Site soil physical and chemical property testing is a fundamental component of environmental site investigation, providing quantitative data on soil texture, moisture, density, pH, organic matter, and ion exchange characteristics. These parameters control contaminant fate and transport, support risk assessment under standards such as GB 36600-2018 and the HJ 25 series, and guide remediation and engineering design. This article outlines the sampling procedures, testing items, analytical methods, and practical applications of site soil physicochemical characterization performed by accredited third-party laboratories.
Technical Overview
Determination of physical and chemical properties of site soil refers to the systematic measurement of the physical and chemical characteristics of soil at a target site, including texture, structure, water content, density, acidity, organic matter, and exchangeable ions. In environmental site assessment, these measurements complement contaminant screening data by describing the medium in which pollutants occur, migrate, and transform. Regulatory frameworks such as HJ 25.1 (site environmental investigation), HJ 25.2 (site environmental monitoring), and HJ 25.3 (risk assessment of soil contamination of development land) explicitly rely on soil physicochemical parameters as model inputs for deriving screening values and remediation targets under GB 36600-2018 and GB 15618-2018.
The typical workflow consists of four stages: preparation of a sampling plan based on the conceptual site model; field collection and preservation of representative samples; laboratory pretreatment (air-drying, disaggregation, and sieving); and instrumental or chemical analysis with full quality control. Accredited third-party laboratories perform the work under recognized national and international standards, ensuring that data are defensible for regulatory submission, litigation support, engineering design, and remediation performance verification.
- Physical characterization quantifies texture, water, density, and hydraulic behavior of the soil matrix.
- Chemical characterization quantifies pH, organic matter, salinity, exchange capacity, and nutrient status.
- Combined results explain contaminant adsorption, mobility, and bioavailability at the site.
Testing Samples
Surface Soil Samples
Surface samples are typically collected from the 0–20 cm layer, or from the 0–50 cm interval when specified by the investigation plan, using grid-based or judgmental sampling layouts. Surface samples characterize the zone of direct human contact, dust generation, and runoff transport, and are the primary basis for screening against first-screen values in GB 36600-2018.
Subsurface and Borehole Soil Samples
Subsurface samples are recovered from drilled boreholes using split-spoon samplers, hollow-stem augers, or direct-push rigs. Samples are generally taken at intervals of 1.5 to 3 meters, at every lithologic change, and immediately above the groundwater table or bedrock. These samples define vertical stratigraphy, identify potential migration pathways, and support contaminant delineation at depth.
Undisturbed Soil Samples
Undisturbed samples are collected with cutting rings (commonly 100 cm³ or 61.8 cm³ stainless-steel rings) or thin-walled tubes to preserve the natural structure and water regime of the soil. They are mandatory for laboratory measurement of bulk density and permeability, where any compaction or disturbance would invalidate the result.
Soil Profile Samples
Where test pits or trenches are excavated, samples are taken from each genetic horizon of the soil profile to document horizon-specific properties. Profile sampling is frequently used for agricultural land quality evaluation and for characterizing heterogeneous fill material at industrial and brownfield sites.
Testing Items
Testing programs are tailored to the site use and regulatory trigger, but the following parameters constitute the core panel of site soil physicochemical determination.
Physical Property Parameters
- Particle size distribution (sand, silt, and clay fractions) and USDA texture classification
- Natural water content and dry matter content
- Bulk density (wet and dry) and particle density (specific gravity)
- Porosity and void ratio (derived from density data)
- Atterberg limits: liquid limit, plastic limit, and plasticity index
- Hydraulic conductivity (permeability coefficient)
- Soil color and structural description
Chemical Property Parameters
- Soil pH in water or salt (KCl/CaCl2) suspension
- Organic matter content and total organic carbon (TOC)
- Cation exchange capacity (CEC) and exchangeable base cations (Ca, Mg, K, Na)
- Electrical conductivity and total soluble salt content
- Carbonate content
- Redox potential (Eh)
- Nutrient status: total nitrogen, available phosphorus, and available potassium (for agricultural assessments)
Testing Methods
Sample Collection and Pretreatment
Sampling follows HJ 25.1, HJ 25.2, and HJ/T 166-2004 (technical specifications for soil environmental monitoring). Samples for moisture and redox-sensitive parameters are stored in sealed containers and transported under refrigeration at approximately 4°C, while samples for pH, texture, and organic matter are air-dried at room temperature, disaggregated, and sieved—typically through 2 mm for pH and salinity, 0.25 mm for organic matter, and finer fractions for specific analyses—in accordance with ISO 11464.
Physical Property Test Methods
- Water content: gravimetric oven-drying at 105 ± 5°C per HJ 613-2011, ASTM D2216, and ISO 11465
- Particle size distribution: combined sieving and hydrometer or pipette sedimentation per ASTM D6913/D7928, ISO 11277, and NY/T 1121.3; laser diffraction is an accepted supplementary technique
- Bulk density: cutting ring method per GB/T 50123 and NY/T 1121.4; particle density by pycnometer per ASTM D854
- Atterberg limits: Casagrande liquid limit device and rolling test per ASTM D4318 and GB/T 50123
- Hydraulic conductivity: laboratory constant-head and falling-head permeameter tests per ASTM D5084 and GB/T 50123, with field infiltration tests where in-situ values are required
Chemical Property Test Methods
- pH: potentiometric glass electrode method on a soil-to-water suspension, commonly at a 1:2.5 ratio, per HJ 962-2018, ISO 10390, and ASTM D4972
- Organic matter and organic carbon: potassium dichromate oxidation with titrimetric or spectrophotometric detection per HJ 695 and ISO 14235, or high-temperature combustion oxidation with non-dispersive infrared detection per HJ 658-2013 and ASTM D2974
- CEC and exchangeable cations: ammonium acetate or barium chloride exchange per ISO 13536 and NY/T 1121.5, with cation quantification by ICP-OES or flame photometry
- Electrical conductivity and soluble salts: conductivity measurement on a 1:5 soil-to-water extract per standard soil salinity procedures
- Carbonate content: volumetric calcimeter method using hydrochloric acid reaction per ISO 10693
- Nutrients: Kjeldahl digestion for total nitrogen, Olsen or Mehlich extraction with spectrophotometry for available phosphorus, and flame emission or ICP-OES for available potassium
Quality assurance includes method blanks, laboratory duplicates on at least 10% of samples, certified reference soils, calibrated balances and meters, and documented method detection limits, ensuring data comparability and regulatory acceptance.
Applications
Physicochemical property data serve multiple technical and regulatory purposes across the project life cycle of site development and remediation.
- Environmental site assessment: characterization of soil conditions during Phase II investigations, supplementing contaminant screening under HJ 25.1 and HJ 25.2.
- Human health and ecological risk assessment: input of soil pH, organic matter, bulk density, and hydraulic parameters into exposure and fate models under HJ 25.3, influencing site-specific screening values under GB 36600-2018.
- Remediation design and optimization: reagent dosing for stabilization and solidification depends on pH and buffer capacity; bioremediation requires balanced carbon-to-nitrogen-to-phosphorus ratios and adequate moisture; soil washing efficiency is governed by particle size distribution.
- Contaminant fate and transport modeling: organic carbon content controls sorption coefficients for hydrophobic organics, while permeability and texture govern leaching to groundwater.
- Geotechnical and construction engineering: classification, compaction, and consolidation parameters per GB/T 50123 and GB 50021 for foundation design and earthworks.
- Land quality and agricultural evaluation: fertility and salinity assessment against GB 15618-2018 for cultivated land and land reclamation projects.
FAQ
What is the difference between physicochemical property testing and soil contamination testing?
Contamination testing measures concentrations of pollutants such as heavy metals, VOCs, SVOCs, and pesticides against screening values. Physicochemical property testing instead measures inherent soil attributes—texture, moisture, density, pH, organic matter, and exchange capacity—which explain how contaminants behave and provide essential inputs for risk assessment and remediation design. The two datasets are typically acquired together during a site investigation.
How deep should site soil samples be collected?
Sampling depth is defined by the conceptual site model. Surface samples are generally taken from 0–20 cm or 0–50 cm, while boreholes extend through potentially impacted fill and native soil to the saturated zone, bedrock, or a depth at which impacts are demonstrably absent—commonly 3 to 6 meters at simple sites and deeper at complex industrial sites, consistent with HJ 25.1 requirements.
How much sample is required, and how should samples be preserved?
A minimum of 500 g to 1 kg of sieved soil is typically sufficient for the full physicochemical panel; undisturbed ring samples are required for density and permeability. Samples for moisture and redox-sensitive tests are sealed and chilled at approximately 4°C, while samples for pH, salinity, organic matter, and texture are air-dried before analysis. All containers are inert glass or polyethylene and are cleaned to prevent cross-contamination.
Which standards govern site soil physicochemical testing?
Primary references include the HJ 25 series for site investigation, monitoring, and risk assessment; HJ/T 166-2004 for soil sampling and pretreatment; HJ 962, HJ 613, HJ 658, and HJ 695 for individual parameters; the NY/T 1121 series for soil testing methods; GB/T 50123 for geotechnical testing; and international equivalents such as ISO 10390, ISO 11277, ISO 13536, ASTM D2216, ASTM D4318, and ASTM D5084.
How long does testing take?
Most physical and chemical property tests are completed within 5 to 10 working days after sample receipt, depending on pretreatment time, drying requirements, and the number of parameters. Permeability and specialized analyses may require additional time, and expedited schedules can usually be arranged with the testing laboratory.