Mahmoud El Araby 'IMVUL' Research project

Project title: Borehole water level response to barometric pressure as an indicator of groundwater vulnerability

Supervisors: Dr. Noelle Odling, Dr. Jared West, Dr. Roger Clark

Project description:

Atmospheric (barometric) pressure changes that accompany changing weather can have a significant effect on water levels in monitoring boreholes. The magnitude of this response depends on whether the aquifer is confined or unconfined, and on the properties of the aquifer and its overlying units. The nature of the aquifer response to barometric changes is a measure of the extent to which the aquifer is confined with the greatest responses shown by boreholes in well confined aquifers. Thus the response also reflects the effectiveness of a confining unit as a protective layer against aquifer contamination and therefore groundwater vulnerability.

In this study the response of monitoring borehole water levels to changing barometric pressure and the use of such data to characterize groundwater vulnerability in the confined/semi-confined region of the Chalk aquifer in East Yorkshire, UK. The chalk aquifer in East Yorkshire is an important source of water for industrial and domestic use and water quality is threatened particularly by nitrates from agricultural fertilizers. A pilot study has already shown that the response of water levels in monitoring boreholes to barometric pressure varies with the nature of the confining unit of this aquifer (see Figure). The present project will seek to quantify these variations in terms of confining unit properties and link this to groundwater vulnerability.

In the project, time series data on water levels and barometric pressure will be collected automatically from boreholes (using programmable pressure transducers). The use of historic hydrographs will also be investigated in collaboration with the Environment Agency and Yorkshire Water (associated partners in the IMVUL network). These data will be analysed for the properties of the aquifer and the confining units using signal processing techniques developed for earthquake and exploration seismology. The results will be compared with the structure of the confining units as revealed by geophysical surveying (GPR and resistivity) in the vicinity of selected monitoring boreholes. Corrected water level records will also be used to investigate the hydraulic environment within the aquifer such as response to near and distant pumping, surface drain levels and springs, and to refine source protection zones for abstraction wells. Transient flow modeling (with e.g. MODFLOW) will be used to investigate the sensitivity of borehole responses to confining unit heterogeneity. The results of data analysis and modeling will be used to develop a methodology for the use of monitoring borehole water level and atmospheric pressure records in assessing groundwater vulnerability in confined and partially confined aquifers.