FEEDER 9 (F9) – RIVER HUMBER PIPELINE REPLACEMENT PROJECT

Geotechnical & Geoenvironmental Non-Technical Executive Summary

October 2015

FOREWORD

The purpose of this Geotechnical & Geoenvironmental Non-Technical Executive Summary is to summarize key issues related to the (F9) Ground and Groundwater investigation (Geotechnical Site Investigation or GSI) using basic non-technical terminology.

The summary, outlines chronologically the sequence of events, commencing with a brief history, followed by preparation, planning and execution of the GSI, primarily split into two sections – land drilling on the east/west banks of the Humber – (boreholes prefixed ‘L’ i.e. L07); and overwater/marine drilling – (boreholes prefixed ‘M’ i.e. M07). Cone penetration testing (CPT) was also carried out.

GSI works, encountered ground and groundwater conditions and the interpretation (required for safe tunnel / pipeline design and construction) is also summarized using non-technical terminology.

1.0 BRIEF HISTORY

The current No. 9 Feeder transports between 70 and 100 million cubic metres per day of gas from the entry points in East Yorkshire into the wider transmission system in Lincolnshire, through a crossing under the River Humber.

In 2010 it was found that approximately 73m of pipeline was exposed, due to erosion. A short to medium term solution was put in place from November 2010 to December 2011 by installing fronded mattresses and gravel ‘dumpy’ bags to prevent further erosion.

It is proposed to construct a new 5km (F9) pipeline from Goxhill above Ground Installations (AGI’s) to Paull. The location of the site and GSI study areas are shown in Figure 1 below.

Figure 1 – Site Location Plan

2.0 GEOTECHNICAL, GEOHYDROLOGICAL FIELD WORKS – Programme, Planning and Execution

2.1 Geophysical Survey A geophysical survey was undertaken of the marine study area between October 21st and November 18th 2013 (no geophysical surveys were carried out on land). The aim of the marine geophysical survey was to provide information on:-

Water depths along the proposed pipeline route corridor;

Seabed features and obstructions;

Seabed sediments and depths to key geological boundaries;

Ground (soil/rock) anomalies (if any)

Different geological units within the Chalk (where possible.).

Full details on the scope of works and specification for the geophysics work can be found in

CS/064298/REP/001B “Nearshore Geophysics Scope of Work”, and details of survey results can be found in ESG interpretive report No. L3224-13 carried out for CAPITA and submitted in December 2013.

2.2 CAPITA Geotechnical Desk Study (GDS)

Interpretation of the geophysical survey became part of the GDS, required both by British Standards (BS) and Eurocodes (EC7); details of the GDS can be found in CAPITA Report CS/064298/F9/GEO/RPT/001 dated 22nd January 2014.

2.3 CAPITA Geotechnical Ground and Groundwater Design & Specification

Interpretation of the results of the geophysical survey led to development of the GDS, which in turn led to GSI design in accordance with UK Specification for Ground Investigation 2nd Edition: 2012.

The GSI specification/BoQ document originally identified twenty two Marine boreholes (reduced to sixteen – M01 to M14 and M19 and M20) following interpretation of the geophysical survey report and revised tunnel alignment; and eighteen Land boreholes (L01 to L08 at Goxhill and L09 to L18 at Paull) reduced to just twelve – see 2.4 below and Concluding Comments.

2.4 GSI Field Works – Tranche 1, 2 and 3

CAPITA, as the appointed Principal Contractor/Designer, awarded the Land and Marine GSI works to Soil Engineering Geoservices Ltd; who in turn appointed RED7MARINE (an International Jack Up Barge Owners Association certificated company utilizing two jack-up barges, a Haven Seaway and a Haven Seajack 3) to drill the overwater boreholes.

The marine drilling works were carried out between 1st May and 26th May 2014.

Land drilling works were carried out between 23rd April and 4th July 2015. However, some significant Geo-field problems resulted in only Seven boreholes being sunk at Goxhill (L01: L02: L03: L04*: L05*: L06*: and L08); and Five at Paull (L14: L15: L16: L16A and L18) – *See Plate 1.

Due to the geo-field problems encountered, coupled with access difficulties (boreholes L09 and L10), geo-environmental risks associated with drilling in mud flats and salt marshes (boreholes L07 and L17) and potentially contaminated ground (boreholes L11 and L12), the incomplete GSI works were later, referred to by CAPITA, as Phase 1 or Tranche 1 – see section 5.0; Concluding Comments.

The scope of works for Tranche 2 included, L07 (see Plate 2) close to the west bank of the Humber high water mark, in land owned by the Environment Agency, plus L09 and L10 located in a field east of the Humber, and L17 located on a spit, also on the east side of the Humber Estuary.

CAPITA, as the designer, awarded the Tranche 2 contract to Fugro Engineering Services (FES) who carried out the drilling works between 24th June and 10th July 2015. FES submitted their draft Factual Report (Contract No. G151022U) dated October 2015.

On 7th March 2014 CAPITA issued a Memo entitled “Suspected Asbestos Containing Material (ACM) in a Field Owned by Stoneledge Transport Ltd.,” – in proximity of proposed receive shaft.

On 10th March 2014, National Grid (NG) and Alcontrol technical specialists visited the site, to carry out a Site Reconnaissance in accordance with BS10175 – “Investigation of Potentially Contaminated Sites: Section 6.2.2; which included a Health & Safety Risk Assessment.

CAPITA decided that GSI works at such sites was outwith their current scope and advised, that a specialist drilling contractor be appointed by (NG) to carry out the works albeit, to CAPITA’s Design.

Thus for Tranche 3 (boreholes L11 and L12) NG appointed Wardell Armstrong (WA) to assess the health and safety hazards and risks relating to carrying out investigations in ACMs, design and manage the GSI. WA awarded the contract to Ian Farmer Associates, Geotechnical & Geoenvironmental Specialists who carried out the drilling works between 29th September and 12th October 2015.

3.0 SIMPLIFIED GEOLOGICAL INTERPRETATION

Table 1 summarizes (in layman’s terms) the Generalised Geological Succession encountered during GSI (land and Marine) borehole drilling works.

Geological Age

Summarised Geology

Brief Description (Layman’s terminology)

Quaternary

(2 – 3 million Years ago)

Alluvium

Soft to firm silty CLAY containing layers of silt, sand, peat and gravel

Tidal Flat/Salt Marsh deposits

Soft silty CLAY, with layers of sand, gravel and peat

Glacial Till

Sometimes referred to as ‘Boulder Clay’ – a highly variable mixture of rocks, boulders, and soil picked up by a moving glacier and carried along the path

of the ice advance. The glacier deposits this till along its path: on the sides of the ice sheet, at the toe of the glacier when it recedes,

Kelsey Hill (beds)

Muddy sand and gravel with red-brown clay

Cretaceous (60 – 150

million Years ago

Flamborough Chalk Formation

White, well-bedded, flint free chalk with common marl seams, hard chert nodules were sometimes encountered.

Burnham Chalk Formation

White, thinly-bedded chalk with tabular and discontinuous flint bands, and sporadic Marl seams.

Table 1 : Generalised Geology encountered during Land and Marine drilling works

The GSI was specifically designed and scheduled by CAPITA to identify superficial strata sequence, and rock lithology, from ground level to designed borehole termination depth, with frequent sampling and in-situ testing – on average every 1½ metres (or change in strata, whichever occurred the soonest).

Full details of all in-situ (field) and (laboratory) soil/rock testing can be found in Geotechnical reports prepared by respective drilling contractors:-

Tranche 1 – Soil Engineering Services Ltd, dated 31st July 2014; followed by the CAPITA GSI Report CS/064298/59/GEO/101 – dated 16th September 2014

Tranche 2 – Fugro Engineering Services Ltd; Report G151022U dated 21st October 2015, and

Tranche 3 – Ian Farmer Associates, Geotechnical & Geoenvironmental Specialists; November 2015 (draft report to be Quality Assured by WA).

In Summary: Glacial deposits are present from near ground surface to approximately 9m below ground level (bgl) at Goxhill with minimal Alluvium cover. However, the Glacial deposits thin considerably from borehole L04 northwards across the Humber Estuary as far as M11 where substantive thicknesses of Alluvium were found.

Occasional layers of peat were found in boreholes L04; L05 and L08 (Goxhill). Occasional thin layers of peat were also found in boreholes L09; L10; L11 and L12 at Paull. However, relatively thick layers – of extremely ‘low strength’ PEAT and silt were found at borehole L09 – see summary below.

To the northern side of the estuary from M12 northwards to Paull, the Alluvium thins, and once again, substantive thicknesses of Glacial Till overlying the chalk were found.

In the Flamborough Chalk stratum, many of the boreholes (both land and marine) encountered a layer of weathered structureless chalk (referred to as ‘Putty Chalk’) of variable thickness (frequently greater than 5 metres).

With the exception of borehole L16 (aborted at 18.00m due to further geo-drilling difficulties) chalk was encountered in all boreholes drilled during the GSI.

The Flamborough Chalk, described above, and through which approximately two thirds of the tunnel will be constructed, was found to be ‘very weak’ (locally extremely weak) with laminations of grey ‘Marl’ [a loose or crumbling earthy deposit (sand, silt, or clay) that contains a substantial amount of calcium carbonate].

The Flamborough Chalk is quite heavily fractured and locally stained orange with cream shell fragments and trace fossils – the chalk was observed to be ‘flint free’.

There is no discernible increase in strength with depth. In broad terms an Unconfined Strength value of between 5 and 15 MPa may be considered appropriate.

The Burnham Chalk, mostly encountered in the boreholes sunk at Goxhill (L01 to L07) and marine boreholes (M01 to M06) can be described as ‘very weak to weak’ with very closely spaced thin laminations of grey marl. Fractures are ‘extremely’ to ‘medium’ spaced with frequent angular to sub-rounded gravel-sized grey/brown flint.

Flint band thicknesses generally varied from 10mm to 300mm; the older Burnham Chalk underlies the Flamborough Chalk in the GSI study area.

As with the Flamborough Chalk, there is no discernible increase in strength with depth. In broad terms an Unconfined Strength value of between 5 and 20 MPa may be considered appropriate. NB: CAPITA commissioned Dr Rory Mortimore (a recognized leading authority on chalk) to review all chalk cores; his comprehensive report (CS/064298/F9/GEO/RPT/102) was issued on November 2014.

3.1 Land Boreholes

The land boreholes at Goxhill and Paull were primarily designed to identify:-

1. Superficial deposits (Alluvium; Glacial Till etc.,) – type and thickness

2. Classification of superficial deposits (including strength characteristics)

3. Groundwater characteristics, and

4. Depth to Rockhead.

Details of items 1 to 4 can be found in the various Geotechnical Reports as bulleted above.

In Summary:

Tranche 1 – Soil Engineering Ltd drilled twelve boreholes (L01; L02; L03; L04; L05; L06; L08; L14; L15; L16; L16A; and L18). Borehole base depths ranged from 18.00m (L16) to 54.80m (L18) – chalk encountered at 31.40m bgl.

Tranche 2 – Fugro Engineering Services drilled four boreholes (L07*1; L09*2: L10 and L17*1). Borehole base depths ranged from 15.80m (L09*2) to 40.00m (L07) – chalk encountered at 16.60m bgl.

*1 Site specific groundwater pressure units (Vibrating Wire Piezometers) were installed – tip depth = 30.00m bgl with respective ‘response zones’ of 28.50 to 31.50m bgl – presumed centre of proposed tunnel alignment.

*2 Borehole L09 encountered thick bands of extremely ‘low strength’ PEAT and silt 5.70 to 6.10m and 11.00m to 13.55m bgl.

Tranche 3 – Ian Farmer Associates drilled two boreholes (L11 and L12). Borehole base depths ranged from 35.00m (L12) (chalk encountered at 28.80m bgl) to 35.16m (L11) (chalk encountered at 28.90m bgl).

Manual measurement of water levels both during drilling and following unit installation was carried out on ALL land boreholes to establish a database of groundwater levels / pressures and to establish groundwater monitoring assessments. Preliminary assessment indicated that there is nominal ‘Tidal influence’ within the Glacial Till deposits at Goxhill, but not at Paull. Groundwater quality appears to vary from clear non-brackish to moderately brackish – future monitoring and analysis will further clarify this initial assessment.

3.2 Marine Boreholes

The sixteen Marine boreholes (M01 to M14 and M19 and M20) generally revealed a variable sequence of ‘silty SAND and Gravel interbedded with soft to stiff sandy gravelly CLAY’ overlying Chalk of the Flamborough Formation.

Borehole ‘base’ depth ranged from 34.00m (M13) to 51.40m (M19) bgl. Depth to chalk ranged from 5.50m (M19) to 21.10m (M04) bgl – see Ground Summarized Model Section below:

Marine & Estuarine Alluvium

Glacial Deposits

Flamborough Chalk

Burnham Chalk

Black dashed line indicates irregular Flamborough Chalk Rockhead (likely cause - erosion)

4.0 GEOHYDROLOGY (Simplified) During drilling operations (land and marine), groundwater strikes and response zones were noted and recorded on boreholes logs. Site specific schedules were prepared by CAPITA for the design and installation of groundwater monitoring units, some of which incorporated ground gas monitoring.

Groundwater levels on the Goxhill side of the site, range from 2.5m AOD to 1.9m AOD (1.5 to 1.7m below ground level).

Groundwater levels on the Paull side of the site, range from 3.6m AOD to -7.1m AOD (2.2m to 9.1m below ground level).

Where considered appropriate, in-situ permeability tests (ease with which water flows through a soil/rock media) were carried out, although some difficulty was experienced whilst trying to perform ‘Falling Head’ permeability tests (as per schedule) due to rising groundwater and hydrostatic pressure.

Such groundwater information is essential for the design of site specific dewatering systems and/or groundwater control measures for drive pit and receive shaft construction works. To establish more detailed groundwater flow systems, NG appointed OGI (Groundwater Technical Specialists) to carry out pump tests at Goxhill.

The tests were primarily, to address key issues raised by the Environment Agency (EA), and to ascertain site specific Geohydrological characteristics (transmissivity/permeability etc.,) at Goxhill, to permit further detailed design, relative to groundwater control for safe launch pit construction and proposed F9 geo-engineering tunnel operations.

4.1 OGI Pump Tests

Following several meetings and presentations, OGI were commissioned by NG to carry out (what is now referred to, as ‘mini pump tests’) – a simplified system coordinating and using existing boreholes at Goxhill. The mini pump system and associated geohydrological operations was designed and agreed with the Environment Agency.

Following a review of Phase 1 (Tranche 1) ground and groundwater evaluations and subsequent groundwater monitoring, OGI developed a site specific ‘mini pump test’ designed to establish groundwater flow characteristics – see Plate 3 for typical pump test set up, and Plate 4 showing site visit and field input from EA Specialists.

The site works were undertaken over 8 days between 24th August 2015 and 3rd September 2015. This included 4 days of testing and 2 days of monitoring and sampling before and after the tests. No works were undertaken over the bank holiday weekend (29th-31st August). The data loggers installed within the wells were modified to record at higher frequencies (every 30 seconds) between 25th August and 2nd September (for the duration of the pumping tests).

Pump test results – Flow rates (litres/second); drawdown and recovery can be found in OGI Factual and Interpretive Report J14-468-022R-Rev0 September 2015.

OGI were also commissioned by NG to:-

1. Prepare a ‘stand-alone’ report for the EA, to fully address their concerns, and

2. Review the Hyder Hydrogeological Impact Assessment (HIA) and prepare an Addendum, to build on the Hyder HIA findings with additional investigations, modeling and consultations, with a focus on the hydrogeological behaviour local to the pits with a preliminary groundwater control design.

More detailed information can be found in OGI Report No. J14-468-016R-Rev2 ‘Groundwater Control – HIA Addendum’.

4.2 Groundwater Monitoring – see also section 3.1

Although detailed on the designers schedule, groundwater monitoring units (mentioned above) were generally designed in accordance with the encountered ground and groundwater conditions at each land borehole. The designed installations coupled with a database logging system, were primarily established to determine:-

1. Changes in groundwater level (if any)

2. Tidal influence/impact on groundwater movement, and

3. To permit groundwater sampling and testing pre-during-post construction

Initially CAPITA contracted all groundwater/ground gas monitoring to Soil Engineering Services for all Tranche 1 works; Fugro for all Tranche 2 works. Following completion and initial monitoring of Tranche 3 boreholes, NG will be taking over monitoring responsibility for ALL land-based boreholes.

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5.0 CONCLUDING COMMENTS

Ground and Groundwater investigation (GSI) works at the site (Figure 1) proved difficult due to a combination of circumstances, commencing with delayed issue of the Geotechnical Desk Study (January 2014) after the GSI had been scheduled and Specification prepared (December 2013).

Problems were further exacerbated by the adoption of questionable drilling techniques and mechanisms for land borehole works; i.e. usage of conventional rotary drilling methods instead of ‘Geobor Wire-line’. Since this document has been prepared as a ‘Non-technical Executive Summary’ it should be sufficient for the ‘layman’ reader to understand, that, ‘conventional drilling with core barrel (in weak chalk) generally results in borehole collapse when core barrel is removed; whilst with ‘Geobor Wire-line’ the hole remains supported. NB: The significance of adopting incorrect drilling methodologies was emphasized whilst drilling Borehole L03 – commenced 24/04/2014 and not completed until 28/06/2014 – almost 8 weeks to sink the borehole to 47.00m bgl. Significant ground loss was also experienced at L02 – some 63 x 25kg bags of Bentonite pellets and 15 x 25kg bags of pea gravel required for unit installation and backfill of borehole.

Further problems in the field resulted in the works being aborted, with only twelve of the eighteen boreholes being sunk. This enforced a revised programme of works which led to the scheduling of a second phase (referred to in this document as Tranche 2 – during which a further four boreholes were sunk).

Other issues led to the appointment of a third specialist drilling contractor to finally complete the GSI in October 2015 (referred to in this document as Tranche 3) some eighteen months after commencement of land drilling works. Closing comments:- 1. Though the factual and interpretative reports for Tranche 3 GSI are not yet available, since fieldwork

was only completed on 12th October 2015, the preliminary results and observations support the results of the previous investigations carried out on the project. Notwithstanding this, it is unlikely, that Tranche 3 will be the last phase of GSI. Boreholes at Paull clearly highlighted variability of glacial deposits and it can be expected that more boreholes will be required, particularly at receive shaft location, to assist with the detailed design.

2. In addition, no pump tests have been carried out at Paull, and since groundwater control measures will almost certainly be required for safe shaft sinking, it is likely that pump tests will be carried out in this area to assist with the detailed design.

NB: BH L11 - water strike at 18.40m bgl rose to 0.90m bgl after 20 minutes and BH L12, water strike at 8.40m bgl rose to 3.50m bgl after 20 minutes.

3. Whilst the overland borehole GSI proved to be problematical from the outset, the marine (overwater)

drilling works commenced on time (and continued) without problem, completing within the allotted time-frame.

PLATES

Plate 1 Plate 2

Plate 3 Plate 4

Plate 1: Rotary Rigs drilling L06 (foreground) and L04 (background : Mid-fenced off area L05 (22nd May 2014)

Plate 2: Rotary rig drilling L07 on west bank of the River Humber (9th July 2015)

Plate 3: General Set-up for L06 Pump Test (26th August 2015)

Plate 4: Borehole / Well L06 Environment Agency Groundwater Specialists Discussing Pump Tests and Site Specific

Groundwater Control Issues (26th August 2015)

Allen E Cartmell Envirogeotechnical adviser 28th October 2015