Remediation case study

A remediation project at the Umbogintwini Industrial Complex (UIC) was initiated in 1995 to address the contamination of land and groundwater resources due to historical activities associated with the manufacture, storage and distribution of chemicals, agrochemicals and fertilizers.

In 2009, the project's progress was recognised in the biodiversity category of the annual eThekwini Mayor's Award for Excellence. The motivation for the award focused on best practice remediation, conservation and education work to address legacy issues. In particular, the Vumbuka Reserve, a 27 hectare area in the north-west portion of the UIC was highlighted. This area was previously used for the disposal of liquid and semi-solid wastes generated from manufacturing activities at the UIC from the mid-1950s until 1998.

The Vumbuka Reserve includes:

• a series of effluent precipitation and settling dams;
• two disused, partially-lined mercury sludge dams; and
• the drums area, where drums originally containing chlorinated hydrocarbon wastes were buried.

STRATEGY

Remediation to address soil and groundwater impacts began in 1995 when the area was classified as a waste site to enable AECI to meet its legal and constitutional obligations to avoid nuisance and harm to others, to improve the environment and to comply with good governance requirements. In the process, a rehabilitation strategy for the Vumbuka Reserve evolved into the UIC's Environmental Management Plan.

The principles prioritised in formalising and implementing the strategy were:

• the protection of human health and the environment is paramount;
• commitment to the use of good science;
• the efficacy of scientific solutions must be demonstrated;
• AECI must balance its duty to shareholders with its duty to protect human health and the environment by utilising the best available techniques, not entailing excessive cost;
• a risk-based approach, founded on comprehensive risk assessments, must be followed;
• regular liaison with regulatory authorities must take place; and
• information must be shared with interested and affected parties, and they must be encouraged to participate in the problem-solving process.

The strategy has six technical elements together with community participation, the over-arching management element.

PROCESS

To prevent groundwater contamination, boreholes were sunk to abstract water from sludge in and around the settling and precipitation dams and adjacent to the site boundary with the neighbouring community. The idea was to create a hydraulic barrier to control the migration of the groundwater plume off-site. Water is treated prior to safe disposal to sea via a marine outfall. Dewatering of the sludge also served to reduce the head of pressure that was driving groundwater beyond the boundaries of the dams and the UIC. Agricultural drains were installed to capture seepage around the dams and in the neighbouring residential area of Ezimbokodweni.

Leaching is managed with standard engineering interventions such as drains, conduits and pipes and, where appropriate, surface profiling has been undertaken to promote run-off of excess precipitation and to ensure the appropriate drainage of clean stormwater.

In the drums area, additional boundary wells were installed to intercept and abstract groundwater to control its off-site migration. All arisings are captured and transferred to the UIC's effluent treatment plant prior to safe disposal to sea.

Avoiding the recharge of the dewatered dams by the infiltration of rain was always recognised as being key to the clean-up of Vumbuka. In evaluating options for capping the dams, the project developed what is arguably its most distinctive intervention. As it became apparent that vegetation was re-establishing itself unaided in the area, extensive work was undertaken to determine whether this natural process could be sustained and enhanced to benefit long-term clean-up. This led to the eventual choice of a vegetative, evapo-transpiration (ET) cover as the preferred option for the Reserve's dam area. The drums area was capped with a conventional, engineered cover.

The ET cap provides long-term, natural sustainability for remediating the dams area of Vumbuka since the microbial action associated with vegetation and its growth reduces maintenance and provides contaminant source reduction as roots grow deeper into the waste body.

RESULTS

Effluent precipitation and settling dams, after closure.

The Vumbuka Reserve today.

Investigations undertaken by independent consultants show that waste in the former effluent dams can sustain a variety of plant and animal life and that waste below the root zone is being biodegraded into less hazardous substances. Indigenous plant life is flourishing in what was considered to be an extremely unfavourable environment, and is controlling infiltration whilst simultaneously aiding general clean-up of chemical contamination.

The ET cover has been approved by the Department of Water Affairs, subject to its effectiveness being monitored as part of the project's Environmental Management Plan into the future.

To reduce contamination at source in the drums area, augmented natural attenuation was the preferred remedial option. A bio-barrier was created to contain and, eventually, reduce pollutants in the source zone to acceptable levels. To create the bio-barrier nutrients and additional micro-organisms were introduced into the subsurface via injection wells in 2008 and early in 2009. The aim was to augment natural processes at work. Initial results are tentative but encouraging, indicating a good probability that by augmenting natural processes already underway, the time spans to effect clean-up can be shortened appreciably. The success of the work will continue to be monitored closely and it is hoped that the results of analyses to be carried out in 2010 will confirm the positive trend noted.

Throughout the project, a policy of transparency has been applied. During the evolution and implementation of the rehabilitation strategy, risks associated with historical chemical-related activities at Umbogintwini and resultant levels of contamination have always been made known to relevant parties. Progress is reported annually at stakeholder forum meetings and groundwater monitoring will be an agenda item at the UIC's quarterly Licence Advisory Forum meetings.

CONSERVATION AND EDUCATION

The Vumbuka Reserve has been transformed from a series of waste disposal dams into a conservation area with over 10 000 indigenous flora and increasingly diverse wildlife. When combined with the other already well established conservation areas at the UIC, namely Umbogavango and Mamba Valley, 77 hectares or 30% of the UIC's developed land is now a green belt. Some fencing at Umbogavango has been removed, creating a link with Vumbuka and allowing the free movement of wildlife, including the Cape Clawless Otter, between the various green belt areas. Umbogavango is characterised by coastal forest, secondary grassland and a herbaceous wetland. Vervet monkeys abound and Banded and Water Mongoose, Blue Duiker, and Spotted Genet are also seen. Over 200 bird species have been identified.

An alien vegetation eradication programme that began at Umbogavango in 2005 is being expanded to cover extensive new areas. A portion of the recreation area has been upgraded, with a section being paved to allow easy wheelchair access. Adjacent areas have also been re-grassed.

Two disused explosives magazines are within Umbogavango. One is being used to provide owl houses and perches, the other to establish a bat roost.

Thanks to the sponsorship of a number of site companies, the Umbogavango Resource Centre is made available to the Wildlife and Environment Society of South Africa for its environmental outreach programme.

Umbogavango, Mamba Valley and Vumbuka are open to visitors by appointment.