The DC Bioretention Cells EarthCache

Have you ever wondered how large cities (DC In particular) manage to keep large gardens proliferating around their buildings? If you have then this is the cache for you! If not, prepare to learn anyway! For more information on this cache, please visit: http://epa.gov/greeningepa/stormwater

Background Information:

In front of you is one of many Bioretntion Cells, also known as "Rain Gardens," located in the greater Washington DC area. Bioretention is not only a way to create asthetically pleasing gardens, it is also a way to treat poluted stormwater in a natural way. As the EPA states on their website: 

Bioretention is a best management practice (BMP) developed in the early 1990's by the Prince George's County, MD, Department of Environmental Resources (PGDER). Bioretention utilizes soils and both woody and herbaceous plants to remove pollutants from storm water runoff. Runoff is conveyed as sheet flow to the treatment area, which consists of a grass buffer strip, sand bed, ponding area, organic layer or mulch layer, planting soil, and plants. Runoff passes first over or through a sand bed, which slows the runoff's velocity, distributes it evenly along the length of the ponding area, which consists of a surface organic layer and/or ground cover and the underlying planting soil. The ponding area is graded, its center depressed. Water is ponded to a depth of 15 centimeters (6 inches) and gradually infiltrates the bioretention area or is evapotranspired. The bioretention area is graded to divert excess runoff away from itself. Stored water in the bioretention area planting soil exfiltrates over a period of days into the underlying soils. The basic bioretention design shown in can be modified to accommodate more specific needs. The City of Alexandria, VA, has modified the bioretention BMP design to include an underdrain within the sand bed to collect the infiltrated water and discharge it to a downstream sewer system. This modification was required because impervious subsoils and marine clays prevented complete infiltration in the soil system. This modified design makes the bioretention area act more as a filter that discharges treated water than as an infiltration device. Design modifications are also being reviewed that will potentially include both aerobic and anaerobic zones in the treatment area. The anaerobic zone will promote denitrification.  

What this boils down to is that Rain Gardens are a man made features which help filter pollutants out of water before the runoff is returned to the water table or nearby river systems. This is an aesthetically pleasing feature which serves a utility purpose as well!

To Log the Find:

Read through the information provided at GZ to determine the answers to the below questions and message me via the message center with the answers. You do not need to wait for a reply from me to log the smiley, however I will contact you if there is a problem with your answers. 

1. When a rain garden is created an area is excavated and filled with what type of stone?
2. Why are plants essential to include in making a rain garden?
3. The plants that are selected should be tolerant to what two types of environmental conditions?
4. Optional: Take a picture of the rain garden and/or yourself at the garden and post it with your logs.

I hope you've enjoyed this Earthcache, this is my second earthcache.

Other Earthcaches by STNolan:

1. GC5TFRE: The Ross Sea Earthcache
2. GC6J68X: The Hood Canal Watershed Earthcache
3. GC6X15G: Honeycombing at Laguna Beach
4. GC6QZEK: Lava Dams of the Grand Canyon Earthcache

First To Find:

Congratulations to UnusualSuspect for the First to Find!