Site soil remediation completion testing is the decisive verification step that determines whether a contaminated land treatment project has achieved its cleanup targets and can be formally closed out. Performed by accredited third-party laboratories in accordance with GB 36600-2018, the HJ 25 series of technical guidelines, and ISO/ASTM sampling standards, this testing delivers defensible analytical evidence of remediation effectiveness for regulators, landowners, and developers. This article explains the sample types, testing parameters, analytical methods, acceptance criteria, and typical applications of soil remediation project closeout verification.
Technical Overview
Site soil remediation completion testing, also referred to as remediation effect evaluation or final acceptance verification, is performed after remediation and risk control measures have been implemented at a contaminated site and before the land is released for redevelopment or unrestricted use. Its core objective is to confirm, through independent sampling and laboratory analysis, that residual contaminant concentrations in soil, groundwater, and soil gas meet the remediation targets established in the approved remediation plan and the underlying human health and ecological risk assessment.
In China, the governing framework is anchored in HJ 25.5-2018 (Technical Guidelines for Risk Management, Control and Remediation Effect Evaluation of Soil at Contaminated Sites), supported by HJ 25.2-2014 for site environmental monitoring. Risk-based acceptance criteria are drawn from GB 36600-2018 for development land, GB 15618-2018 for agricultural land, and GB/T 14848 for groundwater quality. International projects commonly reference ISO 10381 and ISO 18400 soil sampling standards, ISO 11074 terminology, and ASTM environmental site assessment and risk-based corrective action practices such as ASTM E1527, ASTM E1903, ASTM E1739, and ASTM E2081.
A complete completion testing program typically consists of six stages: desk review of the site investigation, risk assessment, and remediation design documents; confirmation of remediation boundaries, depths, and technology performance claims; design of the verification sampling grid; field sampling with full quality assurance and chain-of-custody documentation; laboratory analysis at an accredited third-party laboratory; and statistical evaluation of results against remediation targets. The final completion testing report supports formal project acceptance, removal of the site from the contaminated land register, and regulatory approval for subsequent land use.
Testing Samples
Soil Samples
Soil is the primary matrix for completion verification. Samples are collected across the remediation footprint, including the base and sidewalls of excavated areas, in-situ treatment zones, and buffer zones adjacent to the remediation boundary. Sampling extends from the surface to the maximum confirmed contamination depth identified during site investigation, with discrete depth intervals to rule out vertical residual contamination.
Groundwater Samples
Where the remediation plan includes groundwater targets, samples are collected from upgradient, source-zone, and downgradient monitoring wells to verify that dissolved-phase contamination has been reduced to acceptable levels. Well purging, low-flow sampling, and field parameter stabilization follow ISO 5667-11 and HJ 25.2 practices.
Soil Gas and Vapor Samples
For sites with volatile contaminants, soil gas probes and sub-slab vapor points are sampled to confirm that residual vapor concentrations do not pose an unacceptable intrusion risk to future buildings, consistent with the risk assessment scenarios defined for the intended land use.
Treated Soil and Solidified or Stabilized Materials
Projects using solidification and stabilization require core or molded specimens of the treated monolith to verify contaminant immobilization, leaching performance, and engineering properties such as strength and permeability.
Backfill and Imported Materials
All imported clean soil, aggregate, or engineered fill placed after excavation must be verified as meeting the applicable screening values before acceptance as part of the completed works.
Process Waste Streams
When remediation generates wastewater, spent GAC or filter media, condensate, or off-gas, representative samples of these streams are tested to demonstrate compliant discharge, disposal, or reuse.
Testing Items
The parameter list for completion testing is derived from the contaminants of concern identified in the site investigation and risk assessment, and must cover every substance for which a remediation target was set.
Heavy Metals and Inorganic Contaminants
- Base metals: arsenic, cadmium, copper, lead, nickel, zinc, chromium, and thallium
- Specific valence and species: hexavalent chromium, mercury (total and where relevant methylmercury), antimony, beryllium, and vanadium
- Other inorganics: total cyanide, easily released cyanide, fluoride, and soluble salts
Volatile Organic Compounds (VOCs)
- Monocyclic aromatics: benzene, toluene, ethylbenzene, xylenes, and styrene
- Halogenated solvents: trichloroethylene, tetrachloroethylene, cis- and trans-1,2-dichloroethylene, 1,1- and 1,2-dichloroethane, vinyl chloride, chloroform, and carbon tetrachloride
- Other volatiles: chlorobenzenes, ketones, ethers, and fuel oxygenates
Semi-Volatile Organic Compounds (SVOCs)
- Polycyclic aromatic hydrocarbons (PAHs), including benzo(a)pyrene and the priority PAH suite
- Phthalate esters, phenols, nitroaromatics, and chlorinated anilines
- Polychlorinated biphenyls (PCBs), organochlorine pesticides, and where warranted dioxins and furans
Petroleum Hydrocarbons and Site-Specific Parameters
- Total petroleum hydrocarbon fractions, typically C6 to C9 and C10 to C40
- Methyl tert-butyl ether and other gasoline additives
- Emerging contaminants or process reagent residues defined in the remediation design
Physical, Geotechnical, and Leaching Characteristics
- Soil pH, moisture and dry matter content, and organic carbon content
- Particle size distribution and permeability for solidified or stabilized materials
- Unconfined compressive strength of treated monoliths
- Leaching behavior using HJ/T 300, HJ 557, GB 5085.3 procedures, or internationally recognized leaching methods such as ASTM D3987
Testing Methods
Sampling Design and Field Procedures
Verification sampling follows a grid-based design across each remediation unit, commonly at a density of one verification point per 20 m by 20 m cell, adjusted to the site-specific conditions and the requirements of HJ 25.2 and HJ 25.5. Excavation bases and sidewalls are sampled at defined intervals, and grid layouts are documented with survey coordinates. Field quality assurance includes equipment decontamination, field duplicates at a typical rate of at least 10 percent, trip blanks for volatile parameters, field blanks, and strict chain-of-custody handling in accordance with ASTM D4840. Volatile organic samples are collected with zero-headspace or syringe techniques and preserved at low temperature to minimize losses.
Analytical Methods
- Metals: microwave or acid digestion followed by ICP-MS (HJ 700), ICP-OES, or atomic fluorescence spectrometry for arsenic, mercury, selenium, and antimony (HJ 680); hexavalent chromium by alkaline extraction with spectrophotometric or atomic absorption finish
- Field screening: portable X-ray fluorescence for real-time metals delineation and photoionization detectors for vapors, used only to guide sampling, not for final acceptance
- VOCs: purge-and-trap gas chromatography-mass spectrometry (HJ 605) or headspace GC-MS (HJ 741)
- SVOCs: solvent extraction with GC-MS determination (HJ 834); PAHs by HPLC or GC-MS (HJ 784, HJ 805); PCBs by GC-MS (HJ 743); organochlorine pesticides by GC-MS or GC-ECD
- Petroleum hydrocarbons: GC determination of C10 to C40 (HJ 921) and C6 to C9 by purge-and-trap GC (HJ 1021)
- Supporting parameters: pH by potentiometry (HJ 962), dry matter (HJ 613), organic carbon (HJ 658), strength and permeability of solidified soil per GB/T 50123 and ASTM D5084
Data Evaluation and Acceptance Criteria
All analytical data undergo validation against method quality control criteria before evaluation. Acceptance is judged by comparing verification results with the remediation targets in the approved plan: every verification sample must meet the target concentration, and where the guideline allows, the 95 percent upper confidence limit of the mean may be used for area-wide statistical conclusions. If any sample exceeds its target, the affected area requires supplementary remediation, expanded delineation sampling, and re-verification until closure criteria are satisfied.
Applications
Completion testing is required wherever a soil remediation technology project must demonstrate that cleanup goals have been achieved before regulatory closure or land transfer. Typical scenarios include:
- Industrial relocation and brownfield redevelopment of former chemical, pesticide, coking, gasworks, electroplating, tannery, and iron and steel plants
- Petroleum sites such as refineries, tank farms, oil depots, and fuel retail stations contaminated with hydrocarbons and fuel additives
- Mining, smelting, and associated farmland affected by heavy metals such as cadmium, arsenic, and lead
- Municipal landfill and hazardous waste disposal site closures
- Verification of specific treatment trains, including excavation and disposal, soil vapor extraction, bioremediation, chemical oxidation, thermal desorption, solidification and stabilization, soil washing, and phytoremediation
- Emergency response and accident spill sites requiring formal confirmation that response actions were successful
The resulting report is submitted to the competent ecological environment authority, reviewed by an expert panel where required, and used to remove the parcel from the contaminated land inventory so that clean-land development and transaction can proceed.
FAQ
When should completion testing be carried out?
Testing is conducted after the remediation contractor has completed all treatment works and passed internal self-inspection, and before formal project acceptance. For multi-phase projects, staged verification can be performed area by area to accelerate redevelopment scheduling.
How many verification samples are needed?
Sample count is driven by the size and depth of each remediation unit and the applicable guideline. Grid-based designs of roughly one point per 400 square meters, with additional points on excavation walls and floors, are common; larger or more heterogeneous sites require denser grids.
Who is qualified to perform the testing?
All sampling and analysis should be executed by accredited third-party laboratories holding recognized accreditation for the specific methods, and the verifier must be organizationally independent of the remediation contractor to ensure objectivity.
What happens if results exceed the remediation targets?
Exceedances trigger supplementary remediation of the affected zone, boundary delineation to define the residual contamination extent, and a further round of verification sampling until every point complies. Partial exceedances confine rework to the affected areas only.
How long does the completion testing process take?
Field work typically requires one to two weeks depending on site size and well development needs, while routine laboratory analysis takes ten to twenty working days. Specialized determinations such as dioxins and furans require additional time.
How are the results used for project closure?
The validated dataset is compiled into a completion testing and effect evaluation report, compared against the approved remediation targets, presented for expert review, and filed with the regulator as the technical basis for site closure and land use change approval.