031 MANAGEMENT OF THE SOUTH WI TBANK COLLIERY DECANT EMALAHLENI WATER RECLAMATION PLANT’S UNTOLD STORY

Wendy Mey*, Chris Naude** and Steven Bloy***

*BHP Billiton Energy Coal , PO Box 6182, Marshalltown, 2107, Tel: +27 (0)11 376 9111, Fax: +27 (0) 13 243 2168, e-mail: [email protected] **BHP Billiton Energy Coal South Africa, Mine Closure Operations, PO Box 13143, , 1038, Tel: +27 (0)13 689 3168, Fax: +27 (0) 13 689 3179, e-mail: [email protected] ***BHP Billiton Energy Coal South Africa, Mine Closure Operations, PO Box 13143, Witbank, 1038, Tel: +27 (0)13 689 3028, Fax: +27 (0) 13 689 3179, e-mail: [email protected]

ABSTRACT

The start-up of the eMalahleni Mine Water Reclamation Plant is a significant milestone in the evolution of mine water management in the South African mining industry. Much has been presented around the Anglo Coal, BHP Billiton joint initiative but there is an aspect of the project about which little has been shared. This is the need to address the management of the long term decant of mine affected water once mining operations are complete. South Witbank Colliery is one of the participating mines in the eMalahleni Water Reclamation Plant, contributing only ten percent of the feed to the plant. Mining at this colliery dates back to 1891 with operations ending in 1991. A legacy of mine closure issues remain, one of which is long term sustainable management of the water percolating through the old South Witbank Colliery workings and finding its way back to surface in a state that cannot be allowed to flow into the receiving environment. This is the untold story of South Witbank Colliery and its solution to water management as part of the eMalaheni Water Reclamation Plant.

BACKGROUND OF SOUTH WI TBANK COLLIERY

BHP Billiton Energy Coal South Africa’s Mine Closure Operations Around the world, BHP Billiton is responsible for a number of sites that are in the closure phase of their life cycle. The manner in which closure is managed depends on the number and locality of closure sites. (1) In South Africa, a dedicated team of specialists is committed to caring for the environment with the long term welfare of society as its guiding principle. BHP Billiton Energy Coal South Africa (BECSA) Mine Closure Operations (MCO) is a well established rehabilitation unit responsible for the effective rehabilitation and subsequent sustainable closure of the company’s 18 defunct collieries in South Africa. (2) South Witbank Colliery forms part of the MCO portfolio.

Location and History of the Mine South Witbank Colliery is a defunct coal mining operation in the Klipspruit catchment, located Upper Olifants Catchment. The nearest towns are eMalahleni (formally) Witbank, located 4 km to the east and Bronkhorstspruit, which is located 21 km to the west. (3) Refer to Figure 1 for a regional map.

Figure 1: Location of South Witbank Colliery

A tar road linking eMalahleni and runs through the mining area. The mine site is currently traversed by numerous small tracks made by people living in informal settlements, farmers, and pedestrians on their way to the town.

The colliery is located in the Highveld Coalfield, . Mining started in the early 1900s and ceased in 1991 with a period of inactivity between 1975 and 1989. South Witbank Colliery is an underground board-and-pillar mine with a small opencast section on the shallower coal seams at the edge of the underground workings. Depth of mining in the most economical No. 2 seam ranges between 15 and 65 m below surface. The thickness of No. 2 seam varies between 3 and 7 m, with an average of 5 m. The floor elevation of the mine dips from the north-east to the south-west with elevations between 1560 and 1495 mamsl over a distance of about 5 km. The mine stopped underground operation in 1975. Opencast mining was undertaken between 1989 and 1991. The underground workings and the opencast void have been filled with seepage and drainage water since mining ceased in 1991. 69 56T-009 -

Figure 2: South Witbank Mine Layout

The Water Management Challenge Water has been percolating into underground workings since 1975 when underground mining operations ceased. The accumulation of water over the past 30 years has flooded the workings, and is now finding its way back to the surface in a state that cannot be allowed to flow into the receiving environment. Extensive work has been undertaken to date in an attempt to reduce the volume of water infiltrating underground workings from surface, and to prevent water decant to natural river systems. This work included: A title deed survey, aerial photography and mapping of surface and underground workings; • A geo-hydrological investigation including the drilling, monitoring and modeling of groundwater quality and m o ve me n ts; • A preliminary surface water impact assessment; • Rehabilitation of two surface discard dumps; • Partial rehabilitation of the opencast void to remove all steep slopes and to prevent storm water ingress into the remaining open portion of the void • Filling and rehabilitation of more than 150 areas of surface subsidence in the mining area; and • The removal and rehabilitation of several redundant structures and rubble on large portions of the property.

An acid drainage collection system was also constructed, and a temporary lime neutralisation plant was being operated for the neutralisation of the mine water, before discharging to the natural stream whilst a sustainable solution was sought.

Numerous water management options to deal with the decant were investigated, some of these include, containment of water at site, transfer of water to the Department of Water Affairs and Forestry (DWAF) Brugspruit water treatment plant, alternative uses for the water, passive biological treatment using as system of wetlands. None of these options have proved feasible (practical, reliable), and BECSA decided to undertake active treatment of decant.

THE WATER MANAGEMENT S TRATEGY

Interim Measures The groundwater study by IGS (4) concluded that if the water level in underground workings is allowed to increase above the 1532 mamsl contour level, mine water will report to surface as a seepage zone on the Townshipspruit. Thus, the water management strategy adopted by the MCO team during the interim period until a long term solution was implemented, was to maintain the water elevation in the underground workings below the 1532 mamsl seepage level. This was done through the installation of a siphon pipe into the workings abstracting the water under gravity to the final void. By maintaining the level below 1532 mamsl, seepage of the acid water to the Townshipspruit was prevented.

Figure 3: Schematic Layout of Interim Water Management system

A temporary neutralization plant was erected at the site to neutralize the water in the void. The neutralisation treatment comprised the following: • Diesel power generation providing power to liming plant; • Lime storage silos; • Lime screw conveyer; • Mixing tank; and • Water circulating pump. Water was pumped from the final void into the mixing tank where the lime is fed into the water in a controlled manner. The energy of the water pumped to the mixing tank agitated the water to achieving mixing with the lime. Neutralised treated water overflowed back into void at two places, one close to the discharge point and a second at the centre of the void. The precipitated metals dropped out, falling to the floor of the opencast void.

Water Pollution Prevention Methods Initial measures to limit the impact of the mining operations on the water quality included the closure of all entrances into the mine, including shafts and sinkholes which could possibly provide a conduit for free exchange of air between the atmosphere and the underground mine. Preventing oxygen exchange between surface and underground results in diminishing oxygen concentrations within the underground mine, which in turn reduces the chances of spontaneous combustion and oxidation of pyrite and other minerals which causes pollution of the water. T he MCO team conducted an aerial photo interpretati on of the underground mi ned area in 1996. More than 150 subsi ded and crown sinkhole areas were identified. The areas of subsidence are spread over the entire mining area and there are no localised areas with an apparent high subsidence risk. These areas have been documented and located in the field. During 1996 and 1997 all the sinkholes were closed. Work has been completed around all of these subsidence areas to prevent the local ingress of surface runoff into the underground workings. Since 1997 annual aerial inspections have been carried out. If any new subsidence is found, immediate action is taken to close the sinkholes and cracks. A detailed investigation and engineering design for the reshaping and rehabilitation of the old dumps on the mine complex have been implemented. The dumps have been reshaped and flattened to a slope not exceeding 1:5, top soiled and vegetated. Storm water is drained from the dumps surface in a controlled manner to limit the recharge into the dump and prevent erosion.

Storm Water Management Storm water management measures have been implemented around the final void. Permanent contours were installed in the rehabilitated portion of the void to effectively drain storm water away from the rehabilitated portion of the void. The storm water is directed away from the void towards the natural water course, the Townshipspruit. The void has been partially in filled and temporary storm water diversion berms have been constructed to divert clean storm water runoff around the open section of the void towards the Townshipspruit. The diversion berms have been designed to cater for the peak flow rate generated for a 1 in 100 year storm event. The temporary berms around the open section of the void will be demolished during final rehabilitation, involving the total infilling and rehabilitation of the final void to provide a free draining surface. Additional storm water management measures have been installed around the two discard dumps. Berms have been installed to ensure that surface water runoff is diverted around the dumps, and only direct rainfall will come into contact with the dump.

Minimisation and Reuse of Mine Water There is limited opportunity for the further minimization and reuse of mine water due to the fact that the mine is not operational.

The Long Term Plan Despite the measures taken in the form of prevention of pollution and storm water management an excess in the order of 2.2Mℓ/day decants from the mine workings. The temporary liming facility is by no means a sustainable solution to the problem and MCO had to secure an alternative long term water management strategy. The solution presented itself through a joint initiative between Anglo Coal and BECSA and takes the form of a partnership with Anglo Coal in the shared use of the eMalahleni Water Reclamation Plant.

ANGLO COAL AND BECSA JOINT INITIATIVE

In May 2002, Anglo Coal and BECSA (then Ingwe Collieries) agreed to jointly collaborate on the development and implementation of water management strategies that will contribute to the achievement of in-stream water quality and quantity objectives for the Olifants River Catchment. The initiative aims to: • Identify synergies between neighbouring operations of Anglo Coal and BECSA to implement water management strategies at source. • Find optimum solutions for each mine or group of mines on a catchment basis. • Develop partnerships to identify and develop action plans to implement water management strategies on a cost effective and sustainable manner. • Identify opportunities to use, recycle and reuse water in a sustainable manner. Collaboration began shortly after the signing of the agreement and a Pre-Feasibility Study into Collective Mine Water Reclamation and Reuse in the Upper Olifants Catchment (5 ) was done. Several mine water reclamation and re-use schemes were identified through this study completed in November in 2004, namely eMalahleni/Witbank Scheme, Steve Tshwete/Middelburg Scheme and Hendrina/Kwazamakhuhle Scheme. The eMalahleni/Witbank Scheme concept progressed into the eMalahleni Water Reclamation Plant, and the project was executed by Anglo Coal. The plant was officially opened 21 November 2007.

EMALAHLENI WATER RECLAMATION PLANT (EWRP)

EWRP Overview The eMalahleni Water Reclamation Plant (EWRP) is a mine water treatment facility, central to a several collieries west and south of eMalahleni. The plant accepts mine water from Kleinkopje, Greenside, Navigation and South Witbank Collieries. The water is treated to potable standard, and distributed to local water users in the eMalahleni Town.

South Witbank Abstraction Point As can be seen from the floor contours shown in Figure 4, the contours are highest at the north east section and are lowest at the southern corner of the underground workings. Any water entering the underground workings will therefore drain to the southern corner. The excess water from the underground workings currently pushes up to the small opencast final void, located along the north-western part of the mine.

Figure 4: 2 Seam Floor Contours with Key Monitoring Boreholes

To maintain the water level below 1526 mamsl in the opencast section, the water in the mine is extracted by pumping the water from the underground workings at the southern most corner and transferring it to the site of the EWRP.

Figure 5: South Witbank Borehole Farm from where Water is Abstracted

Transfer Pipeline The nature of the mine water is such that when in contact with air, precipitates form and scaling tends to occur. The mine water is can also be abrasive and corrosive. To convey mine water with the above mentioned characteristics, the following design criteria (6 ) was applied: • Maintain a minimum velocity of 1 m/sec, • Where practically possible all efforts must be made to keep air out of the system, • Due to the corrosive nature of water, only pipes manufacture from inert materials can be considered, • Pipe joint details must be selected to minimize the risk of spillages or leaks, • To prevent damage from vandalism and fires all pipelines must be buried, • T he verti cal ali gnment of the pi peline must be desi gned to maintain a mi nimum cover of 900 mm, • The pipe bedding must be designed for a flexible type pipe, • Air valves must be located at high points and scour valves must be located at low points. The collection pipeline from the South Witbank Colliery to the Treatment Plant is 2373m in length and is aligned along the existing conveyor. The collection and distribution pipelines are shown in Figure 6

Figure 6: Map of eMalahleni area indicating EWRP and Associated Infrastructure

Mine Water Storage Dam The excess mine water from South Witbank Colliery is delivered to a central storage dam at the treatment plant. The central storage dam is an open dam using compacted earthworks and plastic liner construction. The mine water dam is split into two compartments for operational flexibility. This dam has a total storage capacity of 46 Mℓ, which equates to 48 hours of retention time.

Figure 7: South Witbank Delivery into the EWRP feed dams

Mine Water Treatment Once in the mine water storage dam, the South Witbank water blends with the water from the other three collieries. The South Witbank contribution to the plant is an average of 2.2Mℓ/day, and this forms approximately 10% of the feed to the facility. The EWRP process entails limestone neutralisation, ultra-filtration and reverse osmosis desalination, with the brine being concentrated up through 3 reverse osmosis stages. The water treatment process produces waste in the form of sludge (solid) and/or brine (liquid with a high salt content) as a result of the membrane-based treatment process. This waste is disposed of in a responsible manner in order to ensure that environmental impacts are minimized. The Potable Water is piped to the eMalahleni Town bulk supply reservoirs.

ROAD TO CLOSURE OF SOUTH WI TBANK

The long term water management approach for the closure situation at South Witbank Colliery has been finalised. Permanent infrastructure has been put in place to abstract water from the deepest point in the underground workings for transfer to the EWRP for treatment to potable standards and reuse in the local municipality is in place. The decant control philosophy is to maintain the water elevation in the underground workings at 1520 mamsl. This allows for adequate storage volume in the workings in the event of several consecutive above average rainfall wet seasons without risk of decant at the 1532 mamsl mark. It also maintains sufficient water in the workings to control the risks of spontaneous combustion and subsidence. EWRP replaces all water treatment activities based at the opencast void. Liming will continue in the opencast void until it is entirely dewatered, where after it will be removed and the surface area rehabilitated as part of the surface land use rehabilitation process.

CONCLUDING REMARKS

An important aspect of this project is the way in which two highly competitive global resource companies can come together to resolve problems affecting everyone. (7 ) The gl ue that bi nds Angl o Coal and BECSA in thi s case i s the community. Both companies have a common goal of ensuring that their operations are sustainable in the long term. On the business front there is vigorous competition for markets and resources. However, where efforts can be pooled to uplift communities, this should be done. The EWRP is a shining example of intersecting objectives resulting in a solution that exceeds anything that either of the companies or the municipality could have achieved alone.

Figure 8 - Unveiling the Plaque at the EWRP Opening Ceremony, 21 November 2007. From left to right, Hon Clr Linah Mal atjie eMalahl eni Local Muni ci pal ity, Mr. Phili p Baum CEO Anglo American, Mr Don Turvey, VP Proj ect Devel opment BECSA

REFERENCES

1. BHP Billiton Intranet Documents on Mine Closure 2. Mine Closure Operations BHP Billiton Intranet Website 3. South Witbank Colliery Interim Closure Plan 4. Institute of Groundwater Studies Report number: 2006/03/FDIH 5. Pre-Feasibility Study into Collective Mine Water Reclamation and Re-Use Upper Olifants River Catchment, Golder Associates Africa Report No : 6753/6532/4/W 6. Detailed Design of the South Witbank Drainage System Golder Associates Report No : 8230/8321/4/ 7. eMalahleni Water Reclamation Project Opening Ceremony Speech by Don Turvey on 21 November 2007