developing an appropriate proportionate contaminated october … · 2018-10-29 · rps presenters ....

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Developing an Appropriate CSM and DQRA to Support Proportionate Contaminated

Land Management

24th October 2018

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RPS Presenters Phil Thomas Technical Director (BSc, MSc, CGeol, RoGEP) Phil is a Technical Director with RPS. Phil has over 17 years’ experience of managing the environmental aspects of contaminated land projects in support of planning due diligence, redevelopment and permitting.

Richard Graham Associate Director (BSc, MSc, FGS) Richard is an Associate Director with RPS. Richard has 20 years’ professional experience of environmental consultancy as a Geophysicist and Hydrogeologist. Richard specialises in the Water Sciences and manages delivery of technical assessments within the fields of land quality.

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A Series of Case Studies:

• The Value of Robust Conceptualisation in Defining an Appropriate CSM

• Asbestos Characterisation and Risk Assessment

• Development of a CSM to Underpin an Appropriate Monitoring Strategy

Presentation Structure

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The Value of Robust Conceptualisation in Defining an Appropriate CSM

‘Understanding your sources, pathways and receptors’

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Site Context

• Long industrial heritage over 150 years • Legacy contamination including gross soil

contamination and free product

• Ground conditions: • 1-8 m of Made Ground • 2-4 m of Glacial Till (unproductive strata) • >27 m of Coal Measures (Secondary Aquifer)

• Surface water features located circa 500 m to the south

east and south west

• 8 separate assessments over 30 years, with similar CSMs

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A Simplistic CSM The majority of assessments identified a similar CSM

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A Simplistic CSM

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A Simplistic CSM

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A Simplistic CSM

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A Simplistic CSM

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A Simplistic CSM

Simplistic CSM = risk to CW = large scale remediation = excessive costs

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A More Robust CSM A more detailed consideration of pollutant linkages and identified a refined CSM

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A More Robust CSM

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A More Robust CSM

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A More Robust CSM

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A More Robust CSM

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A More Robust CSM

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A More Robust CSM

Robust CSM = no unacceptable risk CW = limited soil remediation = limited cost

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What About Construction?

• Potential new pathways associated with pilled foundations

• Appropriate construction method

• Offensive groundwater monitoring

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Asbestos Characterisation and Risk Assessment

‘Pitfalls and opportunities’

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Site Context

• Site was open fields up until circa 1940s

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Site Context

• Site was open fields up until circa 1940s • Between 1930s and 1970s developed as an

agricultural research facility comprising a series of low rise buildings.

• Facility ceased operation in the 1990s.

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Site Context • The site operations / processes did not include

the use of asbestos materials, although the structures of the building clearly included asbestos materials and were in poor state of repair

• The site was laid predominantly to hardstanding

On paper a relatively low risk site!

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Characterisation

Extensive investigation undertaken over multiple phases between 1995 and 2010 comprising : • 47 boreholes distributed across the site • 8 trial pits, targeting non-hardstanding areas • 11 samples tested for the presence of asbestos • Asbestos identified at one trial pit location within

shallow soils in unsurfaced area Characterisation suggested; localised isolated presence of asbestos. Conclusion: Observed asbestos linked to buildings

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Actual Extent of Asbestos

• Demolition commenced in 2016 with removal of all above ground structures and asbestos soft strip from building

• During removal of the hardstanding

there was clear visual evidence of frequent bound and unbound forms of asbestos within sub base / capping layer

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Actual Extent of Asbestos • Subsequent laboratory testing confirmed the

presence of fibres within 22 of 77 samples analysed

Conclusion: Asbestos was imported onto site in capping and sub base materials associated

with construction of the facility!

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Why the Discrepancy?

Key Factors: • Concerns relating to storage and accumulation of radioactive waste restricted ground

investigation works to WS boreholes in most areas. CAR Soil states Paragraph 307 states:

“trial trenches and trial pits are better at uncovering asbestos than boreholes”

• Changed analytical techniques / sample preparation. • Pre 2011 asbestos identification undertaken on as received wet samples • Post 2011 asbestos identification undertaken dried samples

• Investigation and Laboratory procedures, whilst reasonable in site context, limited the potential to readily identify asbestos

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Risk Assessment • Risk assessment undertaken in accordance with CIRIA C773:2014 • Risk Assessment identified that:

• The identified free respirable fibres for Amosite (0.001% w/w) and Chrysotile (0.003% w/w) did not present an intolerable risk

• Detectable concentrations of Crocidolite did present a potentially intolerable risk

• Risk assessment allowed targeted remediation comprising of: • Removal of subbase and capping materials with frequent occurrences of

asbestos or unbound asbestos material • Hand picking of fragments of asbestos where infrequent asbestos was present • Testing to demonstrate residual fibres were at acceptable concentrations

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Development of a CSM to Underpin an Appropriate Monitoring Strategy

‘Dealing with uncertainty’

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Private PWS Borehole : Background • Licensed groundwater abstraction

• Large potable supply

• Multiple stakeholders at impasse

• Private Water Supply Regulations

• Risk uncertainty

• Stakeholders at impasse

• CSM to inform monitoring strategy

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Private PWS Borehole : Key Monitoring Variables • Area of interest

• Groundwater flow regime

• Frequency and Duration

• Locations - defensive vs. offensive

• Determinands

• Trigger and Action Levels

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Private PWS Borehole : Derived Monitoring Strategy • Correlated CoC to SPZ Capture Zones

• CoC linked to historic landfill sites, chemical

works and paint manufacturing

• Monthly sampling during 90-day pump test

• Broadscan organic analysis utilising library of 10,000 compounds, TPH/PAH, dioxins/furans and microbiology

• Robust evidence gathered to satisfy Local Authority and assist in supply treatment design

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Any Questions?

Phil Thomas thomasp@rpsgroup.com T: 07919535844

Richard Graham grahamr@rpsgroup.com T: 07966125207