Performance of engineered soil and trees in a parking lot bioswale

On the perimeter of a parking lot in Davis, CA, two adjacent test sites were constructed to assess the capacity of engineered soil to reduce stormwater runoff from the parking lot, improve water quality by removing pollutants from runoff, and allow for tree growth. The treatment site included a 10 x 2.4 x 1 m bioswale filled with engineered soil; the control site was of a similar size, but with the native clay loam soil. In each test site, a Bloodgood London plane tree (Platanus hybrida ‘Bloodgood’) was planted. Runoff was reduced by 88% and total pollutant load by 95% in the bioswale. Tree growth appeared slightly better in the engineered soil than in the compacted control soil.