Spectral characterization of dissolved organic matter in groundwater to assess mixing with oil-field water near selected oil fields, southern California

Samples of oil-field water (oil wells, injectate, disposal ponds) and groundwater near selected oil and gas fields in southern California were analyzed for dissolved organic carbon (DOC) concentration and by optical spectroscopic techniques (i.e., absorbance and fluorescence) to assess whether these measurements can be used to distinguish between oil-field water (Oil Field), native groundwater (WG(nat)), and native groundwater mixed with oil-field water from surface (WG(surf)) or subsurface sources (WG(sub)), and if so whether commonly reported optical measurements can be used as a screening tool to identify such water. Concentrations of DOC were significantly (p < 0.0001) higher (67 to 2934 mg C L-1) in oil-field water compared to native groundwater samples (<5.0 mg C L-1). Individual optical properties varied by water category and frequently overlapped. However, multivariate statistical analysis showed that when evaluated in combination, 10 optical properties were determined by discriminant analysis to be significant (p < 0.05) in distinguishing among water categories. Principal component analysis of those 10 optical properties showed that these properties can be used to successfully distinguish Oil Field samples from WG(nat), WG(surf), and WG(sub) even when mixing fractions are low (approximately 10 %).

Automated summary

This study analyzed dissolved organic carbon concentration and optical spectroscopic techniques (absorbance and fluorescence) of oil-field water and groundwater samples in southern California. The results showed significantly higher DOC concentrations in oil-field water compared to native groundwater samples. Multivariate statistical analysis identified 10 optical properties that were significant in distinguishing water categories. Principal component analysis demonstrated the ability to successfully differentiate oil-field water samples from native groundwater mixed with oil-field water.