ARCHIVED REPORTS_SECOND SEMIANNUAL 2018 GROUNDWATER MONITORING REPORT

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JACOBS® Second Semiannual and 2018 Annual Groundwater Monitoring Report installed the HydraSleeve samplers on March 7, 2018, after collecting the samples for the prior semiannual sampling event. . The top of the HydraSleeve sampler was set approximately at the midpoint of the well screen (or slightly below) if the water table was above the screen, it was set in the middle of the water column • (or slightly below) if the water table was below the top of the screen. Upon retrieval, water from the samplers was transferred into sample containers. After the containers were filled, physical parameters (temperature, electrical conductivity [EC], pH, dissolved oxygen [DO], oxidation-reduction potential [ORP], and turbidity)were measured from a portion of the sample as follows: . • Groundwater was poured into a Myron L Ultrameter to read temperature, pH, EC, and ORP. . • Groundwater was poured into the Hach Turbidimeter to measure turbidity. • A measurement cup was filled with groundwater, and DO was measured with a YSI 550 DO Meter. • Two of the wells had insufficient water for sampling with a HydraSleeve and were sampled using a bailer. M-8 had 0.80 foot of water, and M-10 had 1.48 feet of water in the bottom, as calculated by subtracting the depth to water from the total depth of the well on the field data forms (Appendix A). The samples were labeled, placed in a chilled cooler, and delivered to Alpha Analytical, Inc., a California-certified analytical laboratory located in Sparks, Nevada, for analysis. Chain-of-custody protocol was maintained throughout the sample-handling process. • 2.1.1.2 Groundwater Analytical Methods Groundwater and quality assurance/quality control (QA/QC) samples were analyzed for the following: • • Total petroleum hydrocarbons as gasoline (TPH-g) and as diesel (TPH-d) using U.S. Environmental Protection Agency (EPA) Method 8015 modified • Benzene, toluene, ethylbenzene, and total xylenes (BTEX) using EPA Method 8260B The following QA/QC samples were collected.- 0 ollected:• Duplicate sample from well N-7 (labeled DUP-1) • • One equipment blank sample (labeled EB-1) • One trip blank sample for the cooler of samples (labeled TB-1) Sample analyses were conducted within a standard 10-day laboratory turnaround time. Copies of the laboratory reports from Alpha Analytical, Inc., are provided in Appendix B. 2.1.2 Results 2.1.2.1 Groundwater Elevation and Flow Groundwater level data collected on September 7, 2018, are presented in Table 2. Groundwater elevation contours for these data are shown on Figure 3. These data are included in the tabulation of the 10 most recent historical monitoring events in Appendix C. Hydrographs of the historical data are provided in Appendix D. Groundwater Elevations Groundwater elevation data for the September 7, 2018, monitoring event are summarized as follows: • Shallow-interval groundwater monitoring wells are constructed with total depths between 14 and 23.5 feet bgs. Calculated elevations for the shallow-interval groundwater monitoring wells ranged from 3.40 feet above mean sea level (msl) at well M-2, located in the northwestern portion of the site near Trapper Slough, to-10.33 feet msl at wells N-18 and N-19, located in the southeastern portion of . the site. AX1015181035SCO • M