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LIVE OAK GEO ENVIRONMENTAL, INC. 4 407 W. Oak St., Lodi, CA 95240 ❖ (209)369-0375 •S logelodi.com June 2, 2020 Project Number: 1921 Jeffrey Wong, REHS San Joaquin County Environmental Health Department 1868 E. Hazelton Ave. Stockton, CA 95205 Regarding: Addendum to Soil Suitability/Nitrate Loading Study Ng Property 7670 E. Melton Rd., Manteca, CA Original report dated May 13, 2019 Mr. Wong: You contacted our office on Thursday, May 28, 2020 regarding the new percolation test Live Oak conducted for the above Site; you inquired why the percolation rate was slower in the new test compared with the test completed on the Site in 2019. This letter will address both percolation tests and provide our understanding of the likely cause of the difference. In the original Soil Suitability/Nitrate Loading Study dated May 13, 2019, a percolation rate of 4.6 min/in was obtained during a one-hour percolation test conducted on May 1, 2019. Mr. Ng had specified the test location, near the proposed septic leach field. The orchard on the Site had just been removed, and the ground had not been worked. The soil was found to be clayey sand to approximately 1.7 feet below ground surface, followed by slightly cemented silty sand to the full depth of the hole. Live Oak understands that, between May 1, 2019 and April 28, 2020, Mr. Ng proceeded under permit with construction of his house, including importation of approximately 12 to 14 inches of local sandy soil and earthwork to ready the area for construction. The construction area was then graded so that storm water will flow away from the house. It is Live Oak's understanding that Mr. Ng spoke with Michael Kith, Lead REHS at the San Joaquin County Environmental Health Department, regarding the option of completing a new percolation test on the Site. Mr. Ng and Mr. Kith discussed the possibility that a mounded septic system would not be required if a new percolation rate of 5.1 min/in or higher could be obtained from the new test. Live Oak was then retained for that purpose. A rate of 5.1 min/in would represent a difference of 0.5 min/in from the original test result, likely within the margin of error of this type of testing. The new percolation test was completed on April 28, 2020. Again Mr. Ng specified the test location; at this time, he had redone the site plan so that the proposed septic leach field would be on the north side of the house; the percolation test was conducted within this area. The soil observed in the boring was found to be silty sand to a depth of 1.25 feet, followed by slightly Environmental ❖ Engineering Geology Geophysics