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7_Annexure E Stormwater Management Plan.pdf - Assmang Manganese

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					       Assmang Manganese Limited – Cato Ridge

Stormwater Management plan for the Assmang Manganese
             Smelter Complex, Cato Ridge


                  Reference : 08-914R04

                   Dated: August 2009
                  Assmang Manganese Limited – Cato Ridge

    Stormwater Management plan for the Assmang Manganese
                 Smelter Complex, Cato Ridge




                                      Reference : 08-914R04

                                        Dated : August 2009




MOORE SPENCE JONES (PTY) LTD
Consulting Geotechnical, Environmental & Civil Engineers
2nd Floor, Pharos House, 70 Buckingham Terrace, Westville, 3630
PO Box 1263, Wandsbeck, 3631
Tel : +27 (0)31 267 7202
Fax : +27 (0)31 266 5322
             Assmang Manganese Limited – Cato Ridge
       Stormwater Management plan for the Assmang Manganese
                    Smelter Complex, Cato Ridge
Reference : 08-914R04                                                              Dated : August 2009

TABLE OF CONTENTS


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

1.1      Scope of the report ........................................................................................................................................ 1 

1.2      Terms of reference ........................................................................................................................................ 1 

1.3      Legislative requirements ............................................................................................................................... 1 

2.       SITE DESCRIPTION ..................................................................................................................................... 2 

2.1      Location ......................................................................................................................................................... 2 

2.2      Land use ........................................................................................................................................................ 2 

2.3      Topography ................................................................................................................................................... 2 

2.4      Drainage ........................................................................................................................................................ 2 

2.5      Stormwater infrastructure .............................................................................................................................. 3 

2.6      Climate .......................................................................................................................................................... 3 

2.7      Subsoil Conditions......................................................................................................................................... 4 

3.       SURFACE WATER QUALITY ....................................................................................................................... 4 

3.1      Ongoing monitoring programme ................................................................................................................... 4 

3.2      Monitoring at SW6 and SW7 ......................................................................................................................... 4 

3.3      Runoff quality at the small retention dam ...................................................................................................... 5 

4.       STORMWATER MANAGEMENT STRATEGIC OBJECTIVES .................................................................... 5 

4.1      Retention of all polluted water ....................................................................................................................... 6 

4.2      Isolation of the clean and dirty areas ............................................................................................................ 6 

4.3      Reduction of the extent of dirty areas ........................................................................................................... 6 

4.4      Curtail the release of contaminants into the dirty stormwater system. ......................................................... 6 

4.5      Treatment and utilisation of stormwater ........................................................................................................ 6 

5.       HYDROLOGICAL ASSESSMENT ................................................................................................................ 7 

5.1      Rainfall data .................................................................................................................................................. 7 

5.2      Catchment delineation .................................................................................................................................. 8 


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5.3      Runoff coefficients ......................................................................................................................................... 9 

5.4      Runoff calculations ........................................................................................................................................ 9 

6.       PROPOSED STORMWATER INTERVENTIONS ...................................................................................... 10 

6.1      Retention requirement ................................................................................................................................. 10 

6.2      Proposed interventions for Catchment A: New Slag Facility and MRP ...................................................... 11 

6.3      Proposed interventions for Catchment B: Plant area and Coarse Slag Dumps ......................................... 11 

6.4      Proposed interventions for Catchment C: Slimes dams and utilities area .................................................. 12 

6.5      Proposed Storage Dam for Catchment D: Catomix area ............................................................................ 12 

6.6      Further Interventions ................................................................................................................................... 13 

6.7      Dam design guidelines ................................................................................................................................ 13 

7.       STORMWATER MANAGEMENT – OPERATIONAL PLAN ....................................................................... 13 

7.1      Operational Strategy ................................................................................................................................... 13 

7.2      Metering and quality monitoring. ................................................................................................................. 14 

8.       TREATMENT OF RETAINED STORMWATER .......................................................................................... 14 

8.1      Volume of water to be treated. .................................................................................................................... 14 

8.2      Proposed treatment works .......................................................................................................................... 15 

9.       RECOMMENDATION ................................................................................................................................. 15 



FIGURES
Figure 1: Locality Plan
Figure 2: Topographical survey
Figure 3: Stormwater Management Flow Chart


DRAWINGS
08-914-007: Proposed Stormwater Management Plan




                                              Stormwater Management Plan for the Assmang Manganese, Cato Ridge                                       Contents
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            Assmang Manganese Limited – Cato Ridge
      Stormwater Management plan for the Assmang Manganese
                   Smelter Complex, Cato Ridge

Reference : 08-914 R04                                       Dated : August 2009



1.      INTRODUCTION


1.1     Scope of the report

        This report describes the Stormwater Management Plan (SWMP) that has been developed for the
        Assmang Manganese Smelter Complex located at Cato Ridge. The SWMP has been developed to
        provide an overview of the existing stormwater drainage, and to propose interventions to rationalise the
        drainage to comply with applicable legislative and operational requirements.


1.2     Terms of reference

        Moore Spence Jones has been appointed by Kwezi V3 Engineers on behalf of Assmang Manganese to
        develop a Stormwater Management Plan (SWMP) for the Assmang Cato Ridge Manganese Refinery.


1.3     Legislative requirements

        The need for a SWMP emanates from a legal obligation to comply with the National Water Act (Act No. 36
        of 1998) and specifically with the Regulations on use of water for mining and related activities aimed at the
        protection of water resources as promulgated in Government Gazette Notice No.704 of 4 June 1999.

        The listed activities under these regulations extend to the mineral extraction operations, the materials
        handling operations and the handling of residual materials. The requirement for stormwater management
        measures is set out in clause 6 which states that:

        Every person in control of a mine or activity must-
        (a)   confine any unpolluted water to a clean water system, away from any dirty area;
        (b)   design, construct, maintain and operate any clean water system at the mine or activity so that it
              is not likely to spill into any dirty water system more than once in 50 years;
        (c)   collect the water arising within any dirty area, including water seeping from mining operations,
              outcrops or any other activity, into a dirty water system;
        (d)   design, construct, maintain and operate any dirty water system at the mine or activity so that it is
              not likely to spill into any clean water system more than once in 50 years;
        (e)   design, construct, maintain and operate any dam or tailings dam that forms part of a dirty water
              system to have a minimum freeboard of 0.8 metres above full supply level, unless otherwise
              specified in terms of Chapter 12 of the Act;
        (f)   design, construct and maintain all water systems in such a manner as to guarantee the
              serviceability of such conveyances for flows up to and including those arising as a result of the
              maximum flood with an average period of recurrence of once in 50 years.



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2.    SITE DESCRIPTION

2.1   Location

      The Assmang Manganese Smelter Complex is located on the Assmang property that extends to the R103
      road to the south, the D1022 road to the north, Eddie Hagen Drive (P423) to the east, and the Cato Ridge
      escarpment to the west as shown in Figure 1.

2.2   Land use

      The aerial photograph attached as Figure 2 highlights the extent of development. The fenced-in Smelter
      Complex site is approximately rectangular in shape, about 2000 meters long and 450 to 650 meters wide
      with a total area approximately 82 hectares. A new lined slag disposal facility is planned on an area of 15
      hectares just to the north of the site, to replace the existing slag heaps.

      The central portion of the site is occupied by the blast furnace structure, with offices, workshops and other
      service buildings positioned around the periphery. Slag waste from the furnaces has been stockpiled over
      the northern portion of the site. The southern portion of the site is occupied by two active lined slimes
      dams and decommissioned slimes dams, together with stockpiles of baghouse dust and slimes.

      Approximately 4 ha has roof cover, and another 6 ha is formally surfaced. More than 55 ha is utilised for
      associated activities such as slag heaps, raw material stockpiles, slimes dams, loading areas, rail yards,
      informal roads and parking. In some areas remnants of dumping or stockpiling is visible. Only 14ha within
      the site has vegetation and less than 10ha may be regarded as undisturbed or marginally disturbed.

      In the past, slag waste was also dumped on the western side of the Complex. An area of 20ha outside
      the western fence has scattered remnants of these dumps.

2.3   Topography

      The Smelter Complex is situated on an elevated plateau near the edge of an escarpment.                           The
      topography to the west of the plateau is dominated by the deeply incised valley of the Umgeni River and
      its tributaries. The margin of the plateau is distinguished by very steep slopes to near vertical cliffs, below
      which are steep, eroded spurs.

      The plateau area is characterised by rolling grassland and lies at an average elevation of approximately
      800 metres above Mean Sea Level. The network of rivers and streams that form the Umgeni River
      catchment lie approximately 400 metres below the plateau on which the Smelter Complex is situated.

2.4   Drainage

      Surface drainage on that part of the plateau occupied by the Smelter Complex is towards the west. Prior
      to development the site would have had a gentle westward slope of 1 in 140 to the edge of the
      escarpment. Runoff would naturally drain towards the plateau’s edge, eventually forming small streams
      which debouch over the escarpment into a network of stream tributaries of the Mshwati River which joins
      the Umsinduzi River. The Umsinduzi River joins the Umgeni River downstream of Nagle Dam.



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          Stormwater discharges into the valley below at five locations (see Drawing No. 08-914-007) namely:

      •     The Far Northern stream,
      •     The Northern stream;
      •     The Central stream;
      •     The Southern stream and
      •     The Doornrug stream.

          A concrete lined cut-off drain has been constructed on the eastern side of the Smelter Complex to divert
          the upslope runoff around the site to the Northern stream and to the Doornrug Stream. This drain will be
          extended northwards when the new lined slag disposal facility is developed, and will then discharge into
          the Far Northern stream. The drain is designed for a 100 year flood, but the culvert crossing at the
          entrance to the Catomix plant restricts the discharge to below the 50-year flow-rate.

2.5       Stormwater infrastructure

          A network of stormwater pipes and channels has been installed on the site. This drainage system is not
          well documented. Layout plans are schematic and incomplete, with little information of exact pipe location,
          pipe sizes, pipe material and gradients. Almost all of the open drains are simply informal unlined furrows.

          Stormwater pipes have been installed in the plant area, east and west of the furnace buildings. A risk
          assessment that was done indicates that these pipes will not accommodate a 20-year storm event.

          Most of the stormwater from the plant area and the southern side of the slag dumps discharges at
          irregular intervals into the 700m long main collector drain west of the rail yard. This open drain, which will
          be referred to as the western drain, varies in shape, width, depth and gradient and can at best, be
          described as a long flat shallow overgrown trench. The stormwater drains terminating in the western drain
          are indicated on Drawing No.08-914-007.

          The western drain has outlets at SW6 and SW7, where metering flumes with flow recorders and electrical
          conductivity (EC) recorders were installed in 2005.

      Drainage has been provided around the slimes dams, to capture leachate and surface runoff, that is then
      pumped to the water treatment plant. Stormwater from the area adjacent to the slimes dams is channelled
      toward the approximately 3000m3 retention dam east of the treatment works. When the capacity of the
      dam is exceeded, runoff will spill to the southern stream.

2.6       Climate

          Cato Ridge lies in an area of summer rainfall. An average rainfall of approximately 780 mm per year has
          been recorded over a 10 year period at Cato Ridge by the Agricultural Research Council. The wettest
          months are November to March. Maximum rainfall occurs in January when the average monthly rainfall is
          about 127 mm, while June and July are the driest months, with average monthly rainfalls below 10mm.

          Daily rainfall readings are taken by Assmang. An automatic rainfall recorder was installed in 2004 that
          records rainfall at 5 minute intervals.



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2.7       Subsoil Conditions

          The site is underlain by a thin cover of fill material and natural soils overlying sandstone bedrock of the
          Natal Group. The fill that underlies the site attains a maximum thickness of approximately 1.4 metres and
          comprises predominantly very dark grey, silty clayey sand, and/or gravel size slag, and often contains
          abundant larger pebble and boulder size fragments of slag.

          Generally the fill material is underlain by a thin layer of greyish brown, slightly clayey, fine to medium
          colluvial sand, which in turn is overlain by a layer of orange brown and reddish brown, firm to stiff, slightly
          silty residual clay of varying thickness. The clay is absent in the north-western portion of the site.

          The weathered sandstone bedrock sandstone underlying the site at a depth of 1,10 to 3,80 metres, is
          generally well cemented and hard rock in strength. The porosity of the intact material is likely to be low.
          The permeability of the sandstone is consequent upon the fractures and fissures in the rock, and is low.

          Perched groundwater conditions have been encountered at a depth of 0,4 to 1,8 metres below existing
          ground level, in some locations.


3.        SURFACE WATER QUALITY

3.1       Ongoing monitoring programme

          A water quality monitoring programme has been implemented at the site and surrounding streams.
          Continuous and routine sampling is done at the following sampling points:

      •      Steams down gradient of the site at sampling points SW1 to SW5, SW 8 and SW9

      •      Run-off from the Smelter Complex at two flumes SW6 and SW7

      •      In the cut-off drain up gradient of the slimes Dams and the remainder of the site at sampling points
             SW10 and SW11

      •      At the Active Slimes Dams at sampling points SW12 and SW13

      •      At the leak detection system of the two Active Slimes Dams at sampling points AS1 and AS2

          Comprehensive water quality assessments are done to determine the concentrations of the determinants
          of concern. The results are reported bi-annually, highlighting trends, anomalies and water quality in terms
          of the Department of Water Affairs and Forestry guidelines for drinking water.

          In this report only the key findings of the monitoring programme are highlighted.

3.2       Monitoring at SW6 and SW7

          Metering equipment records the precipitation, stormwater flow-rate and the electrical-conductivity at SW6
          and SW7 locations at 5 minute intervals. Data is downloaded monthly and analysed to ascertain the
          trends, and to report on correlation between precipitation, flow-rates and the contamination levels.




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      During the course of the monitoring programme there have been extended periods of incomplete data
      primarily due to equipment failure after lightning strikes and power interruptions.

      Runoff from the coarse slag dumps, the slag cooling ponds, the crusher and a small part of the plant
      drains towards SW6 section of the western drain, while the balance of the smelter complex drains towards
      the SW7 section of the same drain. During severe floods there may be a flow from the SW7 section
      toward SW6, which will affect readings. The western drain is not lined and may restrict flow. This
      attenuation effect will also affect readings.

      The monitoring results reveal the following:

      • A good correlation between rainfall and stormwater flow with a 30 to 40 minute time lag between onset
         of significant rain and the stormwater peak.

      • Operational releases (significant flow recorded in periods of little or no precipitation) were identified
         and reported throughout the monitoring programme, usually once or twice a month. Flow-rate and
         duration of these releases varied with some releases exceeding 150m3.

      • Dry weather base flows between the rainfall events generally fell below the measurable limit of 1m3 per
         hour, indicating insignificant seepage water contributions.

      • EC generally showed an increase during the operational releases, indicating the presence of one or
         more of the EC inducing elements in the released water. On a few occasions the EC showed a slight
         decrease indicating a release of cleaner water.

      • EC generally increased with initial rise in stormwater flow, and then dropped as flow continued at
         elevated levels. This indicates a degree of first flush pick-up, and dilution thereafter.

      • For a 10-year storm event, EC fell to 25% of the pre-storm levels.

      The quality of the surface water passing through the flumes during the monitoring period was generally
      unacceptable (Class IV) in terms of the DWAF drinking water classifications.

3.3   Runoff quality at the small retention dam

      Water analysed from the active slimes dam area, that drains into the small retention dam, had elevated
      electrical conductivity, total dissolved solids, sodium, potassium, manganese, ammonia, chloride, sulphate
      and fluoride. The unlined retention dam has limited capacity, and there is evidence that the dam overtops.


4.    STORMWATER MANAGEMENT STRATEGIC OBJECTIVES
      The primary objective of the Stormwater Management Plan is to achieve full compliance with all the
      provisions of the National Water Act (Act No. 36 of 1998) and the Regulations on use of water for mining
      and related activities aimed at the protection of water resources as promulgated in Government Gazette
      Notice No.704 of 4 June 1999

      The principle requirements can be met through the following strategies:




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4.1   Retention of all polluted water

      Retention capacity should be provided to retain all contaminated or potentially contaminated stormwater.
      The retention dams must effectively retain a 1 in 50-year flood event (i.e. a storm of duration equal to the
      time of concentration of the catchment), but should also provide a buffer between the inflow during wet
      periods and the capacity of the stormwater treatment and disposal system.

4.2   Isolation of the clean and dirty areas

      Clean runoff must not traverse areas with a contamination potential, or discharge into dirty water retention
      dams. Clean runoff should be diverted around the dirty areas wherever possible.

      It may be possible to install a separate stormwater system for small pockets of clean areas that are found
      within dirty areas. Such areas should not be regarded as clean areas unless the risk posed by
      surrounding contamination can be discounted. Dirty stormwater drainage systems could be rerouted to
      avoid clean areas. Cut-off berms and trenches could be installed along clean/dirty interfaces.

4.3   Reduction of the extent of dirty areas

      Operations should be concentrated on the smallest area practical. Areas that are no longer utilised should
      be remediated. Residual waste and slag dumps should be removed from these areas. The impacted soil
      should be removed, replaced, and where necessary the vegetation should then be re-established.

4.4   Curtail the release of contaminants into the dirty stormwater system.

      Wherever possible operational releases or incidental spillages of contaminated water (e.g. draining of
      cooling systems, pipe bursts or opening of pressure relief valves) should be intercepted as close to the
      source as possible. High risk areas should have bunds and/or emergency sumps, and intercepted water
      should be pumped to the treatment facilities.

      Interceptors should also be provided before retention dams to intercept dry-weather flow, seepage water
      from subsoil drains and low intensity runoff, to improve the water quality in retention dams.

4.5   Treatment and utilisation of stormwater

      All contaminated stormwater that has been retained or intercepted should be treated and disposed of as
      soon as possible. Retention dams should be emptied as rapidly as possible to provide reserve capacity
      for the next storm event.

      Treated stormwater and less impacted stored water can be used to reduce the consumption of potable
      water, and can possibly be used for dust suppression on roads and slag heaps.

      In principle treated some stormwater could be reintroduced into the streams to maintain seasonal flow. It
      is however more important to reduce the risk of pollution, and release of treated stormwater should only
      be considered as a last option.




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5.    HYDROLOGICAL ASSESSMENT

5.1   Rainfall data
      A comprehensive database of storm rainfall estimates has been made available by Ethekwini Municipality,
      wherein the aggregate rainfall for the full range of return periods, and for durations between 5 minutes and
      7 days is tabled for the municipal area at 1’ latitude and 1’ longitude intervals. The data is summarised in a
      very convenient table, giving both the storm rainfall and the extreme wet weather period rainfall. The
      rainfall-duration estimates for the Assmang site is given in Table 1.



                                                        DURATION
      Return period     5 min      10 min      15 min     30 min      45 min      60 min      90 min
         2 years         11.6       15.4        18.2        23.0       26.5        29.2         33.5
         5 years         16.9       22.4        26.5        33.5       38.5        42.5         48.8
        10 years         21.3       28.3        33.4        42.3       48.6        53.7         61.6
        20 years         26.4       35.1        41.4        52.5       60.3        66.5         76.4
        50 years         34.5       45.9        54.1        68.6       78.8        87.0         99.9


                                                        DURATION
      Return period     2 hrs       4 hrs       6 hrs      8 hrs      10 hrs      12 hrs       24 hrs
         2 years         37.0       43.2        47.3        50.4       53.0        55.2         64.4
         5 years         53.9       62.9        68.8        73.4       77.1        80.3         93.8
        10 years         68.0       79.4        86.9        92.6       97.4       101.4        118.4
        20 years         84.3       98.4       107.7       114.8       120.7      125.7        146.7
        50 years        110.2       128.6      140.8       150.2       157.8      164.4        191.8



                                                        DURATION
      Return period     1 day      2 days      3 days      4 days     5 days      6 days      7 days
         2 years         54.6       69.3        79.7        86.1       91.4        96.0        100.0
         5 years         79.5       101.0      116.1       125.4       133.1      139.8        145.6
        10 years        100.4       127.5      146.6       158.3       168.0      176.4        183.8
        20 years        124.4       158.0      181.7       196.2       208.2      218.6        227.8
        50 years        162.7       206.6      237.5       256.5       272.3      285.9        297.9


                   TABLE 1: RAINFALL DATA FOR ASSMANG CATO RIDGE
          (AGGREGATE RAINFALL IN mm FOR VARIOUS RETURN PERIODS AND RAINFALL
                                         DURATIONS)



      The table shows for example that 297.9mm rain can be expected in a 7 day period for a 50 year return
      period, and that 68.6mm could be expected for a storm with a duration of 30 minutes.

      The flow recorders at SW6 and SW7 consistently indicated time lags of 30 to 45 minutes between peak
      rainfall and the peak flow. Storm durations of 30 minutes will therefore be used to determine the peak flow
      rate for each catchment.



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5.2   Catchment delineation

      The topography of the site and the various open drains and stormwater pipes has been taken into
      consideration to identify 4 logical sub-catchments. The catchment boundaries and the main drainage
      routes have been identified and indicated on Drawing No. 08-914-007. The characteristics of the 4
      catchments are described below:

      a. New Slag Facility and Metal Recovery Plant (23.8ha)

           This area comprises the metal recovery plant, the BTG operations, reworked stockpiles of aggregate,
           the north sloping coarse slag dumps, and the new slag facility. It is assumed that the new slag facility
           will be developed in phases, limiting the impacted area at any time to 50% of the site. An effective area
           of 15.80 hectare is therefore assumed for this catchment. The catchment area drains in a westerly
           direction to the northern stream.

      b.    Eastern boundary zone (7.6ha)

           This area between the eastern fence and the slag dump haul road is in its natural undisturbed state
           except for the aggregate haul road, the Catomix batch plant and a stockpile of aggregate. A shallow
           canal and pipe culvert currently drains this area into the eastern diversion canal. The area will be
           reinstated to a “clean” catchment. The impact of the Catomix concrete plant will be addressed.

      c. Coarse slag dump and plant area (35.6 ha)

           This area includes the southern portion of the coarse slag dumps (that are to be worked away where
           economically justified or that will be decommissioned and capped) and the plant area. The plant area
           is extensively utilised for the furnaces, recovery plant, crushers, loading areas, raw material stockpiles,
           slag cooling ponds, roads, rail yards, offices, car parks, and for other associated activities. The area
           drains westward to a number of stormwater pipe systems that all drain into the western stormwater
           drain between SW6 and SW7.

      d. Utilities area and slimes dam area (20.7ha)

           This area is extensively utilised for the offices, car parks, workshops, stores, electricity sub-stations,
           loading areas, raw materials stockpiles, finished product stores, the 2 active slimes dams, the 2 old
           unlined slimes dams, the old capped slimes fill and the briquette plant. The area currently drains
           westwards to the small retention dam, and toward the Doornrug stream.

           Open drains and canals capture the leachate, supernatant water and run-off from the newer slimes
           dams. This water is collected in a lined dam from where it is pumped to the treatment works. Slimes
           from the active slimes dam and baghouse dust are also stockpiled in dumps north and west of the
           slimes dams. The effluent treatment plant and the retention dam are also in this catchment.

           An undisturbed area of approximately 2.9ha along the eastern fence can be allowed to drain to the
           eastern cut-off drain.




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5.3   Runoff coefficients

      Empirical methods have been applied to determine run-off coefficients for calculating peak stormwater
      flows using the slope of the catchment, the permeability of the soil and the ground cover as parameters.

      The runoff coefficients for the coarse slag dumps have been reduced by 50% for low intensity rainfall,
      below 3mm per hour, as the materials have high absorption properties.

      Runoff coefficients have been calculated for the various sub-catchments of the site. These coefficients are
      listed in Table 2 below.

        Catchment                 Description               Area         Runoff coefficient             Long duration
                                                            (ha)                                       Runoff coefficient

            A         New slag disposal facility & MRP      15.80                0.45                        0.35

            B         Coarse Slag dump & Plant Area         35.6                 0.56                        0.50

            C         Utilities and Slimes dam              20.7                 0.51                        0.50

           Total                                            72.1



                           TABLE 2      RUNOFF COEFFICIENTS FOR EACH SUB-CATCHMENT



5.4   Runoff calculations

      The estimated runoff has for the 50 year return period are summarised in Table 3 and Table 4 below.

      In Table 3 the peak flow rate for a 50 year recurrence for a 30 minute duration is calculated. These flows
      can be used to determine the required capacity of the stormwater systems for each catchment, and more
      importantly the capacity of the outfalls to each retention dam.



       Catchment                 Description              Area           Runoff               Intensity         Flood peak
         Area                                             (ha)          coefficient          (mm/hour)             (m3/s)

                                                            A               C                      i            =c.i.A/3600

            A        New slag disposal facility & MRP     15.80           0.45                                      2.71

                                                                                               137.20
            B        Coarse Slag dump & Plant Area        35.60           0.56                                      7.60


            C        Utilities and Slimes dam             20.70           0.51                                      4.02




                         TABLE 3       PEAK RUNOFF FOR 50 YEAR 30 MINUTE STORM




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           In Table 4 the total runoff for a wet period of seven days for a 50 year recurrence is calculated.
           These volumes can be used to determine the required capacity of the stormwater retention facilities
           for each catchment.


             Catchment           Description       Area (ha)        Runoff           Aggregate           7 day runoff
               Area                                               coefficient       rainfall (mm)           (m3)

                                                       A              C                    r                =C.r.A


                 A        New slag disposal          15.80           0.45                                   16,474
                          facility & MRP


                 B        Coarse Slag dump &         35.60           0.56                                   53,026
                                                                                        297.9
                          Plant Area


                 C        Utilities and Slimes       20.70           0.51                                   30,833
                          dam

              TOTAL                                  72.10                                                 100,333

                             TABLE 4     TOTAL RUNOFF FOR 50 YEAR 7-DAY STORM


6.    PROPOSED STORMWATER INTERVENTIONS

6.1   Retention requirement

      To prevent any runoff from “dirty” catchment areas leaving the site under any 50-year storm, all runoff
      must be retained in retention dams. The combined capacity of the dams should be sufficient to contain the
      projected inflow of short duration flash floods and for prolonged extreme wet weather, assuming a realistic
      rate at which the retained water can be treated and disposed of.

      The dams have been sized using a disposal rate of 2600m3/day, a rate that will empty the full dams within
      30 days following a 50-year storm event of duration of up to 7 days. Facilities must be provided to treat
      some of this water for consumptive usage (in place of the potable water supply) and to dispose of the
      balance responsibly.

      The retention dams have been modelled for any 50-year storm event of duration of up to 7 days:
      a. To have 800mm freeboard assuming drawdown of 2,600m3/day.
      b. Not to overtop if no drawdown takes place
      c.   Not to overtop assuming a 25% storage level before a storm and a drawdown of 2,600m3/day.

      To meet the above criteria, a total storage capacity is of 82,100m3 is required

      The potable water account indicates that up to 800m3/day could be utilised for operational consumption,
      with a peak demand of 1,200m3/day. (This must still be verified.) The mean annual runoff is estimated at
      257,000m3 p.a. or 701m3/day. In summer months the runoff will rise to 1,425m3/day, while in winter the
      yield will be less than 200m3/day.

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      A wastewater treatment facility of 1,200m3/day is proposed, with the treated water temporarily stored in a
      2,000m3 covered reservoir. Under normal circumstances the plant will only operate at 50% of full load, or
      12 hours per day.

      As the required drawdown rate for extreme circumstances, that has been set at 2,600m3/day, exceeds the
      demand for treated water, allowance should be made to dispose of 2,600m3/day through alternative
      applications. This will be explained in the following sections.

      The layout of the proposed infrastructure is shown on Drawing No. 08-914-007

6.2   Proposed interventions for Catchment A: New Slag Facility and MRP

      The Eastern cut-off drain will be extended northwards and the existing east-west leg of the drain will be
      used to collect runoff from the catchment. A lined retention dam will be provided at the end of the drain.

      The total storage requirement for this catchment is estimated at 13,440m3. This is based on a drawdown
      rate of 433m3/day. The steep topography at the lower end of the catchment, and the shallow bedrock, is a
      constraint to the size of dam that can be created. It is therefore proposed that a smaller dam is provided,
      with the balance of the storage at a storage dam (dam D) northwest of the Catomix Plant, to which
      stormwater can be pumped.

      A smaller dam at the lower end of the catchment will require a higher drawdown rate to meet the retention
      criteria. The retention dam has been modelled for any 50-year storm event of duration of up to 7 days for
      a drawdown rate of 1,200m3/day, indicating that storage of 11,400m3 is required.

      The proposed dam (dam A) will have a floor area of 3,780m2, a storage depth of 2.4m, and a freeboard of
      0.8m.    Flood routing calculations indicate that the dam will not overtop during a 50-year/7-day storm
      event, even if the drawdown is interrupted for 3 days (e.g. due to pump failure).

      Concrete-lined silt traps that will be provided at the two inlets to the dam will also have pump sumps. Two
      pumpsets will be installed to pump 15l/s through a 150mm diameter rising main to Dam D.


6.3   Proposed interventions for Catchment B: Plant area and Coarse Slag Dumps

      The total storage requirement for this catchment is estimated at 43,926m3. This is based on a drawdown
      rate of 1,300m3/day. Space is restricted at the lower end of the catchment, west of the rail line and
      western stormwater drain, by power lines and servitudes and also constrained by the topography and the
      shallow bedrock. It is therefore proposed that a smaller dam is provided, with the balance of the storage at
      a storage dam (dam D) northwest of the Catomix Plant, to which stormwater can be pumped.

      The retention dam has been modelled for any 50-year storm event of duration of up to 7 days for a
      drawdown rate of 3,600m3/day, indicating that storage of 32,450m3 is required.

      Part of the capacity will be provided by upgrading the 700m long open western drain serving the
      stormwater pipes and drains from the plant. This trapezoidal open drain will be upgraded and lined in
      2009 to a storage capacity of 10,200m3. The drain will be 550m long, with a base width of 5.5m, a storage
      depth of 2.2m, 0.8m freeboard and side slopes of 53°.


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      The open drain will have a geosynthetic liner and a trafficable concrete lining, and will incorporate a cut-off
      barrier extending to bedrock. This drain will act as the primary stormwater receptor, and as a silt trap. The
      canal will be divided into 6 sections to accommodate the topography and for operational purposes.

      A 22,250m3 overflow dam (dam B) will be constructed at the southern end of the canal. This dam will have
      a floor area of 11,600m2, a storage depth of 1.75, and a freeboard of 0.8m. Dam B will be designed so
      that stormwater will overflow into dam B when the canal reaches full storage level, and will return to the
      canal when the storage level in the canal drops below 25%.

      Flood routing calculations indicate that dam B will not overtop during a 50-year/7-day storm event, even if
      the drawdown is interrupted for 3 days (e.g. due to pump failure).

      Pumps will be installed in each of the 6 canal sections. Water will be pumped at a maximum rate of 42l/s
      through a 200/250mm diameter rising main to dam D. The rising main will also convey water from dams A
      and C to dam D, and will be utilised as the delivery pipe from dam D to the proposed treatment plant.


6.4   Proposed interventions for Catchment C: Slimes dams and utilities area

      The total storage requirement for this catchment is estimated at 24,800m3. This is based on a drawdown
      rate of 870m3/day. Space at the lower end of this catchment, west of the rail line is restricted by power
      lines and servitudes and also constrained by the topography and the shallow bedrock. It is therefore
      proposed that a smaller dam is provided, with the balance of the storage at a storage dam northwest of
      the Catomix Plant, to which stormwater can be pumped.

      The retention dam has been modelled for any 50-year storm event of duration of up to 7 days for a
      drawdown rate of 2,400m3/day, indicating that a dam of 17,450m3 is required.

      The proposed dam (dam C) will have a floor area of 5,040m2, a storage depth of 2.7m, and a freeboard of
      0.8m.   Flood routing calculations indicate that for a 50-year/7-day storm event the dam will not overtop
      even if the drawdown is interrupted for 3 days (e.g. due to pump failure).

      A concrete-lined silt trap that will be provided at the inlet to the dam will also have a pump sump. A
      pumpset will be installed to pump 28l/s through a 150mm diameter rising main to Dam D.

      The open drains on the southern and western side of the slimes dams must be reinstated to divert runoff
      to the retention pond C. This will prevent runoff from the slimes dams draining southwards to the eastern
      diversion drain, and to the Doornrug stream. An open drain must also be provided along the rail on the
      western side of the utilities area.


6.5   Proposed Storage Dam for Catchment D: Catomix area

      A 20,800m3 stormwater storage dam is proposed just northwest of the Catomix Plant, located between
      the haul roads, This dam will make up for the shortfall in retention at dams A, B and C, bringing the total
      storage to the required 82,100m3.




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      The proposed dam (dam D) will have a floor area of 5,600m2, a storage depth of 3.0m, and a freeboard of
      0.8m.    Water will be pumped from dams A, B, and C at a combined rate of 7,200m3/day (83l/s), in
      accordance with the operational parameters. As and when required, water will be released to the
      treatment plant for re-use.


6.6   Further Interventions

      The following interventions are recommended:

      a. The area west of the site, above the escarpment, should be cleaned and re-vegetated when the
           retention dams are constructed.

      b. The area between the eastern fence and the slag dumps, shown as Catchment D, should be cleaned
           so that storm runoff from this area can be diverted to the eastern cut-off drain.

      c.   A restriction should be placed on the use of “clean” areas within operational areas, especially the area
           south-east of the training centre and workshops and the area south of the briquette plant.

      d. A concerted effort should be made to limit operations to the smallest footprint necessary, to clean up
           the open area, to clean drains, to keep the haul roads clean, and to formalise stockpiles.

      e. Operational releases should be intercepted and pumped to the process treatment works, and be
           prevented from being discharged into stormwater.

      f.   Leachate collection drains should be provided for all the slimes dams and stockpiles.


6.7   Dam design guidelines

      The three catchment retention dams (A, B and C) will normally be empty, as all retained water will
      normally be pumped to storage dam D at the prescribed drawdown rates. A single 2mm geosynthetic
      lining will be installed to prevent contamination from these three dams.

      Dam D will store stormwater for extended periods. It is therefore recommended that a single
      geosynthetic liner be installed with a leakage detection system to ensure that the competency of the
      primary liner can be monitored.

      Silt traps will be installed in dams A and C that will also have sumps for the drawdown pumps. The silt
      traps will be lined with a trafficable surface to allow access for cleaning.

      A high level emergency spillway will be installed in all dams to safely discharge water in the unlikely
      event that the level in a dam exceeds 75% of the freeboard depth.


7.    STORMWATER MANAGEMENT – OPERATIONAL PLAN

7.1   Operational Strategy

      The stormwater management flow chart is shown on Figure 3.




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      The guiding principle is to pump all water to the central storage dam (dam D) thereby keeping the 3
      catchment retention dams (dams A, B, and C) as low as possible.

      Pumping from the catchment dams will be interrupted when dam D reaches 100% capacity. Pumping will
      resume if any of the three catchment dams reaches 100% capacity, irrespective of the level at dam D, but
      will be stopped when Dam D reaches 130% of the design storage capacity or 75% of the freeboard depth.

      Drawdown of dam D should ideally be balanced with the need for operational water, especially when the
      dam levels are low or there are favourable weather conditions. The need for operational water is expected
      to average 800m3/day and should vary between 200m3 per day to 1200m3/day.

      The drawdown rate should only be increased above the need for water if the volume of retained water
      exceeds 25% of the total storage, or flood warnings have been issued. The operational drawdown rate
      can be lowered to that which would dispose of all retained water within 30 days, i.e. 3.2% of the total
      retained water. When the total storage exceeds 100% of capacity, the operational drawdown rate will be
      2,600m3 per day.

      This operational strategy has been tested for a 50-year/7day extreme wet weather occurrence. The
      analysis shows that if the dams were 25% full (20,500m3) at commencement of a storm event, the total
      inflow of 100,300m3 would raise the dams to 30% above the full supply capacity, and therefore only use
      30% of the available freeboard capacity.


7.2   Metering and quality monitoring.

      A water quality programme should be implemented to monitor the quality of water as follows:

      a. water in the four retention dams (weekly)
      b. water received at the treatment works (daily) and
      c.   water delivered by the treatment works (daily)

      Flow metering is recommended on all pipelines, with level recorders on all dams. This data could be
      correlated with rainfall data to validate the design parameters for the SWMP.


8.    TREATMENT OF RETAINED STORMWATER

8.1   Volume of water to be treated

      The potable water balance indicates that up to 800m3/day of treated water could be utilised for operational
      consumption, with a peak demand of 1,200m3/day.

      The mean annual runoff for the 72.1ha catchment, using the runoff coefficients listed in Table 2, is
      estimated at 257,000m3 p.a. or 701m3/day. In summer months the runoff will rise to 1,425m3/day, while in
      winter the yield will be less than 200m3/day.




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         A wastewater treatment facility of 1,200m3/day is proposed, with treated water temporarily stored in a
         2,000m3 covered reservoir. Under normal circumstances the plant will only operate at less than 50% of full
         load, or 12 hours per day.

         Treated water should as far as possible be utilised in the plant to reduce the use of potable water.
         Treated water (or retained water of an acceptable quality) could also be used for dust control on haul
         roads and slag stockpiles, and for irrigation of vegetated areas.

8.2      Proposed treatment works
         The waste treatment works should have the ability to treat water to standard that will be acceptable for re-
         use in the plant (or that will be acceptable at the process water treatment plant). The treatment works
         should also be capable of treating water to a standard that will allow water to be returned to the streams in
         extreme circumstances.

         The proposed 1.2 Ml/day stormwater treatment works should preferably be located between retention
         dam B and retention dam C. The rising main from the catchment retention dams to dam D will also act as
         gravity pipeline to supply retained stormwater to the treatment works.


9.       RECOMMENDATION
         The Stormwater Management Plan (SWMP), as set out in this report, should be implemented as soon as
         possible to eliminate the discharge of contaminated water into the streams.




MOORE SPENCE JONES (PTY) LTD
Consulting Geotechnical, Environmental & Civil Engineers
2nd Floor, Pharos House, 70 Buckingham Terrace, Westville, 3630
PO Box 1263, Wandsbeck, 3631
Tel : +27 (0)31 267 7202
Fax : +27 (0)31 266 5322




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