Geology topics
Publications and source records attributed to Peter E. Church.
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Ground water provides about 7.7 million gallons per day, or 28 percent of total water use in the Rhode Island part of the Blackstone River Basin. Primary aquifers in the basin are stratified glacial deposits, composed mostly of sand and gravel along valley bottoms. The ground-water and surface-water system in the Blackstone River Basin is under stress due to population growth, out-of-basin water transfers, industrialization, and changing land-use patterns. Streamflow periodically drops below the Aquatic Base Flow standard, and ground-water withdrawals add to stress on aquatic habitat during low-flow periods. Existing hydrogeologic data were reviewed to examine historical water-level trends and to generate contour maps of water-table altitudes and transmissivity of the sand and gravel aquifer in the Blackstone River Basin in Rhode Island. On the basis of data from four long-term observation wells, water levels appear to have risen slightly in the study area during the past 55 years. Analysis of available data indicates that increased rainfall during the same period is a likely contributor to the water-level rise. Spatial patterns of transmissivity are shown over larger areas and have been refined on the basis of more detailed data coverage as compared to previous mapping studies.
A plume of volatile organic compounds in ground water extends northward from the former Nyanza Property in Ashland, Massachusetts, and discharges into the Sudbury River and the upstream end of Mill Pond. A network of polyethylene-membrane passive-vapor-diffusion samplers was installed in February 2001 to help define the lateral extent of the plume under the pond, including an area vegetated by wetland herbs, sedges, and shrubs. Chlorobenzene and trichloroethene were detected with passive-vapor-diffusion samplers at five locations in the bottom sediments of the southern part of the approximate one acre of vegetated area in Mill Pond. Vapor concentrations of chlorobenzene ranged from 178 to 2,210 parts per billion by volume, and vapor concentrations of trichloroethene ranged from 20 to 96 parts per billion by volume. Chlorobenzene also was detected in one sediment-pore-water sample extracted with a push-point sampler in this area; the concentration was 25 micrograms per liter. Toluene was detected with passive-vapor-diffusion samplers at three sites in the open pond area north of the vegetated areas. Vapor concentrations of toluene ranged from 20 to 90 parts per billion by volume. Specific conductance and temperature of sediment-pore waters were measured at selected sampling sites in Mill Pond to examine their possible associations with the presence of volatile organic compounds. Temperature in the sediment-pore water also was measured to convert vapor concentrations of volatile organic compounds collected with diffusion samplers to equivalent water concentrations. These equivalent water concentrations were then to be compared with water concentrations collected with a push-point sampler. Because of the limited detections of volatile organic compounds at sites where water samples were collected and where specific conductance and temperature were measured, these potential associations and conversions could not be assessed.
Polyethylene-membrane passive-vapor-diffusion samplers, or PVD samplers, have been shown to be an effective and economical reconnaissance tool for detecting and identifying volatile organic compounds (VOCs) in bottom sediments of surface-water bodies in areas of ground-water discharge. The PVD samplers consist of an empty glass vial enclosed in two layers of polyethylene membrane tubing. When samplers are placed in contaminated sediments, the air in the vial equilibrates with VOCs in pore water. Analysis of the vapor indicates the presence or absence of VOCs and the likely magnitude of concentrations in pore water.
A U.S. Army facility on a peninsula in South Pond of Lake Cochituate was designated a Superfund site by the U.S. Environmental Protection Agency in 1994 because contaminated ground water was detected at the facility, which is near the Natick Springvale public-supply wellfield. The interaction between South Pond and the underlying aquifer controls ground-water flow patterns near the pond and determines the source of water withdrawn from the wellfield.A map of the bathymetry and the thickness of fine-grained pond-bottom sediments was prepared on the basis of fathometer, ground-penetrating radar, and continuous seismic-reflection surveys. The geophysical data indicate that the bottom sediments are fine grained toward the middle of the pond but are coarse grained in shoreline areas. Natick Springvale wellfield, which consists of three active public-supply wells adjacent to South Pond, is 2,200 feet downgradient from the boundary of the Army facility. That part of South Pond between the Natick Springvale wellfield and the Army facility is 18 feet deep with at least 14 feet of fine-grained sediment beneath the pond-bottom. Water levels from the pond and underlying sediments indicate a downward vertical gradient and the potential for infiltration of pond water near the wellfield. Head differences between the pond and the wellfield ranged from 1.66 to 4.41 feet during this study. The velocity of downward flow from South Pond into the pond-bottom sediments, determined on the basis of temperature profiles measured over a diurnal cycle at two locations near the wellfield, was 0.5 and 1.0 feet per day. These downward velocities resulted in vertical hydraulic conductivities of 1.1 and 2.9 feet per day for the pond-bottom sediments.Naturally occurring stable isotopes of oxygen and hydrogen were used as tracers of pond water and ground water derived from recharge of precipitation, two potential sources of water to a well in a pond-aquifer setting. The isotopic composition of pond water varied seasonally and was distinctly different from the isotopic composition of ground water. The isotopic composition of shallow water beneath and adjacent to South Pond near the wellfield corresponds to the temporal variation of pond water, indicating that nearly all water at shallow depths was derived from pond water. A two-component mixing model based on the average stable isotope values of the source waters indicated that 64 ?15 percent at the 95-percent confidence interval of the water withdrawn at the public-supply wells was derived from the pond; pond water accounted for most of the uncertainty in the result. The rate of infiltration of pond water into the aquifer and discharging to the wellfield was 1.0 million gallons per day at the average pumping rate.
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Volatile organic compounds are present in soils and ground water at the Centredale Manor Superfund Site in North Providence, Rhode Island. In September 1999, water-to-vapor diffusion samplers were placed in the bottom sediments of waterways adjacent to the site to identify possible contaminated ground-water discharge areas. The approximate12-acre site is a narrow stretch of land between the eastern bank of the Woonasquatucket River, downstream from the U.S. Route 44 bridge and a former mill raceway. The samplers were placed along a 2,250-foot reach of the Woonasquatucket River, in the former mill raceway several hundred feet to the east and parallel to the river, and in a cross channel between the river and former mill raceway. Volatile organic compounds were detected in 84 of the 104 water-to-vapor diffusion samplers retrieved. Trichloroethylene and tetrachloro-ethylene were the principal volatile organic compounds detected. The highest vapor concentrations measured for these two chemicals were from diffusion samplers located along an approximate 100-foot reach of the Woonasquatucket River about 500 feet downstream of the bridge; here trichloroethylene and tetrachloroethylene vapor concentrations ranged from about 2,000 to 180,000 and 1,600 to 1,400,000 parts per billion by volume, respectively. Upstream and downstream from this reach and along the former mill raceway, trichloroethylene and tetrachloroethylene vapor concentrations from the diffusion samples were generally less than 100 parts per billion by volume. Along the lower reaches of the river and mill raceway, however, and in the cross channel, vapor concentrations of trichloroethylene exceeded 100 parts per billion by volume and tetrachloroethylene exceeded 1,000 parts per billion by volume in several diffusion samples. Although diffusion sample vapor concentrations are higher than water concentrations in surface waters and in ground water, and they should only be interpreted qualitatively as relative values, these values provide important information as to potential discharge areas of contaminants.
Accurate and representative precipitation and stormwater-flow data are crucial for use of highway- or urban-runoff study results, either individually or in a regional or national synthesis of stormwater-runoff data. Equally important is information on the level of accuracy and representativeness of this precipitation and stormwaterflow data. Accurate and representative measurements of precipitation and stormwater flow, however, are difficult to obtain because of the rapidly changing spatial and temporal distribution of precipitation and flows during a storm. Many hydrologic and hydraulic factors must be considered in performing the following: selecting sites for measuring precipitation and stormwater flow that will provide data that adequately meet the objectives and goals of the study, determining frequencies and durations of data collection to fully characterize the storm and the rapidly changing stormwater flows, and selecting methods that will yield accurate data over the full range of both rainfall intensities and stormwater flows. To ensure that the accuracy and representativeness of precipitation and stormwater-flow data can be evaluated, decisions as to (1) where in the drainage system precipitation and stormwater flows are measured, (2) how frequently precipitation and stormwater flows are measured, (3) what methods are used to measure precipitation and stormwater flows, and (4) on what basis are these decisions made, must all be documented and communicated in an accessible format, such as a project description report, a data report or an appendix to a technical report, and (or) archived in a State or national records center. A quality assurance/quality control program must be established to ensure that this information is documented and reported, and that decisions made in the design phase of a study are continually reviewed, internally and externally, throughout the study. Without the supporting data needed to evaluate the accuracy and representativeness of the precipitation and stormwater-flow measurements, the data collected and interpretations made may have little meaning.
The distribution of salinity in ground water at Calf Pasture Point, a small coastal peninsula bounded by Narragansett Bay on the east and Allen Harbor on the west, in Davisville, Rhode Island, was interpreted from borehole-geophysical data and previously collected salinity data to help identify potential flowpaths of contaminated ground water to surface-water bodies. The surficial material at this 40-acre site, which ranges in thickness from about 30 to 85 feet, is composed of an upper sand unit, a silt unit, and a till unit overlying bedrock. Borehole-geophysical data indicate that fresh ground water is present in all surficial units in the northern and northwestern part of the site. In the central and eastern parts of the site, where most of the current land surface is composed of dredged fill placed in a small saltwater embayment, brackish and saline ground water predominate. Fresh ground water moving into this area from upgradient and recharge to this extended land surface from precipitation is diluting the saline groundwater in the upper sand and till units, and to a lesser extent in the silt unit. In this area, the freshwater-flow system is slowly expanding towards Narragansett Bay and the entrance channel to Allen Harbor.
Road-salt contamination of public and private water supplies has become a serious and costly problem, particularly in the Northeast and Midwest. For example, reports of road-salt contamination from 100 of the 351 municipalities in Massachusetts from 1983 through 1990 required an expenditure of about 2.5 million dollar to investigate and remediate. Nationally, an estimated 10 million dollar are spent annual ly by State and local governments to prevent and remediate road-salt contamination. One method used by State highway agencies to reduce road- salt contamination of public-water supplies is to divert the salt-laden highway runoff through drainage systems from section of highway that pass near public-water supplies to less sensitive areas. The U.S. Geological Survey (USGS), in cooperation with the Massachusetts Highway Department (MHO), has conducted an investigation of the relative effectiveness of four highway-drainage systems in preventing road-salt contamination of ground water. This fact sheet describes the highway-drainage systems tested, the general hydrogeology of the study area, and the methods used to evaluate the drainage systems; and presents preliminary findings of the effectiveness of the systems in preventing road-salt contamination of ground water. These findings are based on data collected from November 1990 through May 1992. The re ult of this investigation will have wider application than just in the snow-belt regions of the United States, Canada, and Europe, as other contaminants in highway runoff either can be diverted from sensitive areas by drainage systems or allowed to seep into the ground, potentially contaminating ground water.
The quality of water in unsaturated zones and groundwater is affected by the major ions in deicing chemicals applied to roads and highways. The assessment of the environmental effects of highway runoff requires investigations to determine whether other major and trace constituents are mobilized during deicing chemical migration through the unsaturated zone and groundwater. In this regard, groundwater samples were analyzed in February and August 1991, and March, August, and November 1993 at a test site along Route 25 in southeastern Massachusetts. Analyses indicated that concentrations of major and trace chemical constituents of highway runoff in groundwater are substantially higher downgradient than upgradient from the highway.