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Soil Suitability/ Nitrate Loading Study Addendum Irerracon <br /> Arriaga Property ■ Stockton, California <br /> August 31, 2020 ■Terracon Project No. NA207046 <br /> "natural" conditions, groundwater concentration containing nitrate is no more than about 13.5 <br /> milligrams per liter(mg/L) nitrate (NO3) or (3 mg/L-N). Areas having 24.75 mg/L-NO3 (5.5 mg/L- <br /> N)or more, are those in which nitrate concentrations may be increasing (Hull, 1984). <br /> DBCP (dibromo chloropropane) is a nematocide and soil fumigant for vegetables and grapes. It <br /> is thought to cause health problems consisting of kidney damage, liver damage, and cancer. The <br /> use of DBCP was discontinued in 1979. <br /> Based on the historical information, the past agricultural land use, former onsite septic system, <br /> and septic systems in the area should be considered potential groundwater contamination <br /> sources. According to the State Water Resources Control Board website, there were no nitrate <br /> impacted wells reported within 2,000 feet of the site. <br /> 1.4.3 Water Sample Location <br /> Refer to Terracon's prior Nitrate Loading Study (NLS) report dated April 26, 2019 (Terracon <br /> Project No. NA187059)and Section 2.2 for further discussion. <br /> 1.4.4 Groundwater Sample Analysis <br /> Based on Terracon's 2019 NLS, nitrate as N (5.9 mg/L)was identified in a groundwater sample <br /> collected from the onsite domestic below the MCL of 10 mg/L-N. A second groundwater sample <br /> reported below laboratory detection limits for DBCP. Refer to Terracon's prior NLS report dated <br /> April 26, 2019 (Terracon Project No. NA187059)for further discussion. <br /> 1.4.5 Groundwater Sample Handling <br /> Refer to Terracon's prior NLS report dated April 26, 2019 (Terracon Project No. NA187059). <br /> 1.5 Soil Profile and Geologic Information <br /> The site is depicted on the Geologic Map of California 2010, as within generalized quaternary <br /> Pleistocene and Holocene deposits which are comprised primarily of unconsolidated and semi- <br /> consolidated alluvium, lake, playa, and terrace deposits. <br /> Terracon reviewed the United States Department of Agriculture (USDA) Natural Resources <br /> Conversation Service (NRCS) Web Soil Survey and USDA Soil Survey of San Joaquin County <br /> (1992) for information regarding soil properties. Based on information obtained from the USDA <br /> sources, the northern half of the site consists of Jacktone clay soils with 0 to 2 percent slopes. <br /> Parent material is alluvium derived from mixed rock sources. Typical soil profiles consist of 0 to <br /> 34 inches clay, 34 to 37 inches indurated, 37 to 46 inches stratified sandy loam to clay loam, 46 <br /> to 60 inches cemented soils. <br /> Responsive ■ Resourceful ■ Reliable 8 <br />