Soil pollution status assessment is a systematic, standards-driven investigation that identifies, quantifies, and evaluates contaminants in soil to determine whether pollutant concentrations exceed regulatory risk screening values such as those specified in GB 36600-2018 and GB 15618-2018. This technical article explains the complete assessment workflow, including sampling strategies, testing parameters covering heavy metals, VOCs, SVOCs, and petroleum hydrocarbons, analytical methods based on ICP-MS and GC-MS, quality control requirements, and typical applications in industrial redevelopment, agricultural land management, and site remediation projects.
Technical Overview
Soil pollution status assessment is a structured, multi-stage investigation designed to determine whether a parcel of land is contaminated, to characterize the type, concentration, and spatial distribution of pollutants, and to evaluate the potential risks to human health and the environment under current or planned land use. The process integrates historical land-use review, site reconnaissance, systematic sampling, laboratory analysis, and comparison of analytical results against regulatory screening and intervention values.
In jurisdictions applying the Chinese national framework, the assessment is governed by a coherent set of standards: GB 36600-2018 (risk control standard for soil contamination of development land), GB 15618-2018 (risk control standard for agricultural land), and the HJ 25 technical series covering site investigation (HJ 25.1-2019), monitoring (HJ 25.2-2019), risk assessment (HJ 25.3-2019), remediation (HJ 25.4-2019), and remediation effect evaluation (HJ 25.5-2019). Comparable workflows rely on ISO 10381 for sampling and ISO/IEC 17025 for laboratory competence.
A complete assessment typically proceeds through three stages:
- Phase I – Pollution identification: review of historical maps, production records, chemical inventories, and site reconnaissance to identify potential contamination sources and target analytes.
- Phase II – Preliminary sampling: systematic grid-based soil, groundwater, and soil gas sampling with laboratory analysis of basic contaminant indicators and comparison against screening values.
- Phase III – Detailed sampling and risk assessment: denser sampling around confirmed contamination, site-specific exposure and toxicity evaluation, and derivation of risk control values where screening values are exceeded.
Under GB 36600-2018, 85 controlled indicators are listed, of which 45 are mandatory basic items consisting of seven heavy metals and inorganic species, 27 volatile organic compounds, and 11 semi-volatile organic compounds. Screening and intervention values are differentiated by land-use sensitivity class, distinguishing sensitive uses such as residential, educational, and medical facilities from less sensitive industrial and commercial uses.
Testing Samples
Surface Soil Samples
Surface samples are generally collected from the 0 to 50 cm depth interval for development land investigations, and from the 0 to 20 cm tillage layer for agricultural assessments following the soil environmental monitoring specifications. Surface soil reflects historical spills, atmospheric deposition, and dust-borne contamination and is critical for evaluating direct-contact exposure pathways such as incidental ingestion and dermal contact by site users.
Subsurface and Deep Soil Samples
Subsurface samples are obtained from drilled boreholes at regular vertical intervals, typically every 1 to 2 meters or at each significant stratigraphic change, extending until uncontaminated native soil is reached. Deep profiling is essential for tracing contaminant migration through the vadose zone, identifying dense non-aqueous phase liquid (DNAPL) sources from chlorinated solvents, and locating confined contamination layers beneath former tank farms, workshops, and waste disposal areas.
Groundwater Samples
Groundwater is collected from temporary or permanent monitoring wells installed within boreholes, screened across the water table or targeted aquifer zones. Because many organic contaminants are highly mobile in groundwater, groundwater chemistry is used to delineate leaching risk, define plume boundaries, and confirm whether soil contamination has impacted receiving waters.
Soil Gas Samples
Soil gas is sampled from permanent gas probes or sub-slab points to evaluate the vapor intrusion pathway, in which volatile compounds migrate from soil or groundwater into overlying buildings. Soil gas data are particularly important at sites with histories of petroleum storage, dry cleaning, or solvent use where occupied structures exist or are planned.
Testing Items
Basic Physicochemical Parameters
Foundation parameters include pH, moisture content, organic matter, cation exchange capacity, soil texture, and electrical conductivity. These parameters influence contaminant mobility, bioavailability, and the validity of risk models, and are required inputs for site-specific risk assessment calculations.
Heavy Metals and Inorganic Contaminants
The mandatory inorganic analytes under GB 36600-2018 are arsenic, cadmium, hexavalent chromium, copper, lead, mercury, and nickel. Site-specific expansions commonly include zinc, manganese, cobalt, vanadium, antimony, thallium, beryllium, total chromium, cyanide, and fluoride, depending on historical processes such as electroplating, smelting, mining, or coal gasification. GB 15618-2018 adds zinc to the core agricultural set of eight metals, with screening values differentiated by soil pH and crop type (paddy versus upland cultivation).
Volatile Organic Compounds (VOCs)
The 27 regulated VOCs include benzene, toluene, ethylbenzene, xylenes, chlorinated solvents such as trichloroethylene, tetrachloroethylene, and chloroform, as well as chloromethane, carbon tetrachloride, and vinyl chloride. These compounds are prioritized at former chemical plants, pharmaceutical facilities, printing operations, and dry-cleaning sites due to their toxicity, volatility, and vapor intrusion potential.
Semi-Volatile Organic Compounds (SVOCs)
The 11 basic SVOCs include polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene, benzo(a)anthracene, and naphthalene, together with phthalate esters, nitrobenzene, aniline, and o-cresol. PAHs are signature contaminants at gasworks, coking plants, and oil refineries, while phthalates are associated with plastics manufacturing.
Site-Specific and Special Contaminants
Depending on site history, additional analytes may include total petroleum hydrocarbons (C10–C40), polychlorinated biphenyls (PCBs), organochlorine and organophosphorus pesticides, dioxins and furans (PCDD/Fs), and explosive-related compounds. Dioxin analysis is mandatory for sites formerly used for pesticide production, waste incineration, or chlor-alkali processes utilizing graphite electrodes.
Testing Methods
Sampling Design and Pretreatment
Sampling locations are typically selected using systematic grids combined with judgmental placement at former source areas, in accordance with HJ 25.2-2019 and the ISO 10381 series. For preliminary investigations, sites of 5,000 m² or less generally apply a 40 m × 40 m grid, while larger sites are divided into a minimum of approximately 20 grid cells with one sampling point per cell; detailed investigations densify the grid to about 20 m spacing around confirmed exceedances. VOC samples are transferred directly into pre-weighed zero-headspace vials or methanol-preserved vials to minimize volatilization losses. Physical, chemical, and heavy metal samples are air-dried or freeze-dried, disaggregated, sieved, and homogenized following ISO 11464 pretreatment procedures.
Heavy Metal Analysis
Heavy metals are extracted by aqua regia digestion under reflux or microwave-assisted acid digestion following methods consistent with EPA Method 3050B, ISO 11466, or HJ 803-2019. Quantification is performed by inductively coupled plasma mass spectrometry (ICP-MS, EPA 6020B) or inductively coupled plasma optical emission spectrometry (ICP-OES, EPA 6010D) for multi-element determination, while flame and graphite furnace atomic absorption spectrometry (AAS) serve as confirmatory techniques. Mercury and arsenic are determined with high sensitivity by atomic fluorescence spectrometry (AFS) following HJ 680-2013. Hexavalent chromium requires separate alkaline extraction under buffered conditions followed by AAS or spectrophotometric determination per HJ 1082-2019, because total chromium digestion destroys the original valence speciation.
Organic Contaminant Analysis
VOCs are quantified by purge-and-trap or headspace gas chromatography–mass spectrometry (GC-MS) following HJ 605-2011 or EPA Method 8260D, achieving detection limits at the microgram-per-kilogram level. SVOCs are extracted by accelerated solvent extraction or ultrasonic extraction with dichloromethane/acetone and analyzed by GC-MS in selected ion monitoring mode per HJ 834-2017 or EPA Method 8270E. Total petroleum hydrocarbons in the C10–C40 range are determined by gas chromatography with flame ionization detection (GC-FID) following HJ 1021-2019. Dioxins and furans require high-resolution gas chromatography coupled with high-resolution mass spectrometry (HRGC-HRMS) to meet the ultra-trace toxic equivalent (TEQ) reporting limits required by GB 36600-2018.
Field Screening and In-Situ Techniques
Portable X-ray fluorescence (XRF) analyzers operated per EPA Method 6200 enable real-time screening of metal concentrations to guide borehole placement and depth selection. Photoionization detectors (PID) and flame ionization detectors (FID) provide rapid headspace screening for volatile organics. Membrane interface probe (MIP) and cone penetration testing with resistivity and conductivity sensors support high-resolution vertical contaminant delineation in complex stratigraphy, reducing the number of confirmatory laboratory samples required.
Quality Assurance and Quality Control
All analyses should be performed by accredited third-party laboratories operating an ISO/IEC 17025 management system. Field QA/QC measures include duplicate samples at a rate of at least 10 percent, equipment rinsate blanks, trip blanks for VOC vials, and field blanks. Laboratory QC encompasses method blanks, laboratory control samples, matrix spikes, parallel duplicates, calibration verification standards, and surrogate recoveries for organic methods. Data validation against national QA protocols precedes any comparison with regulatory screening values, and results are reported on a dry-weight basis with full metadata on sampling coordinates, depths, lithology, and groundwater levels.
Applications
Redevelopment of Industrial and Brownfield Sites
Soil pollution assessment is a legal prerequisite before former industrial, mining, and storage land can be re-zoned for residential, commercial, or public use. The assessment defines the remediation scope, supports remediation design per HJ 25.4-2019, and provides the baseline documentation required for regulatory closure and effect evaluation after treatment.
Agricultural Land Classification and Safety Utilization
Based on GB 15618-2018 screening values and results from national detailed soil surveys, cultivated land is classified into priority protection, safe utilization, and strict control categories. Assessment data determine whether crops require variety adjustment, soil amendment, deep plowing, or planting structure changes to keep agricultural products within food safety limits.
Mining Areas, Landfills, and Solid Waste Disposal Sites
Abandoned mines, tailings ponds, informal dumping grounds, and legacy landfills require assessment of heavy metals, leachate indicators, and persistent organics to evaluate migration toward groundwater and downstream receptors, informing engineered containment, capping, or source control measures.
Environmental Due Diligence, Compliance, and Litigation
Assessment reports support environmental responsibility allocation in mergers, acquisitions, and land transactions, verify compliance with pollution discharge and soil prevention legislation, and provide forensic evidence for contamination source apportionment in environmental disputes and damage quantification.
FAQ
Question: When is a soil pollution status assessment legally required?
Answer: An assessment is generally mandatory when land use is changed to a more sensitive purpose such as residential or educational development, when an industrial enterprise ceases operation or relocates, when contamination is suspected through spills or waste burial, or when required by regulators during environmental supervision, land transactions, or remediation planning.
Question: What is the difference between screening values and intervention values?
Answer: Under GB 36600-2018, contaminant concentrations below the screening value are generally considered acceptable for the specified land use, while concentrations between the screening and intervention values trigger a site-specific risk assessment. Concentrations above the intervention values indicate unacceptable risk, requiring risk control measures or remediation before the land can be safely used.
Question: How many sampling points are needed for a typical site?
Answer: In preliminary investigations, sites of 5,000 m² or less usually apply a 40 m × 40 m grid, and larger sites are divided into at least approximately 20 grid cells with one sampling point per cell. Detailed investigations apply denser grids, typically around 20 m spacing, plus judgmental points at identified source areas and monitoring wells for groundwater.
Question: To what depth must soil samples be collected?
Answer: Sampling extends from the surface through all potentially affected strata until uncontaminated native soil or bedrock is encountered, commonly several meters at industrial sites. VOC and SVOC samples are taken at each contamination-suspected interval, and groundwater samples are collected whenever the water table lies within the investigated depth range.
Question: How long does a complete assessment take?
Answer: Phase I document review and reconnaissance typically requires two to four weeks, field sampling one to three weeks depending on well installation, and laboratory analysis ten to twenty working days. A full investigation and assessment cycle, including reporting and review, generally ranges from two to four months for medium-sized sites.
Question: What happens if analytical results exceed the screening values?
Answer: Exceedances require a detailed investigation to delineate the full extent of contamination, followed by a site-specific risk assessment per HJ 25.3-2019 that calculates carcinogenic risk and hazard quotients for current and future receptors. If calculated risks exceed acceptable thresholds, site-specific remediation target values are derived and remediation or risk control is implemented, with a final effect evaluation confirming that the land meets its intended use.