Geotechnical Investigation and Contamination Assessment Report
St. Mary’s Garage, Fore Street, Kingskerswell, Newton Abbot, Devon
Mrs S Wells March 2010
SR/SB/DT/10127/GICAR St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
REPORT CONTROL SHEET
SITE ADDRESS: ST. MARY’S GARAGE FORE STREET KINGSKERSWELL NEWTON ABBOT DEVON CLIENT: MRS S WELLS REPORT TITLE: GEOTECHNICAL INVESTIGATION AND CONTAMINATION ASSESSMENT REPORT ISSUE DATE: 31 MARCH 2010 REPORT NO.: SR/SB/DT/10127/GICAR
PREPARED BY: STEVE BISHOP SIGNATURE: POSITION: ENGINEERING GEOLOGIST QUALIFICATIONS: BSc (Hons). MSc. FGS.
ISSUED BY: SIMON RUDDLESDEN SIGNATURE: POSITION: DIRECTOR QUALIFICATIONS: BSc (Hons). MSc. DIC. FGS.
RUDDLESDEN GEOTECHNICAL LTD 65 LANGATON LANE PINHOE EXETER EX1 3SP TEL: 01392 678082 FAX: 01392 678083 e-mail: [email protected] web: www.ruddlesden.co.uk
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CONTENTS
1.0 INTRODUCTION 1 1.1 General 1 1.2 Scope of Investigation 1 1.3 Scope of Report 2
2.0 THE SITE 3 2.1 Site Location 3 2.2 Site Description 3
3.0 DESK STUDY 5 3.1 General 5 3.2 Site History 5 3.3 Site Geology 6 3.4 Environmental Information 6 3.5 Underground Tank Information 7 3.6 Initial Conceptual Model 8 3.7 Sampling and Analysis Plan 10
4.0 FIELDWORK 12 4.1 General 12 4.2 Window Sample Boreholes 12
5.0 LABORATORY TESTING 13 5.1 General 13 5.2 Geotechnical Testing 13 5.3 Contamination Testing 13
6.0 RESULTS OF THE INVESTIGATION 15 6.1 General 15 6.2 Ground Conditions Encountered 15 6.3 In-Situ Testing 16 6.4 Groundwater 16
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6.5 Geotechnical Laboratory Testing 17 6.6 Contamination Laboratory Testing 17
7.0 GEOTECHNICAL ASSESSMENT 18 7.1 Proposals 18 7.2 Ground Profile 18 7.3 Foundations 19 7.4 Retaining Walls 21 7.5 Roads 22 7.6 Groundwater and Excavations 22 7.7 Soakaways 23
8.0 CONTAMINATION ASSESSMENT 24 8.1 General 24 8.2 Human Health Risk Assessment 24 8.3 Controlled Waters Risk Assessment 26 8.4 Ground Gas Assessment 28 8.5 Revised Conceptual Model 28 8.6 Discussion and Recommendations 29 8.7 Off-Site Disposal of Excavated Soils 33
9.0 CONCLUSIONS 34
10.0 REFERENCES 35
11.0 TERMS AND CONDITIONS 36
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APPENDICES
APPENDIX A WINDOW SAMPLE BOREHOLE LOGS (6 pages)
APPENDIX B PHOTOGRAPHS (4 pages)
APPENDIX C LABORATORY TESTING RESULTS Geotechnical Laboratory Testing (2 pages) Contamination Laboratory Testing (9 pages)
APPENDIX D DESK STUDY INFORMATION Landmark Envirocheck Report (66 pages) Underground Tank Information (5 pages)
APPENDIX E SITE PLANS Site Location Plan (1 page) Aerial Photograph (1 page) Window Sample Borehole Location Plan (1 page)
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EXECUTIVE SUMMARY
It is proposed to redevelop land at St. Mary’s Garage, Fore Street, Kingskerswell, Newton Abbot, Devon, for residential purposes. Old Ordnance Survey maps showed the site to have been largely undeveloped until at least 1955, by which time a “garage” building is present at the location of the main building today, near the centre of the site. Since that time, various additional buildings were built until 1980, when the site resembled its present day layout. The site was used as a petrol filling station until 1998.
Six window sample boreholes generally encountered ground conditions of topsoil or made ground, underlain by stiff to very stiff reddish brown silty gravelly clay, underlain by very dense grey silty gravel.
Foundation recommendations are strip or trench-fill foundations at a minimum depth of 0.90m below existing or proposed ground levels, whichever is deepest. Foundations should be deepened below any made ground and in accordance with NHBC Standards where building near trees for soils of low volume change potential. Foundations might need to be re-designed, e.g. deep trench-fill or reinforced beam, if proposed properties are built over the infilled excavations of the former tanks.
Elevated levels of contamination were recorded within the ground, particularly in the area of underground fuel tanks, which represent an unacceptable risk of causing harm to human health, given the proposed end-use. Proposed remedial measures include providing 600mm of inert subsoil and topsoil underlain by a geo-textile membrane in garden areas and the excavation and off-site removal of all underground fuel and surrounding contaminated soil.
No radon protection measures are required and ground gas protective measures are not considered to be necessary.
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1.0 INTRODUCTION 1.1 General
In March 2010, a combined Phase 1 and Phase 2: Geotechnical Investigation and Contamination Assessment was undertaken by Ruddlesden geotechnical ltd on behalf of Mrs S Wells, for the proposed residential re-development of land at St. Mary’s Garage, Fore Street, Kingskerswell, Newton Abbot, Devon.
The investigation was undertaken to determine subsurface ground conditions, to provide recommendations for foundations and associated structures, and to assess the extent of any contamination at the site.
The investigation comprised a desk study and walkover survey followed by the formation of six window sample boreholes with in-situ and laboratory testing.
1.2 Scope of Investigation
The investigation covers geotechnical and contamination aspects relating to the development. The brief was understood to comprise the following: Carry out desk study and walkover survey. Undertake exploratory holes. Schedule geotechnical and contamination laboratory testing. Establish the ground conditions across the site. Make recommendations for foundation design. Make recommendations covering other geotechnical aspects, including drainage. Undertake a contamination risk assessment. Provide details of any contamination remedial measure requirements.
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1.3 Scope of Report
The report is presented as a description of the procedures employed and the data obtained. This is followed by a thorough description of the ground and groundwater conditions, together with an assessment of material and mass ground parameters. The final part of the report comprises analysis, recommendations, and conclusions, which are provided in two separate parts: geotechnical and contamination.
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2.0 THE SITE 2.1 Site Location
The site is located at St. Mary’s Garage, Fore Street, Kingskerswell, Newton Abbot, Devon, see Appendix E (Dwg. No.’s 10127/01 and 10127/AP). The British National Grid Reference of the site is 287900, 67770.
The site is situated in a predominantly residential area of the village of Kingskerswell. The surrounding topography is hilly. Access to the site is gained from Fore Street, to the north.
2.2 Site Description
The site is irregular in shape, measuring approximately 50m x 40m (0.20Ha), and is generally level with a gentle slope down to the southwest for the most part, although the most southern part of the site slopes very steeply down towards the southwest.
The site comprises a garage (St. Mary’s Garage). A car sales forecourt, with numerous cars, is present in the northern part of the site. An underground workshop, with a southerly facing downward slope leading to it, is present in the western part of the site, above which is situated on open yard area. The existing garage building, comprising a sales showroom and repair centre, is present in the central area of the site. A single-storey residential dwelling is present in the southern part of the site (Lyndhurst) and another single storey bungalow (St Mary’s Bungalow) and small domestic garage building is present in the eastern part of the site. The site is covered by a mix of bitmac, concrete and grass. Several large manhole covers were noted during the walkover survey, notably in the northern and western parts of the site. A retaining wall, approximately 2m in height, runs along the southern boundary of the site.
The site is surrounded to the north by a road (Fore Street) before residential housing and shops, to the east by residential dwellings with associated gardens, to the south by a road (Daccabridge Road), approximately 7m below
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 3 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd general site ground level before residential dwellings with associated gardens, and to the west by a commercial building (Datel Electricals) and residential dwelling (Little Gara).
Photographs of the site are presented in Appendix B of this report and the main site features are shown on the borehole location plan (Appendix E, Dwg. No. 10127/02).
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3.0 DESK STUDY 3.1 General
A desk study was undertaken to provide background information, comprising the consultation of: Old Ordnance Survey maps. Geological maps and memoirs. Environmental information. Underground tank information
This information was used to produce a “conceptual model” of the site so that an appropriate intrusive investigation could be carried out.
3.2 Site History
A full set of old Ordnance Survey maps of the site was obtained as part of the Landmark Envirocheck report (Appendix D of this report). The salient points are listed below:
1888 The site is largely undeveloped, being covered by orchard trees. A small building, possibly a shed, is present in the southeast of the site. The site is surrounded predominantly by a mixture of orchard trees and small buildings. “Fore Street” is shown in its current day position, running along the northern boundary of the site, with a “Post Office” shown on the opposite side of the road. 1905 Generally as 1888. 1937 Generally as 1905. 1955 The site is now occupied by a building labelled as “Garage” in the central northern part of the site, at the location of the main building present today, and scrub/ orchard land. A small building is present in the western part of the site. 1969 The scrub/ orchard land is no longer present, and a small building is now present in the central area of the site.
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1980 Further buildings are now present in the eastern and southern areas of the site, including “St Mary’s Bungalow”, and the site resembles its current day layout. A ramp, leading to the present day underground work shop, also now appears to be present in the western part of the site. 1993 Generally as 1980. 1999 Generally as 1993. 2006 Generally as 1999. 2009 Generally as 2006.
Anecdotal information revealed that the site was used as a petrol filling station until 1998.
In summary, the site was largely undeveloped until at least 1955, by which time a “garage” building is present at the location of the main building today, near the centre of the site. Since that time, various additional buildings were built until 1980, when the site resembled its present day layout.
3.3 Site Geology
The British Geological Survey (BGS) map of the area shows the site to be underlain by Permian Watcombe Breccia, which is described as a reddish brown breccia (coarse grained sedimentary rock).
3.4 Environmental Information
The key environmental information contained within the Landmark Envirocheck Report is listed below:
The nearest surface water feature is 68m to the southwest of the site (Aller Brook). There are no abstraction points within 1km of the site.
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The underlying strata are classified as a Minor Aquifer. These can be fractured or potentially fractured rocks, which do not have a high primary permeability, or other formations of variable permeability including unconsolidated deposits. Although not producing large quantities of water for abstraction, they are important for local supplies and in supplying base flow to rivers. The nearest recorded landfill site is located 688m to the northwest of the site (Yannon Lane – Landfills taking other wastes (Construction, Demolition, Dredgings)). The British Geological Survey (BGS) information indicates that no radon protective measures are necessary in the construction of new dwellings.
3.5 Underground Tank Information
Details of the decommissioning of the underground fuel tanks used during the site’s time as a petrol filling station were provided by the client and these are included in Appendix D of this report.
This information shows that the underground fuel tanks were decommissioned in 1998 by Devon Fire and Rescue Service, acting on behalf of Devon County Council. The adjoining tanks, 4550 and 9100 litres in size, were located in the northwest of the site. They were filled with concrete slurry.
A further tank, 2275 litres in size, located adjacent to the western boundary, remained in the ground and was used for waste oil storage.
An above ground paraffin tank was also present adjacent to the car showroom.
Additional information also provided by the client shows that the tanks were installed in 1974 and that they were set in concrete.
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A further plan shows the precise locations of the tanks: the concrete filled tanks are 4.30m from the western boundary and 3.80m from the northern boundary.
It is inferred from the latter two documents that originally the tank currently used to store waste oil in the west of the site was used to store petrol, with the pumps located to the west of the garage building. In 1974, new, larger, tanks were installed in the northwest of the site, with new pumps then placed to the north of the main garage building. The tank in the west of the site has since been used for the storage of waste oil.
3.6 Initial Conceptual Model 3.6.1 Geotechnical Conceptual Model
The site is situated on the top of a very steep southwesterly facing slope, and so some may ground is expected, possibly having been historically placed in an effort to level the site.
From the published information, the expected underlying geology is Watcombe Breccia, comprising reddish brown breccia (coarse grained sedimentary rock). If encountered at shallow depth, it is considered these deposits should provide a sufficient bearing capacity for the adoption of traditional strip/ trench-fill foundations.
3.6.2 Contamination Conceptual Model
Source
Old maps showed the site to be occupied by the present garage building since at least 1955. Although the site has most recently been used as a car lot/ showroom and for vehicle maintenance purposes, the site is known to have previously been used as a petrol filling station, with at least three underground tanks known to still be present beneath the site, presenting a possible source of contamination.
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Petrol filling stations and garages are a potential source of contamination of the ground. The main source of potential contamination is normally fuel storage tanks (in this case underground) and leakages from them; a small leak that goes undetected for any significant length of time can cause significant contamination of the ground. Significant contamination is more associated with older tanks as they tend to be less well constructed than newer tanks, which are also now monitored for discrepancies between input and output rates.
The former locations of the fuel pumps are also considered potential sources of contamination at this site.
Whilst modern practices dictate that waste oil is now disposed of responsibly, in the past, waste oil is likely to have been disposed of directly into the ground or down a drain, which may have leaked.
Therefore, past and, to a lesser extent, present on-site land uses may have potentially caused some contamination of the ground.
Located in a predominantly residential area, and based on desk study information, it is considered that past and present surrounding land uses are unlikely to have caused any significant contamination of the ground beneath the site.
Pathway
In accordance with the CLEA model for a residential land use, exposure pathways potentially linking contamination to humans include:
Direct soil and indoor dust ingestion. Consumption of homegrown produce. Consumption of soil adhering to homegrown produce. Skin contact with soils and indoor dust.
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Inhalation of indoor and outdoor dust and vapours.
If present, groundwater flow is considered to be the main migration pathway linking any contamination to controlled waters receptors.
Receptor
As a residential land use, end-users are considered as potential receptors of any contamination, with a young female child (aged zero to six years old), being the critical receptor.
In the absence of an abstraction point within 1km of the site, the nearest water course, located 68m to the southwest of the site, and groundwater beneath the site are considered to be the main potential controlled waters receptors.
3.7 Sampling and Analysis Plan
In order to confirm the above conceptual models, an intrusive site investigation was undertaken.
Window sample boreholes were considered to be the most suitable exploratory technique, as these would enable sufficient geotechnical and environmental information to be obtained without excessively disrupting the areas of existing hardstanding or daily site activities.
The boreholes were located so as to provide a reasonable spread of information and an accurate representation of subsurface ground conditions. The borehole locations also included the most probable locations of contamination based on the conceptual model, i.e. underground fuel tanks, fuel pumps, vehicle servicing area etc. Due to a lack of headroom, it was not possible to carry out a borehole in the southwestern corner of the site. The boreholes were strategically located as follows: WS1 – garden/ top of slope – possible made ground.
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WS2 – adjacent to repair garage/ former above ground paraffin tank and fuel pump location. WS3 – adjacent to underground waste oil tank and infilled underground former petrol tanks. WS4 – garden (general coverage of northeast of site). WS5 – Car forecourt area and former fuel pump area. WS6 – adjacent to infilled underground former petrol tanks.
Geotechnical laboratory tests were undertaken to determine the volume change potential of the soil for foundation design and concrete class requirements. Samples were taken for geotechnical testing from six different locations, at different depths.
Representative samples were tested for the former ICRCL suite of contaminants, speciated PAH and total TPH, which provides a broad and general suite of contaminants that may be present. In addition, a sample taken adjacent to a buried fuel tank (WS3) was tested for speciated TPH, to enable a more detailed risk assessment to be made. Samples were selected for contamination testing from all six of the boreholes from a range of depths within the top 1m, as, in accordance with the CLEA model, for most exposure pathways the contamination is assumed to be within one metre of the surface. In addition, where sufficient groundwater allowed, a groundwater sample was taken for groundwater analysis (WS5 – former fuel pump location and near to underground fuel tanks).
Samples were selected for testing to provide an accurate representation of ground conditions encountered.
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4.0 FIELDWORK 4.1 General
All fieldwork was undertaken on 05 March 2010. The siting and setting out of all the boreholes was the responsibility of Ruddlesden geotechnical ltd, who also determined the extent of testing and sampling.
The boreholes were located so as to provide a reasonable spread of information and an accurate representation of subsurface ground conditions.
All fieldwork was undertaken in accordance with BS5930 (1999): British Standard Code of Practice for Site Investigation, British Standard BS10175 (2001): Investigation of Potentially Contaminated Sites – Code of Practice and Eurocode 7 (2007): Part 2 Ground Investigation and Testing.
4.2 Window Sample Boreholes
Six window sample boreholes were formed to depths of between 2.34m and 5.45m using a Competitor 130 (percussive soil sampling rig).
Observations and samples were taken from the recovered soil cores. The supervising geologist provided a detailed description of the ground conditions, groundwater and stability and also obtained samples at representative locations, which were placed into suitable containers.
At regular intervals, Standard Penetration Tests (SPT’s) were carried out using either a split spoon sampler or a solid 60 cone. The results of these tests are given as a Standard Penetration N-Value or as a blow count for a given penetration at the appropriate position on the borehole logs.
Details of ground and groundwater conditions encountered can be found on the borehole logs (Appendix A). The borehole locations are shown on the borehole location plan (Dwg. No. 10127/02, Appendix E).
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5.0 LABORATORY TESTING 5.1 General
All laboratory testing was scheduled by Ruddlesden geotechnical ltd and the results are presented in Appendix C of this report.
5.2 Geotechnical Testing
The programme of laboratory testing was carried out in accordance with BS 1377 (1990) “Methods of Test for Soils for Civil Engineering Purposes”.
The following tests were carried out on six samples: Moisture Content Plasticity Index Tests pH Value Sulphate Content
5.3 Contamination Testing
In order to test the conceptual model of the site (see section 3.5.2 of this report), six soil samples and one water sample were tested for the following suites of tests; the testing was UKAS accredited:
Former ICRCL Tables 3 and 4 Arsenic, cadmium, chromium, copper, lead, mercury, nickel, selenium, zinc, total PAH, total sulphate, soluble sulphate, pH, boron, free cyanide, total cyanide, hexavalent chromium, phenols, sulphur, sulphide, thiocyanate.
Speciated Polyaromatic Hydrocarbons (PAH) Acenaphthene, acenaphthylene, anthracene, benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(g,h,i)perylene, benzo(k)fluoranthene, chrysene, dibenzo(a,h) anthracene, fluoranthene, fluorene, indeno(1,2,3-cd)pyrene, naphthalene, phenanthrene, pyrene.
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Total Petroleum Hydrocarbons (TPH) Total TPH.
Soil Organic Matter (SOM)
In addition, one of the samples taken from adjacent to the underground fuel tank (WS3) was tested for the following suite:
Speciated Total Petroleum Hydrocarbons (TPH) TPH aliphatic >C5-C6; TPH aliphatic >C6-C8; TPH aliphatic >C8-C10; TPH aliphatic >C10-C12; TPH aliphatic >C12-C16; TPH aliphatic >C16-C21; TPH aliphatic >C21-C35; TPH aromatic >C5-C7; TPH aromatic >C7-C8; TPH aromatic >C8-C10; TPH aromatic >C10-C12; TPH aromatic >C12-C16; TPH aromatic >C16-C21; TPH aromatic >C21-C35.
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6.0 RESULTS OF THE INVESTIGATION 6.1 General
The following sections provide a summary of ground conditions encountered, groundwater and laboratory testing. Further details are provided in the Appendices of this report.
The results of this investigation broadly concur with the predicted conceptual model.
6.2 Ground Conditions Encountered 6.2.1 Topsoil
In WS1 & WS4 only (located in the grassed garden areas of “St Mary’s Bungalow”), brown silty (slightly gravelly in WS4) clay with frequent rootlets was encountered to a depth of between 0.20m and 0.30m.
6.2.2 Made Ground
In WS3, WS5 and WS6 bitmac, underlain by black mottled grey sandy gravel, was encountered to depths of between 0.25m and 0.30m.
In WS2 concrete was encountered to a depth of 0.37m.
6.2.3 Natural Geology
Beneath the topsoil or made ground, the following ground conditions were encountered:
In WS4 only, stiff brown mottled grey silty very gravelly clay, was encountered to a depth of 0.50m. In all of the boreholes, these deposits were underlain by stiff to very stiff reddish brown silty slightly gravelly to gravelly clay, to a depth of between 2.20m and 5.45m (base of borehole). In all of the boreholes (other
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 15 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd than WS5) these deposits were recorded as having pockets of grey or dark grey gravel.
In WS3 a strong hydrocarbon odour was noted at approximately 2.10m.
These deposits were underlain by, in WS3 and WS6, very dense grey silty gravel to a depth of between 2.34m and 4.36m (base of the boreholes).
6.3 In-Situ Testing
The following SPT N-values were recorded in the boreholes: 1.00m – 5, 6, 8, 8, 8, 28 2.00m – 7, 7, 7, 8, 9, >50 3.00m – 8, 8, 9, 11, 24 4.00m – 12, 13, 18, 40, >50 5.00m – 3, 5, >50
6.4 Groundwater
Groundwater was encountered at the following locations during the course of investigation:
Table One: Occurrence of Groundwater Hole ID Depth (mBGL) WS2 5.20m WS4 4.20m WS5 4.00m
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6.5 Geotechnical Laboratory Testing
All the geotechnical laboratory testing results are presented in Appendix C of this report. The main points are summarised in the table below: Table Two: Summary of Laboratory Classification Testing Results
WS1 WS2 WS3 WS4 WS5 WS6 3.50m 3.00m 2.00m 2.50m 1.50m 1.00m Moisture Content 13.5 16.9 13.7 15.0 14.6 13.6 (%)
Liquid Limit (%) 34 38 36 33 33 34
Plastic Limit (%) 16 18 17 16 17 16
Plasticity Index (%) 18 20 19 17 16 18
%passing 425μm 60.4 58.7 67 53.8 66.8 69.5 sieve Modified Plasticity 11 11 12 9 11 12 Index (%) Volume Change Low Low Low Low Low Low Potential
pH Value 7.8 7.7 7.9 8.0 7.6 8.4
Sulphate Content 0.02 0.02 0.02 0.10 0.04 1.3 (g/l)
6.6 Contamination Laboratory Testing
All the laboratory testing results, together with the Generic Assessment Criteria (GAC) to which they have been compared, are presented in Appendix C of this report and the implications are discussed in section 8 of this report.
In summary, slightly elevated levels of sulphate, naphthalene, benzo(a)pyrene, dibenzo(a,h)anthracene, total TPH ,TPH (Aliphatic EC>6-8), TPH (Aliphatic EC>8-10), TPH (Aliphatic EC>10-12), TPH (Aromatic EC>8- 10) and TPH (Aromatic EC>10-12) have been recorded in the soil samples, but no significantly elevated levels of contamination were recorded in the one water sample tested.
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7.0 GEOTECHNICAL ASSESSMENT 7.1 Proposals
It is understood that the site is to be redeveloped for residential purposes. No further details were provided at the time of writing this report.
7.2 Ground Profile
The ground conditions encountered have been summarised in section 6.0 of this report and the individual borehole logs, photographs and laboratory testing results should be referred to for further details. Within this section of the report the general ground profile is reviewed and the engineering significance of individual layers is discussed.
Beneath a surface covering of topsoil and/ or made ground, stiff to very stiff reddish brown silty gravelly clay was typically encountered. The SPT test results indicate that this deposit was of sufficient bearing capacity to provide a suitable founding stratum for strip or trench-fill foundations.
Laboratory testing classified the soils as being of low volume change potential in accordance with NHBC Standards, chapter 4.2.
It is noted that some made ground (estimated depth 3.00m) will be present in the area of the underground tanks and that this will not provide a suitable founding stratum.
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7.3 Foundations 7.3.1 General
The results of this investigation indicate that strip or trench-fill foundations are suitable to support the proposed structures.
However, it is noted that underground tanks are currently present in the northwest of the site. For contamination purposes, these will need to be excavated and removed from site (see section 8 of this report). The excavations will subsequently leave areas of deep (~3m) made ground. Should proposed properties be built over the infilled excavations of the former tanks foundations might need to be re-designed accordingly, e.g. deep trench- fill, reinforced beam, etc.
7.3.2 Strip/ Trench-Fill Foundations
It is considered that a safe nett allowable bearing pressure of 150kN/m2 may be placed on the stiff clay by strip or trench-fill foundations of least width 600mm at a minimum depth of 0.90m below existing or proposed ground levels, whichever is deepest.
Foundations must be built at least 0.20m below any superficial soft deposits, made ground and former foundations, which are to be removed and fully grubbed out.
Where building near trees, foundations should be deepened in accordance with NHBC Standards, chapter 4.2, for soils of low volume change potential.
Where foundations are stepped to take account of the influence of trees or due to the slope of the site they should be stepped gradually with no step exceeding 0.50m.
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Any soft or loose material in the base of foundation excavations should be removed and replaced with compacted lean mix concrete prior to pouring the foundations.
7.3.3 Ground Floor Slabs
Where NHBC building near trees requirements mean that foundation depths are greater than 1.50m or where the depth of made ground is more than 600mm (including areas of grubbed out former foundations), fully suspended ground floor slabs are required.
Where NHBC building near trees requirements mean that foundation depths are less than 1.50m and where the depth of made ground is less than 600mm, ground bearing slabs may be adopted.
7.3.4 Sulphate and pH Aggressivity
The results of the pH and sulphate tests have been compared to Table C1 of BRE Special Digest 1 “Concrete in Aggressive Ground”. This comparison indicates the elevated level of soluble sulphate recorded in the sample from WS6 (1.3g/l) to be above the threshold value above which sulphate resistant concrete is required.
However, it is noted that the sample from WS6 was taken adjacent to a concrete filled former fuel tank. It is considered that the recorded level of sulphate in this location is associated with this concrete and is anomalous and therefore should not be considered in the assessment of concrete class requirements at this site. As this soil will also probably be removed as part of the tank removal process (see section 8 of this report), its omission from the assessment is also further justified.
The results of the pH and sulphate tests have been compared to Table C2 of BRE Special Digest 1 “Concrete in Aggressive Ground”. This comparison indicates the Design Sulphate Class for the site to be DS-1. As the site is
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 20 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd considered to be brownfield, groundwater can be treated as static and neutral pH values were recorded, Aggressive Chemical Environment for Concrete (ACEC) class AC-1 is required for all buried concrete at this site, i.e. no special precautions.
7.3.5 Radon Protective Measures
BR Report 211 “Radon: Guidance on Protective Measures for New Dwellings” and British Geological Survey (BGS) information obtained as part of the Landmark Envirocheck report (Appendix D) indicate that no radon protection measures are required at this site.
7.4 Retaining Walls
The development will involve a number of retaining walls. The foundations for all of the retaining walls should be founded in the stiff clay, which will provide a safe nett allowable bearing pressure of 150kN/m2.
Based on field observations and guidance provided in BS 8002: 1994: Code of Practice for Earth Retaining Structures, the following geotechnical parameters are estimated for retaining wall design:
Unit weight – 1.8Mg/m3 Angle of Friction ( ’) – 30° Cohesion (c’) – 0kN/m2
The groundwater table can be taken as being below the base of the retaining wall foundations, though adequate drainage should be incorporated into the design of the retaining wall.
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 21 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
7.5 Roads
From an assessment of the ground conditions encountered, a CBR value of 2% is estimated and this value may be used for road pavement design.
This should be confirmed prior to construction with full-scale in-situ CBR tests at road level in accordance with BS1377.
Laboratory testing indicated the soils to be frost-susceptible.
7.6 Groundwater and Excavations
Groundwater was encountered in three of the six boreholes at depths of between 4.00m and 5.20m and so only deep excavations are likely to require de-watering.
It is noted that groundwater levels fluctuate according to the season and from year to year. It is noted that in the weeks prior to the investigation the weather had been average to dry for the time of year. Therefore, higher groundwater levels may be encountered during periods of wetter weather.
Some collapsing of the boreholes was encountered in two locations and so some shoring of temporary excavations may be required.
No problems with excavatability are foreseen.
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 22 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
7.7 Soakaways
From a visual assessment of the ground conditions encountered, i.e. clayey, it is considered that soakaways are not a suitable means for surface water drainage.
Soakaways are also not recommended on potentially contaminated sites as they can promote contamination migration.
If soakaways are required, soakaway testing should be undertaken in accordance with BRE 365 to establish permeability values for use in soakaway design.
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 23 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
8.0 CONTAMINATION ASSESSMENT 8.1 General
It is understood that the site is to be redeveloped for residential purposes with the construction of eight residential units. No further details were available at the time of writing this report.
The contamination assessment has been carried out in accordance with the latest Environment Agency guidance using a source-pathway-receptor analysis method, so that appropriate remedial measures may be proposed.
8.2 Human Health Risk Assessment 8.2.1 Generic Assessment Criteria
The results of the contamination laboratory testing have been compared to Generic Assessment Criteria (GAC) to aid the evaluation of the extent of contamination at the site. If any of the GAC are exceeded, this may be indicative of an unacceptable risk to the health of site-users and that further investigation and/ or remediation is required.
The proposed end-use of a residential land use has been used in this risk assessment.
Where Soil Guideline Values (SGV’s), published by DEFRA and derived from the Contaminated Land Exposure Assessment (CLEA) model, are available, the results of the laboratory testing have been compared against the published SGV’s for the proposed end-use.
For analytes where SGV’s have not yet been produced, GAC produced by Land Quality Management (LQM) and the Chartered Institute of Environmental Health (CIEH) have been referenced. The LQM/ CIEH GAC have been derived using the DEFRA and Environment Agency CLEA UK (beta) model, which is the same methodology as the Government’s Soil
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 24 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
Guideline Values (SGV’s) and is the Environment Agency’s currently recommended exposure model.
In the absence of a SGV or LQM/ CIEH GAC, for determinands that are either not particularly harmful to human health or for which toxological and physio- chemical information is particularly difficult to obtain, the Dutch or ICRCL intervention values have been used as initial screening values. A Detailed Quantitative Risk Assessment (DQRA) is undertaken if any of these initial screening values are exceeded.
For determinands that are primarily deleterious to building materials, levels provided in BRE Special Digest 1, Concrete in Aggressive Ground, are considered to be the most appropriate for comparison.
8.2.2 Comparison of Testing Results to GAC
Of the six soil samples tested, the following Generic Assessment Criteria were exceeded for a residential land use.
Table Three: Contamination Testing Results Exceeding GAC
Location No. of Highest of Highest values Source of Determinand Unit GAC Recorded Recorded exceeding GAC Value Value GAC
Sulphate (2:1 extract) g/l 1.2 1.3 WS6 1 of 12 BRE
Total TPH mg/kg 50 1300 WS3 1 of 6 DUTCH
1% 2.5% 6% Naphthalene mg/kg SOM SOM SOM 1.6 WS6 1 of 6 LQM/ CIEH 1.5 3.7 8.7 1% 2.5% 6% Benzo(a)pyrene mg/kg SOM SOM SOM 1.3 WS1 1 of 6 LQM/ CIEH 0.83 0.94 1.0 1% 2.5% 6% Dibenzo(a,h) anthracene mg/kg SOM SOM SOM 1 WS2 1 of 6 LQM/ CIEH 0.76 0.86 0.90 1% 2.5% 6% TPH (Aliphatic EC >6-8) mg/kg SOM SOM SOM 170 WS3 1 of 1 LQM/ CIEH 73 160 370 1% 2.5% 6% TPH (Aliphatic EC >8-10) mg/kg SOM SOM SOM 410 WS3 1 of 1 LQM/ CIEH 19 46 110 1% 2.5% 6% TPH (Aliphatic EC >10-12) mg/kg SOM SOM SOM 96 WS3 1 of 1 LQM/ CIEH 93 230 540 1% 2.5% 6% TPH (Aromatic EC >8-10) mg/kg SOM SOM SOM 430 WS3 1 of 1 LQM/ CIEH 27 65 151 1% 2.5% 6% TPH (Aromatic EC >10-12) mg/kg SOM SOM SOM 200 WS3 1 of 1 LQM/ CIEH 69 160 346
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 25 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
It is considered that the recorded levels of total petroleum hydrocarbons (TPH), naphthalene, benzo(a)pyrene and dibenzo(a,h)anthracene present a significant risk of causing significant harm to human health.
It is noteworthy that the location of elevated levels of total petroleum hydrocarbons (TPH) contamination corresponds to the location of the former underground fuel storage tanks (downgradient of the infilled tanks and upgradient of the waste oil tank).
8.3 Controlled Waters Risk Assessment
The controlled waters risk assessment has been undertaken in accordance with the principles contained within current Environment Agency (EA) guidance (Remedial Targets Methodology: Hydrogeological Risk Assessment for Land Contamination (2006)). The Agency methodology is based on a tiered approach to determine risk-based remedial targets for soil and groundwater.
The first tier of assessment, Level 1, compares appropriate assessment criteria with concentrations present in the pore water located within source area soils in order to determine if the parameters have the potential to cause impact to a receptor.
The initial conceptual model (section 3.6.2 of this report) identified the underlying groundwater and the Aller Brook, 68m to the southwest of the site, as the most significant controlled water receptors of contamination at this site. Of these, the Aller Brook is considered to be the most critical.
The results of the soil contamination testing indicate elevated levels of contamination to exist within the soil at this site. In particular, elevated levels of TPH have been recorded in WS3, which is adjacent to underground fuel tanks.
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 26 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
Groundwater was recorded in three of the boreholes from depths of between 4.00m and 5.20m. In the absence of any other information, it is assumed that groundwater has an overall southwesterly flow direction, following the contours of the land, towards the Aller Brook, i.e. towards the most critical potential receptor.
In order to provide an indication of the level of groundwater contamination beneath the site, one groundwater sample was taken where sufficient groundwater was encountered (WS5). This locations also coincided with the location of former fuel pumps and was near to the underground fuel tanks, both of which are considered as potential sources of contamination.
In order to maintain conservatism, the assessment has assumed no attenuation such as dilution and dispersion in the first instance between the source and receptor. In the Level 1 assessment, the results of the contamination analysis undertaken on the groundwater samples indicate all the levels to be below the threshold values for UK drinking water. Notably, no detectable levels of PAH or TPH were recorded.
That is to say, even before factors such as dilution and attenuation are taken into to account, the levels of contamination in the groundwater do not pose a significant risk of causing harm to controlled waters. It is therefore concluded that the levels of contamination at this site do not pose a significant risk of causing harm to controlled waters.
In addition, further assurance of the protection of controlled waters is provided with the knowledge that remedial measures to protect human health include the excavation and off-site removal of all underground fuel tanks and surrounding contaminated soil (see section 8.6 of this report).
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 27 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
8.4 Ground Gas Assessment
The breakdown of organic material in made ground can produce ground gas, though it may also be produced by other, natural, sources (e.g. coal, peat). The principal components of ground gas are methane (potentially explosive) and carbon dioxide (potential asphyxiant).
There are no recorded landfill sites within 250m of the site and no significant made ground was encountered.
Although some hydrocarbon contamination was recorded, the heaviest contaminated soils are to be excavated and removed from site (see section 8.6 of this report).
Ground gas protection measures are therefore not considered to be necessary at this site.
8.5 Revised Conceptual Model
Prior to the investigation, it was considered that the former underground fuel storage tanks, fuel pumps and vehicle servicing and repair area present on- site were the most likely causes of any potential contamination of the ground.
The results of this investigation indicate slightly elevated levels of contamination to be present at this site that are potentially harmful to human health. This is considered to be a result of leakage/ spillage in the areas around the former underground fuel storage tanks and fuel pumps. However the possibility of unidentified contamination in other areas should not be discounted.
The controlled waters risk assessment indicated there to be no significant possibility of significant harm to controlled waters.
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 28 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
It is noted that no exploratory holes were possible in the workshop in the southwest due to restricted headroom. Whilst some contamination of the ground may be possible in this area of the site, based on the initial conceptual model, it is considered probable that it would be no worse than that recorded in other parts of the site.
It is also noted that no contamination would have been expected in the area of “St Mary’s Bungalow”. However, contamination testing results recorded a slightly elevated level of benzo(a)pyrene. This may be anomalous, but it is considered that due to the general past usage of the site and relatively small size of the site, the whole site should be characterised as having slightly elevated levels of contamination, with slightly heavier levels of contamination being present in the area of the underground tanks.
Therefore, the “source” and “pathway” and “receptors” relating to human health only, as described in the initial conceptual model, are considered to still be applicable.
8.6 Discussion and Recommendations
This risk assessment has shown that, left unremediated, the levels of contamination in the ground could potentially be harmful to human health given the proposed end-use.
In order to make the site safe for the proposed end-use, the source-pathway- receptor chain has to be broken.
Given the relatively small size of the development and the nature of the contamination, the most suitable remedial technique is considered to be localised contamination source removal combined with a covering of hardstanding or a suitable depth of capping of inert soil in garden areas.
Alternative remedial methods such as the use of chemical, biological or physical treatments to destroy or immobilise the contamination would be likely
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 29 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd to prove prohibitively expensive and impractical due to the small size of the development.
In garden areas, a depth of 600mm of inert subsoil and topsoil is considered sufficient to reduce exposure to acceptable levels and to enable healthy plant growth. This may be achieved by either removing and replacing contaminated soils and/ or raising site levels.
Given the potential for unidentified contamination to exist, a simple capping layer is not considered to provide sufficient protection to end-users. It is therefore recommended that the clean topsoil/ subsoil be underlain by a geo- textile (e.g. Terram) membrane. The placement of the geo-textile membrane at the base of the cover system provides a physical barrier that also acts as a visual marker to discourage excavation. The geo-textile layer also prevents mixing of the clean soil with underlying contaminated soils, reduces root penetration and prevents animal excavation of contaminated soil.
The placement of the capping layer in gardens is to be validated by an independent part, to ensure that the soil is sufficiently clean and present to sufficient depth. This is to take the form of trial pits with photographs and laboratory testing.
Two of the underground fuel storage tanks, which are considered to be one of the main sources of contamination at this site, have been infilled with concrete slurry, whilst another remains in use for waste oil storage. In order to ensure that no unacceptable levels of contamination remain in the ground, these main sources of contamination should also be removed from site. The tanks and any surrounding contaminated soil (identified by staining and/ or odour) will need to be excavated and removed from site. The tanks are also likely to need to be removed to enable foundation construction.
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 30 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
The following methodology is to be followed for the tank removal:
1. If still present, all fluid within the tank is to be pumped out and removed from site by a specialist contractor. 2. The area is to be fenced off from the public using solid fencing and all site personnel are to wear appropriate Personal Protective Equipment. 3. The tank and surrounding contaminated soil (identified by staining and/ or odour) are to be excavated under the supervision of a suitably qualified Engineer to ensure that the agreed method statement is followed correctly. 4. All excavated materials are to be placed on polythene sheeting to prevent contaminants leaching into the soil. 5. All oil stained and/ or odorous soil is to be “chased-out” and excavated. 6. Any spoil heaps are to be covered to provide a water tight barrier between the elements and stockpiled soil. The temporary stockpile(s) must be designed to withstand wind, rain, hail, snow and sun damage when left unattended until the soil is removed from site. 7. The sides and bottom of the excavation are to be sampled by a suitably qualified Engineer for laboratory analysis to determine the effectiveness of excavation in removing soils containing unacceptable levels of contamination. 8. All samples are to be placed in amber glass jars and placed in a cool box before being transported to the laboratory by overnight courier. 9. Should the laboratory analysis show that unacceptable levels of contaminated soil remain in the ground, additional soil will have to be excavated and removed/ treated. 10. The excavations are to be backfilled with inert fill, compacted in layers. All backfilled material is to be certified as inert from the supplier or by contamination testing.
Following removal of the tanks and any surrounding contaminated soils, any groundwater, if present, should be sampled and tested to confirm the absence of groundwater contamination. A Validation Report is then to be produced to
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 31 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd confirm the satisfactory removal of the interceptors and that no unacceptable levels of contamination remain in the ground.
The above methodology should also be followed if any currently unknown underground tanks are identified during construction activities and if any contaminated soils are identified beneath concrete hardstanding in the area of the former fuel pumps, above ground storage tank and workshop.
Some hydrocarbon contamination has been recorded, which could corrode plastic pipes. In order to prevent contamination entering drinking water supplies, all drinking water pipes should be upgraded to withstand hydrocarbon attack in accordance with the local water authority’s specification. Appropriate materials would be ductile iron pipe with wrapped joints or Protectaline, or similar, (HDPE pipe with an aluminium core) that is resistant to hydrocarbons.
However, if any unexpected discoveries are encountered during construction activities (i.e. anything substantially different from the findings of this investigation), Ruddlesden geotechnical ltd should be contacted so that appropriate recommendations may be provided.
Also, in line with general good practice, comprehensive and accurate site records should be kept, including details of where soil has been moved to or from site and tip receipts.
If contamination aspects are a planning condition, these recommendations are subject to the approval of the local authority.
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 32 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
8.7 Off-Site Disposal of Excavated Soils
From an assessment of the contamination testing results, it is considered that excavated soil is likely to be classified as Non-Hazardous or Hazardous Waste for off-site disposal purposes.
However, this classification should be confirmed by passing these results to a licensed tip operator.
If necessary and required by the tip operator, Waste Acceptance Criteria (WAC) testing could be carried out on soil to be removed from site to confirm the classification of the soil.
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 33 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
9.0 CONCLUSIONS
1. The site was largely undeveloped until at least 1955, by which time a “garage” building is present at the location of the main building today, near the centre of the site. Since that time, various additional buildings were built until 1980, when the site resembled its present day layout. The site was used as a petrol filling station until 1998.
2. Ground conditions encountered were generally topsoil or made ground, underlain by stiff to very stiff reddish brown silty gravelly clay, underlain by very dense grey silty gravel.
3. Foundation recommendations are strip or trench-fill foundations at a minimum depth of 0.90m below existing or proposed ground levels, whichever is deepest. Foundations should be deepened below any made ground and in accordance with NHBC Standards where building near trees for soils of low volume change potential. Should proposed properties be built over the infilled excavations of the former tanks foundations might need to be re-designed accordingly, e.g. deep trench-fill or reinforced beam.
4. The results of the contamination risk assessment indicate that the levels of contamination within the ground represent an unacceptable risk of causing harm to human health, given the proposed end-use. Proposed remedial measures include providing 600mm of inert subsoil and topsoil underlain by a geo-textile membrane in garden areas combined with the excavation and off-site removal of underground tanks and surrounding contaminated soil.
5. No radon protective measures are required and ground gas protective measures are not considered to be necessary.
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 34 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
10.0 REFERENCES
British Geological Survey (1976): England and Wales Sheet 339, Newton Abbot. British Standard BS5930 (1999): Code of Practice for Site Investigation. British Standard BS10175 (2001): Investigation of Potentially Contaminated Sites – Code of Practice. Building Research Establishment (2001): Special Digest 1: Concrete in Aggressive Ground. Building Research Establishment (2007): Report BR 211: Radon: Guidance on Protective Measures for New Dwellings. DEFRA & Environment Agency (2004): CLR 11: Model Procedures for the Management of Land Contamination. Environment Agency (2006): Remedial Targets Methodology: Hydrogeological Risk Assessment for Land Contamination. Environment Agency (2009): Human Health Toxological Assessment of Contaminants in Soil. Environment Agency (2009): Updated Technical background to the CLEA Model. Eurocode 7 (2007): Part 2 Ground Investigation and Testing.
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11.0 TERMS AND CONDITIONS
1. This report has been prepared for the sole use of the specified client in response to an agreed brief and for the stated purpose. The recommendations used in this report should not be used for any other schemes on or adjacent to this site without further reference to this company.
2. The copyright of this report is owned by Ruddlesden geotechnical ltd. With the exception of the named client, who may copy and distribute the report to deal with matters directly relating to its commission, this report may not be reproduced, published or adapted without written consent of the company.
3. New information, improved practices and legislation may necessitate an alteration to the report in whole or in part after its submission. Therefore, with any change in circumstances, this report should be referred to Ruddlesden geotechnical ltd for reassessment and, if necessary, reappraisal.
4. The comments given in this report assume that ground conditions do not vary beyond the range revealed by the investigation. There may, however, be conditions at or adjacent to the site that have not been disclosed by the investigation and which, therefore, have not been considered in this report. Accordingly, a careful watch should be maintained during any future groundworks and the recommendations of this report reviewed as necessary.
5. Whilst confident in the findings of the report, the recommendations may not necessarily be accepted by other authorities without question. It is advisable that, where appropriate, the report be submitted to the relevant statutory authorities and approval obtained before detailed design, site works or other irrevocable action is undertaken.
6. All comments and recommendations are based on groundwater conditions encountered at the time of investigation. It should be noted that groundwater levels might fluctuate according to the season and from year to year. This may have implications on other recommendations, including foundations and excavations.
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR 36 St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
APPENDICES
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
APPENDIX A
WINDOW SAMPLE BOREHOLE LOGS
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR St. Mary’s Garage, Kingskerswell Ruddlesden geotechnical ltd
KEY TO TRIAL PIT AND BOREHOLE LOGS (COMMON SYMBOLS)
STRATA LEGEND Made Ground Chalk
Topsoil Limestone
Clay Coal
Silt Mudstone
Sand Siltstone
Gravel Sandstone
Peat Fine grained igneous rock (e.g. basalt) Composite soil types will Medium grained igneous be signified by combined rock (e.g. granite) symbols, e.g. silty sand Fine grained metamorphic rock (e.g. slate)
GROUNDWATER INSTALLATIONS Groundwater strike CEMENT SEAL
Standing groundwater BENTONITE SEAL level FILTER PACK (SLOTTED PIPE)
SAMPLES IN-SITU TESTING D Small disturbed sample SPT Standard Penetration Test J Small disturbed sample (split spoon sampler) (amber glass jar) SPT(C) Standard Penetration Test B Disturbed bulk sample (solid cone) U100 Undisturbed sample (100mm V Shear vane test diameter) CBR California Bearing Ratio W Water sample (estimated from soil assessment (mexe) cone penetrometer)
ROTARY DRILLING SPT RESULTS (EXAMPLES) TCR Total core recovery (%) 30 “N” Value (blows recorded SCR Solid core recovery (%) for 300mm penetration, RQD Rock quality designation (%) following 150mm seating FI Fracture Index (fractures/ m) drive) NI Non-intact 50/125 50 blows for 125mm penetration
Geotechnical Investigation and Contamination Assessment Report Report Ref: SR/SB/DT/10127/GICAR IDENTIFICATION AND DESCRIPTION OF SOILS (Taken from BS 5930: 1999, Table 13) Density/Compactness Composite Soil Principal Example Soil Particle Particle Visual Minor Example /Strength Discontinuities Bedding Colour Types (mixtures of SOIL Stratum Group Shape Size Identification Constituents Descriptions Term Field Test basic soil types) TYPE Names Only seen Scale of spacing of For mixtures involving Loose Scale of bedding thickness BOULDERS complete in pits or discontinuities very coarse soils By inspection of exposures voids and particle 200 Recent Mean Mean c) Often difficult to Very soils packing Approx % Shell fragments, Deposits Loose brown very coarse Dense Term spacing Term thickness Term COBBLES recover whole from secondary pockets of peat, sandy sub-angular mm mm Angular boreholes 60 gypsum crystals, fine to coarse flint Very Over Very thickly Red Sub Borehole with SPT N-value Over 2000 Coarse Easily visible to flint gravel, Alluvium GRAVEL with small widely 2000 bedded Orange Slightly angular naked eye; fragments of pockets (up to 30 d) <5 20 2000 to Thickly Yellow (sandy ) Sub particle shape can brick, rootlets, mm) of clay Very loose 0-4 Widely 2000 to 600 Medium GRAVEL 600 bedded Brown rounded be described; plastic bags etc. Weathered (Terrace Gravels) 6 Mercia 600 to Medium Green Rounded Grading can be Loose 4-10 Medium 600 to 200 Fine Mudstone 200 bedded Blue described (sandyd)) 5 to 20 b) 2 using terms such Thinly White Flat Medium dense 10-30 Closely 200 to 60 200 to 60 as: bedded Cream Lias Clay Medium dense light Very Very thinly Grey Tabular Coarse brown gravelly Dense 30-50 60 to 20 60 to 20 with rare clayey fine SAND. closely bedded Black Very b) d) >20 Embankment Gravel is fine Extremely Thickly etc. (sandy ) Elongated Very dense >50 Under 20 20 to 6 0.6 with occasional Fill (Glacial Deposits) closely laminated Visible to naked Thinly Under 6 eye; with abundant/ laminated No cohesion when frequent/ Topsoil Coarse soils Medium SAND dry; numerous Visual Grading can be Stiff very closely examination: Breaks into SAND Minor described. Made Ground sheared orange Slightly pick removes blocks along b) 0.2 (over ~65% sand andgravel sizes) Fissured AND About 50 constituent or Glacial mottled brown cemented soil in lumps unpolished GRAVEL type Deposit ? etc. slightly gravelly which can be discontinuities CLAY. abraded Fine Gravel is fine and Calcareous, % defined on a medium of rounded Inter- Alternating layers of Shelly, site or material quartzite. bedded 0.06 Easily moulded different types, Light Glauconitic, specific basis or (Reworked c) Micaceous Only coarse silt subjective Weathered London or crushed in the prequalified by Approx % Term Coarse visible with hand Clay) fingers Breaks into thickness term Secondary blocks along if in equal Using terms lens; Un-compact Sheared proportions. such as: 0.02 Exhibits little polished Dark discontinuities Otherwise plasticity and thickness of slightly Medium SILT marked dilatancy; and spacing calcareous Slightly granular or Firm thinly 0.006 silky to the touch; laminated grey Can be moulded between Mottled calcareous Disintegrates in CLAY with closely or crushed by subordinate Slightly Compact e) <35 Fine water; spaced thick strong pressure layers defined. (sandy ) very Lumps dry quickly; laminae of sand. in the fingers Inter- calcareous 0.002 (Alluvium) Finger easily laminated Very soft Dry lumps can be pushed in up to broken but not Cu 0 – 20kPa 25mm % defined on powdered between Soft Finger pushed in a site or the fingers; Spacing terms also used They also Fine soils Cu 20 – 40kPa up to 10mm material Plastic brown for distance between disintegrate under Thumb makes specific basis clayey amorphous Firm partings, isolated beds water but more impression (sandye)) 35 to 65a) or subjective PEAT. C 40 – 75kPa or laminae, desiccation, slowly than silt; u easily (Recent Deposits)
(over ~35% silt and clay sizes) cracks, rootlets etc. CLAY Smooth to the Stiff Can be indented touch; Cu 75 – 150kPa slightly by thumb Exhibits plasticity Very stiff Can be indented but no dilatancy; Cu 150 - 300kPa by thumb nail Sticks to the fingers Hard (or very Very a) and dries slowly; Can be f) >65 weak (sandy ) Shrinks appreciably scratched by mudstone) on drying usually thumb nail Cu > 300kPa showing cracks Transported mixtures Colour NOTES Slightly organic clay or silt Grey as Contains finely divided or discrete Fibre already Plant remains recognizable a) Or described as coarse soil Firm Fibrous Slightly organic sand mineral particles of organic matter, often with d) Gravelly or sandy and/or compressed together and retains some strength depending on mass behaviour Organic clay or silt Dark grey distinctive smell, may oxidize rapidly. silty or clayey Organic sand Dark grey Describe as for inorganic soils using b) Or described as fine soil depending Very organic clay or silt Black terminology above. on mass behaviour e) Gravelly and/or sandy Very compressible and Pseudo- Plant remains recognizable, Spongy Very organic sand Black open structure fibrous Strength lost f) Gravelly or sandy Accumulated in situ Predominantly plant remains, usually dark brown or c) % coarse or fine soil type assessed Organicsoils Can be moulded in hand Recognizable plant remains black in colour, distinctive smell, low bulk density. Can excluding cobbles and boulders Plastic Amorphous Peat and smears fingers absent contain disseminated or discrete mineral soils. {[ + # $ X '#$^ {=@'@^ '#$^ {=@'@$ ] + + Z + ] ! + _ \ ] _ |} |} #'#^= '['$#' _ # # ! ! ! _ X X
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