

river

s; o

vera

ll st

ream

gra

dien

t <I%

, ba

nk sl

opes

var

iabl

e 25

% to

loca

lly

sub-

vert

ical

1 Sh

allo

w R

ocky

Soi

ls as

socia

ted

with

rock

out

crop

or e

xpos

ed

rock

with

skel

etal

gra

vely

sa

ndy

or lo

amy

soils

1 Sh

allo

w u

nifo

rm m

ainl

y co

arse

to

med

ium

-text

ured

ver

y ro

cky

soils

; roc

k ou

tcro

p is

com

mon

Cz

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ozoi

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cludi

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lluvi

al a

nd C

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posit

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and

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ugin

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rave

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re

wor

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late

rite

1 De

pres

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shal

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cised

dr

aina

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ays,

Inte

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iate

st

ream

terr

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and

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flat

s, fre

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d su

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t to

surfa

ce

wat

er p

ondi

ng fo

llow

ing

wet

pe

riods

; slo

pes m

ostly

<l %

2 Gr

avel

ly S

and,

Loam

s or C

lays

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ediu

m to

dee

p un

iform

or

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kly

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atio

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avel

cont

ent

thro

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of t

he

solu

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Tert

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Em

eral

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rmat

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terit

ised

sedi

men

ts, l

ater

ite,

clays

tone

, silt

ston

e,

sand

ston

e, a

nd p

ebbl

y sa

ndst

one.

2 Ne

ar fl

at to

gen

tly u

ndul

atin

g al

luvi

al p

lain

, gen

tly in

cline

d ou

twas

h slo

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valle

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ts a

nd

inte

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iate

and

hig

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iver

te

rrac

es a

nd b

ack

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lope

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<2%

2.3

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y or

thin

silt

to cl

ay lo

am

surfa

ce so

ils w

ith le

nses

of

grav

elly

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or c

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y gr

avel

s un

derla

in b

y st

rong

ly a

cidic

clay

subs

oils

or H

WR

belo

w 0

.5-

1.0m

P-T

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o-Tr

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rmat

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ston

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d in

terb

eds o

f lith

ic sa

ndst

one

3 Un

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ith b

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ently

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n slo

pe

inte

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ear l

evel

to g

ently

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ping

cres

tal a

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on

mes

as a

nd

erod

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late

au re

mna

nts;

slop

es

mos

tly 2

-3%

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lly u

p to

5%

3 Gr

adat

iona

l Red

and

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llow

Ear

th S

oils.

3.

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ndy

loam

to lo

amy

surfa

ce

soils

gra

ding

to re

d, re

ddish

br

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or y

ello

wish

bro

wn

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al m

assiv

e sa

ndy

clay

or

light

, or m

ediu

m to

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vy cl

ay

subs

oils

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P. SU

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ge 1

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33

Geo

logi

cal R

egim

e La

ndfo

rm

Soils

Fo

rmat

ion

/ Lith

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il Ty

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ater

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th

e Ra

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rmat

ion

and

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orm

atio

n -

carb

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eous

mud

ston

e ,

thin

ly in

terb

edde

d m

udst

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and

fine

sand

ston

e, si

liceo

us

silts

tone

, cal

care

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nd

feld

spat

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ands

tone

4 M

oder

atel

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ndul

atin

g la

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regu

lar l

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unde

d ris

es a

nd m

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d di

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inte

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shal

low

ly in

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gulli

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p-up

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opes

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to a

bout

12%

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e st

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ts

4 Te

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4.

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w to

med

. dee

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ten

ston

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in lo

amy

surfa

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ex so

ils w

ith d

ark

brow

n,

brow

n or

redd

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row

n m

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vy cl

ay

subs

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R

5 Un

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to ro

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rise

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ntly

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ely

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ectio

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pe

inte

rfluv

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nd fo

otslo

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slop

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tly in

the

rang

e 6-

15%

4.2

Mos

tly d

eep,

thin

silty

to lo

amy

surfa

ce d

uple

x so

ils w

ith b

row

n or

redd

ish b

row

n ne

utra

l to

stro

ngly

alk

alin

e m

ed. t

o he

avy

clay

subs

oils

6 Irr

egul

ar lo

w h

ills a

nd ri

ses a

nd lo

w

hilly

land

s, w

ith m

oder

atel

y st

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diss

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n slo

pe in

terfl

uves

; slo

pes

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tly u

p to

25%

, loc

ally

stee

per

area

s occ

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5 Un

iform

(or w

eakl

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adat

iona

l) Fi

ne- t

extu

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(Non

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to m

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rface

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wn,

yel

low

ish

brow

n or

redd

ish b

row

n un

iform

or w

eakl

y gr

adat

iona

l med

ium

to h

eavy

an

d he

avy

clay

soils

ove

r HW

R

EIM

P. SU

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t Unc

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r Con

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1 of

33

Geo

logi

cal R

egim

e La

ndfo

rm

Soils

Fo

rmat

ion

/ Lith

olog

y N

o.

Des

crip

tion

- (Su

rfac

e Fo

rm a

nd

Slop

e R

ange

) G

roup

N

o.

Maj

or S

oil G

roup

So

il Ty

pe

Soil

Des

crip

tion

7 Hi

lly la

nds w

ith st

eep

irreg

ular

pl

anar

hill

slop

es m

ostly

with

in th

e ra

nge

25- 3

5%

5.2

Mai

nly

deep

uni

form

or w

eakl

y gr

adat

iona

l bro

wn

or y

ello

wish

br

own

med

ium

to h

eavy

al

kalin

e cla

y so

ils w

ith su

rface

st

one

and

som

e st

ony

lens

es

inclu

ded

8 St

eep

esca

rpm

ent s

lope

s, 25

-50m

hi

gh, w

ith st

eep

irreg

ular

pla

nar

and

loca

lly b

ench

ed sl

opes

typi

cally

in

the

rang

e 35

– 6

0% to

loca

lly

sub-

vert

ical.

5.3

Deep

uni

form

or w

eakl

y gr

adat

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l bro

wni

sh b

lack

, da

rk g

rey-

brow

n or

dar

k br

own

stro

ngly

stru

ctur

ed a

lkal

ine

clay

soils

of m

ediu

m to

hig

h or

hig

h pl

astic

ity; (

incip

ient

crac

king

cla

y)

6 Un

iform

(Cra

ckin

g) C

lay

Soils

6.

2 M

ainl

y de

ep b

row

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bla

ck,

dark

gre

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own,

dar

k br

own

or

brow

n, u

nifo

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rong

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stru

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alk

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Exam

ple:

Ter

rain

Uni

t (Q

a1/6

.2-5

.3) G

eolo

gica

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Qa,

Land

form

1, S

oil T

ype

6.2-

5.3

GEOLOGY Ensham mine is located in the western part of the Bowen Basin, which is one of five major foreland sedimentary basins formed along the eastern side of Australia during the Permian period. The Bowen Basin is the largest productive coal basin in Australia and stretches from Townsville, to south of the Queensland-New South Wales border in a north to south direction.

Table 2-2 provides a summary of the stratigraphic sequence in the Ensham area. This comprises unconsolidated Quaternary aged sediments, unconformably overlying consolidated Tertiary and Permian sediments.

TABLE 2-2. STRATIGRAPHY

The Permian and Triassic strata form regular layered fluvio-deltaic sedimentary sequences, while the Quaternary sediments are more complex and irregular. The coal seams mined at Ensham Mine are found within the Rangal Coal Measures, which is the uppermost Permian unit of the portion of the Bowen Basin.

The Rewan Group aquitard overlies the Rangal Coal Measures and separates the Nogoa River and associated floodplain alluvium from the underground workings. Each are discussed in more detail in (Table 2-2).

The underground mine surface geology is dominated by the Nogoa River alluvium, with the Tertiary sediments mapped to the south and the north.


Document Uncontrolled when Printed. Refer to SHMS Intranet for Controlled Version. Page 13 of

33

GROUNDWATER REGIME The principal groundwater bearing formations in the Ensham area are associated with the Permian coal seams. The Triassic Rewan Group siltstones and sandstones are considered a regional scale aquitard. A conceptual hydrogeological model is shown in Figure 2-3.

Alluvial deposits are associated with the Nogoa River and its anabranch (Figure 2-3). The Quaternary aged alluvium comprises shallow sequences of clay, silty sand and sand, underlain by discontinuous basal sands and gravel. A comprehensive network of bores listed in the EA are located in the alluvium to monitor any impact of mining on the alluvial aquifers.

FIGURE 2-3. CONCEPTUAL HYDROGEOLOGICAL MODEL CROSS SECTION (EIS SUBMISSION, 2021).

LAND USE Ensham mine is located within a rural setting, typical of the Central Queensland region, within the rural margins between a range of central township nodes. The largest nearby townships include Emerald, which is located approximately 35 km south-west, and Blackwater which is located 49 km south-east. The small township of Comet is located approximately 18 km south-east of the mine site.



33

The predominant land uses within the wider region include cropping, grazing and resource activities (Figure 2-4). The existing land uses include resource activities, cropping, grazing land and waterways with fringing riparian vegetation.

As part of Cultural Heritage Management Plans with the traditional owners’ groups over Ensham, two preservation areas above underground workings have been set up where significant amounts of artefact material is stored (refer Figure 2-4). Both areas have been mined under, are fenced and are subject to periodic inspection.



33

FIGURE 2-4. LAND USES AT ENSHAM MINE (2021).



33

PREDICTED SUBSIDENCE

INTRODUCTION The bord and pillar mining layout at Ensham has been specifically designed to ensure that there will be no caving of the roof or collapse of the pillars. The long-term stability of the underground workings has been assessed using the design Factor of Safety (FoS), pillar dimensions (width to height ratio) and stability of the overburden.

Unlike longwall mining, where the subsidence comprises two main components namely sag subsidence and strata compression, in the Ensham mining area, the subsidence will be due to strata compression alone. This results in low levels of surface lowering and minimal associated surface effects due to the associated low tilts, curvatures and strains.

The underground workings are designed where practical to avoid geological structures that may be associated with poorer mining conditions. Seismic surveying is used in future mining areas to delineate these structures prior to mining, allowing the optimization of the underground workings. For every panel that is mined, a hazard panel plan is produced that collates the available geological information such as:

Location of geological structures. Depth of cover. Seam thickness. Seam levels. Roof strength.

Furthermore, the maximum extraction heights to maintain the required minimum FoS, in both the roadways and bell outs, are detailed on the Permit to Mine (PTM) for each mining area. The final roadway and pillar profiles are surveyed to confirm compliance with the design extraction heights.

PILLAR DESIGN The stability of the coal pillars in the Ensham underground mine are assessed using the industry accepted University of New South Wales Pillar Design Procedure to determine the design FoS as follows (Galvin et al, 1998):

FoS = Strength of Pillar/Load on Pillar

The strength and load carried by the pillars in the Ensham Area are calculated using the UNSW Pillar Design Power Strength Formulae and tributary area loading methodology respectively.

A minimum design FoS of 1.6 has been applied to ensure the long-term stability of the underground workings below the flood plain (Figure 3-1). Where pillars are located below the flood plain, a conservative temporary flood depth of 6 m should be applied to the load calculations in Figure 3-1.



33

FIGURE 3-1. MAXIMUM MINING HEIGHT FOR A FOS OF 1.6

The long term stability of the pillars (in excess of 200 years) has been confirmed by three separate industry recognized geotechnical consultants who have peer reviewed the subsidence assessment for the extension mining area. Below the Nogoa River channel, a FoS of 2.11 will be adopted for mining, equating to a probability of failure of 1 in 1 million.

The barrier pillars between panels and sub-panels are also designed to ensure FoS values greater than 2.11, equating to a probability of failure of 1 in 1 million.

COMPRESSION ANALYSIS The deformation induced at the surface by bord and pillar mining due to strata compression can be estimated analytically by calculating the combined pillar, roof and floor compression using modulus values as follows.

The pillar compression is then calculated as follows using the methodology of Poulos and Davis (1974) for analysing rigid footings:

Compressionpillar = (σc * h)/E

Where:

σc = Vertical stress change (MPa) h = Pillar height (m)



33

E = Young’s modulus of coal pillars (MPa)

The compression of the roof and floor is calculated as follows:

Compressionroof or floor = IP*(σc * w/2)/E

Where:

σc = Vertical stress change (MPa) IP = Influence Factor (for a rigid footing) = 1.4 w = Pillar width (m) E = Young’s modulus of roof or floor (MPa)

The change in vertical stress on the pillars can be estimated as:

σc = Tributary Area Stress – Virgin Stress

PREDICTED SUBSIDENCE Lidar has been used to determine the existence of any subsidence over previously mined areas, with no trends or evidence being observed. Subsidence predictions for future mining areas indicate levels less than 40 mm which is less than the accuracy of Lidar and less than natural ground movement (IESC, 2015).

SURFACE AND SUBSURFACE CRACKING No surface or sub-surface cracking has been observed in the Ensham underground mined area since underground bord and pillar mining began in 2011.

SUBSIDENCE IMPACTS Underground mining at Ensham considers potential impacts to the following aspects:

Groundwater. Surface water - Nogoa and Anabranch and other creeks and flood plain. Flora and fauna. Surface infrastructure (mining). Agricultural infrastructure including laser levelled irrigation paddocks. Cultural Heritage.

SUBSIDENCE MONITORING Subsidence monitoring at Ensham comprises:



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LIDAR (+/- 50 mm accuracy). Real time GPS monitoring (+/- 5 mm accuracy). General surface inspections if monitoring indicates exceedance of one or more subsidence

trigger levels. Groundwater monitoring to determine whether Environmental Authority (EA) trigger levels

have been exceeded. Prior to mining in new areas, baseline assessments will be carried out particularly in areas of strategic cropping. As part of these assessments, the surface is mapped to produce terrain models.

LIDAR MONITORING LIDAR data was collected over the underground mine initially in 2009, then on an annual basis since 2016 including areas where bord and pillar has been or will be carried out. No discernible surface movement due to subsidence has been able to be detected to date.

Example profiles have been produced for each different soil type to define the amount of surface movement that can be expected naturally from climatic conditions and discussed as follows.

4.1.1 Soil Type 6.2 This is a uniform (Cracking) Clay Soil. Much of the underground mining is located below this soil type (Figure 2-2). The transect below is located between the main channel and the anabranch of the Nogoa River, has never been subject to mining activities but has been covered by the 2010/2011 flood and periodic vegetation control and burning (Figure 4-1). There is no discernible pattern over time and is a reflection of the climatic conditions at the time of the survey. Similar, patterns have been measured in the same soil type over the unmined 502 Panel (Error! Reference source not found.). Considerable movement is expected over time in this soil type.



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FIGURE 4-1. LIDAR TRANSECT ACROSS AN AREA OF UNMINED SOIL TYPE 6.2.

152.2

152.4

152.6

152.8

153

153.2

153.4

153.6

153.8

0 100 200 300 400 500 600

AHD

(m)

Distance (m)

Soil Type 6.2

2020 2019 2018 2017 2016 2009



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FIGURE 4-2. LIDAR TRANSECT ALONG AN AREA OF 502 PANEL WITH SOIL TYPE 6.2

From the data provided by lidar monitoring, the surface movement from climatic conditions can range from 200 – 400 mm. It is proposed that an average value of 300mm be used as a trigger value to investigate the potential for subsidence in this soil type (refer Table 4-1. Monitoring Schedule).

4.1.2 Soil Types 2.3, 5.2, and 4.2 These soil types are typically gravelly sand, loams or clays, duplex or non cracking clay soils. Panel 114 is located under a mixture of these soil types in which the principal natural movement appears to be soil movement down the slopes and deposition on the flatter areas (Figure 4-1).

154

154.1

154.2

154.3

154.4

154.5

154.6

154.7

154.8

154.9

155

155.1

155.2

0 100 200 300 400 500 600

AHD

(m)

Distance (m)

502 panel

2020 2019 2018 2017 2016



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FIGURE 4-3. LIDAR TRANSECT ALONG AN AREA OF 114 PANEL WITH SOIL TYPES 2.3, 4.2 & 5.2

FIGURE 4-4. EXPANDED LIDAR TRANSECT ALONG AN AREA OF 114 PANEL

158

160

162

164

166

168

170

172

174

0 50 100 150 200 250 300 350 400

AHD

(m)

Distance (m)

114 Panel - Soil Type 2.3, 4.2 & 5.2

2020 2019 2018 2017 2016

164

164.5

165

165.5

166

166.5

167

167.5

168

40 50 60 70 80 90 100 110

AHD

(m)

Distance (m)

114 Panel - Soil Type 2.3, 4.2 & 5.2

2020 2019 2018 2017 2016



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From the data provided by lidar monitoring, the surface movement from climatic conditions can range from 200 – 500 mm. It is proposed that a value of 400mm be used as a trigger value to investigate the potential for subsidence in this soil type. This soil type mainly occurs in areas of steeper terrain used for cattle grazing.

REAL TIME MONITORING Based on Lidar monitoring to date and more recently, fixed monitoring GPS stations, any ground movements resulting from bord and pillar mining are shown to be less than natural ground movement. Mitigation measures have therefore not been necessary to date for bord and pillar mined areas.

Fixed monitor GPS stations have been installed in 2021 and provide a much higher level of accuracy of +/- 5 mm (Figure 4-5) than LIDAR. These stations are installed 1.5 m into the ground surface to be able to better determine ground movement and reduce the measurement of surface soil movement. Ensham have now installed several of these remote GPS monitoring stations above the planned 114 and 502 Panels in the current underground area, as shown in Figure 4-6. There are three monitoring stations over the 500 Mains/502 Panel and two monitoring stations over the 114 Panel . These monitoring stations commenced recording data in mid-April 2021. Soil type 6.2 which is a heavy clay soil, occurs on the surface above 502 Panel. Soil types 2.3, 4.2 and 5.2 all occur on the surface above 114 Panel.

This monitoring has been set up by GNSS Monitoring and the data can be easily accessed remotely in real time.

FIGURE 4-5. FIXED MONITORING STATION.



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FIGURE 4-6. LOCATION OF REMOTE SUBSIDENCE MONITORING – ENSHAM UNDERGROUND AREA.

As of mid-July 2021, there has been no mining below 114 Panel in the northern part of the underground area (Figure 4-6). In the 500 Mains and 502 Panel area, pillars and roadways were developed below the 500 Mains monitoring station 502_1 in late May 2021 (Figure 4-7). By mid July 2021, roadways had been extended more than 150 m to the north and 200 m to the west of this monitoring station. The production schedule indicates that mining will be carried out below all the monitoring stations installed over 114 and 502 Panels during 2021 and early 2022. This will allow long term monitoring of any subsidence effects to be carried out.



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FIGURE 4-7. SUBSIDENCE MONITORING ABOVE 500 MAINS, 502 AND 503 PANELS.

MONITORING SURVEYS As shown in Figure 4-8, the measured vertical movement on station 502_1 above the pillars mined in the 500 Mains Panel is within the quoted accuracy of +/- 5 mm. Significantly, the same variation in the measurements is evident in survey stations 502_2 and 502_3, which are recording data over as yet unmined coal in 502 Panel (Figure 4-8).

This initial subsidence data suggests that mining in the 500 Mains has had negligible subsidence impacts on the surface within the accuracy of the survey monitoring. Furthermore, rainfall events appear to be related to more distinct changes in the survey readings measured by these stations as seen in Figure 4-8.

Similar characteristics and trends are evident on the two 114 Panel stations, which at this stage have no underground workings below them (Figure 4-9). Mining has recently commenced in 114 Panel (end of July 2021) and it is anticipated mining will be completed below these two stations in the latter half of 2021.



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FIGURE 4-8. MONITORING DATA – 500 MAINS AND 502 PANEL STATIONS.

FIGURE 4-9. MONITORING DATA – 114 PANEL STATIONS (NO MINING AS OF JULY 2021).

The extraction ratio in the 500 Mains below station 502_1 is 38.5%, at 195 m depth of cover, comparable with the deeper part of the extension area. The FoS of the 500 Mains pillars for a 3.5 m mining height in this area is 1.90, equivalent to a probability of failure of 1 in 90,000.



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It is anticipated that prior to mining in the extension area, more data of the natural surface movement will allow interpretation to determine any subsidence movement component. This data will be reviewed in conjunction with rainfall records and also the location of underground mining, to provide some guidance on the proportion of movement due to both mining induced subsidence and also the seasonal variation in ground levels due to changes in moisture content.

It is considered that LIDAR surveys will still be applicable in assessing ground movements over larger areas above predicted subsidence levels.

This monitoring should confirm the subsidence predictions and any significant changes in subsidence will trigger a review of the relevant impact assessments and associated mitigation and management measures as discussed further in section 4.8.

This review will also provide additional calibration data for any future subsidence predictions and assessments of subsidence effects.

A subsidence monitoring report will also be produced every two years and monitoring of subsidence impacts will be continued after the completion of mining either:

For five years or Until the surrender of the mining lease or A suitably qualified and experienced person produces a report confirming a lesser

monitoring period is appropriate.

UNDERGROUND SURVEYING As well as the surface monitoring, underground surveying of the completed mined roadways and pillar dimensions is carried out. The FoS and width: height ratio of the as-mined pillars can be calculated and checked against the design values.

These values can be referenced when reviewing the subsidence predictions.

SURFACE INSPECTIONS Detailed surface inspections will be carried out on areas that have been identified through Lidar or fixed GPS monitoring as having triggered an investigation as discussed in section 4.7.

GROUNDWATER MONITORING Ensham Mine’s existing groundwater monitoring bore network is extensive and allows for the compilation of groundwater data from the Quaternary (alluvium), Triassic age sediments, Rewan Group, and Rangal Coal Measures (Figure 4-10). The existing groundwater monitoring plan for the current Ensham includes baseline, operations and post closure.



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Ensham Mine proposes to maintain the current monitoring network and frequency with new monitoring bores to be added as proposed by the Groundwater Management and Monitoring Program defined in EA Condition C47. The location of existing monitoring bores along with the trigger levels in the EA are sufficient to require an investigation to be undertaken.



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FIGURE 4-10. GROUNDWATER MONITORING BORES



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MONITORING SCHEDULE AND TRIGGER LEVELS The monitoring schedule for the various aspects detailed in this SMP are summarised in Table 4-1. This schedule also includes the frequency and responsible department. Trigger levels have also been specified to initiate a review.

4.7.1 Subsidence Trigger levels Variation of between 0.2m and 0.5m of the soil surface has been measured between Lidar surveys over unmined areas at Ensham. Based on these measurements a Lidar trigger level of 0.3m is therefore considered a realistic value for cracking clay soils and 0.4m for other soils located on slopes.

Similarly, a 50 mm variation in the more accurate fixed GPS ground monitoring is considered a valid trigger level based on the initial monitoring over 114 and 502 Panels (Figure 4-8 and Figure 4-9).

TABLE 4-1. MONITORING SCHEDULE

Monitoring/Survey Who by How often Trigger Levels

LIDAR Technical

Services/Survey Annual

>0.3m for cracking clay soils

>0.4m for other soils

As shown in Figure 2-2

Fixed GPS Technical

Services/Survey Real Time 50mm

Surface Surveying Technical

Services/Survey

As per land compensation

agreements

As per land compensation

agreements

Underground Surveying

Survey Daily As per strata Control

Management Plan

Surface Inspections Environmental Annual (if

investigation is triggered)

Water ponding,

New gully erosion,

Changes to Nogoa River banks (that may indicate an impact to



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fish passage) determined from Lidar

Groundwater Monitoring

Environmental Quarterly

Refer Schedule C of EA conditions for groundwater quality and water level triggers

SUBSIDENCE MANAGEMENT MEASURES Due to the low-level subsidence effects measured and observed as a result of bord and pillar mining at Ensham, remedial management measures are presently not required unless a significant deviation in the level of subsidence identified from future monitoring.

Any significant detection of subsidence will trigger a review of underground mining activities as detailed in Section 4.7. Depending on the land use and risk involved in the activity, different mitigation measures may be required:

Grazing – rip to eliminate risk to stock Dry land cropping – plough out if effecting crop yield Irrigated cropping – re-level to ensure continued drainage.

Where surface levels indicate a difference in elevation greater than the trigger levels in Table 4-1, and, likely as a result of mining activities, an investigation will be undertaken by Ensham. Where the investigation supports that the elevation change is associated with mining, then a report will be prepared and submitted to the Administering Authority and to the land owner/land occupier. The investigation will nominate the necessary rehabilitation to be undertaken if necessary.

LEGAL COMPLIANCE AND REFERENCES

TABLE 5-1. REFERENCES

Legislation / Recognized Standards

Environmental Authority EPML00732813 Environmental Protection Biodiversity Conservation Act 1999. Water Act 2000

TERMS AND ABBREVIATIONS

ABBREVIATION AND DESCRIPTION TABLE 6-1. TERMS



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Abbreviation Description

EA Environmental Authority

EPBC Act Environment Protection and Biodiversity Protection Act 1999 (Commonwealth).

GM General Manager

HSE Health, Safety and Environment

SSE Site Senior Executive

REVIEW HISTORY

This Subsidence Monitoring Plan will be subject to review every 3 years or under the following conditions due to:

Change to license conditions and/or reporting requirements. Significant change to current mine plan/operations. An investigation report reccomendation

TABLE 7-1. REVIEW HISTORY

Date of review Revision Number Trigger for review New revision Number

ROLES AND RESPONSIBILITIES

Survey Section

Carry out monitoring – fixed monitor and LIDAR. Prepare monitoring data. Ensure compliance of the dimensions of the underground pillars and roadways.

Environmental Section

Surface inspections.



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Monitor creeks/rivers/groundwater. Liaise with landowners.

Technical Services Section

Underground inspections. Plan subsidence monitoring requirements. Prepare subsidence monitoring report Review and reconcile subsidence monitoring data. Facilitate review if trigger levels are exceeded. Liaise with landowners.

Documents

S EIMP.06.00.06M ANAGEMENT PLAN