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Chapter 4
Treatment BMPs
1.0 Overview
UDFCD has established design criteria, procedures, and details Treatment BMPs in Volume 3
for a number of BMPs providing treatment of post-construction
urban runoff. Additionally, general guidance has been
• Grass Swale
developed and included for green roofs and underground BMPs.
As discussed in Chapter 2, BMPs provide treatment through a
• Grass Buffer
variety of hydrologic, physical, biological, and chemical • Bioretention (Rain Garden) 1
processes. The functions provided by BMPs may include
volume reduction, treatment and slow release of the water • Green Roof
quality capture volume (WQCV), and combined water
quality/flood detention. Ideally, site designs will include a
• Extended Detention Basin
variety of source control and treatment BMPs combined in a • Retention Pond
"treatment train" that controls pollutants at their sources,
reduces runoff volumes, and treats pollutants in runoff. Sites • Sand Filter Basin
that are well designed for treatment of urban runoff will include
all of the steps in the Four Step Process discussed in Chapter 1.
• Constructed Wetland Pond
Building upon concepts and procedures introduced in Chapters
• Constructed Wetland Channel
1 through 3, this chapter provides design procedures for
• Permeable Pavement Systems
treatment BMPs. Table 4-1 provides a qualitative overview of
key aspects of the post-construction treatment BMPs included in • Underground Practices
this chapter. The table includes the degree to which the BMP is 1 Also known as Porous Landscape
able to provide various functions, general effectiveness for Detention
treating targeted pollutants and other considerations such as life
cycle costs. The table indicates which BMPs provide a conveyance function or a WQCV function. This
distinction is important because not all treatment BMPs provide the WQCV. Wherever practical,
combinations of BMPs in a treatment train approach are recommended. For example, BMPs that provide
sedimentation functions can potentially improve the lifespan and reduce the maintenance frequency of
filtration-oriented BMPs when the two BMPs are paired in series. Table 4-1 is based on best professional
judgment from experiences in the Denver area along with data from the International Stormwater BMP
Database (www.bmpdatabase.org) and is intended for general guidance only. Specific BMP designs and
site-specific conditions may result in performance that differs from the general information provided in
the table. In the case of underground and proprietary BMPs, wide variations in unit treatment processes
make it difficult to provide generalized characterizations. Additionally, with regard to pollutant removal,
in some cases, BMPs may be able to reduce pollutant concentrations, but this does not necessarily mean
that the BMPs are able to treat runoff to numeric stream standards. For example, various studies have
indicated that bioretention and retention pond BMPs may be able to reduce fecal indicator bacteria in
urban runoff, but not necessarily meet instream primary contact recreational standards (WWE and
Geosyntec 2010).
After reviewing physical site constraints, treatment objectives, master plans, and other factors, the
designer can select the BMPs for implementation at the site and complete the engineering calculations
and specifications for the selected BMPs. This chapter provides Fact Sheets for treatment BMPs that can
be used in conjunction with the WQCV and volume reduction calculations in Chapter 3 in order to
properly size and design the BMPs for the site. For new developments and significant redevelopments,
designers should provide treatment of the WQCV with a slow release designed in accordance with criteria
for the selected BMP. Additionally, sites that drain to impaired or sensitive receiving waters or that
include onsite operations requiring additional treatment may need to implement measures that go beyond
the minimum criteria provided in the Fact Sheets in this chapter.
November 2010 Urban Drainage and Flood Control District 4-1
Urban Storm Drainage Criteria Manual Volume 3