wastewater storage and recycle system

7/30/2019 Wastewater Storage and Recycle System

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PROPOSED WASTEWATER STORAGE

AND

RECYCLE SYSTEM

AT

RICHARDS BAY COAL TERMINAL Co (Ltd)

Prepared by

SKP Engineers cc

PO Box 326, Westville, 3630

Tel: 031-2668101 Fax: 031-2669001

April 2004


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PROPOSED WASTEWATER & RECYCLE SYSTEM AT RBCT SKP Engineers cc

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INDEX

EXECUTIVE SUMMARY ....................................................... ........................................................... ....................... 3

1. BACKGROUND ..................................................... ........................................................... ................................. 5

2. OBJECTIVE ........................................................... ........................................................... ................................. 5

3. REGULATIONS .................................................... ........................................................... ................................. 6

3.1 PREVIOUSWATERACT .............................................................................................................................. 6

3.2 NATIONALWATERACT ..................................................... ........................................................... ............. 6

3.2.1 Definitions ................................................... ........................................................... ................................. 6

3.2.2 Quality / quantity of wastewater discharge ................................................... .......................................... 7

3.2.3 Capacity requirements of dirty water systems ........................................................ ................................. 7

3.2.4 Storage of water containing waste for re-use ......................................................... ................................. 7

3.3 MARINEWATERQUALITYGUIDELINES ...................................................... .......................................... 7

3.4 STATUTORYREQUIREMENTS .................................................... ........................................................... ... 7

4. PRESENT SITUATION .................................................. ........................................................... ....................... 8

4.1 SOURCEOFWASTEWATER ......................................................... ........................................................... ... 8

4.2 EXISTINGSURFACEWATERMANAGEMENTSYSTEM ........................................................... ............. 8

4.3 QUALITYOFWASTEWATER ....................................................... ........................................................... ... 9

4.3.1 Total Suspended Solids.............................................................. ........................................................... ... 9

4.3.2 Oils, Soaps & Grease ...................................................... ........................................................... ........... 10

4.3.3 Faecal coli forms ................................................... ........................................................... ..................... 10

4.3.4 Chemical Oxygen Demand ........................................................ ........................................................... . 11

4.3.5 Colour ......................................................... ........................................................... ............................... 11

5. SPECIALIST STUDIES .................................................. ........................................................... ..................... 11

5.1 CONCLUSIONS................................................................................ ........................................................... . 12

5.2 RECOMMENDATIONS ......................................................... ........................................................... ........... 12

6. PROPOSED WASTEWATER STORAGE & RECYCLE SYSTEM ........................................................ . 13

6.1 TARGETDILUTIONS .................................................. ........................................................... ..................... 13

6.2 DESIGNDEPTHOFPRECIPITATION ..................................................... .................................................. 13

6.3 DETERMINATIONOFSTORAGEVOLUME ................................................... ......................................... 14

6.4 PROPOSEDSTORAGEANDRECYCLESYSTEM ................................................................................... 16

6.4.1 Settling Ponds........................................................ ........................................................... ..................... 16

6.4.2 Storage/Retention Ponds ........................................................... ........................................................... . 16

6.4.3 Discharge Canal ................................................... ........................................................... ..................... 17

6.4.4 Recycle Water.............................................. ........................................................... ............................... 17

6.5 MODIFICATIONOFEXISTINGSTORMWATEROUTLETS .................................................................. 176.6 MONITORINGPROGRAMME ................................................................................................................... 17

6.6.1 Monitoring at Settling Ponds .................................................... ........................................................... . 17

6.6.2 Monitoring at Storage/Retention Pond Outlet Works ...................................................... ..................... 17

6.6.3 Monitoring of Marine Water ..................................................... ........................................................... . 17

6.7 RISKASSESSMENT .................................................... ........................................................... ..................... 18

6.7.1 Settling Ponds........................................................ ........................................................... ..................... 18

6.7.2 Storage/Retention Ponds ........................................................... ........................................................... . 18

7. MITIGATION MEASURES AND ARGUMENTS SUPPORTING PROPOSED SCHEME ................... 18

8. CONCLUSION ....................................................... ........................................................... ............................... 19


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EXECUTIVE SUMMARY

The Richards Bay Coal Terminal (RBCT) is involved in receiving, storing and exporting unsizedwashed coal from Richards Bay Harbour. The Terminal occupies an area of approximately200ha of which 110ha is allocated to storage of coal in open stockpiles.

The main source of the wastewater is stormwater runoff from the coal stockyards and roadways.Although the stockpiles are sprayed twice a day, very little runoff reaches the settling ponds.This is because the amount of water sprayed onto the coal stockpiles is just sufficient to wet thesurface of the stockpiles to reduce the generation of airborne dust.

Presently surface water runoff is collected in settling ponds designed to contain the first flushvolume arising from 20 minutes of runoff from a 1 in 20 year storm event. The capacity of theseponds is insufficient to contain any reasonable rainfall, resulting in frequent overflow into theharbour.

Over the past 7 years various improvements have been made to the surface water management

system. More recently new settling ponds have been constructed under the wharf conveyors toeliminate the exceptionally high concentrations of suspended solids being discharged from thissource.

Various specialist studies were commissioned for the Phase 5 Expansion EIA. During the EIAprocess a Baseline Study was carried out at the request of the DWAF to determine the impactof the current operation on selected aspects of the aquatic ecology in the harbour adjacent toRBCT. Although it is concluded that the stormwater discharge from RBCT has had nomeasurable impact on the harbour, the specialists recommend that the current surface watermanagement system be improved to reduce the quantity of wastewater discharge and quantityof waste present in the water.

Dr. A Connell of the CSIR also recommends that the suspended solids in the stormwater runoffbe limited to 50mg/l and that the stormwater be discharged below the surface water level toachieve better dilution.

A review of the statutory requirements was carried out to establish regulations dealing with thedisposal of wastewater into a marine environment and the storage of wastewater for re-use. Itbecame apparent that no clear statutory requirements exist for the disposal of water containingwaste into a harbour, since in terms of the regulations a harbour is not a water resource. Designparameters and limits will therefore need to be approved by DWAF taking into considerationtechnical, economical, social and environmental aspects of the proposed storage / disposalsystem.

Samples of water taken from the existing settling ponds are tested regularly and compared withthe General Limit Values. Typically the concentration of suspended solids exceeds the GLV byan order of magnitude on rain days. However if the water is allowed to stand the concentrationof suspended solids has been found to decrease to less than 25mg/l in a 48 hour period.

The proposal is to collect all surface water runoff generated during dry weather conditions andfor rain events not exceeding the design storm, and to pump this water into storage/retentionponds where the water will be allowed to stand. After the suspended solids have settled out toacceptable levels the clear water will be pumped back to the storage reservoirs on site andrecycled.

Since the current impact on the harbour is minimal, it is not justified in terms of economic orenvironmental considerations to design for large storm events. Recognising this, the regional


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office of DWAF agreed in principle to accept 5% non-compliance i.e. not more that 18discharges a year.

Using an upper limit of 5% non-compliance, it was established that the proposed stormwatersystem should be designed for 60mm daily rainfall and that 80Ml of storage would be requiredto ensure that neither the settling ponds nor storage/retention ponds overflowed more than 18times a year. This was done using the historical record for Richards Bay which goes back to1923.

When the design storm is exceeded, the installed pumps will have insufficient capacity to pumpthe flow into the settling ponds to the storage/retention ponds, and water will overflow into theemergency bypass system. In mitigation this will happen infrequently and at times when theconcentrations in the seawater will be elevated.

The existing stormwater outlets from the terminal settling ponds will be maintained asemergency bypasses. However, it is proposed that a length of pipe be connected to each ofthese outlets on the coal quay so that the excess stormwater is discharged below the surface.

The proposed scheme will meet the objectives to reduce the quantity of wastewater and wastein the water since:

i) Under normal weather conditions no wastewater will be discharged from the site.ii) During extreme wet weather conditions the settling ponds and storage/retention ponds are

unlikely to overflow more than 10 times/year and 17 times/year respectively. This issignificantly less than the present situation and is less than 5% of the time.

iii) Overflow from the storage/retention pond during large storms is likely to have aconcentration of suspended solids of less than 50mg/l since the incoming water will bediluted by the clear water in the ponds.

iv) The proposal to modify the existing stormwater outlets so that the wastewater is

discharged below the water surface will reduce the aesthetic impact of the dirty waterplume.

v) Rainfall in excess of the design value will overflow into the harbour via the emergencybypass systems. During these events the concentration of suspended solids will exceedambient level by more than 10%. However the quality of the water in the harbour will alsohave much higher concentrations of waste emanating from runoff from industries in thearea.

vi) When the system is overloaded, stormwater will be discharged at points approximately300m apart along the coal quay, at an outlet opposite SP10 at the southern end of theterminal, and at the canal outfall from the storage/retention pond. The effect of this will beto distribute the discharge over a larger area thereby decreasing the concentrations ofwaste in the seawater and hence reducing the required number of dilutions to meet the

Water Quality Guideline Values for Marine Waters.vii) RBCT will reduce its potable water consumption by approximately 350Ml per annum.viii) RBCT will extend the monitoring programme to include testing samples of seawater taken

opposite the stormwater outlets.

RBCT is committed to achieve and demonstrate sound environmental performance. They haverecently been accredited ISO 14001 certification and have undertaken to implement theproposed scheme at a cost exceeding R30million even if the Phase 5 Expansion does not goahead.

RBCT have been involved in negotiations with the DWAF to licence their stormwater dischargesince 1993. Key elements in the imminent Phase 5 Expansion Project are affected by thisproposal. It is therefore essential that approval be obtained as a matter of urgency.


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1. BACKGROUND

Richards Bay Coal Terminal (RBCT) is located in the South Dunes area of Richards BayHarbour. Its function is to receive, store and export washed unsized coal of nominal sizeless than 50mm from Berths 301 to 305.

RBCT commenced operations in 1976 with a throughput capacity of 12 million tonnes perannum (Mt/a). Increasing demands for steam coal has resulted in four major expansionsat the Terminal raising its export capacity to 72 Mt/a.

The Terminal occupies an area of approximately 200 ha of which 110 ha is used tostockpile coal. The stockyards are constructed on engineered fill graded to falls. Acompacted layer of carpet coal seals the surface and forms the working platform.

RBCT is committed to achieve and demonstrate sound environmental performance.Environmental protection and conservation are key aspects in their mission statement. Inpursuance of this objective, RBCT initially adopted the BS 7750 management system. In

1993 RBCT was accredited ISO 14001 certification.

Since 1993, RBCT has had numerous meetings with officials from the Department ofWater Affairs & Forestry (DWAF), and has submitted various applications to DWAF tolicence the discharge (water containing coal) from the Terminal. To date no applicationshave been approved.

In 1997 RBCT voluntarily commissioned a programme to reduce wastewater emissionsfrom the Terminal. This entailed inter aliamodifying the existing settling ponds to containthe first flush volume arising from 20 minutes of runoff from a 1 in 20 year storm eventand more recently installing new settling ponds under the wharf conveyors.

Shortcomings in this surface water management system were identified in the proposedPhase 5 Expansion Environmental Impact Assessment. Various specialist studies werecarried out to determine the impact of the proposed expansion on the environment and itwas recommended that runoff arising from normal rain be collected and recycled.Environmental approval for the Phase 5 Expansion Project was obtained March 1993.

In parallel to the Phase 5 Expansion EIA process, DWAF required that a Baseline Studybe carried out to determine the impact of the current operation on selected aspects of theaquatic ecology in the harbour adjacent to RBCT. The findings of this and other specialiststudies are summaries the report A summary of findings from a series of specialiststudies of the impact of Richards Bay Coal Terminal current operations, on the naturalenvironment surrounding the facility in Richards Bay harbour prepared by Dr AD Connell,CSIR.

2. OBJECTIVE

This objective of this Technical Report is to present a proposal to DWAF in sufficient detailto enable the Department to licence the discharge from RBCT.


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3. REGULATIONS

Although policy statements relating to marine disposal were provided by the DWAF underthe previous Water Act (Act 54 of 1956), the authors are not aware of any policies underthe new National Water Act (Act 36 of 1998).

3.1 PREVIOUS WATER ACT

Under the previous Water Act (act 54 of 1956), exemptions to discharge to sea weregranted under the following conditions:

a) An official application has been lodged with the DWAF.b) A full scale EIA based on Integrated Environmental Management principles has

been carried out to determine the best disposal option for the effluent.c) It is neither justified nor practically feasible to treat the effluent sufficiently to

return it to its source of origin or to make it available for re-use.

d) The effluent will not result in the deterioration of the marine environment to suchan extent that it interferes with the beneficial uses.

e) Public opinion has been taken into consideration.

Upon approval exemption was granted containing specifications on the volume and qualityof the effluent and the specific area of discharge.

3.2 NATIONAL WATER ACT

The National Water Act (Act 36 of 1998) (NWA) regulates the use, storage and disposal ofwater into a water resource. The statutory requirements applicable to RBCT are discussed

below.

3.2.1 Definitions

The Act defines the meaning of the following words or phrases as follows:

Commercial activity means those activities identified in the Standard IndustrialClassification of All Economic Activities.

Domestic wastewater means wastewater arising from domestic and commercialactivities and premises, and may contain sewage.

Estuary means a partially or fully enclosed body of water which is open to the seapermanently or periodically and within which the sea water can be diluted, to an extentthat is measurable, with fresh water drained from land.

Waste includes any solid material or material that is suspended, dissolved ortransported in water (including sediment) and which is spilled or deposited on land or intoa water resource in such volume, composition or manner as to cause, or to be reasonablylikely to cause, the water resource to be polluted.

Wastewater means water containing waste, or water that has been in contact withwaste material.

Water resource includes a watercourse, surface water, estuary or aquifer. The definitionspecifically does not include marine environments.


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3.2.2 Quality / quantity of wastewater discharge

Since no major watercourses drain into the Richards Bay Harbour, it is highly improbablethat the harbour can be classified as an estuary. This being the case the Richards BayHarbour is not a water resource and therefore the regulations concerning the quality andquantity of wastewater discharge into the harbour do not apply.

3.2.3 Capacity requirements of dirty water systems

Capacity requirements for dirty water systems discharging into a marine environment arenot regulated by the Act. The requirements contained in the Regulations on Use of Waterfor Mining and Related Activities aimed at the Protection of Water Resources do not applysince the harbour is not a water resource.

3.2.4 Storage of water containing waste for re-use

In terms of Regulation 4.7 of Section 39 of NWA (General Authorisations), a person maystore up to 5000 cubic metres of domestic and/or biodegradable industrial wastewater forthe purpose of re-use.

However it can be argued that this regulation is intended to limit the storage of waterwhich otherwise could have been used by a downstream user. For the case underconsideration, since the source of the water is rain and the point of discharge is theRichards Bay Harbour, the author can see no justification to place a limit on the quantity ofwater to be stored for re-use.

3.3 MARINE WATER QUALITY GUIDELINES

Although not legislated, the South African Water Quality Guidelines for Coastal MarineWaters (DWAF, 1995) provide a reference framework for settling marine quality objectivesfor the natural environment.

These guidelines set target values to be met for coastal marine waters but do not offerany guidance on design parameters to be used for the dirty water system.

3.4 STATUTORY REQUIREMENTS

In terms of Schedule 1, Clause 1f of the NWA a person may, subject to the Act, discharge:

i) waste or water containing waste; orii) run-off water, including stormwater from any residential, recreational, commercial or

industrial site, into a canal, sea outfall or other conduit controlled by another person

authorised to undertake the purification, treatment or disposal of waste or watercontaining waste, subject to the approval of the person controlling the canal, seaoutfall or other conduit.

It is apparent that no clear statutory requirements exist for the disposal of water containingwaste into the Richards Bay Harbour, which is permitted in terms of the above regulation.Design parameters and limits will therefore need to be approved by DWAF taking intoconsideration technical, economical, social and environmental aspects of the proposedstorage / disposal system.


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4. PRESENT SITUATION

The source of the wastewater and operation of the existing first flush system is brieflydescribed below.

4.1 SOURCE OF WASTEWATER

The prime source of wastewater is stormwater runoff from the coal stockyards androadways. Although the stockpiles are sprayed twice a day (currently with potable water),very little runoff reaches the settling ponds. This is because the amount of water sprayedonto the coal stockpiles is just sufficient to wet the surface of the stockpiles to reduce thegeneration of airborne dust.

The other source of wastewater is from cleaning the conveyors and washing of equipment(wash down water).

It should be noted that all surface water runoff at RBCT is collected in a single system,with no provision having been made from inception (1975) for the separation of clean(roofs) from dirty (ground surface) runoff. The proposal contained in this document doesnot change this principle.

4.2 EXISTING SURFACE WATER MANAGEMENT SYSTEM

At present all the surface water runoff is collected in settling ponds located around thesite. The locations of the main settling ponds are shown in Figure 1.

The purpose of these ponds is to capture the first flush volume, which is assumed to

carry most of the suspended and transported solids collected from the stockpiles androadways. When the ponds are full, subsequent flow bypasses the ponds and isdischarged directly into the harbour.

It should be noted that only settling ponds SP 1, 2, 4, 10, 12A and 13 discharge directlyinto the harbour. Flow from the other settling ponds pass through SP2, SP10 , SP12A andSP18.

After it has rained, the water is allowed to stand for period of 48 hours so that thesuspended solids can settle out. It has been established from tests that the TotalSuspended Solids (TSS) reduces from 500mg/l to less than 25mg/l in a 48-hour period.

After the settling period has elapsed, valves that are connected to floating strainers(Dolphins) are opened to empty the ponds. The clear water is emptied into the stormwaterbypass system that ultimately discharges into the harbour. The valves are then closed.Since water is drawn off from just below the surface, any oil that may have found its wayinto the pond will be left behind for later removal.


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Figure 1 Existing Terminal

4.3 QUALITY OF WASTEWATER

Water discharged from RBCT is sampled regularly and the results are submitted to theDWAF Regional Office for their monitoring. The samples are tested against the GeneralLimit Values although the Marine Water Guideline Limits are considered to be moreappropriate.

Limits that are most often exceeded are:

Total Suspended Solids

Oils, Soaps & Grease

Faecal Coli forms Chemical Oxygen Demand Colour

Each of these will be discussed in more detail below.

4.3.1 Total Suspended Solids

Test results for samples of water taken from settling ponds during a storm event lastingmore than one day are shown in Table 1. These results show that the TSS present in thesettling pond increases with increased rainfall intensity.

The concentration of TSS generally exceeds 25mg/l when the settling ponds overflow onrainy days.


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However, during dry weather conditions, the quantity of daily surface water runoff is verysmall relative to the installed storage capacity of the settling ponds. Under theseconditions the settling ponds seldom, if ever, overflow. They are however routinelyemptied after the concentration of TSS has decreased to less than 25mg/l.

Table 1 TSS measured at settling ponds during rainy periods

Date Pond Location TSS (mg/l)Antecedent Rainfall

(mm)

DailyRainfall(mm)

20/9/2000

SP 7 Bypass weir 10939 (over 2 days)(ponds overflowedon 19/9/2000)

44SP 9 Discharge valve 71

SP 12A Discharge valve 103

20/11/2000

SP 1 Discharge valve 221

237 (over 2 days)

(ponds overflowedon 18/11/2000) 155

SP 2 Discharge valve 235

SP 4 Discharge valve 146SP 12A Bypass weir 313

SP10/14 Discharge valve 331

21/11/2000

SP 7 Inside pond 1254

405 (over 3 days) 38

SP 7 Bypass weir 2577


SP 8 Bypass weir 2348


SP 12 Bypass weir 241SP 12A Inside pond 588

SP 12A Bypass weir 402

4.3.2 Oils, Soaps & Grease

Most of the oil spillage occurs at the tipplers. Oily water containing fine coal particles iseither pumped or gravitated to an oil trap near each of the tipplers where it is removed byrecycling the water through a mechanical oil-separating unit. The treated water is finallydischarged into the stormwater system. Oily water that occasionally overflows into thestormwater system when the traps are overloaded during heavy rainfall is trapped in SP2

or SP12A.

Localised oil spillage occurring at the conveyor drive stations, diesel-filling points andworkshops are dealt with at the source. However, as all of the runoff from site is routedthrough settling ponds, oil from these sources will ultimately be collected in the pondswhere it is removed.

4.3.3 Faecal coli forms

Faecal coli form counts over 1000 are occasionally recorded in the settling ponds. RBCTmanagement is aware of the cause of this problem, which is reportedly a result of staffusing the open channels as a toilet. Steps have been taken by management to address

this source of contamination.


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4.3.4 Chemical Oxygen Demand

The Chemical Oxygen Demand is found to exceed the limit when the wastewater has ahigh concentration of suspended solids. However this limit is not significant for marinewaters.

4.3.5 ColourDuring periods of uncontrolled discharge (i.e. during storm events) the seawater isdiscoloured in the vicinity of the stormwater outlets. No turbidity tests are carried out onthe seawater.

5. SPECIALIST STUDIES

Numerous specialist studies have been carried out to determine the impact of surfacewater runoff from a coal terminal in Richards Bay. These include:

Luger, S and Taljaard, S and Connell, AD. 1998. South Dunes Coal Terminal EIA: Impact

of stormwater discharge on marine water quality in Richards Bay Harbour. CSIRReport ENV/S-C 98079.

Van Ballegooyen, R and Luger, S. 2001. Richards Bay Coal Terminal Expansion EIA:Assessment of the Stormwater Discharge and atmospheric fallout from theRichards Bay Coal Terminal on the distribution of coal particles in the marineenvironment of Richards Bay. CSIR Report ENV-S-C-2001-023.

Peralta, D. 2001. Richards Bay Coal Terminal Phase 5 Expansion EIA: Assessment of thepotential environmental impact associated with the surface water runoff from theRichards Bay Coal Terminal. SKP Engineers cc.

Connell, AD. 2001. The impact ofcoal spills and stormwater runoff on the benthic fauna inthe vicinity of the coal-loading quays at Richards Bay Coal Terminal. CSIR ReportENV-C-D-2001-011.

Ward, CJ. 2002. An investigation into possible effects of RBCT-related activities onsurrounding vegetation: an illustrated report on findings and suggestions forremediation, where applicable.

Lorenz, SA. 2002. An investigation into possible effects of RBCT-related activities onsurrounding vegetation.

Naidoo, G. 2002. Impact of coal dust on photosynthesis in mangroves at selected sitesadjacent to RBCT.

Forbes, AT and Demetriades, NT. 2002. An assessment of the ecological impacts of theRichards Bay Coal Terminal operations.

Connell, AD. 2002. A summary of findings from a series of specialist Studies of the impactof Richards Bay Coal Terminal current operations, on the natural environmentsurrounding the facility in Richards Bay harbour. CSIR Report ENV-D-C-2002-082.

Field JG. 2003. Review of Richards Bay Coal Terminal assessment reports. MarineBiology Research Institute University of Cape Town.


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Only the CSIR Report ENV-D-C-2002-082 is provided with this document since itsummaries the findings of the other specialist studies commissioned. The other reportsare available from RBCT should they be required.

5.1 CONCLUSIONS

In earlier work for the South Dune Coal Terminal, Luger, Taljaard and Connell (CSIRReport ENV-S-C-1998-079) concluded that:

during storm events the SA Water Quality Guidelines for Coastal Marine Watersare likely to be exceeded for a limited period of time in a localised impact zone. Basedon the constituents in the stormwater effluent, the predicted duration of exposure andthe size of the impact zone, no significant ecological impact is however envisaged asa result of the stormwater discharge.

Van Ballegooyen and Luger (CSIR Report ENV-S-C-2001-023) have determined the extentand thickness of accumulation of fine coal particles in the Richards Bay Harbour for variousdischarge scenarios. They conclude that the main area of accumulation will be in the deepwater adjacent to the quay, which will in any event be dredged on a regular basis.

Smaller amounts of coal fines were predicted to accumulate in the shallow waters at thesouthern end of the terminal. Samples from this area have been analysed by Forbes andDemetriades, and are reported on in their work An Assessment Of The EcologicalImpacts Of The Richards Bay Coal Terminal Operations. They concluded that:

In all these situations, no evidence was found that the coal-dust caused anyadverse impact on marine or estuarine benthic communities, in concentrationssimilar or greater than those found adjacent to RBCT in Richards Bay harbour. For

example, in the Severn estuary, 2% coal in sediments was common while at somesites it was as high as 10%, yet neither showed evidence of impacted fauna. Themaximum coal-dust in Richards Bay harbour sediments from the current set ofstudies was about 2%.

It can be inferred from these studies that the wastewater discharge from RBCT is currentlynot detrimental to the environment and that aesthetics (discoloration of the water) is themajor impact.

5.2 RECOMMENDATIONS

The studies have all emphasised the importance of improved storm-water control at RBCTto minimise the cumulative impact on the harbour, and support the proposal to collect,treat and recycle water from the site.

It is also recommended that the suspended solids in the stormwater runoff be limited to50mg/l and that the stormwater be discharged below the surface water level to achievebetter dilution (pers. comm. Dr A Connell, CSIR).


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6. PROPOSED WASTEWATER STORAGE & RECYCLE SYSTEM

RBCT propose to collect the surface water runoff from the terminal and to pump it tostorage ponds situated on a new lease area to the north east of the Terminal or if spacepermits on the present lease area. The intention is to recycle the water collected in the

storage ponds after the suspended solids have settled out to acceptable concentrations.

Design parameters to be used to size the pumping stations and storage ponds areproposed below. This is followed by a description of the proposed scheme and operationphilosophy.

6.1 TARGET DILUTIONS

Studies carried out by the CSIR (see section 5) have determined that 10 dilutions areachievable for stormwater discharging into the harbour, with localised impact zones. Thecalculations were based on an ambient concentration of suspended solids in the seawater

of 25mg/l. This value is considered conservative and is more likely to be much higher.

In order to comply with the Water Quality Guidelines for Coastal Marine Waters (WQG),this would require that the concentration of suspended solids in the wastewater should beless than 50mg/l.

In terms of toxicity, it is expected that the Minimum Acceptable Toxicant Dilution (MATD)will be less than 10 if the concentration of suspended solids in the wastewater is less than50mg/l (pers. Comm., Dr A Connell CSIR).

Since the suspended solids in the stormwater runoff generally exceeds 50mg/l, a systemthat will reduce the frequency of discharge and concentration of suspended solids isrequired.

6.2 DESIGN DEPTH OF PRECIPITATION

In Section 4, it was stated that during a storm event the concentration of suspended solidspresent in the wastewater generally exceeded 25mg/l and is typically around 200mg/l. Ifthe wastewater is given the opportunity to stand, suspended solids in the water will reduceto below 25mg/l after two days. Thus in order to comply with the WQG, the stormwaterrunoff from the site should be stored for approximately two days before being releasedinto the harbour.

The difficulty lies in selecting a storage volume large enough to ensure that the risk ofovertopping is acceptable. Since the current impact on the harbour is minimal, it is notjustified in terms of economic or environmental considerations to design for large stormevents. Recognising this, the regional office of DWAF agreed in principle to accept 5%non-compliance i.e. not more that 18 discharges a year.

An analysis of the daily rainfall was undertaken to determine the rainfall event that wouldsatisfy the design risk of up to a maximum of 18 events in a year. This was done usingrainfall records for Richards Bay, which exist from 1923. Although there are some missingand questionable records, this database forms a reliable basis on which to establish thedesign storm. Taking in consideration cumulative rainfall events, it was determined that

60mm of rainfall would be exceeded at most 15 times per year using the historical record.The result of this analysis is shown in Figure 2.


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Frequency Cumulative Rainfall Events Exceeded 60mm

Precipitation

0

2

4

6

8

10

12

14

16

1924

1930

1934

1937

1941

1944

1947

1951

1955

1957

1960

1964

1968

1971

1975

1978

1982

1986

1990

1993

1997

2001

Year

FrequencyRainfallExceede

d

60mm

Figure 2 Frequency of cumulative rainfall events exceeding 60mm of rainfall

Using conventional hydrological estimating techniques the return period corresponding to60mm daily precipitation is slightly greater than 1 year.

It is proposed that that the storage ponds and pumping systems be designed for 60mmdaily rainfall as this represents a risk of excedence of less than 5% of the time.

6.3 DETERMINATION OF STORAGE VOLUME

The SCS-SA method was used to calculate the storm flow depth and hence the requiredstorage volume. Essentially this method assesses the potential water retention propertiesof the soil and uses this index to calculate the storm flow depth. Hardened areas will havea low retention index while sandy areas will have a high index. The method is applicableto catchment areas less than 30km2 and has been shown to be more reliable than othermethods used to determine storm flows.

It has been determined that approximately 40Ml of storage will be required to contain the

design storm, but that 80Ml will be required to ensure that the ponds are stormwater runoffis not discharged more than 18 times a year. The existing settling ponds have the capacityto contain 12Ml of wastewater. It is proposed that an additional 20Ml of on-site storagecapacity be provided to attenuate the flow into the pump sumps and hence reduce thepumping rate to the storage ponds.


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Figure 3 Proposed Environmental System Upgrade (ESUP)


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6.4 PROPOSED STORAGE AND RECYCLE SYSTEM

The proposed scheme is shown on Figure 3. A brief description of each element isdescribed below.

6.4.1 Settling PondsSurface water runoff will be collected in the settling ponds as before. The main differencebetween the existing system and proposed system is that the wastewater will be pumpedfrom the terminal settling ponds (see Figure 3) to the storage dams. The existing settlingponds will essentially behave as grit traps and pump sumps.

The floating Dolphin strainers will be retained in the existing ponds and also installed inthe new ponds. This device is effective in skimming off the clean water and will help inpreventing any oil that may have accumulated in the ponds from entering the storagedams. The valve connected to the Dolphin should normally be kept open to allow water todrain to the pump sumps at the terminal settling ponds.

The emergency bypass system at SP2, SP4, SP12A and SP9/10/14 will be retained;however the level of the overflow weirs will be raised to ensure that overflow only occursduring exceptional rainfall events. This may result in partial flooding of the site for a shortperiod.

6.4.2 Storage/Retention Ponds

The wastewater will be pumped to the storage/retention ponds located on a new leasearea to the north east of the Terminal. The Department of Agriculture and EnvironmentalAffairs have approved the construction the storage ponds at this location. However RBCTreserve their right to investigate constructing these ponds within the existing lease area.

The purpose of the storage/retention ponds is to contain the wastewater and to allow thesuspended solids to settle out before the water is pumped back to the two reservoirs onsite, where the water will be recycled. The concentration of suspended solids in the waterarriving at the dams is unlikely to exceed 500mg/l. From tests carried out by others, thewastewater will require 48 hours of settling time to reduce the TSS to less than 25mg/l. Amonitoring programme will be put in place to sample and test the water against theGeneral Limit Values as is currently the case at the settling ponds.

The ponds will be approximately equal in size, each having a capacity of 40Ml. Thewastewater will arrive at the inlet works where it will be diverted into the storage pond.During large storm events, the storage pond will fill up and overflow into the storm pond. Ifthe design depth of precipitation is exceeded, the storm dam will overflow into the outfall

canal and discharge into the Richards Bay harbour. The quality of the overflow understorm conditions is expected to be approximately 50mg/l.

It is proposed that the ponds be lined using an impermeable membrane to preventcontamination of the ground water.

The ponds will need to be cleaned once every 2 to 5 years depending on the annualrainfall. This would be done manually, with the coal silt being pumped from the outletworks to a silt drying bed (SDB). After drying the collected coal would be removed to theTerminal stockpiles and blended as is the case with coal removed from the settling ponds.

A concrete outlet structure will be provided at the northern end of the ponds. Submersiblepumps will be installed on floating platforms (one for each pond), and clear water pumpedback to the reservoirs on site where it will be recycled.


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A scour pipe will be installed at the outlet structure with a control valve, to allow acontrolled release of water from either pond to the outfall canal. A flow recorder andturbidity meter will be installed to monitor the quality and quantity of the discharge.

6.4.3 Discharge Canal

The outlet structure at the storage/retention ponds will be connected to an outfall canalthat will discharge on the southern bank of the harbour entrance near the positionpreviously investigated by Luger, Taljaard and Connell (CSIR Report ENV-S-C-1998-079).

6.4.4 Recycle Water

RBCT currently uses 1.6Ml of potable water a day to suppress dust and to wash downconveyors and equipment. With the implementation of the proposed scheme RBCT wouldreduce their potable water consumption by approximately 60%.

6.5 MODIFICATION OF EXISTING STORMWATER OUTLETS

Better dilution would be achieved it the stormwater is discharged below the water surfacein the harbour (pers. comm. Dr A Connell, CSIR).

The existing stormwater outlets from the terminal settling ponds will be maintained asemergency bypasses. However it is proposed that a 16m length of pipe be connected toeach of these outlets on the coal quay so that the excess stormwater is discharged belowthe surface. This will assist in reducing the aesthetic impact of the dirty water plume thatwould otherwise float on the surface.

6.6 MONITORING PROGRAMME

6.6.1 Monitoring at Settling PondsSince all inflow into the settling ponds arising from runoff from storm events smaller thanthe design storm will be pumped to the storage dams, no quantity or quality monitoringequipment will be provided at the settling ponds. For larger storm events, wastewater willoverflow into the harbour via the existing outlet pipes through the coal quay. It has beendetermined that the maximum frequency that the settling ponds will overflow is 10 time ayear.

6.6.2 Monitoring at Storage/Retention Pond Outlet Works

A flow recorder and turbidity meter will be installed on the scour pipe at thestorage/retention pond outlet works. The turbidity meter will monitor concentration ofsuspended solids present in the discharge, and this information will be automaticallyrecorded and analysed. The control valve will close automatically if the suspended solidsis found to exceed 50mg/l.

As part of the ongoing water quality testing programme, a private company will becommissioned to test water samples taken from the outlet works to establish otherconstituents in the water so that appropriate action may be taken.

6.6.3 Monitoring of Marine Water

It is further proposed that the quality of the seawater opposite the emergency outlets bemonitored on a regular basis


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6.7 RISK ASSESSMENT

6.7.1 Settling Ponds

The areas of risk at the settling ponds are twofold:

a) Pump failure

Should any of the pumps fail during the design storm event, overflow will occur viathe emergency bypass system into the harbour. It would be uneconomical to installany standby pumps since the duty pumps are expected to run infrequently.

b) Design storm is exceeded

When the design storm is exceeded, the installed pumps will have insufficientcapacity to pump the inflow into the settling ponds to the storage/retention ponds,and overflow will occur as noted above.

6.7.2 Storage/Retention Ponds

If the design storm is exceeded and rain continues to fall on consecutive days it ispossible that the storage/retention ponds will overflow. The spillway will be designed topass the flow into the dam for a 1 in 100 year event.

7. MITIGATION MEASURES AND ARGUMENTS SUPPORTING PROPOSEDSCHEME

It has been establish by various specialists that the stormwater discharge from RBCT hasno measurable impact on the marine environment in the Richards Bay Harbour. However

they recommend that RBCT reduce the quantity of wastewater discharge andconcentrations of waste in the water to minimise the cumulative accumulation of fine coalparticles in the harbour.

The prime areas of concern are the concentration of suspended solids in the water andthe aesthetic impact this has in the harbour. By limiting the concentration of suspendedsolids to less than 50mg/l it is expected that the toxicity will be within acceptable limits.

Occasionally the concentration of oils and soaps exceed the Target Values. The source ofthis contamination is from the Tippler Yard. A Central Oil Treatment Plant is budgeted forin the Phase 5 Expansion Project. It will be designed to collect contaminated water fromall of the Tipplers and to mechanically remove the oil from the water before being

discharged into the stormwater system.

The proposed scheme will meet the objectives to reduce the quantity of wastewater and wastein the water since:

a) Under normal weather conditions no wastewater will be discharged from the site.b) During extreme wet weather conditions the settling ponds and storage/retention

ponds are unlikely to overflow more than 10 times/year and 17 times/yearrespectively. This is significantly less than the present situation and is less than 5%of the time.

c) Overflow from the storage/retention pond during large storms is likely to have aconcentration of suspended solids of less than 50mg/l since the incoming water willbe diluted by the clear water in the ponds.


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d) The proposal to modify the existing stormwater outlets so that the wastewater isdischarged below the water surface will reduce the aesthetic impact of the dirtywater plume.

e) Rainfall in excess of the design value will overflow into the harbour via theemergency bypass systems. During these events the concentration of suspendedsolids will exceed ambient level by more than 10%. However the quality of the waterin the harbour will also have much higher background concentrations of wasteemanating from industries in the area. Although no specific measurements havebeen taken to quantity the concentration of suspended solids in the harbour duringstorm events, it is likely to be significantly higher than the ambient level andprobably in the same order of magnitude as found in the wastewater from RBCT.

f) When the system is overloaded, stormwater will be discharged at pointsapproximately 300m apart along the coal quay, at an outlet opposite SP10 at thesouthern end of the terminal, and at the canal outfall from the storage/retentionpond. The effect of this will be to distribute the discharge over a larger area therebydecreasing the concentrations of waste in the seawater and hence reducing therequired number of dilutions to meet the WQG.

g) RBCT will reduce its potable water consumption by approximately 350Ml perannum.h) RBCT will extend the monitoring programme to include testing samples of seawater

taken opposite the stormwater outlets.

8. CONCLUSION

RBCT is committed to achieve and demonstrate sound environmental performance. Theyhave undertaken to implement the proposed scheme at a cost exceeding R30million evenif the Phase 5 Expansion does not go ahead.

RBCT have been involved in negotiations with the DWAF to licence their stormwaterdischarge since 1993. Key elements in the imminent Phase 5 Expansion Project areaffected by this proposal. It is therefore essential that approval be obtained as a matter ofurgency.

wastewater storage and recycle system

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