Engineering with Nature Research Program - Microbial Induced Calcite Precipitation (MICP)

Description

Background:There are hundreds of reservoirs and thousands of miles of navigation channels that provide invaluable flood control, commercial transport of materials, water supply, recreation, and stream flow regulation. This navigation and flood control infrastructure protects millions of Americans who work and live beside these control structures. This protection of life and property is threatened by large-scale wildfires across the western United States” (Haring, et al. 2021). In 2021, 58,968 wildfires impacted 7.1 million acres and burned nearly 6,000 structures nationwide, 60% (3,577) of which were residences (USGS website). Also, in January 2018, directly following the nearby Thomas Fire, a storm struck Montecito, California, resulting in several landslides that killed 23 people. Wildfires damage watersheds by denuding landscapes, reducing infiltration rates, and increasing runoff rates. “Immediately following a wildfire, [the ground is void of] vegetation, the organic soil horizons are reduced to ash, and the soil remaining is altered such that it repels [instead of absorbs] rainwater. These effects dramatically increase the potential for erosion, which destabilizes stream channels, and increases infilling of reservoirs thus reducing their capacity. Together these adverse ground conditions significantly increase runoff, discharge, sediment transport, and subsequently increase the risks of flash flooding and destructive debris flows, as described above.” (Haring, et al 2021). As the climate has changed, fire seasons around the world have grown longer. According to Wibbenmeyer and McDarris (2020), the period from 2000-2018 was the driest 19-year span that southwestern North America has experienced since the late 1500s, and the second driest since 800 CE. These trends will only increase the likelihood of more wildfires and subsequent increased risks to our nation’s environment and flood protection infrastructure. The primary technical objective of this project is to provide a sustainable, nature-based and cost effective soil treatment technology for improving the mechanical properties of wildfire-altered soils, to decrease erosion. The treatment of interest is Microbial Induced Calcite Precipitation (MICP). Microbial-induced calcite precipitation (MICP) is a relatively new process that uses naturally occurring bacteria to bind soil particles together through calcium carbonate (CaCO3) precipitation. MICP is a biologically driven precipitation technology that is sustainable, does not introduce contaminants into the soil, and is not a high-energy process. The MICP treatment is a relatively new technique used by geotechnical engineers for ground improvement (strength) of sandy soils, like those in the western regions of the US.In theory, this method would also lessen the drying effects of drought on soils. The treatment increases water content of the soil, which deters erosion, slows runoff, and flash flooding. Brief Description of Anticipated Work: Determine the efficacy of MICP to improve engineering properties of soils affected by wildfires through conventional laboratory soil testing and through field demonstrations. To accomplish this, the following is anticipated: Literature review on MICP and effect of wildfires on soils. This research, performed only by the ERDC, will provide the basis for identifying the best type of soils and soil conditions for MICP treatment as well as defining the effects of wildfire on soils. Information will be acquired through discussion with USACE Districts that commonly experience wildfires in their regional area of jurisdiction. The activities discussed below will be undertaken by the contractor, with guidance and consideration by ERDC Principal Investigator. Activity 1: Identify the source(s) for soil sampling and testing. The contractor will consider ERDC’s findings from the literature research and start communication with ERDC and USACE Districts in the arid southwestern States and determine which wildfire affected site(s) will be researched. Government offices such as the Sacramento District, and Albuquerque District where wildfire clean up and forest restoration activities are common are the likely regions for conducting this research. Research locations will be determined based upon quantity and availability of site data and government experience (NRCS, USGS, USACE) in the regions. Activity 2: Acquire soil samples/travel. This activity will involve Government and University personnel acquiring soil samples from wildfire-affected areas discovered in Activity 2. Soil samples will be shipped to ERDC and University soil laboratories. The volume collected will be approximately of nine 5-gallon buckets. Activity 3: Soil index properties testing and microscopic mineral identification. The soil collected will be tested for their index properties including: sieve analysis, specific gravity, organic content, triaxial and direct shear strength. The soil property testing requires standard equipment and must follow typical ASTM procedures. Activity 4: Optimize MICP treatment. The duration and frequency of treatment as well as the concentration of the bacteria and type of nutrients to grow the bacteria will be determined in the lab. This activity requires a bio-engineering specialist. Activity 5: Treat and test soil samples. Testing of treated soils will be performed by a civil engineering graduate student and supervised by a geotechnical faculty. Microscopic mineral identification will be performed by a junior ERDC engineer and supervised by the PI. Lab testing will include shear strength (direct and triaxial) infiltration properties, erodibility properties. The testing requires standard equipment and must follow ASTM procedures. Tests conducted in triplicates will ensure repeatability. Results and analyses will be documented in a data report or a technical paper. Activity 6: Field demonstration. Select one site of the sampled wildfire sites that is most suitable to demonstrate the treatment application and protocol through a number of field tests including infiltration, erodibility and plate load. ERDC and university team members will coordinate testing plans and on wildfire exposed and un-exposed (control) sections of the site. The duration of treatment and field testing will be determined after the above field tests have taken place. This activity involves travel to the site, application tools, media and bacteria strain. Field activities, test results, and analyses will be documented in a data report and/or a technical paper. Public Benefit: Engineering with Nature research program, is the intentional alignment of natural and engineering processes to efficiently and sustainably deliver economic, environmental, and social benefits that improve public’s quality of life through community collaboration. This project will investigate the implementation of a sustainable, economic and eco‐friendly treatment for mitigating post‐fire effects on the natural environment and communities downstream of wildfires. If successful, MICP treatment has potential to decrease the threat of flash flooding and debris flows that threaten communities and USACE flood protection projects downstream of wildfires. This project will involve a previous EWN research effort in the Santa Clara Pueblo in northern New Mexico. These are native American lands where engineering solutions to environmental problems should be consistent with the Native American culture.

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