Bitterfeld - Risk Management Scenarios

Contents

Basic Scenarios

The first comprehensive remediation framework concept for Bitterfeld was completed in 1994. Until then, the risks to receptors were not as severe, particularly due to the remaining pumping activities. The conclusion that the groundwater itself constitutes one large source, lead to corresponding source-oriented measures.

The complete decontamination was considered technically and economically not feasible. Therefore, the main objective was the risk reduction while guaranteeing the continuous industrial use of the site.

The following primary measures were generally considered to take into account the scale of the contamination, the complex site-specific conditions as well as the development of the hydraulic conditions after the closure of the mining activites:

1. Complete enclosure of the industrial area by means of a sheet pile wall incl. the required hydraulic measures to catch the groundwater recharge;
2. Hydraulic retaining measures (groundwater withdrawal in the outflow N, E and SE) incl. treatment.

During the construction time but also as support, additional measures (so-called secondary measures) were foreseen, if needed to meanwhile hinder the mobilization and the migration of the contaminants in the groundwater. These measures included injection (possibly in combination with a wall), partial slurry walls, and additional groundwater withdrawal.

Further, in case of areas, where immediate action was required, use restriction and prohibited access was applied.

By means of research activities, it was proven that the input from the original sources (particularly landfill sites) does not contribute significantly to the already existing groundwater contamination. Hence, it was decided to treat the groundwater separately from soil issues.

The remediation framework concept was updated and concretized already in 1998, considering hydraulic safety measures for the protection of the city Bitterfeld and the community Greppin. Further, the installation of a sheet pile wall in the outflow or inflow direction of the industrial area was proposed including the required hydraulic measures in the inflow resp. outflow area. Also the implementation of reactive barriers was discussed. However, the results of the research project (SAFIRA) are still to be awaited.

The concept referred to two levels of receptors. 
-On the one hand, it aimed at the protection of the receptor groundwater, i.e. at the protection of the Risk Management Zone (RMZ). This part of the concept was generally developed on megasite-level. However, some elements vary according to the characteristics of the cluster (e.g. treatment facilities etc.) and the implementation is geared to the clusters regarding the management of the measure.
-On the other hand, all other receptors than groundwater are dealt with (as mentioned above: e.g. the residential areas) on cluster basis.

The implementation of a complete enclosure and the installation of sheet pile walls in the inflow or outflow were dismissed following a more intensive investigation of the technical feasibility. The reasons were:

• Low tool life / low long-time stability;
• Construction time 5 – 10 years requiring intensive hydraulic measures;
• Required depth approx. 50 m;
• Construction was considerably impaired by wires and pipes in the underground;
• Still need for "pump and treat" of considerable amounts of groundwater.

When the flood event took place in 2002, the entire situation accelerated and the management was more than ever forced to apply hydraulic measures to deal with the situation. Since then, the contamination is being mobilised and receptors are affected. Hence, the updated remediation framework concept (presented in 2003) focuses on the implementation of short-term effective hydraulic measures and immediate safety measures (closing of cellars etc.). On the mid- and long-term, the hydraulic measures will be complemented by source removal measures, and additional measures (e.g. NA) along the pathway aiming at the successive closure of the hydraulic measures on the long-term.

The basic measures and scenarios included in the current concept are presented in the table below.

The entire process of concept development has always been carried out on an estimative level considering technical feasibility as well as costs and benefits of risk reduction measures. In fact, in Bitterfeld, the entire section 3 has been gone through several times, but everytime on a more detailed level. The examples presented here represent the basic scenarios developed in the scope of a long-lasting iterative process including the continuous update of the boundary conditions and the risk reduction objectives. The costs and benefits assessment is included in the next step of the IMS.

The concept development can be taken in more detail from the deliverables D3.3 and D3.4.

Table 1: Technical feasible measures for Bitterfeld

Potential scenarios

Based on the preselection of the basic scenarios for the risk reduction in Bitterfeld, the potential scenarios were developed including the following 4 phases:

1. Hydraulic outflow measure;
2. Hydraulic outflow and inflow measure;
3. Hydraulic outflow and inflow measure and source removal;
4. Hydraulically controlled bioreactor.
   
   Except for the hydraulic inflow measure, all phases are planned to be implemented in each cluster of the megasite. The exception is due to the fact, that the area in cluster Bitterfeld North will in future be covered by the inflow measure of the cluster Bitterfeld South due to the changing hydraulic conditions (groundwater flow direction). 
   
   Currently, the first phase is being implemented. This part of the concept is the most elaborated one, since immediate action for the management of the hydraulic conditions and the contamination situation was required. However, the mid- and long-term concept including the next three phases is build on the existing measures. These potential scenarios constitute the remediation framework. The implementation of further technologies, especially innovative technologies, is allowed for planning within any phase of the remediation. 
   
   During all phases, the measures are always subject to optimization with regard to technical issues as well as cost-efficient implementation. The measures are supplemented by an appropriate monitoring to survey the efficiency of the measures and the expansion of the contaminants. 

1. Phase: Hydraulic outflow measure 

Hydraulic safety measure in the outflow of the megasite is aimed at hindering the further expansion of heavily contaminated groundwater out of the industrial areas. The withdrawn groundwater is treated by different technologies depending on the specific contamination. 

2. Phase: Hydraulic inflow measures 

Additional wells in the inflow of the megasite aiming at the optimization of the outflow measure: reduction of water volume to be pumped and treated in the outflow, thereby optimizing cost-efficiency. 
Additionally, the uncontaminated groundwater of the quaternary and tertiary inflow is catched up in order to prevent its contamination. 
The relief of the outflow measure also serves as preparation for phase 3 and 4 (partly shut off of the measure, see below).

3. Phase: Hydraulic measures and source removal 

Remediation of the sources is aimed at the reduction of the further input of contaminants providing for areas with sufficient potential for natural attenuation processes. 
At first, the further operation of the hydraulic measures in the in- and outflow is required as a transitional protection of the area. Depending on the success of the measure, first parts of the hydraulic outflow measure can be put out of operation. 

4. Phase: Hydraulically controlled bioreactor (MNA/ENA) 

When natural conditions are obtained to the greatest possible extent, monitored and enhanced natural attenuation are used to keep the residual contamination within the risk management zone and to achieve a long-term reversal of the trend. The processes are supplemented by the hydraulic measure in the inflow in order to control the reaction zones, creating a so-called hydraulically controlled bioreactor. 

Final scenario

The selection of the final scenario and the planning of the detailed design depends on the following aspects:

• The results of the hydraulic modelling
• The comprehensive risk assessment
• The definition of precise risk reduction objectives (target values, planes of compliance etc.)
• The decision made in terms of source remediation options
• The results of the research carried out within the SAFIRA-project at the Bitterfeld megasite with regard to the natural attenuation potential of the underground
• Etc.

Based on these activites, their results and the increased knowledge, the remediation framework concept can be finally designed in detail. As consequence, the comprehensive cost estimation can be carried out as well as the cost-benefit-analysis leading to the optimisation, the specification and the adjustment of the concept if required.