| dc.description.abstract | Climate change poses a threat to freshwater availability around the world, especially in dryland regions. Yunnan province of China is one such region that is facing this problem. Even though Yunnan rains just as much as the Netherlands, a country considered to be 'wet', the province is experiencing a shortage of groundwater which contributes to its degraded land and lack of water supply for its population. It follows that climate change is not the only factor contributing to the shortage of groundwater. The bedrock in the subsurface is fractured, allowing for rapid infiltration of water to seep towards deeper depths, which is why little to no groundwater is found beneath the soil surface.
To solve this issue, a cheap and environmentally friendly solution that can seal these subsurface fractures is needed to establish a groundwater table in the overlying soil. BioSealing, a proven technique developed by Deltares using nutrients to feed naturally occurring microorganisms in the soil to grow biomass to seal leaks, could be that solution. This leads to the research question of this study, which is "To what extent is the BioSealing technique effective in sealing a single hole fractured rock to establish a groundwater table in the overlying soil?".
To address the question, a sandbox type experiment with the BioSealing technique was conducted from a top-down approach under unsaturated conditions to seal a single hole plate that mimics a fractured bedrock. To observe the effectiveness of BioSealing, the decline in effluent flow rate was monitored and analyzed for its clogging factor. The saturation distribution was also measured for a potential rise in groundwater table by using the dual gamma-ray transmission method and 5TE sensors. To ensure that BioSealing took place in the correct area of the soil system, a bacterial count analysis was done per layer.
The experiment results were hindered by an unexpected outcome of a saturated tank, even though nutrients were not injected yet. This meant that establishing a groundwater table is no longer possible, so a decision was made to continue the experiment under saturated conditions. Despite the tank being fully saturated, the saturation measurements fluctuated for every measured location after some nutrients were present in the soil, indicating that BioSealing has taken place. The effluent flow rate declined with a clogging factor of 11 as a result. However, the extent to which this was due to BioSealing near the surrounding area of the leakage hole is doubtful because the bacterial count analysis revealed that most of it occurred just below the soil surface and only some happened near the leak.
As a consequence of the results, this research cannot fully address the research question but can conclude, to a small extent, that BioSealing is effective in reducing the seepage flow rate. Some knowledge and insights found in this study validated some theories and experimental results from BioSealing and bioclogging literature as well. | |
