Hailsham South WTW Geotechnical and Geo-environmental Interpretative Report
17/05/2018 Issue 00
MWH Project Code: 41523623 Document No: 41523623/GEO/RP/639176/001 Version Date Description/Amendment Prepared by (Author) Checked by Reviewed by 00 17/05/2017 For Issue G I Davies (Geotechnical) / L Connelly (Geotechnical) / J R Harris (Geotechnical & Geo- F Giacomello (Geo-Env) J Hoy te (Geo-Env) Env)
Contents
Introduction and Proposed Works ...... 1 Purpose and Objectives of Report ...... 2 Site Information ...... 2 Existing Reports ...... 2 Weeks Consulting Limited Investigation (2002) ...... 2 MWH Geotechnical Desk Study (2017) ...... 2 ESG Limited Ground Investigation (2017) ...... 2 Site Setting ...... 2 Historical Land Use ...... 3 Ground Conditions ...... 4 Geology ...... 4 Hydrogeology ...... 4 Hydrology ...... 4 Scope of Investigation ...... 5 Results and Interpretation ...... 5 Ground Conditions ...... 5 Made Ground (surfacing / sub-base) ...... 7 Made Ground (re-worked Weald Clay) ...... 7 Alluvium ...... 7 Weald Clay Formation ...... 7 Geotechnical Testing ...... 7 Made Ground (concrete / sub-base) ...... 7 Made Ground (re-worked Weald Clay) ...... 8 Alluvium ...... 9 Weald Clay Formation ...... 10 Resistivity Testing ...... 12 Summary ...... 13 Engineering Considerations ...... 14 Foundations ...... 14 Tertiary Treatment Plant Area ...... 16 Centrifuge Plant Area ...... 16 Ferric Dosing Plant Area ...... 17 Oxidation Ditch Area ...... 17 Excavation and ground support ...... 17 Slopes ...... 18
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Pipework, Ducting and Chambers ...... 18 Groundwater, Flotation and Dewatering ...... 18 Groundwater Control ...... 18 Buoyancy and Flotation ...... 18 Ground Aggressivity / Concrete Design ...... 19 Design of Buried Concrete ...... 19 Design of Ferrous Pipework ...... 19 Geo-Environmental considerations ...... 19 Soil Quality Assessment ...... 20 Scope of Assessment ...... 20 Soil Screening Results and Recommendations ...... 20 Health and Safety ...... 20 Assessment of Disposal Options for Excavated Materials20 Screening Methodology ...... 20 Screening Results ...... 21 Groundwater Assessment ...... 21 Ground Gas Assessment ...... 22 Material Suitability for Reuse ...... 22 Recommendations for Further Work ...... 23 References ...... 24 Appendices ...... 26
Appendices
1. Site Layout Drawing and Proposed Works Details 2. Topographic Survey 3. ESGL Factual Report on Ground Investigation 4. Land Quality Screening Results Summary and Atkins CatWaste Soil Hazardous Properties Assessment
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Abbreviations
ACEC Aggressive Chemical Environment Class BGS British Geological Survey DI Ductile Iron DS Design Sulphate FE Final Effluent HST Humus Settlement Tank LCP Local Control Panel OS Ordnance Survey PST Primary Settlement Tank SAF Submerged Aerated Filter TPS Total Potential Sulphate WTW Wastewater Treatment Works
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Introduction and Proposed Works Various upgrades to the treatment process plant are proposed at Hailsham South WTW, of which the following new structures are proposed which require geotechnical and geo-environmental input to the design:
Tertiary Treatment Plant Area • Four Actiflo AS5 units, each on a 13.90m x 4.05m reinforced concrete base slab of 0.50m thickness with the underside +3.40mOD; the gross ground pressure imposed by each unit is 48.21kPa • MCC, sand storage, mess room, lab for jar testing and poly make-up kiosk, all on a common 13.40m x 10.40m reinforced concrete base slab of 0.40m thickness with the underside at +3.50mOD; the gross ground pressure imposed is 22.88kPa • Tertiary pumping station comprising a 5.05m x 5.96m x 2.45m deep dry well chamber (underside +2.00mOD) and an adjoining 4.02m x 5.76m x 5.01m deep wet well chamber (underside -0.76mOD); the gross ground pressure imposed is 57.52kPa • Phosphate monitoring kiosk, around 3.00m x 3.00m in plan with the underside at +3.86mOD • Final effluent chamber of 8.25m x 3.00m plan dimensions and 3.50m deep with the underside at +1.70mOD; gross ground pressure imposed is 65.37kPa • Welfare building, a 9.80m x 6.40m blockwork structure on twelve foundation pads of 0.60m x 0.60m with the underside at +3.60mOD; the gross ground pressure imposed by the pads is 107kPa • Hardstanding surrounding the tertiary treatment plant Centrifuge Plant Area • Centrifuge structure, on a 11.00m x 9.00m reinforced concrete base slab of 0.30m thickness with the underside at +3.35mOD; the gross ground pressure imposed is 18.03kPa • Two sludge cake vessels, each on a 9.00m x 8.00m reinforced concrete base slab of 0.30m thickness with the underside at +3.33mOD; the gross ground pressure imposed by each vessel is 11.32kPa • Poly make-up plant kiosk and MCC for the centrifuge, on a 8.00m x 4.00m reinforced concrete base slab of 0.30m thickness with the underside at +3.54mOD; the gross ground pressure imposed is 24.88kPa • Road extension for the centrifuge/ cake vessel plant Ferric Dosing Plant Area • 30m3 ferric storage kiosk on a 9.89m x 4.20m reinforced concrete base slab of 0.40m thickness with the underside at +4.03mOD; the gross ground pressure imposed is 34.97kPa • Fuel tank for 800kVA generator (13,000 litres capacity), on a 3.20m x 1.80m reinforced concrete base slab of 0.3m thickness with the underside at +3.95mOD; the gross ground pressure is 34.06kPa. • Switchboard kiosk, on a 7.00m x 3.00m reinforced concrete base slab of 0.30m thickness with the underside at +2.71mOD; the gross ground pressure imposed is 32.04kPa Oxidation Ditch Area • Blowers and ventilation plant, on a 13.00m x 7.00m reinforced concrete base slab of 0.30m thickness with the underside at +3.18mOD; the gross ground pressure imposed is 17.99kPa
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Inlet Works Area • Screening handling units / cover and skip rail The site layout and details of the proposed works are included in Appendix 1.
Purpose and Objectives of Report A ground investigation was carried out in June 2017; this report presents a summary of ground conditions encountered and indicates some of the pertinent geotechnical and geo-environmental issues that need to be addressed as part of the design.
Site Information Existing Reports The following reports are relevant to the proposed works: Weeks Consulting Limited Investigation (2002) A ground investigation was carried out by Weeks Consulting Limited in 2002 (WCL, 2002), the investigation comprised a single machine excavated trial pit and a single cable percussion borehole. MWH Geotechnical Desk Study (2017) A desk study specific to the proposed works was carried out (MWH, 2017). The desk study scope included a review of historic OS maps and existing ground investigation data (in particular the Weeks Consulting Limited investigation records) in order to determine the likely ground and groundwater conditions at the site, including ground stability for excavation; foundation assessment; groundwater levels; and outline proposals for further ground investigation based on the proposals at that time. ESG Limited Ground Investigation (2017) Following on from the ground investigation proposals in the desk study a ground investigation was carried out (ESGL, 2017). The ground investigation scope is discussed in Section 3. Site Setting Hailsham South WTW is located 1.5km south-east of the centre of Hailsham. The site may be located by National Grid Reference 559860E 108430N, a site location plan is shown in Figure 1.
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Site
Figure 1: OS Site location plan
A topographic survey included in Appendix 2 shows the site relatively level and low lying at between +3.00 to +5.50mOD. The site is located at the western edge of the Pevensey Levels (low-lying marshland liable to flooding and criss-crossed by drains), to the north and west of the site ground levels rise toward Hailsham town. Drains associated with the Pevensey Levels run along the southern and eastern boundaries of the site. The treatment works itself is split into two distinct sections; the western half comprises the main treatment plant area whilst the eastern half comprises three large lagoons. These sections are divided by a soil mound which is generally of around 2m in height and was shown as a ‘landscaping area’ on the original proposals for the WTW (see Section 2.3 below). It is expected that these mounds comprise arisings from construction of the various tanks elsewhere within the works. The tertiary treatment plant and centrifuge plant are to be constructed at the western end of the main works area, between the main works and the lagoons. The southern part of the tertiary treatment area and the centrifuge area are located in areas currently occupied by the soil mounds, which are to be removed so that the finished ground level is similar to that of the site roads.
Historical Land Use A full review of available Ordnance Survey maps was carried out as part of the geotechnical desk study (MWH, 2017). In summary, Hailsham South WTW was developed on undeveloped farmland circa 1979, replacing the earlier Hailsham sewage works 220m to the north-west. Up until 1971 there was no development in the area immediately surrounding the site except for an isolated tank just north of Old Swan Lane; the area east of the site was used as Allotments. Sometime between 1961 and 1979 a caravan park and fishing tackle factory appeared along Station Road (to the west), and another caravan park appeared near Mill Road (to the north-east). However the area immediately surrounding the site remained undeveloped and the tank just north of Old Swan Lane was no longer shown.
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A historic Southern Water site plan dated 1979 showed the WTW site with the main treatment plant laid out in similar locations to present day, however the lagoons to the east were not shown. The soil mound along the western side of the main treatment plant (over part of the proposed tertiary treatment plant and centrifuge plant footprints) was shown as a ‘landscaping area’. There was a small pond just east of Final Settlement Tank No. 2, which was to be infilled during construction, and this was shown in the area that is proposed for the washwater booster set and final effluent chamber. Present day mapping show little change to the site or the immediate surrounding area.
Ground Conditions Geology The published geological map covering the site (BGS, 2006) and Geology of Britain Viewer (BGS, 2018) show the site to be underlain by Weald Clay Formation (mudstone and sandstone, limestone seams and ironstone bands, likely to be weathered to a clay and silty clay in the upper few metres). The Weald Clay Formation is underlain by the Tunbridge Wells Sand Formation (siltstone, mudstone and sandstone) which is mapped daylighting at surface beyond a geological fault indicated near the south western boundary. No superficial deposits are mapped at the site however Head Deposits (sandy silty clay, locally gravelly, sandstone fragments) are mapped approximately 60m from the south-western boundary and Alluvium (clay, silt and sand, locally organic, locally with gravel) is mapped approximately 170m from the south-eastern boundary. These distances are for guidance purposes only. Made Ground associated with construction of the treatment works, possibly including sludges and other sewage works waste, buried concrete and pipework is to be expected, in addition to the landscaped area discussed above (which is assumed to be of arisings placed during construction of the WTW). The Made Ground may locally extend slightly deeper in the vicinity of the proposed final effluent chamber owing to the backfilled pond. Hydrogeology The BGS bedrock aquifer mapping shows the Weald Clay Formation, which is expected to underlie the entire site, as unproductive strata (i.e. material with low permeability that has negligible significance for water supply or river base flow). The Tunbridge Wells Sand Formation, which underlies the Weald Clay Formation at depth, is shown as a Secondary A aquifer (i.e. material with permeable layers capable of supporting water supplies at a local rather than strategic scale, and may be an important source of base flow to rivers). The BGS aquifer designation mapping shows both the Alluvium and Head Deposits, which overlie the bedrock strata to the south, as Secondary undifferentiated aquifers (i.e. materials that may contain permeable layers similar to that of a Secondary A aquifer, or may contain lower permeability layers which store and yield only limited amounts of water). The site is not located within a groundwater Source Protection Zone. Hydrology The site is located at the western edge of the Pevensey Levels (low-lying marshland liable to flooding and criss-crossed by drains) and drains associated with the Levels run along the southern and eastern boundaries of the site.
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Scope of Investigation ESG were instructed to carry out ground investigation at the site. Whilst the specification was based on an early iteration of the proposals, the current proposals are broadly similar. The scope comprised the following: • Seven dynamic (windowless) sampler boreholes, one to 6m depth (for the tertiary pumping station) and the others all to 4m depth or 2m into firm or better Weald Clay Formation (whichever was deeper). Three of these boreholes installed with standpipes for groundwater/ground gas monitoring. • Three undisturbed samples taken for laboratory California Bearing Ratio (CBR) testing for the proposed road extensions / hardstanding areas. • Five in-situ apparent resistivity tests. • Soil sampling for geotechnical and geo-environmental laboratory analysis. The investigation was carried out in general accordance with the specification between 5th June and 12th June 2017 as follows: • Seven dynamic (windowless) sampler boreholes were sunk to between 3.95 and 6.15m depth, all met the target depth except the borehole for the tertiary pumping station which was scheduled to 6m but terminated early at 4.55m depth owing to a band of mudstone. One was installed with a standpipe for groundwater/ground gas monitoring. • Three CBR tests were cancelled as the material obtained was unsuitable for lab CBR testing. • Five in-situ apparent resistivity tests were carried out; the Wenner array was shortened for one test due to space constraints. • Soil sampling for geotechnical and geo-environmental laboratory analysis was carried out; testing was scheduled by MWH. The ESG factual report dated October 2017 is contained in Appendix 3. Results and Interpretation Ground Conditions A summary of ground conditions proven in the existing ground investigation data which is relevant to the proposed works is included in Table 1 and Table 2 below.
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Table 1: Ground Investigation Data 2002 2017 Ground Investigation Ground Investigation Stratum Description BH1 TP1 WS1 WS2 WS3 WS4 WS5 WS6 WS7 CBR1 CBR2 CBR3 (2002) (2002) Ground Level (mOD) +4.73 +5.13 +4.90 +4.62 +5.33 +4.11 +4.12 +4.69 +4.62 +4.98 +3.56 +4.20 Top of stratum, m bgl (mOD) Made Ground Concrete surfacing overlying gravel (granite 0.00 0.00 (surfacing / ------and flint) (+4.11) (4.12) sub-base) Made Ground Firm, stiff or very stiff orangish / greyish (re-worked brown slightly sandy slightly gravelly Clay. Weald Clay) Gravel is of flint, chert, brick and clinker with 0.00 0.00 0.00 0.00 0.41 0.36 0.00 0.00 0.00 0.00 0.00 0.00 (+5.13) very occasional thin beds of sand (+4.73) (+4.90) (+4.62) (+5.33) (+3.70) (+3.76) (+4.69) (+4.62) (+4.98) (+3.56) (+4.20) Possibly
overlain by
Topsoil Soft to firm grey and light brown slightly Alluvium - 1.80 (+3.33) ------organic Clay. Organic odour noted. Stiff or very stiff orangish brown Clay with occasional possibly soft grey silt lenses and rare rootlets,
Becoming closely fissured thinly laminated blueish grey or brownish grey mottled Clay Weald Clay with lenses to very thin beds of harder 2.60 0.30 0.80 1.70 0.89 1.04 1.00 1.00 2.70 (+2.43) - - - Formation material (e.g. extremely weak to moderately (+2.13) (+4.60) (+3.82) (+3.63) (+3.22) (+3.08) (+2.56) (+3.20) strong siltstone/ironstone/mudstone/siltstone, recovered as gravel sized fragments)
Clay is occasionally described as firm, coinciding with water seepages from the more permeable harder material 5.50 4.55 4.50 4.50 4.25 (- 3.95 0.40 0.40 0.40 8.00 3.50 Base of Exploratory Hole, m bgl (mOD) 6.15 (-1.02) (-0.77) (+0.35) (+0.12) (+0.83) 0.14) (+0.17) (+4.29) (+4.22) (+4.58) (-4.44) (+0.70) Water Seepage Seepage Not Not Not Groundwater Strikes ingress at Dry Dry Dry Dry Dry Dry at 3.00m at 4.10m recorded recorded Recorded 4.10m
Table 2: Groundwater measurements (standpipe) Response Zone Highest Monitored Level Borehole Stratum mbgl m bgl (mOD) WS6 1.20 - 4.25 Weald Clay Formation 0.90 (+3.21)
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Made Ground (surfacing / sub-base) These materials were only encountered when coring through existing hardstanding at the WTW (WS6 and WS7). Concrete is 0.19 to 0.24m thick with 8mm reinforcement at 0.08-0.10m depth (the logs indicate reinforcement to be 9mm but the laboratory description made when carrying out destructive testing is 8mm). One borehole suggests that the concrete is of two distinct layers (0.15m thick light brown over 0.04m thick dark grey). Sub-base is a light brown slightly sandy silty gravel; gravel is angular to sub-angular of granite and flint. One borehole notes this to be separated from the underlying Made Ground (re-worked Weald Clay) by a geotextile. Made Ground (re-worked Weald Clay) This material was encountered in all exploratory holes at the WTW except BH1 (2002 investigation) and generally comprises firm to very stiff clays with incorporated anthropogenic materials such as brick, concrete, clinker and occasionally rebar. Apart from the anthropogenic materials the clay is of a similar appearance and exhibits similar properties to the underlying weathered Weald Clay which suggests it is local arisings placed during previous development of the site. This layer is generally thin (up to 1.0m thickness), except for in areas which have been landscaped; WS1 is on raised material around the perimeter of existing oxidation ditch 1 and records 2.60m thickness, WS2 is on raised material at the proposed centrifuge plant area and records 1.80m thickness, and WS5 is on raised material at the proposed tertiary treatment plant area and records 1.70m thickness. Alluvium As discussed in Section 2.4.1, Alluvium is not mapped at the site itself but is shown beyond the south-east boundary. The ground investigation however identified 0.90m thickness of probable Alluvium (soft to firm organic Clay) in the south-eastern corner of the site (WS2 only in the centrifuge area), indicating that this material extends closer to the site than is mapped. Weald Clay Formation Identified in all exploratory holes (except the very shallow trial pits for CBR testing). At shallow depth the material is stiff or very stiff and weathered to orangish brown clay, rapidly becoming closely fissured thinly laminated blueish grey or brownish grey mottled Clay with depth. There are lenses to very thin beds of harder material (e.g. extremely weak to moderately strong ironstone/ mudstone/ siltstone) throughout. Geotechnical Testing The following sections provide a summary of the geotechnical testing carried out and appropriate design parameters. Made Ground (concrete / sub-base) 4.2.1.1 Concrete The concrete cores were subject to compressive strength testing; these tests gave strength results of 56.5 to 60.7N/mm2. 4.2.1.2 Sub-base Bulk Density Based on the soil descriptions this material appears to be an engineered fill. Published guidance suggests a characteristic unit weight range of either 16 or 20kN/m3 for coarse engineered fill above the water table (the value most detrimental to design to be selected) (BSI, 2015)
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Strength Testing Based on the soil descriptions (angular well-graded gravel) published guidance suggests the characteristic constant volume effective cohesion may be taken as c’cv,k=0 and the characteristic constant volume effective angle of friction may be taken as φ’cv,k=38° (BSI, 2015). Made Ground (re-worked Weald Clay) Classification Two particle size distributions (PSD) were carried out; these indicate 23 and 52% clay, 37 and 42% silt, 3 and 4% sand, 7 and 31% gravel, 0% cobbles; this is in general agreement with the typical soil descriptions. Moisture content and Atterberg Limits analysis was carried out on four samples; these indicate moisture contents of 12-26% (although this is of the whole sample rather than the material passing the 425µm sieve only, correcting for this 18-27%), liquid limit of 43-61%, plastic limit of 23-26%, and plasticity index of 19-35% (average 25%), classifying the material as clay of intermediate and high plasticity (BSI, 2004). Strength Testing The consistency indices derived from the Atterberg Limits analysis and corrected moisture contents are 0.83-1.31 (BSI, 2004) - these suggest a stiff to very stiff consistency which is similar or slightly stiffer than the soil descriptions suggest. One undrained triaxial test was carried out on clay described as firm; this gave an undrained shear strength of 27kPa (i.e. low strength clay (BSI, 2015)), which is lower than the soil description suggests (i.e. firm ≥ 40kPa (Tomlinson, 1986)). The accompanying bulk density measurement does not suggest the sample is excessively disturbed. This sample was taken from close to the base of the Made Ground and near a possible seepage, the moisture content of the sample was 32% which is greater than the samples that were tested separately as part of the Atterberg analysis (12-26%). It is likely the Weald Clay prevents downward migration of water from the Made Ground, the increased moisture content at this interface has resulted in a softened zone that is of lower strength than further above/below the interface (this may have occurred naturally or may be a result of the drilling process). Eight hand shear vane tests record undrained shear strengths of 98 to 188kPa, average 149kPa (i.e. high strength clay). In general the characteristic undrained shear strength may be taken as at least 100kPa. However, there is a possibility of the base of the material having a higher moisture content and hence a lower strength and so a structure specific assessment should be made. There is also a possibility that a buried (former) Topsoil may be present at the base marking the interface with the underlying natural Weald Clay. Based on the average plasticity index (25%) and BS8002 guidance (BSI, 2015), the characteristic constant volume effective cohesion may be taken as c’cv,k=0 and the characteristic constant volume effective angle of friction may be taken as φ’cv,k=24.5° (BSI, 2015). Bulk Density Based on the soil descriptions and strength test data (generally medium to very high strength clay) published guidance suggests a unit weight range of either 16 or 23kN/m3 (the value most detrimental to design to be selected) (BSI, 2015). A single bulk density measurement was carried out, this recorded a bulk density range of 1.96 Mg/m3 (unit weight 19.23kN/m3) which falls within the above range but insufficient to narrow it further. For design the characteristic value should be selected as either 16 or 23kN/m3 (the value most detrimental to design to be selected).
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Compressibility No oedometer consolidation testing has been carried out. An approximation of coefficient of volume compressibility (mv) may be derived from undrained shear strength using the relationship mv=1/(200xSu), indirectly from Table 11.13 of the Handbook of Geotechnical Investigation and Design Tables (Look, 2007) where mv=1/E’. In general the characteristic coefficient of volume compressibility may be taken as 0.05 m2/MN based on the above relationship and the characteristic undrained shear strength of 100kPa. However, there is a possibility of the base of the material having a higher moisture content and hence a lower strength and so a structure specific assessment should be made. There is also a possibility that a buried (former) Topsoil may be present at the base marking the interface with the underlying natural Weald Clay. Chemical Testing Five chemical test suites have been carried out in accordance with BRE guidance (BRE, 2005); two of these were water soluble sulphate (as SO4) and pH only, three of these included acid-soluble sulphate and total sulphur for an assessment of pyritic geology. The water-soluble sulphate range is 22-180mg/l, acid-soluble sulphate range is 426-735mg/kg, total sulphur range is 0.043-0.074%, and the pH range is 5.6-8.0. In accordance with BRE guidance the characteristic water-soluble sulphate, TPS and pH derived from these are 200mg/l, 0.1%, and 5.9 respectively (BRE, 2005). Alluvium Classification Moisture content and Atterberg Limits analysis was carried out on one sample; this result indicated a moisture content of 28%, liquid limit of 52%, plastic limit of 25% and plasticity index of 27%, classifying the material as clay of high plasticity (BSI, 2015). Strength Testing (Su) The consistency index derived from the Atterberg Limits analysis is 0.89 (BSI, 2004), suggesting a stiff consistency, this is not consistent with the soil description which is soft to firm slightly organic clay. An attempt was made to take a 100mm diameter thin walled (UT100) sample for strength testing, but the sampler failed to retrieve any of the material which also suggests that this is not stiff clay. An SPT was carried out immediately following the failed UT100 sample, however the Weald Clay was found to be just below and so no the test is not applicable to this strata. Since little is known of this layer a structure specific assessment is recommended, the characteristic undrained shear strength should be taken as 0 to 20kPa. Bulk Density No bulk density measurements have been carried out. Published guidance suggests a unit weight range of either 15 or 20kN/m3 (the value most detrimental to design to be selected) for low and medium strength clay (BSI, 2015), however this does not account for the material being slightly organic. It is therefore recommended that a characteristic unit weight of either 14 or 20 kN/m3 is adopted (the value most detrimental to design to be selected). Compressibility No consolidation testing has been carried out. The description suggests a soft to firm clay that is slightly organic, therefore on that basis the coefficient of volume compressibility has conservatively 2 been estimated as mv=1.5MN/m .
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Chemical Testing One chemical test suite has been carried out in accordance with BRE; the water-soluble sulphate is 547mg/l, pH is 7.8, and total sulphur 0.151%. In accordance with BRE guidance the characteristic values for design are; water soluble sulphate 600mg/l, pH 7.8, and TPS 0.5%. Weald Clay Formation Classification Moisture content tests were carried out on twenty-four samples, and of those samples ten were also subject to Atterberg Limits analysis. These tests indicate moisture content of 16-28%, liquid limit of 36-65%, plastic limit of 19-29% and plasticity index of 14-36% (average 22%), classifying the material as clay of high plasticity (BSI, 2015). One PSD was carried out (on material described as stiff fissured clay); this indicated 35% clay, 64% silt, 1% sand; this is in agreement with the soil description. Strength Testing (Su) The consistency indices derived from the Atterberg Limits analysis are 0.88 and 1.50 (BSI, 2004), suggest a stiff or very stiff consistency, in agreement with the soil descriptions. These show a general trend of increasing stiffness with depth. Eleven undrained triaxial tests were carried out, these record an undrained shear strength range of 67-226kPa (i.e. medium to very high strength clay (BSI, 2015)). These show a general trend of increasing strength with depth, but with significant data scatter which is likely to be in part due to sample disturbance which is often significant with open tube samples taken in clays such as this (fissured, laminated/bedded, with bands of siltstone/ironstone throughout). Fourteen hand shear vane tests were carried out which recorded undrained shear strengths of 84 to 155kPa (i.e. high to very high strength clay (BSI, 2015)). These show a general trend of decreasing strength with depth, however, this is likely to be due to tests above 1.20m depth being carried out in-situ in the inspection pit and deeper tests being carried out on material retrieved in plastic liners by the windowless sampler (the latter material is not confined and so results are likely to be unrealistically low and may be taken as a lower bound). Fifteen SPTs were carried out, giving uncorrected N values ranging from 10 to >50 (i.e. refusal). This includes one SPT which was carried out across the interface between Weald Clay and the overlying Alluvium, but the test drive was almost entirely within the Weald Clay. These results show a general trend of increasing SPT N values with depth. A rough indication of the shear strength has been assessed from the SPT N-values using the Stroud relationship (Stroud, 1989) which suggests that for overconsolidated clays uncorrected N values may be correlated with undrained shear strength using a factor dependent on plasticity. This correlation has the advantage that it is not affected by sampling disturbance. The average plasticity index of the Weald Clay is 22%, for which a ratio of 5.1 is considered appropriate. Therefore the uncorrected SPT N values correlate to undrained shear strengths between 51 and >255kPa (medium to extremely high strength (BSI, 2015) and firm to very stiff consistency (Tomlinson, 2001). This is consistent with the soil descriptions. A design line has been established from the data (Figure 2); this is largely based on the SPT data correlated to undrained shear strength rather than triaxial and hand vane testing owing to the issues described above. Above 5m the undrained shear strength of the clay is taken to increase linearly with depth, locally the harder siltstone, mudstone and ironstone bands would have much higher strength but these are thin and at variable depths so are not relied upon. Below 5m, the undrained shear strength is taken as 255kPa, which is based on a minimum SPT N value of 50 (i.e. refusal, not extrapolated) and also three triaxial tests achieved similar strengths. As above the harder ironstone, mudstone and siltstone beds would have much higher strength but whilst these become more persistent with depth there is evidence to suggest that their presence is not certain.
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SU = 50+41z (for 0 ≤ z ≤ 5m)
SU = 255kPa (for z ≥ 5m), where z is depth below the top of the Weald Clay
Figure 2: Characteristic undrained shear strength of the Weald Clay
Based on the average plasticity index (22%) and BS8002 guidance (BSI, 2015), the characteristic constant volume effective cohesion may be taken as c’cv,k=0 and the characteristic constant volume effective angle of friction may be taken as φ’cv,k=25° (BSI, 2015). Bulk Density Eleven bulk density measurements were carried out, these record a bulk density range of 1.99-2.12Mg/m3 (average 2.05Mg/m3). Based on these it is recommended that a characteristic unit weight of 20.10 kN/m3 is adopted. Compressibility One oedometer consolidation test was carried out on material described in the borehole log as very stiff Weald Clay though the laboratory description described the same sample as firm. For the 40- 2 80kPa pressure range the coefficient of volume compressibility recorded was mv=0.260MN/m which
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is anomalously high for the Weald Clay. This test is carried out on undisturbed samples (same as for the undrained triaxial test), which as discussed above are highly susceptible to disturbance when sampling in this material. The characteristic values of coefficient of compressibility recommended for design are included in Table 3, these are based on published correlations from the SPT N values which are deemed more representative than the single direct measurement; mv=1/E’, where E’/N60=0.9 for overconsolidated clays (Stroud, 1989). This is considered a conservative assessment as this is for clay with a plasticity of around 50 (plasticity of the weathered Weald Clay at the site is much lower), and also does not account for the layers of weak rock (Stroud reported that the correlation for weak rock is E’/N60>1).
Table 3: Characteristic coefficient of volume compressibility (Weald Clay Formation) Equivalent SPT N value Coefficient of Volume Depth below top of the (derived from design Compressibility, mv Weald Clay, m bgl line) (m2/MN) 0-1 14 0.08 1-2 22 0.05 2-3 30 0.04 3-4 38 0.03 4-5 46 0.02 >5 50 0.02
Chemical Testing Eight pyritic-geology chemical test suites have been carried out in accordance with BRE guidance (BRE, 2005) (water-soluble sulphate (as SO4), acid-soluble sulphate, total sulphur, and pH). The water-soluble sulphate range is 65-535mg/l, acid-soluble sulphate range is 316-848mg/kg, total sulphur range is 0.039-0.047%, and the pH range is 5.7-8.2. In accordance with BRE guidance the characteristic water-soluble sulphate, TPS and pH derived from these are 400mg/l, 0.1%, and 6.0 respectively (BRE, 2005).
Resistivity Testing Five apparent resistivity tests were carried out within the WTW site. The results indicate an apparent resistivity range of 9.80-55.23Ohm.m with no suggestion of any significant interference affecting the quality of the results. Data inversion has not been carried to attribute different resistivity values to particular strata or depth; it is recommended that the worst-case value of 9.80Ohm.m is adopted as a characteristic value.
12 Hailsham South Geotechnical & Geo-environmental WTW Interpretative Report
Summary A summary of the characteristic design parameters are included in Table 4 below.
Table 4: Summary of design parameters Stratum Design Parameter Characteristic Value Made Ground Unit Weight 16 or 20 kN/m3 (sub-base) Effective Stress Parameters c’=0, φ’=38° Unit Weight 16 or 23 kN/m3 Generally >100kPa, though a lower Undrained Shear Strength (SU) value may apply to the interface which could be softened or organic Made Ground Effective Stress Parameters c’=0, φ’=24.5° (re-worked Weald Clay) Compressibility mv=1/(200xSU)
Water-soluble Sulphate (SO4) 200 mg/l pH 5.9 Total Potential Sulphate 0.1 % Unit Weight 14 or 20 kN/m3 0-20kPa, structure specific assessment Undrained Shear Strength required Alluvium Compressibility 1.50 m2/MN Water-soluble Sulphate (SO4) 600 mg/l pH 5.8 Total Potential Sulphate 0.5 % Unit Weight 20.10 kN/m3
0 ≤ z ≤ 5m SU = 50+41z* kPa Undrained Shear Strength z ≥ 5m SU = 255 kPa Effective Stress Parameters c’=0, φ’=25° z = 0-1 0.08 m2/MN z = 1-2 0.05 m2/MN Weald Clay Formation z = 2-3 0.04 m2/MN Compressibility z = 3-4 0.03 m2/MN z = 4-5 0.02 m2/MN z > 5 0.02 m2/MN
Water-soluble Sulphate (SO4) 400 mg/l pH 6.0 Total Potential Sulphate 0.1 % Not Strata Specific Apparent Resistivity 9.80 Ohm.m * z is depth below the top of the Weald Clay
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Engineering Considerations The following comments are intended to outline specific matters that should be considered during the design and construction of the proposed works. Foundations Details of the proposed structures in this area are as follows:
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Table 5: Ground Conditions (shallow founded structures) Gross Anticipated Founding Ground Closest Structure Plan Area (m) Anticipated founding stratum Maximum Level (mOD) Pressure Borehole Settlement (mm) (kPa)
Tertiary Treatment Plant Area Actiflo AS5 units (ea) 13.90 x 4.05 +3.40 48.21 WS4,5 Weald Clay Formation 10 MCC, sand storage, mess room, lab for jar testing and poly make-up 13.40 x 10.40 +3.50 22.88 WS3,4 Weald Clay Formation 10 kiosk Phosphate monitoring kiosk 3.00 x 3.00 +3.86 <101 WS4,5 Weald Clay Formation 5
Welfare building (12 no pads, ea) 0.60 x 0.60 +3.60 107 WS5 Weald Clay Formation 5 Centrifuge Plant Area Made Ground (re-worked Weald Clay Centrifuge structure 11.00 x 9.00 +3.35 18.03 WS2 25 Formation) / Alluvium interface Made Ground (re-worked Weald Clay 15 Sludge cake vessels (ea) 9.00 x 8.00 +3.33 11.32 WS2 Formation) / Alluvium interface Made Ground (re-worked Weald Clay Poly make-up plant kiosk and MCC 8.00 x 4.00 +3.54 24.88 WS2 30 Formation) / Alluvium interface Ferric Dosing Plant Area Ferric storage kiosk 9.89 x 4.20 +4.03 34.97 WS7 Made Ground (surfacing/sub-base) 10
Fuel tank 3.20 x 1.80 +3.95 34.06 WS7 Made Ground (surfacing/sub-base) 5
Switchboard kiosk 7.00 x 3.00 +2.71 32.04 WS6 Weald Clay Formation 5 Oxidation Ditch Area Made Ground (re-worked Weald Clay Blowers and ventilation plant 13.00 x 7.00 +3.18 17.99 WS1 10 Formation)
1 Assumed
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Tertiary Treatment Plant Area All shallow structures are to be founded close to the top of the Weald Clay Formation; a thin layer of Made Ground may exist at formation level and it is recommended that this is removed and replaced to ensure ground conditions are uniform. In general any overdig is expected to be local only and not more than 300mm, however there is a possibility of encountering Made Ground deeper than this in the vicinity of the proposed final effluent chamber owing to the backfilled pond. The clays at the Made Ground (re-worked Weald Clay)/ Weald Clay Formation interface are generally softened and occasionally described as firm, so an undrained shear strength of 40kPa is selected as characteristic. For the structures in this area (listed in Table 5) the ultimate bearing resistance of the Weald Clay at the interface is of the order of 216kPa. Therefore all the proposed structures have a factor of safety against bearing capacity failure of at least 2. The results of preliminary settlement calculations are included in Table 5; it must be noted that these do not account for the ground having been previously been pre-loaded by the landscaped bunds. Settlement of any of the proposed structures placed over the former footprint of these bunds is likely to be negligible, therefore if structure footprints are only partially on the footprint (with the remainder of the structure on ground that has not been pre-loaded) then differential settlement should be taken as the same as the total anticipated settlement. The below-ground structures (e.g. tertiary pumping station and final effluent chamber) are expected to be founded entirely in Weald Clay Formation which would provide adequate support. These structures are expected to impose a net reduction in ground pressure at formation level and so settlement issues are no anticipated. As noted above there was a small pond in the vicinity of the final effluent chamber which means that Made Ground may locally extend to greater depth in this area. It is proposed to construct hardstanding around the new structures, with the surface level at around +3.60 to +3.90mOD. Pavements are typically designed using the CBR value, which can be derived from undrained shear strength using the relationship CBR (%) = SU/23 (Black & Lister, 1978). Ground conditions are expected to comprise either Made Ground (re-worked Weald Clay) or Weald Clay. The clays at this interface are generally softened and described as firm, so an undrained shear strength of 40kPa is selected as characteristic, and the corresponding CBR value for design is 1.7%. Centrifuge Plant Area Based on WS2, the centrifuge plant are to be founded close to the Made Ground (re-worked Weald Clay) and Alluvium interface. Alluvium is shown to have a thickness of 0.90m, although is likely to vary across the area (thinning toward the north-west). The Alluvium is described as soft to firm slightly organic clay; for clay with an undrained shear strength of at least 20kPa (at least soft consistency) the ultimate bearing resistance would be of the order of 108kPa. Therefore all proposed structures have a factor of safety against bearing capacity failure of at least 3. The results of preliminary settlement calculations are included in Table 5. It must be noted that these do not account for the ground having been previously been pre-loaded by the landscaped bunds, and hence settlement of any of the proposed structures placed over the former footprint of these bunds is likely to be small. If structure footprints are only partially on the footprint (with the remainder of the structure on ground that is not pre-loaded) then differential settlement should be taken as the same as the total anticipated settlement. In addition to the consolidation settlement, Alluvium being slightly organic would be subject to continued natural decomposition which would result in some further minor movements and would be highly susceptible to seasonal movement as a result of shrink-swell (very high volume change potential). Unless the structures are tolerant of movement it is recommended that foundations are taken down to the underlying Weald Clay Formation.
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It is proposed to construct a road extension up to these structures, with the surface level at around +3.50mOD. Ground conditions are expected to comprise either Made Ground (re-worked Weald Clay) or Alluvium, for which the characteristic undrained shear strength is 20kPa, and hence the corresponding CBR value for design is 0.9%. Since the Alluvium is highly susceptible to seasonal movement it is recommended that flexible surface is used to accommodate this, or alternatively the road foundation is taken down to below 0.6m depth. Ferric Dosing Plant Area The ferric storage kiosk and fuel tank are to be founded directly on the existing hardstanding (either directly onto the existing concrete, on a plinth dowelled to the existing concrete, or on a new concrete slab founded on the sub-base below). Ground conditions are expected to comprise concrete and granular sub-base of total thickness 0.36 to 0.41m, overlying Made Ground (re-worked Weald Clay) of total thickness 0.48 to 0.68m, overlying Weald Clay Formation. In this case the Made Ground (reworked Weald Clay) appears to be softened and is described as firm and slightly organic, and so an undrained shear strength of 40kPa is taken as characteristic. Based on this the ultimate bearing resistance of the Made Ground (re-worked Weald Clay) is of the order of 216kPa and the thin layer of sub-base above much greater. Hence, these structures have a factor of safety against bearing capacity failure of at least 3. The results of preliminary settlement calculations are included in Table 5, a structural engineer will need to confirm if the existing slab can tolerate these loads if it is proposed to construct the structures directly on it or on plinth dowelled to it. The switchboard kiosk is to be founded at +2.71moD (around 1.30m depth) in this area. Ground conditions at formation level are expected to comprise Weald Clay Formation and the ultimate bearing resistance of the Weald Clay is of the order of 270kPa. Therefore the proposed structure has a factor of safety against bearing capacity failure of at least 3. The anticipated preliminary settlement value is included in Table 5. Oxidation Ditch Area Ground conditions at the proposed blowers and ventilation plant is expected to comprise Made Ground (re-worked Weald Clay) extending to 1m below formation level, and then Weald Clay. In this case the Made Ground (reworked Weald Clay) appears to be softened (described as firm and a water seepage is noted close to the Made Ground (re-worked Weald Clay) and Weald Clay interface 1m below formation). An undrained shear strength of 40kPa is taken as characteristic, therefore based on this the ultimate bearing resistance of the Made Ground (re-worked Weald Clay) is of the order of 216kPa. Hence, this structure has a factor of safety against bearing capacity failure of at least 3. The result of the preliminary settlement calculation is included in Table 5, owing to the slab being large and Made Ground being inherently variable it is recommended that the formation is rolled to ensure uniformity and any soft spots should be removed and replaced (e.g. with coarse granular fill such as 6N). Excavation and ground support Shallow excavations at the WTW (e.g. for all structures except the tertiary treatment wet well) are expected to be within the capability of conventional plant and machinery. Bands of weak rock do exist from relatively shallow depth, but at shallow depth these are generally limited to very thin beds mostly of extremely weak siltstone / mudstone, and occasionally or moderately strong ironstone and therefore it is expected that conventional excavation plant with toothed buckets will be able to progress through, albeit at a slow pace. The hard bands become thicker and stronger with depth and hence the wet well excavation and any deeper pipework may require breaking out plant to progress to depth.
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It may be possible to batter excavations where space permits, although particular caution is required with Alluvium which is typically highly mobile. Excavation support may be provided by trench boxes or props, however the driving of sheets is likely to be problematic owing to the presence of hard bands throughout. Slopes The landscaped bund in the vicinity of the centrifuge plant and also some of the tertiary treatment plant is to be removed to allow these structures to be founded at a similar level to the road (there will need to be some cut slopes of up to 2.5m to accommodate the structures). Based on the characteristic effective stress parameters in Table 4, it is recommended that long-term cut slopes in Made Ground (re-worked Weald Clay) and/or Weald Clay Formation are designed with a maximum slope of 1V:2.5H. Pipework, Ducting and Chambers It is understood that the buried pipework, ducting and chambers will in general not exceed 1.5m in depth. At these depths pipework is expected to be placed in either Made Ground or Weald Clay. Construction of these structures is likely to result in a small net reduction in vertical stress at formation level and as such bearing capacity issues are not anticipated. A native soil modulus of 3MN/m2 applies to firm or better clay (e.g. Made Ground (re-worked Weald Clay) or softened Weald Clay Formation at the interface) (BSI, 1997). A native soil modulus of 4MN/m2 applies to stiff or better Weald Clay Formation below any softened zone. Any pipework laid in Alluvium (which may be very soft clay with an organic content) would need to be designed with a native soil modulus of 0.75 MN/m2; the choice of pipeline material and jointing system would need to allow for potential differential movements. Groundwater, Flotation and Dewatering The borehole data indicates that groundwater entries are a possibility in both the Made Ground (re- worked Weald Clay) and also the Weald Clay Formation: Groundwater seepages were recorded in three of the six boreholes: • WS1 recoded a groundwater seepage at 3.00mbgl (+1.73mOD) in very stiff clay (Weald Clay Formation). • WS2 recorded a groundwater seepage at 4.10mbgl (+1.03mOD) in firm clay (Weald Clay Formation), just above a bed of mudstone and just below a bed of ironstone. • WS6 recorded a groundwater seepage at 4.10mbgl (+0.01mOD) in a bed of mudstone (Weald Clay Formation). WS6 was completed with a standpipe (response zone between 1.20 and 4.25m depth in the Weald Clay Formation); this recorded groundwater level rising to 0.90mbgl. The groundwater seepage during boring was at 4.10m depth, which suggests that groundwater may be confined at pressure in the ironstone/mudstone beds at around this level. Groundwater Control In general it is expected that inflows would be limited to slow seepages, faster inflows may occur but it is believed that these are typically related to non-continuous permeable bands and so of limited volume. It is expected that conventional sump pumping will suffice as groundwater control. Buoyancy and Flotation The nature of the Weald Clay (interbedded low permeability clays and high permeability ironstone/ mudstone/ siltstone) has the potential for groundwater to be locally confined (i.e. sub-artesian). WS6
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recorded a seepage at 4.10m depth but much shallower subsequent standpipe readings (up to 0.9m depth), which suggests this. Consideration will need to be given to base heave in all excavations below existing ground level. Ground Aggressivity / Concrete Design Design of Buried Concrete The characteristic water-soluble sulphate, total potential sulphate, and pH summarised in Section 4.2.6 have been used to determine the appropriate DS and ACEC for each soil type (excluding any limited sub-base materials). These are summarised in Table 6 below.
Table 6: DS and ACEC classifications
Stratum DS ACEC
Made Ground (re-worked Weald Clay) DS-1 AC-2Z
Alluvium DS-2 AC-2
Weald Clay Formation DS-3 AC-2Z
Design of Ferrous Pipework Following guidance published by TRL (Eyre & Lewis, 1987) the characteristic apparent resistivity in Table 4 has been used to determine the likely aggressivity of the ground toward ferrous metals. The Made Ground and Weald Clay Formation which are expected to be encountered across much of the site are likely to be highly aggressive toward ferrous metal. This assessment is based on the characteristic apparent resistivity (9.80Ohm.m), the soil comprising clay with a plasticity index greater than 15, groundwater potentially above the level of the structure, moisture content greater than 20%, pH of less than 6, soluble sulphate 200-500mg/l or more, and no aggressive compounds recorded (e.g. cinder or coke). The Alluvium which is expected to be encountered along the western/southern site boundary (i.e. the centrifuge area) is expected to be organic and have a high sulphate content so also is likely to be highly aggressive toward ferrous metal. Since soils that are highly aggressive toward ferrous metal are expected further advice should be sought from the pipe supplier. Geo-Environmental considerations As part of the ground investigation, the following work was performed for geo-environmental purposes: • Selected soil samples were submitted for chemical analysis • Ground gas monitoring was conducted in one standpipe • Groundwater monitoring, including measurement of groundwater levels and collection of one groundwater sample for chemical analysis, was conducted in one standpipe.
Results from the 2017 ground investigation have been screened (Appendix 4) and are summarised below.
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Soil Quality Assessment Scope of Assessment
Twenty-two soil samples (one Made Ground (sub-base), nine Made Ground (re-worked Weald Clay), one Alluvium and, eleven Weald Clay Formation) were collected as part of the 2017 ground investigation and submitted to ESG laboratories for a full suite of chemical analyses including the following: • Metals (arsenic, cadmium, chromium, copper, lead, mercury, nickel, selenium and zinc) • Cyanide (free, total and complex) • Sulphate (acid soluble) • pH • Speciated polycyclic aromatic hydrocarbons (PAHs) • Total petroleum hydrocarbons (TPH) • Benzene, toluene, ethylbenzene and xylenes (BTEX) • Phenols, cresols, naphthols, resorcinol and total phenols • Polychlorinated biphenyls (PCBs)
Eleven of twenty-two soil samples were also screened for asbestos and an additional two Made Ground (sub-base) samples were also collected for asbestos screening only. The soil chemical results were compared against LQM’s and CIEH’s Suitable for Use Levels (S4ULs) (Nathanail et al., 2015) for Commercial Generic Assessment Criteria (GAC) for all locations. Lead results, in the absence of an S4UL, were compared to Defra’s Category Four Screening Level (C4SL) (Defra, 2014) (a C4SL assesses if the land is suitable for use and definitely not contaminated land as defined under Part 2A of the Environmental Protection Act 1990). Soil Screening Results and Recommendations
The results of the assessment show the following: • No visual or olfactory evidence of contamination was reported during the 2017 Ground Investigation or during subsequent groundwater and ground gas monitoring visits. • There were no exceedances of the GAC. • No asbestos was found in the soil samples tested.
Health and Safety A watching brief should be maintained throughout construction. Should visual and/ or olfactory indicators of contamination not identified during Ground Investigation be encountered it is recommended that Southern Water guidelines / good practice are followed to mitigate potential risks. In addition, should any visible asbestos containing materials (ACMs) be identified during works, works should stop and material visually inspected by a competent person. Further testing may also be required (including for waste disposal), as per the Control of Asbestos Regulations 2012.
Assessment of Disposal Options for Excavated Materials Screening Methodology
Soil analytical results for the twenty-two soil samples were screened for waste hazardous properties as identified in Technical Guidance WM3 – Waste Classification – Guidance on the classification and assessment of waste (Environment Agency, 2015). This screen was carried out using the Atkins CatWaste-Soil tool (ATKINS, 2017).
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Thirteen soil samples underwent analysis for landfill waste acceptance criteria (WAC) testing. WAC testing consists of a solid suite and eluate suite, as follows: • Solid suite: o Total moisture, Total Organic Carbon (TOC), Loss on Ignition (LOI), BTEX (total), Polychlorinated biphenyls (PCBs) (7 Congeners), Mineral Oil, speciated polycyclic aromatic hydrocarbons (PAH) (sum of 17), pH and acid neutralisation capacity (ANC). • Eluate suite: o pH, conductivity, chloride, fluoride, sulphate, barium, nickel, chromium, cadmium, copper, lead, zinc, arsenic, mercury, selenium, molybdenum, antimony, total dissolved solids (TDS), dissolved organic carbon (DOC) and phenol index. FA Screening Results
All twenty-two samples according to WM3 are non-hazardous. WAC screening of the thirteen WAC results are as follows: • Ten samples are within the Inert landfill limits:
o Made Ground (re-worked Weald Clay) of WS1 at 0.5m bgl, WS2 at 0.1m bgl and WS4 at 0.1m bgl, o Weald Clay Formation of WS2 at 2.8m bgl, WS2 at 3.7m bgl, WS2 at 4.7m bgl, WS4 at 1m bgl, WS4 at 2m bgl, WS6 at 1.5m bgl, and WS7 at 1.6m bgl.
• Three samples are within the Non-Hazardous landfill limits:
o Made Ground (re-worked Weald Clay) of WS2 at 1m bgl due to exceedances of inert waste thresholds for sulphate (2,160mg/kg vs. 1,000mg/kg) and total dissolved solids (4,330mg/kg vs. 4,000mg/kg). o Alluvium of WS2 at 1.9m bgl due to exceedances of chromium (0.92mg/kg vs. 0.5mg/kg) and lead (0.87mg/kg vs. 0.5mg/kg) o Made Ground (re-worked Weald Clay) of WS7 at 0.5m bgl due to an exceedance of fluoride (15mg/kg vs. 10mg/kg). Hence in summary: • Made Ground (sub-base) was not tested for WAC, it is recommended that testing is carried out if any is to be removed from site. • Made Ground (re-worked Weald Clay) should be suitable for a non-hazardous landfill, • Alluvium should be suitable for a non-hazardous landfill, • Weald Clay Formation should be suitable for an inert landfill. Suitability of waste for disposal at a facility should always be confirmed with the facility operator in advance. Should disposal to landfill be required for material represented by the nine samples where WAC testing has not been undertaken, further WAC testing may be required. Confirmation of further testing requirements should be sought, from the prospective facility operator, prior to material’s removal from site.
Groundwater Assessment A groundwater sample was collected from a standpipe installed in WS6 and submitted to ESG laboratories for chemical analyses including the following: • Metals (arsenic, boron, cadmium, chromium, copper, lead, mercury, nickel, selenium and zinc) • Sulphur (total)
21 Hailsham South Geotechnical & Geo-environmental WTW Interpretative Report
• Sulphide • Chloride • Ammonical nitrogen (free) • pH • Speciated polycyclic aromatic hydrocarbons (PAHs) • Total petroleum hydrocarbons (TPH) and gasoline range organics • Benzene, toluene, ethylbenzene and xylenes (BTEX) • Phenols, cresols, dimethylphenols, trimethylphenols and total phenols The analytical results were screened against the inland surface water receptor (short term) standards due to presence of a drain close to the standpipe and against the default EQS standards for Groundwater due to the presence of a Seconday A aquifer underneath the southern end section of the site. The sample was found to have the following exidances: • Nickel concentration of 131 ug/l above the 34 ug/l inland surface water receptor (short term) standard and above the 15ug/l default EQS standards for Groundwater. • Cadmium concentration of 0.9 ug/l above the 0.1 ug/l default EQS standards for groundwater. Suitable dewatering requirements may be necessary during construction depending on excavation depth. In determining the dewatering procedures and disposal/discharge requirements, the chemical analysis should be sent to the responsible authority / wastewater undertaker to agree which disposal route (e.g. storm drains to surface waters/ sewers) would be permitted.
Ground Gas Assessment Ground gas monitoring was undertaken from standpipes installed in WS6 on three separate occasions (20th, 28th June and 20th July 2017). This produced the following results:
• Methane (CH4) concentrations ranged from 0.0 % v/v to 1.3% v/v. The highest concentration was recorded on 20/06/2017. • Carbon Dioxide (CO2) concentrations ranged from 0.0% v/v to.0.5% v/v. The highest concentration was recorded on 20/07/2017. • Hydrogen Sulphide (H2S) concentrations were below detectable limits on all occasions. • Carbon Monoxide (CO) concentrations ranged from 0.0ppm to.1ppm. The highest concentration was recorded on 20/07/2017. • Oxygen (O2) concentrations ranged from.18.2 % v/v to 21.4 % v/v. Both, highest and lowest concentrations were reported on 28/06/2017. • Gas Flow Rates: a gas flow rate: of 0.01l/h was recorded on 20/06/17 and 28/06/2017. A gas flow rate of 0.0 l/hr was recorded on 20/07/17. • The Gas Screening Value (GSV) for methane is 0.00013 litres / hour. • The GSV for carbon dioxide is 0.00005 litres / hour. Over each of the monitoring events, atmospheric pressure was stable, measured at 1018mB, (20th June 2017), 997mB (28th June 2017), and 1006mB (20th July 2017). CIRIA C665 (Wilson et al., 2007) guidance rates GSVs according to potential risk. Based on the maximum potential flow rate at WS06 and concentrations of carbon dioxide and / or methane recorded, the site is likely to be classified as Characteristic Situation 1, very low risk.
Material Suitability for Reuse Arisings of Made Ground (re-worked Weald Clay), Alluvium, and Weald Clay Formation may be re- used as non-load bearing fill (e.g. for landscape purposes). There are limited amounts of Made Ground (sub-base) below the existing hard standing which have not been subject to geo- environmental testing; if these materials are to be excavated as part of the works it is recommended that testing is carried out to confirm if these are suitable for re-use.
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Current guidance backed by the Environment Agency recommends using a Materials Management Plan with verification for non-permitted or non-exempt soil and subsoil re-use. This is to avoid the possibility of re-used material being regarded as an illegal deposit of waste. Furthermore, if excavated materials require disposal it may be possible to use these on another site under an Exemption from Environmental Permitting or without Exemption by applying the CL:AIRE Code of Practice (CL:AIRE, 2011), with savings in disposal costs. The reuse of inert waste as an aggregate is also possible when following an Environment Agency Quality Protocol. Recommendations for Further Work The following additional work is recommended: • If any Made Ground (sub-base) is to be excavated (either for re-use or waste disposal) then further geo-environmental testing of this material is recommended.
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References ATKINS. (2017). CatWasteSoil. Retrieved from http://catwastesoil.co.uk
BGS. (2006). Geological Survey of England and Wales 1:50,000 scale geological map Sheet 319/334 'Lewes and Eastbourne (Bedrock and Superficial Deposits Edition). British Geological Survey, Keyworth, Notts.
BGS. (2018). Retrieved May 2018, from Geology of Britain Viewer: http://mapapps.bgs.ac.uk/geologyofbritain/home.html
Black, W., & Lister, N. W. (1978). The strength of clay fill subgrades: its prediction and relation to road performance. In ICE (Ed.), Proceedings Conference on Clay Fills. London.
BRE. (2005). Concrete in Aggressive Ground. Special Digest 1 (Third Edition). Watford: Building Research Establishment.
BSI. (1997). BS EN 1295-1:1997 Structural design of buried pipelines under various conditions of loading - Part 1 General requirements. BSI, London.
BSI. (2004). BS EN 14688-2:2004 Geotechnical investigation and testing - identification and classification of soil - Part 2 : Principles for a classification. BSI, London.
BSI. (2015). BS 5930:2015 - Code of practice for ground investigations. British Standards Institution. London: BSI.
BSI. (2015). BS 8002:2015 - Code of practice for earth retaining structures. BSI, London.
CL:AIRE. (2011). The Definition of Waste: Development Industry Code of Practice. Version 2. Contaminated Land: Applications in Real Environments (CL:AIRE), London.
Defra. (2014). SP1010 - Development of Category 4 Screening Levels for Assessment of Land Affected by Contamination. Final Project Report (Version2). Contaminated Land: Applications in Real Environments.
Environment Agency. (2015). Technical Guidance WM3 : Waste classification - Guidance on the classification and assessment of waste.
ESGL. (2017). Hailsham South WTW Factual Report on Ground Investigation. Report No. G7058-17. Maidstone, Kent: Environmental Scientifics Group Limited.
Eyre, D., & Lewis, D. A. (1987). Contractor Report 54 : Soil Corrosivity Assessment. Transport and Road Research Laboratory, Crowthorne, Berkshire.
Look, B. (2007). Handbook of Geotechnical Investigation and Design Tables. London: Taylor & Francis Group.
MWH. (2017). Hailsham South WTW Geotechnical Desk Study. Report ref '639176-2-REP-01 Geotechnical Desk Study Report'. MWH, High Wycombe.
Nathanail, C. P., McCaffrey, C., Gillet, A. G., Ogden, R. C., & Nathanail, J. F. (2015). The LQM/CIEH S4ULs for Human Health Risk Assessment. Land Quality Press.
Stroud, M. A. (1989). The standard penetration test - its application and interpretation. In ICE (Ed.), Proceedings Conference on Penetration Testing in the UK. Birmingham: Thomas Telford.
Tomlinson, M. J. (1986). Foundation Design and Construction (5th ed.). Harlow: Longman Scientific & Technical.
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Tomlinson, M. J. (2001). Foundation Design and Construction (7th ed.). Harlow: Pearson Education Limited.
WCL. (2002). Factual report on ground investigation at Hailsham South water treatment works for Morrison, Brown and Root joint venture. Report ref 14837C. Weeks Consulting Limited, Maidstone, Kent.
Wilson, W., Oliver, S., Mallett, H., Hutchings, H., & Card, G. (2007). Assessing risks posed by hazardous ground gases to buildings, CIRIA Publication C665. Construction Industry Research and Information Association, London.
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Appendices 1. Site Layout Drawing and Proposed Works Details
639176 Hailsham South WTW
Loading Calculations
Document No.: 639176_C_CALC_Loadings Version DatePurpose of Issue Prepared by Checked by Approved 0.1 11/1/17For checking J. Ibanez N. Camilleri Loadings updated 0.2 20/2/17following discussion J. Ibanez N. Camilleri D. Moore and new units added 0.3 26/3/18For WIP D. Olivier N.Camilleri
changes by N.Camilleri in red/yellow CALCULATIONS Unfactored Dimensions (m) Loading (kN)
Actiflo AS5 unit Loading Base slab:
Length (m) 13.9 Width (m) 4.05 Slab depth (m) 0.5 Load 704 Individual slabs have been considered for the 4 No. units
Actiflo AS5 unit Volume of water to coping level (m3) Coag tank 18.2 Floc tank 59.1 Settler tank (approx) 57.1 Unit weight (kN/m3) 9.8 1317
Self weight of steel components, as confirmed by Veolia - estimated installed weights including all mechanical equipment and access steelwork (excluding water). It has then been considered 130 that walkways, hand railing, hydrocyclone and lamella plates for the settler tank are also included here. Sand (negligible) Service overload (kN/m2) 10 563
Total (kN) 2714 Total (kN/m2) unfactored 48.21 CALCULATIONS Unfactored Dimensions (m) Loading (kN)
Actiflo Sand Silo Loading Base Slab /Plinths
Length (m) 4 Width (m) 4 Slab depth (m) 0.3 Load 120
Silo Sand 13000kg (P.Cooper email 09.01.18) 130 Silo empty weight (assumed) 50
0
130
Service overload (kN/m2) 10 160
Total (kN) 590 Total (kN/m2) unfactored 36.88 CALCULATIONS Unfactored Dimensions (m) Loading (kN)
Ferric Plant Loading
Base slab:
Length (m) 9.89 Width (m) 4.2 Slab depth (m) 0.4 Load 415
Service overload (kN/m2) 10 415
30m3 Ferric Unit Ferric kiosk full (assumed) 622
Total (kN) 1453 Total (kN/m2) unfactored 34.97 CALCULATIONS Unfactored Dimensions (m) Loading (kN)
MCC, sand storage, mess room, lab for jar testing & poly make-up kiosk Loading
Base slab:
Length (m) 13.4 Width (m) 10.4 Slab depth (m) 0.4 Load 1394
Service overload (kN/m2) 10 1394
GRP kiosk empty (prorated from Lintott known 131 loadings) MCC panels, air compressors and receiver 40 (assumed) Actisand big bag storage (assumed) 25.0 Sand big bag discharge (assumed) 20 Polymer pallet storage (assumed) 25.0 Poly make up system (assumed) 130 Mess room (assumed) 20 Lab for jar testing (assumed) 10
Total (kN) 3188 Total (kN/m2) unfactored 22.88 CALCULATIONS Unfactored Dimensions (m) Loading (kN)
Blowers and ventilation slab Loading
Base slab:
Length (m) 13 Width (m) 7 Slab depth (m) 0.3 Load 683
Service overload (kN/m2) 10 910
GRP kiosk empty (prorated from Lintott known loadings) 3 No. D/S 85-125kW Blowers and ventilation plant self weight (Mechanical Engineer has 45 confirmed with Xylem)
Total (kN) 1638 Total (kN/m2) unfactored 17.99 CALCULATIONS Unfactored Dimensions (m) Loading (kN)
Centrifuge structure Loading
Base slab:
Length (m) 11 Width (m) 9 Slab depth (m) 0.3 Load 743 Same dimensions as the structure for the centrifuge considered for TWN
Service overload (kN/m2) 10 990
Aldec G3-75 Centrifuge weight (dry - from 32 mechanical engineer) Steelwork, handrailing, flooring and stairs 20 (assumed)
Total (kN) 1785 Total (kN/m2) unfactored 18.03 CALCULATIONS Unfactored Dimensions (m) Loading (kN)
2 No. sludge cake vessels Loading
Base slab:
Length (m) 9 Width (m) 8 Slab depth (m) 0.3 Load 540 Individual slabs have been considered for each one of the vessels
19m3 sludge cake vessel empty (dry weight) - 28 as confirmed by mechanical engineer
25% ds sludge cake weight: Vessel volume (m3) 19 Unit weight (kN/m3) 13 247
Total (kN) 815 Total (kN/m2) unfactored 11.32 CALCULATIONS Unfactored Dimensions (m) Loading (kN)
Switchboard kiosk Loading
Base slab:
Length (m) 7
Width (m) 3
Slab depth 0.3 158
Walls Length (m) 18.8 Width (m) 0.3 Height (m) 1.4 197
Service overload (kN/m2) 10 210
GRP kiosk empty (prorated from Lintott known 68 loadings) Switchboard self-weight (assumed) 40
Total (kN) 673 Total (kN/m2) unfactored 32.04 CALCULATIONS Unfactored Dimensions (m) Loading (kN)
Poly make-up plant kiosk and MCC for centrifuge Loading
Base slab:
Length (m) 8 Width (m) 4 Slab depth (m) 0.3 Load 240
Service overload (kN/m2) 10 320
GRP kiosk empty (prorated from Lintott known 81 loadings) Poly storage tank (10 m3), poly mixing tank (2 m3), dosing pumps and control panel 130 (assumed) Polymer pallet storage (assumed) 25
Total (kN) 796 Total (kN/m2) unfactored 24.88 CALCULATIONS Unfactored Dimensions (m) Loading (kN)
Fuel tank for generator Loading
Base slab:
Length (m) 3.2 Width (m) 1.8 Slab depth (m) 0.3 Load 43
13,000-litre fuel tank (wet - as confirmed by supplier). NB This tank is sized for an 800 kVA 153 generator, but only 727 kVA will be required for Hailsham South.
Total (kN) 196 Total (kN/m2) unfactored 34.06 Davies, Gareth (High Wycombe)
From: Camilleri, Nathan
Follow Up Flag: Follow up Flag Status: Flagged
Gareth
That’s fine. Answers below Gareth :
1. Actiflo units underside of slab +3.4mAOD 2. Welfare building : Top of pad 4.4 underside of pad 3.6mAOD 3. Final Effluent chamber underside of slab 1.7mAOD 4. Actiflo MCC kiosk, polymer kiosk and Actisand kiosk : underside of slab +3.5mAOD 5. Phosphate Monitoring kiosk underside of slab : underside of slab +3.86mAOD 6. Tertiary PS underside of wet well ‐0.76 Valve chamber +2.0mAOD 7. Sludge Bins Slab : underside of slab +3.33mAOD 8. Centrifuge Slab : underside of slab +3.35mAOD 9. Sludge polymer and MCC kiosk : underside of slab +3.54mAOD 10. Ferric kiosk : underside of slab +4.03mAOD 11. LV switchboard kiosk : underside of slab +2.71mAOD 12. Generator fuel tank : underside of slab +3.95mAOD 13. Blower Slab 3.18mAOD
Regarding the washwater pumping station we are now looking to install this within an existing building, apologies I should have told you.
Location of new tertiary PS on site plan attached and below, apologies the label is missing.
Thanks Gareth
Nathan
1