Groundwater
Water stored below the surface forms the largest reservoir of available fresh water. In the UK the Environment Agency are responsible for ensuring the protection of these waters and will, as part of the planning process, require an assessment to be made as to any likely impacts on groundwater from a development. To a certain extent the nature of the geological strata underlying a site will determine its permeability and as such its ability to hold water and act as an aquifer.
The Environment Agency differentiates between 3 different types of aquifer:-
- Major Aquifer (Confined/Unconfined) – Highly productive
- Minor Aquifer – May be important for local supplies
- Non-Aquifer – Negligible permeability
The proximity of Potable Water Abstractions will also have an important bearing on the sensitivity of a site and whether it lies within the:-
- Inner Zone - 50 day travel time to abstraction point
- Outer Zone – 400 day travel time to abstraction point
- Total Catchment - area within which all groundwater recharge is presumed to discharge at that source
It is first necessary to determine whether the groundwater below a site is a potential receptor and that there is a plausible pathway from any contaminants that may be derived from the surface. The sensitivity of groundwater, including an assessment of the below ground strata, locations of abstractions and discharges together with the aquifer status would be fully assessed as part of a Phase 1 Desk Study. Groundwater monitoring may then be incorporated into a Phase 2 Intrusive investigation.
In some cases it may be necessary to undertake a quantitative risk assessment in accordance with the Methodology for the Derivation of Remedial Targets for Soil and Groundwater to Protect Water Resources, Environment Agency R&D Publication 20, which can be incorporated into a Phase 2 Intrusive Investigation and the results used to determine the requirements of any Phase 3 Remediation.
At Terragen our consultants have a wide range of experience in assessing the sensitivity of groundwater resources, designing and carrying out intrusive investigations and interrogating the results. Should you require further information or additional advice, please do not hesitate to contact us at info@terragenenvironmental.co.uk
Groundwater monitoring may be required for several reasons:-
- To assess whether groundwater is contaminated – from the site or surrounds
- To determine the hydraulic gradient and therefore direction of groundwater flow
- To provide baseline data – prior to development or as part of an IPPC application
- To monitor the impact of remediation excavations groundwater quality
- To determine the need and method of remedial measures to decontaminate groundwater
Dependent on the site groundwater may be several to tens of metres below the surface. Recovery of samples therefore requires the installation of a monitoring well, which can be excavated through various drilling techniques. The technique chosen is dependent on a range of factors including the anticipated depth, the aquifer status of the site and the nature of the below ground strata.
Having identified suitable locations, the most suitable drilling technique and the required response zone over which monitoring was required, one of our consultants would attend site to oversee the installation of the boreholes. During drilling the profile of the borehole would be logged in accordance with BS5930 and if necessary soil samples collected for analysis.
After a suitable period of settlement our consultants would then undertake a programme of monitoring. Monitoring would include measurement of the depth to groundwater, using a dip meter and recovery of representative water samples. Industry standard process, as stated in Waste Management Paper 4, requires 3-well volumes to be removed from a borehole prior to groundwater sampling. After purging the borehole a sample would be recovered, any required in-situ readings obtained i.e. pH, temperature and then returned to one of our selected accredited laboratories for analysis.
After the results of the in-situ readings and laboratory testing have been collated we would present our findings in a fully interpretative report including an assessment of any contamination identified and where necessary an assessment of its potential risk to surrounding receptors.
At Terragen we can manage all aspects of a groundwater monitoring programme from its formulation and installation through to monitoring and assessment. Should you require any further information or advice, please do not hesitate to contact us at info@terragenenvironmental.co.uk
N.B. It is possible for installations to combine groundwater and gas monitoring facilities.