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The Kabwe Scoping and Design Study PDF Print E-mail
The Kabwe Scoping and Design Study The KSDS three main primary objectives were defined, each to be addressed by a discrete ‘Phase’ of project work. The objectives of the KSDS are summarised below:
  • Determination of the extent and magnitude of contamination by Pb and other toxic substances arising from historical mining and mineral processing activities.
  • Characterization of the main pathways of Pb exposure to residents through the development of a Conceptual Site Model (CSM) and numerical risk assessment for each impacted community.
  • Formulation of a revised decommissioning plan for the mine site, and of appropriate measures for the reduction of mine-derived toxin exposure, (in particular Pb levels in human blood).
Exposure to Pb in the vicinity of the Kabwe mine has been recognised for more than a decade, and was highlighted in ZCCM's Rehabilitation and Decommissioning Plan (1995) as the site's primary environmental issue is to provide an overview of the environmental and social conditions within the Copperbelt of Zambia, particularly those related to the impacts of present and previous mining activities. While the CEMP Phase I and Investor Environmental Management Plans focused on legal compliance and the subdivision of responsibilities between ZCCM-IH and New Investor, CEMP II has the wider scope of clarifying the overall impact of mining activities on public health and ecosystem function, and providing an adequate basis for determining mitigation measures priorities. A foremost consideration has been to identify and prioritise environmental liabilities that are to be addressed by the EMF. It is important to appreciate that, inspite of being called an "Environmental Management Plan", the primary aim of the study is not to provide detailed management plans on the local level, as these already exist as for Copperblet mine sites. Once approved by the Environmental Council of Zambia, the KSDS will be a live document to serve as a blue print for mine related environmental management.

KEY ENVIRONMENTAL CONCERNS IN KABWE
2.1 Determination of the Extent and Magnitude of Contamination by Pb and Other Mining-derived toxins in the Kabwe Environment (KSDS Phase 1)

Phase 1 of the KSDS was executed during the period July 2004 to June 2005. It involved an evaluation of the effects of historical mining activities on environmental quality in all of Kabwe’s principal residential areas. Areas of concern included the former mine townships of Chowa and Kasanda, however, areas of low density housing more distant from the mine, such as Luangwa, were also included in the investigations. Katondo and Makululu were considered to be key focuses for the KSDS due to their size and the high level of inherent vulnerability of many of the residents present.

Surveys were undertaken to define spatial trends of contamination by Pb and a range of other metals/metalloids in Kabwe’s soils, areas of mine waste deposition, surface water, groundwater, domestic and market crops and atmospheric particulates. These surveys essentially provided the database which permitted elucidation of the relative significance of different environmental media as sources of Pb exposure to Kabwe’s residents.

2.2.1 Soil Contamination
A soil contamination survey of Kabwe was performed through the collection and analysis of soil samples (0-10 cm depth) from approximately 1,000 locations.
The results indicated that soil over a substantial area is highly contaminated with Pb. Median concentrations of soil Pb in Kasanda (3,008 mg/kg), Makandanyama (1,613 mg/kg), Chowa (1,233 mg/kg), Mutwe Wansofu (1,148 mg/kg), Makululu (870 mg/kg) and Luangwa (507 mg/kg) all exceed levels generally regarded as acceptable by international authorities with respect to residential areas.

The Kabwe Main Canal extending southeastward from the mine was used historically as the conduit for discharging water pumped from Kabwe’s underground mine workings and metallurgical operations. Sediment from the canal was periodically dredged and deposited along the banks of the channel. Remobization of this material during intermittent flooding events, and by wind erosion, has resulted in acute contamination of soil to distances of around 100m to either side of the watercourse. Down-profile Pb trends investigations around Kabwe to assess the stratigraphic distribution of Pb in the soil cover highlighted Pb to be concentrated in the superficial part of the soil profile, with concentrations falling by a factor of between 5 and 10 from the surface to around 50 cm depth. Over Kabwe as a whole, the area in which soil Pb concentrations exceed the threshold of 1,000 mg/kg for defining areas warranting soil clean-up is approximately 21 km2.

2.2.2 Mine Waste
Phase 1 of the KSDS relating to the chemistry of Kabwe’s mine waste dumps has confirmed that significant waste material stored on the mine site is classifiable as toxic. An additional hazard associated with the waste dumps arises from the generation of fugitive dust, much of which is transported by the prevailing wind to community areas such as Kasanda and Makandanyama. Concentrations of Pb in these materials are recorded in excess of 20% by weight.

2.2.3 Air
The seasonally poor vegetation cover throughout much of Kabwe results in the development of a generally dusty environment in many residential areas. Monitoring was performed under Phase 1 of the KSDS of the concentration of Pb in atmospheric particles of a size sufficiently small to be inhaled (PM10). The results of this exercise confirm the presence of a dust hazard in several locations. Highest atmospheric Pb concentrations (>0.5 µg/m3) are recorded in Kasanda, and generally fall with distance from the mine.

 2.2.4 Water
The potential for contamination of district-wide groundwater resources as a consequence of the flooding of the Kabwe mine workings at closure was identified as a major community concern prior to the initiation of the KSDS. A water quality assessment was therefore performed under Phase 1 of the project.
This included the collection and analysis of samples from the mine’s pits and shafts, plus in excess of 100 shallow and deep groundwater sources used for potable or domestic supply throughout the district. The results of this exercise suggest that contamination of water is negligible, and that most of the principal water supply sources in the district are of good quality.

Concentrations of Pb in the resurgent mine waters do not exceed a few parts per billion, while concentrations of dissolved Pb in both shallow and deep wells are systematically below the WHO potable water guideline of 0.01 mg/l. The suite of wells sampled included the primary municipal and domestic supply sources for Kasanda, Makululu, Wire, Katondo, Central and Luangwa. While the results of the Kabwe water quality survey confirm that drinking water is extremely unlikely to present a tangible Pb exposure risk (regardless of township or area of residence) occasional exceptions to this trend are observed with respect to the total concentrations of Pb in samples from certain shallow (hand dug) wells at dwellings in Makululu and Makandanyama. These are associated with the presence of Pb enriched particulates (mainly soil) in the water drawn from such wells. Effective filtration of water from these sources should therefore be regarded as a key factor in health protection.

2.2.5 Contamination of Crops
Contamination of crops was investigated under Phase 1 of the KSDS through sampling and analytical exercise that targeted a group of 11 crop types most commonly acquired from market and/or domestic sources for consumption by Kabwe residents. Samples were collected from numerous points of harvest (private gardens) and points of sale (markets and roadside stalls) across Kabwe. These were subsequently sub-sampled to produce washed and unwashed fractions, and were then analysed for Pb and a range of other metals.

The results of crop analyses demonstrate that crops grown in the Kabwe area do tend to contain Pb concentrations which are modestly in excess of the typical global range. Such a range for the edible portions of plants from uncontaminated locations is of the order of 0.001 to 0.008 mg/kg (fresh weight), while most samples from gardens and markets in Kabwe contain Pb levels greater than 0.01 mg/kg. The Pb concentrations in Kabwe vegetables are nonetheless significantly lower than reported for many acutely contaminated industrial sites, in which fresh weight values can enter the range 10 to 50 mg/kg.

Generally, vegetables collected at points of harvest contain twice the Pb of samples from points of sale. Lead concentrations in unwashed samples are routinely 1 to 3 times greater than those of washed samples. Human exposure to Pb through consumption of locally produced crops is therefore likely to be more strongly influenced by the method of preparation (thoroughness of washing) than by provenance.

2.2.6 Screening for other Possible Environmental Contaminants
A comparison of the analytical database generated for a wide range of heavy metals in Kabwe’s soils, mine waste deposits, water resources, air and crops was performed in relation to internationally established ‘trigger levels’ for the respective media. These trigger levels essentially signify whether the observed concentrations of heavy metals in each material could be regarded as potentially hazardous to human health. Results of the above process indicate that in addition to Pb, a small group of elements in Kabwe soils is enriched to a degree warranting more detailed investigation to assess potential human exposure risks. These elements comprise cadmium (Cd), arsenic (As) and vanadium (V). Investigations into the health implications of the two most inherently toxic of these elements (Cd and As) were therefore performed under the KSDS. In water, the principal solutes which are enriched relative to internationally established potable supply standards are sulphate and manganese (Mn). In crops, the principal element in addition to Pb which attains concentrations in excess of CODEX standards (as applied internationally for the regulation of food quality) is Cd.

2.2.7 Levels of Pb in Blood
Blood lead (B-Pb) monitoring at Kabwe was undertaken under Phase 1 of the KSDS in two phases (September 2004 and June 2005). The objective was to define levels of human exposure to Pb across Kabwe, and ultimately to relate these to the patterns of environmental Pb contamination recorded in soils and other media. The B-Pb survey was conducted concurrently with a socio-demographic profiling exercise, so as to permit interpretation of inter- and intra-community B-Pb trends within the context of lifestyle and behavioural factors. A total cohort of approximately. 2,500 residents were sampled, with particular emphasis on high vulnerability groups (children aged 0-7 years old and women of childbearing age).

Results of the Kabwe B-Pb survey indicate that only 4 communities yield B-Pb geomean B-Pb levels for children aged 0-7 which lie below the WHO guideline level for public health protection of 10 µg/dL. These are all located at considerable distance from the Kabwe Mine. Geomean B-Pb levels for children aged 0-7 in communities in closer proximity to the mine such as Chowa (31.7 µg/dL), Kasanda (32.8 µg/dL), Makandanyama (38.2 µg/dL) and Makululu (31.3 µg/dL) are all substantially elevated. Blood Pb levels which may be considered liable to induce sub-acute toxicological effects (>65 µg/dL) were observed in numerous instances. These occur exclusively in children aged 0-7, and are apparently confined to the communities of Makandanyama (7 cases from a cohort of 59), Kasanda (4 cases from 119), Chowa (1 case from 45), Makululu (19 cases from 408), Mutwe Wansofu (1 case from 68), Katondo (2 cases from 232) and Railways (1 case from 101).

These cohort data can be applied to provide an approximate guide to the probable incidence of B-Pb >65 µg/dL occurrences in the total population of children aged 0-7 in each community. Based on estimates of gross population size in each community, it is likely that there would be approximately 650 cases of B-Pb >65 µg/dL across the study area as a whole, with the majority occurring in Makululu, Makandanyama and Kasanda.

3. Characterisation of the Pathways of Lead Exposure (KSDS Phase 2)
Phase 2 of the KSDS focused on developing an understanding of the range (and relative importance) of environmental, social and lifestyle factors which control human Pb exposure at Kabwe. Results of the KSDS Phase 2 indicate that:
  •  Mine waste and contaminated soil constitute the primary sources of Pb exposure over an area of at least 20 km2, within which soil Pb concentrations exceed 1,000 mg/kg.
  • The intensity of Pb hazard sources is greatest in communities located in close proximity to the Kabwe Mine site, and declines progressively with distance. An important exception to this trend occurs along the axis of the Main Canal to the south-east of the mine, where highly contaminated dredged sediments remain as discrete piles, and have dispersed during flood events to cause locally intense soil contamination. Human lead intake, as reflected by blood lead levels, shows a general correlation with the district-wide pattern of environmental contamination. This is consistent with the influence of a wide range of socio-economic, lifestyle and cultural influences which together influence the inherent vulnerability of residents to Pb exposure.
  • Geophagia and pica tendencies are common throughout Kabwe. These habits constitute the principal cause of human B-Pb values, which exceed those which could reasonably be expected on the basis of ambient levels of environmental Pb contamination. The incidence and significance of this tendency is such that geophagia would probably result in the prevalence of sporadically high B-Pb levels in all Kabwe communities regardless of the efficiency or comprehensiveness of any environmental clean-up exercise.
4. Formulation of Appropriate Measures for the Reduction of Human Health Risks (KSDS Phase 3)
Phase 3 of the KSDS was undertaken during the period September 2005 to March 2006. It involved the elaboration of a Site Rehabilitation and Environmental Management Plan (SREMP) in two Parts:
  • SREMP Part I: Kabwe Mine Rehabilitation Plan (RP)
  • SREMP Part II: Community Lead Risk Mitigation Strategy (CLRMS).
4.1 Kabwe Mine Rehabilitation Plan
The Kabwe Mine RP is designed to ensure the long-term rehabilitation of all areas of the former mine compound. These rehabilitation actions are described in terms of four principal sectors: i. Plant area ii. Pit lakes iii. Waste dumps iv. And areas of disturbed ground

4.2 Community Lead Risk Mitigation Strategy
Part II of the SREMP has given a detailed Community Lead Risk Mitigation Strategy (CLRMS) aime at achieving a sustainable reduction in environmental exposure to Pb in all residential areas in the vicinity of the Kabwe mine site. The CLRMS also strives to address public health concerns associated with Pb exposure in a manner which is pragmatically balanced against the resources available for mitigation and the wide range of competing health and developmental challenges (HIV/AIDS, malaria, waterborne diseases etc) faced at the local and regional scale. The CLRMS is structured into several discrete sub-project components each of which has a specific geographic area of coverage. The main components of the CLRMS comprise:
  1. Canal zone rehabilitation project
  2. Targeted soil remediation program
  3.  Vegetation barrier program iv. Water supply improvement
  4. Removal of mine waste from residential areas
  5. Public information and risk communication
  6. Integrated case management