contaminated land: dealing with hydrocarbon contamination

Contaminated land: dealing Contaminated land: dealing with hydrocarbon with hydrocarbon

contaminationcontamination

Conceptual models for Conceptual models for petroleum hydrocarbon sitespetroleum hydrocarbon sites

Environmental Simulations International

Contents of Contents of presentation presentation

Key contaminantsKey contaminants– Compounds of particular interestCompounds of particular interest– The challenge of TPH analysisThe challenge of TPH analysis

Hydrocarbon-contaminated sitesHydrocarbon-contaminated sites– Important source considerationsImportant source considerations– NAPL sourcesNAPL sources– Important pathwaysImportant pathways– Common receptorsCommon receptors

Developing and refining the conceptual Developing and refining the conceptual modelmodel

Contaminant interactionsContaminant interactions


Key componentsKey components

Will depend on the case but most common Will depend on the case but most common hydrocarbon risk drivers are:hydrocarbon risk drivers are:– BTEXBTEX– PAH’sPAH’s

Weathering may change priorities with timeWeathering may change priorities with time When relevant, consider MTBE (etc.), lead, When relevant, consider MTBE (etc.), lead,

other metalsother metals You will need to consider component You will need to consider component

interactions interactions – Discussed laterDiscussed later


Key components – Key components – more on BTEXmore on BTEX

Main pathways are often migration as Main pathways are often migration as dissolved plume and/or as vapourdissolved plume and/or as vapour– Relatively soluble in water Relatively soluble in water

Benzene ~1790 mg/lBenzene ~1790 mg/l

– Relatively volatileRelatively volatile ToxicologyToxicology

– Benzene is a carcinogenBenzene is a carcinogen– TEX relatively toxic but not carcinogenicTEX relatively toxic but not carcinogenic


Key components – Key components – more on PAH’smore on PAH’s

Main pathways are often ingestion, dust Main pathways are often ingestion, dust inhalation, direct contactinhalation, direct contact– Low to very low solubility in waterLow to very low solubility in water

e.g, naphthalene ~30 mg/l; benzo[a]pyrene ~0.003 e.g, naphthalene ~30 mg/l; benzo[a]pyrene ~0.003 mg/lmg/l

– Adsorb onto solidsAdsorb onto solids– Relatively low volatility (although naphthalene Relatively low volatility (although naphthalene

can be significant)can be significant) Variable toxicityVariable toxicity

– Some are carcinogen’s (e.g., benzo[a]pyrene)Some are carcinogen’s (e.g., benzo[a]pyrene)– Effects can be additiveEffects can be additive


Key componentsKey components

Don’t forget NAPL migrationDon’t forget NAPL migration


A brief digression – A brief digression – TPH analysisTPH analysis

TPH = Total petroleum hydrocarbonsTPH = Total petroleum hydrocarbons A quick and easy screening assayA quick and easy screening assay

– Everyone uses themEveryone uses them– Can help identify the type of oil and the Can help identify the type of oil and the

extent of weatheringextent of weathering Don’t always believe the lab.’s interpretationDon’t always believe the lab.’s interpretation

But what do the concentrations tell us?But what do the concentrations tell us?


TPH analysisTPH analysis

Various methodsVarious methods– Gravimetric Gravimetric

Not recommended!Not recommended!

– IRIR– GCGC– GC/MSGC/MS

Fresh Grease '1' (Current Grease)

3500 3000 2500 2000 1500 1000

1.5

1.0

0.5

0.0

Wavenumber

Absorb

ance


What’s wrong with TPH What’s wrong with TPH measurement?measurement?

Nothing, provided the data are used Nothing, provided the data are used correctlycorrectly– Do you know which standards were used?Do you know which standards were used?– Different methods give very different answersDifferent methods give very different answers– No direct relationship to hazards posed by the No direct relationship to hazards posed by the

componentscomponents Work in progress to provide a standard TPH Work in progress to provide a standard TPH

analysis methodology that can link directly analysis methodology that can link directly into standard risk assessment techniquesinto standard risk assessment techniques– Environment Agency/Institute of PetroleumEnvironment Agency/Institute of Petroleum– US methodologyUS methodology


The US approachThe US approach

http://www.aehs.com/

1. Define appropriate hydrocarbon fractions for

assessment

2. Define key properties of each fraction

3. Determine toxicity based on data derived for

the fraction or key components within it

4. Integrate fate/toxicity data and determine risk


How does the process How does the process work?work?

GC/FID screen to derive TPH GC/FID screen to derive TPH fractionsfractions

Screening concentrations per Screening concentrations per fraction for main exposure routesfraction for main exposure routes

More detailed GC/FID or GC/MS More detailed GC/FID or GC/MS analysis of fractionsanalysis of fractions

Procedure for deriving site-specific Procedure for deriving site-specific valuesvalues


Conceptual modelsConceptual models

Hardstanding

River intercepts plume

Deep borehole


Why do we need Why do we need conceptual models?conceptual models?

A ‘pollutant linkage‘ is the relationship A ‘pollutant linkage‘ is the relationship betweenbetween– a contaminant (source)a contaminant (source)– a pathwaya pathway– a receptora receptor

The presence of all three elements is The presence of all three elements is required for land to be defined as required for land to be defined as ‘contaminated’‘contaminated’

So, we need a conceptual So, we need a conceptual understanding of our site!understanding of our site!


A conceptual model …A conceptual model …

Allows targeting of subsequent investigationAllows targeting of subsequent investigation– Use the model iterativelyUse the model iteratively– And is a requirement for SI (BS10175:2001)And is a requirement for SI (BS10175:2001)

Provides the context for quantitative risk Provides the context for quantitative risk assessmentassessment

Demonstrates an appreciation of the Demonstrates an appreciation of the problem problem – ……beyond the purely factual data gatheringbeyond the purely factual data gathering

Aids communicationAids communication Is a good QA toolIs a good QA tool


Some considerations Some considerations for hydrocarbon for hydrocarbon sources - 1sources - 1

What?What?– What was released?What was released?

Source materialSource material Additives (MTBE, lead?)Additives (MTBE, lead?) Co-contaminants?Co-contaminants?

– e.g., degreasing solventse.g., degreasing solvents

– When?When? Weathering?Weathering?

– How?How? Distribution and weathering?Distribution and weathering?


Some considerations Some considerations for hydrocarbon for hydrocarbon sources - 2sources - 2

How much?How much?– Estimate of source massEstimate of source mass– NAPL likely?NAPL likely?– Residual?Residual?

Where?Where?– Weathering?Weathering?– Spatial variabilitySpatial variability– Fracture Fracture versusversus matrix flow matrix flow

And so on …And so on …


NAPL sourcesNAPL sources

Flowing or immobile?Flowing or immobile?– If flowing, where to?If flowing, where to?

Smearing?Smearing? How much?How much? How reliable are the thickness How reliable are the thickness

measurements?measurements? Do it’s properties match theory?Do it’s properties match theory?


Chlorinated solvents

Oil and petroleum products

EthanolAntifreeze

Metals (e.g., lead)

Some possible source Some possible source behavioursbehaviours


NAPL sourcesNAPL sources


NAPL smearing – NAPL smearing – spreading the source?spreading the source?

Raising water table may not displace freeproduct lens which remain in initial position.

Idealized spreading on water table.(actually, capillary fringe)

Soil heterogeneities result in “fingering”

Water table moving below initial level results in further descent of free

flowing NAPL.


Some pathway Some pathway considerations - 1considerations - 1

Geological settingGeological setting Hydrology/hydraulicsHydrology/hydraulics

– Recharge processes and unsaturated zone flowRecharge processes and unsaturated zone flow– Groundwater flowGroundwater flow

Essentially horizontal or vertical? Essentially horizontal or vertical?

– Discharge pointsDischarge points Natural or anthropogenic?Natural or anthropogenic?

– Fast pathways (Fast pathways ( early arrival of contaminants) early arrival of contaminants)– Slow pathways (Slow pathways ( persistence of contaminants) persistence of contaminants)– Barriers to flowBarriers to flow



Groundwater pathwaysGroundwater pathways– Advection and DispersionAdvection and Dispersion– DispersionDispersion– Sorption/retardationSorption/retardation– BiodegradationBiodegradation

NAPL flowNAPL flow Gradient of water tableGradient of water table Penetration of preferential flow pathsPenetration of preferential flow paths



Vapour pathwaysVapour pathways– Advection and DispersionAdvection and Dispersion– Sorption/retardationSorption/retardation– BiodegradationBiodegradation

Solid phase contactSolid phase contact– Dust transportDust transport– Direct contactDirect contact

Inter-phase partitioningInter-phase partitioning Plant uptake?Plant uptake?


Some possible Some possible important receptorsimportant receptors

Who/what?Who/what?– HumansHumans– Controlled watersControlled waters

AquifersAquifers Surface watersSurface waters

– Water supplyWater supply Plastic pipelinesPlastic pipelines

– Utilities structuresUtilities structures CablingCabling SewersSewers

– EcosystemsEcosystems– BuildingsBuildings

Fit for purpose

?


Component Component interactionsinteractions

Hydrocarbon components will behave Hydrocarbon components will behave very differently from each othervery differently from each other– MTBE can behave very differently in MTBE can behave very differently in

groundwater – high mobility, often slow groundwater – high mobility, often slow biodegradationbiodegradation

Components can affect the behaviour of Components can affect the behaviour of othersothers– BiodegradationBiodegradation– SorptionSorption– Solubility Solubility – Vapour composition…Vapour composition…


Component Component interactionsinteractions

An example - benzeneAn example - benzene

ParameterParameter Pure Pure benzenebenzene

Typical Typical petrolpetrol

Solubility in Solubility in groundwater groundwater (mg/l)(mg/l)

17901790 36.536.5

Equilibrium vapour Equilibrium vapour concentrationconcentration

(mg/l)(mg/l)

400400 6.76.7


ConclusionsConclusions

We need conceptual modelsWe need conceptual models Hydrocarbons have some specific Hydrocarbons have some specific

properties that are important to properties that are important to considerconsider– And many that are common to all And many that are common to all

contaminantscontaminants Consider the effect of the component Consider the effect of the component

mixtures when testing the modelmixtures when testing the model Ask the questionsAsk the questions

contaminated land: dealing with hydrocarbon contamination

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