Dawn Keim 'IMVUL' Research project

Project title: Groundwater Vulnerability in the Unconfined Fractured Chalk Aquifer –East Yorkshire

Supervisors: Dr. Jared West, Dr. Noelle Odling, Dr. Pippa Chapman

Project description:

Groundwater quality is increasingly under threat from rising levels of pollution, especially from nitrates and pesticides (Fig. 1). Planning water treatment requirements for public well abstractions, and developing policy for regulation of agrochemical applications, requires better understanding of solute transport processes, especially those above the water table (unsaturated zone). This is because the unsaturated zone provides a buffer, in which pollutants applied at the ground surface may be delayed, degraded or attenuated before reaching the water table. The extent of delay depends on the characteristics of the aquifer but it is particularly difficult to predict for fractured aquifers, especially those with both fractures and a porous matrix like the Chalk, because contaminants can become trapped in the matrix, or alternatively bypass it via flow in fractures. Understanding flow behaviour and hence the range of pollutant travel times through the unsaturated zone of the Chalk is vital to predicting future trends in groundwater quality.

Figure 1. Rising nitrate levels in ground water abstracted from the Chalk aquifer (Supplied by Yorkshire Water Services Ltd)

This project comprises a study of the pollution vulnerability of fractured rock aquifers, focusing on the soil zone and unsaturated zone of the unconfined Chalk aquifer in East Yorkshire. Project research will mainly focus on investigations into the nature of water flow and contaminant transport in the unsaturated zone by monitoring inflows into an underground installation. Nitrate concentrations will also be monitored within the soil zone via sampling tensiometers and repeat core analysis, and in drip water collected from the underground installation deep within the unsaturated zone. A soil water balance approach will be applied to obtain a recharge estimate. The estimated recharge rate along with the concentrations of nitrate found in core samples from the soil and weathered chalk will be used to calculate a nitrate leaching rate. This project includes two experimental sites; a soil monitoring plot and an underground installation. The soil monitoring plot has been equipped with state of the art soil moisture probes (Fig. 2) and sampling tensiometers (Fig. 3). The underground installation has been equipped with drip collection units, flow rate monitoring devices and logging fluid conductivity probes (Fig. 4 & 5). Data will be collected over a two-year period, covering two hydrological recharge years.

Fig 2. Soil moisture probes	Fig. 3 Sampling tensiometer
Fig . 4 Drip collection & flow rate monitoring unit	Fig. 5 Conductivity probe

The results of the field experiments will be interpreted via mass balance approaches and modelling of unsaturated zone flow and solute transport. Field results will be compared to those from laboratory experiments conducted by network partners. Work will also be carried out with network industrial partners to develop practical tools for assessing groundwater vulnerability of the unconfined fractured rock aquifers and to evaluate potential future impacts of nitrate contamination on groundwater quality in a range of regulatory and climate change scenarios.