If you have ever looked at groundwater monitoring results from different months and wondered why the data sets don’t match, join the crowd. Groundwater levels ebb and flow in seasonal cycles; these changes can influence problems from flood risk to how people sample.

Background groundwater levels are typically at their peak in late winter/early spring, although some delayed autumn peaks may be observed following very wet winters. This is because there tends to be more rainfall with cooler temperatures and less water evaporated away by growing plants. Additional rain is more likely to be able to infiltrate down into the soil and recharge aquifers. As a result, springs may flow at their peak in winter and early spring when pumping is generally not allowed, but through late spring into summer as the weather warms, increasing evaporation, and vegetation uses more water, groundwater levels can fall.

These latent patterns can be amplified by local conditions. With clay-heavy soils, infiltration may be slowed, whilst sandy or chalky ground will allow for greater recharging. Whether or not boreholes and monitoring wells will show accurate pictures of geological formations depends greatly on how large the rivers are, what their drainage area might be; construction dewatering practices often play a significant role, and even long periods without rain can lead to great distortion.

Different times of the year matter because they can alter how contaminants act. Pollutants that have been bound within soil may be mobilised by rising groundwater, or a contamination plume can further spread. Changes in levels can make sample concentrations look higher or lower depending on dilution, direction of flow, and where the sampling point is with respect to the water table. For Groundwater Remediation, visit //soilfix.co.uk/services/groundwater-remediation/

Many monitoring plans carry out multiple samples over different seasons to provide reliable decisions. This introduces greater clarity to actual groundwater conditions at your site, better informing remediation and drainage planning.