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January 3, 2025 <br />HWA Project No. 2021-159-21 <br />Geotechnical Engineering Report 50 HWA GEOSCIENCES INC. <br />Port Gardner Storage Facility <br />continued industrial use of the site and maintenance of hardscape. Additionally, it recommends <br />decommissioning of an abandoned stormwater pipe near the southern border of the site and <br />paving of the entirety of the site to act as a protective cap for potentially contaminated surface <br />soils. Finally, they recommend that a drainage barrier be constructed to contain all surface runoff <br />from the site, to be managed via the planned combined-sewer outfall (CSO) facility that will be <br />constructed at the site. <br />The sampling and analyses conducted by HWA were very limited, not intended for site <br />characterization (e.g., explorations were selected solely on geotechnical criteria) and is not fully <br />representative of site conditions with respect to hazardous materials. <br />Although contaminated soils may be left in place if not disturbed during construction, some soils <br />excavated for project construction may be impacted and may need to be properly managed and <br />disposed. In addition, contaminated groundwater may also be present at the site. Based on the <br />impacts identified by prior investigators, and the laboratory analysis of samples from HWA’s <br />April 2022 and October 2023 geotechnical explorations, HWA recommends the following: <br />• Develop a contaminated media management plan (CMMP) and project specifications that <br />outline proper techniques for field screening, testing, handling, and disposal of any net <br />export contaminated soil and/or groundwater removed during project construction. These <br />specifications inform the contractor of known or potential contaminants and include any <br />reports available for the contractor’s review. <br />• Some excavated soils generated during construction that require off-site removal (i.e., net <br />export soils) that do not contain contaminants exceeding cleanup levels may still require <br />treatment or disposal at a licensed facility, as many fill sites will not accept soils with <br />staining, odor, or detectable concentrations of contaminants, and liability may be incurred <br />by the project owner for improper disposal of soils. <br />• Potential contaminated dewatering discharge options include discharge under permit to <br />sanitary sewer, or treatment and discharge to the storm system. Criteria (chemical <br />concentrations) for disposal to sanitary sewer under permit are typically much higher than <br />for discharge to the storm drainage system, with most dewatering effluent suitable for <br />discharge with little or no pre-treatment. Conversely, discharge to the storm drainage <br />system typically requires very high-quality water, with regards to chemical <br />concentrations and also turbidity. <br />• Utilize best management practices for stormwater and erosion control. <br />• Follow Ecology underground storage tank (UST) reporting and removal regulations if <br />abandoned or unreported USTs are encountered during construction.