Faulkners Down Farm silage clamps: Design, Construction ...

Prepared on behalf of Earthcare Technical Limited By:

Emily Pitts, BSc (Hons), MIEMA, CEnv

Doc Ref: ETL/ESP/00124/R00001: SSAFO Notification, Yelspa Ltd, June 2015

Earthcare Technical Ltd

Manor Farm, Chalton, Waterlooville Hants PO8 0BG

Tel: 07866 024 096

E-mail: [email protected]

Yelspa Limited, Apsley Farms, Faulkners Down House, Picket Piece, Andover, Hampshire, SP11 6LZ

A Review of the Design, Construction & Maintenance of the Faulkners Down Farm Silage Clamps

Emily Pitts, June 2015

mailto:[email protected]

TABLE OF CONTENTS

Page

1 Introduction .................................................................................................................................... 1

2 Purpose ........................................................................................................................................... 1

3 Limitations....................................................................................................................................... 1

4 Context ............................................................................................................................................ 1

5 Location ........................................................................................................................................... 2

6 Environmental Constraints ............................................................................................................. 2

7 Specifications of the Silage Clamp .................................................................................................. 3

8 Review of Compliance with SSAFO Regulations ............................................................................. 6

9 Inspection and Maintenance .......................................................................................................... 6

10 Risk Assessment and Summary ....................................................................................................... 7

Appendix A – Silage Clamp Location Plan ............................................................................................... 8

Appendix B – Map Showing Groundwater Vulnerability ........................................................................ 9

Appendix C – Site Photographs (Site Visits 06/05/15 & 10/06/15) ...................................................... 10

Appendix D1 – Cross Section of Silage Clamp Containment Layers (Drawing supplied by Yelspa

Limited) ................................................................................................................................................. 19

Appendix D2 – Cross Section of Rainwater and Silage Effluent Sumps (Drawing supplied by Yelspa

Limited) ................................................................................................................................................. 20

Appendix E1 –Silage Effluent Drainage Plan Overview (Drawing supplied by Yelspa Limited) ............ 21

Appendix E2 – Silage Effluent Drainage Plan Detail (Drawing supplied by Yelspa Limited) ................. 22

Appendix F - Technical Specifications of Materials ............................................................................... 23

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© Earthcare Technical Ltd. Doc Ref: ETL/ESP/00124/R00001: SSAFO Notification, Yelspa Ltd, June 2015

1 INTRODUCTION

This report has been prepared by Earthcare Technical Ltd (ETL) on behalf of the Client, Yelspa

Limited, who operate an Anaerobic Digestion (AD) and Biogas Facility on land at Faulkners Down

Farm. The report comprises a review of the silage clamps at Faulkners Down Farm in accordance

with the requirements of The Water Resources (Control of Pollution) (Silage, Slurry and Agricultural

Fuel Oil) (England) Regulations 2010 and as amended 2013 (SSAFO Regulations)1

2 PURPOSE

This report provides supporting information for the Environment Agency (EA) silage clamp

notification form (WQE3) under SSAFO Regulations. It comprises a risk based review of the silage

clamps. The report is structured in the following way.

• The location and environmental constraints

• Specifications of the silage clamps

• Review of compliance with SSAFO Regulations

• Inspection and maintenance

• Risk assessment

3 LIMITATIONS

This report is not a review of the engineering standards relating to the construction of the silage

clamps, in particular no judgement can be made as to whether the silage clamps have been

constructed to meet the appropriate British Standards required by SSAFO Regulations, namely BS EN

13108-4:2006 for hot-rolled asphalt bases. Further the clamp design incorporates earth bunding. It

is not known whether the earth bunds have been constructed to the appropriate standard as

required by SSAFO.

4 CONTEXT

The AD plant has been in operation since October 2012. The AD plant utilises purpose grown crops

for feedstock and therefore does not require an Environmental Permit under the Environmental

Permitting Regulations 2010.

Yelspa Limited were not aware of the pre- notification requirements imposed by the SSAFO

Regulations. They did not know that silage clamps associated with AD facilities are required to be

constructed in accordance with the requirements of the Regulations. However the company

recognises that this was an error and has sought external advice.

1 http://www.legislation.gov.uk/uksi/2010/639/contents/made

http://www.legislation.gov.uk/uksi/2010/639/contents/made

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It is therefore hoped that through seeking advice and commissioning the writing of this report, it can

be shown that the company wishes to comply with the relevant environmental legislation. The aim

of this report is therefore to provide a basis for retrospective approval of the silage clamp structures.

The client had to react very quickly, in constructing silage clamps, in order to keep the AD project

economically viable in the face of changing requirements under the Renewable Heat Incentive (RHI)

scheme, administered by Ofgem, for the installation of renewable heat technologies. Specifically, in

early February 2015 further guidance on the eligibility criteria for RHI was published which meant

that the original business plan to use grain as the primary feedstock was no longer financially viable.

Following clarification on the eligibility criteria, the client would have needed to obtain sustainability

certification from their grain suppliers which would not have been possible in the short time frames

imposed.

In light of the changes to the RHI sustainability criteria, there was an urgent need to provide silage

clamps that could cater for an alternative range of feed stocks, and to mitigate any potential effects

of storing these materials on the wider environment. Hence, our client is in the process of

developing a state of the art silage clamp so that the AD facility can operate uninterrupted in the

production of renewable energy and to meet their contractual obligations.

The proposed feed stocks for ensiling are maize, potatoes (crop residues), whole beet, rye and grass.

The ensiling process enables the initial degradation of the feed stocks in the absence of oxygen in

order to maximise the AD plant efficiency and biogas production once the feed stocks are introduced

to the digester.

5 LOCATION

Address: Faulkners Down Farm, Picket Piece, Andover, Hampshire, SP11 6LZ.

National Grid Reference: SU 41001 47296

Local Authority: Basingstoke and Deane Borough Council

See Appendix A - Silage Clamp Location Plan

6 ENVIRONMENTAL CONSTRAINTS

There are no watercourses within the vicinity of the site.

The site is on chalk and upon a major aquifer of high vulnerability outside any Groundwater

Protection Zones.

See Appendix B – Map Showing Groundwater Vulnerability

It is the protection of groundwater which is the main consideration in relation to the design,

construction and maintenance of the silage clamps. They have been designed with this objective in

mind.

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7 SPECIFICATIONS OF THE SILAGE CLAMP

7.1 Overview

The silage clamps consist of excavations to create four rectangular silage clamps which run across

the face of the natural slope of the site from South West to North East. Each store is 120m long and

20m wide, with a depth of about 3m providing a total of 28,800m3 of feedstock storage. Each clamp

is to be made up of a series of layers designed to protect the underlying chalk from contamination

from silage effluent.

7.2 Containment layers

As can be seen in Appendix C - Site Photographs and Appendix D - Design Drawings, the chalk has

been excavated down to create four rectangular silage clamps with sloping sides and trapezoidal

divisions comprising in situ earth bunds between the clamps.

The following layers are then placed on the chalk base in a continuous layer over the bases and the

intermediate supporting earth divisions (see Appendix F - Technical Specifications of Materials

Used):

Flock material –liner protection layer (Enviroseal)

Impermeable 2mm High-density polyethylene (HDPE) ‘Enviroseal’ liner- the liner is to be

continuous over all of the bases and over the intermediate supporting earth divisions. It is

welded to the standard described in the Enviroseal Lining Solutions – Supply and Installation

Manual (Appendix F - Technical Specifications of Materials Used).

Second flock layer – liner protection layer (Enviroseal)

The following materials are then placed upon the second flock layer in the base of each clamp:

Pre cast concrete kerbs defining the longitudinal base area of each clamp

Tarmac scalpings – 150mm

Stabilised concrete made from hydraulically bound materials (HBM) (Allasso Recycling) -

150mm

Specialised treated tarmac ‘Ulti farm’ (Lafarge Tarmac) which is acid resistant to pH3 – 40-

50mm and meets EN 13108-1 Bituminous mixtures — Material specifications —Part 1:

Asphalt Concrete. The tarmac was poured and rolled continuously to ensure no cold joints in

the tarmac which may provide weak points.

The following materials are placed on both of the sides of each clamp up to halfway up (1.5m from

base):

Layer of dry concrete or natural compacted chalk

HDPE liner welded to the base liner at top and connected to the pre-cast concrete kerb at

the base through placing around a baton and screwing into the kerb every 20cm

(Enviroseal).

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7.3 Silage effluent collection

Silage effluent from the ensiled material will flow into the silage effluent collection system which is

within the containment system, above the HDPE liner and beneath the tarmac.

As shown in Appendix E – Silage Effluent Drainage Plans, the silage effluent in each clamp drains

along a fall from South West to North East and from there into a drain running along the apron along

a fall from North West to South East and into a sump sitting at the most southerly point of the apron

as shown in Appendix E – Silage Effluent Drainage Plans. The silage effluent pipes in each clamp run

lengthways along the whole length of the clamp. The collection system is off centre but parallel to

the dividing earth banks.

The pipework laid to carry silage effluent is UPVC waste pipe that sits within a trench lined with

HDPE. The effluent drains have been retrofitted into the tarmac scalpings as shown in Appendix C –

Site Photographs. A series of UPVC manholes have been installed within the tarmac base at 20

metre intervals along the length of the clamp. As stated each clamp is 120 metres in length. This

therefore equates to five manholes for each clamp.

Each manhole can either be sealed using a manhole cover made from fibre of the type used at petrol

stations (as shown in Appendix C – Site Photographs) which effectively prevents effluent or water

entering the manhole or left open using a grate which allows effluent to or water to run into the

manhole whilst preventing large items of debris blocking the drain. The manholes under ensiled

material will be covered and the fall on the clamp surface will ensure that silage effluent produced

will run to the next open (grated) manhole and into the silage effluent collection system.

The silage effluent sump is made from concrete rings set into concrete as shown in Appendix D –

Design Drawings (Cross Section of Rainwater and Silage Effluent Sumps). Earthcare Technical have

advise the client to provide additional containment within the silage effluent sump and as such the

client is in the process of sourcing a suitable tanking solution to paint in the chamber. The

specifications of this tanking solution were not available at time of writing.

Silage effluent provides a valuable gas rich feedstock for the AD plant. The effluent is therefore fed

into the AD facility. The sump is fitted with a submersible pump. Effluent pumping is controlled by a

flow device. When a set level is reached in the sump, the effluent is pumped into the pre-tank of the

AD plant along the route shown in Appendix E1 – Silage Effluent Drainage Plan Overview. The pump

is fitted with a telemetry alarm which will trigger in the case of pump failure. The telemetry is part of

the system used to monitor the AD plant 24/7 and connected to the mobile phones of employees on

call. If the submersible pump in the silage effluent pump sump failed, the effluent would overflow in

to the surface water lagoons (described in 7.5 Clean Water Collection) but this is unlikely as the

telemetry alarm would allow the problem to be spotted immediately.

The pre-tank of the AD plant is a 220m3 poured concrete tank which is lined with Enviroseal. The pre

- tank of the AD plant is also controlled by telemetry managing the risk of overfilling. There will also

be a manual switch of the silage effluent drainage system which will allow the effluent to be diverted

to the digestate lagoon if process monitoring of the AD plant indicates that the biology of the AD

plant doesn’t require further feeding or if the pre-tank is full.

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7.4 Dirty water collection from aprons

In front of the silage clamps (North East) there is impermeable tarmac apron which drains dirty

water from the apron into the silage effluent drainage system. Similarly to the rear of the clamps

(South West) there is a tarmac apron of approximately 10 metres edged with a concrete kerb to

drain any dirty water in this area towards the clamps and into the silage effluent drainage system.

This means that feedstock loading areas are designated as dirty.

7.5 Clean water collection

There are perforated pipes in shingle running lengthways along the silage clamps underneath the

liner; the function of these pipes is to drain any clean water collecting underneath the containment

system.

There is an ingenious means of collecting rainwater from areas of silage clamp not in use thus

managing the amount of rainwater that entered the silage effluent drainage system. This aids the

management of silage effluent. Along the length of each clamp, within the HDPE lined trench there is

the silage effluent pipe but also a perforated pipe that will remove clean water and direct it to a

clean water sump on the apron at the most southerly point of the clamps. The rainwater pipework

and connection to the clean water sump is shown in Appendix D2 – Cross Section of Rainwater and

Silage Effluent Sumps. The water is this sump runs into the adjacent surface water lagoons described

below.

The collection of rainwater form within the silage clamp containment area provides a means of leak

detection. If the rainwater collection system was found to be contaminated through visual

inspections or water quality sampling then it would be clear that the tarmac layer or the waste pipe

had been compromised in some way. Any polluted water could be retained in the surface water

lagoons as described below.

As shown in Appendix E1 – Silage Effluent Drainage Plan Overview, adjacent to the feedstock storage

area, there are three rectangular water lagoons approximately 50m long and 17m wide with a depth

of about 3m. They are lined with 2mm HDPE Enviroseal liner (see Appendix F – Technical

Specifications). These lagoons are used to store clean water run-off from clean yard areas and from

clamps not currently being use for feedstock storage (this can be achieved via the use of blocking

manhole as described in 7.3 Silage Effluent Collection). The lagoons also allow the operator to reuse

clean water on the farm reducing volumes of raw water usage.

These lagoons are located in series and will allow some natural attenuation of any low levels of

organic pollutants entering the system. There is a final discharge point to a soakaway.

The client has been advised by Earthcare Technical to retrofit a shut - off valve or similar device to

enable the blocking off the discharge to soakaway so that the clean water lagoon may be used to

contain polluted water in the case of an overflow from the silage effluent pump sump or detection

of a leak in the silage clamp containment system.

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8 REVIEW OF COMPLIANCE WITH SSAFO REGULATIONS

It must be emphasised that the EA has responsibility for confirming compliance with the SSAFO

Regulations. The following comments are based on information provided by the client and further to

the site visits made on the 6th May and 10th June 2015.

All parts of the silage clamps are more than 10 metres from any inland water.

The silage clamp, through use of appropriate materials, has been designed to be

impermeable and resistant to corrosion.

The base doesn’t have collection channels around the outside however the innovative

design allows silage effluent to drain towards the centre of the clamp and into a sealed

collection system inside the containment system.

The earth banks running between the clamps provide support to the ensiled material.

Whether they could be termed ‘walls’ with reference to the SSAFO Regulations is a matter of

interpretation. The base of the silo doesn’t extend beyond the walls, which in the case of

this design would not serve any function.

The collected effluent is conveyed to a purpose-built underground pump sump and from

there into the above ground poured concrete tank (pre-tank of the AD plant).

The pre-tank of the AD plant is 220m3. The lagoon has a capacity of 12,000m3 so there is

ample capacity for silage effluent storage.

Calculation for minimum volume of silage effluent storage:

For silos with a capacity exceeding 1,500 cubic metres the effluent tank must be at least 30 cubic

metres, plus 6.7 litres for each cubic metre of silo capacity in excess of 1,500 cubic metres.

Volume of silage clamp exceeding 1500m3 = 28,800-1,500 = 27,300m3

6.7 litres of capacity required for every m3 in excess of 1,500m3:

27,300 x 6.7 = 18,2910 litres

182,910 litres = 183 m3

Total silage effluent capacity required = 30 + 183 = 213 m3

9 INSPECTION AND MAINTENANCE

The client is committed to ongoing inspection and maintenance of the silage clamps to prevent any

pollution of land or groundwater. The silage clamp infrastructure will be inspected annually when

the clamps are empty and any repairs undertaken as necessary to ensure that the silage clamp is fit

for purpose.

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10 RISK ASSESSMENT AND SUMMARY

The primary environmental risk from the silage clamps is from silage effluent affecting local

groundwater through loss of containment from the silage clamp.

The consequences of exposure of groundwater to silage effluent is considered to be high due to the

fact that the silage clamps are located upon a major aquifer of high vulnerability, albeit that they are

not located within a Groundwater Protection Zone.

The risks to groundwater will be managed through:

The containment systems as previously described;

Storage of silage effluent in an above ground tank;

The clients’ commitment to inspection and maintenance as previously described.

For these reasons it is deemed that the probability of exposure of groundwater to silage effluent is

low.

Taking into account control measures, the residual risk of silage effluent affecting local groundwater

is deemed to be low.

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APPENDIX A – SILAGE CLAMP LOCATION PLAN

(c) Crown Copyright and database rights 2015. Ordnance Survey 100022861

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APPENDIX B – MAP SHOWING GROUNDWATER VULNERABILITY

http://maps.environment-agency.gov.uk/wiyby

4th June 2015

http://maps.environment-agency.gov.uk/wiyby

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APPENDIX C – SITE PHOTOGRAPHS (SITE VISITS 06/05/15 & 10/06/15)

Laying of base flock layer and Enviroseal liner. The lined silage effluent channel can also be seen (off

centre in clamp base).

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Enviroseal liner in place, white protective flock layer covering and tarmac scalpings being spread on

top of flock.

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Pre cast concrete kerb place along base of clamp side. Rolling of concrete on base and around silage

effluent collection manholes

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Placement of hot rolled tarmac

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UPVC silage effluent collection pipework and manhole

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Concrete seal around silage effluent manhole

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Silage effluent manhole fitted with cover

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Close up of manhole cover

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APPENDIX D1 – CROSS SECTION OF SILAGE CLAMP CONTAINMENT LAYERS (Drawing supplied by Yelspa Limited)

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APPENDIX D2 – CROSS SECTION OF RAINWATER AND SILAGE EFFLUENT SUMPS (Drawing supplied by Yelspa Limited)

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APPENDIX E1 –SILAGE EFFLUENT DRAINAGE PLAN OVERVIEW (Drawing supplied by Yelspa Limited)

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APPENDIX E2 – SILAGE EFFLUENT DRAINAGE PLAN DETAIL (Drawing supplied by Yelspa Limited)

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APPENDIX F - TECHNICAL SPECIFICATIONS OF MATERIALS

Refer to separate documents attached to report:

N-Std Secutex GRK 151'3, 201'3, 251'4, 301'5 C Rev 6_en (flock layer technical specification)

Enviroseal HDPE technical specification

Apsley Farm Estate - HBM Material Data Sheet (stabilised concrete layer technical specification)

126B0HK2 ULTIFARM 10 SURF 40-60 H-S TT - 2015 - PA – with EN tarmac technical specification

Enviroseal Lining Solutions - Supply and Installation Manual

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