Soils Sampling & Analysis

Collect subsoils samples to understand the native subsoils characteristics impacting green stormwater infrastructure (GSI) design

Overview

Once project areas are identified, native subsoils information can be collected. Field soil surveys are recommended, which involves collecting soil samples, creating soil profile descriptions, and performing field measurements that indicate how water moves through soil such as hydraulic conductivity (Ksat). The Ksat of soils can vary greatly depending on the soil type, structure, porosity, and other factors. Higher Ksat values imply better infiltration. Soils data is then incorporated into green stormwater infrastructure design and performance modeling.

Outcomes

When the site soils analysis is completed, stormwater professionals will have a characterization of the subsoils types in the project area. These subsoils types inform recommendations for green stormwater infrastructure design.

Recommended Involvement

The below offers broad recommendations for who might be involved in soils sampling and analysis. As always, evaluate participation in accordance with your specific project.

For site soils sampling and analysis, it is necessary to coordinate soils researchers and technicians with community leaders and others regarding approvals, access, permission, and dates for soil sampling. Site visits and soils fieldwork can be coordinated with community soils education. 

To learn more see the Engagement step of the design process.

Technical expertise for onsite soil fieldwork, description, and measurement is recommended to accomplish the analysis. Community members and municipal staff members should work with expertly trained field soil survey personnel (e.g. Illinois State Geological Survey, USDA-Natural Resources Conservation Service, private geotechnical engineering firms) and use the best research practices—sampling procedures should be standardized and quality controlled with repeated measurements in a set.

To learn more about professionals and their roles in GSI Design, see Who Might be Involved in GSI Design?

Coordinating with local government is necessary to conduct soils field studies as this work requires site access, permission, and permits to sample, utility avoidance, considerations of other activities occurring in the community (main replacements, construction work, etc.), and knowledge of any previous site soils disturbance. Municipal staff members provide: input into soils sampling sites; access to soils testing sites; coordination with other agencies conducting soils testing; meeting attendance to discuss and plan soils sampling; and discussions with the team regarding soils analysis, modeling results, and final selection of sites.

To learn more about the stormwater management authority of local government, see Illinois regulations.

Tasks

Consult existing soils data for the site to develop an understanding of its history, including existing and previous land uses and structures. Use this data in concert with a community engagement process to pinpoint soils sampling sites.

 

Soil sampling involves developing a soil sampling protocol, including: working with soils technicians to follow their respective agency protocols; sending formal requests to property owners for access, permission and permits to sample at the selected site locations; and informing partners of soils field work logistics (how long and when each type of soil field work will take at each soil sampling location, and equipment and personnel that will be on site).

Prior to beginning field work, create a map and diagram of soil sample locations and conduct site visits to confirm site location on the maps and ground conditions at the sites. Field work includes collecting soils directly from the site and conducting infiltration/Ksat tests. Field studies can include the (1) Amoozemeter to measure soil water conductivity and (2) drill truck to measure soil water conductivity as well as other soil properties. Considerations include: avoidance of utilities, shade trees, and other activities occurring in the community (main replacements, construction work, etc.); and previous site soils disturbance (to ensure the characterization of natural local soils in the sampling rather than anthropogenic fill).

 

Soil scientists, in partnership with landscape architects, will present soil field work and analysis results to communities, including information on surficial geology and Ksat values from the Amoozemeter field work, to facilitate a discussion of soils characteristics (Ksat by texture by city, Ksat data vs. texture). Soils scientists will also provide the data to engineers and landscape architects who will incorporate soils data into green stormwater infrastructure design modeling. The implications of soils analysis results for GSI site selection and design are discussed with the community so that soils information can be applied to problems of urban flooding.

Resources

Example: The data in Table S1. AMOOZEMETER SITE LOCATIONS.xlsx was obtained using 1–2 pickup truck and soil samples were obtained largely with hand tools. The soil boring samples were transported to the Illinois State Water Survey laboratory and analyzed to determine soil texture. Results were summarized in descriptive soil boring logs (Soil boring descriptions), particle size (particle size data), water content and Ksat. Ksat values were statistically compared to soil texture classes.