Blast Management & Consulting - CESNET Tete Iron Ore ENGLISH CB127_180115...Blast Management & Consulting ... 10.9 Blast operations impact on wildlife ... Aerial view and surface plan

Blast Management & Consulting

Ref No: CES~TeteIronOre~EIAReport141130V01

Quality Service on Time

Date: 2014/11/30 Signed:

Name: JD Zeeman

CK 97 31139 / 23

Cell: 082 854 2725

Tel: +27 (0)12 345 1445 Fax: +27 (0)12 345 1443

PO Box 61538 Pierre van Ryneveld Centurion 0045

61 Sovereign Drive Route 21 Corporate Park Irene

Note: This document is the property of Blast Management & Consulting and should be treated as

confidential. No information in this document may be redistributed nor used at any other site than the

project it is intended for without prior consent from the author. The information presented is given with

the intention of assisting the receiver with optimized blast results and to ensure that a safe and healthy

blasting practice is conducted. Due to unforeseen rock formations that may occur, neither the author

nor his employees will assume liability for any alleged or actual damages arising directly or indirectly

out of the recommendations and information given in this document.

Report:

Environmental Impact Assessment:

Ground Vibration and Air Blast Study

Baobab Resources

Tete Iron Mine Project

Dated 30 November 2014

Blast Management & Consulting Page 2 of 73 18. blasting assessment 18. blasting assessment

Table of Contents

Executive Summary ........................................................................................................................... 8

1 Introduction ............................................................................................................................. 9

2 Objectives ................................................................................................................................. 9

3 Scope of Blast Impact Study ................................................................................................ 10

4 Study Area ............................................................................................................................. 10

5 Methodology .......................................................................................................................... 12

6 Assumptions and Limitations .............................................................................................. 12

6.1 Mining and Blasting Operations ...................................................................................... 13

7 Effects of blasting operations ............................................................................................... 16

7.1 Ground vibration .............................................................................................................. 16

7.1.1 Ground Vibration Prediction ........................................................................................ 17

7.1.2 Ground vibration limitations on structures .................................................................. 19

7.1.3 Ground vibration limitations with regards to human perceptions ................................ 22

7.2 Air blast ........................................................................................................................... 23

7.2.1 Air blast limitations on structures ................................................................................ 23

7.2.2 Air blast limitations with regards to human perceptions ............................................. 24

7.2.3 Air blast prediction....................................................................................................... 24

7.3 Fly rock ............................................................................................................................ 26

7.3.1 Fly rock causes ............................................................................................................. 27

7.3.2 Fly rock predictions ..................................................................................................... 27

7.3.3 Impact of fly rock ......................................................................................................... 28

7.4 Noxious Fumes ................................................................................................................ 28

7.4.1 Noxious Fume Causes .................................................................................................. 29

7.4.2 Noxious Fume Control ................................................................................................. 30

8 Baseline Results ..................................................................................................................... 34

9 Construction Phase: Impact Assessment and Mitigation Measures ................................ 38

10 Operational Phase: Impact Assessment and Mitigation Measures .................................. 38

10.1 Review of expected ground vibration .............................................................................. 40

10.1.1 Calculated Ground Vibration Levels ........................................................................... 41


10.1.2 Summary of ground vibration levels ............................................................................ 46

10.2 Ground Vibration and human perception ........................................................................ 47

10.3 Potential for vibration upsetting adjacent communities .................................................. 48

10.4 Cracking of houses .......................................................................................................... 49

10.5 Air blast ........................................................................................................................... 49

10.5.1 Review of expected air blast ........................................................................................ 51

10.5.2 Summary of findings for air blast ................................................................................ 54

10.6 Fly-rock Modelling Results and Impact of fly rock ........................................................ 55

10.7 Noxious fumes ................................................................................................................. 58

10.8 Water well influence ........................................................................................................ 58

10.9 Blast operations impact on wildlife - crocodiles ............................................................. 59

10.10 Potential Environmental Impact Assessment: Operational Phase ............................... 60

11 Closure Phase ........................................................................................................................ 64

12 Alternatives (Comparison and Recommendation)............................................................. 65

13 Monitoring ............................................................................................................................. 65

14 Recommendations ................................................................................................................. 66

14.1 Safe blasting distance from communities ........................................................................ 66

14.2 Evacuation ....................................................................................................................... 66

14.3 Road / Travel Closure ...................................................................................................... 66

14.4 Monitoring ....................................................................................................................... 67

14.5 Photographic Inspections ................................................................................................. 67

14.6 Recommended ground vibration and air blast levels ....................................................... 68

14.7 Stemming length .............................................................................................................. 69

14.8 Blasting times .................................................................................................................. 69

14.9 Third party monitoring .................................................................................................... 69

15 Knowledge Gaps .................................................................................................................... 69

16 Conclusion.............................................................................................................................. 69

17 Curriculum Vitae of Author ................................................................................................ 70

18 References .............................................................................................................................. 71


List of Acronyms used in this Report

Air Pressure Pulse APP

Blasted Tonnage T

Distance (m) D

Duration D

East E

Explosive Mass (kg) E

Explosives (Trinitrotoluene) TNT

Frequency Freq.

Gas Release Pulse GRP

Interested and Affected Parties I&AP

Magnitude/Severity M/S

North N

North East NE

North West NW

Noxious Fumes NOx’s

Peak Particle Velocity PPV

Points of Interest POI

Probability P

Rock Pressure Pulse RPP

Scale S

Site Constant a and b

South S

South East SE

South West SW

United States Bureau of Mine USBM

West W

With Mitigation Measures WM

Without Mitigation Measures WOM

List of Units used in this Report

Air Blast dB

Air Blast Limit dBL

Ammonium nitrate/fuel oil ANFO

Blast Management & Consulting BM&C

Burden (m) B

Centimetre cm

Charge Energy MJ

Charge Height M

Charge mass / m (kg/m) Mc


Coordinates (South African) WGS 84

Cup Density Gr/cm3

Drill hole angle θ

East E

Energy Factor MJ/m³ or MJ/t

Environmental Impact Assessment EIA

Factor value k

Frequency Hz

Gravitational constant g

Ground Vibration mm/s

Kilometre km

kPa kilopascal

Latitude/Longitude Hours/degrees/minutes/seconds Lat/Lon hddd°mm'ss.s"

Mass kg

Maximum Throw (m) L

Meter m

Milliseconds ms

Nitrogen Dioxide NO2

Nitrogen Monoxide NO

Nitrogen Oxide NOx

Parts per million ppm

Pascal Pa

Peak Acceleration mm/s2

Peak Displacement mm

Peak Particle Velocity mm/s

Percentage %

Pounds per square inch psi

Powder Factor kg/m3

Powder factor kg/m³ or kg/t

Scaled Burden (m3/2

kg-1/2

) Bs

South S

Stemming height (m) SH

Vector Sum Peak Particle Velocity mm/s

Volume mᵌ


List of Figures

Figure 1: Locality of the project area ................................................................................................. 11

Figure 2: Proposed mining area layout .............................................................................................. 12

Figure 3: A blast located on the edge of the pit. ................................................................................ 14

Figure 4: Blast hole layout with indication of explosives charge and stemming. ............................. 15

Figure 5: Blast initiation sequence from timing applied. ................................................................... 15

Figure 6: Blast timing contours with maximum instantaneous charge obtained from the timing

sequence applied. ............................................................................................................................... 16

Figure 7: Ground vibration over distance for the two charge masses used in modelling .................. 19

Figure 8: USBM Analysis Graph ....................................................................................................... 21

Figure 9: USBM Analysis with Human Perception ........................................................................... 22

Figure 10: Predicted air blast levels ................................................................................................... 26

Figure 11: Schematic of fly rock terminology ................................................................................... 27

Figure 12: Predicted Fly rock............................................................................................................. 28

Figure 13: Aerial view and surface plan of the proposed mining area with points of interest

identified. ........................................................................................................................................... 36

Figure 14: Typical building style ....................................................................................................... 38

Figure 15: Site topography ................................................................................................................. 40

Figure 16: Ground vibration influence from minimum charge.......................................................... 42

Figure 17: Zoomed area for ground vibration influence from minimum charge ............................... 43

Figure 18: Ground vibration influence from maximum charge ......................................................... 45

Figure 19: The range of 6 mm/s for minimum and maximum charge (blue line). ............................ 47

Figure 20: The effect of ground vibration with human perception and vibration limits ................... 48

Figure 21: Air blast influence from minimum charge ....................................................................... 52

Figure 22: Air blast influence from maximum charge ....................................................................... 54

Figure 23: Air blast influence area for 120 dB – minimum and maximum charge ........................... 55

Figure 24: Predicted Fly rock............................................................................................................. 56

Figure 25: Predicted Fly rock points for mitigation ........................................................................... 57

Figure 26: Predicted Fly rock range of influence .............................................................................. 58

Figure 27: Sensitive river area ........................................................................................................... 60

Figure 28: Structures at North Pit Area that are identified where mitigation will be required. ......... 63

Figure 29: Monitoring Positions suggested. ...................................................................................... 66

Figure 30: 1000m area around North pit area identified for structure inspections. ........................... 67

List of Tables

Table 1: Information on blast designs used ....................................................................................... 13

Table 2: Expected Ground Vibration at Various Distances from Charges Applied in this Study ..... 18

Table 3: Damage Limits for Air Blast ............................................................................................... 23

Table 4: Air Blast Predicted Values ................................................................................................... 25

Table 5: List of points of interest used (WGS –UTM L36) ............................................................... 36

Table 6: POI Classification used ........................................................................................................ 37

Table 7: Ground vibration evaluation for minimum charge .............................................................. 43


Table 8: Ground vibration evaluation for maximum charge .............................................................. 45

Table 9: Expected air blast levels ...................................................................................................... 50

Table 10: Air blast evaluation for minimum charge .......................................................................... 51

Table 11: Air blast evaluation for maximum charge ......................................................................... 52

Table 12: Evaluation matrix criteria .................................................................................................. 61

Table 13: Risk Assessment Outcome before mitigation ................................................................... 62

Table 14: Risk Assessment Outcome after mitigation ....................................................................... 62

Table 15: Structures identified as problematic .................................................................................. 64

Table 16: Mitigation suggested for blasting operations – Reduced charge ....................................... 64

Table 17: Mitigation suggested for blasting operations – Minimum distance required .................... 64

Table 18: Recommended ground vibration air blast limits ................................................................ 68

Table 19: Recommended ground vibration air blast limits ................................................................ 68


Executive Summary

Blast Management & Consulting (BM&C) was contracted to perform a review of possible impacts

with regards to blasting operations in the proposed new opencast mining operation. Ground

vibration, air blast, fly rock and fumes are some of the aspects that result from blasting operations.

The report concentrates on the ground vibration and air blast and intends to provide information,

calculations, predictions, possible influences and mitigations of blasting operations for this project.

The project area consists mainly of one opencast pit area. The evaluation of effects yielded by

blasting operations was evaluated over an area as wide as 3500 m from the opencast pit area. The

typical structures of concern in the area are mainly rural buildings – very few brick and mortar

structures, mainly wood and mud huts.

The project area has the possibility of people present at very close distances to the operations. The

location of structures around the pit areas are such that the charges evaluated showed possible

influences due to ground vibration. Ground vibration mitigation will be required for two identified

areas of interest. Mitigation on drilling and blasting operations will be required to levels of ground

vibration that are within the accepted norms.

Air blast levels are of less concern. Air blast levels calculated showed no specific damage concerns.

Levels calculated do show that levels could be high enough to generate complaints from neighbours

up to a distance of at least 700 m. Mitigation of ground vibration will also contribute to mitigation

of air blast. Stemming control will be needed to maintain levels within acceptable norms. Stemming

control for air blast will also contribute to control on fly rock. Complaints from air blast are

normally based on the actual effects that are experienced due to rattling of roofs, windows, doors

etc. These effects could startle people and raise concern of possible damage.

One concern identified is the Revubué River located on the western side of the pit. The river is very

close to the pit area. Possible presence of crocodiles and aquatic life may be influenced by ground

vibrations yielded. Expected levels are higher than proposed limits. Crocodiles and other aquatic

life are known to occur in the river, based on the faunal assessment for this ESIA.

This concludes this investigation for the Tete Iron Ore Mine Project. It will be possible to operate

this mine in a safe and effective manner provided attention is given to the areas of concern and

recommendations as indicated.


1 Introduction

The Baobab Resources, Tete Iron Ore mine project is located in Tete Province of Mozambique. The

project area is 53 km north east of the town Tete next to the Revubué River at UTM coordinates 36

L 582544 8261469. The Tenge pit within the project lies close to the villages of Tenge-Makodwe

and Pondandue. The project area is located in a hilly area amidst rural areas with various villages in

the vicinity. More detail is provided in the Social Impact Assessment (please refer to volume 2 for

the SIA undertaken by COWI).

Blast Management & Consulting (BM&C) was contracted as part of the Environmental Impact

Assessment (EIA) to perform an initial review of possible impacts with regards to blasting

operations in the proposed new opencast mining operation. Ground vibration, air blast, fly rock and

fumes are some of the aspects that result from blasting operations. This study will review possible

influences that blasting may have on the surrounding area in respect of these aspects. The report

concentrates on the ground vibration and air blast and intends to provide information, calculations,

predictions, possible influences and mitigations related to blasting operations for this project.

2 Objectives

The objective of this document is to outline the expected environmental effects that blasting

operations could have on the surrounding environment and neighbouring communities, and to

propose specific mitigation measures that will be required. This study investigates the related

influences of expected ground vibration, air blast, fly rock, and noxious fumes. These effects are

investigated in relation to the surroundings of the blast site and possible influence on the

neighbouring houses and owners or occupants.

The objectives are investigated by taking specific protocols into consideration. As far as could be

established there are no specific laws governing limits for ground vibration and air blast in

Mozambique specifically. The protocols applied in this document are based on the author’s

experience, guidelines from literature research, client requirements and general indicators from

various legislated requirements in South Africa. There is no direct reference in the following acts

with regards to requirements and limits on the effect of ground vibration and air blast specifically,

and some of the aspects addressed in this report. The South African acts consulted are:

National Environmental Management Act No. 107 of 1998,

Mine Health and Safety Act No. 29 of 1996,

Mineral and Petroleum Resources Development Act No. 28 of 2002 and

Explosives Act No. 26 of 1956 and amended No. 15 of 2003.

The guidelines and safe blasting criteria are based on international accepted standards and

specifically the United States Bureau of Mines (USBM) criteria for safe blasting for ground

vibration and recommendations on air blast. However, it is accepted that the protocols and

objectives will fall within the broader spectrum as required by the mining industry in Mozambique.


There are no specific South African standard and the USBM is a well accepted standard for South

Africa.

3 Scope of Blast Impact Study

The scope of the study is determined by the terms of reference to achieve , summarized below

according with regards specifically to ground vibration and air blast due to blasting operations.

Background information of the proposed site

Structure Profile

Mining operations and Blasting Operation Requirements

Effects of blasting operations:

o Ground vibration

o Air blast

o Fly rock

o Noxious fumes

Site specific evaluation blasting effects for each area in relation to the points of interest

identified

Risk Assessment

Mitigations

Recommendations

Conclusion

4 Study Area

The Baobab Resources, Tete Iron Ore Mine project Tenge pit is geographically located at UTM

coordinates 36 L 582544 8261469 This is within the Tete Province of Mozambique. The project

area is 53 km north east of the town Tete next to the Revubué River. Figure 1 shows a locality plan

of the proposed project area. Figure 2 shows the proposed mining area layout and infrastructure.


Figure 1: Locality of the project area


Figure 2: Proposed mining area layout

5 Methodology

The detailed plan of study consisted of the following:

The study is mainly a desktop study with data and information supplied from Coastal and

Environmental Services and Baobab Resources plc.

Site Structure Profile: Identifying all surface structures / installations that are found with the

3500m possible influence area. A list of POI’s are created that will be used for evaluation.

Site evaluation: This consists of evaluating the mining operations and the possible influences

from blasting operations, by modelling the expected impact based on expected drilling and

blasting information for the project. Various accepted mathematical equations are applied to

determine the attenuation of ground vibration, air blast and fly rock. These values are then

calculated over distance and shown as amplitude level contours. Overlay of these contours with

the location of the various receptors then gives an indication of the possible impact and

expected effects of potential impacts. Evaluation of each receptor according to the predicted

levels then gives an indication of possible mitigation measures. The possible environmental or

social impacts are then addressed in the detailed EIA phase investigation.

Reporting: All data is prepared in a single report and provided for review.

6 Assumptions and Limitations


The project is at a stage where certain assumptions and limitations are applicable. Geotechnical

domains have been defined based on the weathering profile and mineralisation. Geotechnical

Domains were defined as Weathered, Fresh Mineralised and Fresh Waste1.

6.1 Mining and Blasting Operations

Opencast mining will be done using the typical drilling, blasting load and haul operations. Two

scenarios are considered for total mine operations. A 0.5MTPA and 1.0 MTPA life of mine . These

scenarios however do not influence the required drilling and blasting parameters per sae. Two

material types are considered for drilling and blasting namely weathered and fresh material. 100%

drilling and blasting is assumed at the moment with no free digging.

A report prepared by Mining Dingo “Blasting Requirements Tenge Pit for the Tete Pig Iron Project

Baobab Resources, Xavier Hill 11/20/2014” suggested the following drilling and blast parameters.

Consideration was also given in the report for larger drill diameters but it is not confirmed yet if this

will be applicable. It is my opinion that larger diameter drill holes will not be efficient for the bench

heights to be considered. Table 2 below shows the drilling and charging parameters applicable in

this report.

Table 1: Information on blast designs used

Technical Aspect Weathered Fresh

B/H Diameter (mm) 165 165

Explosive Density (g/cm3) 1.25 1.25

Burden (m) 4.4 4

Spacing (m) 5.1 4.6

Bench Height (m) 10 10

Average Depth (m) 10 10

Blast Hole Depths Incl. Subdrill (m) 10.50 10.50

Linear Charge Mass (kg) 26.73 26.73

P/F Blast hole (kg/m3) 0.86 1.05

Stemming Length (m) 3.30 3.30

Column Length (incl. Subdrill.) (m) 6.7 6.7

Explosives Per B/H (incl. Subdrill+airgap) (kg) 192 192

Include SubDrill (Yes/No) yes yes

Sub-drill (m) 0.50 0.50

Stemming Length vs BHDia 20.0 20.0

Timing – on Spacing 25 25

Timing – on Burden 20 20

1 Report: Coffey Mining Pty Ltd, Pre-Feasibility Study Baobab Mining Services Pty Ltd Tete Pig

Iron and Ferro-Vanadium Project Dated 15 May 2013.


Using the information provided a blast can be simulated to determine expected detonation sequence

and charge masses detonating in the blast. The possible influence from blasting operations is

dependent on the charge mass per delay that is achieved through the detonation sequence. Thus

depth of blast hole, diameter, charge mass, stemming length and timing are parameters that have

influence. The following figures show the simulated blast in a part of the proposed mining area:

Figure 3 shows a blast on the western side of the pit – this was randomly selected.

Figure 4 shows blast hole layout with an indication of explosives charge and stemming.

Figure 5 shows initiation sequence from timing applied.

Figure 6 shows the timing contours with maximum instantaneous charge obtained from the timing

sequence applied.

Figure 3: A blast located on the edge of the pit.


Figure 4: Blast hole layout with indication of explosives charge and stemming.

Figure 5: Blast initiation sequence from timing applied.


Figure 6: Blast timing contours with maximum instantaneous charge obtained from the timing

sequence applied.

7 Effects of blasting operations

Blasting operations effect the surroundings, usually manifested in the form of ground vibration, air

blast, fumes, fly rock etc. The application of explosives to break rock will always have a positive

and negative manifestation of different energies. It is the effects that have negative outcome that we

concentrate on and that will need to be managed. The following sections address the reason,

prediction, modelling and control on aspects like ground vibration, air blast, fly rock and fumes.

7.1 Ground vibration

Explosives are used to break rock through the shock waves and gasses yielded from the explosion.

Ground vibration is a natural result from blasting activities. The far field vibrations are inevitable,

but are un-desirable by products of blasting operations. The shock wave energy that travels beyond

the zone of rock breakage is wasted and could cause damage and annoyance. The level or intensity

of these far field vibrations are dependent on various factors. Some of these factors can be

controlled to yield desired levels of ground vibration and still produce enough rock breakage

energy.

Factors influencing ground vibration are the charge mass per delay, distance from the blast, the

delay period and the geometry of the blast. These factors are controlled by planned design and

proper blast preparation.


1. Charge mass - The larger the charge mass per delay - not the total mass of the blast, the

greater the vibration energy yielded. Blasts are timed to produce effective relief and rock

movement for successful breakage of the rock. A certain quantity of holes will detonate

within the same time frame or delay and it is the maximum total explosive mass per such

delay that will have the greatest influence. All calculations are based on the maximum

charge detonating on a specific delay.

2. Distance - Secondly is the distance between the blast and the point of interest / concern.

Ground vibrations attenuate over distance at a rate determined by the mass per delay, timing

and geology. Close to the blast high levels will be experienced and with distance the levels

dercrease.

3. Geology - The geology of the blast medium and surroundings has influences as well. High

density materials have high shock wave transferability where low density materials have low

transferability of the shock waves. Solid rock i.e. norite will yield higher levels of ground

vibration than sand for the same distance and charge mass. Changes in geology around the

blast will also influence the levels. Each geological interface a shockwave encounters will

reduce the vibration energy due to reflections of shock wave and have an added reducing

mechanism. The precise geology in the path of a shock wave cannot be observed easily, but

the influence on the shockwaves can be tested for if necessary in typical signature trace

studies - which are discussed shortly below.

7.1.1 Ground Vibration Prediction

When predicting ground vibration and possible decay, a standard accepted mathematical process of

scaled distance is used. The equation applied (Equation 1) uses the charge mass and distance with

two site constants. The site constants are specific to a site where blasting is to be done. In new

opencast operations a process of testing for the constants is normally done using a signature trace

study in order to predict ground vibrations accurately and safely. The utilization of the scaled

distance prediction formula is standard practice. The analysis of the data will also give an indication

of frequency decay over distance.

Equation 1:

√

Where:

PPV = Predicted ground vibration (mm/s)

a = Site constant

b = Site constant

D = Distance (m)

E = Explosive Mass (kg)

Applicable and accepted factors a & b for new operations is as follows:


Factors:

a = 1143

b = -1.65

Utilizing the abovementioned equation and the given factors, allowable levels for specific limits and

expected ground vibration levels can then be calculated for various distances.

Review of the type of structures that are found within the possible influence zone of the proposed

mining area and the limitations that may be applicable, result in different limiting levels of ground

vibration been required. This is due to the typical structures observed surrounding the site. Structure

types and qualities vary greatly and this calls for limits to be considered as follows: 6 mm/s, 12.5

mm/s levels and 25 mm/s at least.

The blast design indicates 192 kg will be loaded in a 10 m deep hole at 165 mm diameter through

weathered and fresh material blast holes. Blast simulation indicates that a maximum of 770 kg is

detonated within the same time frame of 8 ms. In order to evaluate the possible influence two

charge masses that will span the range of possible charge mass per delay were selected. A single

blast hole charge at 192 kg and a four times blast hole charge at 770 kg. This range of charges will

span the expected charging to be done in these areas, and these charge masses were used for

modelling in this report. Applying the above charge masses, the following ground vibration

calculations were done and considered in this report. Attention is given to levels of 6 mm/s, 12.5

mm/s and 25 mm/s.

Based on the designs presented on expected drilling and charging design, Table 2 shows expected

ground vibration levels (PPV) for various distances calculated at the two different charge masses (a

low charge mass and a maximum charge mass as worst case scenario). The charge masses are 192

kg and 770 kg.

Table 2: Expected Ground Vibration at Various Distances from Charges Applied in this Study

No. Distance (m) Expected PPV (mm/s) for 192 kg Charge Expected PPV (mm/s) for 770 kg Charge

1 50.0 137.6 432.6

2 100.0 70.5 221.6

3 150.0 22.5 70.6

4 200.0 14.0 43.9

5 250.0 9.7 30.4

6 300.0 7.2 22.5

7 400.0 4.5 14.0

8 500.0 3.1 9.7

9 600.0 2.3 8.7

10 700.0 1.8 5.6

11 800.0 1.4 4.5

12 900.0 1.2 3.7

13 1000.0 1.0 3.1


14 1250.0 0.7 2.1

15 1500.0 0.5 1.6

16 1750.0 0.4 1.2

17 2000.0 0.3 1.0

18 2500.0 0.2 0.7

19 3000.0 0.2 0.5

20 3500.0 0.1 0.4

Figure 7 below shows the relationship of ground vibration over distance for the two charges

considered as given in Table 2 above. The attenuation of ground vibration over distance is clearly

observed. Ground vibration attenuation follows a logarithmic trend and the graph indicates this

trend, as well as the limits that should be applicable due to the various structures and types of

installations in this area. The graph can be used to scale expected ground vibration at specific

distances for the same maximum charges as used in this report. The expected vibration level at

specific distance can be read from the graph, provided the same maximum charges are applicable,

or by rough estimate if the charge per delay should be between the charge masses applied for this

case. It indicates that ground vibration is not significant at distances of 300m (low charge mass) and

600m (high charge mass).

Figure 7: Ground vibration over distance for the two charge masses used in modelling

7.1.2 Ground vibration limitations on structures

0

20

40

60

80

100

120

140

0 500 1000 1500 2000 2500

Pre

dic

ted

Gro

un

d V

ibra

tio

n (

mm

/s)

Distance (m)

Baobab Resources Tete Iron ProjectExpected Levels of Ground Vibration for Various Charges @ Specific Distances

Single BH / Delay 4xBH / Delay Bottom Limit (mm/s) Mid. Limit (mm/s) Top Limit (mm/s)


Limitations on ground vibration are in the form of maximum allowable levels for different

installations and structures. These levels are normally quoted in peak particle velocity or as ground

vibration in millimetres per second (mm/s). As far as could be established there are no specific

standards for ground vibration and air blast related blasting operations in Mozambique. The same is

applicable for South Africa and currently South Africa accepts the United States Bureau of Mines

(USBM) criterion for safe blasting as the guideline applicable where private structures are of

concern. This is a process of evaluating the vibration amplitudes and frequency of the vibrations

according to set rules for preventing damage. The vibration amplitudes and frequency is then

plotted on a graph. Figure 8 shows a simplified example of a USBM analysis graph. Limit lines

applicable to drywall walls are excluded. The graph indicates two main areas:

The Safe Blasting Criteria Area

The Unsafe Blasting Criteria Area

When ground vibration is recorded and the amplitude in velocity (mm/s) is analysed for frequency

it plots this relationship on the USBM graph. If data falls in the lower part of the graph then the

blast was done safely (below green area on graph). If the data falls in the upper part of the graph

then the probability of inducing damage to mortar and brick structures increases significantly (red

area on graph). There is a relationship between amplitude and frequency due to the natural

frequencies of structures. This is normally low - below 10 Hz - and thus the lower the frequency,

the lower the allowable amplitude. Higher frequencies allow for higher amplitudes. Due to

possible poor structures in the area additional 6 mm/s (Green line) and 12.5 mm/s (Red line) limit

lines were added. Figure 8 shows an example of a USBM analysis graph with the 6 mm/s and 12.5

mm/s guidelines added.

The USBM graph for safe blasting was developed by the United States Bureau of Mines through

research and data accumulated from sources other than their own research.


Figure 8: USBM Analysis Graph

Additional limitations that should be considered as well are as follows, determined through research

and various institutions:

National Roads/Tar Roads: 150mm/s

Steel pipelines: 50mm/s

Electrical Lines: 75mm/s

Railway: 150mm/s

Concrete aged less than 3 days: 5mm/s

Concrete after 10 days: 200mm/s

Sensitive Plant equipment: 12 mm/s or 25 mm/s depending on type – some switches could

trip at levels less than 25 mm/s.

Considering the above limitations, BM&C work is based on the following:

USBM criteria for safe blasting

The additional limitations provided above

Consideration of private structures

Should these structures be in poor condition the basic limit of 25 mm/s is reduced to 12.5

mm/s. When structures are in very poor condition limits will be restricted to 6 mm/s

We also consider the input from other consultants in the field locally and internationally.

6 6

12.5 12.5

0.1

1

10

100

1000

1 10 100

Gro

un

d V

ibra

tio

n (

mm

/s)

Frequency (Hz)

Baobab Resources Tete Iron ProjectGround Vibration Limits

Safe Blasting Zone

Above Limit Zone


7.1.3 Ground vibration limitations with regards to human perceptions

A further aspect of ground vibration and frequency of vibration is the human perception. It should

be realized that the legal limit for structures is significantly greater than the comfort zones for

people. Humans and animals are sensitive to ground vibration and vibration of the structures.

Research has shown that humans will respond to different levels of ground vibration and at different

frequencies.

Ground vibration is experienced as “Perceptible”, “Unpleasant” and “Intolerable” (only to name

three of the five levels tested) at different vibration levels for different frequencies. This is

indicative of the human’s perceptions on ground vibration and clearly indicates that humans are

sensitive to ground vibration. This “tool” is only a guideline and helps with managing ground

vibration and the respective complaints that people could have due to blast induced ground

vibrations. Humans already perceive ground vibration levels of 4.5 mm/s as unpleasant. (See Figure

9).

Generally people also assume that any vibrations of the structure - windows or roofs rattling - will

cause damage to the structure. Air blast also induces vibration of the structure and is the cause of

nine out of ten complaints.

Figure 9: USBM Analysis with Human Perception

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Baobab Resources Tete Iron ProjectGround Vibration Limits & Human Perception

Perceptible

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Safe Blasting Zone

Above Limit Zone


7.2 Air blast

Air blast or air-overpressure is pressure acting and should not be confused with sound that is within

audible range (detected by the human ear). Sound is also a build up from pressure but is at a

completely different frequency to air blast. Air blast is normally associated with frequency levels

less than 20 Hz, which is the threshold for hearing. Air blast is the direct result from the blast

process and is influenced by meteorological conditions, the final blast layout, timing, stemming,

accessories used, covered or not covered etc. .

The three main causes of air blasts can be observed as:

Direct rock displacement at the blast; the air pressure pulse (APP)

Vibrating ground some distance away from the blast; rock pressure pulse (RPP)

Venting of blast holes or blowouts; the gas release pulse (GRP)

7.2.1 Air blast limitations on structures

The recommended limit for air blast currently applied in South Africa is 134dB. This specifically

pertains to air blast or otherwise known as air-overpressure. This takes into consideration where

public are of concern. All attempts should be made to keep air blast levels generated from blasting

operations below 120dB or lower magnitude in critical areas where public are of concern. This will

ensure that the minimum amount of disturbance is generated towards the critical areas surrounding

the mining area.

Based on work carried out by Siskind et.al. (1980), monitored air blast amplitudes up to 135dB are

safe for structures, provided the monitoring instrument is sensitive to low frequencies (down to

1Hz). Persson et.al. (1994) have published the following estimates of damage thresholds based on

empirical data (Table 3). Levels given in Table 3 are at the point of measurement. The weakest

point on a structure are the windows and ceilings.

Table 3: Damage Limits for Air Blast

Level Description

>130 dB Resonant response of large surfaces (roofs, ceilings). Complaints start.

150 dB Some windows break

170 dB Most windows break

180 dB Structural Damage

All attempts should be made to keep air blast levels generated from blasting operations well below

120dB where public is of concern. This will ensure that the minimum amount of disturbance is

generated towards the critical areas surrounding the mining area and limit the possibility of

complaints due to the secondary effects from air blast.


7.2.2 Air blast limitations with regards to human perceptions

Considering the human perception and misunderstanding that could occur between ground vibration

and air blast, BM&C generally recommends that blasting be done in such a way that air blast levels

are kept below 120dB. In this way it is certain that fewer complaints will be received for blasting

operations. Air blasts that startle people have very little effect on structures as it is the actual

influence on structures like rattling of windows or doors or large roof surface’s that startle people,

rather than actually cause damage. These effects are sometimes misjudged as ground vibration and

considered as damaging to the structure.

Air blast levels predicted in this report is evalauted as “Acceptable” (below 120 dB), “Complaints

can be expected” (between 120 dB and 134 dB) and “Problematic” (greater than 134 dB).

7.2.3 Air blast prediction

An aspect that is not normally considered as pre-operation definable is the effect of air blast. This

is mainly due to the fact that air blast is an aspect that can be controlled to a great degree by

applying basic rules. Air blast is the direct result from the blast process, and although influenced by

meteorological conditions, the final blast layout, timing, stemming, accessories used, covered or not

covered etc. are all factors that can be used to mitigate the effects of air blast.

Standards do exist and predictions can be made, but it must be taken in to account that predictions

of air blast are effective only when measured and calibrated according to the circumstances where

blasting is taking place.

The following equation is associated with predictions of air blast, but is considered by the author as

subjective. In this report a standard equation to calculate possible air blast values was used. This

equation does not take temperature or any weather conditions into account. Values were calculated

using a cube root scaled distance relationship from expected charge masses and distance. Equation

2 is normally used where no actual data exists.

Equation 2:

Where:

dB = Air blast level (dB)

D = Distance from source (m)

E = Maximum charge mass per delay (kg)

Although the above equation was applied for prediction of air blast levels, additional measures are

also recommended in order to ensure that air blast and associated fly-rock possibilities are

minimized as best possible. As discussed earlier the prediction of air blast is very subjective. Table


4 below provides a summary of values predicted according to Equation 2. Figure 10 shows the

graphical relationship for air blast as set out in Table 4. This graph shows that the effect is

significantly less after 1km and minimal disturbance will take place after 1km. However, there are

other influences that could increase these effects which need to be taken into account when blasting

is done.

Table 4: Air Blast Predicted Values

No. Distance (m) Air blast (dB) for 192 kg Charge Air blast (dB) for 770kg Charge

1 50.0 142 147

2 100.0 138 143

3 150.0 131 136

4 200.0 128 133

5 250.0 126 131

6 300.0 124 129

7 400.0 121 126

8 500.0 118 123

9 600.0 117 123

10 700.0 115 120

11 800.0 114 118

12 900.0 112 117

13 1000.0 111 116

14 1250.0 109 114

15 1500.0 107 112

16 1750.0 105 110

17 2000.0 104 109

18 2500.0 102 107

19 3000.0 100 105

20 3500.0 98 103


Figure 10: Predicted air blast levels

7.3 Fly rock

Blasting practices require some movement of rock to facilitate the excavation process. The extent

of movement is dependent on the scale and type of operation. For example, blasting activities

within large coal mines are designed to cast the blasted material much greater distances than

practices in a quarry or hard rock operations. This movement should be in the direction of the free

face, and therefore the orientation of the blasting is important. Material or elements travelling

outside of this expected range may be considered to be fly rock.

Fly rock can be explained and defined in the following three categories:

Throw - the planned forward movement of rock fragments that form the muck pile within

the blast zone.

Fly rock - the undesired propulsion of rock fragments through the air or along the ground

beyond the blast zone by the force of the explosion that is contained within the blast

clearance (exclusion) zone. Fly rock using this definition, while undesirable, is only a safety

hazard if a breach of the blast clearance (exclusion) zone occurs.

Wild fly rock - the unexpected propulsion of rock fragments, when there is some

abnormality in a blast or a rock mass, which travels beyond the blast clearance (exclusion)

zone.

Figure 11 below shows the schematic fly rock terminology

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Baobab Resources Tete Iron ProjectAirblast Predictions

Single BH / Delay 4xBH / Delay Top Limit (dB) Mid. Limit (dB) Bottom Limit (dB)


Figure 11: Schematic of fly rock terminology

7.3.1 Fly rock causes

Fly rock from blasting can result from the following conditions:

When burdens are too small rock elements can be propelled out of the free face area of the

blast.

When burdens are too large and movement of blast material is restricted and stemming

length is not correct rock elements can be forced upwards creating a crater forming fly rock

from this.

If the stemming material is of proper quality or too little the stemming is ejected out of the

blast hole and fly rock created.

Stemming of correct type and length is required to ensure that explosive energy is efficiently used

to its maximum and to control fly rock.

7.3.2 Fly rock predictions

The occurrence of fly rock in any form will have a negative impact if found to travel outside the

safe boundary. A general unsafe boundary is normally considered to be within a radius of 500 m.

If a road, structure, people or animals are within the 500 m unsafe boundary of the blast,

irrespective of the possibility of fly rock or not, precautions must always be taken to stop the traffic,

remove people and / or animals for the duration of the blast.

Calculations are also used to help and assist determining safe distances. Two methods are currently

applied by BM&C, one according to Little (2007) and another according to the International

Society of Explosives Engineers (ISEE) Blasters Handbook. Using these calculations the minimum

safe distances can be determined that should be cleared of people, animals and equipment. Figure

12 shows the results from the ISEE and Little calculations for the proposed drill diameter. The

calculations in the designs are based on a 20x blast hole diameter stemming length. The absolute


minimum exclusion zone for the two scenarios is 239 m (based on Little, 2007) and 464 m (based

on ISEE).. These calculations are guidelines and any distance cleared should not be less. The

occurrence of fly rock can however never be excluded 100%, and hence best practices must be

implemented. The occurrence of fly rock can be mitigated but the possibility of the occurrence there

off can never be eliminated.

Figure 12: Predicted Fly rock

7.3.3 Impact of fly rock

The occurrence of fly rock in any form will have impact if found to travel outside the safe

boundary. This safe boundary may be anything between 10m or 500m. If a road or structure or

people or animals are closer than the safe boundary from a blast irrespective of the possibility of fly

rock, precautions should be taken to stop the traffic, and to remove people or animals for the period

of the blast. The fact is fly rock will cause damage to the road, vehicles or even death to people or

animals. This safe boundary is determined by the appointed blaster. BM&C normally recommends

no shorter distance than 500m.

7.4 Noxious Fumes

Explosives currently used are required to be oxygen balanced. Oxygen balance refers to the

stoichiometry of the chemical reaction and the nature of gases produced from the detonation of the

explosives. The creation of poisonous fumes such as nitrous oxides and carbon monoxide are

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Baobab Resources Tete Iron ProjectMaximum Throw Distance vs Burden/Stemming Height

Planned Stemming Little Fly Rock Calc Planned Stemming ISEE Fly Rock Calc

Fly Rock Calc - ISEE Fly Rock Calc - Little


particular undesirable. These fumes present themselves as a red brown cloud after blast detonation.

It has been reported that 10ppm to 20ppm has been mildly irritating. Exposure to 150 ppm or more

(no time period given) has been reported to cause death from pulmonary edema. It has been

predicted that 50% lethality would occur following exposure to 174ppm for 1 hour. Anybody

exposed must be taken to hospital for proper treatment.

7.4.1 Noxious Fume Causes

Factors contributing to undesirable fumes are typically: poor quality control on explosive

manufacture, damage to explosive, lack of confinement, insufficient charge diameter, excessive

sleep time, and specific types of ground can also contribute to fumes.

Poor quality control on explosives will yield improper balance of the explosive product. This is

typically in the form of too little or too much fuel oil or incorrect quantities of additives to the

mixture. Improper quality will cause break down on the explosives product that may result in poor

performance. A “burning” may occur that increases the probability of fumes in the form of NO and

NO2.

Damage to explosives occurs when deep blast holes are charged from the top of the hole and

literally fall into the hole and get damage at the bottom. The bottom is normally the point of

initiation and damaged explosives will not initiate properly. A slow reaction to detonation is forced

and again contributes negatively to the explosives performance and fume creating capability.

Studies showed that inadvertent emulsion mixture with drill cuttings can also be a significant

contributing factor to NOx production. The NO production from the detonation of emulsion equally

mixed (by mass) with drill cuttings increased by a factor of 2.7 over that of emulsion alone. The

corresponding NO2 production increased by factor of 9; while detonation propagated at a steady

Velocity of Detonation.

Water also has visible effects on the generation of fumes from emulsion explosives. Tests have

shown that the detonation velocity may not be influenced as much but the volumes of fumes

generated were significantly higher.

Certain ground types, especially oxidized type materials, could have an adverse effect on explosives

as well. These ground material types tend to react with the explosives and cause more than expected

fumes.

Drill diameter is also a contributing factor to explosive performance and the subsequent generation

of fumes. Explosives are diameter dependant for optimal performance. If the diameter is too small

for a specific product improper detonation will occur and may result in a burning of the product

rather than detonation. This will have an adverse effect of more fumes created. Each explosive


product has a critical diameter. It is the smallest diameter where failure to detonate properly occurs.

ANFO blends are normally not good for small diameter blast holes and emulsion explosives can be

used in the smaller diameter blast holes.

7.4.2 Noxious Fume Control

Control actions on fumes will include the use of the proper quality explosives and proper loading

conditions. Quality assurance will need to be achieved from the supplier with quality checks on

explosives from time to time. Further action is to prevail from loading blast holes at long periods

prior to blasting. Excessive sleeping of charged blast holes will add to fumes generation and should

be prevented. Additional measures could include placing stemming plugs at the bottom of the hole

and loading emulsion from the bottom up will excluded mixing of drill chippings with the

explosives in initiation area. The checking of blast holes for water will ensure that the charging

crew charges blast holes from the bottom (which should be a standard practise) and displaces the

water. This will also ensure proper initiation of the blast hole.

7.5 Vibration will upset adjacent communities

The effects of ground vibration and air blast will have an influence on people. These effects tend to

create noises on structures in various forms and people react to these occurrences even at low

levels. As with human perception given above – people will experience ground vibration at very

low levels. These levels are well below damage capability for most structures.

Much work has also been done in the field of public relations in the mining industry, and one aspect

that stands out is “Promote good neighbourliness”. This is achieved through good communication

with the neighbours. Consider their concerns and address them in a proper manner.

The first level of good practice is to avoid unnecessary problems. One problem that can be reduced

is the public's reaction to blasting. Concern for a person's home, particularly where they own it,

could be reduced by a scheme of precautionary, compensatory and other measures which offer

guaranteed remedies without undue argument or excuse.

In general it is also in an operator's financial interests not to blast where there is a viable alternative.

Where there is a possibility of avoiding blasting, perhaps through new technology, this should be

carefully considered in the light of environmental pressures. Historical precedent may not be a

helpful guide to an appropriate decision.

Independent structural surveys are one way of ensuring good neighbourliness, but there is inherent

difficulty in using surveys as the interpretation of changes in crack patterns that occur may be

misunderstood. Cracks open and close with the seasonal changes of temperature, humidity and

drainage, and numbers increase as buildings age. Additional actions need to be done in order to

supplement the surveys as well.


The following measures for controlling ground vibration, overpressure and fly rock have many

features in common and are used by the better operators, and many of the practices also aid cost-

effective production. The measures include the following:

Correct blast design is essential and should include a survey of the face profile prior to

design, ensuring appropriate burden to avoid over-confinement of charges which may

increase vibration by a factor of two,

The setting-out and drilling of blasts should be as accurate as possible and the drilled holes

should be surveyed for deviation along their lengths and, if necessary, the blast design

adjusted,

Correct charging is obviously vital, and if free poured bulk explosive is used, its rise during

loading should be checked. This is especially important in fragmented ground to avoid

accidental overcharging,

Correct stemming will help control air blast and fly rock and will also aid the control of

ground vibration. Controlling the length of the stemming column is important; too short and

premature ejection occurs, too long and there can be excessive confinement and poor

fragmentation. The length of the stemming column will depend on the diameter of the hole

and the type of material being used,

Monitoring of blasting and re-optimising the blasting design in the light of results, changing

conditions and experience should be carried out as standard.

7.6 Blast operations impact on wildlife - crocodiles

The location of the site next to the Revubué River could result in impacts on crocodiles. The

specific influences due to interaction between wild life and mining operations are a developing

study area. The following is summary on crocodiles is limited but significant as one of the only

pieces of work done in this area.

In order determine possible influences a literature search was done, which involved searches on the

internet and communication with specialist in the field of crocodiles. In particular Mr. Xander

Combrink was very helpful in this regard.

There is an abundance of information on crocodiles but very little that really addresses the question

of influence from blasting operations. In fact one report and court case was documented about

blasting operations apparently contributing to the deaths of various crocodiles at a crocodile farm in

Kwa-Zulu Natal in 1989. The incident was followed by a court case between the farm owner and

the blasting company doing blasting operations near the farm on the N2 national route. It is not the

objective to give full details of the case but to highlight the fact that on a previous occasion a claim

was made that the effects from blasting contributed to the deaths of multiple crocodiles. The main


reasons given were stress caused by the blasting that contributed to this. There was unfortunately no

specific data reported in this paper on the recordings made or the specific influences. Comparisons

were made from the analysis of blood samples from the stressed crocodile group and a group of

crocodiles at the Natal University (considered the control ). The crocodiles at the farm were

inspected and factors were observed that could indicate signs of stress. Further to this autopsies

were conducted and blood samples taken and compared to the control group. It was also mention

that other factors such an early winter and a virus could possibly have had an influence on the stress

of the crocodiles. A significant group of the crocodiles at the farm were imported from Namibia not

too long before this incident.

The court case following the claim did however conclude that there was no clear evidence that the

crocodiles died as a direct result of the blasting operations. There was no specific evidence of a

relationship between the deaths and blasting. The situation at the Tete site, is however different. In

the above case, crocodiles were kept in confined spaces, and could not avoid the effects of the

blasting. At Tenge, in all likelihood, the crocodiles will simply move away from the area and avoid

the direct effects of blasting.

This confirms that there is still no real data that can indicate a relationship of ground vibration and

air blast influence on crocodiles. It is known that crocodiles use the lower jaw bone to feel vibration

from fish when hunting and thus dependant on this for their survival.

Further research also included studies that were conducted on the hearing capability of crocodiles

and turtles, and there is more specific data available on these subjects. The basic outcome from

these studies indicate the likelihood that turtles have hearing capability in frequency ranges of 100

Hz and 3000 Hz. Various aspects of the ear functions were tested. Pressure tested ranged between

just less than -20 dB to greater than 30 dB. This is indicated as normal functioning of the turtle ear.

This corresponds to pressure levels between 0.008 Pa and 302 Pa. Crocodiles are likely to have

hearing capability ranging in frequency between 30 Hz and 5000 Hz. The tests conducted on

crocodiles indicated best sensitivity between 300 Hz and 2000 Hz. The intensities tested ranged

between -60 dB and +40 dB. This corresponds to pressures in the order of 0.0001 Pa and 10 Pa.

What is of importance from this data is the frequency range capability of crocodiles and turtles.

Noise could be within the same range as that of crocodiles and turtles.

Research work done in Canada on fish when blasting operations are done resulted in specific

recommendations when blasting is done in water and close to water. This is the closest to a solution

and in view of the lack of information as presented above, the data and recommendations from the

Canadian study is proposed. The specific recommendations that could be applicable here are:

a. No explosive to be knowingly detonated within 500 m of any aquatic animal.

b. The stemming of a blast hole must be done using angular gravel with a particle size of

approximately 1/12th

the size of blast hole diameter.


c. No explosive to be detonated in or near fish habitat that produces an instantaneous pressure

change of greater than 100 kPa.

d. For confined explosives the distance between habitat and blast must not exceed the 100 kPa

overpressure.

e. No explosives to be detonated that will produce vibration greater than 13 mm/s in a

spawning bed during egg incubation. (For the sake of simplicity this will be used

irrespective of spawning or not).

Considering the above summary the following will be important to consider.

a. Location of crocodile concentrations must be known.

b. Location of freshwater fauna (including fish) must be known.

c. Air blast will have to be controlled in relation to the surroundings where crocodiles and

fresh water fauna are found.

d. The pressure levels of should not exceed 100 kPa at water’s edge.

e. Ground vibration should not exceed 13 mm/s.

f. Air blast frequency should be less than 30 Hz.

The levels of ground vibration can be managed by specific blast design that will contribute to lower

levels. Ground vibration is likely to be transferred from solid to water but with reduction due to

reflections of the shockwave on the interface between solid and water. Air blast on the other hand is

less like to transfer to the water as a shockwave. The specific characteristics are rather an upward

direction away from the ground and this will make it highly unlikely causing a significant pressure

pulse in the water. Distance and location will be imperative in determining possible influences.

7.7 Water well Influence from Blasting Activities

Domestic and Agricultural boreholes may be present around the proposed site. The author has not

had much experience on the effect of blasting on water wells but specific research was done and

results from this research work are presented.

Case 1 looked at 36 case histories. Vibration levels up 50mm/s were measured. The well yield and

aquifer storage improved as the mining neared the wells, because of the opening of the fractures

from loss of lateral confinement, not blasting. This is similar to how stress-relief fractures form. At

one site the process was reversed after the mine was backfilled. It was more likely the fractures

were recompressed. It was stated that blasting may cause some temporary (transient) turbidity

similar to those events that cause turbidity without blasting, such as:

1. Natural sloughing off inside of the well bore due to inherent rock instability. This can be

accelerated by frequent over pumping. This is common in wells drilled through considerable

thickness of poorly consolidated and/or highly fractured clay stones and shale’s, which is not the

geology of the Tete site.


2. Significant rainfall events. The apertures of the shallow fractures that are intersected by a

domestic well are commonly highly transmissive, thus will transmit substantial amounts of

shallow flowing and rapidly recharging water. This water will commonly be turbid and can enter

the well in high volumes. The lack of grouting of the near surface casing commonly allows this

to happen. Also, if the top of the well is not grouted properly surface water can enter along the

side of the casing and flow down the annulus.

The Berger Study observed ground-water impacts from manmade stress-release caused rock mass

removal during mining, but nothing from the blasting. The water quality and water levels were

unaffected by the blasting. The “opening up” of the fractures lowered the ground-water levels by

increasing the storage or porosity.

A study tested wells 50m from a blast. Wells exhibited no quality or quantity impacts. Blast

pressure surges ranged from 3cm to 10cm. Blasting caused no noticeable water table fluctuations

and the hydraulic conductivity was unchanged. The pumping of the pit and encroachment of the

high wall toward the wells dewatered the water table aquifer.

It may then be concluded from the studies that, depending on the well construction, litho logic units

encountered, and proximity to the blasting, it is believed that large shots could act as a catalyst for

some well sloughing or collapse. However, the well would have to be inherently weak to begin

with. Small to moderate shots will not impact wells. The minor water fluctuations attributed to

blasting may cause a short term turbidity problem, but do not pose any long term problems. This

fluctuation would not cause well collapse, as fluctuations from recharge and pumping occurs

frequently. Long term changes to the well yield are more likely due to the opening of fractures from

loss of lateral confinement. Short term dewatering of wells is caused by the opening of the fractures

creating additional storage. Longer term dewatering is caused by encroachment of the high wall and

pumping of the pit water, as the pit acts like a large pumping well. It is not believed that long term

water quality problems will be caused by blasting alone. The possible exception is the introduction

of residual nitrates, from the blasting materials, into the ground water system. This is only possible

through wells that are hydrologically connected to a blasting site. Most of the long term impacts on

water quality are due to the mining (the breakup of the rocks). The influence will also be dependant

if wells are beneath the excavation. Stress relief effects occur at shorter distances in this instance,

and these impacts have been addressed in the geohydrological study.

The results observed and levels recorded during research done showed that levels up to 50mm/s or

even higher in certain cases did not have any noticeable effect. It seems that safe conditions will be

in the order of 50mm/s. In addition to this there are certain aspects that will need to be addressed

prior to blasting operations.

8 Baseline Results


The base line information for the project is based on zero influence with regards to blast impacts.

The project is currently not active with any blasting operations being done. As part of the baseline

all possible structures in a possible area of influence are identified.

The site was reviewed / scanned using Google Earth imagery. The kind of surface structures that are

present in a 3500m radius from the proposed mine boundary were identified as they will require

consideration during modelling of blasting operations. This could consists of houses, general

structures, power lines, pipelines, reservoirs, mining activities, roads, shops, schools, gathering

places, possible historical sites etc. A list was prepared for each structure in the vicinity of the north

and south pit areas. The list prepared covers structures and points of interest (POI) in the 3500m

boundary. A list of structure locations was required for determining the allowable ground vibration

limits and air blast limits possible. Figure 13 shows an aerial view of the mining area and

surroundings with points of interest. The list of points identified is provided in Table 5 below.

Please note that each and every house was not marked. Where there are groups of houses a point

was placed for the group or in some cases two points were placed to identify the closest point and

furthest point.

Tenge Pit Area:


Figure 13: Aerial view and surface plan of the proposed mining area with points of interest

identified.

Table 5: List of points of interest used (WGS –UTM L36)

Tag Description Classification Y X

1 Rural Houses 1 581864 8261250

2 Rural Houses 1 583497 8261914

3 Rural Houses 1 583450 8262099

4 Rural Houses 1 583587 8262455

5 Rural Houses 1 583075 8262460

6 Rural Houses 1 582741 8262433

7 Rural Houses 1 583241 8263178

8 Rural Houses 1 583010 8263893

9 Rural Houses 1 584340 8263044

10 Rural Houses 1 584564 8263031


Tag Description Classification Y X

11 Rural Houses 1 585057 8263042

12 Rural Houses 1 584683 8263830

13 Rural Houses 1 584506 8263944

14 Rural Houses 1 584665 8264063

15 Rural Houses 1 584908 8264174

16 Rural Houses 1 584533 8264177

17 Rural Houses 1 584820 8264294

18 Rural Houses 1 580165 8264183

19 Rural Houses 1 579839 8262958

20 Rural Houses 1 579857 8263488

21 Rural Houses 1 580294 8259402

22 Rural Houses 1 580815 8258954

23 Rural Houses 1 580245 8259189

24 Rural Houses 1 581226 8259137

25 Rural Houses 1 580447 8258628

26 Rural Houses 1 581311 8260232

27 Rural Houses 1 581436 8261254

28 River Crossing 6 582962 8262432

29 Rural Houses 1 583045 8263231

30 Agricultural Fields 6 583523 8264178

31 River 6 582503 8261822

32 Rural Houses 1 583202 8265230

33 Rural Houses 1 581785 8259651

34 Rural Houses 1 581660 8259231

35 Rural Houses 1 581799 8259087

36 Mine Plant Area 5 583535 8260950

The type of POI’s identified are grouped into different classes. These classes are indicated in the

“Classification” column above. Table 6 below presents the descriptions of the classifications used.

Table 6: POI Classification used

Class Description

1 Rural Building and structures of poor construction

2 Private Houses and people sensitive areas – not at the site

3 Office and High rise buildings – not at the site

4 Animal related installations and animal sensitive areas – not at the site

5 Industrial buildings and installations

6 Earth like structures - no surface structure

7 Graves & Heritage

No specific site visit was done by the author but it was confirmed from the Social Impact

Assessment that typical structures in the area are similar to other areas in Mozambique. Figure 14

below shows an example of typical building in the area.


Figure 14: Typical building style

9 Construction Phase: Impact Assessment and Mitigation Measures

During the construction no mining drilling and blasting operations are expected. It is uncertain if

any construction blasting will be done. If any blasting will be required for establishment of the plant

area it will be reviewed as civil blasting and addressed accordingly.

10 Operational Phase: Impact Assessment and Mitigation Measures

The area surrounding the proposed mining area was reviewed for structures, traffic, roads, human

and animal use etc. The only installations and structures observed were rural houses, as listed in

Table 5. This section concentrates on the outcome of modelling the possible effects of ground

vibration, air blast and fly rock specifically to these points of interest and the mines plant area to be

established. In evaluation two different charge mass scenarios were considered with regards to

ground vibration and air blast. Review of the charge per blast hole and the possible timing of a blast

resulted in two different charge masses of 192 and 770 kg being selected to ensure proper source

coverage. The option of evaluating two charges gives an immediate indication of the area of

influence if reduction of charge mass from blasting is required. If timing is changed to facilitate a

single hole firing then the single charge mass of 192 kg will be applicable.


Ground vibration and air blast was calculated from the edge of the pit outline and modelled

accordingly. Blasting further away from the pit edge will certainly have lesser influence on the

surroundings. A worst case is then applicable with calculation from pit edge. As explained

previously reference is only made to some structures and these references cover the extent of all

structures surrounding the mine.

The following aspects with comments are addressed for each of the evaluations done:

Ground Vibration Modelling Results

Ground Vibration and human perception

Vibration will upset adjacent communities

Cracking of houses

Air blast Modelling Results

Impact of fly rock

Noxious fumes Influence Results

Lowest vibration limit area of influence

The modelling of the ground vibration levels over distances is a basic model. Without specific

testing it is nearly impossible to estimate the levels of vibration over distance in relation to the site.

This mining area has a river on the western side, the proposed mining area is located on top a small

hill and the slope towards the east is more gradually. Factors like the river and the location on a hill

will certainly influence the ground vibration levels expected. The actual ground vibration will

certainly be influenced; and a reduction of ground vibration is expected from these influences. The

western side will be influenced more – thus more reduction is expected. The eastern side ground

conditions are constant with no rivers or significant changes in geology . It is expected that this

side will be influenced less. The data is based on good practise applied internationally and estimates

based on the information provided and supplied in this document are regarded as good. Figure 15

shows the topography for the mining area and immediate surroundings.


Figure 15: Site topography

10.1 Review of expected ground vibration

Expected ground vibration levels were calculated for each of the structure locations or POI’s

surrounding the mining area. Evaluation is given for each POI with regards to human perception

and structure concerns. The evaluation is done based on the criteria that humans experience and

where structures could be damaged. This is according to accepted criteria for prevention of damage

to structures and when levels are low enough to have no significant influence. Tables are provided

for each of the different charge modelling done with regards to Tag, Description, Specific Limit,

Distance (m), Predicted PPV (mm/s), and Possible Concern for Human perception and Structure.

The “Tag” No. is number corresponding to the location indicated on POI figures.

“Description” indicates the type of the structure.

“Distance” is the distance between the structure and edge of the pit area.

“Specific Limit” is the maximum limit for ground vibration at the specific structure or

installation.

“Predicted PPV (mm/s)” is the calculated ground vibration for the structure.

“Possible concern” indicates if there is any concern for structure damage or not or human

perception.


Indicators used are “perceptible”, ”unpleasant”, “intolerable” which stems from the human

perception information given and indicators such as “high” or “low” are used where there is a

possibility of damage to a structure or no significant influence is expected and concern is low.

Levels below 0.76mm/s could be considered to be low or negligible influence.

Ground vibration is calculated and modelled for the north and south pit areas at the minimum,

medium and maximum charge mass at specific distances from the opencast mining area. The charge

masses applied are according to blast designs in section 6. These levels are then plotted and overlaid

with current mining plans to observe possible influences at structures identified. Structures or POI’s

for consideration are also plotted in this model. Ground vibration predictions were done considering

distances ranging from 50m to 3500m around the opencast mining area.

Indicators of the ground vibration limits used are also provided with each stimulation: 6 mm/s, 12.5

mm/s and 25 mm/s. 6 mm/s is indicated as a “Solid Blue” line, 12.5 mm/s “Intermittent Blue” line

and 25 mm/s as a “Intermittent Red” line. This enables immediate review of possible concerns that

may be applicable to any of the privately owned structures, social gathering areas or installations.

Consideration can also then be given to influences on sensitive installations within the mine

boundary.

Data is provided firstly for the minimum charge and then the maximum charge and presented as

follows: Vibration contours followed by table with predicted ground vibration values and evaluation

for each POI. Additional colour codes used in the tables indicates the following:

Vibration levels higher than proposed limit applicable to Structures / Installations are coloured

“Mustard”

Vibration levels indicated as Intolerable on human perception scale are coloured “Yellow”

10.1.1 Calculated Ground Vibration Levels

Simulations for expected ground vibration levels from minimum and maximum charge masses are

presented. Figure 16 shows evaluation minimum charge, and Figure 17 shows a zoomed area of

figure 16. Figure 18 shows evaluation of ground vibration for maximum charge.


Minimum Charge per Delay – Tenge Pit Area – 192 kg

Figure 16: Ground vibration influence from minimum charge


Figure 17: Zoomed area for ground vibration influence from minimum charge

Table 7: Ground vibration evaluation for minimum charge

Tag Description Specific Limit

(mm/s)

Distance

(m)

Total

Mass/Delay

(kg)

Predicted

PPV (mm/s)

Human

Tolerance

@ 30Hz

Structure

Response @

10Hz

1 Houses 6 313 192 6.7 Unpleasant Problematic

2 Houses 6 710 192 1.7 Perceptible Acceptable





7 Houses 6 1440 192 0.5 Too Low Acceptable










(mm/s)

Distance

(m)

Total

Mass/Delay

(kg)

Predicted

PPV (mm/s)

Human

Tolerance

@ 30Hz

Structure

Response @

10Hz














28 River

Crossing 150 644 192 2.0 Perceptible Acceptable


30 Agricultural

Fields 150 2477 192 0.2 Too Low Acceptable

31 River 12 91 192 51.2 Intolerable Problematic





36 Mine Plant

Area 50 853 192 1.3 Perceptible Acceptable


Maximum Charge per Delay – Tenge Pit Area – 770 kg

Figure 18: Ground vibration influence from maximum charge

Table 8: Ground vibration evaluation for maximum charge


(mm/s)

Distance

(m)

Total

Mass/Delay

(kg)

Predicted

PPV (mm/s)

Human

Tolerance

@ 30Hz

Structure

Response @

10Hz

1 Houses 6 313 770 21.0 Intolerable Problematic





6 Houses 6 604 770 7.1 Unpleasant Problematic














(mm/s)

Distance

(m)

Total

Mass/Delay

(kg)

Predicted

PPV (mm/s)

Human

Tolerance

@ 30Hz

Structure

Response @

10Hz











28 River

Crossing 150 644 770 6.4 Unpleasant Acceptable


30 Agricultural

Fields 150 2477 770 0.7 Too Low Acceptable

31 River 12 91 770 161.1 Intolerable Problematic





36 Mine Plant

Area 50 853 770 4.0 Perceptible Acceptable

10.1.2 Summary of ground vibration levels

The opencast operation was evaluated for expected levels of ground vibration from future blasting

operations. Review of the site and the surrounding areas showed that houses varied in distances

from the opencast pit area. The structures identified range in distance from the pit area between 313

m and further than 3500 m. The nearest structures are found at 313 m and indicate that care must be

taken when blasting is conducted in the areas close to points of interest and proper planning must be

done. Mitigation will be required.

The minimum charge showed the lowest levels of influence as expected for the pit area. Only one

POI (01) was identified with a possibility of been negatively influence due to blasting. Levels

expected are greater than the 6 mm/s limit. Ground vibration levels calculated for the maximum

charge shows an increase in levels for houses at POI 1 and 6. Mitigation will be required in order to

ensure that levels of ground vibration are within accepted norms. The expected ground vibration

levels for maximum charge ranged between 0.4 mm/s and 161 mm/s.

Figure 19 shows the extent of area where a ground vibration levels of 6 mm/s can be expected for

minimum and maximum charge mass. POI 13 is the river and levels expected are relatively high –

161 mm/s. In general this high level will have no significant influence on the river. As discussed

later it may be problematic when aquatic life is be considered.


Figure 19: The range of 6 mm/s for minimum and maximum charge (blue line).

10.2 Ground Vibration and human perception

Considering the effect of ground vibration and human perception, vibration levels calculated were

applied to an average of 30Hz frequency and plotted with expected human perceptions on the safe

blasting criteria graph (See Figure 20 below). The frequency range selected is the expected average

range for frequencies that will be measured for ground vibration.

The maximum charge in relation to human perception shows that just less than 2500 m from the

blast people could possibly experience the ground vibration as “Perceptible”. At 800 m the


expected ground vibration levels are still less than the lower safe blasting limit – less than 6 mm/s

(broken green line) but will be experienced by people as “unpleasant”. At a distance of 400m and

closer there is a strong indication that people will experience the ground vibration as “Intolerable”.

Distances closer than 675 m will exceed the minimum 6 mm/s proposed safe limit for rural type

structures. Figure 20 below shows this effect of ground vibration with regards to human perception

for maximum charge.

Figure 20: The effect of ground vibration with human perception and vibration limits

10.3 Potential for vibration upsetting adjacent communities

Ground vibration and air blast generally upset people living in the vicinity of mining operations.

There are communities, farming areas and roads that are within the evaluated area of influence.

Structures are found ranging from 313 m to 3434 m around the pit area. Ground vibration levels at 7

POI’s could be regarded as perceptible at distances up to 1041 m for maximum charge.

People tend to react negatively when experiencing the effects of blasting, especially ground

vibration and air blast. Even at low levels when damage to structures will not occur, it may upset

people. Proper and appropriate communication with neighbours about blasting, monitoring and

actions done for proper control will be required.

2500m 2500m

800m 800m

400m 400m

6 6

12.5 12.5

0.1

1

10

100

1000

1 10 100

Gro

un

d V

ibra

tio

n (

mm

/s)

Frequency (Hz)

Baobab Resources Tete Iron ProjectGround Vibration Limits & Human Perception

Perceptible Unpleasant Intolerable Vibration @30 Hz 2500m

800m 400m 6mm/s Limit 12.5mm/s Limit

Perceptible

Unpleasant

Intolerable

Safe Blasting Zone

Above Limit Zone30Hz Vibration levels


10.4 Cracking of houses

The structures found in the area of concern are rural buildings. These types of structures are

generally prone to natural cracks forming due to the materials being used. Building style and

materials are the biggest contributor to cracking apart from influences such as blasting operations.

Cracks will be found on all structures and this does not necessarily to indicate devaluation due to

blasting operations but rather devaluation due to construction, building material, age, and

construction standards . Thus damage in the form of cracks will be present. Exact costing of

devaluation for normal cracks observed is difficult to estimate. The mining operations may not

change the status quo of any property if correct precautions are considered.

The proposed limits as applied in this document i.e. 6 mm/s for rural buildings is considered

sufficient to ensure that additional damage is not introduced to the different categories of structures.

It is expected that, should levels of ground vibration be maintained within these limits, the

possibility of inducing damage is limited.

10.5 Air blast

The effect of air blast, if not controlled properly, is in my opinion a factor that could be

problematic, not in the sense of damage but rather having an nuisance impact. Structures built with

hard materials such as corrugated iron, roof tile etc., glass windows and doors could experience -

even at low levels - some form of rattling or noise. These effects could result in complaints from

people. In more than one case this effect is misunderstood and people consider this effect as being

ground vibration and thus damaging their structures. In the case of rural buildings – straw roofs -

these effects may not be as prominent on roofs but the area is very remote and the effect of blasting

unknown. Blast noise may have a more significant influence than in areas where mining is already

part of life. Section 6 gives detail on the selection of the charge sizes applied, which are the same

air blast limits as for less rural areas.

The effect of meteorological conditions cannot specifically be considered with the predictions done

in this report. Wind direction, wind speed, cloud cover, humidity etc. are factors known to have

influences on the levels of air blast. The only aspect that can be mentioned specifically is that small

changes in the control of stemming will have significant influences on the air blast levels yielded.

As with ground vibration, evaluation is given for each structure with regards to the calculated levels

of air blast and concerns if applicable. Evaluation is done in the form of the criteria that humans

experience and where structures could be damaged. This is according with accepted criteria for the

prevention of damage to structures. Tables are provided for each of the different charge modellings

done with regards to Tag, Description, Specific Limit, Distance (m), Predicted Air blast (dB) and

Possible Concern. These terms were defined earlier. The “Air Blast (dB)” is the calculated air blast


level at the structure and the “possible concern” indicates if there is any concern for structure

damage or not or human perception. Indicators used are “Problematic" where there is real concern

for possible damage, "Complaint" where people will be complaining due to the experienced effect

on structures – not necessarily damaging, ”Acceptable” is if levels are less than 120dB and low

where there is very limited possibility that the levels will give rise to any influence on people or

structures. Levels below 115dB could be considered as to be low or negligible possibility of

influence.

Table 9 shows the applied limits and recommended levels for each of the charges considered. The

maximum charge may exceed limits up to a distance of 200 m. The recommended limit of 120 dB is

observed at distance of 700 m for maximum charge (green row below) and 400 m for minimum

charge (red row). These distances are reduced to 150 m for the minimum charge allowed limit and

200 m for recommended limit. This clearly indicates that with increased charge masses the

distances of influence increases. An area of 700 m influence would occur if care is not taken to

manage air blast levels.

Table 9: Expected air blast levels

No. Distance (m) Air blast (dB) for 192 kg

Charge

Air blast (dB) for 770 kg

Charge

1 50.0 142 147

2 100.0 138 143

3 150.0 131 136

4 200.0 128 133

5 250.0 126 131

6 300.0 124 129

7 400.0 121 126

8 500.0 118 123

9 600.0 117 121

10 700.0 115 120

11 800.0 114 118

12 900.0 112 117

13 1000.0 111 116

14 1250.0 109 114

15 1500.0 107 112

16 1750.0 105 110

17 2000.0 104 109

18 2500.0 102 107

19 3000.0 100 105

20 3500.0 98 103

Figures 21 and 22 below present the expected air blast level contours. Discussion of level of air

blast and relevant influences are also given for the pit area. Air blast was calculated and modelled

from the boundary for minimum, medium and maximum charge mass at specific distances from

each of the pit areas. This means that air blast is taken from the edge – the most outer point of the


pit area on plan as if it would be the closest place to the area of influence where drilling and blasting

will be done. The calculated levels are then plotted and overlaid with current mining plans to

observe possible influences at identified POI’s. Air blast predictions were done considering

distances ranging from 50 to 3500m around the opencast mining area.

10.5.1 Review of expected air blast

Simulations for expected air blast levels from two different charge masses are presented. Minimum,

medium and maximum charge evaluations are shown in the figures below and summary table of the

outcome given after each charge configuration air blast contour. Figure 21 shows an evaluation of

air blast for minimum charge and Figure 22 shows an evaluation maximum charge.

Colour codes used in tables are as follows:

Air blast levels higher than proposed limit is coloured “Mustard”

Air blast levels indicated as possible Complaint is coloured “Yellow”

Minimum Charge per Delay – Tenge Pit Area – 192 kg

Table 10: Air blast evaluation for minimum charge

Tag Description Distance (m) Air blast (dB) Possible Concern?

1 Houses 313 123.4 Complaint

2 Houses 710 114.8 Acceptable




























28 River Crossing 644 N/A Problematic


30 Agricultural Fields 2477 101.8 Acceptable

31 River 91 N/A Problematic





36 Mine Plant Area 853 112.9 Acceptable

Figure 21: Air blast influence from minimum charge

Maximum Charge per Delay – Tenge Pit Area– 770 kg

Table 11: Air blast evaluation for maximum charge






























28 River Crossing 644 N/A Problematic


30 Agricultural Fields 2477 106.6 Acceptable

31 River 91 N/A Problematic





36 Mine Plant Area 853 117.8 Acceptable

2


Figure 22: Air blast influence from maximum charge

10.5.2 Summary of findings for air blast

As indicated the prediction of air blast is subjective and is used to help identify critical points as

best as possible. Actual blasting operation preparation plays a very significant role in the outcome

of air blast levels. If care is not taken then this prediction could be rendered useless and not

applicable. It is known that air blast is the aspect that contributes to complaints from neighbours

more than ground vibration even at levels not in range of causing damage.

Review of the air blast levels shows trend of lesser influence than ground vibration. Structures

within 200m from the pit boundaries are generally problematic and structures found up to 600m

could experience levels of air blast that could contribute to complaints. Complaints from air blast

are normally based on the actual effects that are experienced due to rattling of roof, windows, doors


The possible negative effects from air blast are expected to be less than that of ground vibration. It

is maintained that if stemming control is not exercised this effect could be greater with greater

number of complaints or damage. The pit area is located such that “free blasting” – meaning no

controls on blast preparation – will not be possible.


No points of concern were identified where possible damage could be expected. Minimum charge

showed one POI with levels that could lead to complaints and maximum charge showed two POI’s

with levels that could lead to complaints.

Figure 23 shows areas covered for 120 dB air blast from minimum and maximum charges.

Figure 23: Air blast influence area for 120 dB – minimum and maximum charge

10.6 Fly-rock Modelling Results and Impact of fly rock

Based on a review of the factors that contribute to fly rock it is concluded that if no stemming

control is implemented there will be fly rock. A stemming length of 3.3 m in the blast is expected to

yield fly rock that could travel as far as 239m. Possible further reduction of stemming length will


certainly see fly rock travelling further. A distance of 464 m is calculated for consideration as an

exclusion zone that should be cleared for safe blasting. At a distance of 464 m there are only 3

points of interest. These do however include a group of houses on the south western side, the river

and what seems to be an area that is used as a river crossing. There is nothing specific here but it is

identified as a place where people may be present, specifically if this is the only river crossing for

some distance. Figure 24 below shows the relationship burden or stemming length towards expected

throw distance. Throw distance of elements considered here is on the same level as the free face.

Landing level of elements lower than free face – down hill - could result in greater distances.

Optimal throw distance is also observed at 45 degree angles of departure and at the elevated levels

of blasting care must be taken as fly rock travel distance may be further than anticipated. Careful

attention will need to be given to stemming control to ensure that fly rock is minimised as much as

possible. Figure 25 indicates the points to be considered during mitigation with regards to fly rock

control. Figure 26 shows the extend or area that is covered under the range of the fly rock travel.

Figure 24: Predicted Fly rock

239

464

0

200

400

600

800

1000

1200

1 1.5 2 2.5 3 3.5 4 4.5 5

Th

row

Dis

tan

ce

(m

)

Burden / Stemming Length (m)

Baobab Resources Tete Iron ProjectMaximum Throw Distance vs Burden/Stemming Height

Planned Stemming Little Fly Rock Calc Planned Stemming ISEE Fly Rock Calc

Fly Rock Calc - ISEE Fly Rock Calc - Little


Figure 25: Predicted Fly rock points for mitigation


Figure 26: Predicted Fly rock range of influence

10.7 Noxious fumes

The occurrence of fumes in the form of NOx gas is not certain and is very dependent on various

factors. However the occurrences of fumes should be closely monitored. It is not assumed that

fumes will travel to any POI’s but again if anybody is present in the path of cloud travel it could be

problematic.

10.8 Water well influence

It is uncertain at the moment where domestic and agricultural boreholes are located in the area.

Based on a limit of 50mm/s all boreholes further than 200m from pit boundary should not be

influenced negatively.


10.9 Blast operations impact on wildlife - crocodiles

Domestic animals and wildlife, including crocodiles, do occur in the area An area of possible

concern is the river but the specific influence from blasting operations is not well defined. Due to

the presence of crocodiles the following is recommended.

If the Canadian guidelines (as discussed earlier) are used Tenge Pit shows an area of concern with

regards to minimum and maximum charge. These charges are likely to yield ground vibration levels

greater than 13 mm/s at water’s edge. Due to crocodiles in this part of the Revubué River it must be

considered a sensitive area. The charge mass per delay that will yield 13 mm/s over a distance of

approximately 100 m from pit to water’s edge is low at 44 kg. This charge mass is less than the

minimum charge, and mitigation will be required. Relocation of crocodiles could be considered and

evaluated, or a change in drilling parameters for the western side of the pit could be negotiated. This

will entail a 5m bench and smaller diameter blast holes. An 89 mm diameter blast hole 5.5 m deep

will require 29 kg charge. The air blast levels expected at 100 m from maximum charge is in the

order of 140 dB. This relates to 0.2 kPa over pressure. This level is significantly less than the limit

of 100 kPa and not expected to be lethal nor have any significant influence on river life.

Figure 27 below shows area of Revubué River that could possibly be influenced based on the

expected ground vibration levels for minimum and maximum charges.


Figure 27: Sensitive river area

It is very difficult to specifically ascertain whether there will be any influence without any direct

investigation. The sensitivity of the possible influences is understood but based on effects such as

ground vibration and air blast there is reason to believe that expected levels will be less than what

will be required to induce injury of death. Social behaviour or changes of social behaviour in these

circumstances are unknown at this stage, but it is anticipated that crocodiles will simply move away

from the area.

10.10 Potential Environmental Impact Assessment: Operational Phase

The following is the impact assessment of the various concerns covered by this report. The matrix

below in Table 31 was used for analysis and evaluation of aspects discussed in this report. The

outcome of the analysis is provided in Table 32 before mitigation and Table 33 after mitigation..


Table 12: Evaluation matrix criteria

Occurrence Severity

Probability of occurrence Duration of occurrence Magnitude (severity) of

impact Scale / extent of impact

To assess each impact, the following four ranking scales are used:

Probability Duration

5 - Definite/don’t know 5 - Permanent

4 - Highly probable 4 - Long-term

3 - Medium probability 3 - Medium-term (8-15 years)

2 - Low probability 2 - Short-term (0-7 years) (impact ceases after the

operational life of the activity)

1 - Improbable 1 – Immediate

0 - None

SCALE MAGNITUDE

5 - International 10 - Very high/don’t know

4 - National 8 - High

3 - Regional 6 - Moderate

2 - Local 4 - Low

1 - Site only 2 - Minor

0 - None

The significance of the two aspects, occurrence and severity, is assessed using the following formula:

SP (significance points) = (magnitude + duration + scale) x probability

The maximum value is 150 significance points (SP). The impact significance points are assigned a rating of

high, medium or low with respect to their environmental impact as follows:

SP >75

Indicates high

environmental

significance

An impact which could influence the decision

about whether or not to proceed with the project

regardless of any possible mitigation.

SP 30 – 75

Indicates moderate

environmental

significance

An impact or benefit which is sufficiently

important to require management and which could

have an influence on the decision unless it is

mitigated.

SP <30

Indicates low

environmental

significance

Impacts with little real effect and which should not

have an influence on or require modification of the

project design.

+ Positive impact An impact that is likely to result in positive

consequences/effects.

Potential impacts were assessed using the above calculation and rating system, and mitigation measures

were proposed for all relevant project phases (construction to decommissioning).

Table 13: Risk Assessment Outcome before mitigation

Nr Activity Impact P D S M/S Significance Before

Mitigation

Score Magnitude Score Magnitude Score Magnitude Score Magnitude Score Magnitude

Pre-Construction and Construction Phase

1 None 0 Positive

Operational Phase

1 Blasting Ground vibration Impact on houses 3 Medium Probability 4 Long Term 2 Local 6 Moderate 36 Moderate

2 Blasting Air blast Impact on houses 3 Medium Probability 4 Long Term 2 Local 6 Moderate 36 Moderate

3 Blasting Fly Rock Impact on houses 3 Medium Probability 4 Long Term 2 Local 6 Moderate 36 Moderate

4 Blasting Impact of Fumes - Houses 3 Medium Probability 4 Long Term 2 Local 6 Moderate 36 Moderate

Closure and Post-Closure Phase

1 None 0 Positive

Table 14: Risk Assessment Outcome after mitigation

Nr Activity Impact Mitigation Measures P D S M / S Significance

Score Score Score Score Score Magnitude

Pre-Construction and Construction Phase Pre-Construction and Construction Phase

1 None 0 Positive

Operational Phase Operational Phase

1 Blasting Ground vibration Impact on houses Reduce charge mass per delay 2 4 2 4 20 Low

2 Blasting Air blast Impact on houses Stemming control 2 4 2 2 16 Low

3 Blasting Fly Rock Impact on houses Stemming control 3 4 2 4 30 Low

4 Blasting Impact of Fumes - Houses Quality explosives use 1 4 2 2 8 Low

Closure and Post-Closure Phase Closure and Post-Closure Phase

10.10.1 Mitigations

Ground Vibration

Specific mitigation will be required with regards to ground vibration, especially for the structures

located at POI 1, 6 and 31– closest to the pit area. Figure 28 below shows the identified POI’s of

concern for blasting operations and mitigation to be considered. POI 31 seems to be a river crossing

area. There is no structure there but is identified as a point of interest as people may be present at

this point. Only mitigation for POI 1 and 6 are discussed.

Ground vibration mitigation can be done in two ways: reduce the charge mass per delay – in other

words, plan blasting operations considering different initiation and charging options. Secondly

increase distance between the blast and the structure of concern. These are the main factors to be

considered for mitigation.

Figure 28: Structures at North Pit Area that are identified where mitigation will be required.


Table 15: Structures identified as problematic

Tag Descriptio

n Y X

Specific

Limit

(mm/s)

Distance

(m)

Total

Mass/Delay

(kg)

Predicted

PPV

(mm/s)

Human

Tolerance

@ 30Hz

Structure

Response

@ 10Hz

1 Houses 581864 8261250 6 313 770.0 21.0 Intolerable Problematic

6 Houses 582741 8262433 6 604 770.0 7.1 Unpleasant Problematic

In order to ensure that levels of ground vibration and air blast are within acceptable limits, the

following table presents a combination of reduced charge mass per delay and increased distance

from the structures of concern. The location of these structures is such that specific design changes

are required for the blast operations on the northern side of the pit area. This will be dependent on

the actual drill depths, quantity of charge per blast hole and the initiation system used. The

recommendations made are based on minimum and maximum charge allowed to facilitate

acceptable levels of ground vibration. A charge mass per delay that is less than that specified will

allow for shorter distances. The possible options in order to obtain acceptable ground vibration are

more than what is given here but without discussion and actual position of the specific blast the

table below gives the best solution for the moment. Air blast and fly rock can be controlled using

proper charging methodology. Blasting operations in any area in the pit further than the distances

given below will yield lower levels of ground vibration. It is advisable that a detail plan of action is

put in place to manage ground vibrations in the areas of concern. Table 16 shows identified

problematic POI’s with reduced charge required to facilitate ground vibration levels within limits.

Table 17 shows the minimum distance required between blast and POI at the maximum charge used

to maintain accepted levels of ground vibration.

A further option to mitigate these effects is to relocate the houses in the impact zone, and this must

be considered in the project’s Resettlement Action Plan.

Table 16: Mitigation suggested for blasting operations – Reduced charge

Tag Description Y X

Specific

Limit

(mm/s)

Distance

(m)

Total

Mass/Delay

(kg)

Predicted

PPV

(mm/s)

Human

Tolerance

@ 30Hz

Structure

Response

@ 10Hz

1 Houses 581864 8261250 6 313 160.0 5.7 Unpleasant Acceptable


Table 17: Mitigation suggested for blasting operations – Minimum distance required

Tag Description Y X

Specific

Limit

(mm/s)

Distance

(m)

Total

Mass/Delay

(kg)

Predicted

PPV

(mm/s)

Human

Tolerance

@ 30Hz

Structure

Response

@ 10Hz



11 Closure Phase


During the closure no mining, drilling and blasting operations are expected. It is uncertain if any

blasting will be done for demolition. If any demolition blasting will be required it will be reviewed

as civil blasting and addressed accordingly.

12 Alternatives (Comparison and Recommendation)

No alternatives are currently under discussion or considered for drilling and blasting.

13 Monitoring

It is highly recommended that a blast monitoring program be put in place. This includes monitoring

ground vibration and air blast for every blast. Ground vibration and air blast is monitored using a

seismograph. Monitoring can be done in permanent stations or on an ad hoc basis – per blast basis

monitoring. Additionally to this it is recommended that video footage of each blast is captured as a

standard. Monitoring of ground vibration and air blast is done to ensure that the generated levels of

ground vibration and air blast comply with recommendations. Proposed positions were also selected

to indicate the nearest points of interest at which levels of ground vibration and air blast should be

within the accepted norms and standards as proposed in this report. The monitoring of ground

vibration will also qualify the expected ground vibration and air blast levels and assist in mitigating

these aspects properly. This will also contribute to improved relationships with the neighbours.

Currently four monitoring positions were identified – more can be used if necessary. Monitor

positions are indicated in Figure 29. These points will need to be defined finally from testing during

first blasts.


Figure 29: Monitoring Positions suggested.

14 Recommendations

The following recommendations are proposed.

14.1 Safe blasting distance from communities

A minimum safe distance of 464 m is required but it is recommended that a minimum of 500 m be

maintained from any blast done. This may be greater but not less. The blaster has a legal obligation

concerning the safe distance and he needs to determine this distance.

14.2 Evacuation

All persons and animals within 464 m from a blast must be cleared and where necessary evacuation

must be conducted with all the required pre-blast negotiations.

14.3 Road / Travel Closure

There are small road ways and specifically the river crossing around the site. All blasting closer

than 500 m to these areas will require closure procedures when blasting is done. These roads may


be used daily and people may be present on these tracks. There are no major roads in close

proximity to the pit area.

14.4 Monitoring

It is highly recommended that a monitoring program be put in place. This will also qualify the

expected ground vibration and air blast levels and assist in mitigating these aspects properly. This

will also contribute to proper relationships with the neighbours. Section 13 gives detail of proposed

monitoring points.

14.5 Photographic Inspections

A structure survey is recommended for structures located within a 1000 m radius of the pit area.

This does not replace relocation of households as may be considered by the client but will certainly

help in managing complaints due to blasting operations. A survey will also assist in determining

final limits that may be applicable due to structure integrity. This process can however only succeed

if done in conjunction with a proper monitoring program. 1000 m equates to 3.1 mm/s of expected

ground vibration for the charge used. This level of ground vibration is already perceptible and

people in structures could experience ground vibration negatively. Figure 30 shows structures

within the 1000 m area from the pit.

Figure 30: 1000m area around North pit area identified for structure inspections.


14.6 Recommended ground vibration and air blast levels

The following general ground vibration and air blast levels are recommended for blasting

operations in this area. Table 18 below gives limits for ground vibration and air blast. Guidelines for

application of the limits for the project are shown in Table 19. These guidelines shows charge

masses and distances to maintain the appropriate limits suggested.

Table 18: Recommended ground vibration air blast limits

Structure Description Ground Vibration Limit

(mm/s) Air Blast Limit (dBL)

National Roads/Tar Roads: 150 N/A

Electrical Lines: 75 N/A

Railway: 150 N/A

Transformers 25 N/A

Water Wells 50 N/A

Telecoms Tower 50 134

General Houses of proper construction USBM Criteria or 25 mm/s Shall not exceed 134dB at point

of concern but 120 dB preferred Houses of lesser proper construction 12.5

Rural building – Mud houses 6

Table 19: Recommended ground vibration air blast limits

Type Threshold Charge (kg) Humans

Perception

Structure

Influence Dist (m)

Ground vibration 6mm/s 192 Unpleasant Acceptable 335

6mm/s 770 Unpleasant Acceptable 670

Ground vibration

perception 6mm/s 1250 intolerable Problematic 400

6mm/s 1250 unpleasant Problematic 800

6mm/s 1250 Perceptible Acceptable 2500

Surrounding communities 5mm/s 1421 Perceptible Acceptable 1014

Safe limit for rural

structure 6mm/s 785 rural type 675

Air blast 120 dB 245 450

120 dB 935 700

Fly rock min 239

max 464

River crocodiles 13mm/s 192 N/A N/A 210

13mm/s 770 N/A N/A 418


14.7 Stemming length

The current proposed stemming lengths at least must be maintained to ensure control of fly rock.

Specific designs where distances and blast is known should be considered with this.

14.8 Blasting times

A further consideration of blasting times is when weather conditions could influence the effects

yielded by blasting operations. It is recommended that no blasting takes place too early in the

morning when it is still cool or there is the possibility of inversion, or too late in the afternoon in

winter . Do not blast in fog nor in the dark. Refrain from blasting when wind is blowing strongly in

the direction of an outside receptor. Do not blast with low overcast clouds. These “do not’s” stem

from the influence that weather has on air blast. The energy of air blast cannot be increased but it is

distributed differently to unexpected levels where it was not expected.

It is recommended that a standard blasting time is fixed and blasting notice boards setup at various

routes around the project area that will inform the community about blasting dates and times.

14.9 Third party monitoring

Third party consultation and monitoring should be considered for all ground vibration and air blast

monitoring work. Additionally assistance may be sought when blasting is done close to the

highways. This will bring about unbiased evaluation of levels and influence from an independent

group. Monitoring could be done using permanent installed stations. Audit functions may also be

conducted to assist the mine in maintaining a high level of performance with regards to blast results

and the effects related to blasting operations.

15 Knowledge Gaps

Considering the stage of the project, the data observed was sufficient to conduct an initial study.

Surface surroundings change continuously and this should be taken into account prior to any final

blast design and review of this report. This report is based on data provided and international

accepted methods and methodology used for calculations and predictions.

16 Conclusion

Blast Management & Consulting (BM&C) was contracted to perform a review of possible impacts

with regards to blasting operations in the proposed new opencast mining operation. Ground

vibration, air blast, fly rock and fumes are some of the aspects that result from blasting operations.

The report concentrates on the ground vibration and air blast and intends to provide information,

calculations, predictions, possible influences and mitigations of blasting operations for this project.


The project area consists mainly of one opencast pit area. The evaluation of effects yielded by

blasting operations was evaluated over an area as wide as 3500 m from the opencast pit area. The

typical structures of concern in the area are mainly rural buildings – very few brick and mortar

structures, mainly wood and mud huts.

The project area has the possibility of people present at very close distances to the operations. The

location of structures around the pit areas are such that the charges evaluated showed possible

influences due to ground vibration. Ground vibration mitigation will be required for two identified

areas of interest. Mitigation on drilling and blasting operations will be required to levels of ground

vibration that are within the accepted norms.

Air blast levels are of less concern. Air blast levels calculated showed no specific damage concerns.

Levels calculated do show that levels could be high enough to generate complaints from neighbours

up to a distance of at least 700 m. Mitigation of ground vibration will also contribute to mitigation

of air blast. Stemming control will be needed to maintain levels within acceptable norms. Stemming

control for air blast will also contribute to control on fly rock. Complaints from air blast are

normally based on the actual effects that are experienced due to rattling of roofs, windows, doors


One concern identified is the Revubué River located on the western side of the pit. The river is very

close to the pit area. Possible presence of crocodiles and aquatic life may be influenced by ground

vibrations yielded. Expected levels are higher than proposed limits. Crocodiles and other aquatic

life are known to occur in the river, based on the faunal assessment for this ESIA.

This concludes this investigation for the Tete Iron Ore Mine Project. It will be possible to operate

this mine in a safe and effective manner provided attention is given to the areas of concern and

recommendations as indicated.

17 Curriculum Vitae of Author

Author joined Permanent Force at the SA Ammunition Core for period Jan 1983 - Jan 1990.

During this period I was involved in testing at SANDF Ammunition Depots and Proofing ranges.

Work entailed munitions maintenance, proofing and lot acceptance of ammunition. For the period

Jul 1992 - Des 1995 Worked at AECI Explosives Ltd. Initially I was involved in testing science on

small scale laboratory work and large scale field work. Later on work entailed managing various

testing facilities and testing projects. Due to the restructuring of Technical Department I was

retrenched but fortunately could take up appointment with AECI Explosives Ltd.’s Pumpable

Emulsion explosives group for underground applications. December 1995 to June 1997 I gave

technical support to the Underground Bulk Systems Technology business unit and performed


project management on new products. I started Blast Management & Consulting in June 1997.

Main areas of concern were Pre-blast monitoring, Insitu monitoring, Post blast monitoring and

specialized projects.

I have obtained the following Qualifications:

1985 - 1987 Diploma: Explosives Technology, Technikon Pretoria

1990 - 1992 BA Degree, University Of Pretoria

1994 National Higher Diploma: Explosives Technology, Technikon Pretoria

1997 Project Management Certificate: Damelin College

2000 Advanced Certificate in Blasting, Technikon SA

Member: International Society of Explosives Engineers

Blast Management & Consulting has been active in the mining industry since 1997 and work has

been on various levels for all the major mining companies in South Africa. Some of the projects

where BM&C has been involved are:

Iso-Seismic Surveys for Kriel Colliery in conjunction with Bauer & Crosby PTY Ltd, Iso-Seismic

surveys for Impala Platinum Limited, Iso-Seismic surveys for Kromdraai Opencast Mine,

Photographic Surveys for Kriel Colliery, Photographic Surveys for Goedehoop Colliery,

Photographic Surveys for Aquarius Kroondal Platinum – Klipfontein Village, Photographic Surveys

for Aquarius – Everest South Project, Photographic Surveys for Kromdraai Opencast Mine,

Photographic Inspections for various other companies including Landau Colliery, Platinum Joint

Venture – three mini pit areas, Continuous ground vibration and air blast monitoring for various

Coal mines, Full auditing and control with consultation on blast preparation, blasting and resultant

effects for clients e.g. Anglo Platinum Ltd, Kroondal Platinum Mine, Lonmin Platinum, Blast

Monitoring Platinum Joint Venture – New Rustenburg N4 road, Monitoring of ground vibration

induced on surface in Underground Mining environment, Monitoring and management of blasting

in close relation to water pipelines in opencast mining environment, Specialized testing of

explosives characteristics, Supply and service of seismographs and VOD measurement equipment

and accessories, Assistance in protection of ancient mining works for Rhino Minerals (PTY) LTD,

Planning, design, auditing and monitoring of blasting in new quarry on new road project,

Sterkspruit, with Africon, B&E International and Group 5 Roads, Structure Inspections and

Reporting for Lonmin Platinum Mine Limpopo Pandora Joint Venture 180 houses – whole village,

Structure Inspections and Reporting for Lonmin Platinum Mine Limpopo Section : 1000 houses /

structures.

BM&C have installed a World class calibration facility for seismographs, which is accredited by

Instantel, Ontario Canada as an accredited Instantel facility. The projects describe and discussed

here are only part of the capability and professional work that is done by BM&C.

18 References


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Control – By Chance or Design, Paper Presented at ISEE Conference – New Orleans.

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Otherwise Cryptic Responses of Forest Elephants to Oil Exploration. The Elephant Listening

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Shriver, D., Arnason, B. T., Hart, L. A. Wild elephant (Loxodonta Africana) breeding herds

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Princeton University, 10 March 1956. Proceedings of the N.A.S., Volume 42, 1956.

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N.A.S., Volume 68, July 1971.

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SocietyStable

mailto:[email protected]

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