Redahegn Sileshi

Assessing the Impact of Soil Media Characteristics on Stormwater Bioinfiltration Device Performance: Lab and Field Studies

Bioinfiltration devices are a potentially effective option for the treatment and discharge of stormwater runoff from urban areas. However, the performance of these systems and other infiltration devices can be affected by factors such as texture, structure and degree of compaction of the media during their construction. The main goal of this study is to provide insight on media characteristics of a poorly operating biofilter facility located in Tuscaloosa, AL. Double ring infiltrometer tests and soil compaction measurements were conducted along a large biofilter to determine the in-situ characteristics of the media. Infiltration observations were also made during actual rain events. The effects of different compaction levels on the infiltration rates through the soil media were examined during laboratory column tests for comparison to the field observations. Similar tests were also conducted examining compaction effects of the media after mixing with varying amounts of filter sand to investigate restoration options. These results indicate that soil compaction has dramatic effects on the infiltration rates; therefore care needs to be taken during stormwater treatment facilities construction to minimize detrimental compaction effects.

Enhanced biofilter treatment of stormwater by optimizing the residence time.

The treatment of stormwater by biofilters is dependent on the hydraulic residence time in the device for some critical pollutants. The effective use of biofilters for the control of stormwater in combined sewered areas is also related to residence time, as it is desired to retain the water before discharge to the drainage system in order to reduce the peak flows to the treatment plant. This paper will describe the initial results from a series of tests being conducted to determine the hydraulic characteristics of sand-based filter media (having a variety of particles sizes representing a range of median particle sizes and uniformity coefficients) during pilot-scale trench tests. The drainage rate in biofiltration devices is usually controlled using an underdrain that is restricted with a small orifice or other flow-moderating component. These frequently fail as the orifices are usually very small (<10 mm) and are prone to clogging. A series of tests are also being conducted using a newly developed foundation drain material (SmartDrain) that offers promise as a low flow control device with minimal clogging potential. A pilot-scale biofilter using a trough 3m long and 0.6 x 0.6m in cross section is being used to test the variables affecting the drainage characteristics of the underdrain material (such as length, slope, hydraulic head, and type of sand media). Current tests are also being conducted to test the clogging potential of this drainage material. This paper describes the initial tests that have investigated the basic hydraulic properties and the clogging potential of this drain material.

Impacts of Soil Media Characteristics on Stormwater Biofiltration System Performance

Stormwater bioinfiltration systems can be effective options for the treatment and disposal of stormwater runoff from urban areas. However, the performance of these systems and other infiltration devices can be affected by factors such as texture, structure and degree of compaction of the treatment media. This study provides insights on media characteristics of a poorly operating biofilter facility located in Tuscaloosa, AL, along with supporting laboratory investigations. Double ring infiltrometer tests and soil compaction measurements were conducted along a large biofilter to determine the in-situ infiltration and compaction characteristics of the media. Infiltration measurements were also made during actual rain events by observing falling water levels in ponded areas. The effects of different compaction levels on the infiltration rates through the soil media were also examined during controlled laboratory column tests for comparison to the field observations. Similar tests were also conducted examining compaction effects of the media after mixing with varying amounts of filter sand to investigate restoration options. These results indicate that soil compaction results in increased bulk densities, decreased moisture capacities and has dramatic effects on the infiltration rates.

Flow Rate and Sediment Trapping Laboratory Experiments using Various Biofilter Media

Appropriate hydraulic characteristics of the filter media, including treatment flow rate, clogging capacity, and water contact time are critical for optimal performance of stormwater biofiltration systems in urban areas. A series of controlled laboratory column flow tests were conducted using sand-peat mixture, Tuscaloosa surface and subsurface soils, along with media from current Kansas City, North Carolina, and Wisconsin biofilters. Besides the flow tests, sediment-trapping experiments were also performed for the sand-peat media mixtures and Tuscaloosa soils using challenge water. The laboratory tests indicated that compaction has a significant effect on the infiltration rates; however, amending the sand mixtures with peat reduced the degraded flow rate effects associated with compaction. The particle-trapping experiments indicated that significant particulate trapping occurred for most lab columns with little difference for the different column media mixtures. However, columns with local area soils had increased discharges of very small particle sizes compared with the influent water due to washing of the fines from the media.

Laboratory Column Test for Predicting Changes in Flow with Changes in Various Biofilter Mixtures

The performance of biofiltration and other infiltration systems in urban areas is affected by factors such as media particle size distributions and uniformity,…

Stormwater Management in the Aftermath of Natural Disasters

After the April 17, 2011 tornado that devastated the City of Tuscaloosa, AL, community leaders, business owners, and homeowners all wanted to rebuild as soon as possible. There were a number of issues that needed to be addressed, including providing safe housing for affected people and initial massive cleanup of the destroyed areas and drainage conveyances. Financial hardships also caused delays in reconstruction in many areas. After more than a year, many of the damaged homes and business have been repaired, and some of the destroyed sites have now been rebuilt, but many areas are still vacant. One of the issues needing to be addressed by the land owners is compliance with new building code provisions, including some that affect stormwater management. Over the years, various stormwater research activities have been conducted in the Tuscaloosa area, including land development surveys and development of effective remote sensing techniques, inappropriate discharge detection research, stream sediment contamination, advanced stormwater treatment development and testing, urban bacteria sources and fates, and stormwater characterization monitoring. One area of special interest and need to support the redevelopment activities is the role of disturbed urban soils and the design of infiltration systems in compacted soil areas. This paper focuses on the role of urban soils and the designs and expected performance of infiltration facilities, especially how they can be most suitably sized and located in small commercial establishments. Special surface and subsurface infiltration tests were conducted soon after the tornado for comparison with our earlier work to assist in the development of performance production functions for the types of infiltration facilities most suitable for the area and soils.

Examining the Clogging Potential of Underdrain Material for Stormwater Biofilter

The drainage rates in biofiltration devices are usually controlled using an underdrain that is restricted with a small orifice or other flow-moderating component. These frequently fail, as effective orifices that are used for flow control are usually very small (< 10 mm) and are prone to clogging over time. The main goal of this study is to evaluate the performance of a foundation drain material (SmartDrain TM ) under a variety of challenging conditions. SmartDrains TM work by capillary action, requiring very little head to initiate flow through the use of a siphon. This paper will present the results from a series of tests conducted to determine the flow capacity and clogging potential of the SmartDrain TM material during biofouling experiments under controlled pilot-scale biofilter conditions. A pilot-scale biofilter that consists of a tall Formica-lined plywood box, 0.90 m by 0.85 m in cross sectional area and 1.20 m tall was used for the tests. The tests were conducted using two different species of green algal that were encouraged to grow in the biofilter device for several weeks before draining. The results indicated that the biofouling had only a small effect on the discharge rates, even though the algal growth was extensive. Prior tests evaluated the SmartDrain TM performance after excessive loadings by fine ground silica particulates (Sileshi et al., 2010b) and also for a range of length and slopes using clean water