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6.B. - Page 17 of 28 Appendix 3 - Additional Archaeological Investigation, South Main Mixed Use Development Project (1601 EI Camino Real), Statement of Work and Cost Consultant will conduct subsurface mechanical excavations and Geoprobe coring in order to confirm the presence of, and evaluate the significance of, an archaeological site (P-41-000506 / CA -SMA- 358/H) that has been previously documented within the proposed South Main Mixed Use Development Project, 1601 EI Camino Real, Redwood City (Project). The Project by Greystar GP II, LLC proposes a mixed-use and transit -oriented project on approximately 8.3 acres on five parcels (A through E) along the EI Camino Real corridor in Redwood City. The project site is bounded by EI Camino Real, Maple Street, Elm Street, Chestnut Street, and Cedar Street, and is bisected by Beech Street, Main Street, and Lathrop Street. The Project proposes underground parking on every parcel, a disturbance of between 21 to 38 feet below the ground surface. The archaeological site was originally identified during utility installation in 2001 and described as having both prehistoric and historic -era components, located on either side of Main Street, between Chestnut and Beech streets, with the main portion of the archaeological deposit between Cedar and Beech streets. The original site record also notes that Main Street was originally called Mound Street, and that the purported prehistoric component of the site could be the result of grading and redeposition of nearby shellmounds during the early historic -era. A subsequent investigation in 2007 expanded the site boundaries east of the Caltrain corridor. A 1 by 0.5 meter unit was hand -excavated to a depth of 0.8 meter within the Caltrain corridor behind the roller rink, and was found to contain a disturbed historic -era archaeological deposit and a scant prehistoric deposit. Despite the disturbed context within the Caltrain right-of-way, based on the previous investigation of the area, CA -SMA -358/H was recommended as eligible for listing in the National Register of Historic Places under Criterion D — likely to yield information regarding important questions in prehistory and history. However, given the documented disturbed context and lack of supporting analysis, this recommendation is questionable. Additional work is necessary to confirm the presence of the site within the Project area and, if present, whether the site retains sufficient integrity for eligibility to the California Register of Historical Resources (CRHR). Consultant will provide a limited subsurface investigatory program to better define potential impacts to this previously identified resource. Consultant offered two methodologies, which have different benefits and constraints. Utilizing a backhoe or small excavator, a maximum of five (5) test pits would be provided, measuring approximately 10 to15 feet long by 5 feet deep, which will be mechanically excavated within the area along Main Street that was identified as the center of the deposit during the initial recording of the site. Mechanically excavated test pits have the benefit of allowing for a relatively large "window" into subsurface conditions, which will aid in a more accurate characterization of the previously identified site, and assessment of the site's potential CRHR eligibility. However, this type of investigation also has the potential to cause greater disruption to surrounding businesses (e.g., the Self Serve Carwash and Towne Auto Body), as the test pits would be excavated in the open areas of those lots, if feasible. All excavations would be backfilled, compacted, and finished with asphalt "cold patch," to return the areas to usable condition. Geoprobe borings would also be used to expose soils up to or deeper than the depth of Project impacts. The advantage of Geoprobe over conventional trenching means being able to test below depths of approximately 12 feet below ground surface (proposed project effects being up to 38 feet). In addition, due to the built -out nature of the Project area, the Geoprobe boring would have a much smaller area of impact (each core being 6 inches in diameter). While Geoprobe continuous coring is better for assessing deeper subsurface conditions, the smaller "window" provided by the cores provides less recovery and makes it more difficult to assess the condition and eligibility of the near -surface archaeological site. A maximum of ten (10) Geoprobe borings will be placed in areas extending east and west off Main Street and advanced to a maximum depth of approximately 40 feet below ground surface. In addition to the subsurface identification investigation, additional historic context will be needed as part of the CRHR eligibility determination, to determine if the identified historic -era archaeological resources are directly associated with a particular historic residence or business. Consultant will use the historic research previously completed for the Historical Resource Inventory and Evaluation Report, to develop the necessary historic context. ATTY/AGR/2019/AMENDM ENTS/AM END NO.1 - AECOM REV: 06-17-19 PR Page 11 of 22