Novel approaches to assess the site-specific risks to groundwater on former gasworks Dr Matt Riding, Senior Consultant Prof. Russell Thomas, Technical Director

22 March, 2018

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What makes former gasworks complex sites?

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• Stable Isotope Chemistry • Coal Tar Forensics

Did the contamination

come from site?

• Electrical Resistivity Tomography • Automated time-Lapse Electrical

Resistivity Tomography (ALERT)

How can we locate and

monitor the contamination?

• Bio-Traps and Stable Isotope Probing (SIP)

Is the contamination

likely to naturally attenuate?

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Electrical Resistivity Tomography (ERT) Well established technique for identifying sub-surface structures A single snap-shot of ground conditions

Locating Contamination

Former gas

holder

Buried Service

Elevated conductivity possibly relating to biodegradation

Former tar tank

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How can we Monitor the Contamination?

Graphics and images used with kind permission of the BGS

− British Geological Survey (BGS) developed a system for Automated time-Lapse Electrical Resistivity Tomography (ALERT)

− Measures hydrogeophysical characteristics

− Enables identification of: − Contaminant distributions

and transport; − Pollutant linkages; and, − Areas requiring remedial

works.

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Statutory contaminated land (Part IIA Site)

Application to a Former Gasworks Site

Graphics and images used with kind permission of the BGS

Off-site gasworks

On-site gasworks

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Graphics and images used with kind permission of the BGS

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Graphics and images used with kind permission of the BGS

Assumed groundwater

flow direction Actual groundwater

flow direction

Bioremediated Infilled

Ground

Alluvium

River Terrac

e Alluvium River

Terrace

Initial Image Image after 10 Months Change in Resistivity

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− Molecular Biological Tools (MBTs)

Is the Contamination Likely to Naturally Attenuate?

Are the correct types of bacteria

present?

DNA tests for key organisms

(qPCR)

Specific biomarkers

PFLA analysis for specific and general community features

biomarkers

Is the contaminant

biodegrading?

Stable Isotope

Probing (SIP)

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Deploy in on-site wells for ~30 days

Evaluate the microbial community and measure the 13C enrichment in the

biomass

13C Stable isotope of the contaminant of concern

13C Stable isotope loaded on to 2-4 mm in diameter, Nomex® and powdered activated

carbon (PAC)

Powdered activated carbon provides a surface on which microorganisms can grow

Images acquired from Microbial Insights (www.microbe.com)

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Did the Contamination come from Site?

Agriculture or cemeteries Nitrogenous contamination

Former gasworks • Ammonium from ammoniacal

liquor; • Spent oxide; • Foul lime; and, • Ammonium sulphate fertiliser

Current or former factories/works producing nitrogenous waste

Sewage works Nitrogenous waste from and cracked sewers

Sea or estuarine

water Saline intrusion

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− Nitrogen and oxygen isotopes to discriminate between sources of nitrogenous contamination

Source Appropriation using Stable Isotope Chemistry

Commercial Fertiliser

Nitrate in explosives

Organic nitrogen in

soil

Animal or human waste

Groundwater contaminated by gasworks sources

40 -

30 -

20 -

10 -

-10 -

δ15N

-20 -10 10 20 30 40 δ18O

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Case study: Former Gasworks in South East England

Groundwater

Estuary Alluvial Deposits

Peat

Gasworks Sewage Works

Neighbouring Industry

Geochemical analysis • Total Alkalinity • Nitrogen • Nitrite • Nitrate • Ammoniacal Nitrogen • Major Ions (Na; K; Ca; Mg; Cl-l; SO4-2)

Isotope Analysis • Total Nitrogen

15N(Total) • Nitrate δ15N(NO3) • Nitrate δ18O(NO3) • Ammonium δ15N(NH4)

• Mixture of organic and inorganic compounds, of which many can be toxic or carcinogenic from coal carbonisation.

• Generally regarded being one substance. • Actually a family of residuals from processes which thermally

degrade (carbonise or gasify) organic feedstocks. • Basis of some important toxicology work, however:

• Research papers often focus on limited samples types; • Limited suite of analysis. e.g. PAH • Unrecorded production processes. e.g. Culp et al. • Published papers have advanced little since the 1950’s

• Generally only PAH considered - more recent research started to review other CoC within Coal tar.

• Research undertaken in partnership with the University of

Strathclyde and National Grid to answer what is Coal tar composed of, does it vary and can it be analysed rapidly?

Coal Tar – Forensic Investigation

19th Century Gas Manufacturing Processes

• Low temp. horizontal retort

• Hand operated • Gas coals • Radiant heated • Low temps • Used on small gasworks

• High temp. horizontal retort

• Mechanised • Gas coals • High temps • Used on medium-large gasworks

• Inclined retort

• Mechanised • Gas coals • High-low temperatures

• Tar exposed to differential thermal degradation

• Carb. Water Gas

• Mechanised • Coke - self heated from partial combustion of coke.

• Medium-low Temps. • Enriched with oil • Oil based tars with coke signature.

gas gas

heat heat

gas Thermal gradient

heat

gas

Coal Coal

Coal

Coke

Oil

20th Century Gas Manufacturing Processes

• Coke Oven

• Mechanised • Coking coals • High temperatures • Tar exposed to thermal degradation on very hot oven walls

• Low temperature Coalite process also

• Chamber Ovens

• Mechanised • Coking coals • High temperatures • Tar exposed to thermal degradation but greater potential for gas/tar to escape

• Oil Gas

• Mechanised • Oil heated • Relatively low temperature process.

• Tars entirely oil based

• Vertical retort

• Mechanised • Gas coals • Hig-Low temps • Differential heating • Tar/gas able to migrate vertically through coal avoiding thermal degradation.

Thermal gradient Coal Crushed

coal Coal Oil

Effect of Temperature on Coal Tar

Incl. & Vertical Retorts

Low temp horizontal retorts

High temp coke ovens

High temp horizontal retorts

CWG & Oil Gas

Vertical chamber ovens

Low temp coke ovens

Analytical Approaches to Tar

Aliphatic petroleum hydrocarbons from CWG tar.

Aromatic compounds from coal tar.

• Able to detect a vast array of different compounds with one method.

• GCxGC involves the use of two columns of different polarity to separate organic compounds across horizontal and vertical dimensions.

• Traditional GC only separates

across horizontal dimensions.

• GCxGC allows for the separation of complex organic mixtures that cannot be resolved by traditional GC analysis

High Resolution Analysis of Coal Tar

• Able to detect a vast array of different compounds

with one method. • Generates a very large dataset- assessed using

Principle Component Analysis (PCA). • A statistical method that emphasises trends and

patterns in the data.

1 = Benzonitrile 2 = Quinoline 3 = Indole 4 = C1-indoles 5 = Naphthonitrile 6 = Benzofuran 7 = Naphthalene 8 = Benzothiophene 9 = C1-naphthalene and C1 Benzothiophene 10 = Acenaphthylene 11 = Dibenzofuran 12 = Phenol 13 = C1-phenols 14 = C2-phenols 15 = C3-phenols 16 = C4-phenols 17 = Hydroxybenzoic acid 18 = Naphthols 19 = C1-naphthols 20 = C2-naphthols 21 = Linear C17 22 = Linear C18 23 = Pristane 24 = Phytane

A = N-aryls B = PAHs, O and S-aryls C = TMS-phenols D = Cycloalkanes E = Linear alkanes F = Branched alkanes

Samples Manufacturing processes Years of Operation

1-6 Vertical retort, CWG, Oil Reforming and early horizontal retort tar 1836-1971

7 Horizontal retort. 1856-1969

8 Horizontal retort. 1856-1971

9 Horizontal retort (early low temp), vertical retort and CWG plant. Ceased 1953

10 Horizontal retort. 1849-1981

11 Wood Preservation. Unknown

12 CWG, horizontal & vertical retorts, chemical works & oil reforming. 1854-unknown

13 CWG plant. 1885 to unknown

14 &17 Horizontal retorts, potential traces of CWG and coke oven tar. Unknown

15 Tully Gas plant, a combination of vertical and water gas. 1841-1961

16 Early low temperature horizontal retorts. 1854-1946

18/19 Coke ovens. 1970’s/ 30’s to present

20 Vertical retorts, potential traces of CWG tar. 1885 to unknown

21-22 Early low temperature horizontal retorts. 1840-1870

23 Vertical retorts. 1896-1979

50 Inclined chamber oven - UK Circa 1920’s

48 Intermittent Vertical Chamber Oven - Netherlands Circa 1920’s

Unknown sample from US Circa 1950’s

Vertical Chamber Oven

Do Tars Produce Unique Signatures?

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First Component

Seco

nd

Com

pone

nt

-10 -5 0 5 10

7.5

5.0

2.5

0

-2.5

-5.0

Vertical Retort

Low Temp. Horizontal Retort

High Temp. Horizontal Retort

Coke Ovens

Carburetted Water Gas/Creosote

PCA score plot of the coal tar data set, allows the coal tars to be assigned to the different processes used to manufacture them.

Inclined Chamber Oven

Unknown US sample

The samples plot according to: • Extent of thermal

degradation; • Influence of oil

based feedstocks • Forensic technique

suitable for Source Apportionment.

Organic Constituents of Coal Tar PAH e.g. Pyrene Alkyl PAH e.g.

Methyl Pyrene PASH e.g. Phenanthro(3,4-b) thiophene 380 PASH det. The PASH were generally more toxic than their analogous PAH. PASHs and their metabolites can be carcinogenic or mutagenic. Common forms are thiophenes or dibenzothiophenes.

PANH e.g Carbazole

262 PANH det. More stable and recalcitrant to biodegradation than analogous to PAH. PANH’s more soluble than PAH analogues. Nitro & amino groups enhance toxicity by up to 100-fold, suspected carcinogens.

196 Alkyl PAH det. Alkyl PAH contribute to the toxicity of PAH mixtures, can account for 80% of the toxic burden. About 45% of PAH in coal tar are Alkyl PAH. 16 Alkyl PAH feature in the US EPA 34 PAH. Less soluble than analogous PAH.

948 PAH detected. Typically only 18 PAH analysed. Long term modelling of Coal tar plumes predict that after 1000 yrs, 89% of the initial mass of Phenanthrene would remain, with 60% of moderately & 95% sparingly soluble components remaining.

Oxy PAH e.g Dibenzonfuran & Phenols

209 Oxy & 359 Hydroxy PAH Det. More stable and recalcitrant to biodegradation than analogous to PAH. Toxic and ecotoxic. More polar and soluble than analogous PAH.

Within 16 coal tar samples 2369 Compounds detected incl. 15 Mixed heterocycles.

The 173 Compounds found in all Tars

Vertical Retort

CWG

Coke Oven

Horizontal Retort

Variation & Similarity in Tar Composition

Composition of tar and its distillates Component % by

weight Specific Gravity Viscosity cP Remarks

Coal Tar 100 1.10-1.28 Crude London tar

Amm. Liquor 2-3 Ammonia & Phenol

Light Oils 3-5 0.91-0.95 LNAPL

Middle/Carbolic Oil 7-12 1.02 LNAPL/NNAPL/DNAPL

Heavy/Creosote Oil 10-12 1.03-1.07 DNAPL

Anthracene oils 11-16 1.1 DNAPL

Pitch 50-65 1.25-1.44 Solid at STP

Horizontal retort n/a 1.18-1.33 1136-4924* DNAPL

Inclined retort n/a 1.15-1.25 757-2272* DNAPL

Vertical retort n/a 1.08-1.16 1431-2863* NNAPL/DNAPL

Coke oven n/a 1.15-1.26 227-2271* DNAPL

Low temperature 0.95-1.12 151-378* LNAPL/NNAPL/DNAPL

CWG n/a 1.061-1.125 12-89** LNAPL/NNAPL/DNAPL

Oil Gas (PWC) n/a 1.206-1.317 100** DNAPL (Poss. of LNAPL)

Gas making oils n/a 0.704-1.049 204-2181** LNAPL/NNAPL/DNAPL

Incr

easin

g Vi

scos

ity

Incr

easin

g Sp

. Gra

v.

Viscosity at * 100°C or ** 37°C

Considerations for Tar Remediation

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Groundwater flow

Dissolution from Immobile pitch

Horizontal tar migration with dissolved phase plume

Coal Tar DNAPL Highly Viscous

Tar tank tank

Distilled Fractions Light oil → Anthracene Oil

• Coal tar, typically DNAPL – low mobility restricted by viscosity & density

• Gradual & persistent source of pollution • Distilled fractions different properties

• CWG & Oil gas tars can be DNAPL, NNAPL & LNAPL • Mobile, can form large product plumes in groundwater. • Can readily emulsify • Detection of Alkyl Cyclohexanes suggests CWG & Coal tar mixed

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Groundwater flow

Some CWG tar, LNAPL/NNAPL Low Viscosity

Limited Vertical migration long NAPL Plumes

Relief Holder Tar tank

Limited Horizontal migration of DNAPL Oil gas tars, CWG tars & mixed coal/CWG Tars

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Thank you! Please contact us if you have any further questions.

Prof. Russell Thomas +44 (0)7879 602509 Russ.Thomas@wsp.com Gasworks and innovation specialist

Dr. Matt Riding +44 (0)7469 402326 Matt.Riding@wsp.com