Landfill Groundwater and Hydrogeology
The underlying geology and hydrogeology of a landfill is especially significant if there is an aquifer that is relied upon for drinking water or other extraction purposes.
The relevance of the hydrogeological setting within which a landfill is located arises from the need to assess the technical precautions and engineering requirements for a landfill to be authorised such that unacceptable environmental impacts are prevented.
Definition of Aquifer
One definition of an aquifer is from Freeze and Cherry (1979): “An aquifer is best described as a saturated permeable geologic unit that can transmit significant quantities of water under ordinary hydraulic gradients”.
In England and Wales, the EA categorize aquifers to be consistent with the Water Framework Directive. The categories are Principal Aquifer, Secondary Aquifer and Unproductive Strata. Previously the phrases major aquifer and minor aquifer were utilized. Similar arrangements exist in Scotland and are supervised by SEPA. In locating landfills, consideration is given to aquifers in terms of their Source Protection Zoning (see below).
Relevance of Aquifer and HRA
The hydrogeologiclal setting within which a landfill is located is assessed via a Hydrogeological Risk Assessment (HRA).
This is submitted as supporting document to an Environmental Permit application and takes a risk-based approach to the location of the landfill and the engineering required. Again, similar arrangements are in place in Scotland, Wales and Northern Ireland.
In the case of Principal Aquifers, which are of the highest quality and use, it is unlikely that any HRA will come to the conclusion, even with extensive engineering, that a landfill will be able to be located above such an aquifer (see Landfill location - below).
Landfill Directive
The basic criteria for suitable landfill locations are set out in the Landfill Directive, which says in Annex 1:
1.1 The location of a landfill must take into consideration requirements relating to:
(a) the distances from the boundary of the site to residential and recreation areas, waterways, water bodies and other agricultural or urban sites;
(b) the existence of groundwater, coastal water or nature protection zones in the area;
(c) the geological and hydrogeological conditions in the area;
(d) the risk of flooding, subsidence, landslides or avalanches on the site;
(e) the protection of the nature or cultural patrimony in the area.
1.2. The landfill can be authorised only if the characteristics of the site with respect to the aforementioned requirements, or the corrective measures to be taken, indicate that the landfill does not pose a serious environmental risk.
The requirements of the Landfill Directive are brought into UK guidance via various pieces of legislation and EA guidance, notably:
- Environmental Permitting (England and Wales) Regulations 2010
- Regulatory Guidance Series, No LFD 1 - Understanding the Landfill Directive - version 2 March 2010 [1]
- Groundwater protection: Principles and practice (GP3) as updated by The Environment Agency’s approach to groundwater protection
Source Protection Zones for Groundwater
In essence these policies rely upon a risk assessment of each proposed landfill location, set into the context of the site and whether or not it is within a Source Protection Zone (SPZ) for a protected groundwater abstraction or within a Major/Principal Aquifer (as defined by the EA)
The relevant EA policy [2] is as follows:
- The Environment Agency will normally object to any proposed landfill site in groundwater SPZ1.
- For all other proposed landfill site locations, a risk assessment must be conducted based on the nature and quantity of the wastes and the natural setting and properties of the location.
- Where this risk assessment demonstrates that active long-term site management is essential to prevent long-term groundwater pollution, the Environment Agency will object to sites:
- below the water table in any strata where the groundwater provides an important contribution to river flow, or other sensitive receptors
- within SPZ2 or 3
- on or in a principal aquifer
Source Protection Zones are defined and determined (and available online [3]) by the EA as follows:
- SPZ1 - also known as the Inner Zone - is any land within 50 days (groundwater) travel time from a groundwater source, with a minimum radius of 50 metres;
- SPZ2 - also known as the Outer Zone - is any land within 400 days (groundwater) travel time from a groundwater source, with a minimum radius of 250 metres;
- SPZ3 - also known as the Total Catchment - is defined as the area around a source within which all groundwater recharge is presumed to be discharged at the source.
References:
- Environmental Permitting Guidance – The Landfill Directive (Version 3.1 March 2010); updated by Guidance LFD 1 – Understanding the Landfill Directive (March 2011); which was then withdrawn in October 2022 and replaced with Guidance on Environmental Permitting (on gov.uk)
- Groundwater Source Protection Zones (SPZ)
- SPZ Mapping
