Comparing dry and wet sieving with laser diffraction to the hydrometer method for particle size analysis of sandy bioretention soil media

Authors: SMITH, JOSEPH - The Ohio State University; TIRPAK, R - The Ohio State University; Osterholz, William; WINSTON, RYAN - The Ohio State University

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2025
Publication Date: 6/7/2025
Citation: Smith, J.S., Tirpak, R.A., Osterholz, W.R., Winston, R.J. 2025. Comparing dry and wet sieving with laser diffraction to the hydrometer method for particle size analysis of sandy bioretention soil media. Soil Science Society of America Journal. 89(3): Article e70079. https://doi.org/10.1002/saj2.70079.
DOI: https://doi.org/10.1002/saj2.70079

Interpretive Summary: Bioretention cells, also known as biofilters or rain gardens, are a widely used stormwater control measure used to infiltrate urban runoff and capture pollutants. Proper blending of the soil media to meet the textural design specifications is critical to the functioning of bioretention cells, with media typically containing 80% sand amended with organic matter and fines (silt and clay). There is currently no standardized particle size analysis method to verify whether bioretention soil media meets design specifications. Three methods – hydrometer, dry sieving plus laser diffraction, and wet sieving plus laser diffraction – were compared to evaluate their accuracy and repeatability for particle size analysis of bioretention soil media from three bioretention cells in Ohio. The hydrometer method resulted in variable sand estimates depending on the size of sample analyzed, but two methods that used dry sieving and wet sieving provided the highest agreement in sand content. For measuring clay content, the most consistent methods involved volumetric measurements of wet fines, which were the hydrometer and wet sieving plus laser diffraction methods. The results indicate that gravimetric measurement (i.e., dry sieving or wet sieving) of the sand fraction and volumetric measurement of the fines (i.e., hydrometer or laser diffraction after wet sieving) are most accurate and repeatable approaches for measuring particle sizes on sandy soils like bioretention soil media. Trade-offs between equipment costs and time requirements should be considered when selecting the method to be used, but in all cases the method used should be clearly reported. These methodological recommendations can improve the consistency and accuracy of bioretention cell implementation and assessment.

Technical Abstract: Standardization of particle size analysis (PSA) is crucial to ensure the proper blending of stormwater filter media, such as bioretention soil media (BSM). BSM typically contains over 80% sand and is amended with organic matter (OM) and fines (silt and clay) to support pollutant removal. However, there is currently no standardized PSA method to verify whether BSM meets design specifications. This study compares three PSA methods—hydrometer, dry sieving plus laser diffraction (DS+LD), and wet sieving plus laser diffraction (WS+LD)—to evaluate their accuracy and repeatability for analyzing sandy BSM. Twenty-seven BSM samples were collected from different locations and depths in three bioretention cells at Lions Park in Sandusky, Ohio, USA. The hydrometer method yielded variable results depending on the BSM sample mass used, with sand content estimates from sedimentation failing to align when checked by wet sieving. Methods that gravimetrically measured the sand fraction, DS+LD and WS+LD, demonstrated the highest agreement in sand content. For measuring clay content, the hydrometer and WS+LD methods—both volumetric measurements involving the wetting of fines—were the most consistent. We recommend a gravimetric measurement of the sand fraction and a volumetric measurement of the fines when conducting PSA on sandy soils like BSM. For fines analysis (LD vs hydrometer), one must consider the trade-off between equipment costs and time requirements. The method used for BSM textural analysis should be clearly reported. Future research should focus on BSM pretreatment (e.g., OM removal, dispersing aggregates, etc.) to establish a standardized method for BSM PSA.