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222�2 FFOINTRODUCTIONs report documents the findings of the first biannual (semiannual) 2026 inspection of the site Wastewater Treatment System(OWTS)/Package Treatment Plant(PTP) serving the Thornton Chevron Service Station Complex. The three MicroSepTec EnviroServers (ES) were operating with no apparent malfunctions. The pump screens were all in need of cleaning, which is typical and completed for every inspection. There continues to be unequal effluent distribution among the three ES by the Orenco® Automatic Distributing Valve. Wastewater chemistry tests were obtained from an equal composite sample from all three ES effluent. Test results indicate the nitrate-nitrogen concentration was determined to be non-detect (ND). The concentrations of the other tested constituents were favorable, except for the Biochemical Oxygen Demand (BOD), which was inexplicably and extraordinarily high. Also noted is that the Laboratory inadvertently failed to initially analyze for Total Kjeldahl Nitrogen (TKN), which was subsequently analyzed. Testing for BOD was also completed a second time because of the initial extremely high concentration, but yielded the same results. MATERIALS AND METHODS In review, and as noted on the Process Flow Diagram, influent from the food production businesses within the Complex flow into a 1.5k gallon grease interceptor tank, which then flows to the first compartment of the 1 Ok gallon septic tank. Influent from the Restrooms flow directly into the 1 Ok gallon septic tank. Effluent from this tank then flows to a 2k gallon pump chamber tank, which is then pressurized through the Automatic Distributing Valve to be distributed among the three ES. As noted in Section 7.12 of the SJC Onsite Wastewater Treatment System Standards, analysis is to be conducted on both influent and effluent. A composite sample was obtained from all three ES on March 27, 2026 and a sample was obtained from the second compartment of the septic tank also on March 27, 2026. (Note: The front compartment of the 1 Ok gallon septic tank contained significant solids buildup which prevented sampling. The tank was subsequently pumped and will be pumped every six months.) All sample containers were provided by Precision Enviro-Tech of Stockton. After sampling, the samples were transported in a cooled ice chest to Precision Enviro-Tech, under the attached Chain of Custody. The Certificate of Analysis Forms and the Chain of Custody Forms are found in Appendix A. Page -1- Chesney Engineering, Inc.