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型钻孔储热系统（SKEWS项目），项目组于2022年2月15日至2月18日安装了3口地下水监测井用于监测工作。上述监测井井深分别为24.5m（GWM 1与2N）及36.5m（GWM 3），其过滤段位于上部含水层中，范围分别为6m至22m（GWM 1与2N）以及8m至32m（GWM 3）（见图1与表1）。管道上沿标高（Pegeloberkante，简称POK）自2022年7月20日完成地表下最终安装后发生了变化。监测井以三角形布局布设，井间距约为20m至40m。地下水水流方向为自南向北。该含水层赋存于强风化玄武岩中，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；同时安装了自动数据记录仪以实现每小时连续监测。需通过现场校准，将记录仪测得的水下深度转换为绝对标高值。数据记录仪曾因电池电量不足出现读数缺失情况，且已剔除因更换电池及临时取出记录仪所产生的异常值。2022年6月9日至6月25日，采用回转钻进法完成了4组地热钻孔换热器（Borehole Heat Exchanger, BHE）约40m深度的管道安装。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回转钻进法，完成了3组地热钻孔换热器750m深度的钻进作业。使用气动潜孔锤钻进时，在40m深度以下出现了大量涌水；使用液压潜孔锤钻进时，则出现了上部含水层失水现象。鉴于钻孔失稳及裂隙带发育，需进行中途固井并采用黏土-淡水钻井液，因此该阶段预计会出现地下水水位波动及化学成分变化。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开展了热功率约120kW的地热响应试验（Geothermal Response Test, GRT）。本数据集包含人工与自动采样的相关表格及图表，此外，监测井的配置与位置信息收录于单独的文件中。