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<br />Precipitation-Chemistry Data at Selected Sites in
<br />Northwestern Colorado, 1980-94
<br />
<br />By Anthony J, Ranalli
<br />
<br />Abstract
<br />
<br />The chemical content of precipitation was
<br />monitored during the period 1980--94 at three
<br />sites at altitudes above 2,400 meters near the
<br />Piceance Basin in northwestern Colorado, Daily
<br />precipitation volumes, specific conductance, pH
<br />(in this report pH is expressed as hydrogen-ion
<br />concentration), concentrations of major cations
<br />and anions, calculated charge balance between
<br />cations and anions, and summary statistics of
<br />chemical concentrations are tabulated, Sampling
<br />sites are plotted on a map of the area, Seasonal
<br />variabilities of major cation and anion concentra-
<br />tions are presented graphically,
<br />
<br />INTRODUCTION
<br />
<br />Knowledge of the chemistry of precipitation is
<br />needed in the preparation of permit requests for new
<br />sources of emissions to the atmosphere and for review
<br />of these requests, One area in which data may be
<br />needed is northwestern Colorado. Energy resources,
<br />such as oil shale and coal, are upwind from the
<br />federally protected Flat Tops Wilderness Area, which
<br />is sensitive to acid rain (Turk and Adams. 1983). The
<br />lack of precipitation-chemistry data in northwestern
<br />Colorado partially was addressed by establishment of
<br />a network of monitoring sites as part of a study done
<br />by the U,S. Geological Survey, in cooperation with
<br />Delta, Mesa, and Rio Blanco Counties, and assisted by
<br />the Rocky Mountain Oil and Gas Association. The
<br />network is located near the oil shale reserves of the
<br />Piceance Basin. Data collected from these sites
<br />provide a baseline for ambient atmospheric deposition
<br />that could be compared to any future measurements,
<br />The data also are suitable for making estimates of
<br />
<br />natural variability in precipitation chemistry. This
<br />report presents data collected at the monitoring sites
<br />from 1980 to 1994 and includes site location,
<br />sampling and laboratory analytical methods, precipita-
<br />tion volume and summary statistics, and seasonal
<br />variability,of major chemical constituents.
<br />
<br />Site Description
<br />
<br />The three precipitation-monitoring sites
<br />(fig. I) are located at Douglas Pass at an altitude of
<br />2,710 meters in a treeless area of sage; at Grand Mesa,
<br />at an altitude of3,I21 meters in a clearing; and at
<br />Marvine Ranch, at an altitude of 2,414 meters in a
<br />clearing.
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<br />Methods
<br />
<br />Precipitation volume and chemistry have been
<br />monitored at Douglas Pass since November 1980, at
<br />Grand Mesa since August 1981, and at Marvine Ranch
<br />since April 1981. Data collection was discontinued at
<br />Douglas Pass and Grand Mesa in October 1991 but is
<br />ongoing at Marvine Ranch, The sampling equipment
<br />and analytical methods are the same at each site. The
<br />sampling intervals, however, varied at each site. The
<br />sampling equipment consisted of a Belfort weighing-
<br />bucket rain gage for the measurement of precipitation
<br />volume and an Aerochem Metrics Model 301 wet/dry
<br />collector for the monitoring of wet deposition, The
<br />samples collected at each site are a combination of
<br />single storms and two or more storms collected into a
<br />single sample, Unfiltered precipitation samples were
<br />analyzed for specific conductance, pH, dissolved
<br />calcium, magnesium, sodium, potassium, ammonium,
<br />chloride, nitrate, and sulfate by the U,S, Geological
<br />Survey National Water-Quality Laboratory in Arvada,
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<br />INTRODUCTION 1
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