Considerations, Opportunities, and Strategies for Infiltration Stormwater BMPs

Infiltration as a Best Management Practice (BMP) is strongly encouraged by many who are focused on water quality, water resources, and regulatory compliance. It is often considered the ideal solution that solves multiple problems. Many practicing engineers, designers, and project approvers however, are concerned about the widespread implementation of infiltration measures, and have initiated restrictive conditions that significantly limit their use. This paper discusses benefits and considerations that should be made when proposing infiltration BMPs, offers potential methods to meet what can be limiting site conditions, and discusses recent applied research/design efforts that been initiated in southern California. Infiltration has numerous potential benefits, particularly in urbanized watersheds. Infiltration BMPs when implemented properly can lead to a) restoration of natural hydrologic cycles; b) mitigation of the degradation of creeks; c) management of water resources; and d) comprehensive watershed -wide water quality improvement. There are, however, numerous design considerations that should be evaluated when proposing infiltration BMPs. These include a) soil type/infiltration capacity; b) groundwater;, c) pre-existing contamination; d) design and hydraulic issues; e) long-term issues such as groundwater mounding and ground settlement; f) introduction of geological hazards such as landsliding, soil liquefaction and their impacts; and i) other issues such as mold and waterproofing that may result from the presence of wet soil. While many of these considerations can be fatal flaws, in some cases innovative engineering approaches can be implemented to increase the viability of infiltration, particularly where choice of satisfactory alternatives is limited. This paper explores some of these methods and impacts related to implementation of these methods. In addition, some recently initiated projects that are expected to contribute to the body of knowledge regarding infiltration concerns and opportunities, and are worthy of further examination and tracking are outlined.