Design Methods, Selection, and Cost-Effectiveness of Stormwater Quality Structures

Implementation of the National Pollutant Discharge Elimination System (NPDES) and Texas Pollutant Discharge Elimination System (TPDES) requires that the Texas Department of Transportation (TxDOT) adopt a variety of stormwater quality measures to meet Clean Water Act, Section 401 requirements. The permanent water quality structures that have been required in the Austin, Edwards Aquifer Zone are relatively expensive when compared to some other options. TxDOT wished to examine a variety of options for meeting stormwater quality requirements and to develop a cost comparison index that could be used to identify the most cost effective type of structure.|This report concludes that a number of stormwater quality structures will meet TxDOT's needs. Furthermore, the research addresses the question of cost effectiveness by examining the lifecycle cost in relation to the structures' efficiency in removing TSS, the primary index pollutant in storm water. The research suggested that a cost index of this kind was only meaningful if special site considerations and land costs were ignored. Therefore, the most cost-effective alternative for a specific site will likely be determined by considerations other than design, construction, and maintenance costs. The report further suggests ways that TxDOT can better utilize the roadside to improve water quality, thereby reducing the cost of end of channel structures. It also provides design methods for estimating pollutant loads and sizing selected structures.