Love Thy Monitoring Network

Lauren Ballarini, technical director Hydrogeology and Hydrology Wardell Armstrong, looks at the minimum groundwater monitoring requirements at landfill sites, saying the Landfill regulations are quite clear…

The Landfill regulations are quite clear about the minimum groundwater monitoring requirements at landfill sites. A minimum of one up-hydraulic gradient and two down-hydraulic gradient monitoring points are required.

Engineered containment at your site? The default position is further boreholes on the down-hydraulic gradient boundary at 100 metre intervals. Engineered liner in poor condition? Reduce that interval to 50 metres. It’s easy to see how the number of groundwater monitoring wells quickly add up at a site.

What of the cost of getting a groundwater monitoring well installed at a site as well? First comes the cost of designing the monitoring well perhaps requiring you to gain the agreement of the Environment Agency on the installation, costs associated with the site investigations including H&S considerations, sub-contractor costs and supervision costs, further costs for drawing up logs and producing factual reports detailing the final installations follow the site investigation phase.

Taken as a whole, one borehole can cost upwards of £2,500 to install and in some cases, depending on the geological complexity, over £5,000.

And what does a site have to show for it at the end of all this work? A series of 0.5 metre high, 10 centimetre in diameter metal tubes sealed into a concrete base and locked with a padlock. It’s easy to see how the humble groundwater monitoring well might be overlooked.

Often groundwater monitoring wells at landfill sites are in poor condition relatively soon after they are installed. Why? Headworks get damaged by the movement of large vehicles which might not spot these relatively low to the ground objects. Locks and lids are missing because of rust damage or loss of padlock keys. Missing end caps can lead to the inundation of surface debris into the monitoring well.

If data collected from a monitoring network is difficult to interpret or showing unusual trends, the Environment Agency will ask about the condition of a monitoring network and the potential effects that condition is having on the collected results.

If data collected from a monitoring network is difficult to interpret or showing unusual trends, the Environment Agency will ask about the condition of a monitoring network and the potential effects that condition is having on the collected results.

Where the monitoring network is not achieving its objectives, new boreholes will be required at additional cost and hence the initial outlay on drilling the monitoring well is repeated, again, to the tune of thousands of pounds.

The power of a well-maintained monitoring network is immense. The ability to provide an unbroken, high quality record of groundwater level and chemistry data gives strength to any technical arguments.

There is no need to cross-correlate monitoring results from old and replacement monitoring wells to establish continuity of data nor is it necessary to provide lengthy discussion and justification as to whether data results are representative of the groundwater in which they are located.

There is just the robust and defensible record of data supporting the conclusion that the landfill is not affecting groundwater.

But is there a monetary worth that can be put on this data rather than just a technical one? What if a landfill, which is currently actively maintaining leachate levels, wishes to alter their permit to increase their leachate head from 1 metre to 2 metres? With a good quality monitoring network and a quality audited database, the application to vary the permit could be completed within four weeks.

A good permit application, where the Environment Agency have been engaged early and the supporting Hydrogeological Risk Assessment Review is robust, should be determined in 12 weeks. However, if the dataset is questionable, from a poorly maintained monitoring well, there is a strong chance that in early engagement with the Environment Agency the question of additional or replacement monitoring wells will be raised. If replacement monitoring wells are needed, then these can take four to six weeks to install.

If additional data collection is required from the new monitoring wells, this may take up to a further 12 months to allow it to be correlated with previous data. During this time, the landfill is still abstracting, tankering and treating leachate at considerable expense. If the current monitoring network had been well maintained, the double whammy of additional replacement monitoring well costs and extended periods of leachate disposal would have been avoided.

Finally, if technical and monetary arguments weren’t sufficient, having usable monitoring wells in agreed locations with the ability to collect the required groundwater level and chemistry data is a stipulation of landfill permits.

As the Environment Agency can fine landfill operators for not meeting the requirements of their permit– isn’t it about time that the poor, neglected monitoring well was shown some respect?

Darrel Moore

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