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Soil Suitability/ Nitrate Loading Study Addendum Irerracon Arriaga Property Stockton, California August 31, 2020 Terracon Project No. NA207046 1.6.5 Percolation Test Procedure On July 28, 2020, the percolation test was conducted in accordance with the requirements of the San Joaquin County Percolation Test Procedure (Form: EHD 42-01-002 Revised 08-23-2011). Water remained in the percolation test borings; therefore, Terracon conducted the percolation tests by following Procedure #1. Terracon added clear water approximately 0.5 feet above the top of the gravel and recorded the drop in water level after a 30 minute period. Measurement of the water level during the percolation test was from a fixed reference point on the PVC casing using a calibrated Solinst electric water level detector with a depth accuracy of 0.01 feet. All tabulated values on the field data sheet are in decimal feet. The percolation test was observed by Ms. Sukhreet Kaur, Registered Environmental Health Specialist. 1.6.6 Percolation Test Forms and Results A shallow percolation test is defined by the EHD as being between 36 and 42 inches in depth. While a deep percolation test is defined by the EHD as being between 42 inches and 25 feet in depth. The shallow percolation test must demonstrate a satisfactory percolation rate of less than or equal to 60 minutes per inch drop in water level within the existing septic system disposal field of a parcel to utilize a standard septic system and 30 minutes per inch or less for septic pits. Details of the percolation tests are summarized in the table below. Table 6. Summary of Percolation Test. Test No., Date Percolation Test Percolation Rate Test Duration Comments Tested Depth feet min/in hours see note Satisfactory B2-8/27/20 3.5 35.7 0.5 Percolation Rate with exception refer to Section 1.67 B4-8/27/20 3.33 125 0.5 Unsatisfactory Percolation Rate Note: A satisfactory percolation rate is 60 minutes per inch or less for shallow leach lines and 30 minutes per inch or less for septic pits per San Joaquin County Onsite Wastewater Treatment Systems Standards(EHD 42-014),January 2017. The completed percolation test form with Ms. Kaur's signature is included in Appendix E of this report. 1.6.7 Discussion of Percolation Test Results Terracon added excess water to the top of boring B2 due to equipment error; therefore, the boring B2 percolation test rate is based on the water drop from the top of the boring and not 0.5 feet above the top of gravel. Terracon anticipates both boring B2 and B4 would have demonstrated similar percolation rates based on the similar clayey soil conditions present at 3.5 feet bgs. Terracon suggests the percolation rate at boring B4 of 125 minutes per is more representative of the clayey soil conditions encountered on the site. Responsive ■ Resourceful ■ Reliable 11