Bioretention for stormwater quality improvement in Texas : pilot experiments.

670113360Technical report; Sept. 2007\uc2\ubfOct. 2009.PDFTech Reporthttp://tti.tamu.edu/documents/0-5949-2.pdfFHWA/TX-10/0-5949-20-5949Storm sewersRunoffTexasTexas Transportation InstituteLi, Ming-HanSung, Chan YongKim, Myung HeeChu, Kung-HuiTexas Transportation InstituteTexas. Dept. of TransportationUnited States. Federal Highway AdministrationNTL-ENERGY AND ENVIRONMENT-Environment ImpactsUS Transportation CollectionThis report summarizes the results of pilot-scale bioretention experiments. Five steel boxes of 6 ft (L) \uc3\u2014 6 ft(W) \uc3\u2014 4 ft (D) were constructed, each of which has a different type of vegetation: (1) shrubs, (2) grassspecies in Texas Department of Transportation (TxDOT) Bryan District seed mix, (3) native grasses, (4)Bermudagrass, and (5) no vegetation as the control. Vegetation was given 14 months to establish beforetesting. Synthetic runoff containing predetermined pollutants with target concentrations was used. Theresults indicate that pilot bioretentions effectively removed zinc (Zn), lead (Pb), total suspended solids(TSS), and ammonia-nitrogen (NH3-N) from stormwater runoff, but exported copper (Cu), nitrate-nitrogen(NO3-N), total nitrogen (TN), and total phosphorus (TP). Vegetation plays an important role on NO3-N andTN removals due to root uptake and the denitrification processes in root zone. However, vegetation couldnegatively affect the water quality if the soil infiltration rate is significantly increased by its root system.This effect was specifically obvious on the TSS removal, in which the control box with the longest detentiontime had much better performance than the vegetated boxes. The results suggest that bioretention is useful totreat stormwater runoff from TxDOT highways, but the design specifications developed in other statesshould be revised to reflect Texas\ue2\u20ac\u2122 unique climate and environmental conditions. Challenges and learnedl essons are described in the report