novel approaches to assess the site-specific risks …...novel approaches to assess the...
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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 [email protected] Gasworks and innovation specialist
Dr. Matt Riding +44 (0)7469 402326 [email protected]