Acceptance testing is the decisive verification step for remediation projects executed under soil pollution key special programs, providing objective, legally defensible evidence that residual contaminants meet national risk control values before a site is formally released for reuse. This article explains the regulatory framework, sampling design, target parameters, laboratory methods, and quality assurance requirements that accredited third-party laboratories apply when performing soil pollution key special project acceptance testing.
Technical Overview
Soil pollution key special project acceptance testing, also referred to as remediation effect assessment or final acceptance monitoring, is the systematic sampling and laboratory analysis performed when a soil remediation or risk control project reaches completion. Its purpose is to determine, with statistical and regulatory confidence, whether the remediation targets defined in the project contract and the approved remediation plan have been achieved across the entire treatment area and depth interval.
The regulatory backbone for this work is anchored in the Soil Pollution Prevention and Control Law and the technical framework of HJ 25.5, the guideline for risk control and remediation effect assessment of contaminated land, together with the risk control standards GB 36600-2018 for development land and GB 15618-2018 for agricultural land. For development land, residual contaminant concentrations must fall below the screening values corresponding to the intended land-use sensitivity class, with the strictest values applying to first-class uses such as residential plots, schools, and medical facilities. For agricultural land, acceptance hinges on whether cadmium, mercury, arsenic, lead, chromium, and other priority contaminants fall below the risk screening or control values applicable to the soil pH and crop type.
A complete acceptance testing engagement typically includes review of the remediation work plan and as-built documentation, preparation of an acceptance monitoring plan defining the sampling grid, density, depths, and analytical scope, field sampling with full chain-of-custody documentation, laboratory analysis in an ISO/IEC 17025-accredited facility, statistical evaluation of the data set, and issuance of an acceptance testing report that regulatory authorities rely upon when approving site closure and land transfer. Because the conclusions carry legal and financial consequences, the testing is performed by accredited third-party laboratories that are organizationally independent of the remediation contractor.
Testing Samples
Remediated Soil Samples
The primary sample matrix. Depending on the remediation process, samples are collected from in-situ treated soil at specified depth intervals, from ex-situ treated soil stockpiles, or from solidified and stabilized masses. Sampling follows grid-based coverage of every remediation unit defined in the remediation plan, with depth-discrete samples at the base and sidewalls of excavations and volumetric sampling of treated stockpiles. Supplementary infill points are added wherever the historical investigation identified hotspots. Imported backfill soil must pass the same testing before placement is accepted.
Groundwater Samples
For sites where contaminants may have migrated to the saturated zone, groundwater is sampled from monitoring wells located upgradient, within, and downgradient of the remediation area. Results are compared against GB/T 14848-2017 groundwater quality standards and any site-specific risk-based cleanup levels derived from the risk assessment.
Surface Water and Sediment Samples
Where the site adjoins rivers, lakes, ponds, or drainage channels, surface water and sediment samples verify that residual contamination has been removed and that off-site migration pathways are controlled. Evaluation references GB 3838 surface water quality standards and applicable sediment quality guidance.
Soil Gas and Vapor Samples
At sites contaminated with volatile organic compounds, soil gas probes, sub-slab soil gas points, and indoor air sampling demonstrate that vapor intrusion risks have been eliminated. This is especially important where engineered risk control rather than complete source removal is the accepted remediation strategy.
Remediation Byproducts and Solid Waste Samples
Excavated spoil, spent reactive materials, wastewater treatment sludge, and off-gas residues are tested for hazardous characteristics, including leaching toxicity, so that disposal routing complies with solid waste and hazardous waste management regulations.
Testing Items
The analytical scope mirrors the contaminants of concern identified in the site investigation and risk assessment, and for development land always includes the 45 basic items of GB 36600-2018, comprising 7 inorganic parameters, 27 volatile organic compounds, and 11 semi-volatile organic compounds. Typical testing items include:
- Heavy metals and inorganic contaminants: arsenic, cadmium, hexavalent chromium, copper, lead, mercury, and nickel as basic items, with zinc, total chromium, antimony, fluoride, and cyanide added where site history warrants.
- Volatile organic compounds: chlorinated solvents such as carbon tetrachloride, chloroform, trichloroethylene, tetrachloroethylene, and vinyl chloride, together with monoaromatics including benzene, toluene, ethylbenzene, xylenes, and styrene.
- Semi-volatile organic compounds: nitrobenzene, aniline, 2-chlorophenol, naphthalene, and the carcinogenic polycyclic aromatic hydrocarbons including benzo(a)pyrene.
- Petroleum hydrocarbons: total petroleum hydrocarbon fractions C6 to C9 and C10 to C40, selected according to the petroleum product type handled at the site.
- Pesticides and persistent organic pollutants: organochlorine insecticides such as hexachlorocyclohexane and DDT, organophosphorus pesticides, polychlorinated biphenyls, and dioxins and furans where combustion or chlorinated-industrial histories exist.
- Supporting parameters: pH, moisture content, organic matter, cation exchange capacity, particle size distribution, and redox potential, which govern contaminant bioavailability and the long-term stability of stabilized metals.
- Leaching behavior: horizontal vibration and acid buffer leaching tests verifying that solidified and stabilized soils will not release metals above regulatory thresholds over time.
Testing Methods
Method selection follows the national environmental protection standards and internationally recognized reference procedures to ensure data defensibility.
Sampling and Pretreatment
Soil sampling follows HJ/T 166 and the acceptance grid requirements of HJ 25.5, supplemented by ISO 10381 and ISO 18400 series guidance. VOC samples are collected with minimal disturbance into pre-weighed airtight vials or dedicated core samplers and preserved at 4 degrees Celsius; metals samples are dried away from direct sunlight, crushed, and sieved per ISO 11464. Groundwater wells are purged to parameter stabilization before low-flow sampling in accordance with HJ 164.
Inorganic Analysis
- Heavy metals are extracted by aqua regia digestion (HJ 803) or microwave-assisted digestion (ISO 12914) and quantified by inductively coupled plasma mass spectrometry or optical emission spectrometry, with graphite furnace atomic absorption spectrometry used for single-element confirmations such as cadmium (HJ 717).
- Mercury and arsenic are determined by atomic fluorescence spectrometry (HJ 680).
- Hexavalent chromium requires alkaline buffer extraction followed by flame atomic absorption determination (HJ 1082), because acidic digestion alters chromium speciation.
- Soil pH is measured potentiometrically in a soil-water suspension (HJ 962, equivalent to ISO 10390).
Organic Analysis
- VOCs are determined by purge-and-trap gas chromatography-mass spectrometry (HJ 605) or headspace gas chromatography-mass spectrometry (HJ 741), consistent with internationally recognized purge-and-trap GC-MS methodology.
- SVOCs and PAHs are extracted by pressurized fluid or Soxhlet extraction and quantified by GC-MS (HJ 834, ISO 18287).
- Petroleum hydrocarbons C10 to C40 are quantified by gas chromatography with flame ionization detection (HJ 1021).
- Organochlorine pesticides are measured by GC-MS (HJ 835) and polychlorinated biphenyls by GC-MS (HJ 743).
- Dioxins and furans are determined by isotope dilution high-resolution gas chromatography-mass spectrometry (HJ 77.4).
Rapid Screening and Field Confirmation
Handheld X-ray fluorescence analyzers and photoionization detectors support on-site decision-making during excavation by confirming that hotspots have been fully removed before final discrete sampling. Membrane interface probe logging guides depth-discrete verification sampling at volatile-contaminated sites. Screening data do not replace laboratory confirmation but materially reduce the risk of failed acceptance and costly remobilization.
Quality Assurance and Quality Control
All acceptance data must be produced by laboratories accredited to ISO/IEC 17025. QA and QC elements include field blanks, trip blanks, equipment rinsates, duplicate samples at a minimum frequency of 10 percent, matrix spikes, laboratory control samples, certified reference materials, and complete chain-of-custody tracking. Data are validated against standardized criteria before being used in the effect assessment, and every detected exceedance triggers confirmation sampling and delineation.
Applications
Acceptance testing under the key special project framework is applied whenever public funding, regulatory obligations, or land transfer transactions demand independent proof of remediation success:
- Final acceptance of national key research and development demonstration projects for soil pollution prevention and control, where technology performance indicators must be verified alongside environmental targets.
- Closure of former industrial sites, including chemical plants, smelters, coking and gas works, electroplating facilities, and pesticide plants, prior to redevelopment for sensitive land uses.
- Safe utilization and remediation of contaminated agricultural land, verifying that cadmium, arsenic, and other reductions bring soil within GB 15618-2018 values for continued crop production.
- Mining and metallurgical sites, including tailings ponds and slag heaps, addressing heavy metals and sulfide-related contamination.
- Petroleum terminals, fuel depots, and pipeline spill sites requiring hydrocarbon, BTEX, and PAH verification.
- Landfill closure, historic fill, and illegal dumping sites where mixed organic and inorganic contamination requires multi-parameter acceptance testing.
- Verification of long-term risk control measures such as engineered covers, vertical barriers, and monitored natural attenuation through post-acceptance tracking monitoring.
FAQ
What standards govern acceptance testing of soil remediation projects?
Development land projects are judged against the screening values of GB 36600-2018 for the intended land-use class, following the effect assessment procedure of HJ 25.5. Agricultural projects are evaluated under GB 15618-2018, and groundwater under GB/T 14848-2017. Supporting method standards such as HJ/T 166, HJ 605, and HJ 834 control how the data are generated.
Who is qualified to perform the testing?
Testing must be carried out by accredited third-party laboratories holding ISO/IEC 17025 accreditation or equivalent national metrology accreditation for every reported parameter. The testing body must be independent from the remediation contractor to eliminate conflicts of interest.
How are sampling locations and density determined?
HJ 25.5 requires sampling coverage of every remediation unit defined in the approved remediation plan, typically on a grid basis, with depth-discrete samples at the base and walls of excavations and per-volume sampling of treated stockpiles. Suspected hotspot areas receive supplementary infill points, and the sampling design must be reviewed and confirmed before fieldwork begins.
What happens if acceptance results exceed the target values?
Any exceedance triggers supplementary delineation sampling, re-treatment or supplementary remediation of the affected unit, and a fresh round of acceptance sampling in that unit. The project cannot pass acceptance until all soil units, all stockpiles, and all groundwater compliance points meet the approved remediation targets.
How long does the acceptance testing process take?
Field sampling typically requires one to three weeks depending on site size and the number of remediation units. Laboratory analysis adds two to four weeks for metals and routine organics, and up to six weeks where dioxins or the full organic suite of GB 36600 is required. Data evaluation and report issuance generally require an additional one to two weeks.
Is on-site rapid screening accepted as final evidence?
No. XRF and PID screening are decision-support tools used to guide excavation limits and sample placement. Regulatory acceptance decisions must rest on laboratory-confirmed results generated by accredited analytical methods, with screening used only to demonstrate adequate spatial coverage of the sampling design.