Water Treatment and Dewatering at SFPUC Biosolids
Water treatment and Dewatering were required for two deep building excavations as part of this project. However, final designs of the Support of Excavation (SOE) walls and the required dewatering scheme was developed during the pre-construction phase. Malcolm performed an early dewatering pump test program to help guide the design of the Support of Excavation (SOE) system and its potential effects on the two nearby active railroad tracks. Due to contaminated soil conditions in some parts of the excavation, Malcolm had to obtain a National Pollutant Discharge Elimination System (NPDES) permit to allow the treated, pumped water to be discharged back to the San Francisco Bay. In total, Malcolm designed and installed 50 dewatering wells targeting three different aquifer zones (shallow, intermediate, and deep) so mass excavation could safely occur in the dry without the risk of bottom heave. Malcolm also installed twelve observation wells to monitor groundwater levels outside the excavation. Malcolm partnered with Clear Creek Systems to provide the water treatment solution as well as WSP, to help provide water sampling, testing, and compliance with the NPDES permit.