Using a geographic information system, a regression model has been developed to identify and to assess potential sources of selenium in the Kendrick Reclamation Project Area, Wyoming. A variety of spatially distributed factors was examined to determine which factors are most likely to affect selenium discharge in tributaries to the North Platte River. Areas of Upper Cretaceous Cody Shale and Quaternary alluvial deposits and irrigated land, length of irrigation canals, and boundaries of hydrologic subbasins of the major tributaries to the North Platte River were digitized and stored in a geographic information system. Selenium concentrations in samples of soil, plant material, ground water, and surface water were determined and evaluated. The location of all sampling sites was digitized and stored in the geographic information system, together with the selenium concentrations in samples. A regression model was developed using stepwise multiple regression of median selenium discharges on the physical and chemical characteristics of hydrologic subbasins. Results indicate that the intensity of irrigation in a hydrologic subbasin, as determined by area of irrigated land and length of irrigation delivery canals, accounts for the largest variation in median selenium discharges among subbasins. Tributaries draining hydrologic subbasins with greater intensity of irrigation result in greater selenium discharges to the North Platte River than do tributaries draining subbasins with lesser intensity of irrigation.

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Concentrations of dissolved selenium (Se) as large as 330 µg 1-1 have been detected in water samples from backfill aquifers in the southern Powder River Basin (PRB) of northeastern Wyoming. During surface coal mining, rock material overlying the coal is redistributed in relation to its original stratigraphic position; exposure of the previously buried material to surface oxidizing conditions decreases the stability of sulfides and organic matter containing Se, increasing Se concentrations in associated ground waters. Groundwater and backfill-core samples were collected from three sites located at two active mines in the PRB. Dissolved organic carbon (DOC) in the groundwater samples was domimrtoo by the acid fraction (sum of hydrophobic and hydrophilic acids) at 38 to 84 % of the DOC; the neutral fraction (sum of hydrophobic and hydrophilic neutrals) ranged from IO to 55% and the base fraction (smn of hydrophobic and hydrophilic bases) was generally less than 10%. Three sorption experiments were conducted to investigate selenite sorption on backfill-core samples. Selenite concentrations in these experiments rangoo from O to 11 mg kl in backfill-core samples. The first experiment determined the selenite sorption capacity of the backfill-core samples with selenite in distilloo-deionized water as a background solution. In the second experiment, selenite in 0.1 M CaCl 2 was used as a background solution. In the third experiment, hydrophobic and hydrophilic acid fractions, isolated and concentrated from groundwater samples, were added to the selenite background solutions. Results of the three experiments indicated that the backfill-core samples have a high sorption capacity for Se (generally, greater than 90% of the added Se) and can sorb as much as 99 % of Se added as selenite. Selenium sorption increased in most samples when 0.1 M CaC1 2 was used as a background solution compared to distilled-deionized water background solution. The increase in selenite removal might have been caused by precipitation reactions or by an increase in positively charged surfaces caused by calcium sorption, or both. A substantial decrease in selenite sorption rates occurred in the presence of individual organic-solute fractions. Hydrophilic acids caused the largest decrease in Se sorption by the backfill-core samples.

Three moisture sensors were tested as a means for determining the surface wetness on carbonate building stones exposed to conditions that produce deposition of moisture. A relative-humidity probe, a gypsum-coated circuit grid, and a limestone-block resistor were tested as sensors for determining surface wetness. Sensors were tested under laboratory conditions of constant relative humidity and temperature and also under on-site conditions of variable relative humidity and temperature for eight weeks at Newcomb, NY. Laboratory tests indicated that relative humidity alone did not cause sensors to become saturated with water. However, the rates of drying indicated by the sensors after an initial saturation were inversely related to the relative humidity. On-site testing of the relative-humidity probe and the gypsum-coated ciruit grid indicated that they respond to a diurnal wetting and drying cycle; the limestone-block resistor responded only to rainfall.