Geochemical survey of stream sediments of the Piceance Creek Basin, Colorado

Abstract

A stream sediment survey was conducted in the Piceance Creek Basin to study the spatial distribution of Zn, Mo, Hg, Cd and As for future baseline considerations. The pH and organic matter were also measured. From samples taken at the mouths (junctions) of most of the named creeks in the basin, it is concluded that none of the streams contained sediments with anomalous trace element concentrations with respect to the basin. But it is thought that Mo and possibly As could be potentially toxic because of their abundance and their mobility under the stream sediments' alkaline condition. From a different sampling plan, designed to describe the background variance of five streams (Roan, Black Sulfur, Parachute, Yellow and Piceance Creeks), it was found that most of the variance occurred at distances from 0-10 m within 2 km stream segments 10 km apart for Mo, Hg, Az, and organic matter. When the variance between the five streams was considered, it was found to dominate the variances of the other factors for Mo, Hg, and Zn. This variance between streams is actually thought to represent the variance between the major drainage system in the basin. When comparison is made between the two sampling design results, it is thought that the trace element concentrations of stream junction samples represented the best range of expected values for the entire basin. The expected ranges of the trace elements from the nested design are thought to be reasonable estimates of preliminary baselines for Parachute Creek, Roan Creek and Black Sulfur Creek within the restricted limits of the streams defined in the text. From the experience gained in pursuing this study, it is thought that composite sampling should be considered, where feasible, to reduce the analytical load and to reduce the small scale variance.