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Coal has been strip-mined in the Healy and Lignite Creek basins of the Nenana coal field. Trace metals concentrations are low in Healy Creek, but are higher in the Lignite Creek basin. Concentrations of trace metals increase as Healy Creek and Sanderson Creek (in the Lignite basin) flow past mined areas, but effects of coal mining cannot be distinguished from those due to a change in lithology or coal outcrop burning. Metals are typically concentrated on the suspended sediment. The source of the trace metals on sediment and in the water is probably the finegrained Tertiary rock of the coal-bearing group. Local coals do not contain high levels of trace metals. Concentrations of dissolved and suspended trace metals in water and total-recoverable trace metals in the bed material do not present an environmental hazard in the Healy and Lignite Creek basins at this time. Mining does not appear to have had any appreciable effect on the quality of ground water in the basins. INTRODUCTION Purpose Coal can adsorb trace metals during coalification, then release them into the environment when the coals are weathered and exposed to erosion. Trace metals in materials associated with the coals also can be released as these materials are disturbed during mining. The purpose of this study was to determine the concentration, distribution, and possible sources of selected trace metals in surface water and stream sediments of the Healy Creek and Lignite Creek basins in the Nenana coal field, Alaska. Acknowledgment The author wishes to thank Dorothy E. Wilcox for her contributions to this report. Ms. Wilcox, who has since resigned from the Geological Survey, conducted field investigations and collected and made preliminary analyses of the data that are the basis of this paper. Location The Nenana coal field, the smallest of Alaska's three major coal basins, lies in central Alaska about 200 mi north of Anchorage and 80 mi south of Fairbanks (fig. 1). The coal-bearing strata lie in a belt about 80 mi long and from 1 to 30 mi wide (Wahrhaftig and others, 1969) which parallels the northern foothills of the Alaska Range. The Healy Creek and Lignite Creek basins are the two principal coal-producing areas in the Nenana coal field. The two creeks flow from the center of the coal field westward to the Nenana River, which flows northward into the Tanana River at Nenana. 180* 70° 172* 164° 156° 148° 140° 132" 124" 0 100 200 300 400 500 KILOMETERS Adapted from U.S.Geological Survey Map C Figure 1.-Location of the Nenana coal field. Geology The Healy and Lignite Creek basins are underlain by Precambrian or Paleozoic metamorphic rocks (Wahrhaftig, 1970). In the lower part of the Healy Creek basin and most of the Lignite Creek basin, this basement rock is unconformably overlain by coal-bearing strata of Tertiary age (fig. 2). The coal-bearing material crops out along Healy and Lignite Creeks; in many areas it is overlain by the Nenana Gravel of Tertiary age and by Quaternary deposits. The coal-bearing formations, which range in age from Oligocene to Miocene, are in east-west striking synclines and are mainly poorly consolidated terrestrial quartz sandstones, siltstones, and claystones, interbedded with coal. Although some abrupt lateral facies changes are present, other strata form thick, laterally persistent beds. Some beds break down easily to cause landslides. Coal of the Nenana field ranges in thickness from thin partings to beds up to 100 ft thick. Much of the coal is blocky-fractured and sub-bituminous with a low (0.2 percent average) sulfur content, average ash content of 10 percent, and moisture content of 24 percent. Average BTU content is 8030 for Healy Creek coals and about 9000 for Lignite Creek coals (National Research Council, 1977). 64 ° 0 0' T 11 S R 8W 14 9° 00 ' R 7W R 6W R 5W 1 48 ° 3 0' R 4W T 12 S T 13 S 63 ° 4 5' I I T er tia ry s ed im en ta ry r oc k h 11 L ow er P al eo zo ic a nd ( or ) Pr ec ar nbr ia n sc hi st b ed ro ck / '* I nf er re d ge ol og ic c on ta ct B as e fr om U .S . G eo lo gi ca l S ur ve y H ea ly , A la sk a, 1 :2 50 ,0 00 ,1 95 6 0 1 2 3 4 5 M IL E S 0 5 K IL O M ET ER S (F ro m W ah rh af tig , 1 97 0) Fi gu re 2 .G en er al iz ed b ed ro ck g eo lo gy in a p ar t of th e N en an a co al f ie ld . 1 Healy C near Usibelli 2 Healy C 0.1 mi above French Gulch 3 Healy C near Suntrana 4 Sanderson C 1.6 mi above Lignite C 5 Sanderson C 0.8 mi above Lignite C 5A Lignite C above Sanderson C 7 Lignite C 0.5 mi above mouth Drainage basin border

Trace metals in surface water and stream sediments of Healy and Lignite Creek basins, Alaska