This document describes the design and construction of a rain garden/bioretention cell project. The project involved excavating an area to create a rain garden that would retain and slowly filter stormwater runoff. Key steps included installing sediment controls, grading the site, adding an underdrain system and layers of aggregate and amended soil, and planting vegetation. Photos show the project's construction progress and performance after large rain events.

1. Rain Garden/Bioretention Cell
• LOW POINT IN A
SMALL WATERSHED
AREA - .37 ACRES
• LITTLE IMPERVIOUS
SURFACE IN
WATERSHED
• POORLY DRAINED
• EXISTING CATCH
BASIN
BEFORE
Green Pilot Project 1

2. Rain Garden/Bioretention Cell
• FOREBAY OF RIVER
STONE TO PREVENT
SEDIMENTATION
• GRADE REQUIRED
BOULDERS TO
SHORE UP SLOPE
DESIGN
Green Pilot Project 1

3. Rain Garden/Bioretention Cell
• DESIGNED TO
RETAIN AND SLOWLY
FILTER WATER
• DESIGNED TO
ABSORB THE FIRST
FLUSH (1.2”) OF ALL
STORM EVENTS
DESIGN
Green Pilot Project 1

4. Rain Garden/Bioretention Cell
TYPICAL CONSTRUCTION SEQUENCE
1. Install sediment control devices as shown on the plans.
2. Grade site to elevations shown on plan. Construct curb openings, and/or
remove and replace existing concrete as specified on the plan. Measures
should be taken to prohibit drainage from entering construction area. At the
end of each workday, all excavations shall be protected by
construction safety fencing or temporary backfill as needed.
3. Stabilize grading within Limit of Disturbance except for Bioretention Area
itself.
4. Excavate bioretention area to proposed invert depth and scarify the existing
soil surfaces, taking care not to compact existing grade.
5. Install underdrain system and observation wells, if specified
6. Backfill with planting soil as shown in the plans and detailed in the
specifications, leaving space for the upper layer of mulch. (Overfilling is
recommended to account for settlement.)
7. Presoak the soil prior to planting, to allow for settlement.
8. Plant vegetation specified in the planting plan for Bioretention Area.
9. Mulch and install erosion protection at entrance points.
Green Pilot Project 1

5. Rain Garden/Bioretention Cell
Step 1
SEDIMENT CONTROL
IN PROGRESS
Green Pilot Project 1

6. Rain Garden/Bioretention Cell
Step 2
EXCAVATION/GRADING
IN PROGRESS
Green Pilot Project 1

7. Rain Garden/Bioretention Cell
Step 3
FILTER FABRIC,
OBSERVATION WELLS
IN PROGRESS
Green Pilot Project 1

8. Rain Garden/Bioretention Cell
Step 4
RIVER STONE FOREBAY
IS IN PLACE, DRAIN
LINES ARE INSTALLED.
FIRST AGGREGATE
LAYER IS BEING
INSTALLED
NOTE: THERE IS NO
STORAGE LAYER IN THIS
DESIGN.
IN PROGRESS
Green Pilot Project 1

9. Rain Garden/Bioretention Cell
Step 5
CHOKER LAYER OF
AGGREGATE IS BEING
SPREAD. NOTICE THE
CARE TO KEEP
SEDIMENT OFF OF THE
AGGREGATE.
IN PROGRESS
Green Pilot Project 1

10. Rain Garden/Bioretention Cell
Step 6
MIXING THE
AMENDMENT INTO
RESERVED TOPSOIL
IN PROGRESS
Green Pilot Project 1

11. Rain Garden/Bioretention Cell
Step 7
PLANTED
MARCH/APRIL, 2008
Green Pilot Project 1

12. Rain Garden/Bioretention Cell
MAY, 2008
Green Pilot Project 1

13. Rain Garden/Bioretention Cell
SEPT 23, 2009
AFTER THE GREAT FLOOD!
NO STANDING WATER
Green Pilot Project 1

14. Rain Garden/Bioretention Cell
JUNE 14, 2010
Green Pilot Project 1