HR: 15:10h
AN: H13L-07    [Abstracts]
TI: Depth-Dependent Changes of Nitrate Concentration in Ground Water, Yucaipa Area, California
AU: * Mendez, G O
EM: gomendez@usgs.gov
AU: Danskin, W R
EM: wdanskin@usgs.gov
AF: US Geological Survey, 5735 Kearny Villa Road Suite O, San Diego, Ca 92123 United States
AB: Depth-dependent water-quality and flowmeter data were used to identify the three-dimensional occurrence of nitrate in the Yucaipa area of southern California. This vertical resolution can aid in defining the source and flowpath of nitrate contamination. In 1996-98, an areal sampling of ground-water quality was done to evaluate the general chemistry of the local Yucaipa aquifer. Composite samples from 3 of 25 sampled wells had nitrate levels exceeding the U.S. EPA maximum contaminant level of 10 mg/L as N. In order to identify the source and age of the nitrate contamination, ground-water quality in the Yucaipa area was reevaluated (2003-04) by obtaining composite samples from 24 wells and depth-dependent samples from 10 sites (six production wells and 4 nested observation wells). Nitrate values ranged from the detection limit of 0.06 to 29.9 mg/L in the composite samples and from 0.57 to 7.66 mg/L in depth-dependent samples. The highest concentrations in the depth-dependent samples were from the shallowest depths. Tritium and carbon14 data were used to evaluate the age of the ground water and to define when the nitrate contamination occurred.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0496 Water quality
DE: 1829 Groundwater hydrology
SC: Hydrology [H]
MN: Fall Meeting 2005