Source Protection Zones

ESI has undertaken a number of projects to define, review and refine Source Protection Zones (SPZs) around groundwater abstractions.  These are detailed below:

Groundwater Protection Zone (GPZ) Network, North West Region

A systematic programme of groundwater modelling was undertaken using MODFLOW and FLOWPATH to develop and refine Groundwater Protection Zones in the North West Region.  Twelve Groundwater Protection Zones required updating within three existing FLOWPATH models. This required validating the database of abstractions and model parameters and refining the FLOWPATH grids where necessary. One pre-existing FLOWPATH model was considered to be inadequate and a new MODFLOW model was constructed. A further nine sources were zoned within a new MODFLOW model.

Groundwater Protection Zones for 20 Sources, Midland Region. (Contractor: Mott MacDonald)

Groundwater Protection Zone modelling was undertaken by ESI as subcontractors to Mott MacDonald. A total of twenty Groundwater Protection Zones were required to be determined, 16 in existing FLOWPATH models, two based on an existing transient MODFLOW model and two manually defined zones.  It was agreed with the Agency that two of the FLOWPATH models would be suitable for migration to MODFLOW and this was undertaken satisfactorily in both cases. All the Groundwater Protection Zones were delineated in accordance with the Standard Agency Methodology.

Groundwater Protection Zone Definition for sources in the Midlands Region.

Groundwater Protection Zones were defined for 15 sources in the Midlands Region.  Existing FLOWPATH groundwater models were reviewed for 7 sources, converted into MODFLOW models and adjustments made as necessary.  Two new MODFLOW models and 8 new manual zones were created.  These have all been used as the basis for the definition of source protection zones.  The zones based on groundwater models have also been subject to uncertainty assessment, allowing zones of confidence and zones of uncertainty to be drawn around the best estimate zones on the source protection maps.  The Agency standard methodologies for Source Protection Zone delineation were implemented in close liaison with Agency technical staff.

Environment Agency Thames Region Source Protection Zones Review

In 2007/8 the Environment Agency Thames Region required a review in the light of abstraction licence variations of existing source protection zones, and delineation of a new set of Source Protection Zones for recently licensed abstractions. Original two-dimensional FLOWPATH models were converted into MODFLOW models. Abstraction rates were updated appropriately and particle tracks were developed for the required travel times. For those sources that abstract groundwater from the confined Chalk beneath the London Clay, a tailored semi-analytical tool was developed. GIS was used to trace Source Protection Zones around the particle tracks, and at this step expert hydrogeological judgement was used to make small adjustments with regard to topograhy and river networks. 

A total of 62 Source Protection Zones were updated covering a broad area largely composed of Chalk based abstractions, although also including other major and minor aquifers. The groups of Source Protection Zones included: South West Chilterns, Lee Valley, North Downs, Central London, the Thames Gravels at Dorney, the Colne catchment, and the Kennet Valley. Further work is ongoing. 

ESI is recognised as a UK centre of excellence for groundwater modelling, and is contracted by both public and private organisations to carry out similar work.

Please contact ESI for more information on Source Protection Zones.