COMPLIANCE INFO_AMENDED JTD 1/5/2026

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Foothill Landfill Storm Water Pollution Prevention Plan Page 68 San Joaquin County proposed a “Natural Background Pollutant Source Demonstration” as described in Section XII.D.2.c of the IGP. The County and its QISPs believe the cause of the iron NAL exceedances to be solely attributable to the natural soils for the following reasons: 1. The 2015/2016 iron NAL exceedance at SW-3 was also accompanied with a TSS NAL exceedance. However, there were no active industrial activities occurring in this drainage area other than the movement of dirt used for daily cover. Vehicles and equipment are not stored or maintained in this area, and, therefore, not a significant source of iron. There are no structures of any kind and no landfilling activities occur in this drainage area. Because the TSS concentration was elevated at 415 mg/L, it can be concluded that sediment was a factor in the elevated iron concentration. The iron concentration was 34.7 mg/L, which was significantly higher than the iron concentrations observed during the 2016/2017 storm season when the TSS values averaged much lower at 8.2 mg/L. 2. The 2016/2017 iron NAL exceedances resulted from samples collected from non- industrial areas ST-1 and ST-7. The concentration of iron was approximately the same at ST-6, which may have had a minor amount of contribution from an industrial area. Therefore, because these concentrations were basically the same for iron and TSS, we believe the source of the iron to be the same for water discharged at all three sampling locations, which is from the native soils. 3. Soil samples were collected at ST-1, ST-6, and ST-7 in April 2017. All nine soil samples had significant concentrations of iron ranging from 15,900 to 27,800 mg/kg. There were no indications of current or previous industrial activities in the areas where the soil samples were collected. 4. NRCS soil survey data shows that the site has soil types derived of volcanic activity. Academic literature references iron to be a significant component of magna derived igneous rocks. The United States Geological Survey (USGS) Mineral Resources Online Spatial Data website (https://mrdata.usgs.gov/), has a listing of shallow soil samples. Without exception, all soil samples from this region are elevated in aluminum and iron. The six nearest samples located within the general vicinity of the landfill were found to have elevated aluminum (4.9 – 9.2% by weight) and iron concentrations (2.0 – 6.5% by weight). Three of the six samples were within the same NRCS soil types as those of the landfill. 5. Field observations note plentiful igneous and/or metamorphic rocks having a reddish hue which is indicative of iron oxide.