Spectral map of landfill leachate

The Comhairle Nan Eilan Siar (Western Isles Council) Bennadrove landfill near Stornoway on the Isle of Lewis, Scotland, consists of a number of historical and active landfill cells, with an extension cell proposed to the site (Cell 1G). Some of the historical cells are unlined and there exists the possibility that cells 1B and 1D in particular are having some limited impact on groundwater quality to the south and west of the existing landfill.

As part of studies into the proposed extension, EGG Consultants Ltd have been commissioned to review existing groundwater chemistry data, especially with regard to potentially elevated concentrations of Ammoniacal Nitrogen, and advice is being given regarding additional sampling and data interpretation. Acquisition and analysis of these data are intended to develop conceptual understanding of hydrogeological system processes and behaviour in and around the landfill site.

The scope of works have the primary objectives of providing:

  1. An initial interpretation of existing groundwater hydrochemical data in terms of data quality, hydrochemical end members and including appropriate graphical representations such as box plots, piper diagrams, stiff diagrams, maps etc. The interpretation will also take into account pertinent local and regional environmental data (e.g. groundwater levels, borehole logs, geological structure where known etc.) as provided by Hydrogeologica Consulting.

  2. Recommendations for further groundwater hydrochemical monitoring, in particular advise on number, location and suite of chemical parameters to be measured in order to characterise source terms and monitoring points. Including advice on potential use of nitrogen isotopes for determining ammoniacla nitrogen sources.

  3. Interpretation of hydrochemical results obtained from the monitoring proposed in #2 above, with a view to determining interactions between the landfill site and surrounding groundwaters, e.g. transport times, mixing, dilution etc. and to also include, where appropriate, box plots, piper diagrams, stiff diagrams, maps etc.. The interpretation is also to include an assessment of groundwater level and other environmental data where appropriate to the analysis of the hydrochemical results, and reporting of the above.

  4. Ad hoc input to groundwater sampling project management/technical advice.

The project is ongoing and at present (February 2016) EGG Consultants are designing and costing for installation of all groundwater monitoring installations on site.

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