SR0087834_NITRATE LOADING STUDY ADDENDUM

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► INTRODUCTION ' Mr. and Mrs. Ferreira are proposing to construct an Accessory Dwelling Unit.(ADU) on their property located at the project address noted on the Title Page. This new single family residential I structure will have three bedrooms. The existing single family residential structure is a two- bedroom home. On August 12, 2023, Live Oak GeoEnvironmental, Inc. (LOGE) submitted a Soil Suitability/ Nitrate Loading Study(Project No. 2325, SR0087039)to the San Joaquin County Environmental Health Department(EHD). Their Study found the nitrate loading from the existing.residential structure and the proposed ADU on the 0.53 acre Parcel to be 16.2 mg/L Nitrogen; 6.2 mg/L N over the Maximum Contaminant Level (MCL) of 10 mg/L N. A Directive Letter issued by the EHD on August 23, 2023, found in Appendix B, requires mitigation of the excessive nitrate loading through an engineered system. In this Report, differing methodology and calculative parameters from those conducted by LOGE have found that under the additional information/data secured for this project, it has been determined that the revised nitrate loading for this project is now under the MCL at 8.8 mg/L N. The disposal area soils consist of lean/fat clays (CL/CH)that are extremely dense and sticky, with high clay content percentages at 49% and 34% from the 24"- 36" and 38"-42" depths,respectively: Percolation test results conducted by LOGE on July 13, 2023, measured a passing perc rate at the depth of 1.81 ft to be 3.79 minutes/inch(mpi). Another test conducted at the 4.48 ft had a minimally failing perc rate of 62.5 mpi. Percolation tests conducted for this Report revealed failing perc rates of 125 mpi at the 24" depth and 0 mpi and the 36" depth. Extremely heavy rainfall during this testing contributed to supersaturated soil conditions. SOIL SUITABILITY INFORMATION To assess the permeability of the existing shallow disposal area soils, two percolation test borings jwere completed as illustrated on the aerial photo in Appendix C. Two horings (36" and 42") borings were initially drilled and soil samples obtained from these two borings. That night and the 1 next day, heavy rains destroyed the test borings. Subsequently, a 24" and a 36" boring were drilled on February 22, 2024. I These shallow borings are depths representative of the permeability that will occur at filter bed depth. The 36-inch deep percolation test boring was completed to measure percolation 12 inches deeper below the floor of the filter bed. This deeper depth test exhibited nonexistent permeability. After drilling,the sidewalls of the shallow borings were scored with a pry-bar to open potentially i smeared soil surfaces and the cuttings removed. Two inches of pea gravel was placed at the i bottom of the two borings and a three-inch perforated PVC pipe was inserted to prevent cave-ins. j Although the soil was extremely saturated from heavy rains throughout this winter,the borings were pre-saturated with 6 inches of water approximately 24 hrs prior to the start of testing. I Page -1- Chesney Engineering, Inc.