Distribution of stable isotopes in ground water in the Rialto-Colton basin, California

Since 1982, imported water originating in the Sierra Nevada has been used to recharge the Rialto-Colton ground-water basin, about 100 km east of Los Angeles. Stable isotopes of oxygen (oxygen-18) and hydrogen (deuterium) were used to determine the disposition of artificially recharged, imported water within the basin. Delta oxygen-18 ratios in water from wells sampled in spring and summer 1992 ranged from -7.65 to -10 permil. Delta deuterium ratios ranged from -46.5 to -65.0 permil. The imported water is isotopically lighter than the native ground water in the basin. For the imported water, delta oxygen- 18 ratios ranged from -8.6 to -10.1 permil, and delta deuterium ratios ranged from -65 to -75 permil. The isotope data show no evidence of mixing between the imported water and the native ground water in the sampled wells. Statistical analyses show that the difference in the isotopic composition of the imported water and the native ground water is highly significant and that the stable isotopes of oxygen and hydrogen can be used to determine the fate and movement of the imported water in the Rialto-Colton basin.