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ASPECT CONSULTING <br />PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL iii <br /> <br />6.2.3 Unit C ................................................................................................. 68 <br />6.2.4 Unit D ................................................................................................. 68 <br />6.2.5 Unit E.................................................................................................. 69 <br />6.2.6 Data Presentation ............................................................................... 69 <br />6.3 Alkaline-pH Groundwater Produced by Crushed Material ......................... 71 <br />6.3.1 Time Trends for Groundwater pH ....................................................... 73 <br />6.4 Ammonia and Sulfide in Groundwater ...................................................... 76 <br />6.5 Nature and Extent of Contamination by Unit ............................................. 77 <br />6.5.1 Unit A.................................................................................................. 77 <br />6.5.2 Unit B.................................................................................................. 90 <br />6.5.3 Unit C ............................................................................................... 100 <br />6.5.4 Log Pond Area of Unit C ................................................................... 104 <br />6.5.5 Unit D ............................................................................................... 111 <br />6.5.6 Unit E................................................................................................ 116 <br />6.5.7 Shoreline Water Quality .................................................................... 118 <br />7 Conceptual Site Model ............................................................................ 122 <br />7.1 Residual Contaminants .......................................................................... 122 <br />7.2 Potentially Complete Exposure Pathways and Receptors ...................... 124 <br />8 Feasibility Study ...................................................................................... 126 <br />8.1 Cleanup Standards ................................................................................. 127 <br />8.1.1 Selection of Indicator Hazardous Substances ................................... 127 <br />8.1.2 Soil Cleanup Standards .................................................................... 129 <br />8.1.3 Groundwater Cleanup Standards ...................................................... 130 <br />8.1.4 Air Cleanup Standards and Remediation Levels ............................... 133 <br />8.2 Potentially Applicable State and Federal Laws ....................................... 133 <br />8.2.1 MTCA Requirements ........................................................................ 133 <br />8.2.2 Solid and Hazardous Waste Management ........................................ 134 <br />8.2.3 State Environmental Policy Act (SEPA) ............................................ 134 <br />8.2.4 Washington Clean Air Act ................................................................. 134 <br />8.2.5 Washington Shoreline Management Act ........................................... 135 <br />8.2.6 Construction Stormwater General Permit .......................................... 135 <br />8.2.7 Other Potentially Applicable Regulatory Requirements ..................... 135 <br />8.3 Remedial Action Objectives (RAOs) ....................................................... 136 <br />8.4 Residual Contamination within Upland Area ........................................... 137 <br />8.4.1 Soil .................................................................................................. 137 <br />8.4.2 Groundwater ..................................................................................... 138 <br />8.4.3 Indoor Air within Warehouse Building ............................................... 138 <br />8.5 Screening of Cleanup Action Alternatives ............................................... 138 <br />8.6 Description of the Cleanup Alternative .................................................... 139 <br />8.6.1 Completed Cleanup Actions ............................................................. 139 <br />8.6.2 Environmental Capping of City Utility Property and Warehouse ........ 140 <br />8.6.3 Groundwater Compliance Monitoring ................................................ 140 <br />8.6.4 Long-Term Cap Inspection and Maintenance ................................... 140 <br />8.6.5 Institutional/Engineered Controls ...................................................... 140