2011 Annual Report 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. 3.Progress Report Deeper ground waters in the western U.S. often have elevated concentrations of arsenic. Use of these waters for irrigation as well as for municipal use requires knowledge of the transport of the contaminant in soils and sediments, to avoid potential contamination of shallow fresh water supplies. We obtained 3 different sediment materials from USGS. We initiated a column leaching study examining the transport of arsenic (V) when applying waters with 30 ug/L and 300 ug/L at pH 6.5 and 8.0. Drinking water standards are set at10 ug/L in the U.S.). Soils were characterized, native arsenic measured and column materials tested for possible contamination or adsorption of arsenic (V). These results are of interest to any users of water with elevated arsenic concentration, be it municipalities evaluating treatment methods or producers using such waters for irrigation, substituting degraded waters for higher quality waters. This research will contribute to develop new knowledge and guidelines related to arsenic hazards in irrigation waters, helping meet NP211 program and project Objective 1, Develop new knowledge and guidelines related to salinity and ion concentrations for the sustained use of degraded waters for irrigation. Research plans and progress were monitored through two on-site visits, and frequent telephone conversations and emails.