remediation strategy and verification plan

Remediation Strategy and Verification Plan

Site: 45 Broadwater Road, Welwyn Garden City

Client: C Field Construction Ltd.

Report Date: 1st July 2021

Project Reference: JN1576

TABLE OF CONTENTS

A INTRODUCTION.....................................................................................................................................................................1

1 AUTHORITY ........................................................................................................................................ 1

2 LOCATION .......................................................................................................................................... 1

THE SITE LOCATION IS INDICATED ON FIGURE 1 WITHIN APPENDIX A. ................................................................................................................ 1

3 PROPOSED CONSTRUCTION .............................................................................................................. 1

4 SCOPE................................................................................................................................................ 1

B BACKGROUND INFORMATION ..........................................................................................................................................2

5 SITE INVESTIGATION WORKS ............................................................................................................ 2

6 SITE HISTORY .................................................................................................................................... 2

7 RELEVANT POLLUTANT LINKAGES ..................................................................................................... 3

C REMEDIAL OBJECTIVES AND OPTIONS............................................................................................................................3

8 REMEDIAL OBJECTIVES ..................................................................................................................... 3

9 OPTIONS APPRAISAL ......................................................................................................................... 3

D REMEDIATION STRATEGY ...................................................................................................................................................5

10 REMEDIATION METHODS .................................................................................................................. 5

11 ASSESSMENT CRITERIA ..................................................................................................................... 5

E VERIFICATION PLAN ............................................................................................................................................................6

12 DATA COLLECTION ............................................................................................................................ 6

13 REPORTING ........................................................................................................................................ 6

14 DISCOVERY STRATEGY ...................................................................................................................... 7

15 GENERAL GUIDANCE ........................................................................................................................ 7

APPENDIX A Site Plans

APPENDIX B Verification Criteria

JN1576 Phase III Contamination Site Investigation Report 1 1 July 2021

A INTRODUCTION

1 Authority

Our authority for carrying out this work was given by Brian Greene of C Field Construction, dated 28th May 2021.

2 Location

The site is located at 45 Broadwater road, in Welwyn City Garden, Hertfordshire AL7 3AX.

The approximate National Grid Reference of the site is TL 24180 12450.

The site location is indicated on Figure 1 within Appendix A.

3 Proposed Construction

It is proposed to construct a four-storey care home, with associated hard and soft landscaping.

For the purposes of the contamination risk assessment, and taking a conservative approach, the proposed development land use is classified as Residential with home-grown produce, (CLEA model1/C4SL report2). The gas sensitivity of the site is therefore rated as High (CIRIA C6653).

4 Scope

This report presents our Remediation Options Appraisal, Remediation Strategy, and Verification Plan for the proposed remedial works at the site.

As with any site there may be differences in soil conditions between exploratory hole positions.

The findings and opinions conveyed via this report are based on information obtained from a variety of sources as detailed within this report, and which Southern Testing Laboratories Limited believes are reliable. Nevertheless, Southern Testing Laboratories Limited cannot and does not guarantee the authenticity or reliability of the information it has obtained from others.

This report has been prepared for the sole internal use and reliance of C Field Construction Ltd. and their appointed Engineers. This report shall not be relied upon or transferred to any other parties without the express written authorization of Southern Testing Laboratories Limited. If an unauthorised third party comes into possession of this report they rely on it at their peril and the authors owe them no duty of care and skill.

The recommendations contained in this report may not be appropriate to alternative development schemes.

1 Environment Agency Publication SC050021/SR3 ‘Updated technical background to the CLEA Model’ (2009). 2 SP1010 Development of Category 4 Screening Levels DEFRA (2014) 3 CIRIA C665 (2006) Assessing risks posed by hazardous ground gases to buildings.


The contamination screening values used are valid at the time of writing but may be subject to change and any such changes will have implications for the assessments based upon them. Their validity should be confirmed at the time of site development.

B BACKGROUND INFORMATION

5 Site Investigation Works

The site has been the subject of a series of site investigation reports, as listed below:

Ref Date Author Title/Ref No. Subject

1 2019 Integral Geotechnique

(Wales) Limited (IGWL)

Not known Phase I and II Site Investigation Report

2 October 2020 A F Howland Associates

Ground Investigation Report for a proposed

residential care home/JAH/20.212/GIR

Phase III ground investigation report

3 July 2021 ST Consult Phase III Contamination

Investigation Site Report

Phase III contamination Investigation

These reports provide good coverage and characterisation of the site and information derived from these reports is discussed below. The reader is referred to the original reports for supporting detail if needed. These reports are referred to below by the number given in the left hand column of the above table.

6 Site History

The desk study was very briefly summarised in [2]. The site has reportedly been occupied by

buildings, used for light industrial activity, since the 1930’s, with some reconfiguration of these

between 1960 and 1990.


7 Relevant Pollutant Linkages

The various site investigations and risk assessments carried out [1, 2 and 3] identified the following Relevant Pollutant Linkages for the site:

Contaminant/Source Pathways Receptors

Asbestos within the made ground (generally low-level)

Soil/dust dermal exposure

Soil/dust ingestion/inhalation

Site/Construction workers

Future residents

PAH’s in Made Ground Ingestion/inhalation/dermal contact

Direct Contact

Future residents and construction Workers

Structures/services

Zinc/Copper in Made Ground Vegetation growing in contaminated soil

Flora

Petroleum Hydrocarbons Soil/dust ingestion/inhalation

Soil/dust ingestion/inhalation

Direct contact

Migration through soil

Site/Construction workers

Future residents

Structures/services

Perched groundwater

C REMEDIAL OBJECTIVES AND OPTIONS

8 Remedial Objectives

It is proposed to construct a four-storey care home, with associated hard and soft landscaping.

On the basis of the investigation carried out date and site proposals, the remediation objectives are as follows:

1. Reduce any risk, to the site workers and future residents, from the asbestos, lead, zinc, lead, PAHs and TPH identified in the made ground material.

2. To reduce the risk to the perched groundwater from the hotspot of diesel identified.

3. To reduce the risk to water main pipes from the generally minor levels of TPH/PAH recorded in the soils on site.

9 Options Appraisal

9.1 Asbestos Containing Materials (ACMs), Lead, Zinc, Copper, TPH and PAHs

The risks to human health receptors from generally low-levels of asbestos, lead, zinc, copper PAHs and TPH in the Made Ground could be dealt with by several methods. In respect of construction and maintenance workers, the use of PPE and safe working practices (minimising disturbance of the soil, creation of dust and the extent and duration of contact with soils) can reduce risk by helping to break the exposure pathways.

However, while use of these measures should be considered as part of good practice in construction


and maintenance, they typically are looked upon as a measure of last resort and need to be used in combination with other measures. Neither are such measures appropriate for future site users (store workers and customers). Breaking the exposure pathway prior to construction by emplacement of imported clean material and/or impermeable cover over the made ground could reduce risks to human health receptors including future site users. Buildings, access roads and car parking spaces constitute impermeable cover and therefore imported soils would only be needed for areas of the site proposed as soft landscaping.

Removing the source by careful selective excavation of affected soils and subsequent off-site disposal to an appropriately licensed facility is also capable of reducing/eliminating the risk to human health receptors. As with emplacement of a barrier of clean material, this would only be required for soft landscaping areas, as buildings, access roads and car parking spaces will break the pathway.

Off-site disposal of contaminated soils and importation of clean materials place additional demands on aggregate resources and waste disposal capacity, and both require significant road haulage. Use of these remediation methods therefore requires that the quantities involved be minimised to ensure the approach remains sustainable in respect of resources, energy and traffic impacts.

A discovery strategy will also need to be in place to deal with any more significant concentrations of asbestos (or any other contamination) that come to light during the site development work (see section 15 below).

9.2 Petroleum Hydrocarbons and PAHs

Although there was no visual and olfactory evidence of any significant organic contamination in the trial holes in the most recent investigation, some basic screening was carried out. In addition, a hotspot of significant diesel contamination was identified by others at depth in WS 105.

Organic contaminants present in the soils, particularly the PAH’s and petroleum hydrocarbons found in some of the Made Ground on site, could affect plastic underground service pipes (such as the types used by water and gas supply companies). Guidance should be sought from the relevant companies regarding any proposed plant in the affected area. Many water supply companies now require higher specification pipe on contaminated sites, even following remediation. At this stage, allow for Protecta Line pipes or similar.

For the diesel contamination at depth, the risk to the perched groundwater, along with any minimal risk to the end users, is best mitigated by excavation and removal. The identified impact appears to be of such small volume to make any more sustainable remediation, such as bio-remediation or other treatments, impractical; furthermore, the diesel impact is not volatile and, therefore, not suitable for any sustainable techniques.

9.3 Zinc and Copper

An isolated high concentration of zinc and copper was reported in the Made Ground analysed from TP4. Although at the concentrations and pH measured the impact is not considered a significant risk, these are phytotoxic metals and some clean cover will be required to provide a growing medium for new planting.


D REMEDIATION STRATEGY

10 Remediation Methods

The Remediation Strategy will comprise the following:

Location Details

Diesel impact at depth 2.7m in WS 105

Removal of any petroleum hydrocarbon impacted soils and perched groundwater. The exposed soil will require inspection and validation testing to confirm that it is suitable to remain on site.

Soft landscaped areas

Provision of 300mm of certified clean topsoil in any new soft landscaping areas. This should be increased to 600mm of certified clean subsoil and topsoil and subsoil for any garden/vegetable growing areas.

New Water Supply pipes Allow for Protecta-Line pipes

11 Assessment Criteria

Post-removal of diesel, the exposed soils in the validation trench will comply with the following re-use criteria:

Soils

Hydrocarbon Substance or Fraction Measured Concentrations in mg/kg*

BTE

X

Benzene 0.087

Toluene 130

Ethylbenzene 47

Xylenes 56

Aliphatics

EC5-EC6 42

>EC6-EC8 100

>EC8-EC10 27

>EC10-EC12 130

>EC12-EC16 1100

>EC16-EC35 1100

Aro

matics

EC5-EC7 (Benzene) 70

>EC7-EC8 (Toluene) 130

>EC8-EC10 34

>EC10-EC12 74

>EC12-EC16 140

>EC16-EC21 260

>EC21-EC35 1100

*LQM/CIEH Suitable 4 Use Levels (S4ULs) for a residential with homegrown produce consumption land use, and a 1% Soil Organic Matter content.


Imported topsoil shall be free from deleterious materials, weeds and contamination. The material to be used will comply with the appropriate BS Specifications for Topsoil (BS 3882:2007) and the analysis shall also comply with the values given for (residential with plant uptake) in the table in Appendix B.

In addition to the certification from the supplier, imported soils may also need to be independently sampled and tested, depending on the source and views of the local authority.

These values are valid at the time of writing but may be subject to change and any such changes will have implications for the assessments based on them. Their validity should be confirmed at the time of site development.

Perched Groundwater

Depending on the views of the regulators, it may be necessary to sample and test the perched water again, in the vicinity of WS 105. This will likely necessitate the installation of a new groundwater monitoring well.

E VERIFICATION PLAN

12 Data Collection

Location Data Responsible party

Diesel Hotspot (WS 105)

Excavation and removal of any petroleum hydrocarbon impacted soils.

Main contractor

Provision of consignment notes for the petroleum hydrocarbon contaminated soils removed from site.

Main Contractor

Sampling & confirmatory laboratory analysis of the exposed soils

ST Consulting

Soft Landscaped areas

Post placement check of thickness

Post placement soil samples (if required)

Consignment Notes (both exported topsoil and certified clean imported topsoil)

ST Consult

ST Consult

Main contractor

Buried services Allowances for fully barrier-protected piping

Main contractor

13 Reporting

At the end of the remediation, a verification report will be produced by ST Consult.


14 Discovery Strategy

As with any site, areas of contamination not identified during site investigation works may come to light in the course of redevelopment. Accordingly, a discovery strategy will be adopted to ensure that any hitherto unknown contamination is identified and dealt with in an appropriate manner, as follows:

• A close watch will be maintained during all demolition and excavation works.

• In the event that unexpected or malodorous soils or liquids are encountered, excavation work shall cease in the affected area.

• The affected area shall be made safe and fenced off to prevent unauthorised access.

• The Site Manager shall notify ST Consult of the discovery, who will attend site to inspect the suspect materials, provide advice and take samples as necessary. Within ST Consult, Joe Kelly shall be the first point of contact.

• The Site Manager shall notify Welwyn Hatfield Borough Council of the discovery. Within the council, the Contaminated Land Officer shall be the first point of contact.

Any suspect excavated soil will be stockpiled separately on polythene sheeting, covered, and tested before being removed.

15 General Guidance

In general terms, the workforce and general public should be protected from contact with contaminated material. There is a range of relevant documents published by the Health and Safety Executive, and organisations such as CIRIA, and the BRE.

Some soils will require removal from site and disposal to suitably licensed landfills. Different guidelines and charges will apply to different waste classifications. As waste producers, the Developer holds responsibilities under the various governing regulations, including:-

• Ensuring that waste is characterised in accordance with current Technical Guidance.

• Ensuring that waste is disposed of at a facility appropriately licensed to receive the waste as classified.

• Keeping accurate records of all waste classification, transfer and a disposal log including information such as:

o Date, Waste Classification, Carrier’s Registration Number, Transfer Note Number, Ultimate Destination.

• Submitting full copies of those records for inclusion in validation/closure reports.

Maintaining those records for potential future regulatory inspection.

APPENDIX A

Site Plans

85.64

85.67

85.6

5

85.60

85.53

85.53

85.5985.59

85. 5

4

85.6

3

85.90

86.05

85.75

85.7

8

85.6

1

85.5

5

85.4

6

85.3

8

85.4785.60

85.4

6

85.44

85.4985.52

85.53

85.65

85.8

285.7

5

85.6

9

85.7

4

85.8

7

85.9

4

85.75

MH S/W CL 85.9585.95

85.71

85.54

85.67

85.84

85.95

86.09

86.3

2

86.5

1

86.5

5

86.6

5

86.4

78

6.3

0

86.2

8

86.1

8

85.9

28

5.7

5

85.7

2

85.8

3

86.0

2

86.2

8

86.2

3

86.1

3

87. 3

387.4

7

87.1

8

87.1

5

86.8

8

85.42

85.60

85.61

85.66

85.65

85.45

85.22

85.70

85.47

85.39

85.36

85.34

85.0

0

85.3

3

85.93

86.12

86.11

86.05

86.06

85.7

7

85.90

85.

87

85.96

85.9

5

85.84

85.6

5

85.7

0

85.6

5

85.62

85.8

5

86.8

5

86.9

0

86.7

5

86.6

8

85.7

5

85.8

6

MH UTLCL 85.78

85.82

85.

72

85.7

2

85.70

85.6

9

86.72

86.5

9

86.5

3

85.85

85.94

85.93

85.88

86.09

85.92

85.63

85.64

85.64

85.65

85.94

85.53

85.65

85.70

85.73

85.67

85.57

85.55

85.42

85.55

85.59

85.64

85.60

85.60

EL 92.36

PW

L 9

5.0

7

85.0

1

85.73

85.9

7

h 6m

Oak

h 6mOak

h 6mOak

h 12mApprox Position

h 12m

Approx Positionh 12m

Approx Position

h 12m

Approx Position

h 12m

Approx Position


h 10m

Sycamore

h 4mMultibole

h 12mSycamore

h 12m

Sycamore

h 12m

Sycamore

h 10m

h 10mSycamore

h 10mSycamore h 10m

Sycamore

h 8m

Sycamore

h 14mSycamore h 10m

Sycamore

h 12m

h 12m

h 8m

h 8m

h 16m

h 10m

h 2m

h 12m

h 12m

h 12m

h 10m

h 10m

h 10m

h 10mSycamore

h 12mSycamore

h 12m

h 8mMultibole

h 8m

Multibole

BT

BT

BT

BT

BT

CA

TV

BT

bu

s s

top

86.7

2

86.7

2

86.7

8

bu

s s

top

b r i c k b u i l d i n g

b r i c k b

b r

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k b

u i l d

i n

g

b r

i

RFL 93.94

PW

L 9

5.0

7

PW

L 9

5.0

9


PWL 95.35


g r a s s

g r a s s

u n s u r f a c e d / t a r m a c

t a r m a c

b r i c k p a v i o r s

b r

i c k

p

a v

i o

r s

b r

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p

a v

i o

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U/S

brick paviors

S/B

gas

box

g r

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s

brick paviors

b u s h

r e f u s e h e a p

w o o d e n p a n e l f e n c e h t 2 . 0 0 m

close boarded fence ht 2.00m

c l o s e b o a r d e d f e n c e h t 1 . 8 0 m

c l o s e b o a r d e d f e n c e h t 1 . 8 0 m

wire m

esh fence h

t 2.0

0m

wire m

esh fence h

t 2.0

0m

wir

e m

esh fence h

t 2.0

0m

site

hoard

ing h

t 2.5

0m

site

hoard

ing

ht 2.5

0m

site

hoard

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ht 2.5

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B R

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S/B

CP

S

S/B

CP

S

IRF

ht 1.0

0m

IRF

ht 1.0

0m

brick paviors

dense foliage

brick

build

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u n

s u

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u n

s u

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u n s u r f a c e d

100

100

100100

IL 84.50

CB

F h

t 2.0

0m

S/B

in-filledchamber

CLF ht 1.80m

concrete slab

85.3

9

approximate fence line

concre

te p

avi

ng s

labs

electricity sub-station

g r a

s s

ele

ctr

icity

sub-s

tatio

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soil

s o i

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LP

brick w

all

ht 1.8

0m

h 10m

S T

R E

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S

C E

N E

E

L E

V A

T I O

N

P

P

PP

PP

P

P

P

P

ST

ST

ST

LP

LP

LP

LP

SP

GY

GY

GY

RS

2

3

4

30

212400N

212450N

RL 9

5.8

0

RL 9

5.7

7

85.1

3

85.3

0

85.4

2

85.6

3

85.8

7

86.0

7

86.2

0

86.3

7

86.5

5

86.7

7

87.0

087.1

287.0

5

86.8

9

86.4

8

86.3

1

86.1

6

85.9

2

85.7

8

85.5

0

85.4

4

85.2

7

MH

CL 8

6.0

7

86.9

2

86.6886.85

87.1

08

7.1

7

87.2

08

7.1

687.1

6

86.8

9

86.78

86.66

86.7

8

86.6

5

86.4

9

86.4

1

86.2

2

85.9

1

85.7

2

85.5

7

85.5

8

85.4

2

85.5

4

85.3

585.3

685.1

6

85.8

7

85.6

2

85.4

8

85.3

4

86.6

7

86.4

9

86.7

6

86.9

0

RF

L 8

9.9

9

RF

L 9

5.3

5

RL 94.88

EL 92.49

RL 9

5.3

3

RL 9

8.9

5

RF

L 9

4.3

0

PW

L 9

5.0

9

RFL 93.77

85.3

8

85.

44

85.5

0

85.9

2

86.4

8

86.5

0

86.86

87.05

87.04

87.08

87.17

87.15

87.0

9

87.1

0

86.0

8

MH UTLCL 85.85

86.33

87.12

86.74

86.69

86.78

86.85

86.63

86.48

86.42

86.41

86.28

86.3

5

86.1

5

85.9

5

85.6

0

85.5

9

85.3

285.4

9

85.6

8

86.0

8

86.2

6

86.4

7

86.40

86.53

86.49

86.58

85.9

4

85.7

7

85.8

4

85.65

85.66

85.68 85.65

85.6

4

85.61

1

25

DROP-OFF

5

10

20

MAINENTRANCE

Bro

ad

wa

ter

Ro

ad

28.5m

27m

21m

30m

24m

26.5

m

26m

RESIDENTIAL

DEVELOPMENT

3 storey residential unit

with limited windows in

end elevation

3 storey residential units with

habitable rooms facing site

Tree/soft planting buffer

zone outside site

Tree/soft planting buffer

zone outside site

AMENITY

GARDEN

85.87

15

ele

ctr

icity

sub-s

tatio

n

SERVICE

ENTRANCE

Change in surface

treatment to dedicated

pedestrian traffic route.

Footpath over RPA to be a

no-dig construction method

Cellweb or similar.

16

26

27

28

33

CS

Lighting

h 6m

Oak

h 6mOak

h 6mOak


h 12m

Approx Positionh 12m

Approx Position

h 12m

Approx Position

h 12m

Approx Position


h 10m

Sycamore

h 4mMultibole

h 12mSycamore

h 12m

Sycamore

h 12m

Sycamore

h 10m

h 10mSycamore

h 10m

Sycamore h 10mSycamore

h 8m

Sycamore

h 14mSycamore h 10m

Sycamore

h 12m

h 12m

h 8m

h 16m

h 10m

h 12m

h 12m

h 12m

h 10m

h 10m

h 10m

h 10mSycamore

h 12mSycamore

h 12m

h 8mMultibole

h 8m

Multibole

PROPOSED

CARE HOME

4 Storeys

REFUSE

STORE

No habitable/resident windows

at upper levels in end elevation

Windows to be provided at

corridor ends

N

Marbrook

NOTES

1. Scheme design is subject to relevant

Statutory Approvals.

2. Drawing based on topographical survey

ref: TS18-448X1.

3. Tree information based on Arboricultural

Survey ref. BS5837.

4. Refer to Deacon Design information for

landscaping and materials.

5. Refer to Canham Consulting information

for levels.

KEY

PARKING

33 car parking spaces

incl. 3No. disabled

GIA m²

Ground Floor 1490

First Floor 1477

Second

1313

Beds/

Suites

27

31

32

Units

2

2

2

Third Floor

1455

90 Beds/

13 Suites

1

TOTAL BEDS/SUITES & GIA

5735

SCHEDULE OF ACCOMMODATION:

CARE HOME

13

Site Boundary

Previous Consent Footprint

Existing Buildings

Proposed Building

Vehicular Access & Parking

Paths

Patio Areas

Existing Tree - Retained

Existing Tree - Removed

Tree Root Protection Area

New Tree

Cycle Shelter - 8 Spaces

Condy Lofthouse ArchitectsCondy Lofthouse Architects

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DRAWING NO. revision

CLIENT

PROJECT

DRAWING TITLE

T: 0151 207 4371 ● F: 0151 207 7087

Construction

For Approval

Tender

Preliminary

REVISION DETAILS date / by

NOTES

MATERIALS PROHIBITED

C

SCALE drawn by date

This drawing is copyright of Condy and Lofthouse Ltd. and may not be reproduced in

any way without their specific permission.

a) high alumina cement in the structural elements;

b) wood wool slabs in permanent formwork to concrete;

c) calcium chloride admixtures for use in reinforced concrete;

d) asbestos or asbestos-containing products, as defined in the 'Control of Asbestos at

Work Regulations, as amended 2012' or any other statutory modification or re-

enactment thereof;

e) any naturally occurring or man made mineral fibres (for example, rock-wool or slag

wool) with a thickness of 3 microns or less and a length of 200 microns or less, unless

they are appropriately sealed to prevent migration of fibres;

f) aggregates for use in reinforced concrete which do not comply with:

'BS EN 12620:2002: properties of aggregates used in concrete.

'BS EN 13139:2002: Properties of aggregates used in mortar.

'BS EN 13055 (Parts 1 & 2): properties of lightweight aggregates.

'Guidance on avoiding alkali-silica reaction and limitations on alkali content in

BRE Digest 330 (2004)' & 'Concrete Society Technical Report 30 (1999)';

g) lead, lead paint or any other materials containing lead which may be ingested,

inhaled or absorbed, except where copper alloy fittings also containing lead are

specifically required in drinking water pipework by any relevant statutory requirement

or where lead flashings or other lead roof coverings are specifically provided for in the

Contract;

h) urea formaldehyde foam or materials which may release formaldehyde in quantities

which may be hazardous with reference to the limits set by the Health and Safety

Executive;

i) calcium silicate bricks or tiles;

j) vermiculite unless it is established as being fibre-free; calcium silicate bricks or tiles;

k) any products containing cadmium referred to in Statutory Instrument 'SI 2006/3311

Controls on dangerous substances and preparations Regulations 2006'. Reference

should also be made to 'HSE IDGE391 Cadmium and you';

l) any new timber treated with pentachlorophenol;

m) non galvanised mild steel structural fixings for building elements particularly susceptible

to erosion;

n) concrete used in circumstances where it is susceptible to alkali/silica reaction;

o) materials containing chlorofluorocarbons (CFC's);

p) solvent based paints except where water based paints are unsuitable for unavailable;

q) any new materials not in accordance with statutory requirements, British Standards,

Codes of Practice and good building practice current at the date of incorporation of

the relevant materials into the Works or the specifications thereof;

Materials prohibited from use, except where used in accordance with 'Good Practice in

the Selection of Construction Materials (March 2011)' or unless required by the Contract:

1:200@A1 CS 03.08.2018

17-132-110

Proposed Site Plan

Broadwater Road

Welwyn Garden City

AL7 3AX

CS

SITE PLAN - AS PROPOSED

0 10

Scale Bar

5 20 Metres15 0 10

Scale Bar

5 20 Metres15 J

Sub-station indicated.A 17.12.2018

'Do Not Scale' notation omitted.B

17.01.2019

'Car parking spaces out of use

during refuse collection' notation

omitted based on Mayer Brown

drawing no. BPWELWYNGC.1/TK10.

C

30.04.2019

GIA increased by 5m² due to Third

Floor balcony redesign as agreed

with Planning on 16.05.2019.

D

17.06.2019

D

17.06.2019

E Frontage trees revised. 04.08.2019

F Existing Oak tree retained and

access footpath and parking

amended to suit. 16-07-2020

G Drop off zone and parking

amended to suit client

comments [meeting with PS

11-08-2020] 13-08-2020

H Main entrance moved and

parking amended to suit [PS

email 30-11-2020]

DD layout shown to amenity

garden 01-12-2020

TENDER ISSUE

I - Levels removed and note

added to refer to Canham info

- Shrubs removed from key and

noted added to refer to Deacon

Design info 15-01-2021

J Hard standing areas amended

to reflect Deacon Design info

08-02-2021

NB: Positions of Boreholes and/or Trial Pits are only indicative

Site: Broadwater Road, Welwyn STL: JN1576 Fig No: 1

Date: 3rd June 2021 Fieldwork Locations

TP2TP2TP2TP2

SSSStockpile tockpile tockpile tockpile samplessamplessamplessamples

SESSESSESSES

Southern Testing: Keeble House, Stuart Way, East Grinstead, West Sussex RH19 4QA ST Consult: Twigden Barns, Brixworth Road, Creaton, Northampton NN6 8NN

TP1TP1TP1TP10000

TP9TP9TP9TP9

TP6TP6TP6TP6

TP7TP7TP7TP7

TP5TP5TP5TP5

TP4TP4TP4TP4

TP1TP1TP1TP1

TP8TP8TP8TP8

SENSENSENSEN

TP3TP3TP3TP3

APPENDIX B

Verification Criteria

Contaminant Screening Values for Imported Soils

Contaminant Units

Proposed Land Use

Residential with homegrown produce

consumption

Residential without

homegrown produce

consumption

Open Space* (Residential)

Open Space* (Park)

Allotments Commercial / Industrial

Arsenic (As) [2] mg/kg 37 40 79 170 43 640

Cadmium (Cd) [2] mg/kg 11 85 120 555 1.9 190

Trivalent Chromium (CrIII) [2] mg/kg 910 910 1,500 33,000 18,000 8600

Hexavalent Chromium (CrVI) [2] mg/kg 6 6 7.7 220 1.8 33

Lead (Pb) [3] mg/kg 200 310 630 1300 80 2330

Mercury (Hg) [1,2,7] mg/kg 7.6-11 9.2-15 40 68-71 6.0 29-320

Selenium (Se) [2] mg/kg 250 430 1,100 1,800 88 12,000

Nickel (Ni) [1,4] mg/kg

pH<6.0 60

pH 6.0-7.0 75

pH>7.0 110

Copper (Cu) [1,4] mg/kg

pH<6.0 100

pH 6.0-7.0 135

pH>7.0 200

Zinc (Zn) [1,4] mg/kg

pH<6.0 200

pH 6.0-7.0 200

pH>7.0 300

Phenol [1,2] mg/kg 120-380 440-1200 440-1300 440-1300 23-83 440-1300

Benzo[a]pyrene [1,5] mg/kg 1.7-2.4 2.6 4.9 10 0.67-2.7 36

Naphthalene [1,2] mg/kg 2.3-13 2.3-13 77-430+ 77-430+ 4.1-24 77-430+

Total Cyanide (CN) [6] mg/kg / / / /

Free Cyanide [6] mg/kg / / / /

Complex Cyanides [6] mg/kg / / / /

Thiocyanate [6] mg/kg / / / /

Asbestos - None detected None detected None

detected None

detected None

detected None detected

Notes:

* Open Space levels calculated on the basis of the exposure modelling developed in the C4SL research.

+ Screening values constrained to saturation limit. Higher values may be acceptable on a site specific basis.

[1] Where ranges of values are given for organic contaminants, the screening value is dependent on the Soil Organic Matter. Where ranges are given for inorganic contaminants, the screening value is dependent on the pH.

[2] LQM/CIEH S4UL (2014). Copyright Land Quality Management Ltd reproduced with permission; Publication Number S4UL 3116. All rights reserved.

[3] C4SL (DEFRA 2014).

[4] Copper Zinc and Nickel may have phototoxic effects at the GAC or SGV concentrations and alternative criteria are given for importation of Topsoil or other soils for cultivation, based on BS3882:2015 (Topsoil) and BS8601:2013 (Subsoil).

[5] Based on the Surrogate Marker approach and modelled using the modified exposure parameters of C4SL but retaining ‘minimal risk’ HCV.

[6] Usually Non-Detect concentrations. Screening criteria to be derived on a site specific basis if test results indicate.

[7] SGV/GAC for Methyl Mercury, higher concentrations may be tolerable if inorganic mercury is the only species present. Lower concentrations apply for elemental mercury.

These screening values are valid at the time of writing but may be subject to change. Their validity should be confirmed at the time of site development.

remediation strategy and verification plan

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