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Soil Suitability/ Nitrate Loading Study Addendum Irerracon Arriaga Property Stockton, California August 31, 2020 Terracon Project No. NA207046 Boring Depth Interval Soil Type Unified Soil Latitude Longitude (ft) Classification Sand, light brown, 0-1.5 loose, dry SW B4 37.90813 -121.16298 1.5-3.5 Clay, hard, dark CL brown, dense, moist During the field work, surface soils appeared to contain fill material including sand, gravel and large rocks. 1.5.4 Discussion of Soil Lithology The soils encountered in our percolation test boring and soil profile consisted primarily of clay. Generally speaking, coarse-grained soil has a greater potential for percolation than fine-grained or cemented soil. Terracon searched the DWR Jii i, Well Completion Records for additional information regarding soil lithology near the site. Refer to Section 1.2 of Terracon's prior NLS report dated April 26, 2019 (Terracon Project No. NA187059)for further discussion. 1.6 Percolation Test Information 1.6.1 Percolation Test Locations Refer to Section 1.5.1 and Appendix A, Exhibit 2. 1.6.2 Number of Percolation Tests Two shallow percolation tests (132 and 134) were performed. 1.6.3 Boring Preparation and Presaturation The percolation test borings (132 and 134) and soil profile (B3) were hand augured on July 27, 2020. Approximately two inches of"pea gravel" was placed in the bottom of the open boring. A 2.0-inch diameter PVC pipe with perforations towards the bottom was installed on top of the gravel and the annular space was backfilled with "pea gravel". Presaturation of the percolation test holes occurred the same day approximately 24 hours prior to the day of testing. The depth of water used to pre-soak the shallow borings was approximately 1.0 foot above the top of the gravel. 1.6.4 Condition of Borings after Presaturation Water remained in the bottom of both percolation test borings (132 and B4) after the 24-hour pre- soak period. Responsive ■ Resourceful ■ Reliablc 10