Contaminated site soil testing is a systematic process of collecting, analyzing, and evaluating soil samples to identify hazardous substances, quantify pollution levels, and assess human health and ecological risks at potentially contaminated land. Governed by national standards such as GB 36600-2018 and technical specifications including the HJ 25 series, this testing is essential for land redevelopment, remediation design, regulatory compliance, and environmental due diligence. This article provides a comprehensive technical overview of sampling strategies, testing parameters, analytical methods, and practical applications of soil testing for contaminated sites.
Technical Overview
Contaminated site soil testing refers to the scientific investigation and laboratory analysis of soil at sites suspected or known to be affected by hazardous substances, typically resulting from historical industrial operations, improper waste disposal, chemical spills, agricultural inputs, or commercial activities such as fuel storage. The objective is to determine the type, concentration, and spatial distribution of contaminants, compare the results against risk-based screening and control values, and support subsequent risk assessment and remediation decisions.
In China, the regulatory framework is primarily established by the Soil Pollution Prevention and Control Law, the Soil Pollution Prevention and Control Action Plan, and the national standard GB 36600-2018, Soil Environmental Quality—Risk Control Standard for Soil Contamination of Development Land. This standard defines screening values and control values for 85 contaminants across two land-use categories: Category I (sensitive land use, such as residential, schools, medical facilities, and parks) and Category II (industrial land use). For agricultural land, GB 15618-2018 applies. The investigation process itself follows the HJ 25 series of technical specifications, including HJ 25.1 for site environmental investigation, HJ 25.2 for site environmental monitoring, and HJ 25.3 for risk assessment.
A typical contaminated site investigation proceeds in phases: a Phase I preliminary review of historical records and site reconnaissance; a Phase II intrusive investigation involving soil borings, sampling, and laboratory analysis; and, where contamination is confirmed, a detailed investigation and site-specific human health risk assessment that determines whether remediation or risk control measures are required. All analytical work should be performed by accredited third-party laboratories holding CMA (China Metrology Accreditation) and CNAS qualifications, ensuring that data are legally defensible and technically reliable.
Testing Samples
Surface Soil Samples
Surface soil, generally collected from 0 to 0.5 meters below ground level, is the most directly exposed medium for human contact, dust generation, and ecological receptors. Sampling points are systematically arranged using grid-based layouts, judgmental placement near visible staining, storage areas, or drainage pathways, or a combination of both. Surface samples are prioritized for volatile organics analysis because many VOCs tend to dissipate with depth.
Subsurface Soil Samples
Subsurface samples are obtained through drilled boreholes or direct-push technology at intervals extending from the surface to the maximum depth of potential contamination, often targeting lithologic transitions, the capillary fringe, and the water table where dense or light non-aqueous phase liquids may accumulate. Each borehole is logged stratigraphically, and samples are screened in the field using photoionization detectors (PID) or X-ray fluorescence (XRF) analyzers to guide the selection of intervals for laboratory submission.
Soil Gas and Vapor Intrusion Samples
At sites contaminated with volatile chlorinated solvents or petroleum hydrocarbons, soil vapor probes may be installed to assess the potential for vapor intrusion into future buildings. Sub-slab soil gas, exterior soil gas, and ambient air samples provide data for evaluating inhalation exposure pathways under risk assessment models.
Ancillary Environmental Media
Because soil contamination frequently co-occurs with groundwater and sediment pollution, site investigations commonly incorporate groundwater monitoring wells and, where surface water bodies exist, sediment sampling. These complementary matrices help delineate contaminant plumes and identify off-site migration pathways, forming an integrated basis for the conceptual site model.
Testing Items
GB 36600-2018 classifies contaminants into basic items and other items. The 45 basic items consist of 8 inorganic parameters and 37 organic parameters that must be tested during the first stage of any investigation. Other items are selected based on site history, industrial processes, and raw materials historically used on site.
Heavy Metals and Inorganic Contaminants
- Basic inorganic items: arsenic (As), cadmium (Cd), chromium (Cr, hexavalent chromium Cr(VI)), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni)
- Supplementary inorganic items: zinc (Zn), thallium (Tl), antimony (Sb), beryllium (Be), cobalt (Co), vanadium (V), manganese (Mn), fluoride, cyanide, and asbestos where applicable
Volatile Organic Compounds (VOCs)
- Halogenated volatiles: chloroform, carbon tetrachloride, trichloroethylene (TCE), tetrachloroethylene (PCE), 1,1-dichloroethane, 1,2-dichloroethane, vinyl chloride, bromodichloromethane
- Aromatic volatiles: benzene, toluene, ethylbenzene, xylenes (BTEX), styrene, chlorobenzene, 1,4-dichlorobenzene
- Other volatiles commonly associated with petrochemical and solvent-handling sites
Semi-Volatile Organic Compounds (SVOCs)
- Polycyclic aromatic hydrocarbons (PAHs): naphthalene, benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene, dibenzo(a,h)anthracene, indeno(1,2,3-cd)pyrene, and other priority PAHs
- Phthalate esters: di(2-ethylhexyl) phthalate (DEHP), di-n-butyl phthalate, and related plasticizers
- Organochlorine pesticides: DDT and metabolites, aldrin, dieldrin, chlordane, heptachlor, hexachlorocyclohexane (HCH)
- Nitroaromatics and anilines: nitrobenzene, 2,4-dinitrotoluene, aniline, and related compounds typical of chemical manufacturing sites
Other Site-Specific Contaminants
- Total petroleum hydrocarbons (TPH) fractions C6–C9, C10–C40 for fuel stations, refineries, and oil depots
- Polychlorinated biphenyls (PCBs) at electrical, transformer, and capacitor manufacturing sites
- Dioxins and furans (PCDD/Fs) at waste incineration, metallurgical, and chlor-alkali facilities
- Phenols, formaldehyde, explosives residues, and heavy fuel oils where site history indicates
Testing Methods
Sampling and Field Protocols
Soil sampling is performed according to HJ 25.1, HJ 25.2, and HJ/T 166. VOC samples are collected first using undisturbed cores transferred directly into pre-weighed methanol vials or sealed headspace syringes to minimize volatilization losses, followed by SVOC and metal samples. Equipment is decontaminated between sampling locations, samples are stored at 4 °C in the dark, and chain-of-custody documentation is maintained from the field to the laboratory. Field duplicates, trip blanks, and equipment blanks are included at prescribed frequencies.
Laboratory Analytical Techniques
- Heavy metals: microwave or hot-plate acid digestion followed by inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectrometry (ICP-OES) per HJ 803 and HJ 680; mercury and arsenic by atomic fluorescence spectrometry (AFS); hexavalent chromium by alkaline digestion with UV-visible spectrophotometry
- VOCs: headspace or purge-and-trap extraction coupled with gas chromatography–mass spectrometry (GC-MS) per HJ 605 and HJ 642, or methods equivalent to EPA Method 8260
- SVOCs: pressurized fluid or ultrasonic extraction with GC-MS analysis per HJ 834, or methods equivalent to EPA Method 8270
- Organochlorine pesticides: solvent extraction with GC-ECD or GC-MS per HJ 835 and HJ 703
- TPH fractions: GC-FID or GC-MS per HJ 921, HJ 1021, and related standards
- PCBs: GC-MS or GC-ECD per HJ 743; dioxins and furans: high-resolution GC-MS per HJ 77.4, consistent with EPA Method 1613
Quality Assurance and Quality Control
Laboratory QC measures include method blanks, laboratory control samples, matrix spikes, surrogate recoveries, calibration verification standards, and continuing calibration blanks. Data validation evaluates holding times, detection limits relative to screening values, duplicate precision, and completeness. Only data meeting the acceptance criteria of the applicable standard methods should be used in the comparison against GB 36600 screening values and in quantitative risk assessment models.
Risk Assessment Integration
Where contaminant concentrations exceed screening values, a site-specific risk assessment is conducted following HJ 25.3, which models exposure pathways such as oral ingestion, dermal contact, and vapor inhalation for current and future land-use scenarios. The assessment derives site-specific remediation target values; where concentrations exceed control values, risk control or remediation is mandatory before the land can be transferred or redeveloped.
Applications
Urban Redevelopment and Land Transfer
Under Chinese regulations, soil environmental quality investigations are legally required before any former industrial or mining land can be reused for sensitive purposes such as residential development, schools, or hospitals. Soil testing reports and risk assessment results form part of the mandatory land-transfer record and determine whether remediation must precede redevelopment.
Industrial Site Decommissioning
Chemical plants, steelworks, electroplating facilities, pesticide manufacturers, and coking plants undergo comprehensive soil investigations upon closure to define contamination footprints, calculate remediation volumes, and support the design of soil remediation technologies such as excavation and disposal, solidification and stabilization, thermal desorption, chemical oxidation, or bioremediation.
Fuel Stations, Oil Depots, and Petrochemical Facilities
Leaks from underground storage tanks frequently generate petroleum hydrocarbon and BTEX plumes. Targeted soil testing around tank farms, pipelines, and dispenser islands supports closure assessments, remediation verification, and environmental liability management during property transactions.
Agricultural Land Safety Utilization
Farmland surrounding mining and smelting operations is tested for cadmium, lead, arsenic, and other heavy metals in accordance with GB 15618 to classify land into priority protection, safe utilization, or strict control categories, guiding planting adjustments and soil amendments.
Environmental Due Diligence and Legal Proceedings
Soil test data support environmental site assessments in mergers and acquisitions, pollution liability insurance underwriting, environmental disputes, and the allocation of remediation responsibility between responsible parties, often alongside international frameworks such as ASTM Phase I and Phase II environmental site assessment practice.
FAQ
What is the difference between screening values and control values in GB 36600-2018?
Screening values are concentration thresholds below which contamination risk is generally considered acceptable and no further risk assessment is required. Control values are higher thresholds above which the risk to human health is unacceptable, and risk control or remediation measures are mandatory. Concentrations falling between the two require a site-specific risk assessment under HJ 25.3.
How deep should soil samples be collected?
Sampling depth depends on the type and depth of potential contamination sources. Investigations typically extend at least to the water table or to a depth that confirms the vertical extent of contamination, with a minimum requirement of penetrating unaffected strata below all identified impacts. Field screening with PID or XRF helps identify contaminated intervals in real time.
How many sampling points are required?
Under HJ 25.1 and HJ 25.2, the preliminary investigation generally requires grid densities on the order of one point per 1,600 square meters (40 m × 40 m) for sites up to 12 hectares, with adjusted spacing for larger or smaller sites. Suspected source areas, such as storage zones and process areas, require judgmental, denser sampling.
How long does a contaminated site soil investigation take?
A routine Phase II investigation, including mobilization, drilling, laboratory analysis, and reporting, typically requires several weeks to two months depending on site size, complexity, number of parameters, and remediation-phase work. Dioxin and other specialist analyses may extend laboratory turnaround times.
Can field screening instruments replace laboratory testing?
No. Portable XRF and PID instruments are valuable for delineating contamination in real time and optimizing sample selection, but regulatory submissions and risk assessments must rely on laboratory results produced by accredited third-party laboratories using validated standard methods with complete QA/QC documentation.
Which land-use category applies to my site?
Category I under GB 36600 applies to sensitive land uses including residential developments, schools, medical institutions, community facilities, and public parks, and imposes stricter screening values. Category II applies to industrial and commercial construction land. Where a site involves mixed use, the more protective Category I criteria generally govern.