Groundwater seepage, soil saturation and associated erosion and subsidence have been occurring adjacent to a college building in Preston, Lancashire. The source of the seepage was unknown, and thought to be associated either with naturally occurring groundwater or due to leakage from water pipes in the vicinity of the college. Determination of the source of the seepage was required in order to address the problem.

EGG Consultants Ltd conducted water sampling from groundwater discharge and local tap water. Interpretation of water chemistry was undertaken with a view to determining whether it represented natural groundwater seepage or leakage from mains or other water pipes. Water samples were analysed for:

• Field parameters (pH, electrical conductivity, dissolved oxygen, temperature)
• Major ion chemistry (Na, K, Ca, Mg, Cl, SO4, Alkalinity)
• Dissolved organic carbon
• Biological oxygen demand
• Drinking water byproducts (trihalomethanes and chlorine)

In combination with review of a previous site investigation (drilling) by a geotechnical contractor, it was found that natural groundwater discharge was much more likely to be causing the observed seepages, due primarily to the underlying geology and the topography of the site. These findings also explained the measured water chemistry. A further proposal is currently with the college to find a solution to the problem.

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