902 N BROADWAY BASE FILE 2025-03-27

Page14 ■ Geochemical Indicators: (carbon dioxide, methane, alkalinity) ■ Nutrients (ammonia, nitrate, phosphorus, sulfate) ■ Dissolved inorganic parameters (iron, manganese) ■ Water quality parameters (field-measured dissolved oxygen, oxidation-reduction potential, pH, specific conductance,turbidity, temperature) The groundwater analytical data will be used to evaluate current plume and water quality conditions and biodegradation processes. TASK 3C: ONGOING INVESTIGATION-DERIVED WASTE MANAGEMENT Well purge water and equipment decontamination wastewater will be temporarily stored in the locked remediation enclosure in sealed, labeled drums, pending disposal. EES assumes that all investigation- derived waste (IDW) soils and groundwater will be characterized as non-hazardous waste and will be suitable for disposal at a RCRA Subtitle D landfill.Any IDW not meeting these criteria may constitute a change in scope. TASK 4: LIMITED INTERIM ACTION: SOIL VAPOR EXTRACTION OPERATIONS Until sub-slab and potential vapor intrusion conditions are better documented for the existing Property building, continued SVE operations and maintenance (O&M) procedures are appropriate as an interim control measure.Task 1 findings under this work plan will help inform an initial understanding of those conditions, at which point interim SVE operations will be reconsidered. In the meantime, EES plans to operate the SVE system on a limited basis during Task 1, until vapor intrusion assessment findings are available. System vacuum will continue to be focused on SVE wells located on the west side of the array nearest to the building, including, SVE-1, SVE-2, SVE-7, SVE-8, and SVE-13. System adjustments will be made during operations at the direction of the project engineer. While the system is operating, minimum O&M activities will include the following: ■ Collect a monthly combined-system vapor sample as required for compliance with Puget Sound Clean Air Agency (PSCAA) air discharge criteria. ■ Monitor operations monthly for function, for influence near the building, and to demonstrate compliance with regional air discharge criteria. SVE operational data and system adjustment information will be reported on a regular basis as noted below. TASK 5: PLANNING & PERMITTING, REPORTING, PROJECT MANAGEMENT AND COMMUNICATIONS TASK 5A: PLANNING & PERMITTING In addition to preparation of this work plan document,the following planning and preparation work will be conducted before initiating scoped activities: EES ENVIRONMENTAL CONSULTING,INC. 2120-02 2024 SOW 20240408f