Contaminated land: dealing with hydrocarbon contamination

Contaminated land: dealing with hydrocarbon contamination
Remediation options for petroleum hydrocarbon-contaminated soil and groundwater

Contents of presentation
Remedial objectives Ex situ remediation techniques In situ remediation techniques Monitored natural attenuation Some comments on NAPL remediation Some comments on MTBE Monitoring and verification Environmental Simulations International

Environmental Simulations International
Remedial objectives Risk management (derived from risk assessment) Remove the source Break the pathway Remove the receptor Not usually an option! Which contaminants? Appropriate cost-benefit performance Are there specific local requirements? But note re. receptor options for wellhead treatment; building ventilation Previous CIEH training on remediation technologies Environmental Simulations International

Remediation selection and licensing
Beyond the scope of this presentation! But feel free to cover in discussion Licensing might include Planning requirements Mobile plant licence Waste management licence IPPC Environmental Simulations International

Main remedial options for petroleum hydrocarbons
Approach Applied at Source Pathway Receptor Move receptor  Restrict access Excavate & treat Pump & treat Barriers/PRB’s SVE & related () In situ bioremediation Thermal techniques MNA Environmental Simulations International

Ex situ remediation Soil Groundwater Excavate and landfill
Excavate and biotreat Excavate and thermal treatment Excavate and soil wash Groundwater Pump & treat Adequate definition of area to be removed? Environmental Simulations International

Excavate & landfill “Dig and dump” Historically the “default option” for soils Future constraints Legislative Cost Total environmental impact emissions, truck movements, etc. Environmental Simulations International

Excavate & biotreat Hydrocarbon degradation in oxygenated treatment systems Windrows, biopiles, etc. Well-established Some common questions Contaminant availability/residuals Speed of treatment Volatilisation Leachate control Indigenous or added microorganisms? Environmental Simulations International

How biodegradable are petroleum hydrocarbons?
“Rapid” BTEX Naphthalenes n-alkanes <C20 “Moderate” Highly substituted monoaromatics n-alkanes C20 – C40 Branched alkanes 3-4 ring PAH’s “Slow” Asphaltenes alkanes >C40 cycloalkanes >4 ring PAH’s Weeks/months/years Environmental Simulations International

Ex situ biotreatment Environmental Simulations International

Excavate & thermal treatment
Hydrocarbons, etc. desorbed from soil at elevated temperatures e.g., rotary kiln Off-gas treatment e.g., catalytic or thermal oxidiser Straightforward technology but rarely used Some common questions Emissions control Fuel use Economics Properties of treated soil Environmental Simulations International

Excavate & soil wash Hydrocarbon removal from soil by water/agitation; treatment of process streams Often pushed as method for PAH remediation Some common questions Process engineering (blockage, attrition, etc.) Slurry handling Water treatment Economics Environmental Simulations International

Pump and treat Break pathway by abstraction of groundwater; treat groundwater Really a containment technology Some common questions How long to pump for? Pump water and/or NAPL? Water treatment technology Hydrocarbons and other components Treated water discharge Long-term costs Environmental Simulations International

In situ remediation Barrier and PRB technologies SVE and related technologies Bioremediation Environmental Simulations International

Barrier techniques Variants Capping Cut-off walls (barriers) Solidification Well-proven But solidification a questionable option for hydrocarbons Some common questions Long-term performance Ensuring integrity Environmental Simulations International

Permeable reactive barriers (PRB’s)
Reactive zones installed across the groundwater plume to enhance contaminant removal or degradation For hydrocarbons, this is mostly likely to involve enhancements of in situ bioremediation We will consider this in a few slides time Environmental Simulations International

SVE and variants Removal of volatile components by moving air through Soil (SVE; high vacuum extraction (HVE)) Groundwater (In situ air sparging (IAS)) Can be combined with removal of contaminated groundwater and/or NAPL Slurping (multiphase extraction) Can be combined with enhanced biodegradation Bioventing, bioslurping… Environmental Simulations International

SVE and variants Environmental Simulations International

SVE and variants Well-established Some common questions Subsurface permeability Subsurface heterogeneity Effectiveness for MTBE Emissions treatment Thermal oxidisers Activated carbon Biofilters Groundwater management Environmental Simulations International

In situ bioremediation
Contaminant degradation by stimulating biological activity in the subsurface Note: hydrocarbon degradation is most effective in the presence of oxygen Many variants on basic process configuration Some common questions Can you supply enough oxygen? Inhibitory effects? Distribution of additives Biofouling problems Speed Environmental Simulations International

“In situ bioreactor” Environmental Simulations International

Biological PRB using ORC
Environmental Simulations International

In situ flushing Addition of solvent or surfactant to subsurface to enhance solubility of NAPL for recovery by pumping Much talked about, little used for remediation Some common questions Getting the additives to the right place Getting the additives back Effects of additives on soil structure Economics Environmental Simulations International

Monitored natural attenuation (MNA)
The effect of combined naturally occurring physical, chemical and biological processes to reduce the risk posed by polluting substances in groundwater to the identified receptors. Monitored natural attenuation Monitoring of groundwater to confirm that NA processes are acting at a sufficient rate to protect receptors and that remedial objectives will be achieved within a reasonable timescale Environmental Simulations International

MNA Widely used in US and elsewhere UK guidance (R&D P95) Some common questions Duration appropriate? Long-term cost-benefit? Monitoring requirements Ensuring continuity Contingency requirements Environmental Simulations International

UK MNA case summary UK oil distribution terminal Gasoline additive release early-1970’s NA monitored since April 1994 Risk-based approach Sandy aquifer Potential minor aquifer Dissolved plume 9-14 m b.g.s. Velocity m/year Environmental Simulations International

Hydrocarbon MNA site Environmental Simulations International

UK MNA case summary Primary line of evidence: mass removal by biodegradation Plume: front stationary and area reducing Benzene concentrations decreasing Rates vary within plume Inversely proportional to concentration? Seasonal effects Rate at plume front = 0.2%/day Case histories are needed to expand knowledge-base and build confidence of all stakeholders. Need to work co-operatively with all parties. Environmental Simulations International

NA data for benzene Environmental Simulations International

UK MNA case summary Secondary evidence: geochemical O2, NO3- and SO42- depletion with increasing BTEX Stoichiometrically, available SO42- could account for 43 mg benzene/litre: sufficient Tertiary evidence: microbiological High microbial numbers, including large sulphate-reducing population Lines of evidence tell us: - Plume not expanding - Mass removal taking place by biodegradation - Rate/extent of biodegradation sustainable by electron acceptors available - Risk mitigated Environmental Simulations International

Technologies for NAPL remediation?
Limited “source” excavation Access permitting! NAPL pumping SVE/HVE/bioventing Sparging/biosparging/slurping Ex situ bioremediation …… or deal with the pathway(s) Pump & treat, trench, etc.  Depending  on  components Environmental Simulations International

Pumping NAPL Works best for light products/recent releases, significant thicknesses and coarse formations NAPL becomes trapped below the water table if pumping stops NAPL will not flow after it reaches residual saturation Many case studies have shown that most of the NAPL remains in place due to trapping Oil/water separation is difficult if product becomes emulsified during pumping Environmental Simulations International

Technologies for MTBE remediation
Unsaturated soil Excavation and disposal SVE and variants Limited efficiency due to partitioning behaviour Bioremediation Not straightforward Groundwater Pump & treat Difficult to treat water Sparging & variants Limited efficiency due to partitioning behaviour Bioremediation Not straightforward Environmental Simulations International

Monitoring & verification
Objectives may include: Confirmation of risk assessment findings Confirmation of remediation performance Determination of when remediation can cease Indication of the need for corrective action Environmental Simulations International

Soil sampling Basic guidance in CLR7 Mean and maximum value tests to determine compliance with target concentrations Useful for relatively straightforward sites but does not consider spatial distribution of contamination Geostatistics Specialist advice… Environmental Simulations International

Groundwater monitoring
Where? Appropriate to site layout and remediation process Upgradient/downgradient Compliance points/sentinel wells What? Contaminants posing significant risk Process indicators/geochemical parameters? When? Depends on the site and the process Establish performance baseline Establish seasonality Can always reduce frequency once the situation is understood Environmental Simulations International

Monitoring NAPL thickness
Why is the thickness changing? Groundwater fluctuations (smearing)? Product trapping? Weathering? Remediation? A combination of the above? Environmental Simulations International

Conclusions There are diverse remediation options for petroleum hydrocarbons Important drivers Risk management Fitness-for-purpose Cost-benefit Duration Ask the right questions! (And beware the sales pitch). Appropriate verification/monitoring Duration? Environmental Simulations International

Conclusions A combination of techniques is often the appropriate option Environmental Simulations International

Contaminated land: dealing with hydrocarbon contamination

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