Assessing the Impact of Animal Waste Lagoon Seepage on the Geochemistry of an Underlying Shallow Aquifer
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- 作者：Walt W. McNab ; Jr. ; Michael J. Singleton ; Jean E. Moran ; Brad K. Esser
- 刊名：Environmental Science & Technology
- 出版年：2007
- 出版时间：February 1, 2007
- 年：2007
- 卷：41
- 期：3
- 页码：753 - 758
- 全文大小：593K
- 年卷期：v.41,no.3(February 1, 2007)
- ISSN：1520-5851
文摘
Evidence of seepage from animal waste holding lagoonsat a dairy facility in the San Joaquin Valley of California isassessed in the context of a process geochemicalmodel that addresses reactions associated with theformation of the lagoon water as well as reactions occurringupon the mixture of lagoon water with underlying aquifermaterial. Comparison of model results with observedconcentrations of NH4+, K+, PO43-, dissolved inorganiccarbon, pH, Ca2+, Mg2+, SO42-, Cl-, and dissolved Ar inlagoon water samples and groundwater samples suggeststhree key geochemical processes: (i) off-gassing ofsignificant quantities of CO2 and CH4 during mineralizationof manure in the lagoon water, (ii) ion exchange reactionsthat remove K+ and NH4+ from seepage water as it migratesinto the underlying anaerobic aquifer material, and (iii)mineral precipitation reactions involving phosphate andcarbonate minerals in the lagoon water in response to anincrease in pH as well as in the underlying aquifer fromelevated Ca2+ and Mg2+ levels generated by ion exchange.Substantial off-gassing from the lagoons is furtherindicated by dissolved argon concentrations in lagoonwater samples that are below atmospheric equilibrium. Assuch, Ar may serve as a unique tracer for lagoon waterseepage since under-saturated Ar concentrations ingroundwater are unlikely to be influenced by any processesother than mechanical mixing.