Geotechnical Evaluation for a Green Infrastructure Project in the County of Los Angeles

The County of Los Angeles is implementing several green infrastructure projects within public roadways. The primary objective of these projects is to capture and infiltrate the stormwater by diverting flows out of the existing storm drains and/or capturing surface flows before entering the storm drain system. Green infrastructure proposed typically consists of a series of large diameter drywells that store and infiltrate stormwater runoff and provide groundwater recharge. As part of the designs, geotechnical evaluations of the subsurface conditions are necessary, including evaluations of depth of groundwater, infiltration characteristics and capacities of the ground, and effect of drywell spacing, etc. The geotechnical engineering aspects are discussed in the paper using the preliminary design of the San Pedro Street Green Improvement Project as a case study. The infiltration capacities were evaluated through drywell infiltration testing. The effect of well spacing was evaluated by numerical modeling that was calibrated by test results; the modeling shows that for a well depth of 38 ft and a well spacing of 100 ft, 96% of well efficiency can be achieved.