In addition to streamflow, geologic, ground water, and chemical water-quality data obtained in the field by personnel of the Geological Survey, information on many wells and borings has been supplied by municipal and state agencies. Also, Metcalf and Eddy, Whitman and Howard, Weston and Sampson, consulting engineering firms in Boston, kindly furnished additional data on wells and borihgs. Further, R.E. Chapman Co., Oakdale, Mass.; Layne-New England Co., Arlington, Mass.; and D.L. Maher Co., North Reading, Mass., drilling companies, generously supplied logs and other records of wells. The authors thank all those who_supplied data and those who allowed personnel of the Geological Survey to install equipment and to collect data on their property. DEFINITION OF TERMS Definition of terms related to streamflow, water quality, and other hydrologic data, as used in this report, are defined as follows: Color is expressed in units of the platinum-cobalt scale proposed by Hazen (1892, p. 427-428). A unit of color is produced by 1 milligram per liter of platinum in the form of the chloroplatinate ion. The extent to which water is colored by material in solution is reported as part of the water analysis because a significant color in water may indicate the presence of organic material that may have some bearing on the dissolved-solids content. Cubic foot per second. (cfs) is the rate of discharge representing a volume of 1 cubic foot passing a given point during 1 second and is equivalent to 7.48 gallons per second, 448.8 gallons per minute, or 646,317 gallons per day. Discharge is the volume of water that passes a given point at a particular instant of time. Tem;,eerature. To convert temperature data shown in degrees Celsius (centigrade, °C) to degrees Fahrenheit (°F), see following table: Temperature conversion table, degrees Celsius (°C) to degrees Fahrenheit (OF) OF = 9/5 (°C) +32 or °C = 5/9 (°F-32) oc