Test well Ch-Bf 146 was drilled to 1,650 ft below land surface to explore and evaluate the Patapsco Formation aquifers deeper than 1,000 ft in the Waldorf/La Plata area of Charles County, Maryland. The test hole penetrated two major aquifer systems above a depth of 1,000 ft and another major aquifer system and aquifer below 1,000 ft. The deepest aquifer system found in the test drilling, the Lower Patapsco aquifer system, is comprised of a group of sands which lie between 1,140 ft and the base of the Patapsco Formation at 1,417 ft. The Waldorf aquifer system, overlies the Upper Patapsco aquifer system and includes sands in the Waldorf/La Plata area that are referred to as the ' Magothy aquifer ' by other. At the test well site, the Waldorf aquifer system consists solely of sands in the Magothy and Monmouth Formations. The three major aquifer systems and the Middle Patapsco aquifer are correlative along the regional strike for at least 10 miles in the Waldorf/La Plata area. Correlations of geophysical logs indicate that individual sands 15 to 25 ft thick can be traced between wells. Geophysical log correlations also indicate that, at some well sites, the Waldorf aquifer system and the Upper Patapsco aquifer system are in sand-on-sand contact and function as one major hydrologic system at these sites. A production well (Ch-Bf 147) was drilled at the site of the test well (Ch-Bf 146). The initial static water level of these aquifers was 9.8 ft below sea level. Evaluation of the 24-hr pumping test of Ch-Bf 147 resulted in a transmissivity of 14,000 gpd/ft (gallons per day per foot) for the first 2 hours of the test and 7,300 gpd/ft for the remainder of the test. The decrease of 6,700 gpd/ft in the transmissivity indicates that the well 's expanding cone of depression intersected a transmissivity boundary after 2 hours of pumping. The Patapsco sands tested in Ch-Bf 147 have a storage coefficient of 0.0016. The hydraulic conductivity of the producing sands in Ch-Bf 147 is 127 gpd/sq ft. The quality of groundwater from the Lower Patapsco aquifer system and the Middle Patapsco aquifer is suitable for most purposes. The water is nearly neutral (pH = 7.4), low in dissolved solids (about 200 mg/L), low in specific conductance, slightly warm (22 C), very soft, naturally fluoridated, and moderately high in dissolved silica. (Lantz-PTT)