190807 501.00180.00269 Borehole Decommissioning Report

BOREHOLE DECOMMISSIONING

REPORT

Prepared for: Roadstone LtdClient Ref: 501.00180.00269

SLR Ref: 501.00180.00269

Version No: Rev0

August 2019

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EPA Export 25-04-2020:12:41:37

Roadstone Ltd

Bennettsbridge Quarry

Filename: 190807 501.00180.00269 Borehole Decommissioning Report and Monitoring Plan

SLR Ref No: 501.00180.00269

August 2019

.

BASIS OF REPORT

This document has been prepared by SLR with reasonable skill, care and diligence, and taking account of the manpower, timescales and

resources devoted to it by agreement with Roadstone Ltd (the Client) as part or all of the services it has been appointed by the Client to

carry out. It is subject to the terms and conditions of that appointment.

SLR shall not be liable for the use of or reliance on any information, advice, recommendations and opinions in this document for any

purpose by any person other than the Client. Reliance may be granted to a third party only in the event that SLR and the third party

have executed a reliance agreement or collateral warranty.

Information reported herein may be based on the interpretation of public domain data collected by SLR, and/or information supplied

by the Client and/or its other advisors and associates. These data have been accepted in good faith as being accurate and valid.

The copyright and intellectual property in all drawings, reports, specifications, bills of quantities, calculations and other information set

out in this report remain vested in SLR unless the terms of appointment state otherwise.

This document may contain information of a specialised and/or highly technical nature and the Client is advised to seek clarification on

any elements which may be unclear to it.

Information, advice, recommendations and opinions in this document should only be relied upon in the context of the whole document

and any documents referenced explicitly herein and should then only be used within the context of the appointment.

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SLR Ref No: 501.00180.00269

August 2019

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CONTENTS

INTRODUCTION ............................................................................................................... 1

SITE VISIT ........................................................................................................................ 2

PROCEDURE FOR DECOMMISSIONING ............................................................................. 3

3.1 Headworks and Casing .............................................................................................................. 3

3.2 Backfilling .................................................................................................................................. 3

3.3 Sealing the Borehole ................................................................................................................. 3

3.4 Recording .................................................................................................................................. 4

DECOMMISSIONING OF BOREHOLE .................................................................................. 5

4.1 Overview ................................................................................................................................... 5

4.2 Summary ....................................................................................... Error! Bookmark not defined.Error! Bookmark not defined.Error! Bookmark not defined.Error! Bookmark not defined.

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SLR Ref No: 501.00180.00269

August 2019

Page 1

Introduction

SLR Consulting (Ireland) Ltd were requested by Roadstone Ltd to produce a borehole decommissioning report

following the decommissioning of groundwater monitoring well GW4 at Bennettsbridge quarry. The monitoring

well decommissioning was carried out in accordance with the following EPA corrective action, as outlined in the

recent site visit report which was based on an EPA site visit carried out on 9th April 2019.

This borehole decommissioning report was completed by SLR’s Principal Hydrogeologist Dominica Baird, and

outlines the methodology to ensure that a potential pathway will not exist following decommissioning.

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SLR Ref No: 501.00180.00269

August 2019

Page 2

Site Visit

A site visit was carried out by Dominica Baird on 26th June 2019 and groundwater monitoring well GW4 was

inspected with Allen Geraghty and Stephen Walsh of Roadstone. Access to the borehole location was discussed

to bring materials to groundwater monitoring well GW4. It was confirmed that a temporary track can be

excavated to transport materials to the groundwater monitoring well.

Groundwater monitoring well GW4 was confirmed at 40.2 metres in depth and 6” diameter.

The headworks at GW4 were noted to be intact, as can be seen in Plate 2-1 below.

Plate 2.1: Borehole GW4

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SLR Ref No: 501.00180.00269

August 2019

Page 3

Procedure for Decommissioning

Groundwater monitoring wells no longer required for any purpose should be sealed (decommissioned) to

specified standards in order to prevent potential pollution of the aquifer body. The following procedure was

outlined to comply with the SEPA guidance document “Good Practice for Decommissioning Redundant Boreholes

and Wells“.

3.13.13.13.1 Headworks and CasingHeadworks and CasingHeadworks and CasingHeadworks and Casing

There was no pump and pipework present at the borehole. The borehole headworks and casing were examined

during the site inspection and were noted to be in good condition, as noted in Plate 2-1 above. Therefore, the

headworks and casing was maintained during the borehole decommissioning.

3.23.23.23.2 BackfillingBackfillingBackfillingBackfilling

The entire borehole needed to be backfilled with low permeability material that will prevent significant vertical

or horizontal movement of groundwater within the borehole.

It was recommended that the borehole is backfilled with clean (washed) coarse limestone aggregate from the

quarry, which will match the ground conditions at groundwater monitoring well GW4. The borehole was to be

backfilled to 8m bgl. The depth of the borehole is approximately 40m bgl.

The borehole is to be backfilled with bentonite grout from 3m - 8m bgl.

The borehole was to be capped with grout and cement from 0m – 3m bgl.

Both the aggregate and bentonite grout should be introduced in a controlled manner to ensure that accidental

‘bridging’ does not occur within the borehole. This is essential to ensure that voids are not present in the

borehole, which could allow for the movement of groundwater. The volume of backfill is to be monitored as it

is placed to check for bridging within the borehole, or any loss to formation.

According to the SEPA guidance, the materials used to backfill must be clean, inert and non-polluting. Suitable

materials include pea gravel, sand, shingle, concrete, bentonite, cement grout and uncontaminated rock.

Therefore, clean aggregate from the quarry is considered to be a suitable material for backfill.

The SEPA guidance further notes that boreholes that penetrate highly fissured aquifers, such as some limestones,

may result in finer aggregates or liquid grout being transported out of the borehole into the body of the aquifer

through fissures. The guidance states that in these cases it may be more appropriate to use coarser aggregates

such as gravel as a backfill, and this specification recommends the use of coarse aggregate from the quarry to

backfill the borehole.

3.33.33.33.3 Sealing the BoreholeSealing the BoreholeSealing the BoreholeSealing the Borehole

The headworks of groundwater monitoring well GW4 are in good condition and will be maintained during

decommissioning. The presence of the headworks will prevent potentially contaminated surface run off or other

liquids entering the backfilled borehole.

The SEPA guidance recommends that a concrete cap of a diameter of at least one meter greater than the width

of the backfilled borehole be installed, see Figure 3-1 below. Therefore, it was recommended that a one-meter

diameter concrete cap is placed around the borehole headworks.

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SLR Ref No: 501.00180.00269

August 2019

Page 4

Figure 3.1: Schematic Diagram for Borehole Seal and Cap (SEPA)

3.43.43.43.4 RecordingRecordingRecordingRecording

The following details should be recorded to verify that the borehole has been decommissioned in accordance

with outlined procedures:

• Measurement of depth of borehole prior to backfilling.

• The depth and position of each layer of backfilling and sealing materials.

• The type and quantity of backfilling and sealing materials used.

• Any problems encountered during the abandonment procedure.

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SLR Ref No: 501.00180.00269

August 2019

Page 5

Decommissioning of Borehole

4.14.14.14.1 OverviewOverviewOverviewOverview

Decommissioning of groundwater monitoring well GW4 in July 2019. In summary, the following

decommissioning was carried out:

• Materials for the decommissioning were stockpiled at the groundwater monitoring well (see Plate 4-1)

• Well depth was confirmed at approximately 40metres

• 40m to 8m filled with 10m limestone chip (see Plate 4-2)

• 8m to 3m filled with bentonite

• 3m to 0 filled with grout and cement (see Plate 4-4 and Plate 4-5)

• Concrete cap 1mx1mx150mm (Plate 4-6)

Plate 4-1: Materials for Backfilling

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SLR Ref No: 501.00180.00269

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Page 6

Plate 4-2: Backfilling with Limestone Chip

Plate 4-3: Measurement of Backfilling Depth

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Page 7

Plate 4-4: Filling the Groundwater Monitoring Well with Grout and Cement

Plate 4-5: Concrete Cap

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SLR Ref No: 501.00180.00269

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Page 8

Plate 4-6: Concrete Cap

4.24.24.24.2 SummarySummarySummarySummary

In summary, groundwater monitoring borehole GW4 has been decommissioned in accordance with SEPA’s

guidance “Good Practice for Decommissioning Redundant Boreholes and Wells”. The borehole has been

backfilled and sealed to ensure that the borehole does not provide a potential pathway for any contaminants to

reach the bedrock aquifer.

The marker post has also been maintained in the ground.

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EUROPEAN OFFICES

AYLESBURY

T: +44 (0)1844 337380

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Documents

190807 501.00180.00269 Borehole Decommissioning Report