Soil pollution assessment is a systematic technical process used to identify, quantify, and evaluate contaminants in soil through standardized sampling, laboratory analysis, and risk-based evaluation against regulatory benchmarks such as GB 36600-2018, ISO, and ASTM standards. This guide explains the complete assessment workflow, including sample types, target analytes, analytical methods, and practical applications for agricultural land, industrial sites, and land redevelopment projects.
Technical Overview
Soil pollution assessment (also referred to as soil contamination evaluation) is a science-based procedure designed to determine whether soil at a given site contains pollutants at concentrations that may pose risks to human health, ecosystems, groundwater resources, or land-use functions. The assessment integrates field investigation, representative sampling, accredited laboratory analysis, and comparison of analytical results against soil environmental quality standards and site-specific risk screening values.
A complete assessment typically follows a phased approach consistent with recognized technical frameworks, including the HJ 25 series of technical guidelines for site environmental monitoring and risk assessment, ASTM E1527 and ASTM E1903 practices for Phase I and Phase II environmental site assessments, and ISO 10381 standards for soil sampling design. The typical workflow includes a preliminary desk study and site reconnaissance, development of a conceptual site model, sampling plan design, field sampling, chemical and physical testing, data validation, and risk characterization.
Key regulatory benchmarks applied during evaluation include GB 36600-2018 (risk control standard for soil contamination of development land), GB 15618-2018 (risk control standard for agricultural land), and related international references such as ISO 18504 guidance on sustainable remediation. Results are compared with risk screening values and risk intervention values to determine whether the land is suitable for its intended use, whether further detailed risk assessment is required, or whether remediation must be implemented.
Testing Samples
Sample type selection depends on the suspected contamination source, site history, geology, and the exposure pathways identified in the conceptual site model. The main sample categories collected during a soil pollution assessment are described below.
Surface Soil Samples
Surface samples, generally collected from the 0–20 cm layer for agricultural assessments or 0–50 cm for development land investigations, capture contaminants from atmospheric deposition, spill residues, historical surface discharges, and pesticide or fertilizer application. Surface sampling is typically performed on a systematic grid, with grid density adjusted according to site size, heterogeneity, and the requirements of the sampling plan.
Subsurface and Deep Soil Samples
Subsurface samples are collected at depth intervals such as 0.5–1.5 m, 1.5–3 m, 3–6 m, and deeper, using soil drilling rigs, direct-push technology, or hand augers. Deep profiling is essential for detecting vertical migration of dense non-aqueous phase liquids, leachable metals, and petroleum products, and for characterizing contamination that may affect groundwater. Depth-discrete sampling avoids averaging effects and supports accurate delineation of contaminant plumes.
Soil Gas and Vapor Samples
Soil gas samples are collected from temporary or permanent vapor probes to measure volatile organic compounds (VOCs) migrating through the vadose zone. This sampling mode is critical for evaluating vapor intrusion pathways into buildings and is typically performed in accordance with active soil gas survey procedures referenced in ISO 22155 and related technical guidelines.
Soil Leachate and Eluate Samples
Leachate testing evaluates the mobility of contaminants under simulated rainfall or groundwater contact conditions. Eluates are prepared from soil samples and analyzed for metals, anions, and organic parameters to assess the risk of contaminant transport to groundwater, using leaching procedures aligned with ISO standards and hazardous waste extraction methods.
Quality Control Samples
Field duplicates, trip blanks, equipment rinsate blanks, and background reference samples are collected alongside primary samples to verify sampling precision, detect cross-contamination, and distinguish site contamination from natural geochemical background levels.
Testing Items
Testing items are selected based on site history, current and future land use, and regulatory requirements. The core parameter groups are summarized below.
Heavy Metals and Metalloids
- The eight basic regulated metals: arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn)
- Extended metals frequently required for industrial sites: antimony (Sb), beryllium (Be), cobalt (Co), selenium (Se), thallium (Tl), vanadium (V), manganese (Mn), and hexavalent chromium (Cr(VI))
- Speciation analysis, such as Cr(VI) determination and sequential extraction of metal fractions to evaluate bioavailability and mobility
Volatile and Semi-Volatile Organic Compounds
- Common VOCs including chlorinated solvents (trichloroethylene, tetrachloroethylene), benzene, toluene, ethylbenzene, xylenes (BTEX), and chloromethanes
- Semi-volatile organic compounds (SVOCs) such as phenols, anilines, nitroaromatics, and chlorinated aromatics
- Sixteen priority polycyclic aromatic hydrocarbons (PAHs), including benzo[a]pyrene and naphthalene
- Polychlorinated biphenyls (PCBs) from electrical equipment and legacy industrial uses
Petroleum and Pesticide Parameters
- Total petroleum hydrocarbons (TPH) fractionated into aliphatic and aromatic ranges (C6–C10, C10–C40)
- Organochlorine pesticides (OCPs) such as DDT, HCH, and endosulfan
- Organophosphorus pesticides (OPPs) and pyrethroid residues
Inorganic and Physicochemical Parameters
- pH, electrical conductivity, and oxidation-reduction potential
- Organic matter content, cation exchange capacity (CEC), and moisture content
- Total nitrogen, total phosphorus, and available nutrients for agricultural assessments
- Total cyanide, fluoride, and soluble salts
Emerging Contaminants
- Per- and polyfluoroalkyl substances (PFAS) associated with firefighting foams and industrial coatings
- Phthalate esters, brominated flame retardants, and pharmaceutical residues
Testing Methods
Analytical methods follow validated national and international standards to ensure data defensibility, comparability, and acceptance by regulatory authorities. All analyses described here can be performed by accredited third-party laboratories holding ISO/IEC 17025 accreditation for the corresponding test methods.
Sampling and Sample Preparation
Field sampling is conducted in accordance with HJ/T 166 and GB/T 36197 for soil environmental monitoring, ISO 10381 series for sampling design and procedures, and ASTM D6418 for baseline site characterization. Soil samples for VOC analysis are collected with minimal disturbance using syringe or EnCore-type coring devices and preserved at 4 °C; samples for metals are air-dried or freeze-dried, sieved, and homogenized, while samples for mercury and organics are stored cold and protected from light.
Heavy Metal Analysis
- Acid digestion using HF-HNO3-HClO4 mixtures per GB/T 17141 or aqua regia extraction per ISO 11466, followed by graphite furnace atomic absorption spectrometry (GFAAS) for trace Cd and Pb
- Inductively coupled plasma mass spectrometry (ICP-MS) per HJ 803 and ISO 17294-2 for multi-element determination at low detection limits
- Inductively coupled plasma optical emission spectrometry (ICP-OES) and flame AAS per ISO 11047 for higher-concentration elements such as Cu, Zn, and Cr
- Atomic fluorescence spectrometry (AFS) per GB/T 22105 for mercury and arsenic, with cold vapor techniques for Hg confirmation
- Hexavalent chromium determined by alkaline digestion followed by colorimetric or IC-ICP-MS analysis
Organic Contaminant Analysis
- VOCs by purge-and-trap or headspace GC-MS per HJ 605, HJ 642, and ISO 22155
- SVOCs and PAHs by accelerated solvent extraction followed by GC-MS per HJ 834 and ISO 18287
- PCBs and OCPs by gas chromatography with electron capture detection (GC-ECD) or GC-MS per GB 5085.3 methods
- TPH fractions by GC-FID covering C6–C40 carbon ranges
- PFAS by liquid chromatography tandem mass spectrometry (LC-MS/MS) with isotope dilution quantification
Field Screening Techniques
- Portable X-ray fluorescence (XRF) spectrometry for rapid in-situ metal screening and delineation support
- Photoionization detectors (PID) for real-time vapor and VOC screening during drilling
- Membrane interface probe (MIP) surveys for continuous subsurface VOC profiling
Data Quality Assurance
Each analytical batch incorporates method blanks, laboratory control samples, matrix spikes, and certified reference materials to verify accuracy, precision, and recovery. Data validation follows standard review procedures covering holding times, calibration verification, and duplicate precision, ensuring that reported results are legally and technically defensible for regulatory submission.
Applications
Soil pollution assessment services support a wide range of environmental, regulatory, and commercial objectives.
- Industrial site redevelopment and brownfield transactions, where assessment results determine remediation scope and land-use suitability under GB 36600-2018
- Agricultural land quality classification and safe food production programs under GB 15618-2018
- Environmental impact assessments and pollution discharge permit compliance for new industrial projects
- In-service industrial site monitoring, including soil pollution prevention plans for listed enterprises subject to mandatory self-monitoring requirements
- Post-remediation validation and acceptance testing to confirm that cleanup targets have been achieved
- Environmental due diligence for mergers, acquisitions, and financing, aligned with ASTM Phase I and Phase II site assessment practices
- Contamination incident investigation, responsibility apportionment, and technical support for environmental litigation
- Research and regional soil quality surveys, geochemical baseline studies, and ecological risk mapping
FAQ
What is the difference between risk screening values and risk intervention values?
Risk screening values define contaminant concentrations below which the risk to human health is considered acceptable and no further action is generally needed. Risk intervention values define concentrations above which the potential health risk is unacceptable and detailed risk assessment or remediation is required. Concentrations between the two thresholds typically trigger a site-specific health and ecological risk assessment to refine the evaluation.
How many soil samples are required for a typical assessment?
Sample quantity depends on site area, heterogeneity, and investigation phase. For preliminary development-land investigations, systematic grids of approximately 40 m × 40 m are commonly applied to suspected contamination areas, with at least one sampling point per grid and multiple depth intervals per borehole. Detailed investigations densify the grid around identified contamination hotspots until plume boundaries are delineated.
How deep should soil samples be collected?
Sampling depth must extend below the deepest expected contamination. For most surface sources, sampling to 3–6 m is sufficient, whereas sites with historical solvent use, underground storage tanks, or deep waste burial may require profiling to 10 m or more, continuing until contaminant concentrations return to background or screening levels for at least two consecutive intervals.
Can contaminated soil be left in place if it exceeds screening values?
In some cases, yes. If a site-specific risk assessment demonstrates that actual exposure pathways are incomplete or controlled—for example, through engineered barriers, land-use restrictions, or institutional controls—residual contamination above generic screening values may remain without unacceptable risk. This determination requires validated exposure modeling and regulatory approval.
How long does a complete soil pollution assessment take?
A typical phased assessment, from desk study through field sampling, laboratory analysis, and reporting, requires four to ten weeks depending on site complexity, number of analytes, and depth of investigation. Rapid screening using portable XRF and field GC-MS can provide preliminary results within days to guide ongoing fieldwork decisions.
Which standards govern soil pollution assessment in international projects?
International projects commonly reference ISO 10381 for sampling, ISO 15175 and ISO 15800 for soil quality and human exposure guidance, ASTM E1527 and ASTM E1903 for phased site assessment, ISO/IEC 17025 for laboratory competence, and jurisdiction-specific national standards such as GB 36600-2018 or EN-based national legislation, depending on where the land is located and which regulatory authority has jurisdiction.