WSP10328

• File Number: 8273.400
• Description: Colorado River Basin Salinity Control - Federal Agencies - Bureau of Land Management
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 3/27/2002
• Author: Schumm and Gregory
• Title: Diffuse-Source Salinity -- Mancos Shale Terrain
• Water Supply Pro - Doc Type: Report/Study

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Agronomists and agricultural engineers use filtered saturated paste
extracts of 1:1 soil-water-ratio extracts to determine the soluble
mineral content (SMC) of soils (U.S. Dept. Agr., 1954). These
determinations are based on a shaking time of one hour or, at times, of
24 hours. The effects of contact time and sediment-water ratios on rate
and extent of dissolution are not taken into consideration in this
technique of determining SMC. Therefore, a different procedure was
developed by Laronne (1977). In order to simulate the dissolution of
transported sediment, he calculated SMC from the quantity of solutes
released from 1.99 sediment/water mixtures.
The calculation of SMC usually requires determination of the
concentration of solutes (SC) of the aqueous solution either by
undertaking a complete chemical analysis or by the evaporation method.
8ecause both techniques are time consuming and expensive,electrical
conductance (EC) has been used as an index of SC by numerous researchers
(Hem, 1970, Lane, 1975). Laronne (1977) derived an empirical
relationstilip between SC and EC of sediment-water mixtures of Mancos
Shale and associated alluvium (Fig. 2-l). Shen et al (l98l) developed
another relationship

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SC = 5.3'10-6EC' + l.05EC -348.4

(2-2)

where SC is expressed in mg/l and EC in ~mho/cm at 250C. The equations
estimate SC equally well and both are non-linear. Linear equations (SC
= kEC, k is a constant) are customarily used for low solute
concentrations (Hem, 1970).
Laronne (1981) sampled alluvium, primarily comprised of sandstone
and sandstone-derived particles from the Mesa Verde Formation, that was
in proximity to Mancos Shale, from the bed, gully walls and banks of
West Salt Creek. Sediment samples were placed in 500 ml Erlenmeyer
flasks to which predetermined quantities of distilled water (EC in the
range 1.5 - 8 ~mho/cm and 5.5 < pH < 6.5) were added. The samples were
shaken for various periods of time. Initiation of these kinetic runs
(time 0) began immediately upon contact of sediment and water. A
similar procedure was used by Jurinak, Whitmore, and Wagenet (1977) to
study the kinetics of salt release from Mancos Shale sampled in the
Price River Basin. Dissoluton rates were derived from EC data.

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