The overall goal of the project Cosma-1: “Geological CO2 storage and other emerging subsurface activities” is the assessment of potential impacts of subsurface activities on shallow aquifers used for drinking water production. The first two deliverables (D 1.1 and D 1.2) dealt with general approaches for risk assessment and a description of potential hazards and hazardous events, which might be a risk for shallow freshwater aquifers, as well as lessons learned from existing geothermal energy production and storage sites in Germany. This Technical Report describes the activities of the second phase of the project COSMA-1 and focuses on the compilation of geological and hydrogeological background data (average values) and the development of a simplified conceptual hydrogeological model for a setting typical for the Northern German Sedimentary Basin. The hydrogeological model of the Cenozoic includes Quaternary and Tertiary aquifers down to the layer beneath the Rupelian clay. On this basis, a numerical model with the program Modflow (PMWIN 5.3) was implemented as no complex geometries had to be considered. The structural geological model of the target formation for underground utilisation, the Detfurth Formation (Middle Bunter), incorporates four different fault systems with nine faults in total enclosing the area of interest. Further, a concept for modeling the interaction between deep, consolidated, saline aquifers with unconsolidated freshwater aquifers in a setting typical for the Northern German Sedimentary Basin was developed. This included the model selection, model parameterization, definition of boundary conditions and implementation in hydrogeological flow model software packages. In the further course of the project, a scenario analysis will be performed by using the numerical hydraulic model of the Middle Bunter and the simplified numerical groundwater model of the Cenozoic. The numerical models will be used to assess the key parameters, having an impact on the upconing of deeper saline groundwater beneath the well fields of water works (in shallow aquifer) due to imposed pressure signals.

This report summarizes relevant available knowledge on the removal of micropollutants from WWTP effluent in natural treatment systems such as constructed wetlands (polishing). Five studies were found investigating removal of various micropollutants in eight different full scale systems located in Spain, southern France, Korea and Sweden (all being different configurations of free water surface wetlands), demonstrating good removal (>80%) for more than 15 micropollutants compounds under summer conditions, e.g. diclofenac, ketoprofen, naproxen, ibuprofen, galaxolide, atenolol, ciprofloxacin, triclosan, glyphosate, ofloxacin and metoprolol. Hydraulic retention times (HRT) ranged from 0.25 to 30d. At HRT of 0.25d, only naproxen and atenolol were removed by >80% in summer, highlighting the importance of HRT for system performance. Another important factor influencing the removal is temperature and season with lower removal in winter. However, in warm climates (e.g. two studies in northern Spain and one study in southern France), reduction of removal efficiencies in winter is less pronounced with values for removal of the majority of investigated pharmaceuticals in winter still being >60%. In 4 FWS wetlands sampled during winter at sub-zero temperatures in Sweden, though, removal was mostly below 50%. A variety of removal mechanisms simultaneously occur in natural treatment systems and are relevant to varying extent for each compound and system type. Important removal mechanisms are biodegradation (e.g. for naproxen, ibuprofen), photodegradation (e.g. for diclofenac, ketoprofen, sulfamethoxazole) and adsorption (e.g. for galaxolide, tonalide). The relevance of plant uptake and phytodegradation as removal mechanisms is not fully understood; however, a few studies demonstrate the translocation of pharmaceuticals (e.g. carbamazepine) to plant tissue. For biodegradation, redox conditions are an important parameter influencing microbial degradation pathways. Design guidelines for eco-engineered treatment systems targeting the removal of micropollutants are not available to date. In addition, data necessary to dimension ecoengineered treatment systems that target the reduction of micropollutants in WWTP effluent (e.g. kinetic data such as removal rates and its dependence on temperature) is lacking. For the development of design guidelines for eco-engineered systems targeting the removal of micropollutants, removal rates for each system type and compound and their dependence from temperatures needs to be determined for all compounds of interest. Furthermore, more research is necessary for a deeper understanding of processes in eco-engineered systems, especially the relevance of the different removal mechanisms and conditions for removal for each individual micropollutant of interest. Nevertheless, eco-engineered treatment systems are a promising technology for polishing of WWTP effluent, including further removal of micropollutants.

The adoption of decision support tools for the definition of cost-effective strategies is seen to gain more importance in the coming years. This development is due for one part to the general degradation of the existing systems and for the other part to changes into the regulations and demands for more transparency in decision-making (Ana and Bauwens, 2007). A key element of decision support systems is the ability to assess and predict the remaining life of the assets (Marlow et al., 2009). For this purpose, deterioration models have been developed to understand and describe the sewer aging based on available CCTV inspections and a list of factors that influence the deterioration. This report first describes the potential sewer deterioration factors and analyzes a panel of literature case studies regarding the relevance of each factor on sewer deterioration. Results are hardly directly comparable, because of the different construction practices, historical backgrounds and environmental conditions of the networks investigated. However, some trends regarding the most significant factors may be identified. In most studies, the construction year and the material seem to be the most relevant factor to explain sewer aging. Pipe size, depth, location and sewer function show generally a medium significance on sewer deterioration. Pipe slope was found to have a low significance for the structural deterioration, but a high relevance on the hydraulic deterioration. The effect of other factors as pipe shape, pipe length, soil type, sewer bedding, presence of trees, installation method, standard of workmanship, joint type, and ground water level have been highlighted but rarely or never investigated. On a second step, this report presents three main approaches for sewer deterioration modeling: deterministic, statistical and artificial intelligence based models. The models can be further categorized into pipe group and pipe level models (Ana and Bauwens, 2010). Pipe group models (e.g. Cohort survival or Markov) can be used to predict the condition of a group of sewers or cohorts and are useful to support strategic asset management, i.e. the definition of long term strategies and budget requirements. These models enable to evaluate the efficiency of several scenarios at the network scale. Pipe level models (e.g. regression, discriminant analysis, neural networks) can be used to simulate the condition of each single pipe. They may be useful to set priorities and justify asset management operations. Pipe level models are tools that can support the utilities in the short and mid-term planning and determine at a finer resolution how, when, and where to rehabilitate sewers. Literature results indicate that cohort survival and Markov models are two useful approaches for modeling the degradation of pipe groups. However, the quality of prediction of these models depends highly on the availability of a large amount of inspection data. Extensive datasets are required to create representative sewer groups (cohorts) with sufficient inspected sewers in each condition state. Regression and Discriminant Analysis were tested on several case studies but showed pretty low prediction performances. Three main reasons could be (i) the non-validity of model assumptions, (ii) the biased distribution of the datasets in terms of number of samples for each condition state and (iii) the lack of data for important deterioration factors. Neural networks have proven to be successful tools for the prediction of the deterioration of individual pipes. However, they require (i) relatively complex and time-consuming training processes and (ii) extensive datasets of CCTV inspection and deterioration factors. Only very few case studies intended to evaluate the quality of prediction of these deterioration models. Furthermore, validation results are often contradictory and hardly comparable since (i) the data available for model calibration differ (percentage of CCTV available, type of deterioration factors available) and (ii) the metrics of the methodologies used to assess the quality of prediction differ. Thus, there is still no clear conclusion about the best modeling approach depending on the modeling purpose (pipe group or pipe level). There is also no clear conclusion regarding the quality of prediction that can be reached since in most case studies only a few percentages of CCTV data were available and many data regarding potential deterioration factors were missing. Further research work is needed in order to (i) identify the most appropriate modeling approach depending on the modeling purpose, (ii) understand the influence of CCTV data availability on the modeling results, (iii) analyze the influence of input data uncertainty (CCTV and deterioration factors) on the modeling processes and (iv) find out the optimum input data requirement (availability of CCTV data and deterioration factors) for model calibration.

Increasing subsurface activities like geothermal energy production, unconventional gas exploitation (EGR – enhanced gas recovery), enhanced oil recovery (EOR) or geological carbon dioxide storage (GCS) are potentially hazardous for the environment. Especially fresh water aquifers used as drinking water resources need to be protected. The first phase of the project COSMA focuses on potential hazards and hazardous events arising from those activities and aims at developing an approach for quantifying and comparing potential risks. A general description of hazards and hazardous events resulting from emerging subsurface activities is given in the first deliverable D1.1 “Geological CO2 Storage and Other Emerging Subsurface Activities: Catalogue of Potential Impacts on Drinking Water Production”. In this 2nd deliverable, reported hazards and hazardous events resulting from geothermal energy production in Germany are described. This report includes analyses of enquiries to experts from all federal states, State Geological Surveys, information from standardization committees, developers, planners, drilling contractors, expert committees, consulting engineers and regulatory authorities such as environmental agencies, water authorities and mining authorities as well as from media reports. It aims to list and categorize observed impacts arising from recent geothermal projects, as there have been increasing activities in this field in the past 10 years in Germany and because there are many similarities to other subsurface activities with respect to drilling processes, fracking methods and reinjection of fluids. The German classification of geothermal systems distinguishes between shallow or nearsurface (< 400 m depth) and deep geothermal energy (> 400 m depth) systems, which will be used in the following chapters. Table 1 shows the difference to international classification schemes, regarding enthalpies and temperatures. The reported case studies of failures potentially leading to contamination of freshwater aquifers are described in chapter 2 with respect to the setting and the reason for failure (if known). Chapter 3 gives some recommendations with respect to possible precautions and countermeasures to prevent such potentially hazardous events. Regardless of the drilling depth there are general hazards and hazardous events that must be taken into account for all subsurface activities. Amongst these are hazardous events during operation which can lead to a contamination of the site, hazardous events during drilling caused by wrongly selected drilling techniques, drilling into unknown caverns, cavities or caves or faulty casing, construction or plugging (sealing). Furthermore, unexpected chemical reactions between fluids and casing or sealing material (e.g. grout) can cause seepage or leakage and therefore hydraulic short circuits. Table 2 gives a summary of general impacts of drilling, especially when multiple aquifers are intersected, as well as from operation of geothermal facilities. Further details are given in COSMA-1 report D 1.1.

Im BMBF-Forschungsverbund „Risikomanagement von neuen Schadstoffen und Krankheitserregern im Wasserkreislauf (RiSKWa)“ wurde die Definition von „Indikatorsubstanzen“ als ein interessantes Querschnittsthema identifiziert. Es wurde dazu eine Arbeitsgruppe gebildet, die sich die Aufgabe stellte, einen Leitfaden zur Zweckbestimmung, Auswahl, Bedeutung und Interpretation von polaren organischen spurenstoffen als chemische Indikatoren zu verfassen. Mit Hilfe der Indikatoren sollten insbesondere anthropogene Veränderungen der Wasserqualität erkennbar sein, sowie natürliche Prozesse und technische Aufbereitungsverfahren überwacht und gesteuert werden können. Diese Indikatoren dienen nicht der Bewertung der Wasserqualität. Mögliche Anwender sind die Bearbeiter in den Verbundvorhaben des RiSKWa-Programms und in weiteren Vorhaben in den Bundesländern, die sich mit Spurenstoffen befassen, Fachbehörden, Forschungseinrichtungen, Wasserlabors der Trinkwasserversorgung und Abwasserreinigung und Ingenieurfirmen, die wassertechnologische Themen der Spurenstoffentfernung bearbeiten. Einen Überblick über mögliche Quellen, Eintragspfade und Barrieren im Wasserbereich zeigt die folgende Abbildung aus dem Bericht eines DECHEMA-Arbeitsausschusses „Pfad- und wirkungsspezifische Indikatorsysteme für Wasser- und Bodensysteme“ (Leitung: W. Dott). Dieser Leitfaden wird dabei sehr wesentliche Teile des dargestellten Systems behandeln.

Wastewater reuse is increasingly considered as possible alternative water source for diverse non-potable uses. Among the major questions, defining which water quality for which reuse is required is crucial. If the demand for reclaimed water is seasonal, the question of reclaimed water storage is also essential. Aquifer recharge for further nonpotable reuse can be a solution to address many final reuse applications, including indirect agricultural or landscape irrigation, saltwater intrusion barriers, subsidence mitigation/aquifer replenishment or other non-potable reuses. Most of the aquifer recharge applications of wastewater reuse so far rely on high-pressure membrane systems or even double-membrane combined with advanced oxidation processes. However, when non-potable reuse is targeted, or the replenishment of a threatened aquifer is planned, recharge with high-quality non-potable water could be envisaged as acknowledged by the legislation of several countries. In this report, the performance of hybrid disinfection/filtration and recharge schemes is assessed in comparison to a high-pressure membrane system working under similar conditions. Among the portfolio of available disinfection and filtration technologies, five treatment trains were chosen – combinations of ozone or UV treatment with sand filters or UF membrane and final infiltration or injection – and compared to a double-membrane system (UF+NF). A synthetic secondary effluent (SE) was considered for this conceptual study on the basis of a worldwide survey of typical SE water qualities. The major legislations from the WHO, the USEPA and Australian guidelines were considered to define the water quality to be reached by these hybrid treatment schemes. The low targeted value in suspended solids (10 mg/L) and microbiological contaminants (1 fecal coliform / 100 mL) requires extensive disinfection and filtration processes. The proposed schemes were selected on the base of a large review of typical pollutant removal efficiencies found in the literature. To perform a comparative Life-Cycle Assessment of the different treatment trains, similar assumptions were made in all cases for a hypothetical case study of a 50,000-PE reuse plant downstream of a secondary sewage treatment plant. All five proposed hybrid treatment trains are capable of supplying very high non-potable water quality, and the combination of disinfection, filtration and aquifer passage proved to be an efficient combination for removing suspended solids, residual BOD and microbiological contaminants. The environmental performance of the treatment trains was compared in terms of carbon footprint, but also energy demand, human toxicity, acidification impact and land footprint. Both the energy demand and carbon footprint of hybrid schemes was found to be considerably lower than for a double-membrane system, besides offering an additional storage solution in the aquifer. Thus, there is a significant margin for lowering the environmental impact, energy demand and operational costs if non-potable water quality is sufficient for the reuse goal. However, the legal context and social acceptability may represent barriers for this intended recharge of nonpotable water to the aquifer. This conceptual study has shown the potential of hybrid solutions to provide high-quality non potable water for aquifer recharge and further reuse. A large portfolio of solutions was proposed to reach the intended non-potable uses. To assist the selection of adequate treatment trains, the strengths and weaknesses of the solutions can be summarized in a decision tree taking into account the reuse goal, aquifer type and space availability, and selecting the least energy-intensive solution for a given legal and sociocultural context.