1a.Objectives (from AD-416):
Conduct laboratory soil column studies, to determine the arsenic adsorption properties of sediments collected by the USGS from Antelope Valley CA.
1b.Approach (from AD-416):
We will examine arsenic adsorption and transport for the different sediment texture and 2 pH values (7.5 and 8.5) and two arsenic concentrations (10 and 100 µg/L) of applied water. We will also evaluate computer model predictions based on comparison with experimental data.
The project is related to Objective 2 of the parent project, "Improve our ability to predict the impact of degraded waters on infiltration into soils and plant response to irrigation with these waters by, a) determining the impact of using degraded waters for irrigation, including the effect of solution chemistry, high dissolved organic matter, and application of organic wastes, on soil physical and chemical properties". ThE overall objective of this project is to evaluate the use of infiltration ponds to remediate waters with elevated arsenic. In this project, we are examining the adsorption characteristics of arsenic as a function of pH on alluvial sediments and the adsorption and transport of arsenic in those sediments. The US Geological Survey (USGS) is examining the potential of utilizing infiltration ponds to remediate ground waters elevated in arsenic and recharge a shallow aquifer with low arsenic water. In consultation with USGS scientists, we earlier adjusted the conditions of the leaching of solutions elevated in arsenate to pH 6.5 and 8.0 and the arsenate concentrations of the leaching solutions to 30 and 300 micrograms per liter (ug/L). During this last year we completed the leaching study of the three unconsolidated sediments provided from the borehole by USGS, examining arsenate transport in these materials at two pH values and two arsenate concentrations with two replicates per material. We also completed the study of arsenate adsorption of these materials including adsorption as a function of pH and adsorption as a function of arsenate concentration (As). Leaching with 50 pore volumes of solution with elevated arsenic resulted in no effluent above the drinking water standard. We conducted a limited desorption study, evaluating the potential of the adsorbed material to be released back into solution. Our preliminary results suggest that As will not be released back into solution at levels above the drinking water standard of 10 ug/L if there is subsequent recharge of rain or uncontaminated water.