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Soil Suitability/Nitrate Loading Study Irerracon Vacant Commercial Property■ Stockton, California December 7, 2018 ■ Terracon Project No. NA187056 shallow, unconfined groundwater, if present, would likely vary depending upon seasonal variations in rainfall and other hydrogeological features. Based on a review of the State Water Resources Control Board GeoTracker website and information associated with S d Food Mart (8200 N. Highway 99), depth to groundwater was reported between 56 and 76 fe ' low grade surface (bgs)with a gradient to the east-northeas , across the s --Re of r to Sevctiori 1.4.2 for further discussion. 1.4.2 Potential Groundwater Contamination Issues The presence of nitrates is not uncommon in shallow groundwater aquifers in San Joaquin County and other parts of the Central Valley. Nitrate in groundwater occurs as a result of the application of fertilizers, livestock waste, and untreated septic tank waste. Nitrate is mobile and often accumulates in the shallow groundwater zones. In the early 1900s, natural levels of nitrate in groundwater were measured in forty-three (43)wells throughout the Sacramento Valley by Kirk Bryan (1923). It was thought that groundwater at that time was close to "natural" conditions. Based on the work by Bryan, it is estimated that under "natural" conditions, groundwater concentration containing nitrate is no more than about 13.5 mg/L-NO3 (3 mg/L-N). Areas having 24.75 mg/L-NO3 (5.5 mg/L-N) or more are those in which nitrate concentrations may be increasing (Hull, 1984). DBCP (dibromochloropropane) is a nematocide and soil fumigant for vegetables and grapes. It is thought to cause health problems consisting of kidney damage, liver damage, and cancer. The use of DBCP was discontinued in 1979. EDB (ethylene dibromide) was used in gasoline to prevent lead deposits and build up. It was also used in pesticides and fumigants. Exposure to EDB is linked to many adverse health effects stemming from organ damage to cancer. On November 29, 2018, Terracon spoke with Mr. Joe Baglietto, owner representative, regarding sampling the on-site groundwater well. Mr. Baglietto indicated groundwater data associated with site remediation was available for the property. Terracon searched the GeoTracker website for additional information and the site was identified under the Speed Food Mart(8200 North Highway 99) listing. Based on a review of the Site Closure Request for Speedy Food Mart dated July 2010, a gasoline station and store were formerly located at the southwestern comer of the site. An unauthorized petroleum hydrocarbon release was identified during the removal of three former 8,000-gallon underground gasoline storage tanks (USTs) and associated dispensers. Elevated levels of total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX), and methyl tertiary butyl ether (MTBE) were identified in soil and groundwater samples collected from the site. Site remediation was conducted under the oversight of the San Joaquin County EHD. Three USTs and approximately 166 tons of contaminated soil were removed in 1998. Remediation and monitoring included multiple groundwater monitoring wells, groundwater extraction wells, and a soil vapor extraction system through 2010. During the final groundwater monitoring period, the majority of the remediation wells were reported below Responsive ■ Resourceful ■ Reliable 9