San Francisco
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SFPUC plans to construct a 1.9-miles long of sewer line improvement from Mission Bay area to the SFPUC’s Southeast Sewer treatment plant (SEP).  The sewer line consists of various pump stations, and shallow and deep tunnels.  AEW was retained by the Stantec and SFPUC to provide consulting and planning services to address environmental issues from conceptual to detailed design phases of the project. 

Primary objectives of our environmental services included (1) a comprehensive understanding of chemical conditions in subsurface media along the proposed alignments; (2) evaluation of potential soil classifications for excess soil requiring off-site disposal; (3) evaluation of groundwater quality for potential wastewater discharge, (4) identification of environmental mitigation requirements and development of the corresponding mitigation measures, (5) environmental sections of the construction bids and specifications development, and (6) support to the Project Team to resolve unexpected environmental conditions encountered during construction.

AEW completed a Phase I ESA on the two alignment alternatives to identify known or suspected environmental issues, Recognized Environmental Conditions (RECs), Historical Recognized Environmental Conditions (HRECs), and Controlled Recognized Environmental Conditions (CRECs) in the subsurface environment that may affect the construction of either alternative.  The Phase I ESA was conducted in accordance with ASTM Standard Practice E1527-13 for Phase I ESA.

AEW worked with the project geotechnical consultant to collect the environmental soil and groundwater samples as part of the geotechnical investigation for minimizing field sampling costs.  Soil and groundwater samples were submitted to a California-Certified laboratory for chemical analyses.  Results of chemical analyses were used to evaluate potential waste classifications of the to-be excavated materials from the alignment construction and for profiling on the disposal of investigative-derived wastes.  AEW plans to obtain pre-approval from offsite landfill facilities for the disposal of excess soil to be generated during construction.  Upon completion of field investigation, AEW prepared reports presenting the results of the hazardous materials investigation.  The reports consisted of field sampling procedures and chemical analysis protocols, results of chemical analyses, conclusions and recommendations on the potential disposal options of the to-be excavated materials during construction.

AEW prepared technical memorandum to present potential waste classification, disposal facilities, and management protocols for the disposal of the muck produced from soil and rock excavation, to be generated during the construction of the CBSIP including shafts, the tunnel, and the required connections.  The technical memorandum was developed based on the design of the alignment, Phase I ESA report, and results of the soil and groundwater investigation.  Information on the lateral and vertical extents and estimated volumes of non-hazardous wastes and hazardous wastes classification were included in the technical memorandum.  In addition, contingency protocols for encountering unknown contamination during construction were presented in the technical memorandum.

AEW developed potential disposal options, and management protocols for the disposal of the dewatered groundwater to be generated during the construction of the shafts, CHTL, and the required connections.  Disposal options: (1) discharge to the San Francisco Bay under RWQCB’s NPDES permit for the project, and (2) discharge to the SFPUC’s sewer treatment system were evaluated.  The evaluation was based on potential volume to be generated, chemical characteristics information including chloride on groundwater samples from the soil and groundwater investigation.  A recommended alternative was proposed to SFPUC for the consideration to dispose of the dewatered groundwater.

Project Challenges

Because of the potential chloride concentrations in dewatered groundwater that can affect the operation of the SFPUC’s sewer system, AEW and the Project Team worked together with the SFPUC’s sewer plant personnel to evaluate the potential of discharging the dewatered groundwater into the sewer system with pre-treatment as well as the limitations of each of the identified alternatives for disposal of the dewatered groundwater during the 35% design.  Such meetings and discussions assist the Project Team to conduct a detailed evaluation of each alternative and develop steps to be conducted prior to completion of the 100% design to implement the recommended alternative.