FLUVIAL ARSENIC IN UTAH VALLEY, SALT LAKE VALLEY AND THE WASATCH RANGE, UTAH: ANALOGY WITH THE GANGES RIVER FLOODPLAIN AND THE HIMALAYAN RANGE

Previous measurements of fluvial As in the Himalayan Range and Ganges River floodplain found that dissolved As was elevated in the Himalayan Range, but fell to undetectable in the floodplain of the Ganges River. The sudden change in dissolved As across the Himalayan-Ganges boundary has been explained by the long residence time in the vicinity of a sediment particle necessary for the large multivalent arsenate oxyanion to adsorb onto sediment, so that the arsenate oxyanion can adsorb onto sediment only when the stream velocity drops. The result that dissolved As falls to undetectable as a river passes from a steep mountain range onto a flat valley floor is so startling and has such major implications for understanding the arsenic cycle and its implications for global public health that the result is being tested in the analogous geological environment of the Wasatch Range of Utah with its corresponding flat valley floors of Utah and Salt Lake Valleys. Twenty water samples each have been collected from the American Fork and Provo Rivers, which traverse the Wasatch Range and Utah Valley to drain into Utah Lake. Ten additional water samples will be collected from Utah Lake as well as twenty water samples from Little Cottonwood Creek, which traverses the Wasatch Range and Salt Lake Valley to drain into Great Salt Lake. Water samples are currently being analyzed with a spectrophotometer for As and the transition elements normally associated with As. Forty sediment samples will be also be collected from the three rivers and Utah Lake to test the hypothesis that dissolved As adsorbs onto sediment at the base of the Wasatch Range. Analysis of the ten most upstream water samples from Provo River have shown elevated dissolved As (As = 0.045 - 0.095 mg/L) at the highest elevations followed by a sharp downstream drop in dissolved As (As = 0.011 - 0.017 mg/L). All As levels thus far exceed the EPA drinking water standard (As = 0.01 mg/L). Further results will be reported at the meeting.