Groundwater is protected by the installation of a 1.5m thick low permeability clay liner and HDPE liner in the base of the site. Groundwater varies between 6.2m and 9.8m below the base of the site.
Groundwater is monitored in 16 boreholes strategically installed around the site. From each borehole on a monthly basis samples are taken and analysed for a wide range of parameters including salts, organic substances and metals. The Environment Agency set trigger levels for selected parameters and for selected boreholes against which the performance of the site is assessed.
In addition we confirm that the Environment Agency is testing the Horsewater Spring in Kings Cliffe Village, and that they already regularly test other water bodies in the area such as streams and rivers including the Willow Brook and River Nene.
Below are presented graphs for boreholes with trigger levels for the most recent 12months of data submitted to the Environment Agency for ammoniacal nitrogen, chloride, cadmium and nickel. For each graph the reason the parameter has been selected and its meaning are explained above the graph. The results are discussed below each graph.
Ammoniacal nitrogen
Ammoniacal nitrogen is an indicator of organic contamination. In combination with elevated chloride it could indicate the presence of landfill leachate. Elevated levels of ammoniacal nitrogen on its own may an organic source such as agricultural waste, seasonal dieback of vegetation. A trigger level 2.4mg/l is set in the Environmental Permit based on background concentrations in the groundwater.
The results show that there is little ammoniacal nitrogen in the groundwater and all results are well within the trigger value.
Chloride
Chloride is a good indicator of the presence of salts. In combination with ammoniacal nitrogen it can indicate the presence of leachate. Elevated levels of chloride on their own can naturally occur or could be due to contamination from road salt. A trigger level of 250mg/l is set based on the UK’s drinking Water Standards.
Chloride results are generally consistently within the trigger limit up and down stream of the site. Elevated results were detected in KO6 on the southern boundary for a short period at the end of 2010. The results did not coincide with elevated ammoniacal nitrogen in the same samples which means that the chloride was not associated with the landfill. Potential sources of the elevated chloride could be agricultural activity or ground surface inundation during the winter including road salt runoff leaking into the boreholes. During 2011 the boreholes were reviewed and seals renewed as necessary to minimise the risk of surface water ingress to the boreholes.
Cadmium
Cadmium is a heavy metal commonly associated with hazardous waste landfill sites (HPA:2010). A trigger level of 0.1µg/l is set based on normal detection limits in Environment Agency guidance.
No cadmium has been detected.
Nickel
Nickel has a trigger limit of 20µg/l as set by the Environment Agency’s Permit for the East Northants Resource Management Facility (ENRMF). This value represents the limit set in the UK Drinking Water Standards.
All groundwater boreholes contain nickel levels significantly below the trigger value.