FREDERICK SHERRELL LTD

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1 FREDERICK SHERRELL LTD CONSULTING ENGINEERING GEOLOGISTS AND GEOTECHNICAL ENGINEERS 66 WEST STREET TAVISTOCK DEVON PL19 8AJ Your Ref: Our Ref: 2962.NS.JR Telephone: Facsimile: Engineering Design Group, Devon County Council Matford Lane Offices, County Hall, EXETER. EX2 4QW 3 rd August 2007 For the attention of Mr. Rob Richards Dear Mr. Richards, Site Investigation for Sewer Pipe Crossing of the River Exe at Ashley, Tiverton In accordance with your instructions on 11 th 13 th June a borehole investigation was carried out of the site of a proposed replacement sewerage pipe beneath the River Exe at Ashley, Tiverton (see Figure 1). We understand that it is intended to install the pipe using directional drilling methods. The purpose of the investigation was to provide information regarding the nature and depth of the soils and bedrock to assist with the planning and design of the proposed directional drilling contract. Two boreholes were sunk on opposite banks of the River Exe by Geotechnical Engineering Ltd using a tracked Comacchio Pioneer drilling rig to obtain core samples of the soil and rock. The borehole locations are indicated in Figure 2 and illustrated in Photographs 1 and 3. The boreholes were logged by an Engineering Geologist from Frederick Sherrell Ltd and representative samples were taken for laboratory testing. Insitu Standard Penetration Tests were carried out during the course of the works and a standpipe was installed in Borehole B1 to allow falling head permeability tests to be undertaken. The borehole logs are appended to this report, together with the results of insitu and laboratory testing. The results of the investigation are summarised in the following paragraphs. 1. THE SITE 1 1. The site is located on the flood plain of the River Exe 2km south of Tiverton, as shown in Figure 1. On the eastern bank of the river is the South West Water Sewerage Treatment Works and on the western bank of the river is farm land and the A396. The flood plain is approximately 300m wide at this location. road and sewerage works lie between the steeply sloping valley sides of the Exe Directors: R.D.J. Gould, B.Sc., C.GeoI., F.G.S. J. Rickeard, B.Sc., A.R.S.M., C.GeoI., F.G.S. Registered Office : 66 West Street, Tavistock, Devon PL19 8AJ. Registered in England No V.A.T. Registration No

2 Valley. The Ordnance Survey map of the area indicates that ground level on the flood plain is approximately 53m above Ordnance Datum at the borehole locations Reference to the published British Geological Survey map of the area, Sheet 310, Tiverton, shows that the site is underlain by Sandstones and Shaley Mudstones of Upper Carboniferous geological age. The map indicates that the bedrock is mantled by alluvium. 2. RESULTS OF THE INVESTIGATION 2 1. Sequence of Soils and Bedrock Detailed logs of the boreholes are appended to this report. The ground conditions revealed by the boreholes are summarised in the table below. Formation Recorded Thickness (m) West Bank (B2) East Bank (B1) Topsoil Alluvial SILT, CLAY and fine SAND Alluvial GRAVEL MUDSTONE and SANDSTONE bedrock. Depth to Rockhead : Depth to Groundwater ( ) : The soils and bedrock are briefly described in the following paragraphs Overburden Soils The boreholes encountered m thickness of agricultural topsoil The topsoil is underlain by alluvial soils comprising an upper layer of relatively finegrained soils and a basal layer of gravels. On the west bank the upper layer comprised soft to firm, locally very soft organic gravelly clay and sandy silt, whilst on the east bank loose to medium dense silty sand was recorded. The basal layer comprises medium dense to dense, becoming very dense, clayey sandy gravels with occasional rounded cobbles of sandstone An N value of 8 was recorded from a Standard Penetration Test in the alluvial clay in - 2 -

3 Borehole B1. Higher N values were recorded in the alluvial gravels, ranging from N = 15 in Borehole B2 at 1.2m depth, to N = at depths greater than 2.5m Bedrock Pinkish grey mudstone bedrock was encountered in the boreholes beneath the alluvial gravels at approximately 3.6m and 4.0m depth below ground level on the west and east side respectfully. At rockhead the bedrock is highly fractured with much clay infill recorded in Borehole B1. Below about 5.7m depth the bedrock is typically slightly weathered and very close to closely fractured with Rock Quality Designation values generally 0% and Solid Core Ratios in the range 0 44%. Bedding planes dip at approximately to the horizontal (locally 45 ) and are rough and undulating. The rock cores are also broken by at least two sets of smooth, planar joints, which dip at oblique to the bedding In BH2 (west bank) fine grained sandstone was encountered below 7.0m depth. Rock Quality Designation values of 0% and Solid Core Ratios in the range 25 90% were recorded in the sandstone. The sandstone is very thinly to thinly bedded with bedding planes dipping at to the horizontal The intact mudstone and sandstone bedrock was described as moderately weak to moderately strong, locally strong in the borehole descriptions. Insitu SPT tests recorded N values typically in the range (extrapolated from penetrations <300mm) in the slightly to moderately weathered bedrock. A lower N value of 60 was recorded in the highly fractured zone close to rockhead (Borehole B1). Low Is 50 values in the range MPa were recorded from Point Load Index Tests, indicating probable failure along incipient fractures within the bedrock samples Groundwater Groundwater was recorded at 2.4m and 3.1m depth below ground level on the east and west sides respectively. A standpipe was installed in BH1 (east side) with the response zone in the slightly weathered mudstone at m below ground level. The results of falling head permeability tests in the standpipe are appended and indicate a moderate permeability of x10-6 m/s

4 3. GEOTECHNICAL CONSIDERATIONS 3 1. Geotechnical Considerations Relating to Construction We understand that the new sewer will be installed within the bedrock beneath the bed of the River Exe using directional drilling techniques. The rockhead profile is likely to dip beneath the river channel and the vertical alignment of the proposed sewer should take account of the need to maintain adequate cover of rock above the pipe crown. The information within the borehole logs and test results should be used by the contractor to determine the most appropriate drilling technique The results of permeability tests indicate a moderate permeability within the bedrock. Higher permeability values might be anticipated within the highly fractured rock near the rockhead and in the overlying alluvial gravel. Water flow within the bedrock is likely to be concentrated along natural fractures within the rockmass rather than through the material itself and there is a risk that drilling fluids could possibly migrate through fracture zones within the rock into the overlying alluvial gravels and thus into the river itself. Drilling operations and pipe installation will need to take account of the risk of migration of drilling fluids or grouts through the bedrock and the requirements of the Environment Agency with regard to protection of the River Exe Chemical Considerations Six samples of soil and rock were tested at the laboratories of Geotechnical Engineering Ltd for the presence of water soluble sulphate and ph value. The test results are summarised in Table 1 and indicate low concentrations of water soluble sulphate (maximum 0.2 g/l SO 4 in 2:1 water : soil extract) and slightly acidic to slightly alkaline ph values in the range One sample of ground water was tested for Sulphate and ph at ALcontrol Laboratories, Chester. The test results are shown in Table 1 and demonstrate low concentrations of sulphate (0.061 g/l) and an alkaline ph value of The results indicate that the site falls within Design Sulphate Class DS 1 of Table C1 of BRE Special Digest 1, Concrete in Aggressive Ground, Table C1 indicates an ACEC class of AC 1 for mobile groundwater

5 We trust that these notes are sufficient for your requirements. Please do not hesitate to contact us if you have any queries. Yours sincerely, for Frederick Sherrell Limited Nigel Singleton - 5 -

6 TABLES

7 Sample Depth Material Water Soluble Sulphate as SO3 2:1 Extract Water Soluble Sulphate as SO4 2:1 Extract Total Sulphate Total Sulphur ph Value m g/l g/l % % BH Alluvial Clay <0.1 < BH Alluvial Gravel BH Mudstone <0.02 <0.024 <0.01 < BH Groundwater BH Alluvial Sand <0.1 < BH Alluvial Gravel <0.1 < BH Mudstone <0.02 <0.024 <0.01 < RIVER EXE CROSSING, TIVERTON SUMMARY OF GEOCHEMICAL TEST RESULTS TABLE 1 Jul. 2007, Job No FREDERICK SHERRELL LTD

8 FIGURES 1 2

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11 PHOTOGRAPHS 1 4

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14 BOREHOLE LOGS

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16 SOIL DESCRIPTIONS Soil descriptions are generally in accordance with BS5930 (1999), with modifications based on Norbury et al (A Critical Review of Section 8, BS5930 Soil and rock description. Proc. 2 nd Regional Meeting, Engineering Group of the Geological Society (1984)). Descriptive System Principal constituent shown in capitals Secondary constituents (% of total soil) Slightly sandy GRAVEL 0 5 sandy GRAVEL > 5 20 very sandy GRAVEL >20 Soils with more than two constituents are described using the same convention, e.g. : slightly silty, very sandy GRAVEL (0 5% silt) (>20% sand) Silt and Clay Soils Mixed silt and clay soils are described as slightly silty/silty/very silty CLAY or slightly clayey/clayey/very clayey SILT, depending on the soil behaviour and index properties. Composite Soils Composite soils such as severely gap-graded deposits, interlayered soils or those with lenticular inclusions and soils containing cobbles and boulders are described using the terms set out in Clause , as follows : Principal soil type with a little (occasional) 0 5% Principal soil type with some > 5 20% Principal soil type with much >20 50% Principal soil type and approx. 50% e.g. silty SAND with occasional/some/much gravel Page 1 of 1 FSLS009 Amended December 2003 FREDERICK SHERRELL LTD CONSULTING ENGINEERING GEOLOGISTS AND GEOTECHNICAL ENGINEERS

17 ROCK DESCRIPTIONS Terminology The description of rocks generally follows the recommendations given in Section 6 of BS5930 (1999), with the exception of the description of weathered state and fracture state. Classification of Weathering The rock weathering scheme used in this report is as defined in Quarterly Journal of Engineering Geology (1972) : TERM Residual Soil DEFINITION Rock is discoloured and completely changed to a soil in which original rock fabric is completely destroyed. Completely weathered Highly weathered Moderately weathered Slightly weathered Fresh Rock is discoloured and changed to a soil but original fabric is mainly preserved. There may be occasional small corestones. The properties of the soil depend in part on the nature of the parent rock. Rock is discoloured; discontinuities may be open and have discoloured surfaces, and the original fabric of the rock near to the discontinuities may be altered. Alteration penetrates deeply inwards, but corestones are still present. (The ratio of original rock to weathered rock is estimated where possible.) Rock is discoloured; discontinuities may be open and will have discoloured surfaces with alteration starting to penetrate inwards; intact rock is noticeably weaker, as determined in the field, than the fresh rock. (The ratio of original rock is estimated where possible.) Rock may be slightly discoloured, particularly adjacent to discontinuities, which may be open and will have slightly discoloured surfaces; the intact rock is not noticeably weaker than the fresh rock. Parent rock showing no discolouration, loss of strength or any other weathering effects. References : BS 5930 : 1999 : Code of practice for site investigations (Formerly CP 2001) (British Standards Institution) QJEG : 1972 : The preparation of maps and plans in terms of engineering geology (Quarterly Journal of Engineering Geology Vol. 5, No. 4) Page 1 of 1 FSLS010 Amended December 2003 FREDERICK SHERRELL LTD CONSULTING ENGINEERING GEOLOGISTS AND GEOTECHNICAL ENGINEERS

18 DEFINITION OF FRACTURE STATE INDICES ROCK CORE SAMPLES The measurement of fracture state has been carried out in accordance with the principles outlined in BS 5930, as follows :- Total Core Recovery (TCR) The length of the total amount of core sample recovered, expressed as a percentage of the length of the core run. (BS 5930 : 1999 Site Investigations, p 136) Solid Core Recovery (SCR) The length of core recovered as solid cylinders (i.e. core with a full circumference) expressed as a percentage of the length of the core run. Length is measured along the core axis. (Modified from BS 5930 : 1999 Site Investigations, p 136) Rock Quality Designation (RQD) The length of core recovered as solid cylinders (i.e. core with a full circumference) each more than 100mm long, expressed as a percentage of the length of the core run. Length is measured along the core axis. (Modified from BS 5930 : 1999 Site Investigations, p 136) Fracture Index (FI) The total number of natural fractures per unit length of core recorded for each core run or for lithological units where appropriate and expressed as fractures per metre. NB : HF = Highly Fractured (>40 fractures/metre) NI = Non-Intact Core NR = No Recovery Length of core run = L (%) Total Core Recovery = T/L (%) L T S R Solid Core Recovery = S/L (%) Rock Quality Designation = R/L (%) (R >10cm) Page 1 of 1 FSLS011 Amended February 2004 FREDERICK SHERRELL LTD CONSULTING ENGINEERING GEOLOGISTS AND GEOTECHNICAL ENGINEERS

19 Site/Project Name RIVER EXE CROSSING, TIVERTON Grid Ref. Ground Level m BOREHOLE BH1 Method Machine Sheet Window Sampling : Rotary Coring (water flush) : m m Comacchio Pioneer of 2 Contractor GEOTECHNICAL ENGINEERING LTD Diameter Core : 89mm Date Symbolic Log Description Depth (m) Level (m ) Sample, Test or Core Recovery % Depth (m) of Sample, Test or Core Run R.Q.D. % (S.C.R. %) Fracture Index (no. per metre) S.P.T. N Value Water Casing Date Brown gravelly sandy clayey TOPSOIL with roots Soft-firm, brown, slightly sandy, gravelly CLAY mottled grey and orange with organic material and occasional rounded cobbles of sandstone /6 N D Very soft-soft, greyey brown, gravelly sandy SILT with fine rootlets. Dense, orangey brown, medium-coarse GRAVEL of sub angular-sub rounded sandstone with much orangey brown clay in upper levels and occasional rounded cobbles of sandstone in the lower levels N D D 3.25 Highly to moderately weathered pinkish grey silty MUDSTONE. Moderately weak to moderately strong. Very close to extremely closely fractured with much clay infill in the upper levels N 43 N (0) 0 (0) 49 for 125mm pen. 50 for 250mm pen m : Becoming slightly weathered and very close to closely fractured. Bedding dips 20 o (locally 45 o ), very thinly - thinly bedded, rough-undulating. Joints dip vertically and 70 o oblique to bedding, smooth-planar 66 N (0) 0 (0) HF for 35mm pen. 11/6 12/6 N (44) for 25mm pen. 100 N (26) 25 (35) for 25mm pen. Comments & Notes Inspection pit dug to 1.20m. Standpipe installed in gravel cell, m. Water standing at 2.47m bgl on Client DEVON COUNTY COUNCIL FSLS001a - Amended January 2005 U Undisturbed Sample (U100) B Bulk Disturbed Sample D Disturbed Sample W Water Sample N Standard Penetration Test K Falling Head Permeability Test Logged by Checked by NS JR RQD SCR V Rock Quality Designation Solid Core Recovery Groundwater First Encountered Standing Water Level Depth of Casing Insitu Vane Shear Test Scale 1:50 Job Ref FREDERICK SHERRELL LTD CONSULTING ENGINEERING GEOLOGISTS AND GEOTECHNICAL ENGINEERS

20 Site/Project Name RIVER EXE CROSSING, TIVERTON Grid Ref. Ground Level m BOREHOLE BH1 Method Machine Sheet Window Sampling Rotary Coring (water flush) : : m m Comacchio Pioneer of 2 Contractor GEOTECHNICAL ENGINEERING LTD Diameter Core : 89mm Date Symbolic Log Description Depth (m) Level (m ) Sample, Test or Core Recovery % Depth (m) of Sample, Test or Core Run R.Q.D. % (S.C.R. %) Fracture Index (no. per metre) S.P.T. N Value Water Casing Date N (9) for 25mm pen. 12/6 Comments & Notes Inspection pit dug to 1.20m. Standpipe installed in gravel cell, m. Water standing at 2.47m bgl on Client DEVON COUNTY COUNCIL FSLS001a - Amended January 2005 U B D W N K Undisturbed Sample (U100) Bulk Disturbed Sample Disturbed Sample Water Sample Standard Penetration Test Falling Head Permeability Test Logged by NS Checked by JR RQD Rock Quality Designation SCR Solid Core Recovery Groundwater First Encountered Standing Water Level Depth of Casing V Insitu Vane Shear Test Scale Job Ref. 1: FREDERICK SHERRELL LTD CONSULTING ENGINEERING GEOLOGISTS AND GEOTECHNICAL ENGINEERS

21 Site/Project Name RIVER EXE CROSSING, TIVERTON Grid Ref. Ground Level m BOREHOLE BH2 Method Machine Sheet Window Sampling : m Rotary Coring (water flush) : m Comacchio Pioneer of 2 Contractor GEOTECHNICAL ENGINEERING LTD Diameter Core : 89mm Date Symbolic Log Description Depth (m) Level (m ) Sample, Test or Core Recovery % Depth (m) of Sample, Test or Core Run R.Q.D. % (S.C.R. %) Fracture Index (no. per metre) S.P.T. N Value Water Casing Date Turf over brown, sandy, clayey TOPSOIL Loose to medium dense, brown, slightly gravelly, silty SAND with rootlets /6 Medium-dense - dense, orangey brown, clayey, sandy, sub angular - sub rounded, GRAVEL 1.40 N D D 2.00 Becoming very clayey below 2.5m. Very dense, grey brown, sub-rounded GRAVEL with cobbles of sandstone and some sandy clay in lower levels ND (0) 0 (0) NI NI 50 for 100mm pen. Moderately to slightly weathered, pinkish grey MUDSTONE. Moderately weak - moderately strong. Bedding dips o, very thinly to thinly bedded, stepped-smooth. Joints strike oblique to bedding, dip o, closely spaced, planar-smooth with some clay infill D 93 N (0) 0 (0) 0 (15) NI HF 50 for 35mm pen. 12/6 13/6 N (0) 50 for 25mm pen Slightly weathered, dark grey, fine grained SANDSTONE. Moderately strong, locally strong. Bedding dips o, very thinly - thinly bedded, planar smooth, Joints dip o, closely spaced, smooth-planar N (17) 0 (90) for 25mm pen. 20 Comments & Notes Inspection pit dug to 1.20m. Water standing at 3.10m depth at start of shift, Client DEVON COUNTY COUNCIL FSLS001a - Amended January 2005 U Undisturbed Sample (U100) B Bulk Disturbed Sample D Disturbed Sample W Water Sample N Standard Penetration Test K Falling Head Permeability Test N for RQD Rock Quality Designation SCR Solid Core Recovery Groundwater First Encountered Standing Water Level Depth of Casing V Insitu Vane Shear Test Logged by Checked by Scale Job Ref. NS JR 1: FREDERICK SHERRELL LTD CONSULTING ENGINEERING GEOLOGISTS AND GEOTECHNICAL ENGINEERS

22 Site/Project Name RIVER EXE CROSSING, TIVERTON Grid Ref. Ground Level m BOREHOLE BH2 Method Machine Sheet Window Sampling Rotary Coring (water flush) : : m m Comacchio Pioneer of 2 Contractor GEOTECHNICAL ENGINEERING LTD Diameter Core : 89mm Date Symbolic Log Description Depth (m) Level (m ) Sample, Test or Core Recovery % Depth (m) of Sample, Test or Core Run R.Q.D. % (S.C.R. %) Fracture Index (no. per metre) S.P.T. N Value Water Casing Date (25) 25mm pen N for 25mm pen. 13/6 Comments & Notes Inspection pit dug to 1.20m. Water standing at 3.10m depth at start of shift, Client DEVON COUNTY COUNCIL FSLS001a - Amended January 2005 U Undisturbed Sample (U100) B Bulk Disturbed Sample D Disturbed Sample W Water Sample N Standard Penetration Test K Falling Head Permeability Test Logged by Checked by NS JR RQD SCR V Rock Quality Designation Solid Core Recovery Groundwater First Encountered Standing Water Level Depth of Casing Insitu Vane Shear Test Scale 1:50 Job Ref FREDERICK SHERRELL LTD CONSULTING ENGINEERING GEOLOGISTS AND GEOTECHNICAL ENGINEERS

23 RESULTS OF INSITU PERMEABILITY TESTS

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26 RESULTS OF LABORATORY TESTS

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37 GENERAL NOTES

38 GENERAL NOTES 1. This report has been prepared for the exclusive use of the client named in the document. Copyright remains with Frederick Sherrell Limited. 2. This report, and interpretation or opinion has been prepared for the specific purpose stated in the document, and in respect of specific development proposals made available to Frederick Sherrell Limited by the client. This report should not be used for other schemes or adjacent sites without further reference to Frederick Sherrell Limited. 3. This report is based on ground conditions encountered in the exploratory holes and/or exposed to view at the site, together with the results of insitu and laboratory testing, as appropriate for the proposed development. There may be specific conditions hidden beneath the ground between exploratory hole locations or between existing exposures, which have not been taken into account in the report. 4. Opinions on the possible arrangement of strata between and beyond the locations of exploratory hole locations or existing exposures are for guidance only, and are subject to risk of undiscovered variations in the ground. Supplementary investigation should be implemented where accurate interpolation or extrapolation is critical. 5. Methods of construction and/or design proposals other than those discussed in the report should be assessed in respect of the available data, and supplementary investigation carried out if necessary. 6. Groundwater conditions recorded during the investigation may be affected by the method and speed of boring, drilling or excavation, and they may vary due to seasonal, tidal or other influences. Page 1 of 1 FSLS008 Amended May 2004 FREDERICK SHERRELL LTD CONSULTING ENGINEERING GEOLOGISTS AND GEOTECHNICAL ENGINEERS