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I I I I I I I I I I I I I I I I I I I 3.9 Air Quality The CDPHE Air Quality Control Division considers the Alamosa River Watershed along with the San Luis Valley an attainment area. The area meets air quality standards for carbon monoxide, ozone, and particulate matter (PM10). The Summitville Mine Superfund project established two air monitoring stations and a meteorological station in the upper portion of the watershed where particulate concentrations were a concern. Air quality parameters tested were total suspended particulates (TSP) and PM10. Results of the air quality and meteorological data in the upper watershed showed (18): · Mean wind speed was 7.1 miles per hour (6.2 knots). · Calm conditions of less than 1 knot exist only 0.7 percent of the time. · Baseline TSP concentrations are 15 :1:3 ug/m3. · Highest TSP concentrations occur April- June and the lowest occur during January- March. 3.10 General Geologic Setting The Alamosa River Watershed is composed of two main physiographic subdivisions; 1) The Alamosa Basin and 2) the San Juan Volcanic Hills forming the San Juan Mountains. The Alamosa Basin is in the lower portions of the watershed and is characterized by a featureless floor comprised of alluvial fan deposits. The San Juan Volcanic Hills that formed the San Juan Mountains is a remnant of a nearly continuous volcanic field that extended over the Rocky Mountains during the Oligocene time. The mountains are made of volcanic rocks, and related shallow rock of middle or late Tertiary age (9). Geologic hazards in the watershed are comprised of avalanches, landslides, rockfalls, mudflows, debris fans, and unstable slopes. The Alamosa River Watershed is composed of alluvial material associated with the Holocene and glacial outwash terraces. The mountains in the upper watershed are of volcanic origin with alpine glaciation. Glacial deposits in the Upper Alamosa River Watershed are unconsolidated heterogeneous mixtures of cobble, gravel, and sand. The lower portion of the watershed is composed of finer alluvial materials of gravel, sand, and cohesive sediment (19). 3.11 Soils The Graypoint soil series is the major soil type in the watershed and is typical of arid soils. Volcanic rock fragments dominate this soil type. Iron oxides interlaced with clay skins occur in these soils. These soils are considered well drained and classified by loamy-skeletal over sand skeletal mixed frigid, typic calciargid. Extensive soil profile descriptions are provided in these references. Some soil studies were performed on the acid buffering capacity of the agricultural Alamosa River Basin soils. The objective of the studies was to determine the impact of acidic irrigation water on the chemical and mineralogical characteristics of the soils in the watershed (20, 21). 3-9