Search

This collection contains 22 papers addressing low impact development technology presented at the 2011 Low Impact Development Conference, held in Philadelphia, Pennsylvania, September 25-28, 2011.

This collection contains nine papers addressing the implementation of low impact development technologies presented at the 2011 Low Impact Development Conference, held in Philadelphia, Pennsylvania, September 25-28, 2011.

Urban stormwater runoff contributes to the degradation of receiving surface waters and groundwater. This degradation is caused both by the increased flows that result from urbanization (i.e., the conversion of land surfaces from being infiltration zones to impervious zones) and by the pollutants (chemical and microbiological) that are carried by runoff. Stormwater management aims to address these problems. It is a fundamental component of site development for new construction and often is required to the maximum extent practicable for redevelopment of urban/suburban lands to minimize/remediate the impacts of urbanization. To assist practitioners of stormwater management (engineers, regulators, plan reviewers, etc.), many regulatory agencies have developed guidance documents to assist in the design of stormwater treatment devices. These manuals typically provide information on approved practices, and many provide information regarding the anticipated performance of these devices to abate flow, targeted pollutants, or both. This Research Digest and the Final Report for project 04SW3 (referred to herein as the “full document”) are not intended to supplant agencies'guidance documents. Instead, they are designed to supplement their content. They also should aid in focusing stormwater management planning, design, and implementation more toward the intended purpose of protecting the receiving water, whether it is ground- or surface water, rather than toward solely fulfilling a regulatory requirement. The documents provide the user with tools to evaluate whether the planned management strategies will meet the regulatory requirement, as well as potentially improving the receiving water quality, or at least preventing degradation. This is a companion piece to the full WERF report 04-SW-3 Infiltration vs. Surface Water Discharge: Guidance for Stormwater Managers.

Available as an eBook only.Stormwater managers are increasingly faced with the need to address many potentially-conflicting issues as part of their activities, ranging from flood prevention to protection of downstream habitat. New urban development philosophies, such as low impact development, no adverse impact, water-sensitive urban drainage systems, etc., establish goals similar to other professions – Do No Harm. This is addressed often through criteria such as maintaining pre-development hydrology to the maximum extent practicable after development with treatment provided to reduce pollutants to their pre-development level. These new management plans incorporate both infiltration and surface treatment/discharge into the development. A series of flowcharts were developed to aid stormwater managers in stepping through the process of selecting an appropriate management/treatment technology that meets both the low-impact goals and the regulatory requirements. These charts refer to the specific document sections that address the issues of concern that should be considered when selecting appropriate stormwater practices. Appendices were developed to provide supporting information for users not familiar with the terminology (Glossary in Appendix A) or the methods and supporting literature. This work has been based on the literature and guidance documents developed around the world. Surface-treatment technologies such as detention and filtration have a long history with much literature published about them. They are better understood than the infiltration practices currently gaining favor. Therefore, several chapters are devoted to the concerns associated with selecting infiltration. The desire to incorporate infiltration raises two potential concerns: 1) acceptance of small-scale infiltration devices, especially by the regulatory authorities, and 2) the potential for groundwater contamination. For the first concern, Appendix B summarizes several references on the issues raised by current stormwater management authorities regarding low impact development and infiltration devices dispersed throughout a watershed. The second concern is that the potential for groundwater contamination is not well-known or documented. Pollutant removal in the subsurface has not been addressed regularly by authors who have either advocated infiltration and/or researched the effectiveness of infiltration at reducing surface water discharge volumes and pollutant loadings, although more recent reports are providing data showing both pollutant removals in the surface discharge, plus subsurface water quality. The third activity under this literature review/guidance document development activity was to identify questions/data gaps in the selection and use of stormwater treatment devices, with a focus on infiltration. The following questions were raised. How effective are current and proposed stormwater management techniques at protecting surface water quality and habitat, as well as protecting groundwater? Groundwater and vadose zone water chemistry information is limited in the literature; it comes primarily from laboratory investigations or basins where the soil has been engineered. Few studies have looked at transport of stormwater-borne pollutants in the vadose zone of non-engineered soils. What soil and water chemistry data should be collected to improve the understanding of pollutant transport? Can water and wastewater treatment theory provide a better foundation in the models that predict BMP performance? Would this reduce the uncertainty that has to be associated with every stormwater pollutant removal calculation? Water and wastewater theory has been applied successfully to the design of sedimentation devices, but it has not been as successful at predicting pollutant removal in filtration or infiltration devices. How do the chemicals secreted by microorganisms affect pollutant mitigation