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As a part of an evaluation of a proposed reactor site, the Geological Survey, in 1955, at the request of the Corps of Engineers, made a ground-water investigation at and in the vicinity of the Maynard Ordnance Test Station, in northeastern Massachusetts about 22 miles west of Boston. The general investigation covered about 6 square miles but the most detailed study was made in an area of about 1 square mile at the Maynard Ordnance Test Station. Land surface in most of the area is a plain at an altitude of about 200 feet above sea level. In several places hills composed of till and of bedrock project above the plain to altitudes as high as 320 feet. Ponds and swamps are numerous, several small brooks whose low flow represents ground-water discharge furnish surface The three main water-bearing units are glacial outwash, glacial till, and bedrock. The outwash has a maximum thickness of about 100 feet and is composed of beds chiefly of sand and gravel in the upper part, and of silt in the lower part. It is the uppermost unit in most of the area and contains the principal water body. During an aquifer test, a well screened in the outwash yielded about 600 gpm with a drawdown of 17 feet after 50 hours of pumping. The transmissibility, permeability, and storage coefficient of the outwash in the vicinity of the well, as determined by the aquifer test, were about 34,000 gallons per day per foot, about 800 gallons per day per square foot, and about 0.20, respectively. Till, composed of compact, unsorted boulders, gravel, sand, silt, and clay, is deposited irregularly on the bedrock surface. Owing to its low permeability the till yields only small quantities of water to wells. The bedrock is composed of igneous and metamorphic rocks of Precambrian(?) and Paleozoic age. It yields small quantities of water from openings along joints, irregular fractures, and cleavage planes. Contours on the surface of the bedrock, drawn largely from seismic refraction data, show a buried valley as deep as 120 feet below the land surface in part of the area. Contours of the water table show that the ground-water divides are relatively low and broad and that most of the streams and ponds intersect the water table. The depth to water ranges from land surface to about 30 feet below. Both the ground water and the surface water generally are soft and have a pH of less than 7.0. The natural beta-gamma activity and the radium concentration of the waters are low. The peak daily withdrawal of ground water E-l E-2 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES within the report area in 1955 was about 612,000 gallons. About 90 percent of the water was pumped from White Pond, a water-table pond, and the remainder mostly from domestic wells. INTRODUCTION SCOPE AND PURPOSE In the spring of 1953 the Geological Survey was asked by the Corps of Engineers, U.S. Army, to make a reconnaissance of the geology and ground water conditions at the Maynard Ordnance Test Station (MOTS) and vicinity for a site-evaluation report. Consideration was being given to establishing a small experimental nuclear reactor, and ground water was to be used for cooling and subsequently returned to the ground. The Maynard Ordnance Test Station is in the southwestern part of Middlesex County, Mass., about 22 miles west of Boston (pi. 1). It occupies parts of the towns of Hudson, Sudbury, Maynard, and Stow. The part of the test station and vicinity referred to as the Maynard area in this report, is almost entirely within the towns of Sudbury and Hudson; a small part is in the towns of Stow and Marlboro. The area was examined in May and June, and an administrative report was submitted in July 1953. That report, prepared by E. S. Simpson, pointed out the need for more specific geologic and hydrologic information, particularly with respect to the availability and the direction of movement of ground water. In February 1955 the Geological Survey was requested by the Corps of Engineers to make a more intensive investigation of the ground-water conditions. A program of construction of test and observation wells was laid out, and plans were made for a seismic refraction survey, periodic measurements of water-level fluctuations in observation wells, measurements of stream discharge, and a detailed pumping test in a proposed supply well. After the fieldwork was completed, a condensed report was submitted to the Corps of Engineers (Perlmutter, 1957). Plans for construction of the reactor installation were abandoned. However, as ground-water conditions in the Maynard area are believed to be representative of those in much of central Massachusetts, it was decided to expand the content and interpretation of the earlier reports and to present all the information in a single published report on the ground-water geology and hydrology. The objectives of this report are to present and to interpret the significant information with respect to (a) extent, thickness, hydraulic continuity, and physical properties of the water-bearing deposits, (b) the configuration of the surface of the bedrock, (c) the direction of movement of the ground water, (d) the quality of the water, and (e) the hydraulic characteristics of the outwash deposits in part of the area as revealed by a pumping test. GROUND-WATER GEOLOGY AND HYDROLOGY, MAYNARD, MASS. E~3 METHODS OF INVESTIGATION Fieldwork began in February 1955 and was virtually completed by the end of September 1955. Initially, the work consisted of extending the inventory of existing wells which had been started by Simpson and others in 1953, examination of the geologic and hydrologic features in the area, and observation of the drilling of five deep test holes by a crew of the Corps of Engineers. Spoon samples of the unconsolidated deposits and cores of the bedrock were taken at each of the test holes. Upon completion of this test drilling, 1%-inch pipe and well points were installed in the unconsolidated deposits to obtain periodic water-level measurements. Seismic refraction surveys were made in May and again in September 1955 by the Geological Survey. In the spring of 1955 a recording rain gage was put into operation at MOTS and water-level recorders were installed on two wells. The Geological Survey constructed a temporary gaging station on Marlboro Brook (pi. 1), equipped with a V-notch weir; and established a site for miscellaneous discharge measurements on a small nearby brook. Corps of Engineers personnel installed 28 small-diameter observation wells and the Geological Survey installed 7 similar wells to provide control for a contour map of the water table. Altitudes of measuring points on these wells, of a small number of privately owned wells, and of 39 swamps and ponds were determined by spirit leveling. The Corps of Engineers did most of this work, and also most of the leveling required for the seismic survey. During July and August 1955 a supply well, 57 feet deep, and 9 nearby observation wells were installed. In September 1955 a 50-hour pumping test was made on the supply well, and water-level readings were taken in 20 observation wells. Water-level measurements, at monthly or shorter intervals, were made at observation wells, ponds, and swamps throughout the summer and fall of 1955, and continued in selected ones of these until the end of June 1956. At the end of September and during the first week of October 1955 a series of water-level measurements were made in all the accessible wells and ponds, both in and near the test station, for use in the preparation of the contour map of the water table (pi. 1). ACKNOWLEDGMENTS The fieldwork and the preparation of the preliminary reports in 1953 and 1957 were done under the immediate supervision of J. E. Upson, formerly district geologist, Mineola district. This report was prepared under the supervision of G. C. Taylor, Jr., district geologist. Henry G. Healy gave considerable help to the writer in the fieldwork. The Corps of Engineers actively participated by constructing test and observation wells and carrying on most of the spirit leveling, and E-4 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES mechanical (particle-size) analyses of core samples. R. C. Gurley and Charles Maillard of the Corps of Engineers were especially cooperative in supplying data, manpower, and field equipment. David F. Barnes, of the Geological Survey, supervised the seismic work and prepared a report (1956) on the results. Records of precipitation at Gates Pond were provided by the town of Hudson. SUMMARY OF BASIC DATA The available new geologic and hydrologic data, together with selected data from the two earlier reports, are presented in tables 1 to 12. Many of the data are illustrated in condensed form in plates 1 to 4 and figures 1 to 7. Tables 1 to 4 give geologic and physical properties of the deposits. Tables 5 and 6 give discharge measurements at the gaging station on Marlboro Brook and on a nearby unnamed tributary. Table 7 summarizes the results of the aquifer test. Table 8 gives chemical analyses of ground and surface water. Table 9 gives the records of wells and test borings in the area and table 10 gives the logs of selected wells and test borings. Table 11 gives individual measurements of water level in selected observation wells; and table 12 gives the measurements of water level at ponds and swamps. The illustrations show the areal extent (pi. 1), particle-size analyses (fig. 5), and lithologic characteristics (pi. 2) of the water-bearing deposits. Typical seismic data and contours on the bedrock are illustrated in figures 3 and 4, respectively. The altitude of the water table is shown on plate 1 and hydrographs for selected wells and ponds are given on plates 3 and 4 and in figure 6. WELL-NUMBERING AND LOCATION SYSTEM Individual wells and test borings are indicated on tables and maps by a number and a location symbol. The wells are numbered serially by towns. AH the wells in the report area are in the towns o

Ground-water geology and hydrology of the Maynard area, Massachusetts