RFI - Attachment F - Engineering Report

The Stormwater Management StormFilter® Performance for
Removal of Total Phosphorus

Phosphorus in the Urban Environment
        Phosphorus loading to freshwater can promote algal blooms and eutrophication that
threaten ecosystems by lowering dissolved oxygen levels. As shown in Figure 1, phosphorus
cycles through the environment in forms organic, inorganic and soluble forms.




                      Figure 1. Inorganic and Organic Cycle (RiverWatch, 2001).

         Total phosphorus (TP), expressed in milligrams/liter is the sum of inorganic phosphate,
organic phosphate, and soluble phosphorus (Ortho-P). Organic phosphates are a part of plants
and animals, their wastes or decomposing rem ains. Inorganic phosphorus originates from
decomposing natural materials and man-made products.
         Non-point source runoff (stormwater) increases phosphorus concentrations in lakes and
streams by transporting sediment and organic matter (bud shatter, leaves, lawn clippings, etc.)
from impervious surfaces. Additional phosphorus sources in stormwater are misapplied
fertilizers, some detergents, and animal waste from birds and domestic pets.
         Phosphorus in urban runoff is typically measured as TP and sometimes Ortho-P is
measured as well. The non-soluble portion of the TP is commonly associated with the total
suspended solids (TSS). Of this form, the phosphorus can be in an organic or inorganic form.
TP concentrations in stormwater are variable but range from 0.01 to 7.3 mg/L (Minton, 2002).
Concentrations of Ortho-P in urban runoff are frequently in concentrations ranging from 0.05 to
0.2 mg/L (Wigginton, 1999). USEPA guidelines indicate that Ortho-P concentrations in stream
in excess of 0.10 mg/L can trigger algae blooms in fresh water lakes.
         Removal of phosphorus can be accomplished by three mechanisms. The first is
removal of organic and inorganic P associated with solids. The second is removal by biological
uptake by plants or bacteria. The third is through chemical precipitation such as the reaction of


                                                                                  10/29/03