remediation of ince central estate in wigan a part 2a site tony brown, silc – director of ground...

REMEDIATION OF INCE CENTRAL ESTATE IN WIGANA Part 2A Site

Tony Brown, SiLC – Director of Ground Engineering

John Crowther, SiLC - Technical Director

22nd September 2009

2

Contaminated Land & Brownfield Remediation Conference Contaminated Land & Brownfield Remediation Conference

Ince Central Estate, Wigan

3


Site Location Plan

4


Estate Layout

5

Engineering & Environment Conference 2008Engineering & Environment Conference 2008

Ince Central Estate, Wigan – Remediation Project

• John Crowther – from Investigation to Options Appraisal

• Tony Brown – Trials and Remediation Works

6


From Investigations to Options Appraisal I

• Supplementary Desk Study• Supplementary Site Investigation• Groundwater issues assessed as not critical• Additional investigation carried out including

sampling within top 1m within each garden plot• Further investigation within ‘clear’ plots

7


Composite Historical Plan

8


GI Plan

9


Results with Averaging Areas Shown

10


From Investigations to Options Appraisal II

Human Health Risk Assessment

• Derivation of Site Specific Values (SSV’s)– BP RISC (organics)– SNIFFER (inorganics)

• Sensitivity Analysis– Arsenic (including PBET)

11


Arsenic SSV Derivation - 1Value mg/kg150 Utilises BP RISC model.

Assumptions:-

soil eating by child up to 6 years of age on 180 days per year as indicated on Table 6.1 of CLR 10

40 % bioavailability

child body weight 14.5kg

89 Utilises BP RISC model.

Assumptions:-

soil eating by child up to 6 years of age on 365 days per year as indicated on Table 4.3 of CLR 10 (discrepancy between tables in CLR10 reported to Environment Agency)

40% bioavailability

child body weight 14.5 kg


Assumptions:-

soil eating by child up to 6 years of age on 365 days per year as indicated on Table 4.3 of CLR 10 (discrepancy between tables in CLR10 reported to Environment Agency)

70% bioavailability


12


Arsenic SSV Derivation - 2


Assumptions:-

soil eating by child up to 6 years of age on 365 days per year.

100% bioavailability (following meeting of 23-12-04)



Assumptions:-

soil eating by child up to 6 years of age on 365 days per year.

100% bioavailability.

child body weight 14 kg.

27 Utilises SNIFFER model (for metals only) following meeting of 27-01-05.

Assumptions:-

soil eating by child up to 6 years age on 365 days per year

100% bioavailability

child body weight 14kg

13


The Appraisal Criteria

1. Impact on residents’ health and quality of life

2. Technical feasibility and sustainability

3. Statutory powers and duties

4. Cost and potential availability of funding

5. Impact on structures, services and foundations

6. Timescales

7. Risks (to delivery of solution)

8. Opportunities

9. Impact on tenants

10. Impact on homeowners

11. Impact on the estate image

12. Wigan Council Housing Strategy and other strategies

14


Total Scores for the Options

6

10

12

4

5

-4

-5 0 5 10 15

Cover front and rear gardens withclean soil

Excavate/replace soil in front and reargardens

Hard cover front and excavate/replace rear

Put the cleared site(s) to public openspace

Cover and redevelop for new homes

Excavate/replace soil and redevelopfor new homes

15


Liaison with Residents

• Only one initial public meeting

• ‘History’ Day

• Interviews – Consultant and Remediation Contractor

• Resident’s Liaison Group Participation

• Regular Newsletters

• Home Visits

• HPA Health Consultation Days

• 3 Stakeholder Meetings

16


Trials & Remediation Works

• Pilot Project

– Pair of semi-detached properties undertaken in May 2005

• Remediation of the first two Phases (1 & 2)

– 32 plots in northern part of the estate

• Lessons learnt for other phases

• ‘Architectural Details’

• Conclusions

17


Remediation Works – Pilot Project

Reasons for undertaking the pilot

– to establish whether residents can remain in their homes without risk to their health.

– to confirm feasibility of methodology adopted.

– to enable residents to appreciate the nature of the works to be undertaken.

Selection of the pilot

– vacant properties

– good access

– contaminated material encountered

18


Remediation Works – Pilot Project44 & 46 The Grove

19



20



• Two techniques implemented

– Excavate & Replace (600mm)

– “Capping” (200mm)

• Environmental Monitoring

– Air Quality (PM10, Nuisance Dust, Dust Analysis)

– Noise and Vibration

• Suitable import materials identified

21



22


23


View prior to work commencing (44 The Grove)

24


Excavation in progress (rear of 44 The Grove)

25


Damaged drain (44 The Grove)

26


Repaired drain (44/ 46 The Grove)

27


Base of excavation (44 The Grove)

28


Filling with sandy subsoil (44 The Grove)

29


Topsoil placed (44 The Grove)

30


New fencing erected. Topsoil placed and trees planted at rear of 46 The Grove

31


Patio area being constructed (46 The Grove)

32


Turf laid (44 The Grove)

33


Excavation in progress (46 The Grove)

remediation of ince central estate in wigan a part 2a site tony brown, silc – director of ground...

Documents

wigan slide

pbet slide

remediation works

years of age

years age

environment agency

sniffer model

site tony brown