The quality of mine water in the 75 square-mile Western Middle anthracite field was determined by sampling discharges and boreholes at about 60 abandoned and flooded mines during 1975-78. Geologically, the field is a synclinal basin, divided by parallel faults into more than a score of smaller basins that contain the coal deposits. An estimated 1.6 billion (1,600,000,000) tons of anthracite were mined. Most of the deep mines are now closed and flooded. The Vulcan-Buck Mountain mine, east-northeast of Mahanoy City, contains an estimated 6,100 acre-feet of water with a specific conductance of from 380 to 460 uS/cm (microsiemens), and a pH of from 4.4 to 4.6 units. Twenty-two mines are in the Mahanoy basin and the Shenandoah complex a 15-square mile area between Mahanoy City and Girardville. Seven of these mines, located in the Mahanoy basin, may contain 30,000 acre-feet of water. Specific conductance ranges from 630 yS/cm in the Tunnel mine to 1,800 uS/cm in the Gilberton mine. Fifteen of these mines are in the Shenandoah complex. Specific conductance ranges from 240 to 310 uS/cm in mines in the eastern end of the complex to 2,400 uS/cm in the western end. The specific conductance of water in eight mines near Mount Carmel ranges from 460 to 980 yS/cm. Seventeen mines are located near Shamokin; water from at least 12 mines drains into other mines before discharging at the surface. Water from the largest single discharge, 11 cubic feet per second, had a specific conductance of 950 yS/cm. The North Franklin mine near Trevorton, contains about 4,900 acre-ft of water with a specific conductance of about 1,100 uS/cm. 'An acre-foot of water is the amount required to cover one acre to the depth of one foot. It is equivalent to approximately 326,000 gal. Geologic Setting Geologically, the Western Middle anthracite field is a synclinal basin that is divided by parallel faults into 26 smaller basins that contain the coal deposits (figs. 2 and 3 on plate 1 at back of book). The most prominent of the coal basins is the 25-mile-long Mahanoy basin, which extends along the southern boundary of the Western Middle field from a point 5 miles east of Mahanoy City to about the same distance west of Locust Gap. The Mahanoy basin is separated from the rest of the basins that comprise the Western Middle field by the Suffolk fault, which extends from east of Mahanoy City to Girardville, and by the Locust Gap fault, which extends from Girardville to west of Locust Gap. North and northwest of Mahanoy City are eight basins that will be referred to collectively as the Shenandoah complex. They are the Mahanoy City,

Anthracite has been extensively mined in four areas of eastern Pennsylvania. Almost all underground mining in the four areas, the Northern, Eastern Middle, Western Middle, and Southern Fields, has been discontinued and many mines are abandoned and flooded. Precipitation on much of the 408 square miles of coal fields infiltrates to the underground mine complexes, and Is discharged as mine drainage from tunnels, mine entrances, and boreholes.Mine drainage was measured and sampled at 251 sites that had a total discharge of 918 cubic feet per second, a total sulfate load of 1,470 tons per day, and a total iron discharge of 79 tons per day. The largest sulfate yield was 5.4 tons per day per square mile from the Western Middle Field. The yields from the Northern, Eastern Middle, and Southern Fields were 4.6, 3.6, and 1.4 tons per day per square mile, respectively. Methods of StudyLocations of mine-water discharges were compiled from published reports and from information obtained from State and Federal agencies, and were verified in the field prior to sampling. Generally, sites having discharges of less than 0.1 ft 3 /s were not included in the 251 sites sampled during the study. Water-quality data were determined from unfiltered samples; except for dissolved iron, which was determined from filtered samples. Samples for laboratory analyses were collected and preserved following standard Geological Survey procedures. To supplement the sampling program, flow and water-quality data were collected monthly at 12 sites. The U.S. Bureau of Mines in Wilkes-Barre and Schuylkill Haven, and the Pennsylvania Department of Environmental Resources assisted with the data collection. DESCRIPTION OF THE STUDY AREA Coal FieldsThe term "anthracite region" as used in this report includes the four anthracite fields and surrounding areas, as shown in figure 1. Anthracite has been extensively mined in four separate coal fields in east-central Pennsylvania the Northern, Eastern Middle, Western Middle, and Southern. The coal fields underlie parts of 10 counties and extend from 20 mi northeast of Harrisburg to 20 mi northeast of Scranton. Their combined area is about 408 mi 2 .