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ASLESON, NESTINGEN, GULLIVER, HOZALSKI, AND NIEBER
<br />hydrologic changes result in widening and increased
<br />instability of stream channels, increase sediment
<br />loads, and degradation of fish habitat (Booth and
<br />Jackson, 1997). In addition to sediments, urban run-
<br />off often contains a wide variety of other pollutants
<br />including: nutrients, oxygen- demanding substances,
<br />pathogens, road salts, petroleum hydrocarbons, heavy
<br />metals, and excess thermal energy (USEPA, 2005).
<br />Such pollutants could cause further degradation of
<br />aquatic habitat as well as limit or eliminate recrea-
<br />tional uses.
<br />In response to the degraded water quality found in
<br />our waterways due to urban stormwater runoff, the
<br />Clean Water Act requires the regulation of municipal
<br />separate storm sewer systems (MS4s) and the imple-
<br />mentation of a two -phase Storm Water Pollution Pre-
<br />vention Program ( SWPPP) (USEPA, 2007). The
<br />SWPPP requires discharge detection and elimination,
<br />construction and postconstruction runoff control, and
<br />pollution prevention measures. Key to pollution pre-
<br />vention efforts in urban areas are the installation
<br />and maintenance of stormwater best management
<br />practices (BMPs). For example, low impact develop-
<br />ment (LID) stormwater BMPs, such as rain gardens
<br />and bioretention facilities, are commonly used to infil-
<br />trate stormwater to reduce outfall stormwater runoff
<br />volume and improve water quality via filtration and
<br />other processes. These systems are gaining interest
<br />among MS4s due to their low impact, potential effec-
<br />tiveness, and high esthetic value. Currently, there is
<br />little guidance on how to properly assess the effec-
<br />tiveness of LID stormwater BMPs after installation.
<br />Consequently, information is lacking concerning how
<br />well these stormwater BMPs perform immediately
<br />after installation, how they perform over time, and
<br />when maintenance may be required. Guidance is
<br />needed regarding assessment of the effectiveness of
<br />LID stormwater BMPs such as rain gardens.
<br />Currently, comprehensive water quantity and
<br />quality monitoring is the most widely used approach
<br />for evaluating the performance of stormwater BMPs
<br />(USEPA, 2002). Monitoring typically involves the col-
<br />lection of stormwater grab samples for analysis of
<br />pollutant concentration and determination of the
<br />water budget of the BMP using flow measurement
<br />devices at all inflow and outflow locations, data log-
<br />gers, and related equipment. Monitoring is especially
<br />useful for watershed -scale studies to assess overall
<br />pollutant loads to receiving waters and the impact of
<br />a group of stormwater BMPs on these loads. Monitor-
<br />ing of individual stormwater BMPs, however, is often
<br />impractical due to the long time period (one or more
<br />rainy seasons) required to observe a sufficient num-
<br />ber and variety of storm events, the effort to setup
<br />and maintain such a system, and uncertainty in the
<br />results (Weiss et al., 2007) as a natural storm event
<br />can neither be controlled nor repeated. This is espe-
<br />cially true for rain gardens, which are often small
<br />( <150 m simple, stormwater BMPs that are widely
<br />distributed throughout urban and suburban neigh-
<br />borhoods. Therefore, alternatives to typical monitor-
<br />ing protocols are needed for assessing the
<br />performance of rain gardens.
<br />In this paper, we discuss the development and
<br />evaluation of three alternative suggested approaches
<br />for rain garden evaluation: (1) visual inspection, (2)
<br />infiltration rate testing, and (3) synthetic drawdown
<br />testing. These assessment approaches differ in terms
<br />of the effort required and the information obtained.
<br />Visual inspection involves examination of the inlet
<br />and outlet structures, vegetation, and soil and is used
<br />to quickly determine if a rain garden is malfunction-
<br />ing and in need of maintenance or replacement. Infil-
<br />tration rate testing involves the use of infiltrometers
<br />to determine near - surface saturated hydraulic con-
<br />ductivity (Ksat) throughout a rain garden. In synthetic
<br />drawdown testing, a fire hydrant or water truck is
<br />used to fill the basin with water and the overall drain
<br />time of the rain garden is determined. They are
<br />described more fully in the next section.
<br />LEVELS OF ASSESSMENT OVERVIEW
<br />Visual Inspection (Level 1)
<br />The visual inspection may be simple or comprehen-
<br />sive depending on the site conditions and the purpose
<br />of assessment;. Simple observations, such as visiting a
<br />site after a storm event to check for standing water,
<br />are valuable and require less effort (1 h), although
<br />limited information is obtained. A comprehensive
<br />visual inspection requires some knowledge of both
<br />vegetation and soils and requires roughly 4 h to com-
<br />plete. For verification of proper construction and
<br />determination of long -term functionality, it is recom-
<br />mended that additional assessment be performed
<br />even if no problems are found during the visual
<br />inspection. This more detailed assessment will be of
<br />interest to officials that certify rain gardens.
<br />Infiltration Rate Testing (Level 2)
<br />The ability of a rain garden to infiltrate water under
<br />saturated (flooded) conditions can be estimated by
<br />determining Ksat at a number of locations throughout
<br />the stormwater BMP using permeameters or infiltrom-
<br />eters. Five field devices [Double -Ring Infiltrometer,
<br />Guelph Perrneameter (Rickly Hydrological Company,
<br />JAWRA
<br />1020 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION
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