Hydrogeologic Data for the Big River–Mishnock River Stream-Aquifer System, Central Rhode Island By Patrick A. Craft Abstract from aquifer tests, and water-quality data. Histori- cal water-level data from other wells within the Hydrogeology, ground-water development study area also are presented in this report. alternatives, and water quality in the Big–Mish- nock stream-aquifer system in central Rhode Surface-water data were obtained from a Island are being investigated as part of a long-term network consisting of surface-water impound- cooperative program between the Rhode Island ments, such as ponds and reservoirs, existing and Water Resources Board and the U.S. Geological newly established partial-record stream-discharge Survey to evaluate the ground-water resources sites, and synoptic surface-water-quality sites. throughout Rhode Island. The study area includes Water levels were collected monthly from the the Big River drainage basin and that portion of surface-water impoundments. Stream-discharge the Mishnock River drainage basin upstream from measurements were made at partial-record sites to the Mishnock River at State Route 3. This report provide measurements of inflow, outflow, and presents geologic data and hydrologic and water- internal flow throughout the study area. Specific quality data for ground and surface water. conductance was measured monthly at partial- Ground-water data were collected from July record sites during the study, and also during the 1996 through September 1998 from a network of fall and spring of 1997 and 1998 at 41 synoptic observation wells consisting of existing wells and sites throughout the study area. wells installed for this study, which provided a General geologic data, such as estimates of broad distribution of data-collection sites through- out the study area. Streambed piezometers were depth to bedrock and depth to water table, as well used to obtain differences in head data between as indications of underlying geologic structure, surface-water levels and ground-water levels to were obtained from geophysical surveys. Site- help evaluate stream-aquifer interactions through- specific geologic data were collected during the out the study area. The types of data presented drilling of observation wells and test holes. These include monthly ground-water levels, average data include depth to bedrock or refusal, depth to daily ground-water withdrawals, drawdown data water table, and lithologic information. Abstract 1 INTRODUCTION Since the mid-1950s, the USGS has investigated the ground-water conditions and examined the bedrock In 1995, the U.S. Geological Survey (USGS) in and surficial geology of the study area shown on the cooperation with the Rhode Island Water Resources four topographic quadrangles (Coventry Center, Board (RIWRB) initiated a hydrogeologic investiga- Crompton, Hope Valley, and Slocum topographic tion in the Big–Mishnock stream-aquifer system quadrangles). These studies were published as a series (fig. 1). This investigation was designed to assess the of ground-water maps, bedrock-geology maps, and hydrogeologic setting and water resources within the surficial-geology maps. Ground-water maps have been study area. This report contains data collected as part published for all four quadrangles, bedrock-geology of this study. maps have been published for three quadrangles, and This report provides regulators, scientists, and three quadrangles have surficial-geology maps (Allen managers with the data needed to understand and eval- and Johnson, 1959; Bierschenk and Hahn, 1959; uate the hydrogeologic factors that affect ground-water Feininger, 1962; Hahn, 1959; Mason and Hahn, 1960; development in the Big–Mishnock stream-aquifer Moore, 1963; Power, 1959; Power, 1957; Quinn, 1963; system. This report presents data on ground-water and and Smith, 1956). surface-water levels within the study area from July In the 1960s, the State proposed to construct 1996 through September 1998. Descriptions of subsur- a reservoir in the study area to meet growing water face conditions, aquifer lithology from samples col- needs. This proposal initiated a number of studies in lected during drilling, stream-discharge measurements, the study area, including a preliminary geotechnical and ground-water-quality data are also included. investigation and a feasibility study (Keyes and The 32-mi2 study area includes the Big River Associates and Metcalf and Eddy Inc., 1977; United drainage basin and that portion of the Mishnock River States Army Corps of Engineers, 1979a, 1979b, 1979c, drainage basin upstream from the Mishnock River at 1980a, 1980b, 1980c; Maguire and Goldberg, Zoino, State Route 3. The Big River portion is about 29 mi2, and Associates, Inc., 1984; A.D. Little, Inc., 1989). The and the Mishnock River portion is about 3 mi2. Both 1989 report by A.D. Little, Inc., states that “the central basins contain stratified-deposit aquifers overlying region is the area of the State with the most critical cur- granite of the Scituate Igneous Suite (Hermes and oth- rent water-supply deficit,” which led to further studies ers, 1994). The study area overlaps Coventry Center, of the Big–Mishnock stream-aquifer system. Crompton, Hope Valley, and Slocum topographic quad- On behalf of the Rhode Island Water Resources rangles. The Big River portion is sparsely populated, Board and the USGS, the author wishes to thank with most of the population living along the upper Scott Michaud, Jennifer Sandorf, Bill Abrahams- reaches of the tributaries to the Big River. Most of the Dematte, Dennis Orlowski, and Dr. Anne Veeger Big River area is woodlands and meadows. The Mish- from the Department of Geosciences at the University nock River portion is moderately to heavily populated of Rhode Island (URI), who volunteered many and the predominant features are Mishnock Lake and hours during the geophysical and water-quality-data Mishnock Swamp. collection efforts. Additionally, the author wishes to Both areas are sub-basins to the South Branch thank Mr. Timothy Brown, General Manager, Kent of the Pawtuxet River Basin. Additional data are in a County Water Authority, for providing public-water- hydrologic data report for the South Branch of the supply-well withdrawal and aquifer-test data associated Pawtuxet River Basin (Gonthier, 1966). with the Mishnock River portion of the study area. 2 Hydrogeologic Data for the Big River–Mishnock River Stream-Aquifer System, Central Rhode Island Wallum Lake Woonsocket Slatersville MASSACHUSETTS Reservoir B Pawtucket l a Reservoir er c v k i st R o n h e c Pascoag n R a i W v Reservoir r e r B oo na s Glocester q u a t Ponaganset u Reservoir c k Pawtucket P e t o James V. Turner n R Reservoir a i v ga Providence n e r s Scituate e Ten Mile R. t Foster R i v e r er Riv Scituate t Reservoir e Pawtucket x u t w a Warren CONNECTICUT RHODE ISLANDP Flat River Reservoir Bristol Mishnock Swamp East Greenwich er r iv BIG–MISHNOCK e R v t i n R u ig H STUDY AREA B iver r e Wickford et R v i R Belleville n r e e Pond v Narragansett Bay Pachet Brook Sakom e i u R Reservoir Q r t - t e g u u v i Little Compton a c R s r p e e t m u e v Indian i x r q e s u Lake Newport R v p qua i U i a d h R t o C t y o e a Great Swamp P w W a r Rive Wakefield h uck Narragansett s t ca Worden A w a Pond P r e v i Watchaug R Pond k Westerly c Point Judith u t a c w 0 a 10 20 MILES P 0 10 20 KILOMETERS Figure 1. Location of the Big–Mishnock stream-aquifer system, central Rhode Island. Introduction 3 SITE-IDENTIFICATION In assigning site-identification numbers to NUMBERS surface-water sites, no distinction is made between continuous-record sites and other types of sites such All data-collection sites associated with this as partial-record sites; therefore, the site number for study, including wells, piezometers, ponds, reservoirs, a continuous-record site indicates downstream-order and streams were assigned identification numbers position in a list made up of all types of sites. Gaps are (pl. 1). The USGS uses two methods to assign identifi- left in the series of numbers to allow for new sites that cation numbers to ground-water sites and surface- may be established; hence, the numbers are not always water sites; both are based on location. The “latitude- consecutive. The first two digits indicate the Part longitude” system is used for ground-water sites, number (formerly used in USGS Water-Supply Papers such as wells, springs, piezometers, and for pond to designate major river systems) and the last six or and reservoir sites. In addition, each ground-water more digits indicate the downstream order within the site is assigned a local well number from the “well- Part. For example, in the site number 01115630, “01” numbering” system. Surface-water sites are assigned a is the Part number for the “North Atlantic Slope number based on the “downstream-order” system. Basins” and the “115630” is the downstream order The 15-digit identification numbers for ground- number. water, pond, or reservoir sites are assigned according to the latitude and longitude at the site. The first six digits HYDROLOGIC DATA denote the degrees, minutes, and seconds of latitude; the next seven digits denote degrees, minutes, and sec- The hydrologic data are divided into ground- onds of longitude; and the last two digits (assigned water data and surface-water data. Within the stream- sequentially) distinguish between data-collection aquifer system there is usually continual interaction sites within a 1-second grid. Once assigned, this site- between ground water and surface water, as in the rela- identification number no longer has locational signifi- tion between decreased streamflow and increased with- cance.