Searches User Guide: Cheshire brine

Abandoned Mine Workings

Rock Salt has been mined by underground mining techniques within the Cheshire Saltfield at various depths but typically within a depth of 90m. A number of these mines were abandoned without the mine having been stabilised and represent a significant subsidence risk. Some of the workings, in particular the bottom bed workings beneath Northwich town centre, have been the subject of a stabilisation scheme. In some instances, shaft records indicate the presence of workings the extent of which is unknown and in formulating this report it has been assumed that such unrecorded workings would lie within a 50m radius surrounding the respective shaft. As an initial sieving procedure, where the records of mine workings held by the Board indicate the presence or assumed presence of mine workings, a 90m reporting buffer has been applied to those boundaries for the purpose of these reports.

Active Mine Consent

There is a single mine operation involving the extraction of rock salt by underground mining techniques currently taking place within the Cheshire Saltfield. This mining is subject to a number of conditions including the control of surface subsidence. The mine layouts have been designed by leading rock mechanics consultants acting for both the operator and planning authority to ensure compliance with the planning conditions.

Brine Wells Shafts

The location of the reported wells/shafts has been derived from source plan records of varying reliability, accordingly their locations have to be regarded as approximate.

Commutations

Where the damage to a property is likely to recur or exceed its market value, there is an option to discharge liability by a once and for all payment involving a commutation under cover of a deed of release. These deeds of release can extinguish any further means of redress and can contain a condition requiring future foundation designs to be approved by the Board to ensure future rights of redress. As a commutation has long term implications these will be declared in the searches back to 1891.

Compensation District

The geographic area prescribed by the Cheshire Brine Pumping (Compensation for Subsidence) Act, 1952 as subsequently amended, largely situated within Cheshire, but excluding Nantwich, and other areas, where redress is generally available for damage associated with the pumping of brine. This report only includes areas covered by the Cheshire Brine Compensation District. There are parts of Cheshire (and other parts of the country) where salt/brine can still pose a risk of subsidence. Further research may be necessary in these areas to determine the nature of this risk (if any).

Consultation Area

There is a statutory obligation to consult the Board with regard to development involving new foundations within these areas. Consultation with the Board is required at both the Planning Application and Building Control approval stages of development. As part of the development proposals, a suitable risk assessment should be prepared for submission and consideration by the Board.

Controlled Pumping Consent

Pumping of brine by controlled methods avoids the significant subsidence problems associated with uncontrolled pumping (wild brine pumping). Subsidence from controlled pumping is eliminated or of very low magnitudes. The current planning consent boundaries are likely to be significantly larger than the operational areas.

GS7 Planning Policy

This policy was introduced by Vale Royal Borough Council to ensure that no development takes place within the area covered by the policy, until such time that the site is rendered fit for development and mitigated against the serious subsidence risk potentially associated with abandoned rock salt mines. Cheshire West and Chester Council is in the process of replacing this policy but the replacement policy is intended to include similar development constraints.

Prescribed Notice of Damage

A remedy for damage due to subsidence associated with the pumping of brine in Cheshire (in particular Northwich) dates back to 1891. However, a large proportion of the records relating to such damage are incomplete and a number of those properties have since been demolished. The Cheshire Brine Pumping (Compensation for Subsidence) Act 1952, introduced a more widespread means of redress for damage due to brine pumping within the identified Compensation District. Regulations introduced on 08 January 1959 provided a specific format for the submission of a notice and progression of redress for damage and as such details of damage notices issued since 08 January 1959 contained in these searches have been limited to those received in accordance with the more formal procedures established on 08 January 1959. In relation to the determination of whether a prescribed notice of damage has been filed in respect of the property, the boundaries of such notices have been identified by best endeavours in the absence of definitive file records and as such can only be regarded as approximate. For larger prescribed notices of damage boundaries, the subject of the notice could be removed from the subject property boundary.

Subsidence Lines

These features related to records of subsidence identified from historic plans. These features are referred to as ‘subsidence hollows’, ‘lines of subsidence’ etc and are regarded to represent areas of potential higher risk of subsidence.