Overview
PWD Stormwater Soil was originally developed by the Philadelphia Water Department as part of a large green infrastructure policy. The PWD Stormwater Soil was designed to mitigate stormwater runoff when used in applications such as rain gardens, bioretention basins and bioswales. The soil is designed to absorb, infiltrate, and filter stormwater runoff into the ground where it can safely recharge groundwater systems and reduce surface flooding. PWD requires blenders to certify their compliance of this mix twice a year. Laurel Valley Soils has been involved with the PWD Green Infrastructure program from inception and has been an approved supplier every year. Many other cities and municipalities have since adopted this well preforming specification. The goal of a bioretention basin is to capture and divert stormwater runoff displaced from impervious surfaces. Well-designed basins also filter out untreated pollutants that otherwise might flow directly into waterways. Many bioretention basins are large in scale and while they can have attractive plantings, these utilitarian designed basins are generally located out of sight, at the low end of a parking lot or downslope from a building or road.
A stormwater management plan is now a requirement with all new construction that creates impervious surfaces. Water must be contained on site or at least slowed down to prevent flooding and pollutant movement. Bioretention basins are part of the building and zoning code and are required for most building projects including renovations and expansions. The understanding and design of these soils is evolving rapidly.
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Ingredients
LVS PWD Stormwater Soil is composed from a mixture of sand, compost, soil, and sometimes mulch, and is designed to meet many specific performance parameters such as soil particle size, structural gradation, infiltration rate, pH and organic matter content. This soil is sometimes designed as a whole system where it is coupled with underdrainage for enhanced performance. Information and design of stormwater, rain garden and bioretention soils is evolving rapidly. The team at Laurel Valley Soils is qualified and happy to offer guidance for Engineers and Landscape Architects in the development or selection of specific bioretention soil solutions and specifications.
Analytical
LVS PWD Stormwater Soil is generally light brown in color, has a light bulk density, and can feel spongy. Often on the sandy side and sometimes containing mulch, this soil has a pH range of 6-7.2 and an average 3-7% organic matter content by weight. With a course sand content over 65% and of clay content of less than 15% this soil will infiltrate at between 2-6 in/hr based on a hydraulic conductivity of 75% Proctor.
Benefits
LVS PWD Stormwater Soil captures, infiltrates, and filters stormwater. It also supports plantings that assist with this process while providing ecologically friendly wildlife habitats and light pollutant absorption.
Benefits at a Glance
- Organic Matter
- Nutrients
- Biology
- Water Holding Capacity
- Improves Soil Structure and Porosity
Applications
LVS PWD Stormwater Soils are often installed in depths ranging from 12-48″. The deeper medias are often installed in lifts that are lightly compacted. The best way to install is when the site conditions allow use of an excavator from outside the basin, a telebelt or a slinger truck. This soil does settle apron instillation and that should be factored into total volumes calculated for ordering on a project.
