Bitterfeld - Risk Assessment

Contents

Megasite characterization

Priority contaminants

In the scope of the activities of the three main industries at the Bitterfeld megasite (open-cast lignite mining, production of energy, chemical industries), more than 5.000 different products and compounds were produced until 1990, in an area covering about 10 km2.

A wide range of these products, including their by-products, metabolites and waste products, has entered the soil and groundwater. In order to enable a focus on the most severe contaminations and the priority risks, the contaminants have been categorized by priority level based on their detection frequency, concentration and toxicity potential. The derivation of the priority contaminants can be facilitated by the PriCon-tool , which was developed within the WELCOME project based on a method invented by Kerndorff.

A selection of the priority contaminants for Bitterfeld and their priority level are shown in the following list:

Clustering

Risk clusters

In Bitterfeld, five clusters have been derived on the basis of the information listed below:
Data and maps of the contamination situation present in all three aquifers (quaternary, tertiary, tertiary base)
Data related to the geological and hydrogeological structures of the area of concern and groundwater dynamics and levels
Data concerning the protective goods present (land use), potentially endangered protected goods as well as land ecosystems
The relevant factors taken into account for the development of the clusters are the following:

• Contamination situation
  • dimension of contamination in all three aquifers (quaternary, tertiary, tertiary base)
  • concentration levels and spreading
  • contaminant characteristics

• Site characteristics
  • geological and hydrogeological structures, aquifers and aquicludes
  • predominant groundwater flow direction towards the receiving stream Mulde, varying particularly in the south due to former mining activities
  • groundwater dynamics: varying due to former groundwater depression and flooding
  • significant groundwater withdrawal (existing hydraulic measures)

• Potentially affected protective goods
  • land use (residential areas, recreational areas, agricultural areas, protected areas)
  • depth to the groundwater, related to land use (affected residential areas, groundwater reservoirs)
  • sensitivity of the protected goods

Overlaying these information lead to the definition of the four cluster areas. They are characterized by the following criteria:

• similar contaminant potential originating from one or more major sources (e.g. land-fills)
• similar groundwater flow direction
• similar situation concerning the protected goods (city of Bitterfeld, community of Greppin, protected areas, surface waters).

Considering the information mentioned above, the following clusters were created:

• Cluster North
• Cluster Northeast
• Cluster Greppin
• Cluster Bitterfeld North
• Cluster Bitterfeld South

Modelling

Hydraulic model for Bitterfeld 

1 Basics 

A hydrogeological structure model as well as a hydraulic flow model were generated for the entire megasite Bitterfeld. Based on the modelling, the planned hydraulic measures are designed and optimised. The presented example shows the optimisation of the hydraulic outflow measure (safety measure) and the hydraulic inflow measure as the first and second phase of the remediation framework concept for Bitterfeld. 

The hydraulic model is based in the hydrogological structure model for the Bitterfeld megasite and includes the area with the coordinates 

The grid width of the model is 25 m, thus each model layer comprises 40128 cells. The model is vertically divided into 17 layers: 

The 3D - hydrogeological structure model is presented in the figure below. 

Site to be modelled
file:///N:/Projects/1202000/1202387/C.%20Report%20-%20advise/WP3/IMS%20(E)/euwelcome/kims/examples/megasite08c2.html?index=130&sec=2&meg=bitger#

2 Parameters 

All hydrogeological layer units are characterised by specific average values for permeability. Specific partial areas are further characterised by reduced permeabilties due to the contamination. As soon as the distribution of parameters has been determined area-specifically for each layer complex, the model will be adjusted and updated. 

Regarding the pore space (total pore space and effective pore space), standardised literature values are used for each layer complex unless laboratory results exist. 

3 Boundary conditions 

3.1 Initial water level (calibration version) 

Initial water levels for the model calibration are defined by the hydroisohypses generated based on the measurement carried out for the upper micaceous sand (layer 13) in October 2003. 

The water levels at the edge of the model are partially linearised and defined as constant head. 

3.2 Groundwater withdrawal 

Groundwater withdrawal for the calibration is defined according to the date of the calibration (October 2003). 

The safety measures at the residential area Bergmannshof/Annahof are considered based on a so-called H-control (i.e. the correspondence of the target values) in all versions. 

*3.3 Groundwater recharge* 

The groundwater recharge for the areas outside of the industrial area (mining pits, residential areas, areas with alluvial clay) is classified based on estimations. A qualified approach can only be applied after the successful modelling of the soil water balance. 

Inside the industrial ares, groundwater recharge categories are determined area-specifically according to the mappig of the sealing in december 2003 and assigned to the grid cells by a complex mathematical procedure. Categories with 25mm/a are defined. Thus, in the model, the groundwater recharge varies in categories from 0 to 225 mm/a. The recharge is assigned to the top of the active layer. 

4 Calibration 

The calibration is done based on approximately 100 calibration wells of the measurement in October 2003 as well as on the hydroisohypses resulting from the measurement in order to optimally correspond to the hydraulic regime. 

The statistical deviation of the calculated mean water level from the measured one amounts to < 5 cm, the mean deviation in the entire model area is < 30 cm. An exact calibration is only possible after the definition of the parameter distribution in each aquifer. 

5 Simulation of groundwater withdrawal and recharge versions 

Based on the calibration version for October 2003, different versions are calculated showing the effect of the groundwater withdrawal by the hydraulic outflow and inflow measure (see figures below), also in combination with different sealing measures in the industrial areas. Based on the model results, both measures are optimised. 

The efficiency of the hydraulic containments is verified by calculating pathlines. As result, e.g. the hydraulic regime was adjusted until a reversal of the contaminated groundwater could be excluded. 

Modelling matrix

Geological structure model

Determination of risk

The risks at the Bitterfeld megasite are determined based on the legal standards for the different currently or potentially affected receptors. Depending on the receptor and its use, different directives apply as shown in this table (pdf). However, as the table shows, only few standards exist for the relevant contaminants. Therefore, further international directives and values as well as toxicity values were consulted. These are listed here (pdf) for a selection of the priority contaminants relevant at the Bitterfeld megasite. 

In case of the receptor groundwater, the insignificance values prescribed by the LAWA (see: starting IMS -> Organizing stakeholders)were used to display the contamination situation. The exceedance of these values based on the sum of the concentrations of the priority contaminants measured at the megasite in 2001 is shown in these maps.

Quaternary aquifer




Tertiary aquifer



From these maps, priority areas can be derived in terms of the protection of the receptor groundwater, i.e. the safeguarding of the Risk Management Zone (RMZ). Further, areas might be identified, where other receptors are impacted or at (immediate) risk. This information has already been included in the cluster derivation.

At this stage of the megasite management, the focus is still on the safeguarding of already affected receptors and particularly endangered areas (groundwater as well as other receptors) according to the derived priorities. For these areas, the risk assessment has been carried out based on sub-models, and respective risk reduction measures have been implemented (e.g. safety measures in the community Greppin and the city Bitterfeld as well as the residential area Bergmannshof).

The complete risk assessment for the entire megasite, including the definition of planes of compliance and local threshold values, will be done based on the groundwater model for the complete megasite. 

Finalize clustering

A general determination of remediation targets applying to the entire Bitterfeld megasite or even only its clusters is impossible due to:

• the highly varying degree of the contamination of the soil,
• as well as of the groundwater over the entire area
• and the wide range of potential receptors
  
  

It can be stated that – according to the EU-Water Framework Directive - the overall goal of the management of the contaminated groundwater is the achievement of a “good condition” of the groundwater, i.e. the reduction of the anthropogenic impact to the largest possible extent. This includes the prevention of further spreading of the contamination and the reversal of the trend. However, at this stage, the initial goal is the definite protection of the receptor groundwater outside the Risk Management Zone (RMZ) and other receptors inside the RMZ. 

The remediation of soil is considered in the case that the soil contamination leads to a significant deterioration of the already exsiting groundwater contamination and in the scope of construction activities. 

Based on these aspects, general risk reduction objectives for Bitterfeld were established, which are listed below. At this stage, the management of the Bitterfeld megasite aims on the prevention of any further impact on the site and its surroundings, i.e. limiting the damage. Precise risk reduction objectives and respective specific threshold values and planes of compliance are determined based on the megasite risk assessment, which in the case of Bitterfeld is currently being carried out. 

The following general remediation strategies and objectives for groundwater were formulated:

1. The main principle is the protection and remediation.
2. Further spread of contaminants from the polluted areas (“yellow area”) into unpolluted groundwater areas is to be prevented by safety measures.
3. Further spread of contaminants from heavily polluted areas (“red area”) into less contaminated areas is to be prevented by safety measures.
4. Remediation targets are to be achieved in accordance with the receptors in a long-term process with frequent re-evaluation.
5. The choice of safety and decontamination measures takes into account the proportionality and technical feasibility of the measures as well as the corresponding target values in each case.
6. The area of groundwater contamination is to be observed by an appropriate surveillance monitoring, which has to continue as a steady measure.

In addition to that, it has been contractually guaranteed to maintain a specifically defined depth to groundwater table in the area of Bitterfeld serving two aspects:

• protection of buildings (statics), lines and wires from corrosive groundwater and
• preventing the exposition of receptors (e.g. flooding of cellars with contaminated groundwater).
  
  

The surface water has to be taken into account in terms of a receptor, since the rivers and the lakes are the receiving streams for the entire contaminated groundwater area.

1. Each groundwater contaminant should be evaluated concerning its discharge into surface water. It is recommended, that the toxicity, the carcinogenic properties and the potential danger for water of each component is to be examined and qualified in each case with regard to the respective surface water. The examination should be supplemented by a consideration of the load.
2. The compliance of the threshold values for groundwater in principal implies the compliance of target values for surface water.
3. The required surface water values are checked regarding the groundwater flux of relevant parameters.
4. The same target values as for groundwater count for surface waters which are fed by the groundwater (baseflow) of the megasite. With regard to the load consideration, the amount of the baseflow into the respective surface water should be determined.
   
   

In terms of the discharge of treated water from the plants into the surface waters, the target values for the discharged water are to be established within a legal proceeding according to water law. 

Re-adjustment of RMZ 

The re-adjustment of the RMZ is still to be done when the risk assessment for the entire megasite has been carried out.