🌍 VES · MODFLOW · RT3D · RBCA · Phreatimeters · Plume Mapping · ASTM E1739 · E2081

Geology & Hydrogeology

Hydrogeological investigations, numerical modelling and risk-based corrective action for contaminated soil and groundwater.

Biogroup has a multidisciplinary team of geologists and hydrogeologists who carry out hydrogeological and geophysical studies to assess the extent of soil and groundwater contamination — integrating field surveys, vertical electrical soundings (VES), phreatimeter networks, MODFLOW groundwater flow modelling, RT3D three-dimensional contaminant transport and risk assessment under the RBCA framework (ASTM E1739 / E2081).

From the initial geological survey through to the numerical model and the risk assessment report — Biogroup provides the complete technical basis for contaminated site characterisation, remediation design and regulatory approval of site closure.

MODFLOW + RT3D
Numerical modelling
VES geophysics
Vertical electrical sounding
RBCA · E1739
Risk-based corrective action
+35 years
Contaminated site expertise
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Field investigation to numerical model
Integrated service from geological survey and phreatimeter installation to MODFLOW groundwater flow modelling and RT3D contaminant transport simulation — the complete technical basis for remediation design and regulatory site closure.
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RBCA risk assessment
Risk-Based Corrective Action (RBCA) under ASTM E1739 and E2081 — the internationally recognised framework for establishing site-specific cleanup targets. Generates defensible risk-based goals that avoid over-remediation.
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Regulatory acceptance
Reports accepted by Argentine environmental authorities — SAyDS, OPDS, provincial agencies — for site characterisation, Phase II ESA, remediation action plans and formal site closure certification.
Field investigation services — subsurface characterisation
From the soil surface to the aquifer — systematic subsurface investigation
Reliable hydrogeological modelling starts with reliable field data. Biogroup's field team combines geological borings, geophysical surveys and phreatimeter installation with soil and water sampling — providing the dataset that drives both the conceptual site model and the numerical simulation.
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Soil Borings & Well Logging
Rotary · hollow-stem auger · direct push
Drilling of exploratory boreholes and monitoring wells using rotary, hollow-stem auger or direct push methods depending on lithology and depth. Continuous soil logging with description of stratigraphy, lithology, grain size, colour and odour. Collection of split-spoon samples at defined intervals for laboratory analysis. Borehole completion with PVC screen and casing for long-term monitoring installation.
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Phreatimeter Construction
Groundwater monitoring wells · HDPE/PVC casing · well development
Design and construction of groundwater monitoring wells (phreatimeters) for long-term aquifer monitoring. Well design parameters — screen interval, slot size, casing diameter and gravel pack specification — adapted to local hydrogeological conditions. Development and purging protocols to ensure representative samples. Installation of dedicated pumping equipment or passive sampling devices where appropriate.
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Geoelectrical Studies — VES
Schlumberger array · resistivity · stratigraphic interpretation
Vertical Electrical Soundings (VES) using Schlumberger electrode array to determine subsurface electrical resistivity profiles. Interpreted to delineate aquifer depth, thickness and lateral extent, identify confining layers and locate the phreatic surface without drilling. Particularly valuable as a low-cost screening tool before committing to a drilling programme.
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Groundwater Sampling
Low-flow sampling · HDPE bailers · field parameters · purge records
Representative groundwater sampling from monitoring wells following low-flow purging protocols. Measurement of field parameters (pH, conductivity, dissolved oxygen, redox potential, turbidity, temperature) during purging to verify sample representativeness. Samples preserved and transported to Biogroup's laboratory under documented chain of custody.
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Hydraulic Testing
Slug tests · bail tests · pumping tests · transmissivity · hydraulic conductivity
Hydraulic testing to determine aquifer hydraulic properties — hydraulic conductivity (K), transmissivity (T) and storativity (S). Slug tests and bail tests for rapid K estimation in monitoring wells. Pumping tests with observation wells for spatial characterisation of aquifer properties needed for MODFLOW parameterisation.
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Soil Sampling for Analysis
Systematic sampling grid · USEPA sampling protocols
Systematic soil sampling for chemical analysis following EPA sampling protocols — grid-based or transect designs for site characterisation, targeted sampling along suspected migration pathways and confirmation sampling at the perimeter of the contaminated zone. Samples submitted to Biogroup's laboratory for full contaminant panel per Table 9 Ley 24.051.
Numerical modelling — MODFLOW and RT3D
The global standard software for groundwater flow and contaminant transport modelling
Numerical groundwater models translate field measurements into predictive tools — enabling simulation of aquifer behaviour, contaminant plume evolution and remediation system performance before any physical intervention. Both models are calibrated against measured field data and validated before use in decision-making.
💧 VISUAL MODFLOW
3D finite-difference groundwater flow modelling · US Geological Survey · industry standard

VISUAL MODFLOW is the industry-standard software for three-dimensional, finite-difference groundwater flow modelling — the graphical interface to the USGS MODFLOW engine. Used to simulate aquifer hydraulics, determine groundwater flow directions and velocities, assess well capture zones and predict the hydrological response to pumping or recharge scenarios.

✓ Steady-state and transient flow simulation
✓ Multi-layer aquifer systems
✓ Calibration against measured water table levels
✓ Groundwater flow direction and velocity maps
✓ Well capture zone delineation
✓ Pumping test interpretation and aquifer parameterisation
✓ Sensitivity analysis and uncertainty quantification
☣️ RT3D — Contaminant Transport Modelling
3D reactive transport · dissolved contaminants · chemical reactions · plume evolution

RT3D (Reactive Transport in 3D) simulates the three-dimensional movement and transformation of dissolved contaminants in groundwater — including advection, dispersion, sorption, decay and chemical reactions. Coupled to MODFLOW flow fields, it predicts plume evolution, receptor exposure concentrations and the effectiveness of remediation interventions over time.

✓ Contaminant plume extent and trajectory prediction
✓ Time-of-travel calculations to receptors
✓ Sorption (Kd, Koc, retardation factor)
✓ Biodegradation rate modelling (first-order)
✓ NAPL dissolution source term
✓ Remediation system performance prediction
✓ Plume stabilisation and natural attenuation assessment
Contour maps and contaminant plume mapping
From sampling data to spatial understanding of contamination

Spatial analysis of sampling data to generate maps that communicate the distribution and extent of contamination clearly and unambiguously — the key communication tool for regulators, site owners and remediation engineers.

Water table contour maps
Equipotential lines and groundwater flow direction arrows from synchronous piezometric level measurements
Contaminant concentration maps
Isopleth maps of chemical concentrations in groundwater and soil — identifying maximum concentration zones and plume boundaries
Exceedance maps
Areas where concentrations exceed regulatory guidelines (Table 9 Ley 24.051, ASTM RBCA tier thresholds) — the basis for delineating the remediation zone
Plume evolution maps
Time-series maps showing historical plume expansion or contraction — critical for MNA (Monitored Natural Attenuation) documentation
Dispersion modelling in surface water
🌊 Contaminant dispersion in rivers and surface water bodies
Advection-diffusion models · mixing zones · downstream concentration profiles
Application of mathematical dispersion models to predict the downstream fate and transport of contaminants discharged to rivers, streams and surface water bodies. Determines mixing zones, time-of-travel, dilution factors and downstream concentration profiles at sensitive receptors (water intakes, bathing areas, fisheries).
✓ Conservative tracer dispersion (advection-diffusion)
✓ Reactive contaminant transport (with decay)
✓ Mixing zone delineation for discharge permits
✓ Downstream receptor concentration prediction
✓ Environmental impact assessment support
✓ Spill response modelling (emergency scenarios)
RBCA — Risk-Based Corrective Action (ASTM E1739 / E2081)
Risk-Based Corrective Action — the internationally recognised framework for contaminated site decisions
ASTM E1739 (petroleum-contaminated sites) · ASTM E2081 (generic RBCA) · human health and ecological risk

RBCA provides a systematic, tiered framework for evaluating risk at contaminated sites and establishing site-specific cleanup goals — moving beyond generic table-based standards to risk-based targets that reflect actual site conditions, exposure scenarios and land use. This prevents over-remediation while ensuring genuine risk reduction.

Tier 1 — Screening
Comparison of site data against published look-up table values (generic risk-based screening levels). Rapid, conservative assessment — requires no site-specific calculations.
Tier 2 — Site-specific
Calculation of site-specific risk-based concentrations using actual site soil properties (porosity, organic carbon, bulk density) and measured hydraulic parameters.
Tier 3 — Full risk assessment
Comprehensive probabilistic or deterministic risk assessment incorporating fate and transport modelling (RT3D), exposure pathway analysis and receptor characterisation.
Human health risk assessment
Exposure pathway analysis (ingestion, dermal contact, inhalation of vapours from soil/groundwater), receptor characterisation (residential, industrial, recreational), cancer risk and hazard quotient calculation. Incremental lifetime cancer risk (ILCR) and hazard index (HI) per EPA risk assessment guidelines.
Ecological risk assessment
Assessment of risks to ecological receptors — soil invertebrates, plants, birds and small mammals — from contaminated soil and groundwater. Ecotoxicological benchmarks (NOEC, LOEC, chronic criteria) compared against measured concentrations per EPA ecological risk assessment framework.
Typical investigation workflow

Biogroup provides all phases of the contaminated site investigation cycle — from desktop review and conceptual site model development through field characterisation, numerical modelling and final risk assessment.

1
Desktop review & conceptual site model
Review of available geological maps, borehole logs, historical site use, previous investigations and aerial imagery. Development of the initial conceptual site model (CSM) defining likely contaminant sources, pathways and receptors.
2
Geophysical survey (VES)
Vertical Electrical Sounding profiles to delineate subsurface stratigraphy, aquifer geometry and depth to water table — before committing to a drilling programme. Identifies optimal borehole locations.
3
Field investigation — borings & phreatimeter installation
Drilling programme, continuous soil logging, split-spoon sampling, phreatimeter installation, hydraulic testing and representative groundwater sampling.
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Laboratory analysis
Soil and groundwater samples submitted to Biogroup's laboratory for the full contaminant panel — TPH, BTEX, PAHs, VOCs, metals, pesticides, per Table 9 Ley 24.051 and site-specific requirements.
5
Data analysis & contaminant mapping
Statistical analysis, water table contouring, contaminant concentration mapping, plume delineation and exceedance mapping against regulatory screening levels.
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Numerical modelling & RBCA risk assessment
MODFLOW groundwater flow model calibration, RT3D contaminant transport simulation, exposure pathway analysis, RBCA tiered risk assessment and site-specific cleanup goal derivation — the final deliverable for regulatory approval.
Applications — when hydrogeological investigation is required
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Petrol stations & fuel spills
Full Phase I/II/III investigation and RBCA risk assessment for UST sites — the most frequent application in Argentina.
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Industrial site transactions
Phase II environmental site assessments for property transactions, plant closures and industrial M&A due diligence.
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Landfill & waste sites
Groundwater impact assessment, leachate plume characterisation and monitoring network design for landfill facilities.
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Remediation design support
Site characterisation data and MODFLOW/RT3D models provide the input for remediation system design (pump-and-treat, PRB, ISCO, MNA).
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Regulatory submissions
Contaminated site investigation reports, risk assessment dossiers and remediation action plans for submission to SAyDS, OPDS and provincial environmental authorities.
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Legal proceedings
Expert witness hydrogeological investigations for environmental litigation — groundwater contamination responsibility, damage extent quantification and plume attribution.
Official registrations
Provincial registry
Official Registry of Environmental Consultants, Experts and Expert Witnesses
Province of Santa Fe, Argentina
Ministerial registry
Registry of Environmental Impact Assessment Consultants
Ministry of Environment, Argentina
Related services
VES · Phreatimeters · MODFLOW · RT3D · RBCA · ASTM E1739 · E2081
Need a hydrogeological investigation or risk assessment?
From a vertical electrical survey and phreatimeter installation to a full MODFLOW/RT3D model and RBCA risk assessment report — Biogroup provides the complete technical basis for contaminated site characterisation and regulatory approval of remediation and site closure.
Request a hydrogeological study →
📞 +54 341 425-6431 📞 +54 341 447-4486 ✉ biogroup@biogroup.com.ar 📍 3 de febrero 920 · Rosario, Argentina Mon–Fri 08:00–17:00