Exfiltration Trench for Post Construction Storm Water Management for Linear Transportation Projects: Volume 1 of 3, Laboratory Study of Pervious Concrete and Filter Media

This report documents a laboratory study on the efficacy of the exfiltration trench, a Best Management Practice (BMP) utilized by the Ohio Department of Transportation (ODOT), to reduce pollutants in post construction stormwater runoff. Runoff flows through media layers of the trench, consisting of pervious concrete, aggregate and sand filter media. The ODOT specified media were first characterized and then pollutant removal tests were conducted. Also, an alternative pervious concrete mix (recommended by the Ohio Ready MixConcrete Association (ORMCA)) and filter media (greensand) were investigated. Porosity, hydraulic conductivity, strength and freeze/thaw characteristics of each pervious concrete mix were determined. No structural or durability issues were evident with either concrete mix. Removal of suspended material via the pervious concrete increased with larger size influent particles. For the ODOT pervious concrete mix, removal in terms of total suspended solids (TSS) of sand, A-6 soil and artificial runoff averaged 60.5%, 4.8% and 39%, respectively. The ORMCA mix achieved an average removal of 38.5% for sand particles, 9.3% for A-6 soil and 16.1% for artificial runoff. Both the sand and greensand achieved over 97% removal of A-6 soil as TSS and 75% and 90%, respectively, for artificial runoff. The composite system of ODOT mix and sand averaged 84% removal of TSS and the Ohio Ready Mix and greensand combination averaged 91% removal. The composite system provided 63% to 98% removal for seven heavy metals (Cd, Cr, Cu, Fe, Ni, Pb, and Zn). Greensand was superior to sand in removing metals from solution. The intermediate aggregate layer was characterized for hydraulic conductivity, and the quantity of TSS emanating from washed and unwashed samples was estimated. Unwashed aggregate averaged 74% more TSS than washed aggregate in initial clean water tests. Maintenance of the pervious concrete was performed using simulated sweeping, vacuuming and jet washing. Recovery of permeability was related to the extent of clogging of the specimens, and for sand-clogged pores only 20% of the original hydraulic conductivity was recovered.