Chemical analysis and data logging of groundwater quality from three monitoring wells at the SKEWS Site, Campus Lichtwiese of TU Darmstadt

For the construction of the seasonal crystalline borehole thermal energy storage (SKEWS-project) at the Lichtwiese campus of the Technical University (TU) of Darmstadt, three groundwater monitoring wells were installed for monitoring purposes from 15.02. to 18.02.2022. These wells with depths of 24.5 m (GWM 1 and 2N) and 36.5 m (GWM 3) have filter sections of 6 m to 22 m (GWM 1 and 2N) and 8 m to 32 m (GWM 3) in the upper aquifer (Figure 1 and Table 1). The height of the upper edge of the pipe (Pegeloberkante = POK) changed since the final completion under the surface took place on the 20th of July 2022. The wells are positioned at a distance of approx. 20 m to 40 m in a triangular arrangement. The groundwater flow is south to north. The aquifer is likely fracture based in highly weathered basaltic rock with an estimated hydraulic conductivity of about 10-5 m/s to 10-6 m/s. Manual groundwater samples were taken twice a week. Automatic data loggers were installed for continuous hourly measurements. The measured depth of the logger in the water must be converted into absolute height values by calibrating it to the measurements on site. Missing readings from the data loggers related to low battery levels. Outliers resulting from battery changes and temporary extractions of the loggers from the well were removed. From 09.06. to 25.06.2022, the approx. 40 m deep pipes of the 4 geothermal borehole heat exchanger (BHE) were installed using the rotary method. The deep drilling of the three geothermal BHEs up to 750 m depth took place from 18.07. to 25.10.22, using both pneumatic and hydraulic down-the-hole hammers, as well as the rotary method with a clay-based drilling fluid. Significant water inflows below 40 m were observed with the pneumatic hammer, as well as water losses from the upper aquifer with the hydraulic hammer. Due to borehole instabilities and fractured zones, intermediate cementations and the use of clay-freshwater drilling fluid were necessary. Consequently, groundwater fluctuations and changes in the chemical composition were to be expected during this period. Short-term pumping tests were conducted on 07.06. - 08.06.22, 15.06. – 22.06.22, and on 08.06.23. Furthermore, from 05.10. to 17.11.2023, a Geothermal Response Test (GRT) was conducted on BHE 2 with a heating power of approx. 120 kW. The dataset consists of tables and figures for manual and automatic sampling. Furthermore, the well configuration and location are included in a separate file.

为在达姆施塔特工业大学（Technical University of Darmstadt, TU）利希特维瑟校区建设季节性结晶钻孔热能储存系统（SKEWS项目），项目组于2022年2月15日至2月18日布设3口地下水监测井以开展监测工作。上述监测井井深分别为24.5m（GWM 1与2N）与36.5m（GWM 3），其过滤器段均位于上部含水层中，其中GWM 1与2N的过滤器段范围为6m至22m，GWM 3的过滤器段范围为8m至32m（详见图1与表1）。该井管道的上沿高度（水位上沿，Pegeloberkante，简称POK）在2022年7月20日完成地下主体施工后发生了变化。监测井呈三角布局，井间距约为20m至40m。地下水流向为自南向北。该含水层赋存于强风化玄武岩地层中，大概率为裂隙含水层，估算导水率约为10^-5 m/s至10^-6 m/s。人工地下水采样频率为每周两次。布设自动数据记录仪以实现每小时一次的连续监测。需通过现场校准，将记录仪在水中的实测深度转换为绝对高程值。数据记录仪因电池电量不足出现过部分读数缺失的情况。因更换电池及临时将记录仪从井中取出所产生的异常值均已剔除。2022年6月9日至6月25日，采用旋转钻进法完成了4口地温钻孔热交换器（Borehole Heat Exchanger, BHE）约40m深的井管安装作业。2022年7月18日至10月25日，采用气动潜孔锤、液压潜孔锤及黏土基钻井液旋转钻进法，完成了3口地温钻孔热交换器的深钻进作业，最大钻进深度达750m。采用气动潜孔锤钻进时，观测到40m以下存在显著涌水；采用液压潜孔锤钻进时，上部含水层出现失水现象。受钻孔失稳及裂隙带发育影响，需开展中途固井作业并改用黏土-淡水钻井液。因此，该阶段预计会出现地下水位波动及地下水化学成分变化。项目组分别于2022年6月7日-6月8日、2022年6月15日-6月22日及2023年6月8日开展了短期抽水试验。此外，2023年10月5日至11月17日，针对BHE 2开展了地热响应试验（Geothermal Response Test, GRT），试验加热功率约为120kW。本数据集涵盖人工采样与自动监测的相关表格与图表，井体配置及位置信息则收录于单独文件中。