Rebecca Stack is a civil engineer, educator, and principal of Designgreen. She is an experienced designer of complex green infrastructure. As a former code official, her contributions to greening the District’s regulations extended from building codes to guidance manuals. This included co-authoring the District of Columbia’s stormwater retention standard. Her firm is the current administrator of DC’s green roof incentive program. Rebecca is committed to aligning her work with positive social impact outcomes and the integration of natural resources within the urban landscape.
Lily discussed storm water requirements in Arlington County. There are both voluntary and regulatory Best Management Practices (BMPs). She spoke about communicating storm water goals to the landscape client as well as the benefits of planting natives, and the benefits to wildlife of both. She stated that Arlington will soon provide a list of BMPs on real-estate listings. When doing various green projects such as permeable paving and rain gardens, anticipate – avoid – prevent the typical problems such as sediment clogging on paving and compaction of the rain garden area by using heavy equipment. She spoke about designing for maintenance of the site including planting densely or using green mulch to avoid weeds. Finally, she mentioned controlling the cost of design by using plugs vs quarts vs gallons in the right places and also obtaining woody plants from Earth Singha or Fairfax ReLeaf.
Chris began his presentation by showing a website called the USDA Web Soil Survey. It can be used to find the location of a new landscape project by outlining a polygon around the site and it will provide information of what kind of soil is in the location. He then discussed some specifics on designing a rain garden, starting with doing infiltration testing. This consists of digging a hole to the depth of the rain garden and a little deeper. Presoak this hole by filling with water 24 hours before the test. Now the soil has been saturated and the actual ability to infiltrate water can be ascertained. Next fill the hole again and see how long it takes for the water to be fully absorbed. It should be within 48-72hours for a good rain garden location. Otherwise the garden will be more of a pond and would breed mosquitoes. For the construction of the garden a flat subgrade is needed. This ensures even absorption of the water. Excavate the area from outside of the infiltration area to avoid compacting the soil and use a toothed bucket if a backhoe is needed. If a smooth bucket is used it acts to create a surface that does not allow water infiltration. Protect the area from run-off until it is ready to “go on-line”. Also, its good idea to familiarize the owner with the regulatory aspects of the rain garden. Finally, he recommends including off-line design to take the extra water when the rain garden if full during a larger rain event.
Fairfax County Soil Information Guide https://www.fairfaxcounty.gov/soil-water-conservation/soils-info