Evaluating Biofiltration in Small Urban Areas: Chico, California Case Study

EPA Grant Number: SV836930
Title: Evaluating Biofiltration in Small Urban Areas: Chico, California Case Study
Investigators: Matiasek, Sandrine
Institution: California State University - Chico
EPA Project Officer: Callan, Richard
Phase: II
Project Period: October 1, 2016 through September 30, 2018 (Extended to September 30, 2019)
Project Amount: $74,971
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2016) Recipients Lists
Research Category: P3 Awards , P3 Challenge Area - Safe and Sustainable Water Resources , Sustainable and Healthy Communities


The overall goals of the proposed research are to improve water quality in small urban cities and campuses and increase awareness about urban green water infrastructure by identifying the practicality of using biofiltration in small urban areas, using the City of Chico and CSU Chico campus as model sites. This requires identifying preferred configurations, evaluating performance of filter media to both remove pollutants and withstand harsh weather conditions, performing a cost-benefit analysis comparing biofiltration to other stormwater runoff BMPs, and disseminating results to the local community using K-12 outreach and meetings with local officials. This research embodies the principles of sustainability and seeks solutions that protect the environment and strengthen communities.

These tasks will be accomplished by a series of laboratory experiments and by performing a life cycle analysis. The project team will design and construct laboratory biofiltration systems out of PVC pipe and other inexpensive materials. The biofilters will use native, drought-resistant, suntolerant plants chosen to represent local conditions. Short-term experiments will examine a variety of physical design factors for biofiltration systems (e.g., infiltration rate; comnbinations of various filter media) and further investigate plant species suitable for biofiltration based on climate conditions. The team will also summarize, generalize and disseminate results to nontechnical audiences so that findings are valuable to other small urban areas and campuses.


Phase II project objectives are to fill in a knowledge gap in biofiltration systems in small urban areas by 1) identifying key design parameters to achieve biofilter resiliency and 2) carrying out detailed long-term hydrologic and pollutant removal performance monitoring of existing biofilters. The innovative aspect of this project lies in its focus on testing pollutant removal efficiency in biofilters, since the monitoring of current systems is mainly limited to hydrologic performance.

The proposed research has a strong potential to shift current engineering practice by developing generalized design parameters and a methodology for finding the most effective media-plant combinations for a specific region’s biofiltration systems rather than following a theoretically-based general design guidance. It will add the “local component” necessary for environmental solutions into design guidance. It is posited that these location-tailored systems will improve water quality more than systems following general design guidance. Although the current study focuses on the small urban community of Chico, California, the methodology used for determining the most effective media-plant combinations could be used by multiple climatic regions. The life cycle analysis produced in this research will represent benefits and costs for small urban areas and campuses, however the model developed could be adjusted to represent other types of communities by inputting different values for parameters. The project outcomes will serve as guidance materials for the design of future biofiltration systems.

The proposed Phase II research is a natural expansion of the research and partnerships initiated during Phase I and will be conducted both in the laboratory and in the field. Long-term (18-month) laboratory experiments will extend investigations from Phase I in order to identify optimal plant-media combinations and design configurations to achieve resilient biofilter designs. In-depth monitoring of biofiltration systems on Chico area college campuses (CSU Chico and Butte College) will assess long-term hydrologic and pollutant removal performance of existing biofilters. In addition, a life cycle analysis will be completed during Phase II in more detail than in Phase I. Increased public awareness about urban green water infrastructure will be achieved through regular education outreach events in the local community.


The team examined theoretical benefits of biofiltration systems through a literature review and consultations with the current president of the local branch of the American Society of Civil Engineers (ASCE). They gained applied knowledge of an existing biofiltration project through their involvement in the revegetation of the Biofiltration Wetland Educational Living Laboratory (BWELL) bioswale at the local community college, Butte College.

To best design laboratory tests, stormwater runoff was sampled at two locations on CSU Chico campus and characterized chemically with a suite of analyses. Water quality of stormwater on CSU Chico campus was good overall, except for a few elevated metals found above Environmental Screening Levels defined by California EPA.

Biofilter test columns were built out of PVC pipe capped at one end and equipped with a drain pipe. All biofilters consisted of the following layers, starting at the bottom: 2 cm of pebbles (for drainage), 1 cm of fine sand (for particles retention), 22 cm of “filtration mix” (test variable), 10 cm of mulch, 3-4 sedges, and a monolayer of lava rock (to prevent mulch erosion). The “filtration mix” was one of five combinations of coarse playground sand and soil. These five filter media combinations were built in triplicates for a total of 15 biofilter columns. The infiltration rate of the constructed biofilters was evaluated. Water drainage was found to be fastest in the biofilters made of sand only, while mixtures of sand and oil resulted in slower drainage. Compaction of filtration media was identified as a key parameter during the construction of biofilters. Additional tests were recommended to better understand important design factors, since compaction is unavoidable during construction of biofiltration systems. Further testing is also necessary to study the effects of repeated storms (biofilter resiliency over time) and of high sediment concentrations in stormwater on biofilter infiltration capacity.

The effect of biofiltration on stormwater composition was evaluated during laboratory tests. A synthetic storm runoff was prepared based on the composition of stormwater sampled on CSU Chico campus. Synthetic runoff was applied to the biofilter test columns composed of various combinations of sand and soil mixtures in their filtration layer.

Biofilters were generally very successful at improving stormwater quality and there were few differences between filter media combinations. The biofiltration process neutralized and aerated storm runoff, which contribute to beneficial conditions for aquatic life. Although salinity was increased by biofiltration, it stayed within an acceptable range for aquatic organisms. Turbidity decreased in all biofilters, except in the columns with filtration layers made of pure sand. The sand filters also released additional nitrate and phosphate in the synthetic runoff, which could have strong negative impacts on aquatic ecosystems. All biofilters efficiently removed ammonium and metals from the synthetic stormwater, even when working with synthetic stormwater with concentrations orders of magnitude larger than concentrations measured in campus stormwater.

Due to time limitations, plant tests and the life cycle analysis will be accomplished during the second part of Phase I. The team presented their results at “This Way To Sustainability” Conference on March 25, 2016 at CSU Chico. They will also formally present their results to the campus Sustainability Committee and City of Chico officials in May and August 2016. Outreach activities will be prepared and implemented for various audiences at the National Sustainable Design Expo in April 2016 and at the CSU Chico Hands-On Lab (grades K-9). For these educational outreach events, a biofiltration infographics will be prepared in addition to hands-on demonstrations. Finally the “Biofiltration Guidelines for Small Cities” guidance pamphlet and a final project report will be prepared during the summer.

Expected Results:

Over the first six months of Phase I of the project, the student team successfully examined the theoretical benefits of biofiltration systems, identified critical design factors, and determined effective media combinations with a series of laboratory experiments. Results from Phase I demonstrated that biofiltration systems offer quantifiable benefits to people, prosperity and the planet. Biofilters were able to remove over 98% of the metals copper, nickel, and zinc. Stormwater quality was generally improved during biofiltration, resulting in decreased turbidity, neutralized and oxygenated water, which directly improve the health of aquatic ecosystems. Increased water quality not only benefits aquatic organisms, but also provides economic benefits to downstream urban and agricultural users, reducing drinking water treatment costs and pollutant impacts on crops in the agricultural Central Valley. To further our understanding of key biofilter design parameters necessary to achieve a performing system, a more in-depth characterization of pollutant fate in filter media and plants is necessary. Similarly, long-term experiments assessing the resiliency of biofiltration systems are critical to identifying the key components to a sustainable design for this green urban water infrastructure.

Publications and Presentations:

Publications have been submitted on this project: View all 23 publications for this project

Supplemental Keywords:

storm water management; water treatment technology; urban water planning; water filtration; pollutant removal; bioretention; low impact development; best management practices; ecological; hydrological; water cycle; cost benefit assessment; environmental education.

Relevant Websites:

California State University, Chico Press Release:  Students Awarded Grant to Develop Sustainable Storm Water Filters Exit

Center for Water and the Environment Exit

Local TV News cast (KRCR): California State University, Chico Students recieve $15,000 grant to make Chico and other small cities more sustainable Exit

Progress and Final Reports:

  • 2017 Progress Report
  • 2018 Progress Report
  • Final Report

  • P3 Phase I:

    Evaluating Biofiltration in Small Urban Areas: Chico, California Case Study  | Final Report