Wekiva Aquifer Vulnerability Assessment

Author : Michael G. Alcorn
Publisher :
ISBN 13 :
Total Pages : 316 pages
Book Rating : 4.:/5 (412 download)

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Download or read book Assessment of Aquifer Vulnerability Influenced by Climatic Differences in Southeast, Southcentral, and Northern Alaska written by Michael G. Alcorn and published by . This book was released on 1996 with total page 316 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Climate and soil characteristics critically influence aquifer contamination potential at Federal Aviation Administration facilities at Juneau International Airport in southeast Alaska, Anchorage Air Route Traffic Control Center in southcentral Alaska, and Dead-horse Airport in northern Alaska. Because of high soil infiltration rates (3crnlmin) the Anchorage aquifer is considered the most vulnerable to surface spill contamination. Soil pits dug revealed about 80 em of silty to very rocky or sandy soil overlying highly permeable (5.7 em/min) unconsolidated sediments. Wells showed the water table is 9 m below ground surface. Large surface spills would infiltrate through the soil and unconsolidated sediments to reach the water table of the 19 m thick, unconfined sand and gravel aquifer in about 2 hours, 50 minutes. Ground water flows due west at about 90 m/year towards the Knik Arm of the Cook Inlet. Water wells located down gradient would be contaminated in an estimated 3 to 5 years after a large surface spill. No known contamination problems exist, however, immediately north of the site on Elmendorf Air Force Base, monitoring wells have detected low levels of fuels, solvents, and metals coming from a closed landfill. Future contamination potential at the site is moderate due to the existence of several above ground fuel storage tanks. The Juneau aquifer is the least vulnerable because low soil infiltration rates (0 - 0.48 em/min) impedes infiltration and will cause spills to flow mostly as surface runoff to streams and the ocean. The coastal location and surface-and ground-water flow directions limit down-gradient contamination potential to undeveloped intertidal zones and coastal waters. Soil pits revealed very silty soils of varying depths over sandy gravel outwash. Although the land beneath the airport runway and its associated buildings has been raised with undifferentiated fill material, aquifer contamination potential remains low because the low permeability of the buried soil. Monitoring wells showed the water table about 1 to 5 m below ground surface. Ground water flows southwest towards the Gastineau Channel in the 60 m thick unconfined aquifer. High precipitation rates of about 1,400 mm/year will help to dilute and disperse contaminant spills. The dominant maritime climate here produces mild temperatures that promote natural attenuation of contaminants by microbial biodegra- dation. Petroleum hydrocarbons and low concentrations of polychlorinated biphenyls have been detected in soil samples, but water samples have been uncontaminated. Spill damage could be minimized by isolating the spill by damming surface flow and promptly recover- ing the product. Future site spill potential is high due to aircraft fuel storage tanks and the operation, maintenance, and storage of aircraft. The Deadhorse aquifer is considered a special case because of complete seasonal freezing due to the arctic climate. Although soil infiltration rates (0.1 to 6.0 em/min) fall between those of Anchorage and Juneau, the unique permafrost environment increases aquifer vulnerability because any remediation efforts would be destructive. Soil pits revealed a thick vegetative mat, 10 to 20 em thick, overlying silty soil which extends below the permafrost at about 5 m below ground surface. Permafrost acts as a near-surface con-fining layer that will restrict contaminant migration. Natural attenuation of contaminants by microorganisms is impeded by cold temperatures. During the short summer when the upper 0.5 m of soil is thawed, a surface spill in unsaturated areas may contaminate the soil down to the frost table, while spills in saturated areas may float on the water surface. Disturbance or removal of the vegetative mat during cleanup operations may result in new freeze-thaw features. Buildings and roads are built on raised gravel pads (1.5 to 2.5 m thick), designed to insulate the soil and keep it perpetually frozen. Liquids spilled on the gravel pads can be expected to infiltrate through the gravel and accumulate on the frost table. The site has no known contamination problems. Future spill potential is moderate due to the limited oper- ation of aircraft and fuel storage."--Document.