Surface and Groundwater Interactions Location of a sub-surface remediation trench.

Abstract

The Water Framework Directive aims to achieve at least “good status” of all surface and groundwater bodies by 2015. In 2009 programmes of measures to achieve this status must be implemented. In 2012 water quality response to these measures will be examined at river basin catchment level. The adoption of the Water Framework Directive from the 1st January 2007 restricts the amount of nutrients which can be applied to agricultural land. A nutrient discharge to a waterbody has a negative impact on the environment and may lead to eutrophication. A broad strategy exists at European level to minimise nutrient loss to a waterbody. This strategy examines the source/pressure, pathway and receptor approach for nutrient transport. Such nutrient management strategies try to minimise nutrient loss while maintaining productivity. Nitrogen usage is now associated with environmental degradation even at lower levels than the maximum allowable concentration (11.3 mg NO3-N L-1). A further strategy proposes that nutrient management and increased utilisation of nutrients alone will fail to recognise nutrient loss even at high levels of efficiency. This strategy attempts to use remediation (Nitrate) and control technologies (Phosphorous) to intercept nutrients before discharge. Another function would be to further reduce concentrations presently at allowable levels. This introduces an interceptor phase into the nutrient transfer model. Groundwater characterisation leads to a better understanding of the nutrient source and pathway to a groundwater or surface water receptor. The interactions between surface runoff, sub-surface drainage (man made) and groundwater are important when dealing with the source pathway receptor concept. Interactions between shallow groundwater and surface water should also be considered. The deeper groundwater body and surface water interactions should also be characterised. A monitoring network incorporating surface, subsurface and groundwater elements was created on the Teagasc Environmental Research Centre, Wexford. A sub-surface drainage system was characterised and water quality monitored. Some breaches of the maximum admissible levels (MAC) of nitrate in groundwater were found in two separate locations (Dairy and Beef farms). A review of remediation options proposed a sub-surface denitrification trench to remediate excess nutrient loss on site. The location of such a permeable reactive barrier in the field to intercept a nitrate plume was investigated. The following investigations were carried out: • A review of “Groundwater remediation systems for the treatment of agricultural wastewater to satisfy the requirements of the Water Framework Directive” was carried out. This proposes options for Ireland. • The groundwater characterisation of the Dairy Farm in Teagasc, Environmental Research Centre, Wexford. • The groundwater and subsurface drainage system characterisation of a 4.2 ha field site on the Beef Farm in Teagasc, Environmental Research Centre, Wexford. • A methodology for the location of in-field remediation techniques was established.