Source Protection Zones. National Dataset User Guide

Transcription

1 Source Protection Zones National Dataset User Guide Version th Jan

2 Contents 1.0 Record of amendment Introduction Description of the SPZ dataset Definition of the zones Source data and the system it is held on Related data sources Public Register and non Public Register data National Security Legislation relevant to the data set Data structure Data quality Data standards Reporting errors to the NDU NDU Validation rules and completeness checks Validation checks specific to the SPZ Data entry stage validation Individual verification of data National verification of data Known quality issues Frequently Asked Questions (FAQ) Useful information when using the data What is not included in the data Recommendations on how to use or analyse the data Limitations when interpreting the data Changes in data collected Glossary Feedback form Appendix

3 1.0 Record of amendment Version number Section number Amendment description Date Minor text revision 20/01/ Paragraph 4 inserted. 20/01/ Minor text revision 20/01/ Minor text revision 20/01/ Text revised 20/01/ Text revised 20/01/ Text added 20/01/ Text added 20/01/ Text added 20/01/ Text revised 20/01/06 3

4 2.0 Introduction This document provides information to accompany the Environment Agency s Source Protection Zone (SPZ) dataset supplied to external users. It can be used to gain a better understanding of the SPZ data when used in conjunction with the current data release. The Product Sheet accompanying this user guide provides a brief introduction to the SPZ national dataset, but for information relating to national datasets in general, please refer to the National Dataset Generic Text document. Details of the Environment Agency s distribution policy can be found in the National Dataset Generic Text document, along with contact details for the National Data Unit (NDU). Information about the Environment Agency s web site can also be found in the National Dataset Generic Text. The SPZ web site is located at: for=spz&any_all=&choose_order=&exactphrase=&withoutwords=# The site includes data analysis reports and links to other web pages of interest. 2.1 Description of the SPZ dataset The parts of aquifers which, according to current techniques and methodologies, are considered to form the catchments to public water supplies and certain other private supplies, have been defined as Source Protection Zones (SPZ). They relate purely to groundwater flow below the water table and do not take account of the nature and thickness of the overlying unsaturated zone and cover, which may have an important influence on groundwater vulnerability. SPZs are presented on source protection maps. The maps are 1:50,000 scale polygon shapefiles, in British National Grid projection. This data has no topology at present.. SPZs have been defined by the Environment Agency for nearly 2,000 groundwater sources (wells, boreholes and springs) used for public drinking water supply. This includes all significant public water supply, and also private wells or boreholes that supply water to potable or equivalent standards, such as mineral waters, breweries and food processing. Though SPZs have only been derived by the Environment Agency for the above types of source, there are many thousands of other licensed and unlicensed abstractions supporting industrial, agricultural, domestic and other uses which would be a local consideration. The SPZ maps are intended to be viewed at a scale of 1:50000, therefore a ground accuracy of 10 metres should be used with a maximum distance of 250 metres between points. 4

5 2.1.1 Definition of the zones SPZs are a tool to support and underpin the Environment Agency s Policy and Practice for the Protection of Groundwater. They provide an indication of the risk to groundwater supplies from potentially polluting activities and accidental releases of pollutants. Generally the closer the activity or release is to a groundwater source the greater the risk. Three zones (an inner, outer and total catchment) are usually defined, although a fourth zone (zone of special interest) is occasionally created. These zones are defined as follows: Zone I (Inner Protection Zone) - defined by a travel time of 50 days or less from any point within the zone, at or below the water table. Additionally, the zone has as a minimum a 50-metre radius. It is based principally on biological decay criteria and is designed to protect against the transmission of toxic chemicals and water-borne disease. Zone II (Outer Protection Zone) - defined by the 400-day travel time, or 25% of the source catchment area, whichever is larger. The travel time is derived from consideration of the minimum time required to provide delay, dilution and attenuation of slowly degrading pollutants. Zone III (Total catchment) - defined as the total area needed to support the abstraction or discharge from the protected groundwater source. Zone of Special Interest - For some groundwater sources an additional Zone of Special Interest may be defined. These zones highlight areas (mainly on non-aquifers) where known local conditions mean that potentially polluting activities could impact on a groundwater source even though the area is outside the normal catchment of that source Source data and the system it is held on The working maps and reports which detail how the SPZs have been derived will be held at the relevant Regional or Area Office of the Environment Agency, and are available for inspection if this is required in relation to site specific assessments. Dissemination and copying of the working maps and reports will be restricted subject to consultation with the relevant Regional or Area Office of the Environment Agency. Source Protection Maps show the position of the sources and all subdivisions of their protection zones (Inner, Outer and Total Catchment) as referred to in the Policy and Practice for the Protection of Groundwater (PPPG) document. These are shown in a form that represents a precautionary approach to the protection of groundwater. They 5

6 incorporate practical consideration of uncertainty in the underlying data, and manual adjustments to take account of local circumstances. The zones are produced by hydrogeologists, based in Area Groundwater & Contaminated Land teams, using sophisticated computer models of groundwater flow systems. The zones produced are then converted to ESRI shapefiles, for uploading to the National digital data set. The existing National GIS data sets consist of 3 components; One data set (point) holding the locations of the abstraction sources. One data set (polygon) holding the individual zones relating to a source. One data set (polygon) holding zones that have been merged together. The NDU receives data for the SPZ national dataset from the Water Management Directorate. It is loaded directly onto the NDU network and without any further processing, is distributed to customers as the SPZ National Dataset. SPZs depend on variables such as the current local abstraction regime and various physical parameters, which may not be well defined. SPZs are therefore not fixed and they require both ongoing management and periodic review. 2.2 Related data sources The SPZ data is related to the Ground Water Vulnerability Zone data. For further information on Ground Water Vulnerability Zones consult the relevant national dataset user guide. 6

7 3.0 Public Register and non Public Register data For a general description of what constitutes public register and non-public register data please refer to the National Dataset Generic Text document. The SPZ data is not public register. 3.1 National Security A discussion of national security issues can be found in the National Dataset Generic Text Document. There have been no exclusions from the SPZ dataset due to National Security. 3.2 Legislation relevant to the data set Under development 7

8 4.0 Data structure The SPZ dataset data is supplied as two shapefiles: Source Protection Locations (source_protection_locations_50k) A point shapefile showing the locations of the Source Protection Zones. Source Protection Zones (source_protection_zones_50k) A polygon shapefile showing the extent of the various SPZs. The detailed data structure of the SPZ dataset is given in the National Dataset Field Attribute document. 8

9 5.0 Data quality 5.1 Data standards For data standards applicable to a number of national datasets please consult the National Dataset Generic Text document. 5.2 Reporting errors to the NDU Methods of reporting errors and the recording of data queries by the NDU, are also included in the general document, whilst a feedback form can be found at the end of this user guide. 5.3 NDU Validation rules and completeness checks Every effort is made to minimise data errors occurring in the SPZ data release. For background information on the data validation process and general completeness checks carried out by the NDU, please refer to the National Dataset Generic Text document. 5.4 Validation checks specific to the SPZ Following is an outline of the validation checks specific to the SPZ dataset Data entry stage validation A minimum scanning resolution of 600dpi is advised to give more accurate digitisation of hard copy SPZ maps. Image manipulation software is used to ensure that the image is not skewed in any way before it is imported into electronic format and georeferenced Individual verification of data Prior to submitting any ESRI shapefiles to the Head Office Water Resources Hydrogeology Policy and Process team, the following checks must be made: All digitised zones must be checked to ensure that they meet the Converting New and Revised Source Protection Zones work instruction specification. All protection zones for a particular source must be plotted together with the source location to ensure that the source lies within the zones, and that each lie within one another (where they are intended to). Where this is not the case, 9

10 adjustments must be made by altering the boundary of zone 3 to fully encompass zones 2 and 1, and the boundary of zone 2 to fully encompass zone 1. Checks should ensure that the digitisation accuracy and/or changes made are within the accuracy of the original modelled zones National verification of data The following processes are used to ensure the SPZs dataset is of an: appropriate standard: The correct identification of changes required to the national SPZ GIS datasets. Dataset alterations must be are carried out in a consistent manner. The conversion of Revised Protection Zones to ESRI shapefiles to be accurate and in accordance with Environment Agency GIS standards. Dataset amendments to be documented thoroughly and recorded correctly to provide a clear audit trail. 5.5 Known quality issues There are no known quality issues with SPZ data. 10

11 6.0 Frequently Asked Questions (FAQ) Q1. Is it possible for borehole locations to have duplicated NGR s? A1. Yes there are borehole sites that have duplicated NGR s. These sites have all been checked with the data custodians, who have confirmed that the duplicate NGR s are correct. This can be due to the scale at which they were digitised. 11

12 7.0 Useful information when using the data It may be helpful to take into account the following information when analysing the data. This section also points out information that is not included in the data, as well as any limitations on interpreting the data. 7.1 What is not included in the data There is no data excluded. 7.2 Recommendations on how to use or analyse the data The following explanatory booklet is available from The Stationery Office: 'Guide to Groundwater Protection Zones in England and Wales' Limitations when interpreting the data Source Protection Maps may be reproduced only with the permission of the Environment Agency. Because the lines are not definitive, the scale of maps may be reduced when copied under permission but must not be increased (i.e. enlarged) above 1:50,000. Whilst every effort has been taken to ensure cartographic accuracy, this cannot be guaranteed due to the complexity of mapping. No liability is accepted by the Environment Agency for any interpretation or use made of Source Protection Maps by third parties. 7.3 Changes in data collected Any major changes identified in the SPZs data will be highlighted in this. An explanation of why the change had occurred is also provided and if you have any questions relating to these changes please contact the NDU. Source Protection Maps contain information that changes from time to time and the Environment Agency may modify them without notice. Reference should be made to the relevant Regional or Area Office for the current position. The polygon data received by the NDU is updated annually. 12

13 8.0 Glossary NDU GWV NGR PPPG SPZ National Data Unit Ground Water Vulnerability National Grid Reference Policy and Practice for the Protection of Groundwater Source Protection Zones 13

14 9.0 Feedback form The NDU welcomes feedback on its databases and if you have any comments please complete the form below and return to the Environmental Data Unit: Name: Phone: Organisation: Fax: National Dataset. (Please enter dataset to which your feedback relates) Comments: Feedback on contents of documentation: Feedback on data content: General feedback: National Data Unit Data Team Leader Environment Agency Tel: Lower Bristol Road Rivers House BATH BA2 9ES 14

15 10.0 Appendix 1 Complete list of all amendments ever made to the document Version number Section number Amendment Description Date Text revised 21/07/ Section finalised 21/07/ Section finalised 21/07/ Section re-named NDU Validation rules and 21/07/05 completeness checks Section number changed from to /07/ Section finalised 21/07/ Section number changed form to /07/ Section finalised 21/07/ Section number changed from to /07/ Section number changed from to /07/ Section number changed form 5.4. to /07/ Section finalised 21/07/ Section removed 21/07/ Text updated 22/04/ Text updated 22/04/ Text updated 22/04/ Text updated 22/04/ Text updated 22/04/ Text updated 22/04/ Table revised 22/04/ Multiple Replaced reference to EDU/DIEU with NDU 22/04/05 15