Stormwater Best Management Practices: Guidance Document

Stormwater Best Management Practices: Guidance Document

January 2013

Stormwater Best Management Practices: Guidance Document

Revised by: Boston Water and Sewer Commission 980 Harrison Avenue Boston, MA 02119 and Prepared by: Geosyntec Consultants 289 Great Road, Suite 105 Acton, MA 01775

Stormwater Best Management Practices (BMP) Proposal and Guidance Document [THIS PAGE INTENTIONALLY LEFT BLANK]

2 | Page

Stormwater Best Management Practices (BMP) Proposal and Guidance Document

TABLE OF CONTENTS

1.0 Selection of BMPs for an Urban Environment............................................................................................... 4

1.1 Purpose..................................................................................................................................................................... 4

1.2 General Considerations ..................................................................................................................................... 5

1.3 BMP Selection Matrix.......................................................................................................................................... 8

2.0 BMP Fact Sheets......................................................................................................................................................... 9

3.0 Technical guidance ................................................................................................................................................. 10

3.1 Green Infrastructure and Low Impact Development Techniques .................................................10

3.2 Massachusetts Stormwater Standards......................................................................................................11

3.3 Priority Pollutants..............................................................................................................................................19

3.4 Evaluation Methods for BMPs.......................................................................................................................22

4.0

References............................................................................................................................................................. 23

APPENDICES

APPENDIX A: BMP Selection Matrix ............................................................................................................................ A-1

APPENDIX B: BMP Fact Sheets

1. Vegetated filter strip ....................................................................................................................................... B-1

2. Hydrodynamic separators............................................................................................................................ B-3

3. Baffle box ............................................................................................................................................................. B-5

4. Bioretention........................................................................................................................................................ B-7

5. Planter box .......................................................................................................................................................... B-9

APPENDIX C: Massachusetts Stormwater Handbook - 2008 ............................................................................ C-1

APPENDIX D: Stormwater Best Management Practices (BMP) Performance Analysis..................... D-1

3 | Page

Stormwater Best Management Practices (BMP) Proposal and Guidance Document

1.0 SELECTION OF BMPS FOR AN URBAN ENVIRONMENT

1.1 PURPOSE

The purpose of this Stormwater Best Management Practices ("BMPs") Proposal and Guidance Document propose a suite of generic stormwater BMPs for potential application by the Boston Water and Sewer Commission ("BWSC") pursuant to Section VII, Part D, Paragraph 25 of the Consent Decree lodged in Conservation Law Foundation et al, v. Boston Water and Sewer Commission, U.S. District Court Civil Action No. 1:10-cv-10250-RGS. This document will identify a suite of proposed stormwater BMPS to address the range of known pollutant discharges, including general information, sizing requirements, critical design parameters and BMPs that are scalable as appropriate to match the discharge volumes, pollutant loads, sub-catchment areas served and anticipated site conditions within each sub-catchment area found within the BWSC's Municipal Separate Storm Water System (BWSC MS4). This proposal emphasizes structural BMPs incorporating both Green-Infrastructure ("GI") and Low-Impact Development ("LID") techniques. This BMP Proposal and Guidance Document will be used by BWSC during site plan review of development projects and when designing capital improvements to institute available BMPs (whether GI or LID) in both public and private development. This document contains discussion on selection of BMPs, fact sheets for a variety of BMPs, a BMP selection matrix, and a technical guidance section that focuses on Low Impact Development Techniques (LID), urban stormwater pollutants, current Massachusetts stormwater standards, and BMP design and sizing techniques. This document will also incorporate the standards found in Volume 2, Chapter 2 of the "Massachusetts Stormwater Handbook" (2008); as well as, the Stormwater Best Management Practices (BMP) Performance Analysis" (December 2008, revised March 2010) prepared by Tetra Tech for U.S. EPA Region 1. This document was originally prepared by Geosyntec in October 2011, but was revised and updated by the BWSC in January 2013. BWSC will continue to update this BMP Proposal and Guidance Document as appropriate as new technologies and applications are more widely employed and tested in the City of Boston and other urban areas.

4 | Page

Stormwater Best Management Practices (BMP) Proposal and Guidance Document

1.2 GENERAL CONSIDERATIONS

An integral step in selecting suitable BMPs for a site within the BWSC MS4 is to assess the existing site conditions. This section focuses on a number of factors that should be considered in regards to the implementation of BMPs in an ultra-urban environment as the BWSC MS4.

Site Suitability

There are a wide range of BMPs available, from rain barrels that require little space to constructed stormwater wetlands that require a much larger footprint. The scale of the BMP is directly related to the size of the construction project. For example, it may be impractical for private landowners of a brownstone in Back Bay to be required to design and install a stormwater wetland for a redevelopment project. However, private landowners could install rain barrels or planter boxes, to capture roof runoff and use for on-site watering demands. Parks or grassed areas adjacent to roadways may be ideal location for the implementation of larger scale BMPs such as a water quality swales or bio-retention areas.

Physical constraints at a site may include soil conditions, watershed size, depth to water table, depth to bedrock and slope. For redevelopment projects, physical constraints may include already compacted soils or the location of underground utilities. Even with physical site constraints, BMPs can be modified and adapted to fit a site needs with site planning and design to meet the applicable stormwater standards.

The BMP selection matrix, found in Section 1.3, contains a column labeled "General Suitability" that designates whether specific BMPs are potentially suitable for private landowners, public property (i.e. parks, sidewalks, roadways, etc.) or both land uses.

Soils

Soils regulate the process of surface runoff, infiltration and percolation, and are a major controlling factor in evapotranspiration through the capacity of the soil to store and release water. Furthermore, soils play an important role in removing pollutants from the water column via sorption to soil particles. The characteristics of soils at any particular site should be carefully considered during site planning.

Soil types and subsequent infiltration rates in the BWSC MS4 Area vary widely and can include glacial till, a wide variety of fill types, possible contamination, organic material such as blue clay, and bedrock such as Roxbury Conglomerate. As a result, soils should be evaluated carefully at each site and BMPs that provide groundwater recharge (i.e., dry wells) should be selected only if the site is comprised of soils that meet the infiltration requirements stated in the Massachusetts (MA) Stormwater Handbook, attached and incorporated herein as Appendix C-1.

5 | Page

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download