Denitrification in a Deep Basalt Aquifer: Implications for Aquifer Storage and Recovery

Abstract

Aquifer storage and recovery (ASR) can provide a means of storing water for irrigation in agricultural areas where water availability is limited. A concern, however, is that the injected water may lead to a degradation of groundwater quality. In many agricultural areas, nitrate is a limiting factor. In the Umatilla Basin in north central Oregon, shallow alluvial groundwater with elevated nitrate-nitrogen of <3 mg/L to >9 mg/L is injected into the Columbia River Basalt Group (CRBG), a transmissive confined aquifer(s) with low natural recharge rates. Once recovery of the injected water begins, however, NO3 -N in the recovered water decreases quickly to <3 mg/L (Eaton et al. 2009), suggesting that NO3 -N may not persist within the CRBG during ASR storage. In contrast to NO3 -N, other constituents in the recovered water show little variation, inconsistent with migration or simple mixing as an explanation of the NO3 -N decrease. Nitrogen isotopic ratios (δ(15) N) increase markedly, ranging from +3.5 to > +50, and correlate inversely with NO3 -N concentrations. This variation occurs in <3 weeks and recovery of <10% of the originally injected volume. TOC is low in the basalt aquifer, averaging <1.5 mg/L, but high in the injected source water, averaging >3.0 mg/L. Similar to nitrate concentrations, TOC drops in the recovered water, consistent with this component contributing to the denitrification of nitrate during storage.

Avaliação de viabilidade de aplicação de técnicas de recarga artificial em aquíferos salinizados, fraturados, Petrolina - PE

“…Tal fato confirma a maior sensibilidade dos isótopos na detecção de misturas de águas. Nelson & Melady (2014) relatam o uso de isótopos de nitrogênio (δ 15 N) e análise hidroquímica para monitoramento de sistemas de recarga artificial do tipo ASR em Oregon nos EUA.…”