Construct the Low Maintenance BMP That You Designed: Green Infrastructure Construction and Inspection
Design of green infrastructure or Low Impact Development (LID) practices is only a part of managing stormwater runoff. If the practices are not properly constructed and maintained they will not function as they are designed. Maintenance of green infrastructure and LID practices has been widely discussed however, little guidance has been provided on properly constructing or inspecting the construction of green infrastructure or LID practices. There are many variables, including construction practices and material delivery, that can have a significant impact on the performance and function of green infrastructure practices. For example, compaction of the subgrade can have a significant impact on infiltration and overall performance of bioretention areas and permeable pavement and should be avoided. Materials used in construction can also have a significant impact. It is important to have a trained person onsite who can determine if the gravel used in the drainage layer has been washed and free of fines and if the bioretention soil media contains the amount and quality of organic material specified in the construction documents.
This presentation will give a brief overview of the proper phasing of construction, inspection of materials upon delivery, a multitude of proper construction practices, and field testing and verification to ensure green infrastructure and LID practices are properly constructed and function as they are designed. The focus will be on specific construction mistakes that have been observed to be made consistently by contractors and how inspectors and resident engineers can prevent those mistakes from occurring on their projects. Simple metrics that contractors and inspectors can use to verify that the materials that are delivered, including the bioretention soil media, drainage stone, pervious concrete, pervious asphalt, and mulch, meet the specifications required in the construction documents. Methods for field verification and testing, including testing the infiltration of the subgrade and a simple test to verify the infiltration capacity of pervious concrete or porous asphalt will also be presented along with a schedule of when the acceptance testing and verification should be performed. The combination of proper construction techniques, materials that meet construction specifications, and field verification and testing should result in green infrastructure and LID practices that perform and function as they are designed.
Tetra Tech has developed a program to train and certify contractors in the construction of green infrastructure and LID practices. This presentation will be based on materials used to develop the program and condensed to the time allotted. Case studies from construction projects across the country will be incorporated to provide specific examples of lessons learned, the impacts of improper construction techniques, and how to ensure that the practices function as they are designed.
Mr. Merrill Taylor is a Water Resource Engineer with eight years of experience in BMP modeling, planning, design, and implementation. During his time with Tetra Tech, he has assisted in several construction projects and has developed standard specifications and details for BMP design. He has led efforts to identify, prioritize, and select potential BMP sites and developed conceptual and full designs in an effort to meet regulatory requirements. His engineering and environmental background enabled his preparation and understanding of best procedures for hydrology and hydraulic modeling and long-term water quality modeling and design.