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WP 1.8

Geochemical impact investigations of near-surface geological heat storage in urban areas


WP 1.8 represents the largest working package in ANGUS+ and includes the four subject areas described in the following:

1. Development and application of rapid tests for the quantification of site and sediment specific near-surface changes of the hydrogeochemical groundwater composition as a function of temperature

(Nicolas Koproch, Ralf Köber, Andreas Dahmke)

To enable site specific estimations of possible process changes induced by temperature increases of up to 70°C even in a practically suitable timeframe of 3-6 month, rapid test are developed. For this purpose batch test are compared with short-term and long-term column experiments, the possibilities for giving evidence are identified and transfer terms are set up if possible. In consideration for this purpose are the main affected changes: microbial catalyzed redox processes, mineral dissolution and precipitation, sorption and gas formation. Different sediment types are used for the respective investigation approaches to check the transferability of the method of testing and to describe geochemical, geophysical (WP 1.4) and microbiological (WP 1.9) changes that can be expected for typical aquifers of North Germany. The obtained results additionally are used for verification of the software developed in WP 2.4.





2. Impact quantification of heat transfer liquids leakages from geothermal heat probes

(Cordula Dörr, Ralf Köber, Dirk Schäfer, Andreas Dahmke)

A risk analysis with regard to ground water concerning the leakage of heat transfer liquids from technical installations is performed on basis of literature research, experimental investigations and numerical model simulations. The literature research includes an updated review on the degradation of organic components of heat transfer liquids (glycols), a research of heat transfer liquid additives (corrosion inhibitors, biocides, wetting agents, fragrances and colourings), the influence of additives on glycol degradation and retention behavior of additives. Previous degradation investigations for glycols and additives were essentially performed as batch tests. But due to unrealistic mass ratios between sediment and solution and non-consideration or underestimation of specific processes (e.g. diffusion limitation), batch tests are normally not particularly suited for degradation quantification and corresponding model prognosis. For these reasons, additional experiments are performed in more realistic flow through systems (column tests) and are accompanied by microbiological investigations (WP 1.9).



3. Quantification of the temperature dependent release characteristic behavior of chlorinated hydrocarbons

(Nicolas Koproch, Ralf Köber, Andreas Dahmke)

The release and mobility of organic contaminants (e.g. chlorinated hydrocarbons) is influenced by different temperature dependent characteristics like e.g. contaminant solubility, sorptivity, viscosity, surface tension and molecular diffusion, which generally lead to increased mobility with increasing temperature. These influencing factors cannot yet be regarded as finally investigated, but there are various studies that can be taken as basis for the preparation of model prognosis. These studies however are based on column or batch test and investigated and quantified only isolated processes. So far there is a lack in more complex studies investigating the interaction of the different temperature dependent sub-processes. To therefore quantify the influence of increased groundwater temperatures on the release and mobility of organic contaminants under close-to-reality conditions, tank experiments with inserted residual NAPL phase are performed at temperatures from 10 to 70°C. Variation of boundary conditions like hydraulic conductivity, flow velocity and NAPL source architecture enables the representation of different contamination scenarios and provides a data collection to verify the developed model approach (WP 3.4). The test design is respectively pre-optimized by numerical simulations.



4. Quantification of temperature dependent mobility behavior of trace elements       

(Svea Hausberg, Markus Ebert, Frank Dethlefsen, Andreas Dahmke)

In the course of heat energy storage, the sorption limited mobility of potential inorganic groundwater contaminants may be influenced, whereby studies regarding a temperature dependence of sorption processes are strongly underrepresented in literature. However, a temperature variation may be induced by geothermal applications or leakages of formation water. For this reason, cation and anion sorption reactions in dependence of varied temperatures are investigated. Zinc and arsenate are used as model substances due to their geogenic abundance in near surface aquifers, where they are associated with sulfide minerals or Fe(III)(hydr)oxides. Additionally, their sorption behavior has already been intensely investigated by applying experiments at ambient temperatures, so that parameterized surface complexation models under normal conditions exist. The investigation of temperature dependent sorption limited mobility are carried out with temperated circulating column test, temperated normal pressure column tests with synthetic sediment mixtures, a high pressure experiment, as well as the titration of surfaces charges at different temperatures and additional batch experiments. At first the results are evaluated using simple geochemical modelling approaches, so that a general reaction scheme can be developed, which can be included in more complex models (WP 2.3 and WP 3.4). In addition, these studies aim at deriving a transfer function to combine different sorption isotherms, created at different temperatures, in a “variotherm surface” or, if necessary, in a “variotherm space” to describe sorption processes coherently at variable temperatures. This approach will be opposed to an extension of surface complexation models to varying temperatures, for the evaluation of a more suitable approach to the description of temperature dependent sorption limited mobility.