Frequency of Maintenance Needs in Biofilters throughout Los Angeles

Abstract Biofilters are one of the most common stormwater control measures (SCMs) in the US. Ongoing operation and maintenance (O&amp;M) is necessary to ensure biofilters function properly and optimize hydrologic retention and water quality treatment performance. The need for O&amp;M can result from poor design or construction, accumulation of trash and debris, blocked inlets or outlets, aging of engineered media, poor vegetation condition or invasive plants, and animal waste or illegal discharges, among others. In this study we created a field deployable rapid assessment survey ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="less than or equals 1 normal h" display="inline" overflow="scroll"> <mml:mtext>≤</mml:mtext> <mml:mn>1</mml:mn> <mml:mtext> </mml:mtext> <mml:mi mathvariant="normal">h</mml:mi> </mml:math> ) to evaluate nine metrics of biofilter functionality. We tested the rapid assessment survey across 30 biofilters throughout urban Los Angeles. Rapid assessment surveys indicated that 93% of the biofilters were in need of at least one O&amp;M activity to operate as expected, and 73% were in need of at least three types of O&amp;M activities. Of the nine key O&amp;M metrics surveyed at each biofilter, the most common needs were to increase mulch quality and coverage (66%), remove invasive vegetation (63%), and unclog inlet drains (45%). Biofilters <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="less than 6 y e a r s" display="inline" overflow="scroll"> <mml:mtext>&lt;</mml:mtext> <mml:mn>6</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>years</mml:mi> </mml:math> old tended to be in better condition than biofilters <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="greater than or equals 7 y e a r s" display="inline" overflow="scroll"> <mml:mtext>≥</mml:mtext> <mml:mn>7</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>years</mml:mi> </mml:math> old, but similar O&amp;M needs were found regardless of age. The biofilters needing the greatest O&amp;M effort were clustered by jurisdiction, indicating that some municipalities invest more in O&amp;M than others. This technical note shows that a rapid assessment survey taking less than 1 h can be a valuable tool for identifying biofilter O&amp;M needs.