Site soil pollution risk control and management assessment is a science-based evaluation that quantifies the risks posed by soil and groundwater contamination to human health and the environment under current or planned land use. This article explains the regulatory framework, sampling strategy, testing parameters, analytical methods, and typical applications of a professional site soil pollution risk assessment aligned with GB, HJ, ISO, and ASTM standards.
Technical Overview
Site soil pollution risk control and management assessment is a systematic technical process used to determine whether contaminants present in soil, groundwater, or soil vapor at a site pose unacceptable risks to human health, ecology, or groundwater resources under current or intended land use. The assessment converts site investigation data into quantitative risk estimates and, where risks are unacceptable, derives risk-based remediation target values and defines appropriate risk control measures such as source removal, engineering barriers, institutional controls, or long-term monitoring.
The evaluation is anchored to national risk control standards, principally GB 36600-2018 (Soil Environmental Quality - Risk Control Standard for Soil Contamination of Development Land) and GB 15618-2018 (Risk Control Standard for Soil Contamination of Agricultural Land), supported by the technical guideline series for investigation, monitoring, risk assessment, remediation, and risk control of contaminated land. International practice is broadly consistent with ASTM E1527 and ASTM E1903 environmental site assessment procedures and ISO 10381 soil sampling standards.
A complete assessment follows the classical four-step risk assessment paradigm, typically implemented in a tiered manner:
- Hazard identification: comparison of measured contaminant concentrations against land-use-specific screening values.
- Exposure assessment: construction of a site-specific conceptual site model identifying contaminant sources, release mechanisms, transport pathways, exposed populations, and intake routes such as ingestion, dermal contact, and vapor inhalation.
- Toxicity assessment: assignment of carcinogenic slope factors and reference doses to each pollutant of potential concern.
- Risk characterization: calculation of carcinogenic risk and hazard quotients, with acceptable thresholds generally set at a carcinogenic risk of 10-6 and a hazard quotient of 1 for each exposure pathway.
The outcome determines whether the site qualifies for safe utilization, requires risk control measures, requires remediation to derived target values, or requires further detailed investigation. All analytical data supporting the assessment are generated by ISO/IEC 17025 accredited third-party laboratories.
Testing Samples
Surface and Subsurface Soil Samples
Surface soil (typically 0 to 0.5 m) and shallow soil (0.5 to 1.5 m) samples are collected on a systematic grid or at judgmentally selected locations based on historical land use. Deep soil samples are recovered as continuous or interval cores from drilled boreholes extending through the identified contamination zone and into uncontaminated reference strata, allowing full delineation of vertical contaminant distribution.
Groundwater Samples
Groundwater is sampled from permanent monitoring wells installed across the contaminant plume and hydraulically upgradient and downgradient of suspected source areas. Low-flow purging and sampling techniques are applied to obtain representative, low-turbidity samples from the target aquifer horizon.
Soil Gas and Vapor Samples
Sub-slab soil vapor, external soil gas, and indoor or ambient air samples are collected where volatile contaminants are present, in order to quantify the vapor intrusion pathway, which frequently governs the risk result at sites contaminated with chlorinated solvents or petroleum hydrocarbons.
Supporting Matrices
Depending on the conceptual site model, the sampling program may also include sediment from adjacent drainage features, soil leachate prepared by horizontal vibration or acetic acid buffer extraction procedures, and uncontaminated local background soil samples used as reference points for naturally elevated elements such as arsenic or heavy metals of geogenic origin.
Testing Items
The analytical parameter list is driven by historical site activities and by the mandatory indicator lists of the applicable land-use risk control standard. GB 36600-2018 defines 85 basic indicators and 40 additional indicators for the two standard land-use classes, residential (Class I) and industrial or commercial (Class II).
Inorganic and Metallic Pollutants
Arsenic, cadmium, mercury, copper, lead, chromium, hexavalent chromium, nickel, zinc, cobalt, antimony, thallium, beryllium, molybdenum, selenium, vanadium, manganese, fluoride, and cyanide.
Volatile Organic Compounds
Halogenated aliphatic compounds such as chloroform, carbon tetrachloride, trichloroethylene, tetrachloroethylene, 1,2-dichloroethane, and vinyl chloride; monocyclic aromatics including benzene, toluene, ethylbenzene, and xylenes; chlorobenzenes; ketones; ethers; esters; and petroleum fractions in the light hydrocarbon range.
Semi-Volatile Organic Compounds
Polycyclic aromatic hydrocarbons including benzo[a]pyrene, naphthalene, and phenanthrene; phthalate esters; nitroaromatic compounds; substituted anilines; phenols; chlorinated phenols; polychlorinated biphenyls; and total petroleum hydrocarbons across the C10 to C40 range.
Pesticides and Persistent Organic Pollutants
Organochlorine pesticides such as DDT, chlordane, aldrin, dieldrin, heptachlor, endrin, mirex, and hexachlorocyclohexane, together with dioxins and furans at sites with combustion, metallurgical, or chlor-alkali histories.
Soil and Groundwater Physical-Chemical Parameters
pH, soil organic carbon content, moisture content, particle size distribution, bulk density, porosity, saturated hydraulic conductivity, cation exchange capacity, and redox potential, all of which serve as mandatory input parameters for fate-and-transport and risk calculation models. Groundwater samples are additionally characterized for general chemistry indicators such as total dissolved solids, hardness, sulfate, chloride, ammonia, and nitrate.
Testing Methods
Sampling design, point density, depth placement, and quality assurance follow the national technical guidelines for site investigation and monitoring, the ISO 10381 series on soil sampling, and ISO 5667-11 for groundwater. Field programs incorporate duplicates, trip blanks, equipment rinsates, and field blanks at prescribed frequencies, and portable X-ray fluorescence and photoionization detectors are used for on-site delineation before laboratory confirmation.
- Metals: acid microwave digestion followed by inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectrometry (ICP-OES); atomic absorption spectrometry (AAS) and atomic fluorescence spectrometry (AFS) for mercury and arsenic.
- Hexavalent chromium: alkaline digestion followed by colorimetric or spectrophotometric determination.
- VOCs: purge-and-trap or headspace gas chromatography-mass spectrometry (GC-MS).
- SVOCs: ultrasonic or pressurized liquid extraction followed by GC-MS, with gel permeation cleanup for oily matrices.
- Organochlorine pesticides: solvent extraction with GC-MS or gas chromatography with electron capture detection.
- Petroleum hydrocarbons: gas chromatography with flame ionization detection across defined carbon ranges.
- Dioxins and furans: high-resolution gas chromatography coupled with high-resolution mass spectrometry.
- Soil parameters: potentiometric pH determination, elemental or oxidative determination of organic carbon, laser diffraction or sieve-pipette particle sizing, and constant-head or falling-head permeameter testing.
Risk calculation applies deterministic and probabilistic (Monte Carlo) exposure models using land-use-specific exposure parameters, with backward calculation of soil and groundwater remediation target values for each pollutant exceeding the acceptable risk level. All confirmatory analyses are performed by accredited third-party laboratories whose method detection limits are demonstrably below the applicable screening values, ensuring valid exceedance decisions at regulatory thresholds.
Applications
Risk control and management assessments are mandatory or highly advisable in a wide range of land management and regulatory scenarios:
- Redevelopment of former industrial land into residential, educational, medical, or parkland uses, where the sensitivity of the exposed population increases.
- Closure, relocation, or ownership transfer of chemical manufacturing, electroplating, pesticide formulation, coking, petroleum refining, smelting, tanning, mining, or waste treatment facilities.
- Gas station and fuel storage terminal closure, including tank removal and dissolved plume delineation.
- Investigation of suspected contamination caused by spills, leaks, accidents, or historical waste disposal.
- Verification of in-situ risk management measures such as capping, vertical cut-off walls, and monitored natural attenuation.
- Post-remediation effectiveness evaluation and regulatory acceptance testing against approved remediation targets.
- Environmental due diligence supporting mergers, acquisitions, financing, and brownfield transactions.
- Categorization and safe-utilization zoning of agricultural land under the applicable farmland risk control standard.
- Regulatory filing and record keeping on the national soil pollution information platform for land that requires risk control.
FAQ
What is the difference between screening values and control values?
Screening values are concentrations below which the health risk associated with the corresponding land use is generally considered acceptable. If concentrations fall between the screening value and the higher control value, a site-specific detailed risk assessment is required to decide whether risk control or remediation is needed. Concentrations above the control value indicate generally unacceptable risk, and risk control or remediation measures are normally mandatory.
When is a detailed quantitative risk assessment necessary?
A detailed assessment is required when any pollutant of concern exceeds its screening value, when the site contains contaminants without established screening values, when sensitive receptors such as drinking water aquifers or schools are nearby, or when the responsible party seeks to derive site-specific remediation targets that are less conservative than default values.
How many sampling points are required?
Point density depends on site size, heterogeneity, and investigation stage. For preliminary investigation of larger sites, systematic grids on the order of one point per 1,600 square meters are common, supplemented by judgmental points placed at former tanks, drains, storage areas, and process units identified from historical records. Detailed investigation stages then infill the grid around every confirmed exceedance until horizontal and vertical delineation is complete.
How long does a complete assessment take?
A typical program requires several weeks for document review and site reconnaissance, several weeks for field investigation and laboratory analysis, and additional time for risk modeling and report preparation, so most projects are completed within two to four months depending on complexity, access constraints, and the number of delineation rounds required.
What happens if calculated risks are unacceptable?
The assessment will derive remediation target values and recommend a combination of measures: source treatment or removal, engineering controls such as clean soil caps, horizontal or vertical barriers, institutional controls restricting land use and groundwater extraction, long-term monitoring of soil, groundwater, and vapor, and periodic re-evaluation to confirm continued protection of human health and the environment.
Which exposure routes are typically evaluated?
For soil, the standard pathways are direct oral ingestion of soil particles, dermal contact with soil, and inhalation of soil-derived particulates and vapors. For groundwater, pathways include ingestion as drinking water, dermal absorption during washing or bathing, and vapor migration into overlying buildings, each evaluated separately for child and adult receptors under the designated land-use scenario.