Groundwater Remediation Frequently Asked Questions

Technology selection should begin with the contaminant distribution, site geology and hydrogeology, groundwater geochemistry, remedial objectives, and anticipated contaminant transport pathways. The same contaminant can require very different approaches depending on whether it occurs as NAPL, a high-concentration source, a dissolved plume, or low-level residual contamination.

Tersus evaluates these factors together rather than selecting a technology based solely on the contaminant. Potential approaches may include enhanced bioremediation, in situ chemical reduction (ISCR), in situ chemical oxidation (ISCO), sorption and biodegradation, surfactant-enhanced aquifer remediation (SEAR), or combinations of technologies.

A well-developed Conceptual Site Model (CSM) is an important starting point because it identifies where contaminant mass resides, how it is moving, and what physical, chemical, or biological processes are likely to control treatment.

Useful design information typically includes contaminant concentrations and distribution, treatment-zone dimensions, lithology, hydraulic conductivity, groundwater velocity and direction, effective porosity, groundwater geochemistry, and the presence of NAPL or strongly sorbed contaminant mass.

For biological remedies, parameters such as dissolved oxygen, oxidation-reduction potential (ORP), pH, sulfate, nitrate, ferrous iron, methane, alkalinity, and dissolved organic carbon can help identify the dominant microbial and geochemical processes.

Molecular Biological Tools (MBTs), Compound-Specific Isotope Analysis (CSIA), mass-flux measurements, and treatability studies can provide additional information when conventional groundwater data do not adequately define treatment potential.

Not every site requires every parameter. Tersus can review available site information and help identify the additional data most useful for technology selection and preliminary design.

Many contaminated sites contain different contaminant phases, concentrations, and geochemical conditions within the same treatment area. As a result, the most effective remedy may use different technologies for different portions of the site.

For example, a concentrated NAPL source may benefit from mass removal using SEAR before treating residual dissolved contamination biologically. At a chlorinated-solvent site, zero-valent iron (ZVI) can provide rapid abiotic reduction while an electron donor supports longer-term biological reductive dechlorination.

The objective is not to apply more technologies, but to match each technology to the conditions where it provides the greatest benefit.

Yes. Tersus routinely works with consultants and project teams during the feasibility and preliminary-design stages.

Available site information can be used to evaluate potentially applicable technologies, identify data gaps, develop preliminary amendment quantities and injection concepts, and determine whether treatability or pilot testing would be beneficial.

The objective is to help the project team develop a technically defensible and cost-effective approach while the consultant retains responsibility for the overall remedial design.

Enhanced reductive dechlorination (ERD) stimulates anaerobic microorganisms capable of transforming chlorinated solvents into progressively less-chlorinated compounds.

Organic electron donors ferment in groundwater to produce hydrogen and other fermentation products. The resulting reducing conditions and available hydrogen support organohalide-respiring microorganisms that can degrade compounds such as PCE and TCE through daughter products including cis-1,2-DCE and vinyl chloride.

Tersus offers both soluble and extended-release electron donors. EDS-ER™ is a water-mixable vegetable-oil-based substrate designed to provide sustained carbon and hydrogen availability for long-term anaerobic treatment.

Electron-donor selection depends on the treatment objective, contaminant mass, groundwater velocity, injection spacing, aquifer characteristics, required treatment longevity, and the ability to distribute amendment through the target interval.

Soluble substrates can provide rapidly available carbon but may migrate or be consumed relatively quickly. Extended-release substrates such as EDS-ER™ are intended to remain available for longer periods and support sustained reducing conditions.

In many applications, the question is not simply which donor provides the most carbon, but which donor can be distributed effectively and deliver usable electron donor over the required treatment period.

Electron-donor demand should consider more than contaminant mass alone. Native electron acceptors—including dissolved oxygen, nitrate, sulfate, and reducible iron and manganese—can consume substantial electron-donor capacity before strongly reducing conditions are established.

Treatment volume, contaminant mass, groundwater flux, competing electron acceptors, desired treatment longevity, and substrate characteristics should therefore be considered together.

Tersus can assist project teams with preliminary amendment calculations using site-specific analytical data and treatment-zone dimensions.

Incomplete dechlorination can result from several factors, including insufficient electron donor, unfavorable pH or geochemistry, inadequate distribution of amendment, or insufficient populations of microorganisms capable of completing the dechlorination sequence.

Monitoring only VOC concentrations may not identify which factor is limiting performance.

Combining groundwater geochemistry with Molecular Biological Tools can help determine whether appropriate dechlorinating microorganisms and functional genes are present. This information can help distinguish between a donor limitation, microbial limitation, or amendment-distribution problem.

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Yes. Combining an organic electron donor with zero-valent iron can create complementary biological and abiotic treatment pathways.

ZVI promotes direct chemical reduction of chlorinated compounds while the organic substrate establishes reducing conditions and supplies hydrogen to support biological reductive dechlorination.

This combined approach can be particularly useful where rapid initial treatment and sustained longer-term biological activity are both desirable.

Under anaerobic conditions, certain microorganisms can use petroleum hydrocarbons as electron donors while using sulfate as a terminal electron acceptor.

Adding soluble sulfate can therefore stimulate naturally occurring sulfate-reducing microbial communities and increase the rate of anaerobic hydrocarbon biodegradation.

Tersus Nutrisulfate® products provide bioavailable sulfate for treatment of petroleum hydrocarbons and fuel-related compounds such as BTEX, MTBE, and TBA. Nutrisulfate® BioBoost™ also supplies nitrogen and phosphorus to support microbial growth where nutrient limitations may be present.

Many petroleum-impacted aquifers are already strongly anaerobic, particularly within source areas and plume cores. Introducing sufficient oxygen into these zones can require substantial amendment demand because oxygen is rapidly consumed by reduced minerals, dissolved iron, and organic matter.

At sites where sulfate reduction is already an important natural attenuation pathway, supplying additional sulfate can enhance the existing anaerobic biodegradation process rather than attempting to convert the aquifer to aerobic conditions.

The appropriate approach depends on site geochemistry, contaminant distribution, treatment objectives, and amendment-delivery considerations.

Sulfate dosing should be based on the amount of contaminant to be treated, background sulfate concentrations, treatment volume, competing geochemical reactions, groundwater flow, and the desired treatment duration.

Adding more sulfate is not automatically better. The objective is to provide sufficient electron-acceptor capacity throughout the treatment zone while maintaining appropriate groundwater chemistry and efficient amendment utilization.

Site-specific calculations and, where appropriate, pilot testing can help establish the appropriate application concentration and volume.

Performance monitoring can include sulfate consumption together with changes in contaminant concentrations and relevant geochemical indicators.

A decrease in sulfate accompanied by contaminant degradation and other evidence of anaerobic microbial activity can provide an important line of evidence. Additional tools such as MBTs and CSIA may be used when greater certainty regarding biodegradation mechanisms is required.

Using multiple lines of evidence is generally more informative than relying on contaminant concentration trends alone.

Yes. Sulfate-enhanced treatment can be incorporated into broader remediation strategies involving source removal, sorption, natural attenuation, or other biological treatment approaches.

For example, NutriBind® can combine powdered activated carbon with sulfate-based amendments to rapidly reduce dissolved contaminant mobility while simultaneously creating conditions that support anaerobic biodegradation.

In Situ Chemical Reduction (ISCR) treats contaminants by introducing reducing agents into the subsurface to promote chemical transformation.

Zero-valent iron (ZVI) is one of the most widely used ISCR reagents. Iron corrosion provides electrons that can chemically reduce chlorinated solvents and other reducible contaminants.

Unlike enhanced bioremediation, which relies primarily on microbial metabolism, ZVI can initiate contaminant destruction through abiotic reactions. The reducing environment generated by ZVI can also complement biological degradation processes.

ZVI can be considered when rapid abiotic destruction is desirable, contaminant concentrations are relatively high, biological treatment alone may be slow or incomplete, or complementary degradation pathways would improve treatment reliability.

ZVI may be applied alone or with an organic electron donor. The appropriate formulation and dose depend on contaminant mass, aquifer geochemistry, treatment-zone dimensions, injection requirements, and the desired longevity of treatment.

Yes. Particle size influences reactivity, surface area, transport, settling behavior, and injectability.

Very reactive particles may provide rapid treatment but can be difficult to distribute effectively. Larger particles may be easier to manage in some applications but have different transport and reaction characteristics.

Suspension chemistry is also important. Tersus offers ZVI formulations and delivery approaches designed to improve stability and subsurface distribution, including ZVI-ironGEL™ and systems using TASK™ sweep-efficiency chemistry.

Concentration reduction alone cannot always distinguish destruction from dilution, displacement, sorption, or groundwater variability.

Performance monitoring may therefore combine contaminant concentrations with geochemical indicators and other lines of evidence. CSIA can be particularly valuable because changes in isotopic composition can provide evidence of contaminant transformation.

Where contaminant transport is also important, mass-flux measurements can quantify changes in the amount of contaminant moving through the aquifer.

Amendment calculations generally begin with the dimensions and effective porosity of the treatment zone to estimate the volume of groundwater being treated.

The calculation is then refined based on contaminant mass, groundwater chemistry, amendment demand, groundwater flux, target concentration, expected amendment longevity, and the treatment mechanism.

For electron donors, competing electron acceptors should be considered. For chemical reductants, natural oxidant demand and contaminant mass are important. For sulfate-enhanced bioremediation, electron-acceptor demand and background sulfate conditions should be evaluated.

Tersus can assist project teams with site-specific amendment calculations during preliminary and final design.

Dilution should be based on the amendment properties, aquifer characteristics, injection method, desired radius of influence, and total volume that can practically be injected.

Increasing the water volume can improve amendment contact and distribution in some formations, but simply adding more water does not guarantee better treatment. Excessive injection volumes can increase field time and cost and may alter groundwater gradients.

The objective is to select a concentration and injection volume that provide adequate amendment mass while achieving effective distribution through the targeted pore volume.

Neither approach is universally better.

A concentrated amendment reduces the volume that must be handled but may provide limited distribution around the injection point. Greater dilution can increase the volume of aquifer contacted but requires additional injection time and water handling.

The optimum approach depends on hydraulic conductivity, heterogeneity, injection pressure, radius of influence, groundwater velocity, amendment properties, and treatment objectives.

There is no universal percentage that applies to every site.

The appropriate injection volume depends on aquifer permeability, effective porosity, treatment-zone geometry, amendment type, injection spacing, groundwater flow, and the degree of amendment distribution required.

Pore-volume calculations are useful for developing an initial design, but field observations during pilot or full-scale injection should be used to confirm whether the assumed distribution is being achieved.

Yes. Tersus can work with project teams to develop preliminary amendment quantities, dilution ratios, treatment volumes, and injection concepts using available site information.

These calculations can also be used to compare alternative amendment strategies and develop budgetary estimates before the final field design is completed.

Injection-point spacing should reflect the expected radius of influence (ROI) under actual site conditions.

ROI is controlled by formation permeability and heterogeneity, injection pressure and flow rate, amendment viscosity, injected volume, groundwater conditions, and injection method. It should not be assumed solely from values achieved at other sites.

Pilot testing can be particularly useful for confirming achievable injection rates, pressures, amendment distribution, and ROI before finalizing a full-scale injection grid.

Both methods can be effective.

Permanent wells provide repeatable access and are useful when multiple injection events or recirculation may be required. Direct-push injection can provide greater flexibility in vertical placement and may reduce installation costs where permanent wells are unnecessary.

The preferred approach depends on geology, treatment depth, access, injection frequency, amendment properties, and project objectives.

Heterogeneous aquifers can cause injected fluids to preferentially follow higher-permeability pathways while bypassing lower-permeability zones.

Strategies can include closer injection spacing, depth-discrete injection, adjusting injection rates and volumes, using multiple injection intervals, recirculation, or selecting amendment formulations with improved transport characteristics.

Understanding the site geology and groundwater flow before injection is essential. Field observations during injection can then be used to adapt the design as necessary.

Excessive pressure can result from low formation permeability, excessive injection rates, biofouling, solids accumulation, amendment viscosity, or insufficient injection interval.

Daylighting occurs when injected fluid follows a preferential pathway to the ground surface rather than remaining within the intended treatment zone.

Injection pressure and flow should therefore be monitored throughout implementation. Reducing flow, changing injection depth, modifying amendment concentration, or moving to another injection location may be appropriate when pressure begins to increase unexpectedly.

Useful field information can include injection flow rate, pressure, total injected volume, amendment concentration, injection depth, groundwater levels, and observations at nearby wells.

Depending on the amendment, parameters such as pH, conductivity, ORP, dissolved oxygen, or amendment-specific tracers may also help evaluate distribution.

Recording these data provides valuable information for evaluating ROI, troubleshooting injection problems, and optimizing subsequent injection events.

Bioaugmentation is most appropriate when the microorganisms required to complete the desired biodegradation pathway are absent or present at insufficient abundance.

At chlorinated-solvent sites, Molecular Biological Tools can be used to evaluate the presence and abundance of organisms and functional genes associated with reductive dechlorination.

If appropriate organisms are already present at sufficient levels, stimulating the indigenous microbial community may be adequate. If key organisms are absent or limited, adding a specialized microbial culture can accelerate or complete treatment.

The microbial populations capable of transforming PCE and TCE are not necessarily capable of completing dechlorination through cis-DCE and vinyl chloride to ethene.

Stalling can therefore occur even when strongly reducing conditions have been established.

Other causes include inadequate electron donor, unfavorable pH, poor amendment distribution, competing electron acceptors, or other geochemical limitations.

MBTs combined with groundwater chemistry can help determine whether the primary limitation is microbial, chemical, or related to amendment delivery.

Bioaugmentation is generally most effective when suitable anaerobic and reducing conditions have been established or are being created within the treatment zone.

Electron donor is commonly injected before or in conjunction with bioaugmentation so that the introduced microorganisms enter an environment capable of supporting their growth and activity.

The sequence and timing should be tailored to site geochemistry, amendment type, groundwater conditions, and the selected culture.

Culture dosage depends on treatment volume, contaminant distribution, injection layout, groundwater conditions, and the characteristics of the culture being used.

More culture is not necessarily better. Successful bioaugmentation depends on both introducing an appropriate microbial population and creating subsurface conditions that allow those organisms to survive, grow, and move through the treatment zone.

Site-specific design should therefore consider culture dosage together with electron donor, groundwater chemistry, and amendment distribution.

Post-injection MBT monitoring can quantify target microorganisms and functional genes and determine whether populations have increased or spread within the treatment area.

These results should be interpreted alongside contaminant concentrations, daughter-product trends, groundwater geochemistry, and, where appropriate, CSIA.

Together, these lines of evidence can demonstrate whether the microbial community has become established and whether the desired degradation pathway is occurring.

SEAR should be considered when significant contaminant mass remains as NAPL or is strongly retained within the formation and conventional groundwater extraction has reached diminishing returns.

The technology is particularly applicable to LNAPL and DNAPL source zones containing petroleum hydrocarbons, chlorinated solvents, coal tar, creosote, and other hydrophobic organic contaminants.

Removing source mass can substantially reduce long-term contaminant loading and improve the effectiveness of subsequent biological or chemical treatment.

NAPL can remain trapped within aquifer pores because of capillary forces at the NAPL-water interface.

Surfactants reduce interfacial tension, allowing trapped NAPL to become mobile or increasing its apparent solubility so it can be recovered through extraction wells.

Tersus TASK™ formulations are designed to achieve very low interfacial tension while producing favorable phase behavior for efficient NAPL recovery.

Surfactant performance depends on the composition of the NAPL, groundwater chemistry, and formation materials.

For this reason, Tersus develops TASK™ formulations using site-specific NAPL, groundwater, and soil samples. Laboratory testing is used to optimize interfacial tension, microemulsion behavior, surfactant concentration, and phase separation.

This allows the field formulation to be designed around the actual contaminant and geochemical conditions rather than relying on an off-the-shelf surfactant.

Hydraulic control is a fundamental component of SEAR design.

Injection and extraction systems are designed so that mobilized NAPL and surfactant move toward controlled recovery points rather than away from the treatment area.

Injection rates, extraction rates, hydraulic gradients, well configuration, and treatment-zone geometry must therefore be evaluated together.

SEAR should be viewed as a controlled injection-and-recovery process rather than simply an amendment injection.

Yes. One of the advantages of source-zone mass removal is that it can create more favorable conditions for subsequent remediation.

After recoverable NAPL mass has been removed, residual dissolved and sorbed contamination may be addressed using enhanced aerobic or anaerobic bioremediation, ISCR, ISCO, or other appropriate technologies.

This treatment-train approach can be more effective than attempting to address a high-mass NAPL source using biological treatment alone.