Water, Wastewater & Stormwater


393538 - Analysis of Loss of Ignition of Root Zone of Bioretention Units at the Edison Environmental Center

Wednesday, June 6
4:00 PM - 5:30 PM
Location: Greenway EF

Six bioretention units (widths 7.1 m) at EPA’s Edison Environmental Center were constructed to evaluate sizing of surface area to watershed area. Three sizes were tested in duplicate with changes in aspect ratio of length from inlet (northern) wall by doubling successive length from smallest (3.7 m) to largest (14.9 m). Each are instrumented for continuous monitoring with water content reflectometers (WCR) and thermistors with monitoring data since November 2009. In late 2012, a survey of shrubs planted in these bioretention units was performed. The combined analyses of moisture content and plant size indicated the smallest units had superior shrub growth due to the more frequent saturation of the root zone as measured by WCR.

In 2017, sediment samples for loss on ignition (LOI) analysis were collected to determine available carbon in the near surface root zone as a secondary proxy for plant health. It was hypothesized that observations of LOI would support the 2012 survey conclusions of shrub sizes in these units.

Samples were taken at a depth of 0.15 m and at 0.3 m intervals along the centerline and starting at the north wall of each bioretention unit. Initial results of three units indicate differences between the northern and southern section of individual units, as well as differences between three unit sizes. The largest LOI values were observed in the smallest unit indicating highest plant density. Although this observation seems to support the stated hypothesis, further sampling and analysis for all six bioretention units is planned.

Thomas Patrick O'Connor, MS, PE, BCEE

Environmental Engineer
U S Environmental Protection Agency

Environmental Engineer
Urban Watershed Management Branch
Work: (732) 321-6723; Fax: (732) 321-6640

Thomas has been an environmental engineer with the U.S. Environmental Protection Agency (EPA), Office of Research and Development (ORD) for 21 years. He currently works for the National Risk Management Research Laboratory, Water Systems Division, Water Resources and recovery Branch (WRRB) Edison, New Jersey. He has conducted research for watershed management and wet-weather flow (WWF), specifically researching WWF control/ treatment technologies and strategies, watershed based strategies, storage and collection system design, sampling and analysis of stormwater best management practices (BMPs), receiving water impacts, characterization of pollutants, stormwater infiltration, stormwater collection and use, cost benefit analysis, retrofitting existing treatment works and systems, green roofs and green infrastructure.

Thomas graduated with an M.S. in Environmental Engineering from Manhattan College in 1993 and a B.S. in Physics 1986. He has written numerous journal articles and reports and is co-author of three book chapters. He is a licensed professional engineer with New York and New Jersey. He is a member of several professional organizations including the American Academy of Environmental Engineers for which he attained status of Board Certified Environmental Engineer. Thomas has received three Bronze Stars in the course of his EPA career. He was named an Outstanding Peer Reviewer for ASCE for years 2014, 2015 and 2016.


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393538 - Analysis of Loss of Ignition of Root Zone of Bioretention Units at the Edison Environmental Center

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