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March 7, 2019 | Page 2 File No. 0504-119-01 <br />from well MW-2. Groundwater samples were submitted to TestAmerica for the following laboratory <br />analyses: <br />a. GRPH using Northwest Method NWTPH-Gx; and <br />b. Benzene, toluene, ethylbenzene, total xylenes (BTEX) using United States Environmental <br />Protection Agency (EPA) Method 8260C. <br />3. Measuring depth to groundwater and calculating relative groundwater elevations to estimate <br />groundwater flow direction and gradient. <br />4. Drumming and labeling investigation-derived waste (IDW). A qualified contractor will be retained to <br />profile and transport the IDW for disposal at a permitted facility. We assume that IDW disposal for the <br />site will be completed in a single “disposal run” at the conclusion of the site monitoring activities. <br />5. Entering the analytical data into Ecology’s Environmental Information Management (EIM) database. <br />6. Preparing this groundwater monitoring report following receipt of the final analytical data. <br />4.0 FIELD ACTIVITIES <br />Groundwater monitoring activities included measuring depth to groundwater in site monitoring wells MW-1 <br />through MW-6, measuring field water quality parameters and collecting groundwater samples. Data <br />collected in the field and laboratory analytical results were then analyzed and interpreted and the results <br />are summarized in this groundwater monitoring report. Field methods are described in Appendix A. <br />4.1. Groundwater Elevations <br />GeoEngineers measured static groundwater levels in site monitoring wells MW-1 through MW-6 on January <br />30, 2019. Depth to groundwater, measured from the top of the PVC well casings, ranged from <br />approximately 3.70 feet (MW-2) to 4.98 feet (MW-6). Groundwater elevations ranged from approximately <br />1569.84 feet in monitoring well MW-5 to 1573.84 feet in monitoring well MW-1. Depth to water and <br />groundwater elevations are presented in Table 1 below. <br />Based on groundwater elevations on January 30, 2019, groundwater flow is generally to the southwest. <br />The estimated hydraulic groundwater gradient across the site was about 0.009 feet per foot (which is <br />approximately 47.5 feet per mile). Hydraulic groundwater gradients increase toward the southwest near <br />MW-5 to about 0.025 feet per foot (which is approximately 132 feet per mile). Approximate groundwater <br />elevations and flow directions are graphically presented in Figure 2. <br />4.2. Groundwater Sampling <br />Monitoring wells MW-1 through MW-6 were purged and sampled using low-flow sampling techniques. <br />A peristaltic pump equipped with disposable tubing was used to purge and sample each well. Groundwater <br />quality parameters generally were measured at 3-minute intervals during well purging. Groundwater <br />samples were collected when each water quality parameter had stabilized in conformance with the criteria <br />presented in Appendix A or a maximum purge time of 30 minutes was achieved. Field methods are <br />described in Appendix A. A duplicate sample was collected from monitoring well MW-2. Groundwater <br />samples were submitted to TestAmerica for chemical analysis using the methods described in “Section <br />3.0” and chemical analytical results are discussed in “Section 5.0.”