Bioinfiltration and bioretention best management practices (BMPs) are stormwater management tools with enormous and cost-effective benefits, according to recent research. Biofiltration is a key component in the low-impact development (LID) approach to managing stormwater.  Bioretention facilities are small, landscaped basins intended to provide water quality management by filtering storm water runoff before releasing into storm drain systems. Bioretention utilizes soils and both woody and herbaceous plants to remove pollutants from storm water runoff. The soil mix used for bioretention systems is central for determining flow control and water quality treatment performance.  To perform properly, the soil must provide the desired infiltration rate, support vegetation and soil biota, and provide water quality treatment.

Specifications for biofiltration soil are outlined by each state. In the state of Delaware, the Delaware Department of Natural Resources and Environmental Control (DNREC), grants certifications to suppliers who have been approved after a testing process.  Suppliers seeking approval must demonstrate not only that soil conforms to the proper mixture ratios, but that they have the appropriate equipment to mix the material, proper storage to keep it dry and free of debris. More specifically, the medium must be a uniform mix, free of stones, stumps, roots or other similar objects larger than two inches and filter medium planting soil must be a uniform mix of equal parts by volume of the following: Clean Concrete Sand, Peat Moss, Triple Shredded Hardwood Mulch (Well Aged – Stockpiled – 6 to 12 Month).

DNREC certified bioretention soil suppliers are listed on the DNREC website: learn more..

In the State of Delaware, bioretention soil may only be supplied from biosoil-certified vendors. Moon Nurseries is a certified vendor for bioretention soil.

In early 2008, Moon Nurseries submitted samples of its bioretention soil mixture (BSM) to a DNREC approved laboratory (Duffield Associates, Consultants in the Geosciences) to obtain certification of its biosoil medium.  Laboratory testing was performed on a representative sample of biofiltration soil to evaluate general conformance of the sample provided with DNREC – Soil and Water Conservation Division’s requirements for biofiltration soil.

Laboratory testing consisted of Particle Size Analysis (ASTM D 422) and Hydraulic Conductivity (ASTM D 5856, Constant Head Method) determination on sample provided. The laboratory performed particle size analysis and hydraulic conductivity testing to review the soil sample for the following DNREC requirements:

• a mix consisting of equal parts by volume of triple-shredded hardwood mulch, peat moss, and clean concrete sand meeting the requirements of AASHTO M-6 or ASTM C-33;
  and
• An infiltration rate of 5 inches per hour

The laboratory concluded that all Mix Components, Sand Gradation, and Infiltration Rate met or exceeded the DNREC required standards. Moon Nurseries has been a reliable, certified supplier of bioretention soil to the Delaware area ever since.

Contact us with your low-impact development or stormwater management needs and we will be happy to explain how Moon Nurseries can help you effectively and economically reach your goals.

• http://www.swc.dnrec.delaware.gov/
  Drainage/ Documents/Sediment%20and%20
  Stormwater%20Program/ Approved_Biosoil_Suppliers4.02.09.pdf
• http://www.epa.gov/owmitnet/mtb/
  biortn.pdf
• http://www.epa.gov/nps/
  bioretention.pdf
• http://www.cabmphandbooks.com/Documents/
  Development/TC-32.pdf
• http://www.stormh2o.com/october-2007/maryland-impact-development.aspx
• http://www.lowimpactdevelopment.org/epa03/
  biospec.htm
• http://psplid.blogspot.com/2009/03/new-bioretention-soil-mix-guidelines.html
• http://www.dnrec.state.de.us/dnrec2000/
  Divisions/Soil/stormwater/
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• http://www.swc.dnrec.delaware.gov/Pages/
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