| Abstract |
The main objective in the research project called Optimal Utilization of Groundwater for Heating and Cooling in Melhus and Elverum (2015-2018) in Norway has been to provide a sufficient and sustainable base of knowledge for optimized utilization and management of the aquifer in the two town centers. Many open system GWHP in the center of Melhus have challenges with clogging of the injection wells due to iron and manganese precipitations, and/or filling of the wells with particles of sand and silt pumped with groundwater. Precipitation of iron and manganese reduce the capacity of wells and affects pumps, pipes and heat exchangers. The infiltration capacity is gradually reduced by the filling of the well screen part of the infiltration well. Therefore, the screened groundwater wells in sand and gravel aquifers, and especially the infiltration wells have gained special attention in this article. Re-infiltration of heat exchanged groundwater to the aquifer seems to be more challenging than pumping groundwater from a production well. Another important point is that the experience with the use of screened infiltration wells at least in Norway, is scarce and almost limited to the open ground source heat pump installations where the first ones were established around 20 years ago. Before the ORMEL-projects including the sequel ORMEL2, there has been little systematic studies on the use of groundwater for energy purposes in Norway. The experience from rehabilitation of an infiltration well in an open system GWHP installation at Melhus, namely Lena Terrace, has been used to illustrate the complexity of the problem to be addressed and the need for a systematic approach with the topic. Here a mix of both precipitation of iron oxides and sedimentations seems to occur. Theoretically and in general, we cannot exclude the possibility that some pumping wells also continuously produces suspended solids with the groundwater. The best rehabilitation results of the infiltration well at Lena Terrace seems to be the steaming and the sectional mammoth pumping. Rehabilitation of drinking water wells also often obtain good results with this method. However, the method is not widely used maybe due to limited availability by the industry and knowledge. Compared to production wells, the need of rehabilitation of infiltration wells seems to be more present with respect to both sediments and precipitation of e.g. iron and manganese oxides. Therefore, it is time to develop the steaming and mammoth pumping procedure further so that this well cleaning method is easily available, effective and can be used on a regular basis and before the infiltration rate in the infiltration well is critically low. Two more important issues are also addressed in the Lena Terrace case, namely the usefulness of the video inspection and the need for good surveillance of the operation of the open system GWHP. Video inspections document, and give a cost effective well condition analysis, and should be used before and after well rehabilitations in addition to hydraulic tests. The need of a central control and monitoring system is essential. With the new central control system available at Lena Terrace this winter, the last rehabilitation in July 2019 was initiated with basis in the monitoring of the water level in the infiltration well and done as a preventive measure before the situation got critical. This broad perspective and approach concerning the use of groundwater to energy purposes should continue taking into account the ongoing plans for establishing a large-scale system in Melhus. This involves further work with design, to understand precipitation mechanisms and conditions, to achieve effective operating strategies with routinely and cost-effective maintenance and targeted well rehabilitation procedures. |