Soil Characterization and Quaternary Pedology Laboratory Services

Moisture and Gravel Content

Moisture and gravel contents of soil and sediment samples may be requested as standalone analyses, but are commonly required as sample pretreatment steps for most of our services. Moisture content is determined gravimetrically by drying bulk soil samples for 24 hours at 105°C (110°C for foreign soils) (ASTM D2216). Thoroughly dried soil samples are sieved to quantitatively separate the >2 mm (gravel) fraction. Additional analyses are commonly conducted on the <2 mm “fine-earth” fraction.

Organic Matter/Carbonate Removal

Removal of soil constituents that may impact our ability to characterize the mineral fraction of soil and sediment samples is commonly recommended as a pretreatment step. The presence of organic materials or soluble salts influence a sample’s particle size distribution. Organic matter and soluble salts (chiefly calcium carbonate) are selectively removed via dissolution during sample pretreatment. See our list of Chemical Analytical services for quantitative determination of these constituents. Organic matter removal is achieved during sample pretreatment by addition of a 30% hydrogen peroxide solution to the sample.  Calcium carbonate removal is achieved during sample pretreatment by leaching the sample in an acetic acid solution.

Milling, Crushing, Grinding, Splitting

The Soils Lab is fully equipped with a rock crushing and milling facility. As needed, whole rock samples are crushed and milled to a target particle size range. Soil and sediment samples may also be milled to powder for select chemical analyses. See our list of Chemical Analytical services for sample requirements. All laboratory samples are properly split using a Gilson splitter so that a representative portion is used for subsequent analyses.

PSDA – Optical Method

We routinely carry out laser particle size analysis (LPSA) of soil, sediment, and suspended sediment samples. Laser diffraction is used to measure the particle size distribution when a laser beam passes through a dispersed sample. The laser light scatters at angles inversely proportional to the particle’s size. The laboratory is equipped with a Malvern Mastersizer 3000, which can measure particle size ranging from 3.5 mm to 0.01 µm. The Mastersizer 3000 can accommodate a variety of particle size class scales including ASTM International (ASTM C1070), United States Department of Agriculture (USDA), Wentworth, Krumbein Phi Scale, as well as custom particle size scales. Sample pretreatment for this analysis commonly includes gravel removal (>2 mm fraction), removal of organic matter and carbonate, and dispersion. See a sample report for this analysis.

PSDA – Stacked Sieve Method

The Soils Lab offers stacked sieve analysis using a RO-TAP sieve shaker machine and sieves with various mesh sizes ranging from 3” to 44 µm. Sieves are stacked in order of coarse (top) to fine (bottom) and shaken with the RO-TAP. The mass retained in each sieve is recorded and provides the percent of sample in the specified size range. This approach is used when continuous size distributions are not required. Several methods are utilized in the Soils Lab, including ASTM D6913. Sample pretreatment for this analysis commonly includes gravel removal (>2 mm fraction), removal of organic matter and carbonate, and dispersion.

PSDA – Pipette Method

The pipette method relies on particle settling velocities to determine the percentage of sand, silt, and clay in a soil or sediment sample. This procedure is based on Stoke’s Law, which states that spherical particles settle in a fluid rate proportional to their radius and mass. Methodology for this analysis is based on Gee and Or, 2002. Pretreatment for pipette commonly includes gravel removal (>2 mm), organic matter and carbonate removal, dispersion, wet sieving to separate coarse (sand) fraction, and dry sieving of sand fraction.

Ion Chromatography – Anion and Cation Suites

Ion chromatography (IC) measures concentrations of a variety of anions or cations in aqueous solutions. Sample solutions may be collected as aqueous samples or may be extracted from soil or sediment samples during a leaching procedure. Sample solutions are pumped through an anion- or cation-exchange column. A conductivity cell continuously measures the solution conductivity signal to produce a chromatogram. Peaks in the chromatogram are identified using calibration standard solutions that also provide conversions to solution concentration for each analyte. Anions commonly measured include fluoride, chloride, nitrite, bromide, nitrate, phosphate, and sulfate. Cations commonly measured include lithium, sodium, ammonium, potassium, magnesium, and calcium.

Fe Oxides – Cit-Dithionite and Hydroxylamine Methods

We measure iron oxides using the citrate-dithionate extraction method which is useful for dissolving nonsilicate iron in soils.  We also offer the hydroxylamine method which is used for removing noncrystalline material from crystalline iron oxides.

X-Ray Fluorescence

The Soils Lab utilizes the Niton portable XRF to measure the elemental composition of a soil or sediment sample via x-ray fluorescence. Lab samples are powdered and packed into plastic cups prior to analysis and are measured against known standards. The GOLDD+ technology and optional helium atmosphere provide additional accuracy and sensitivity for lighter elements.

Carbonate Content

The pressure-calcimeter method is used to determine carbonate content of a soil or sediment sample (Horvath et al., 2005, ASTM D4373-21).  Hydrochloric acid is added to sample vials and weighed standards containing calcium carbonate.  The pressure created by the production of CO2 is then measured by a tensiometer to determine the carbonate content.

Electrical Conductivity

Electrical conductivity can be measured to determine the total soluble salts of a soil or sediment sample.  Potassium chloride conductivity standards (1,000 µS/cm, 11.16 µS/cm) are used to calibrate the Accumet Excel XL 30 Conductivity Meter.  Aqueous soil extracts are dispersed by mechanical shaking and then centrifuged and extracted for conductivity measurement.

Organic Matter Content

The lab is equipped to measure organic matter content using the loss-on-ignition method (ASTM D2974).  Samples are pre-dried to a constant mass, then added to crucibles and placed in a muffle furnace at 400°C.  Sample pretreatment may include moisture content and gravel removal.

pH

The pH of soil is measured using a soil-aqueous matrix suspension using calcium chloride (CaCl2) solution (ASTM D4972).  The Soils Lab utilizes the Accumet pH Meter 915 with pH 4.01 and 10.01 buffer solutions.

Soil Moisture Release Curves

The Soil Lab offers laboratory techniques for determination of hydraulic soil properties from soil moisture release curves. Soil moisture release curves are generated using the Wind/Schindler evaporation method.  The lab is equipped with three METER HYPROP 2 stations for simultaneous measurement of soil or sediment samples and a METER WP4C dew point potentiometer to evaluate samples at high matric suction. The HYPROP 2 has two tensiometers at different levels within a sample to accurately measure water potentials up to ~800 hPa. The WP4C can measure water potentials up to -300 MPa to achieve a moisture release curve that covers the driest end member.

Atterberg Limits

Atterberg Limits are engineering properties of soils that are used to find the critical water content of the fine-grained fraction of soils. This is done to determine the liquid and plastic limits of a soil sample.  Atterberg Limits can be used to characterize different types of silt and clay, and the behavior of the soil when in solid, plastic, and liquid states. We routinely analyze soil and sediment samples to determine their Plasticity Index (Liquid Limit and Plastic Limit), also known as Atterberg Limits using ASTM Method D4318 and D2487 (USCS Soil Classification).

Bulk Density – Wax Peds

Bulk density of soil or sediment clods can be measured using the waxed ped method (ASTM C914). An undisturbed sample clod is weighed, and its volume is then calculated by determining the volume of water it displaces after the sample is coated with paraffin wax and placed in a beaker of water.

Cosmogenic nuclides

We offer a suite of services related to the preparation, analysis, and interpretation of cosmogenic nuclide samples for geochronology and emerging research needs. We have dedicated workspaces for sample crushing, mineral separation, chemical treatment, and cathode packing to ensure high sample preparation quality. We currently offer preparation services for ¹⁰Be, ²⁶Al, and ³⁶Cl nuclides. Our sample crushing facility consists of a jaw crusher and Bico mill with ceramic plates used to reduce rock samples to appropriate size fractions. Our mineral separation lab consists of a Frantz magnetic mineral separator, a heavy liquids separation station, a froth floatation station, a multi-tube vortexer for sample abrasion, and chemical stations for HF etching and ultrasonication. Chemical constraints on mineral separates are evaluated for each sample on our ICP-OES system and can be used for whole-rock analysis of major elemental concentrations. Our protocols follow methods outlined in Stone (2001) for preparation of ¹⁰Be and ²⁶Al targets. Modified procedures of those outlined in Marrero (2012) are used for ³⁶Cl preparation. Please contact Dr. Brad Sion for more information or to discuss potential collaborative opportunities.

Soil as relative dating tools

Soil development can be used to indicate the relative ages of geomorphic landforms (e.g., alluvial fans, fluvial terraces, moraines, etc.). Our joint laboratory- and field-based services can provide a multi-pronged approach to evaluating a variety of Quaternary geoscience problems by using soils as relative dating tools (e.g., Birkeland, 1991). Please contact Dr. Eric McDonald or Dr. Brad Sion for information regarding the application of soils to Quaternary geology problems or to discuss potential collaborative opportunities.

The Soil Characterization and Quaternary Pedology Laboratory follows strict standard operating procedures (SOPs) for all analyses.  Known lab standards and reference materials are routinely analyzed with sample batches for accuracy.  Blanks, sample duplicates, and standards are measured with all relevant analyses.  All analytical scales and balances receive annual certified calibration and are checked weekly by laboratory personnel.  All samples received are logged into the lab using a standardized chain of custody format.  Analyses are only performed by laboratory personnel trained in the methods. To learn more about what ASTM, USDA, EPA, etc. methods we offer, navigate to any of our analyses on this page.