Guidance on the design and installation of groundwater quality monitoring points Science Report SC020093 SCHO0106BKCT-E-P The Environment Agency is the leading public body protecting and improving the environment in England and Wales. It’s our job to make sure that air, land and water are looked after by everyone in today’s society, so that tomorrow’s generations inherit a cleaner, healthier world. Our work includes tackling flooding and pollution incidents, reducing industry’s impacts on the environment, cleaning up rivers, coastal waters and contaminated land, and improving wildlife habitats. This report is the result of research commissioned and funded by the Environment Agency’s Science Programme. Author(s): Published by: B A Fretwell, R I Short and J S Sutton Environment Agency, Rio House, Waterside Drive, Aztec West, Almondsbury, Bristol, BS32 4UD Dissemination Status: Tel: 01454 624400 Fax: 01454 624409 Publicly available www.environment-agency.gov.uk Keywords: ISBN: 1844325342 Borehole design, Groundwater sampling, Groundwater © Environment Agency January 2006 monitoring, Groundwater quality All rights reserved. This document may be reproduced with prior Research Contractor: permission of the Environment Agency. Entec UK Ltd 160-162 Abbey Foregate The views expressed in this document are not necessarily Shrewsbury those of the Environment Agency. SY2 6BZ This report is printed on Cyclus Print, a 100% recycled stock, Environment Agency’s Project Manager: which is 100% post consumer waste and is totally chlorine free. Kamrul Hasan Science Group, Olton Court, Solihull. Water used is treated and in most cases returned to source in better condition than removed. Science Project reference: SC020093 Further copies of this report are available from: The Environment Agency’s National Customer Contact Centre by Product Code: emailing [email protected] or by SCHO0106BKCT-E-P telephoning 08708 506506. ii Science Report SC020093 Science at the Environment Agency Science underpins the work of the Environment Agency. It provides an up-to-date understanding of the world about us and helps us to develop monitoring tools and techniques to manage our environment as efficiently and effectively as possible. The work of the Environment Agency’s Science Group is a key ingredient in the partnership between research, policy and operations that enables the Environment Agency to protect and restore our environment. 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Steve Killeen Head of Science iii Science Report SC020093 Executive summary This report offers practical guidance on the design, construction and installation of groundwater quality monitoring points (GQMP) that will help to improve industry practice along with the quality of monitoring data. The main objective in designing a GQMP is to ensure that representative groundwater samples can be collected. Good design and installation are essential to achieving this goal. This guidance concentrates on the more common procedures for GQMP design, installation, borehole development, maintenance, rehabilitation and decommissioning. Where unusual or novel practices are employed, users may need to adopt additional measures on top of the general advice in this report to ensure that the GQMP meets monitoring objectives. It is assumed that, prior to undertaking the design process, a decision to drill and install a GQMP has been taken and that the reasons for installing that point are clearly defined. The design process requires the monitoring objectives to be clearly defined from the start, although these may be revised during the design process, where additional information and other considerations such as cost may arise. Monitoring objectives Groundwater monitoring objectives can be divided into three broad categories. Strategic monitoring is employed to obtain background water quality information, which can be used to determine broad groundwater quality, diffuse pollution trends, problems and long-term changes in groundwater quality. Defensive monitoring is normally undertaken within and around an actual or potential problem site, or a sensitive receptor, to provide information on the impact of a known or suspected source of contamination. It can also indicate the absence of contaminants and can be used to assess the success of a clean-up operation. Investigative drilling is used to improve the conceptual understanding of a site. It can detect contaminants on known problem sites and can identify interactions between groundwater and the greater environment, such as interactions between groundwater and surface water or a habitat. There may be other reasons for drilling a GQMP which will also influence the design process, particularly the choice of drilling technique. It is important to determine at an early stage whether all objectives can be accommodated in a single borehole drilling operation without compromising the monitoring ones. Design Initial design should be a quick and relatively simple process, focussing on the design basics such as drilling method, GQMP positioning and objectives. It is iv Science Report SC020093 undertaken primarily to identify potential pitfalls and problems, the likely budget for the work and significant health and safety issues. This stage also serves to refine the monitoring objectives to ensure they are achievable. A brief outline design should be undertaken prior to beginning detailed design. This process may be iterative to permit consideration of different options. At the detailed design stage, the initial design is refined to sufficient detail for the work to be commissioned from drilling contractors. Health and safety requirements should be formalised and accurate costs produced. The user should also confirm the suitability of the design with a regulator. Construction The guidance covers the requirements of the construction process, including the need for supervision and the role of the supervisor; necessary documentation; the sequence of construction; and borehole development (the process of returning the conditions around the GQMP to as close to those prior to drilling). Post-construction activities other than groundwater sampling include: • maintenance, which involves routine activities to maintain the performance of the GQMP. Correctly installed GQMPs should not, in general, need much maintenance; • rehabilitation, involving both major and occasional work to restore the performance of the GQMP; • decommissioning, to ensure that the GQMP does not become a pathway for contaminant migration. v Science Report SC020093 Contents Executive summary (iv) Glossary (viii) 1. Introduction 1 1.1 Aims of the report 1 1.2 How to use the technical guidance 2 1.3 Other sources of guidance 3 2. Monitoring objectives and initial design 6 2.1 Introduction 6 2.2 Monitoring objectives 6 2.3 Initial design 9 2.4 Costs 15 2.5 Collecting additional information 18 2.6 Health and safety 18 2.7 Quality assurance 19 2.8 Consultation 20 3. Detailed design 21 3.1 Introduction 21 3.2 Conceptual site model 22 3.3 Drilling technique selection 26 3.4 Installation design 31 3.5 Material selection 33 3.6 Headworks 44 3.7 The surface environment 46 3.8 Consultation and licensing 48 4. Construction of groundwater quality monitoring points 49 4.1 Introduction 49 4.2 Construction monitoring 49 4.3 Borehole drilling practice 50 4.4 Installation practice 51 4.5 On-site decision making 54 vi Science Report SC020093 4.6 Borehole development 54 4.7 Completion 56 5. Post-construction activities 57 5.1 Introduction 57 5.2 Sampling 57 5.3 Routine inspections and maintenance 58 5.4 Rehabilitation 58 5.5 Decommissioning 59 6. References 62 List of tables Table 2.1 Groundwater monitoring objectives - Strategic monitoring 7 Table 2.2 Groundwater monitoring objectives - Defensive monitoring 8 Table 2.3 Groundwater monitoring objectives - Investigative monitoring 8 Table 2.4 Guide to monitoring interval selection 13 Table 3.1 Drilling techniques for fine soils 28 Table 3.2 Drilling techniques for coarse soils 28 Table 3.3 Drilling techniques for rock 29 Table 3.4 Susceptibility of casing materials to degradation in the presence of free phase contaminants 36 Table 3.5 Susceptibility of casing materials to corrosion in aggressive groundwater conditions 36 Table 3.6 Casing suitability for target determinands 37 Table 3.7 Relative casing material strength 38 Table 3.8 Calculation of typical annulus backfill volumes 40 Table 3.9 Headworks types 46 List of figures Figure 1.1 GQMP design and installation summary flow chart 4 Figure 1.2 GQMP design and installation detailed flow chart 5 Figure 3.1. Filter pack design (after Clark 1988) 39 List of appendices Appendix A Information questionnaire and checklists 64 Appendix B Drilling techniques 73 Appendix