Hickson & Welch Project:Solving the “Impossible” Site

The Hickson and Welch site was a chemical manufacturing site for over 100 years, until its closure in 2005. During its lifetime, it operated two private chemical waste landfills and one chemical drum storage area, which, since the site closed, have been identified as contaminated land sites. These sites are adjacent to the River Aire and within a 100-year flood zone.

More than 25 years of site investigations have produced large amounts of environmental data (in the tens of thousands of data points), covering differing aspects of the site and spread across numerous reports, excel files and lab reports. Despite the wealth of data, all previous work provided conflicting and/or unrealistic remediation options and strategies that failed to provide a way forward to stakeholders. The data was not being used correctly, nor was it in a format that could be understood and used for strategic decision making.

Challenge One: The fog of data.

NewFields integrated all data into our bespoke environmental database and GIS allowing a comprehensive review of the site data. This allowed the development of an accurate and detailed Conceptual Site Model (CSM) for the sites and the identification of data gaps.

Ü NewFields approach provided and agreed understanding of sites conditions between all project stakeholders.

Solution: Compile all the data into a single, usable database.

Our client's goal was to remove all their existing liabilities for the site, which meant remediating the site so they could surrender their landfill permits in the most cost-effective way possible. The existing strategy for the site proposed a £40 million remediation operation, which was too expensive, and was likely to not achieve the landfill closure requirements. There were several different remedial options that varied in terms of cost and uncertainty. NewFields performed a Decision Consequence Analysis of the available options to identify the most cost-effective option.

Challenge Two: Identify the optimal way to achieve our client's business goals.

NewFields proposed alternative approach achieved our client's goal whilst saving approximately £10 M.

NewFields integrated data analysis determined that the only control receptor was River Aire, an assessment endorsed by the regulators. By performing detailed hydrological risk assessments as well as human health risk assessments, we determined that a composite cap and effective surface water drainage system would satisfy the remedial targets and allow the client to eliminate their liability in a cost-effective way

Ü NewFields approach reduced irrelevant scope and provided a bespoke cost-effective remedial option.

Despite their close proximity and similar contamination profile all three areas presented different design challenges. Given that the sites are within the flood zone, a comprehensive flood compensation program had to be developed.

This was the first project approved by the Environment Agency involving the capping of chemical landfills in proximity to a major river.

Challenge Three: To design the capping and surface water management system within a flood risk zone.

Solution: Determine precise measurable benefits.

NewFields designed an integrated flood and stormwater management system that improved flood water retention . All three areas were capped using a specific com-bination of natural and synthetic materials achieving long term environmental bet-terment and optimal cost-benefit. Advanced 3D modelling techniques were used to design the topographical reshaping of each of the three areas, minimizing the amount of excavation, material import and respecting boundary constraints.

Ü NewFields focus on precise measurable benefits for each action resulted in remediation design with improved environmental betterment in a cost-effective way.

Challenge Four: Construction of the capping system and construction verification

NewFields managed the bid process, the contractors and was the principal designer for the construction of the three caps and ancillary structures. NewFields is monitoring the site post-construction, providing effective feedback to the regulators and the client. By managing the monitoring results in centralized database and GIS, NewFields has optimized the number of samples and sampling events. Post-construction monitoring has confirmed groundwater improvement, and our client is on the correct path to surrendering their permits.

Cu

mu

lati

ve P

rob

ab

ility

Cost

10%

0%

100%

20%

30%

40%

50%

60%

70%

80%

90%

£0.0 £X £XXX£XX

Capping

Waste Segregation and TreatmentHot Spot Removal Waste and Impacted Soil Excavation and Incineration

Waste and Impacted Soil Excavation and Landfilling

5000 trials Cost Cumulative Frequency View

Low

Nominal

High

bNo

a

AdditionalWaste/SoilDelineation

Cost Low

Nominal

High

Low

Nominal

High

Years ofMonitoring

Low

Nominal

High

d

GroundwaterMonitoring

Costs

Low

Nominal

High

Backfilland Grading

Costs

Low

Nominal

High

VerificationSampling

Costs

Low

Nominal

High

LandfillTaxes

Low

Nominal

High

Haz/Non HazWaste

DisposalCosts

Landfilling c

Amount ofHazardousWaste?

Low

Nominal

High

c

Low

Nominal

High

Amount ofMaterial to

be Landfilled

Incineration

IncinerationUnit

Costs

Low

Nominal

High

WasteDisposalMethod

Low

Nominal

High

ExcavationCosts

Yes b

ExcavationVolume

Waste and Impacted Soil Excavation

Has waste andimpacted soil

been adequatelydelineated

No a

Low

Nominal

High

bYes

Amount of HotSpot

Material tobe ExcavatedHot Spot Removal

Waste beenAdequatelydelineated?

No a

Low

Nominal

High

c

Low

Nominal

High

Waste/SoilStabilisation

Costs

Low

Nominal

High

ExcavationCosts

Yes

ExcavationVolume

Waste Segragation and Treatment

Waste beenAdequatelydelineated?

Low

Nominal

High

Low

Nominal

High

Years ofMonitoring

Low

Nominal

High

LandfillMonitoring

Costs

Low

Nominal

High

CappingCosts

Capping

Area tobe Capped

Low

Nominal

High

d

Low

Nominal

High

Yearsof O&M

Low

Nominal

High

GroundwaterPathway

Control O&MCostsGW Migration Control

GW Barriers (PRW, Plumestop, etc.)

Low Permeability Cap

Insitu Treatment (SVE, Bioremediation, etc.)

MNA

GW Pathway ControlCosts

(Design/Implemenation)

Yes

GW PathwayControlOptions

No d

Groundwater

Property Boundary

River

Do current/future GWConcentrations

exceedstandards at

Compliance Point?

Controlled Waters

Controlled WatersCompliance

Point

Asphalt Capping

Institutional Controls

Surface Soil Excavation

Direct Contact

Direct ContactManagement

MitigationOptions

Vapor Barriers

Institutional Contols

No Vapour Risk

Vapors

VaporManagmentMitigationOptions

Risk Pathway Control

RiskPathway

RemedialAlternatives

Reshaping of the edges of the landfill Excavation of the sludge prior to stabilization Sludge stabilization

Composite cap installation Flood management system construction Current view of the former Landfill 227

Former Hickson & Welch“Main Site”

River Aire

Lowfields Drum StorageFormer 227 Landfill

Green Lane

NewFields expertise in data management, GIS and DCA, resulted in a remediation strategy 40% cheaper than those proposed by other consultancies, and identified a viable solution to what was considered an “impossible site”.