Namib Mine Ground- and Surface Water Specialist Input for ... · SLR Ref. 733.14009.00004 Report No.2013-GS-6 Namib Mine : Ground and Surface Water Specialist Input to EIA Report

Namib Mine

Ground- and Surface Water Specialist Input for EIA Report

SLR Project No.: 733.14009.00004

Report No.: 2013-GS-6

October 2013

North River Resources (Namibia) (Pty) Ltd

P.O. Box 81162

Olympia

Windhoek

Namibia

Namib Mine

Ground- and Surface Water Specialist Input for EIA Report

SLR Project No.: 733.14009.00004

Report No.: 2013-GS-6

October 2013

North River Resources (Namibia) (Pty) Ltd

P.O. Box 81162

Olympia

Windhoek

Namibia

DOCUMENT INFORMATION

Title Namib Mine : Ground- and Surface Water Specialist Input to EIA Report Project Manager Jonathan Church Project Manager e-mail [email protected] Author Jonathan Church Reviewer Arnold Bittner Client North River Resources (Namibia) (Pty) Ltd Date last printed 2013-11-09 16:46:00 Date last saved 2013-11-09 16:20:00 Comments Keywords Namib Mine, Groundwater, Surface Water, EIA, Impact Assessment, Acid

Rock Drainage, Storm-water Management Project Number 733.14009.00004 Report Number 2013-GS-6 Status Client Draft Issue Date October 2013

SLR NAMIBIAN OFFICES

Windhoek, Namibia

Physical Address:

8 General Murtala Muhammed Street

Eros

Windhoek

Postal Address:

P O Box 86386

Windhoek

Namibia

Tel: +264 61 231 287

Fax: +264 61 231 289

Web: www.slrconsulting.com

Swakopmund, Namibia

Physical Address

House Schumacher

6 Tobias Hainyeko Street

Swakopmund

Postal Address:

P O Box 807

Swakopmund

Namibia

Tel: +264 64 402 317

Fax: +264 64 403 327

Web: www.slrconsulting.com

SLR Environmental Consulting (Namibia) (Pty) Ltd

SLR Ref. 733.14009.00004 Report No.2013-GS-6 Namib Mine : Ground and Surface Water Specialist Input to EIA Report October 2013

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NAMIB MINE : GROUND- AND SURFACE WATER SPECIALIST I NPUT TO EIA REPORT

CONTENTS

1 INTRODUCTION.............................................................................................................................. 1

1.1 BACKGROUND ............................................................................................................................. 1

1.2 SITE DESCRIPTION....................................................................................................................... 1

1.3 PURPOSE AND SCOPE OF WORK ................................................................................................... 1

2 CLIMATE ............................................ ............................................................................................. 5

2.1 RAINFALL .................................................................................................................................... 5

2.2 EVAPORATION ............................................................................................................................. 6

3 GROUNDWATER STUDY................................................................................................................ 6

3.1 GEOLOGY ................................................................................................................................... 6

3.2 REGIONAL HYDROGEOLOGY.......................................................................................................... 8

3.3 LOCAL HYDROGEOLOGY ............................................................................................................. 13

3.4 RECOMMENDATIONS FOR GROUNDWATER MANAGEMENT............................................................... 13

4 SURFACE WATER STUDY ................................ ........................................................................... 14

4.1 REGIONAL HYDROLOGY.............................................................................................................. 14

4.2 LOCAL HYDROLOGY AND CATCHMENT DELINEATION ...................................................................... 14

4.3 SURFACE FLOW ESTIMATION ...................................................................................................... 18

4.3.1 DESIGN STORM ESTIMATION ................................................................................................................. 18 4.3.2 CALCULATIONS ................................................................................................................................... 20

5 CONCEPTUAL STORM-WATER MANAGEMENT.................. ....................................................... 21

5.1 SITE SPECIFIC STORM-WATER MANAGEMENT ............................................................................... 23

6 ACID ROCK DRAINAGE ................................. .............................................................................. 26

6.1 INTRODUCTION .......................................................................................................................... 26

6.2 GROUNDWATER QUALITY MONITORING ........................................................................................ 27

6.3 CONCLUSION............................................................................................................................. 33

6.4 RECOMMENDATIONS .................................................................................................................. 33

7 IMPACT ASSESSMENT .................................. .............................................................................. 34

7.1 GROUNDWATER IMPACT ASSESSMENT ......................................................................................... 36

7.2 SURFACE WATER IMPACT ASSESSMENT ....................................................................................... 37

8 SUMMARY AND CONCLUSIONS............................ ...................................................................... 45

9 REFERENCES............................................................................................................................... 47

LIST OF FIGURES

FIGURE 1: REGIONAL SETTING OF NAMIB MINE ............................................................................................... 3

FIGURE 2: PROPOSED SITE LAYOUT ................................................................................................................. 4

FIGURE 3: COMPARISON OF MEAN MONTHLY RAINFALL IN THE REGION ...................................................... 5

FIGURE 4: AVERAGE MONTHLY OPEN WATER EVAPORATION FOR THE REGION.......................................... 6

FIGURE 5: REGIONAL GEOLOGICAL SETTING................................................................................................... 7

FIGURE 6: LOCATION OF MONITORING BOREHOLES ......................................................................................10

FIGURE 7: GROUNDWATER CONTOURS (FROM MONITORING BOREHOLE DATA).........................................10

FIGURE 8: SULPHATE CONCENTRATIONS........................................................................................................11

FIGURE 9: NITRATE CONCENTRATIONS...........................................................................................................11

FIGURE 10: TDS CONCENTRATIONS.................................................................................................................12

FIGURE 11: HYDROGRAPHS OF THE MINE MONITORING BOREHOLES..........................................................12

FIGURE 12: REGIONAL HYDROLOGY NAMIB MINE CATCHMENTS...................................................................15



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FIGURE 13: LOCAL HYDROLOGY.......................................................................................................................16

FIGURE 14: LOCAL RELIEF (USING NRR SURVEY DATA) .................................................................................17

FIGURE 15: PROPOSED STORM-WATER DRAINAGE LAYOUT .........................................................................25

FIGURE 16: PIPER PLOT OF GROUNDWATER IN THE VICINITY OF NAMIB PB-ZN MINE.................................28

FIGURE 17: CONCENTRATIONS OF METALS RECORDED IN GROUNDWATER MONITORING BOREHOLES IN THE VICINITY OF NAMIB PB-ZN MINE ........................................................................................................29

FIGURE 18: CONCENTRATIONS OF MAJOR CATIONS RECORDED IN GROUNDWATER MONITORING BOREHOLES IN THE VICINITY OF NAMIB PB-ZN MINE..............................................................................30

FIGURE 19: CONCENTRATIONS OF MAJOR ANIONS RECORDED IN GROUNDWATER MONITORING BOREHOLES IN THE VICINITY OF NAMIB PB-ZN MINE..............................................................................31

FIGURE 20: CONCENTRATIONS OF GENERAL PARAMETERS RECORDED IN GROUNDWATER MONITORING BOREHOLES IN THE VICINITY OF NAMIB PB-ZN MINE..............................................................................32

LIST OF TABLES

TABLE 1: MEAN MONTHLY RAINFALL FOR THE REGION 1984 TO 2002 (MM) .................................................. 5

TABLE 2: AVERAGE MONTHLY OPEN WATER EVAPORATION FOR THE REGION (MM) .................................. 6

TABLE 3: REGIONAL STRATIGRAPHIC SUCCESSION....................................................................................... 8

TABLE 4: DEPTH DURATION FREQUENCY VALUES (MM RAINFALL) FOR NAMIB MINE SITE (INTERPOLATED AND SCALED FROM TR102 DATA)..............................................................................................................18

TABLE 5: DEPTH DURATION FREQUENCY VALUES FOR DURATIONS OF 0.25 TO 4 HOURS..........................19

TABLE 6: CALCULATED STORM VOLUMES .......................................................................................................20

TABLE 7: CALCULATED CHANNEL DIMENSIONS ..............................................................................................21

TABLE 8: CALCULATED DIRTY WATER VOLUMES FOR CONTAINMENT DAMS ...............................................25

TABLE 9: CRITERIA FOR ASSESSING IMPACTS................................................................................................35

TABLE 10: IMPACT OF RESUMED MINING ON GROUNDWATER RESOURCE (GROUNDWATER ABSTRACTION AND/OR DEWATERING OF THE MINE) .......................................................................................................38

TABLE 11: IMPACT OF RESUMED MINING ON GROUNDWATER QUALITY (CONTAMINATION FROM ACCOMMODATION, OFFICES, ABLUTION FACILITIES, WASTE COLLECTION SITE, REFUELLING AREA).....................................................................................................................................................................39

TABLE 12: IMPACT OF RESUMED MINING ON GROUNDWATER QUALITY (LEACHING OF METALS FROM THE TAILINGS STORAGE FACILITY, WASTE ROCK DUMPS, MARGINAL ORE DUMPS, ROM STOCKPILE) .....41

TABLE 13: IMPACT OF RESUMED MINING ON GROUNDWATER QUALITY (ACID ROCK DRAINAGE) ..............42

TABLE 14: IMPACT OF RESUMED MINING ON SURFACE WATER RUNOFF .....................................................43

TABLE 15: IMPACT OF RESUMED MINING ON SURFACE WATER QUALITY.....................................................44



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ACRONYMS AND ABBREVIATIONS

Below a list of acronyms and abbreviations used in this report.

Acronyms / Abbreviations

Definition

AMSL Above Mean Sea Level ARD Acid Rock Drainage ASTER Advanced Spaceborne Thermal Emission and Reflection Radiometer DWAF Department of Water Affairs and Forestry EIA Environmental Impact Assessment EPL Exclusive Prospecting Licence GARD Guide Global Acid Rock Drainage Guide GDEM Global Digital Elevation Map ICP Inductively Coupled Plasma km Kilometres LOM Life of Mine m Metres MAP Mean Annual Precipitation mbgl Metres Below Ground Level MEND Mine Environment Neutral Drainage Met. Office Meteorological Office, Meteorological Services, Ministry of Works and Transport METI Ministry of Economy, Trade & Industry (Japan) mg/l Milligrams per litre (measure of concentration) ML Mining Licence mS/m Millisiemens per metre (measure of electrical conductance) NAr Arandis Formation NASA National Aeronautics and Space Administration (USA) NCh Chuos Formation NKb Karibib Formation NKs Kuiseb Formation NRs Rössing Formation PL Prospecting Licence ROM Run Of Mine TDS Total Dissolved Solids TSF Tailings Storage Facility



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NAMIB MINE : GROUND- AND SURFACE WATER SPECIALIST I NPUT TO EIA REPORT

1 INTRODUCTION

1.1 BACKGROUND

North River Resources (Namibia) (Pty) Ltd (NRR) is planning to start re-working the existing mine dump

and re-open the main mine shaft and associated activities at the Namib Mine in the Namib Desert

approximately 30 km north-east of Swakopmund. SLR Environmental Consulting (Namibia) (Pty) Ltd

(SLR Namibia) was appointed to conduct a ground- and surface water specialist study as part of the

Environmental Impact Assessment (EIA) which is being undertaken for these activities.

SLR Namibia has been undertaking quarterly sampling and monitoring of the groundwater in the area

surrounding the mine for NRR since July 2012, as well as compiling a Hydrological Assessment Report

for the site in November 2012.

1.2 SITE DESCRIPTION

The topography of the Namib Mine project site and surrounding area is illustrated in Figure 14. The mine

site is located at approximately 280 m AMSL, with a variation in elevation of approximately 200 m within

the Exclusive Prospecting Licence (EPL) 2902 area. The larger study area has a rolling to flat

topography with the Rӧssing Mountain bordering the EPL in the east, with a height at peak of

approximately 650 m. The mine site itself has a relative flat topography with a slight fall towards the west.

There are smaller “koppies” in the north and north-east of the EPL. As presented in Figure 14, digital

terrain model data from NRR was available for the site at a vertical resolution of 10 cm. Consequently,

the elevation in the immediate vicinity of the mine was sourced from this data, while the wider area was

sourced from the ASTER GDEM with a cell size of 30 m (ASTER is a product of METI and NASA). The

ASTER GDEM elevations show a vertical variation of approximately 30 m compared to those of the NRR

data.

1.3 PURPOSE AND SCOPE OF WORK

The report presents a ground- and surface water study for the focus area and relevant surroundings.

The structure of the report is as follows:

• Section 1 is the general introduction to the report;

• Section 2 presents background climate information for the area;

• Section 3 presents the groundwater study including a description of the hydrogeological baseline

conditions of the focus and surrounding areas;

• Section 4 presents the surface water study including a description of the regional and local

hydrology, calculation of catchments and peak flow estimation;

• Section 5 looks at storm-water management strategies for the site and includes conceptual design;



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• Section 6 discusses the possible Acid Rock Drainage assessment and discusses proposed future

laboratory work to gather further information;

• Section 7 presents the impact assessment of the proposed mining expansion relating to

groundwater and surface water;

• Section 8 presents the summary and conclusions.


SLR Ref. 733.14009.00004 Report No.2013-GS-6 Namib Mine : Ground and Surface Water Specialist Input to Report October 2013

Page 3

FIGURE 1: REGIONAL SETTING OF NAMIB MINE


SLR Ref. 733.14009.00004 Report No.2013-GS-6 Namib Mine : Ground and Surface Water Specialist Input to Report October 2013

Page 4

FIGURE 2: PROPOSED SITE LAYOUT



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2 CLIMATE

2.1 RAINFALL

Namib Mine is located an almost equal distance from the rain gauges at Rӧssing Mine and Swakopmund,

which are located approximately 28 km east and west of the Namib Mine. Rӧssing Mine has a rainfall

record from 1984 to present and the Mean Annual Precipitation (MAP) is 31.8 mm and the median annual

rainfall is 24.9 mm. Swakopmund has a rainfall record from 1914 to 2002 (with some periods of lost

record) and the Mean Annual Precipitation (MAP) is 15.4 mm and the median annual rainfall is 9.2 mm.

To calculate an estimated monthly mean rainfall for Namib Mine the period of overlapping data from

Swakopmund and Rӧssing Mine (1984 to 2002) has been taken and the average of these values taken

as representative for Namib Mine. The average monthly distribution is shown in Table 1 and Figure 3.

TABLE 1: MEAN MONTHLY RAINFALL FOR THE REGION 1984 TO 2002 (MM)

MONTH JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC TOTAL

Rӧssing Mean (mm) 3.7 4.0 11.0 4.3 1.5 0.5 0.5 0.2 0.7 0.4 1.0 1.1 29.0

Swakopmund Mean 1.7 1.5 4.6 2.5 0.7 1.1 0.3 0.0 0.4 0.4 0.5 0.5 14.3

Average Namib Mine 2.7 2.7 7.8 3.4 1.1 0.8 0.4 0.1 0.5 0.4 0.8 0.8 21.7

FIGURE 3: COMPARISON OF MEAN MONTHLY RAINFALL IN TH E REGION

Depth-duration rainfall data (mentioned later in this report) was sourced from the TR102 report (Adamson

1981), which is required for the peak flow estimation calculations.



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2.2 EVAPORATION

Monthly evaporation data is also recorded at Rӧssing Mine, so this record has been taken as a

conservative indication of the likely situation at Namib Mine.

The data from Rӧssing Mine is Class-A Evaporation pan data, which has been converted to open water

values, which are more representative of the likely evaporation from ponds or dams at the site. The mean

annual open water evaporation is 1,668 mm, which is approximately 80 times the annual precipitation,

hence making this a water stressed area. The open water monthly data is shown in Table 2 and Figure 4.

TABLE 2: AVERAGE MONTHLY OPEN WATER EVAPORATION FO R THE REGION (MM) Month JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC TotalMean Evap. 149 151 160 150 136 113 120 114 127 137 162 149 1 668Monthly % 8.9% 9.1% 9.6% 9.0% 8.1% 6.8% 7.2% 6.8% 7.6% 8.2% 9.7% 8.9% 100.0%

FIGURE 4: AVERAGE MONTHLY OPEN WATER EVAPORATION FO R THE REGION

3 GROUNDWATER STUDY

3.1 GEOLOGY

The oldest rocks in the geology of the area are granitic orthogneisses of the Abbabis metamorphic

complexis, on which are unconformably lain rocks of the Nosib Group, Khan Formation, which can be up

to 1,050 m thick in the Rӧssing Mountain area, made up mainly of greyish green, massive and thinly to

very thickly bedded clinopyroxene- and hornblende-bearing feldspathic quartzite, with thin, small pebble

conglomerate layers occuring sporadically throughout the succession.

The basal unit of the Swakop Group, the Rӧssing Formation rests directly on the Nosib Group, and has a

highly variable lithology with dolomitic marble dominating the succession in some places and various



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siliclastic rocks in others. Around the Rӧssing Mine there is a local five unit stratigraphy made up of a

lower marble at the base followed successively by lower pelitic gneiss, upper marble, upper pelitic gneiss

and quartzite. There was a period of deformation, uplift and erosion before the Chuos Formation (a

glaciogenic unit), which is composed largely of massive, unsorted diamictite with an abundant matrix. The

Arandis Formation consists of a succession of schist and calc-silicate rock. The Karibib Formation

consists of an interbedded succession of dark grey marble, ribbon marble that is made up of thin

alternating layers of light and dark grey marble, sedimentary marble breccias, grey phyllitic dolomite and

laminae of calc-silicate rock. The Tinkas Formation consists of shelf carbonates and upper and lower

slope turbidites, deposited on the southern passive continental margin of the Congo Craton in the

transition zone between the carbonate shelf and the deep water ocean. The Kuiseb Formation is the

highest stratigraphic unit of the Swakop Group and consists mainly of schist, with a few thin quartzite

layers and occasional calc-silicate layers (generally nearer the base).

Overlying the Swakop Group is the Etendeka Group and the Namib Group which was laid down after a

long period of erosion under humid conditions, which led to the development of the African Surface and

the deep weathering of the bedrock below to depths of 50 m or more. The Etendeka Group comprises

flood basalts, latites and quartz latites and numerous dolerite dyke swarms. The Namib Group consists

of often highly localised deposits that have origins linked to the wave and aeolian-dominated coastal

tract, plus various calcretes, (Miller, 2008).

FIGURE 5: REGIONAL GEOLOGICAL SETTING



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TABLE 3: REGIONAL STRATIGRAPHIC SUCCESSION

Group Subgroup Formation Lithology

Namib Aeolian sand

(Qs) Surficial deposits

Calcretised river sediments, conglomerate

Etendeka Basalt, dolerite

Discordance

Swakop Khomas Kuiseb

(NKs)

Pelitic and semi-pelitic schist and gneiss, migmatite, calc-

silicate rock, quartzite. Tinkas member: Pelitic and semi-

pelitic schist, calc-silicate rock, marble, para-amphibolite.

Navachab Tinkas Mica schist, metagreywacke, calc-silicate rock, quartzite,

marble, amphibolite

Karibib

(NKb)

Marble, calc-silicate rock, pelitic and semi-pelitic schist

and gneiss, biotite amphibolite schist, quartz schist,

migmatite.

Usakos Arandis

(NAr)

Mica schist, para-amphibolite, meta-sediments, marble

(impure), calc-silicate rocks

Chuos

(NCh)

Diamictite, clac-silicate rock, pebbly schist, quartzite,

ferruginous quartzite, migmatite

Discordance

Ugab Rössing

(NRs)

Marble, pelitic schist and gneiss, biotite-horneblende

schist, migmatite, calc-silicate rock, quartzite, meta-

conglomerate

Discordance

Nosib Khan

(NKn)

Migmatite, banded and mottled quartzofeldspathic

clinopyroxene-amphibolite gneiss, horneblende-biotite

schist, biotite schist and gneiss, migmatite, pyroxene-

garnet gneiss ,amphibolite, quartzite, metaconglomerate

Etusis Quartzite, metaconglomerate, pelitic and semipelitic

schist and gneiss, migmatite,

quartzofeldspathicclinopyroxene-amphibolite gneiss,

calc-silicate rock, metaphyolite.

Major unconformity

Abbabis Abbabis Complex Complex Gneissic granite, augen gneiss,

quartzofeldspathic gneiss, pelitic schist and gneiss,

migmatite, quartzite, marble, calc-silicate rock,

amphibolite

3.2 REGIONAL HYDROGEOLOGY

There are no boreholes close to the Namib Mine in the National Groundwater Database (GROWAS)

housed by the Department of Water Affairs and Forestry (DWAF), from which to take data.

SLR Namibia has been sampling and monitoring 9 boreholes around the mine area since July 2012, so

this is the main database from which the hydrogeology will be evaluated.



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Findings and observations from the drilling and groundwater monitoring carried out by SLR Namibia since

2012 are that:

• The majority of boreholes in the area have yields of less than 1 m3/h (SLR May 2012). The

exception is borehole NLZ-W4, which had a blow yield while drilling of 8 m3/h. However, this water

was associated with a large cavity and is not likely to be a sustainable yield. Further test pumping

indicated a sustainable yield of below 2 m3/h.

• Depth to the water table varies between approximately 10 and 100 metres below ground level.

However, in the marbles and schists surrounding the mine it is likely that there is no regional water

table, with the majority of groundwater being restricted to the fractures and faults, as outside of

these structures the bedrocks have generally low transmissivity and are relatively impermeable. An

indication of this is that the main mine shaft has been drilled to approximately 220 m below ground

level, but remains virtually dry. Figure 7 shows the reduced groundwater level contours calculated

from the monitoring borehole data, but this is only produced from data that has been collected in

the small area surrounding the mine and would be more representative if a wider area was able to

be included. The general result shows the reduced groundwater level highest in the north eastern

area (closest to the Rӧssing Mountain) and reducing in a westerly direction.

• Sulphate concentrations vary across the area, with the two highest concentrations being located

closest to the current mine infrastructure (Figure 8). The Namibian National Water Quality

Standards for Class A should be less than 200 mg/l sulphate and greater than 1,200 mg/l is

unsuitable for human consumption, with all boreholes except NLZ-W4 (851 mg/l) being above

1,200 mg/l.

• Nitrate concentrations are highly variable, with values from below 1 mg/l (NLZ-W1) to around

50 mg/l (NLZ-W9), see Figure 9. The Namibian National Water Quality Standards for Class A

should be less than 10 mg/l Nitrate (as N) and greater than 40 mg/l is unsuitable for human

consumption.

• TDS concentrations in all boreholes are high (Figure 10), between 9,660 and 27,550 mg/l (well

above the guideline levels for safe stock-watering according to the Namibian National Water

Quality Standards, which has a cutoff for stock-watering at 6,000 mg/l).

• Water levels in the monitoring boreholes have remained fairly constant, see Figure 11. The

groundwater level in NLZ-W3 has shown a gentle rise over time, but when drilled this borehole was

dry, and the gentle rise is probably the result of limited local seepage into the borehole.

The laboratory results from the quarterly groundwater monitoring indicate that the water quality is

poor, with a number of parameters being above the acceptable limits for Namibian National Water

Quality Standards for human consumption.



Page 10

FIGURE 6: LOCATION OF MONITORING BOREHOLES

FIGURE 7: GROUNDWATER CONTOURS (FROM MONITORING BOR EHOLE DATA)



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FIGURE 8: SULPHATE CONCENTRATIONS

FIGURE 9: NITRATE CONCENTRATIONS



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FIGURE 10: TDS CONCENTRATIONS

FIGURE 11: HYDROGRAPHS OF THE MINE MONITORING BOREH OLES



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3.3 LOCAL HYDROGEOLOGY

There is no additional data to include, so the monitoring borehole data provides the only indication of

hydrogeological conditions in the area. It is known (through personal communications) that there is a fault

running just to the east of the old tailings dam, which is interconnected with the mine shaft, When the

mine was being pumped to removed water which had accumulated some years ago, the water was being

piped to an area just to the east of the tailings dam and after this started, water began to appear coming

through the rock in an area in the lower level of the mine. When the pipe was extended further east, the

water entering the mine ceased.

3.4 RECOMMENDATIONS FOR GROUNDWATER MANAGEMENT

The following are recommended:

• Should mine dewatering by means of abstraction from boreholes become necessary for any

reason, or any groundwater abstraction for mining purposes be required, a groundwater

abstraction permit/ or amendment of existing permits will be required from the Department of Water

Affairs and Forestry.

• Groundwater levels, metered abstraction and pumped yield must be recorded at monthly intervals

from all boreholes that are used for groundwater abstraction and/or mine dewatering purposes.

This is important for the purpose of establishing baseline values, but also to monitor any impacts

from abstraction.

• The groundwater monitoring programme currently in place must be continued and should ideally

be extended.

• Any facility that contains dirty water or dirty water dams/lagoons must be lined.

• It is advisable that a numerical groundwater flow - and transport model should be compiled for the

purpose of groundwater management and to determine the time and spatial extent of potential

contaminant transport.

• It is likely that Acid Rock Drainage (ARD) and leaching of metals will not be an issue at Namib

Mine, but to confirm this further testing should be carried out (see Section 6 for further details).

• A discharge permit will be required from the Department of Water Affairs would it be required to

discharge any surplus ground - or surface water that the mine cannot consume and needs to

discharge.



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4 SURFACE WATER STUDY

4.1 REGIONAL HYDROLOGY

All watercourses in the region are ephemeral rivers and surface water flow occurs only after heavy

rainfall. The study area is located in the lower Namib Desert, situated between but not connected to the

major catchments of the Swakop River (to the south) and the Omaruru River (to the north), see Figure

12. The catchment starts at the western side of the Rӧssing Mountain and consists mainly of indistinct

drainage lines and washes which drain westward towards the coast, but do not reach the sea in any

significant drainage channels. The Swakop River drainage divide is shared with the south eastern edge

of Catchment B in the study area, while the Omaruru drainage divide is located approximately 60 km to

the north of the mine.

4.2 LOCAL HYDROLOGY AND CATCHMENT DELINEATION

Using the data generated from the previous surface water study (SLR Namibia 2012), catchment

boundaries for Catchment A and Catchment B (see Figure 13) plus watercourses were identified and

mapped in relation to the mine infrastructure. Some additional updating of the watercourses in the vicinity

of the mine infrastructure was undertaken using the available satellite imagery (Bing Maps), which was

then confirmed by ground-truthing at some locations during the site visit.



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FIGURE 12: REGIONAL HYDROLOGY NAMIB MINE CATCHMENTS



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FIGURE 13: LOCAL HYDROLOGY



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FIGURE 14: LOCAL RELIEF (USING NRR SURVEY DATA)

Page 18 SLR Environmental Consulting (Namibia) (Pty) Ltd


4.3 SURFACE FLOW ESTIMATION

Although mean annual rainfall is low in the region and drainage patterns are often indistinct in the study area,

significant rainfall events do occur and these events can cause temporary flow of surface water. Surface

water flow can mobilise contaminants from the project site and transport them along the drainage lines in a

generally western direction.

In order to provide meaningful data for the storm water management plan of the proposed project, surface

flow values are required. However, as the mining infrastructure is located close to a watershed boundary,

there will be little runoff generated in the small catchments which have been identified. Figure 14 shows the

local relief, with the higher areas showing as brown shades, and the slightly elevated ridge just to the north of

the mine infrastructure being visible.

From this it can be seen that there will be no runoff generated upstream of the mining infrastructure, as there

is no catchment area upstream to generate runoff, hence the only precipitation that is of concern is that

which falls on the footprint area of the mining infrastructure. Calculations for likely runoff generated can

therefore be made with rainfall calculations and the estimated area of the relevant footprints.

4.3.1 DESIGN STORM ESTIMATION

Design storm estimates for various return periods and storm durations > 24 h were sourced from the report

“Southern African Design Rainfall” (ADAMSON, 1981) which has tables giving derived data for various

Weather Bureau stations across southern Africa. The data was calculated from daily rainfall data from over

8,000 rain gauges across southern Africa, and tables were produced to give rainfall values for various

recurrence intervals at 2,400 selected sites.

The Namib Mine project site is located 28 km north-east of Swakopmund where TR102 data exists and

28 km south-west of Arandis where TR102 data was interpolated and scaled from Swakopmund and Horebis

Meteorological raingauges (SLR, 2012). Design rainfall data for the 2012 study was interpolated from the

Swakopmund and Arandis datasets and is given in Table 4.

TABLE 4: DEPTH DURATION FREQUENCY VALUES (MM RAINFA LL) FOR NAMIB MINE SITE (INTERPOLATED AND SCALED FROM TR102 DATA)

Recurrence Interval (years)

Duration (days)

Minimum annual

maximum recorded

Maximum

annual maximum recorded

2 5 10 20 50 100 200

1 4 43 8 16 23 31 45 59 74

2 7 61 9 17 26 38 57 77 103

3 7 64 9 19 29 40 60 80 107

7 9 66 11 21 31 44 66 89 118



However, as the catchment in which the mine infrastructure is located has no upstream component, any

runoff from an extreme rainfall event will be almost instantaneous, so it is necessary to know rainfall

intensities for periods of less than 1 day, which Table 4 does not provide.

Design storm estimates for various return periods and storm durations < 6 h were estimated with the

modified recalibrated Hershfield equation (ALEXANDER in SANRAL, 2006), which works on the theory that the

intensity of rainfall is related to the mean annual rainfall and to the rainfall region. The modified recalibrated

Hershfield equation can be used to determine point rainfall, which is then converted to intensity by dividing

the point rainfall by the time of concentration for storm durations of up to 6 hours.

PtT = 1.13( 0.41 + 0.64lnT ) ( -0.11+0.27lnT )( 0.79M0.69R0.20 )

Where:

PtT = precipitation depth for a duration of t minutes and a return period of T years

t = duration in minutes

T = return period

M = 2-year return period daily rainfall (from TR102).

R = average number of days per year on which thunder was heard (from TR102).

Design storm estimates were also calculated using the HRU 278 equation where:

For Coastal areas

Intensity = (3.4+0.023*MAP)*Return Period^0.3 /(0.2+Duration/60)^0.75

Taking the average values of the HRU 278 and modified recalibrated Hershfield equations produced values

for shorter durations as shown in Table 5.

TABLE 5: DEPTH DURATION FREQUENCY VALUES FOR DURATI ONS OF 0.25 TO 4 HOURS

Average of HRU 278 & Modified Recalibrated Hershfield Equation

1:50yr 1:100yr Storm Duration

depth Depth

(hours) (mm) (mm)

0.25 8 10 0.5 11 13 0.75 13 16

1 14 17 1.5 16 19 2 18 21 4 21 25



4.3.2 CALCULATIONS

Using the estimated rainfall values from Table 5 it is possible to calculate peak rainfall volumes likely to fall

on different areas of mine infrastructure. It is calculated that the catchments will reach maximum runoff

contribution (time of concentration) in just over 30 minutes. The total areas of the different contributing zones

have been measured and storm volumes have been calculated for these areas. Different runoff coefficients

have been used for the different areas, as the runoff expected will vary. The old tailings dump is expected to

have a reasonably high runoff as the old embankments are no longer intact (so will not contain the runoff)

and there are steep slopes on many of the remaining embankments. The new tailings dump is expected to

have a low runoff, as the majority of the area will be within the retaining embankments, so little rainfall will be

contributing to runoff. The plant infrastructure area is expected to have a high runoff as there will be flat

compacted and possibly paved surfaces as well as some buildings with roofing.

TABLE 6: CALCULATED STORM VOLUMES

Catchment A A B B

Dirty Water Catchment AreaOld Tailings

DamPlant

InfrastructureOld Tailings

DamNew Tailings

DamSurface area (m2) 31 100 63 900 20 700 127 600

Runoff coefficient 0.7 0.8 0.7 0.3

Storm Duration 1:50 year

30 minutes 400 167 297 421

1 hour 510 213 378 536


30 minutes 473 198 351 498

1 hour 619 258 459 651

Storm Volume (m3)

Storm Volume (m3)

Rainfall values from Table 5 were taken to calculate peak flows using the Rational Method (as presented in

the SANRAL Drainage Manual).

The Rational Method equation is:

Where:

QT = Peak Flow (m3/s for specific return period);

C = Runoff Coefficient (%);

I = Rainfall Intensity (mm/hr); and

A = Area (km2).

These calculations produced peak flow rates for the 1:50 year flood of 0.2 m3/s for the Dirty Water

Catchment A area and 0.3 m3/s for the Dirty Water Catchment B area. These values are the recommended

figures for sizing of the dirty water collection channels for Catchment A and B.



The rainfall intensity values used in these calculations were identified by calculating the time of concentration

assuming overland flow for both catchments and calculating the time of concentration for the collection

channels assuming channel flow. This produced a time of concentration of approximately 30 minutes for

each catchment, which was used as the intensity in the peak flow calculations.

The dimensions indicated in the above diagram were calculated for the dirty water collection channels for

Catchment A and B, routing the peak flow rates for the 1:50 year flood, and assuming a constant slope.

Values are shown in Table 7.

TABLE 7: CALCULATED CHANNEL DIMENSIONS

Q50 b1 d1 b2 d2 b3 Q

m3/s m m m m m m

3/s

DW Catchment A 0.2 0.35 0.35 0.35 0.35 0.35 0.28DW Catchment B 0.3 0.35 0.35 0.35 0.35 0.35 0.38

Catchment

5 CONCEPTUAL STORM-WATER MANAGEMENT

The proposed mining operations will alter the natural state of the environment, thereby affecting the

generation and quality of storm-water. Consequently, it is important to identify the effect the mining

operations will have on storm-water production, and manage this water accordingly. The volumes of storm-

water generated are expected to change. The quality of the storm-water generated is also expected to

decrease due to the nature of mining operations. The International Finance Corporation (IFC) provides

guidance on the management of storm-water for mines.

With regard to the IFC guidance the IFC Environmental, Health and Safety General Guidelines (2007),

indicate the following should be applied:

• Storm-water should be separated from process and sanitary wastewater streams in order to reduce

the volume of wastewater to be treated prior to discharge.

• Surface runoff from process areas or potential sources of contamination should be prevented.



• Where this approach is not practical, runoff from process and storage areas should be segregated

from potentially less contaminated runoff.

• Runoff from areas without potential sources of contamination should be minimised (e.g. by minimising

the area of impermeable surfaces) and the peak discharge rate should be reduced (e.g. by using

vegetated swales (where suitable) and retention ponds).

• Where storm-water treatment is deemed necessary to protect the quality of receiving water bodies,

priority should be given to managing and treating the first flush of storm-water runoff where the

majority of potential contaminants tend to be present.

• When water quality criteria allow, storm-water should be managed as a resource, either for

groundwater recharge or for meeting water needs at the facility.

• Oil water separators and grease traps should be installed and maintained as appropriate at refuelling

facilities, workshops, parking areas, fuel storage and containment areas.

• Sludge from storm-water catchments or collection and treatment systems may contain elevated levels

of pollutants and should be disposed in compliance with local regulatory requirements, in the absence

of which disposal has to be consistent with protection of public health and safety, and conservation

and long term sustainability of water and land.

With regards to the IFC guidance, the IFC Environmental, Health and Safety Guidelines for Mining (2007)

identifies the following:

• Dirty Water Areas include beneficiation plants; workshops (where oil is handled); residue disposal

facilities, haul roads, opencast pits, pollution control dams.

• Separation of clean and dirty water areas is required, while minimising runoff, avoiding erosion of

exposed ground surfaces, avoiding sedimentation of drainage systems and minimising exposure of

polluted areas to storm-water.

From exploration onwards, the management strategies include:

• Reducing exposure of sediment-generating materials to wind or water (e.g. proper placement of soil

and rock piles);

• Divert run-off from undisturbed areas around disturbed areas including areas that have been graded,

seeded, or planted (where suitable). Such drainage should be treated for sediment removal;

• Reducing or preventing off-site sediment transport (e.g. use of settlement ponds, silt fences);

• Storm-water drains, ditches, and stream channels should be protected against erosion through a

combination of adequate dimensions, slope limitation techniques, and use of rip-rap and lining.

Temporary drainage installations should be designed, constructed, and maintained for recurrence

periods of at least a 25 year/24-hour event, while permanent drainage installations should be designed



for a 100 year/24-hour recurrence period. Design requirements for temporary drainage structures

should additionally be defined on a risk basis considering the intended life of diversion structures, as

well as the recurrence interval of any structures that drain into them.

From construction onwards, recommended management strategies include:

• Establishing riparian zones (where applicable);

• Timely implementation of an appropriate combination of contouring techniques, terracing, slope

reduction / minimisation, runoff velocity limitation and appropriate drainage installations to reduce

erosion in both active and inactive areas;

• Access and haul roads should have gradients or surface treatment to limit erosion, and road drainage

systems should be provided;

• Facilities should be designed for the full hydraulic load, including contributions from upstream

catchments and non-mined areas;

• Storm-water settling facilities should be designed and maintained according to internationally accepted

good engineering practices, including provisions for capturing of debris and floating matter. Sediment

control facilities should be designed and operated for a final Total Suspended Solids (TSS) discharge

of 50 mg/l and other applicable effluent guidelines, taking into consideration background conditions

and opportunities for overall improvement of the receiving water body quality.

From operations onwards, recommended management strategies include:

• Final grading of disturbed areas, including preparation of overburden before application of the final

layers of growth medium, should be along the contour as far as can be achieved in a safe and

practical manner;

• Re-vegetation of disturbed areas including seeding should be performed (where suitable) immediately

following application of the growth medium to avoid erosion.

5.1 SITE SPECIFIC STORM-WATER MANAGEMENT

From the available survey/elevation data and site visit it can be seen that the catchment watershed between

Catchment A (north western catchment) and Catchment B (south eastern catchment) runs in an

approximately north eastern to south western direction and cuts through the old tailings dam. This means

that there is almost no surface area producing clean runoff which would need to be routed around the mine

infrastructure.

The main storm-water management measures will be the dirty water collection channels surrounding the old

and new tailings dams and the mining infrastructure for processing and storage of rock (Figure 15). Two

separate collection channels will be required, one for Catchment A, which will include the northern edge of



the old tailings dam and the whole of the mining infrastructure, and the second for Catchment B which will

include the southern edge of the old tailings dam and the entire new tailings dam. It is likely that no collection

channel will be required along the western side of the new tailings dam as this appears to be just below the

crest of the watershed, but a more detailed survey of this area will be required to confirm actual site

conditions. There may also be some problems encountered in this area if a collection channel is required,

due to the overhead electrical lines which are located there and the access road for these.

It is likely that construction of these dirty water collection channels will be complicated by the lack of surface

material which can be excavated, so actual site conditions will dictate the applicable measures for

construction. Possible solutions may include constructing lined (either plastic or concrete) channels utilising

embankments constructed from waste material, combined with lined sections excavated through the

bedrock.

Retainment ponds for the Catchment A dirty water collection channels will need to be located in the drainage

line to the south of the mine infrastructure and possibly in the drainage line to the north west of the mine

infrastructure, depending on the local relief. The retainment pond(s) will probably have to be excavated into

bedrock and lined if the bedrock is weathered and fractured. The catchment area within the Catchment A

collection channel is approximately 95,000 m2 and collects dirty water from the northern part of the Old

Tailings Facility and the general mine infrastructure. Depending on local relief, it is planned that all dirty water

can be fed by gravity through the channel to the southern retainment pond, reducing pumping and operating

costs.

For the Catchment B dirty water collection channels it is likely that only one retention pond will be required,

located to the south of the new tailings dam, where the existing retainment walls are located in the drainage

line. Again with the flat relief it is likely that the pond will need to be excavated into bedrock and lined. The

catchment area within the Catchment B collection channel is approximately 148,300 m2 and collects dirty

water from the south eastern part of the Old Tailings Facility and the New Tailings Facility. It is planned that

all dirty water can be fed by gravity through the channel to the retainment pond.

Dirty storm-water from the containment dams should be pumped out of the dams and re-used by operations

at the site. This will be relatively straightforward for Catchment A retention pond, which is located close to the

mine infrastructure, but for Catchment B retention pond it may be easier to pump the water into the tailings

dam if the water balance allows this.

Storm-water calculations carried out in this report are guided by a series of design principles for storm-water

management which have been based on the requirements of Government Notice (GN) 704 established by

the South African Department of Water Affairs and Forestry (DWAF) regulating the use of water for mining.

GN 704 requires that dirty water containment facilities are designed, constructed, maintained and operated

so that they do not spill into a clean water environment more than once in 50 years. A critical component in

sizing the containment pond is the rate at which water is pumped out of the pond for re-use at the site, which



forms part of the site wide water balance and is not addressed within this report. GN 704 also requires that

as a minimum, the 1:50 year design volume and a 0.8 m freeboard allowance should always be available.

FIGURE 15: PROPOSED STORM-WATER DRAINAGE LAYOUT

TABLE 8: CALCULATED DIRTY WATER VOLUMES FOR CONTAIN MENT DAMS

Catchment A A B B

Dirty Water Catchment AreaOld Tailings

DamPlant

InfrastructureOld Tailings

DamNew Tailings

Dam

Surface area (m2) 31 100 63 900 20 700 127 600

Runoff coefficient 0.7 0.8 0.7 0.3


24 hour 675 1 585 449 1 187

Catchment 24 hour 2 260 1 636

Storm Volume (m3) Storm Volume (m3)



6 ACID ROCK DRAINAGE

6.1 INTRODUCTION

Mineralogy and deposit characteristics for the Namib Lead-Zinc (Pb- Zn) Mine have been clearly described in

the CSA Global technical memorandum (CSA Global, 2013 Dr N Reynolds). The main features with regard

to the style of primary mineralisation are as follows:

• The mineralisation is not deformed Mississippi Valley Type (MVT) but intrusive-related replacement

mineralisation, with potential for zonation in metal content and two different mineralisation styles;

• Mineralisation is strongly strata bound within thin-bedded carbonate units of the Arise River member:

mixed marble / calc-silicate schist package;

• Mineralisation has higher zinc than lead and significant silver content;

• Mineralisation is described as coarse semi-massive sulphide comprising: pyrrhotite, pyrite, sphalerite

and galenea. Magnetite is locally abundant; and

• Fluorite is described as ‘prominent in the gangue.

The sulphide minerals identified within the ‘3 domains’ at the Namib Pb-Zn Mine strongly suggest that acid

will be generated through oxidation processes. The amount of acid that would be generated (acid

generating potential (AP)) cannot be quantified without geochemical test work, specifically laboratory Acid

Base Accounting (ABA) and sulphur speciation on representative samples.

Although the sulphide minerals suggest acid generation, the presence of the carbonate minerals within the

host rock (marble and calc – silicate) suggest that they will provide potentially considerable neutralising

potential (NP). The acid buffering capacity of the host rocks cannot be quantified without geochemical test

work, specifically laboratory ABA.

In addition to the potential of acid generation and acid rock drainage, seepage quality from waste rocks

dumps (WRDs) and tailings storage facilities (TSFs) must be considered. The production of acid and

subsequent lowering of pH will in turn promote metal dissolution and seepage from such waste facilities may

contain high concentrations of metals and salt which has the potential to cause contamination of the

underlying aquifer system. Although metal mobility may be limited by the abundance of carbonate rock

associated with the deposits, the seepage quality from such waste facilities and the risk to groundwater

cannot be fully quantified without undertaking appropriate geochemical test work on representative samples.

Groundwater samples, as discussed in the following section, show neutral pH and high sodium-chloride (Na-

Cl) signatures which indicates a potential mine drainage quality issue, even if it is not necessarily an Acid

Rock Drainage (ARD) issue.



6.2 GROUNDWATER QUALITY MONITORING

Quarterly groundwater quality monitoring data from nine monitoring wells (NLZ-W1 to NLZ-W9), located

within a 2.5km radius of the existing mine site have been reviewed. Data are available between July 2012

and June 2013. No groundwater quality data has been identified for the period prior to 2012, so baseline

data can only be discussed for the “post historic mining” situation and no baseline information is available for

the “pre-mining” situation.

Regional groundwater flow direction is assumed to be west towards the Atlantic Ocean.

Concentrations were compared to Namibian Drinking Water Standards. Results show:

• Elevated concentrations of the metals, aluminium (Al), boron (B), iron (Fe), manganese (Mn) and

selenium (Se) were recorded in all samples, but were generally stable over the review period, with the

exception of iron and manganese in borehole NLZ-W1 where a rising trend can be observed (Figure

17);

• The electrical conductivity is high in all samples ranging from 1,532 mS/m (NLZ-W4) and 5,095 mS/m

(NLZ-W3) (Figure 20);

• Concentrations of the cations sodium (Na), magnesium (Mg) and calcium (Ca) (Figure 18) and anions

chloride (Cl), sulphate (So4) and nitrate (NO3) (Figure 19) are elevated in all samples, but

concentrations generally remained steady over the review period, with the exception of:

o Iron concentrations recorded in NLZ-W1 (up-gradient of the mine) significantly rise over the

review period and are significantly higher than concentrations recorded in all other

boreholes:

o Lead concentrations recorded in NLZ-W3 (across-gradient) are significantly higher than

concentrations recorded in all other boreholes. In addition the overall trend observed in

NLZ-W3 does not correspond with the trend observed in all other boreholes;

o Manganese concentrations recorded in NLZ-W1 (up-gradient of mine) and NLZ-W6 (down-

gradient of the mine) are elevated above concentrations recorded in all other boreholes;

• The results suggest that there is no impact from anthropogenic processes (specifically mining), with

natural enrichment of certain elements in groundwater due to the geological setting, although

comparison with pre-mining groundwater quality data would confirm this.

It is noted that the spike in the boron and selenium concentration for December 2012 monitoring round

(Figure 17) are considered to be a result of laboratory or sampling issue rather than an actual effect on

groundwater quality.



A Piper Plot was developed for the nine groundwater samples (as presented in Figure 16) to determine the

water facies. The Piper Plot indicates that the groundwater samples show an older evolved groundwater

signature (i.e. water equilibrated with the aquifer material along its flow path).

The exceedences of both chloride and sulphate are likely to be natural and a function of the geology

(metamorphosed marine sediments) and the arid environment where evaporation is prominent.

FIGURE 16: PIPER PLOT OF GROUNDWATER IN THE VICINIT Y OF NAMIB PB-ZN MINE



Page 29

FIGURE 17: CONCENTRATIONS OF METALS RECORDED IN GRO UNDWATER MONITORING BOREHOLES IN THE VICINITY OF NA MIB PB-ZN MINE



Page 30

FIGURE 18: CONCENTRATIONS OF MAJOR CATIONS RECORDED IN GROUNDWATER MONITORING BOREHOLES IN THE VICINIT Y OF NAMIB PB-ZN MINE



Page 31

FIGURE 19: CONCENTRATIONS OF MAJOR ANIONS RECORDED IN GROUNDWATER MONITORING BOREHOLES IN THE VICINITY OF NAMIB PB-ZN MINE



Page 32

FIGURE 20: CONCENTRATIONS OF GENERAL PARAMETERS REC ORDED IN GROUNDWATER MONITORING BOREHOLES IN THE VICINITY OF NAMIB PB-ZN MINE



Page 33

6.3 CONCLUSION

The geological setting suggests that there is acid generating potential at Namib Pb-Zn Mine due to the

sulphide minerals associated with the ore. The lowering of pH from the acid generated would promote the

mobilisation of metals, however the potential acid generation at Namib Pb-Zn Mine would be buffered by

the acid neutralising potential of the host (carbonate) rock, the degree of which cannot be quantified

without geochemical test work.

Assessment of the risk to groundwater from the Namib Pb-Zn mine and associated waste disposal

facilities (waste rock dump and tailings storage facility) ultimately depends on the geochemical test work

(acid generating potential, associated heavy metals suite, the amount of acid buffering capacity of the

host rocks) along with site specific factors, which include, climatic setting and natural, pre-mining

background characteristics of associated waters.

6.4 RECOMMENDATIONS

The ore deposits at Namib Pb-Zn Mine are associated with sulphidic minerals which have the potential to

generate acid and give rise to mine drainage with elevated concentrations of metals and non-metals.

The groundwater monitoring data reviewed as part of this assessment does not suggest groundwater is

being impacted by anthropogenic (mining) processes, however comparison to baseline data (pre-mining)

has not been undertaken and source term concentrations have not been determined. .

In accordance with best practice, as set out in the GARD Guide and MEND 1.20.1 Report, it is

recommended that all material that will be excavated, exposed and otherwise disturbed during the mining

process be geochemically characterised to predict drainage chemistry prior to mining. Geochemical

characterisation of material is a fundamental factor in the design and management of a mine. It allows the

type, magnitude, location and timing of mitigations measures required to prevent significant

environmental impacts to be identified.

A critical success factor for any geochemical characterisation program is the selection of representative

samples. This should consider material type (e.g. lithology), spatial (eg. vertical and horizontal areas to

be mined) and compositional (eg. ore body, non-ore body, waste rock, tailings) representatively as well

as sample storage and handling (e.g. fresh and / or weathered sample). It is recommended that a

sampling plan is developed prior to sampling.

It is recommended that samples are submitted for initial static geochemical test work, including:

• Acid Base Accounting (ABA);

• Net Acid Generation (NAG) analysis;

• Synthetic Precipitation Leaching Procedure (SPLP) Tests.

The ABA result would allow the assessment of the acid generation and the neutralising potential of

material to be determined and would allow samples to be classified as Potentially Acid Generating (PAG)



Page 34

where the neutralising potential is insufficient to buffer the acid generation or Non-Potential Acid

Generating (Non-PAG) where there is adequate acid buffering capacity. Should samples be classified as

PAG, further geochemical tests, in the form of kinetic tests would be recommended to predict primary

reaction rates and fully understand the potential seepage quality from WRDs or TSFs.

Should a significant acid potential be identified from the ABA results, kinetic testing will be required to

determine the rate of acid generation and neutralisation potential consumption. Kinetic test results will

also allow long-term mine drainage quality to be determined

The iron sulphide mineral rich tailings that are deposited on a surface TSF pose the major potential

environmental concern associated with the deposit. Seepage quality from the TSF during operational

phase of the Life of Mine (LOM) is characterised by the supernatant. It is recommended that a sample of

tailings liquor or process water is collected from site following pilot testing. The sample should be

analysed for a complete set of inorganic parameters, including:

• pH, EC and alkalinity; and

• ICP scan of major and trace elements.

The SPLP leach test results would be compared to relevant water quality and /or effluent standards as a

high level screening process. The resultant concentrations would not be representative of run-off (or

seepage) that could emanate from site as the lab conditions would not represent field conditions.

However, leach testing would identify chemicals of concern (CoCs), that is, elements likely to be

mobilised within leachate and pose a risk to groundwater. Further, leach testing can be used to predict

likely drainage quality from mine facilities such as tailings and waste rock facilities.

The geochemical results are an important part of the mine planning. The geochemical results would be

used as follows:

• to design and develop appropriate schemes to manage waste rock and tailings material to reduce

the potential for poor quality drainage.

• To estimate a source term concentration for the tailing storage facility which could be used in a

groundwater numerical transport model.

• To enable a more comprehensive groundwater and /or surface water impact assessment to be

undertaken.

7 IMPACT ASSESSMENT

An assessment of the various environmental impacts that the mining would have on groundwater and

surface water, together with a severity rating and mitigation measures are presented below, with rating

criteria as explained in Table 9 below.



Page 35

TABLE 9: CRITERIA FOR ASSESSING IMPACTS Note: Both the criteria used to assess the impacts and the methods of determining the significance of the impacts are outlined in the following table. Part A provides the definition for determining impact consequence (combining severity, spatial scale and duration) and impact significance (the overall rating of the impact). Impact consequence and significance are determined from Part B and C. The interpretation of the impact significance is given in Part D.

PART A: DEFINITION AND CRITERIA* Definition of SIGNIFICANCE Significance = consequen ce x probability Definition of CONSEQUENCE Consequence is a function of severity, spatial extent and duration

H Substantial deterioration (death, illness or injury). Recommended level will often be violated. Vigorous community action. Irreplaceable loss of resources.

M Moderate/ measurable deterioration (discomfort). Recommended level will occasionally be violated. Widespread complaints. Noticeable loss of resources.

L Minor deterioration (nuisance or minor deterioration). Change not measurable/ will remain in the current range. Recommended level will never be violated. Sporadic complaints. Limited loss of resources.

L+ Minor improvement. Change not measurable/ will remain in the current range. Recommended level will never be violated. Sporadic complaints.

M+ Moderate improvement. Will be within or better than the recommended level. No observed reaction.

Criteria for rating of the SEVERITY/NATURE of environmental impacts

H+ Substantial improvement. Will be within or better than the recommended level. Favourable publicity.

L Quickly reversible. Less than the project life. Short term M Reversible over time. Life of the project. Medium term

Criteria for rating the DURATION of impacts

H Permanent. Beyond closure. Long term. L Localised - Within the site boundary. M Fairly widespread – Beyond the site boundary. Local

Criteria for rating the SPATIAL SCALE of impacts H Widespread – Far beyond site boundary. Regional/ national PART B: DETERMINING CONSEQUENCE

SEVERITY = L DURATION Long term H Medium Medium Medium Medium term M Low Low Medium Short term L Low Low Medium

SEVERITY = M DURATION Long term H Medium High High Medium term M Medium Medium High Short term L Low Medium Medium

SEVERITY = H DURATION Long term H High High High Medium term M Medium Medium High Short term L Medium Medium High L M H Localised

Within site boundary

Site

Fairly widespread Beyond site boundary

Local

Widespread Far beyond site

boundary Regional/ national

SPATIAL SCALE PART C: DETERMINING SIGNIFICANCE

Definite/ Continuous H Medium Medium High Possible/ frequent M Medium Medium High

PROBABILITY (of exposure to impacts) Unlikely/ seldom L Low Low Medium L M H CONSEQUENCE PART D: INTERPRETATION OF SIGNIFICANCE Significance Decision guideline High It would influence the decision regardless of any possible mitigation. Medium It should have an influence on the decision unless it is mitigated. Low It will not have an influence on the decision.

*H = high, M= medium and L= low and + denotes a positive impact.



Page 36

7.1 GROUNDWATER IMPACT ASSESSMENT

Facilities during the construction phase that are considered for the groundwater impact assessment

include accommodation, offices, ablution facilities, waste collection and storage areas. Facilities during

the operational phase that are considered for the groundwater impact assessment include

accommodation, ablution facilities, waste collection and storage areas, a refuelling area, top-soil stock

piles (if present), tailings storage facilities, waste rock dumps, marginal ore dumps, ROM stockpile and

the crushing and screening plant. Impacts associated with the mining licence area are contamination by

means of lubricants, oils, fuel, blasting, chemical spillages and acid rock drainage.

The groundwater impact assessment considered the following:

• Lowering of the groundwater table due to mine dewatering or groundwater abstraction for any

other purpose (Table 10).

• Groundwater contamination by activities during the construction and operational phases in the

mining licence area including the accommodation, offices, ablution facilities, waste collection sites,

refuelling area (Table 11);

• Seepage of supernatant into the groundwater system from the tailings storage facility and

processing plant (Table 12).

• Acid Rock Drainage (Table 13).

For all mitigated scenarios, the potential impact on the groundwater systems is considered low. The

design of a sufficient groundwater monitoring plan and the drilling of additional monitoring boreholes that

keep track of abstracted volumes, record groundwater levels and make provision for the analyses of the

correct chemical parameters is essential for a well-managed groundwater system. There is a network of 9

boreholes that are currently monitored, but it is recommended that this is expanded before construction

work and mining/processing takes place.

After assessing the hydrogeological regime of the area with the available information, impacts on the

groundwater system are judged to be low, especially taking into consideration the fact that there are no

known groundwater abstractions taking place between the mine and the coast, which would be affected

by any deterioration in groundwater conditions, and that the current water quality is poor (high salinity).

This assessment assumes that the Namibian Environmental and Water Laws and Regulations are

correctly interpreted and applied. In particular this refers to the application for and issue of a groundwater

abstraction permit from the Department of Water Affairs and Forestry, if groundwater is to be abstracted

for mine pit dewatering or any other purpose; to meet the minimum required design criteria for the

specific class fuel storage facility if relevant, and that the discharge criteria for any new effluent or

discharge stream as stipulated in the regulations are met.



Page 37

7.2 SURFACE WATER IMPACT ASSESSMENT

The surface water impact assessment considered the following:

• Reduction of runoff volume to the downstream areas (Table 14);

• Reduction in water quality of surface water due to pollution (Table 15).

The resumption of mining and the associated processing on site would only have a small impact on the

surface water runoff generated by this part of the catchment, as the catchment boundary (watershed)

between Catchment A and Catchment B runs through the old tailings dam, hence there is no significant

upstream contribution that would be intercepted by the infrastructure. Also this generally fairly flat area

has few distinct drainage lines, especially in the sand covered areas, suggesting that much of the runoff

will be overland flow, which reduces the volumes of water reaching the more downstream parts of the

catchment due to interception and losses. This suggests that the expanded mining and infrastructure

area will not have a significant impact on the surface water flow in the area. Some dirty water will be

impounded, but these small amounts will not make a significant reduction to downstream runoff, due to

the expected interception and losses mentioned above.

Pollution from the mining and processing activity at the mining area could be transported in the surface

water if suitable storm water management (infrastructure and procedures) are not part of the mine plan.

There are significant minerals/metals in the material being mined that would cause pollution to the

surface water (eg lead), and there is also a risk of spillage of fuels and lubricants from the equipment

working at the mine which would be mobilised and cause pollution of the surface water during runoff

events. The main pollution impact is likely to be in the form of suspended solids being washed out of the

mining area and metals/hydrocarbons in solution, but with most of the runoff occurring as overland flow

rather than channel flow, the capacity to transport suspended solids significant distances is greatly

reduced.

As with the groundwater situation, there are no known downstream users (except wildlife) who would be

affected by any deterioration in surface water conditions, so for both mitigated scenarios, the potential

impact on the surface water systems is considered low.



Page 38

TABLE 10: IMPACT OF RESUMED MINING ON GROUNDWATER R ESOURCE (GROUNDWATER ABSTRACTION AND/OR DEWATERING OF THE MINE) Unmanaged assessment Managed assessment

Potential impact of the Resumed Mining in the unman aged

scenario on Groundwater Resources.

Sev

erity

Dur

atio

n

Spa

tial S

cale

Con

sequ

ence

Pro

babi

lity

Sig

nific

ance

Managed Scenario / Mitigation measures

Sev

erity

Dur

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Severity:

Groundwater abstraction for mine dewatering or other mining purposes is not anticipated, as the mine is currently dry and water will be piped to site by NamWater. Hence little chance that abstraction might cause a decline in the water-table beyond the mining boundary. Severity is considered low in both cases.

Duration:

The duration could extend over the life of the mine and is therefore medium in both cases.

Spatial scale:

Water levels unlikely to decline outside boundary of the mining area. Spatial scale is low in both cases.

Consequence:

This would not cause problems for any other users, as there are no downstream consumers. Consequence rating is low in both cases.

Probability:

It is unlikely groundwater abstraction would impact the groundwater table, therefore probability is considered low in both cases.

Significance:

Summarising the above assessment, the overall significance is rated as low in both cases.

L M L L L L

Not required as low risk.

Objective:

To establish baseline values for natural groundwater variation of the water-table. To monitor the impact of groundwater abstraction and mine dewatering on the regional water-table.

Actions:

Drill additional monitoring boreholes at strategic localities and continue expanded groundwater monitoring plan.

Measure water levels at regular intervals and meter any groundwater abstraction.

Emergency situations:

None identified.

L M L L L L



Page 39

TABLE 11: IMPACT OF RESUMED MINING ON GROUNDWATER Q UALITY (CONTAMINATION FROM ACCOMMODATION, OFFICES, ABLUTION FACILITIES, WASTE COLLECTION SITE, REFUELLING AREA)

Unmanaged assessment Managed assessment



Sev

erity

Dur

atio

n

Spa

tial S

cale

Con

sequ

ence

Pro

babi

lity

Sig

nific

ance


Sev

erity

Dur

atio

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Spa

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cale

Con

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Pro

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Sig

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ance



Page 40




Sev

erity

Dur

atio

n

Spa

tial S

cale

Con

sequ

ence

Pro

babi

lity

Sig

nific

ance


Sev

erity

Dur

atio

n

Spa

tial S

cale

Con

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ence

Pro

babi

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Sig

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ance

everity:

Groundwater contamination from these facilities unlikely to cause a measureable deterioration or a limited loss of groundwater resources. Few complaints can be expected. Severity is considered low in both the unmitigated the mitigated cases.

Duration:

The duration could extend over the life of the mine and is therefore medium in both cases.

Spatial scale:

Due to the very low hydraulic properties of the present rock types, it is unlikely that contaminant migration would be beyond the EPL area. Spatial scale is considered low in both cases.

Consequence:

Consequence is low in both the unmitigated and the mitigated cases.

Probability:

It is possible groundwater contamination could happen, probability is considered medium in the unmitigated case and low in the mitigated case.

Significance:

Summarising the above assessment, the overall significance is rated as medium in the unmitigated case and low in the mitigated case.

L M L L M M

Objective:

To monitor groundwater quality and to detect contaminants that might migrate off the EPL area. To prevent contamination of groundwater from the (i) accommodation, offices, ablution facilities, (ii) refuelling area (iii) waste collection sites .Numerical modelling study of groundwater.

Actions:

• An expanded groundwater monitoring plan must be designed with additional boreholes drilled to monitor water quality at regular intervals.

• Construct bunds and line the refuelling area and other dirty water areas to prevent any fuel spillages or contaminants from entering the groundwater system;

• Design the ablution facilities with correctly sized design criteria, ensure that effluent discharge meet the requirements set by Department of Water Affairs;

• Clean-up kits on site for any spillage that happens.


If groundwater contamination due to the mining activities is detected in the monitoring boreholes, inform the relevant authorities and any affected downstream consumers. Address the cleanup of the contaminating facility, and groundwater treatment techniques i.e. pumping and treatment.

L M L L L L



Page 41

TABLE 12: IMPACT OF RESUMED MINING ON GROUNDWATER Q UALITY (SEEPAGE OF SUPERNATANT FROM TAILINGS STORAG E FACILITY AND/OR PROCESSING PLANT CAUSING POLLUTION OF GROUNDWATER)




Sev

erity

Dur

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Spa

tial S

cale

Con

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Pro

babi

lity

Sig

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ance


Sev

erity

Dur

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n

Spa

tial S

cale

Con

sequ

ence

Pro

babi

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Sig

nific

ance

Severity:

Tailings liquor produced during processing and pumped to the TSF contains elevated concentrations of metals such as lead and zinc. The supernatant could infiltrate through fractures and faults in the underlying marble and reach the groundwater table.

Duration:

The duration would be the life of the mine and is therefore medium in both the unmitigated and the mitigated cases.

Spatial scale:

Expected that due to the low conductivities of the country rock and the confinement of the mining activities to the Karibib Marble complex, it would mostly be restricted to the mining license area. Spatial scale is low in both cases.

Consequence:

Consequence is low in both the unmitigated and the mitigated cases.

Probability:

It is possible groundwater contamination could happen, probability is considered medium in the unmitigated case and low in the mitigated case.

Significance:


L M L L M M

Objective:

To investigate the local geology with geophysics to identify fracture zones relative to infrastructure; use suitable liners to prevent leakage of tailings liquor; operate tailings facility efficiently to prevent overfilling.

Actions:

Seepage from the tailings dams into the groundwater to be prevented by :

• Tailings material to be placed only on the marble outcrop;

• Avoiding fractured bedrock or grouting /filling identified fractures;

• Installing suitable lining material, (either plastic sheet or inert crushed rock);

• Collection and re-cycling of supernatant/tailings liquor.

Seepage from processing plant to be minimised by stringent operating and maintenance policy.

Groundwater monitoring to identify changes to water quality.


None identified.

L M L L L L



Page 42

TABLE 13: IMPACT OF RESUMED MINING ON GROUNDWATER Q UALITY (ACID ROCK DRAINAGE) Unmanaged assessment Managed assessment



Sev

erity

Dur

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Con

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Pro

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Sev

erity

Dur

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ence

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Sig

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ance

Severity:

Due to low permeabilities in the surrounding country rock, relatively low likelihood that migration of any pollution source will be outside of the EPL area. Since the ore body contains sulphide minerals, it is possible ARD into the groundwater may occur locally. Severity is considered to be low in both cases because of the very low rainfall in the project area.

Duration:

The duration would extend beyond the life of the mine and is therefore high in both the unmitigated and the mitigated cases.

Spatial scale:

Expected that due to the low conductivities of the country rock, it would mostly be restricted to the mining license area. Spatial scale is low in both cases.

Consequence:

Consequence is medium in both the unmitigated and the mitigated cases.

Probability:

It is possible groundwater contamination could happen from ARD, probability is considered medium in the unmitigated case and low in the mitigated case.

Significance:


L H L M M M

Objective:

To investigate the ARD potential, to ascertain local conditions with regard to mining processes.

Actions:

Tailings material must be placed on the marble outcrop, to enable effective buffering of acidity by carbonates, in conjunction with limited ARD testing to quantify the buffering potential of the marbles.

Cover tailings dams with crushed waste rock (marble), to reduce erosion and ARD.

If future monitoring indicates groundwater quality deterioration, implement further ARD studies. Once conditions have been analysed, suitable mitigation measures would be implemented according to any identified concerns.


None identified.

L H L M L L



Page 43

TABLE 14: IMPACT OF RESUMED MINING ON SURFACE WATER RUNOFF Unmanaged assessment Managed assessment


scenario for the Surface Water Runoff.

Sev

erity

Dur

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tial S

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Con

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Pro

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Sig

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Sev

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Dur

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Severity:

Runoff from the catchments captured by mining infrastructure, causing small reduction in volume downstream, however, almost no upstream catchment area, so very limited impact.

Duration:

Any minor impact will be of long term duration as the effects of the mine on the runoff will last beyond the life of mine in both the unmitigated and mitigated cases, hence high in both cases.

Spatial scale:

The reduced runoff downstream will have no effect beyond the EPL boundary. Hence, the influence is only within the site boundary, so the influence is low in both cases.

Consequence:

As no surface water users and based on the above assessment the determining consequence is medium in both cases.

Probability:

The probability of the reduced flood runoff affecting the downstream conditions is possible locally, due to this being the uppermost part of the catchment and there being a small reduction in contributing area, hence low in both cases.

Significance:

Summarising the above assessment, the overall significance is rated as low in both cases.

L H L M L L

Not required as low risk.

Objective:

No clean water needs to be diverted around infrastructure, so only containment of dirty water on site, hence a small amount of runoff likely to be captured.

Actions:

Storm Water Management will produce small reduction in surface water flow downstream, as dirty water retained on site. No significant effects caused downstream.


None identified.

L H L M L L



Page 44

TABLE 15: IMPACT OF RESUMED MINING ON SURFACE WATER QUALITY Unmanaged assessment Managed assessment


scenario for the Surface Water Quality.

Sev

erity

Dur

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Spa

tial S

cale

Con

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Pro

babi

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Sig

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Sev

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Dur

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Severity:

Dirty water runoff from the mining infrastructure and processes, (especially the new tailings dam), causing minor pollution downstream, including lubricants and fuels from machinery. As no downstream users, severity low in both the unmitigated and in the mitigated cases.

Duration:

The duration is long term as pollution of surface water can continue after life of mine in unmitigated case, but is reduced with mitigation during Life of Mine, but after LoM returns to high.

Spatial scale:

The polluted runoff downstream will be outside of the site boundary. The influence is therefore beyond the site boundary, so the influence is medium in the unmitigated and mitigated cases.

Consequence:

No identified downstream users, but wildlife may drink contaminated water, so based on the above assessment the determining consequence is medium in both the unmitigated and the mitigated cases.

Probability:

The probability of the polluted flood runoff affecting the downstream conditions is medium in the unmitigated case and low in the mitigated case.

Significance:


L H M M M M

Objective:

To capture dirty water runoff generated in the mining area and contain for re-use in the mining process or to treat before discharging.

Actions:

• Provide sufficient impoundment for dirty water volumes and treat as required prior to re-use or discharging.

• Mitigation measures will be reduced after Life of Mine, but impoundments will still capture some dirty water and act as settling ponds for suspended solids.

• Capping of tailings facility at end of LoM, to reduce wind and runoff erosion.

• Regular clean-up of crushed ore and waste material which could cause contamination of surface water.

• Prevent ponding of surface water on site plus fencing of retention dams.


None identified.

L H M M L L



8 SUMMARY AND CONCLUSIONS

The planned mining activities at Namib Mine requires a groundwater and surface water specialist study

for the EIA to assess the likely impacts on the groundwater and surface water in the area.

The groundwater assessment looks at the potential impacts on groundwater caused by the planned

mining activities and contamination coming from facilities during the construction and operational phase

of the mining activity. Impact assessments have been undertaken for the scenario of mining activity

causing a reduction in the water-table level and mining activities causing a reduction in groundwater

quality through pollution (from plant, equipment and infrastructure, from seepage of supernatant and from

acid rock drainage). In each of these cases the assessment was low in the mitigated scenarios. This

mitigation requires that continued groundwater monitoring and sampling, with the inclusion of additional

monitoring wells, be implemented to maintain the monitoring of groundwater levels and quality, so that

any changes in water-table levels or groundwater quality can be quickly identified and suitable remedial

action taken. For transparency it is recommended that this monitoring is carried out by a reputable

independent consultant. It should be noted that the current groundwater quality is poor and that there are

no identified downstream groundwater users who would be affected by any future deterioration in

groundwater quality or water-table levels.

A further study should be undertaken to confirm whether the base-rock will sufficiently neutralise any

ARD that may occur. Details of suitable initial analysis have been covered in Section 6 of this report. If

future monitoring identifies a deterioration in the baseline groundwater quality, further ARD studies should

be undertaken to identify the processes, and suitable mitigation measures should be tailored around the

findings of these further studies.

The surface water assessment looks at the likely effects of the planned mining on the surface water

runoff in the area as well as the likely effect on the surface water quality. As the catchment area which is

affected by the proposed resumed mining is not connected to any significant major drainage basins, the

impacts downstream will be low in the mitigated case for both runoff and water quality. Mitigation

measures for the surface water assessments relate to the storm water management measures required

to capture and contain the dirty water component of the runoff generated within the mining area. It should

be noted that the only identified downstream surface water users who would be affected by any future

deterioration in surface water runoff volumes or quality are the wildlife who may drink from temporary

surface water pools after runoff events.

With reference to the Storm-water Management Plan it is recommended that as soon as detailed

information on the planned mining operations and infrastructure layout (including a revised topographic

survey for more detailed catchment delineation in the mine infrastructure area) are available, a revised

storm-water management plan should be developed, detailing the dirty water generating areas and



including detailed design of required structures (collection channels and retainment dams) and then a

management plan with appropriate pumping procedures can be compiled.

The retainment dams and any tailings liquor ponds should be fenced to prevent wildlife from drinking at

the open water, the fencing should be sufficient to prevent large and small wildlife access, so should

consist of game proof fencing and some ground level solid barrier to prevent small wildlife from entering.

Jonathan Church (Project Manager) 16th October 2013

Arnold Bittner (Project Reviewer) 17th October 2013



9 REFERENCES

ADAMSON, P.T., 1981 “Southern African Storm Rainfall”. Technical Report No.TR 102. Department of

Water Affairs, Pretoria, RSA.

ALEXANDER, W.J.R., 2001 “Flood Risk Reduction Measures incorporating Flood Hydrology for Southern

Africa”. S.A. National Committee on large Dams, Pretoria, RSA.

CSA Global (Dr Neals Reynolds, 02/05/2013, Memorandum entitled “Desktop Targeting Assessment of

the Namib Lead-Zinc Project)

DWAF, 1999 “Government Notice 704 (Government Gazette 20118 of June 1999)”. Department of Water

Affairs, Pretoria, RSA.

MENDELSOHN, J., JARVIS, A., ROBERTS, C. AND ROBERTS, T., 2002 “Atlas of Namibia: A portrait of the land

and its people". David Philip Publishers, Cape Town, RSA.

MIDGLEY D.C., PITMAN W.V. (1978),”A Depth-Duration-Frequency Diagram for Point Rainfall in Southern

Africa”. Hydrological Research Unit Report 2/78, University of the Witswatersrand, RSA.

MILLER, R. (2008). “The geology of Namibia. Volume 3. Palaeozoic to Cenozoic”. Windhoek: Ministry of

Mines and Energy. Geological Survey of Namibia.

SANRAL, 2006 “Drainage Manual-Fifth Edition”. The South African National Roads Agency Limited,

Pretoria.

SLR Environmental Consulting (Namibia) (Pty) Ltd, Drilling and Installation of 8 Monitoring Wells at EPL

2902 : Namib Lead & Zinc Mine Report No: 2012-G19-V1, Project No: NLZ-001, May 2012.

SLR Environmental Consulting (Namibia) (Pty) Ltd, Hydrological Assessment : Namib Lead & Zinc

Report No: 2012-S6-V1, Project No: 733.14012.00001 November 2012.

THE WATER ACT (ACT 54 OF 1956), “The Namibian National Water Quality Standards”, Department of

Water Affairs, Ministry of Agriculture, Water and Rural Development, Government of the Republic of

Namibia.

GARD Guide, Global Acid Rock Drainage Guide, www.gardguide.com



Page i

RECORD OF REPORT DISTRIBUTION

SLR Reference: 733.14009.00004 Title: Namib Mine : Ground- and Surface Water Specialist Input to EIA Report Report Number: 2013-GS-6 Proponent: North River Resources (Namibia) (Pty) Ltd

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COPYRIGHT

Copyright for these technical reports vests with SL R Environmental Consulting (Namibia) (Pty)

Ltd unless otherwise agreed to in writing. The rep orts may not be copied or transmitted in any

form whatsoever to any person without the written p ermission of the Copyright Holder. This

does not preclude the authorities’ use of the repor t for consultation purposes or the

applicant’s use of the report for project-related p urposes.

Documents

Namib Mine Ground- and Surface Water Specialist Input for ... · SLR Ref. 733.14009.00004 Report No.2013-GS-6 Namib Mine : Ground and Surface Water Specialist Input to EIA Report