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B. P. Hansen

Publications and source records attributed to B. P. Hansen.

10 recordsLinked to original sources
USGS2001

Use of tree rings to investigate the onset of contamination of a shallow aquifer by chlorinated hydrocarbons

Oaks (Quercus velutina Lam.) growing over a shallow aquifer contaminated by chlorinated hydrocarbons were studied to determine if it was possible to estimate the approximate year that contamination began. The annual rings of some trees downgradient from the contaminant release site contained elevated concentrations of chloride possibly derived from dechlorination of contaminants. Additionally, a radial-growth decline began in these trees at approximately the same time that chloride became elevated. Growth did not decline in trees that contained smaller concentrations of chloride. The source of elevated chloride and the corresponding reductions in tree growth could not be explained by factors other than contamination. On the basis of tree-ring evidence alone, the release occurred in the late 1960s or early 1970s. Contaminant release at a second location apparently occurred in the mid- to late 1970s, suggesting that the area was used for disposal for at least 5 years and possibly longer. Copyright ?? 2001 Elsevier Science B.V.

Journal of Contaminant Hydrology↗
USGS1995

Geohydrology, water quality, and conceptual model of the hydrologic system Saco Landfill area, Saco, Maine

A geohydrologic study of the Saco Municipal Landfill in Saco, Maine, was done during 1993-94 to provide a preliminary interpretation of the geology and hydrology needed to guide additional studies at the landfill as part of the Superfund Program. The Saco Landfill, which was active from the early 1960's until 1986, includes three disposal areas on a 90-acre parcel. Sandy Brook, a small perennial stream, flows from north to south through the land-fill between the disposal areas. Discharge of leachate from the disposal areas to aquifers and streams has been documented since 1974. The landfill was declared a Superfund site in 1990 by the U.S. Environmental Protection Agency. Multiple lines of evidence are used in this study to indicate areas of ground-water contamination and sources of water flow in Sandy Brook. The geohydrologic system on the east side of Sandy Brook consists of an upper water-table aquifer and a lower aquifer, separated by a thick sequence of glaciomarine silt and clay. Depths to bedrock range from 60 to more than 200 ft (feet), on the basis of data from seismic-refraction studies and drilling. The upper aquifer, which is generally less than 15 ft thick, consists of fine-to medium-grained sand deposited in a shallow postglacial marine environment. The lower aquifer, which was deposited as a series of glaciomarine fans, contains two sediment types: Well-sorted sand and gravel and unsorted sediments called diamict sediments. East of Sandy Brook, the thickness of the lower aquifer ranges from 25 to 100 ft, based on drilling at the landfill. The glaciomarine silts and clays (known as the presumpscot Formation) range from 50 to more than 100 ft thick. West of Sandy Brook, the glaciomarine silt and clay is largely absent, and fractured bedrock is very close to land surface under one of the disposal areas in the northwestern part of the property. The lower aquifer is unconfined in the southwestern side of the study area; bedrock slopes towards the south, and the aquifer thickens to 100 ft at the southwestern end of the study area. Preliminary estimates of mean annual streamflow in Sandy Brook, based on a partial year of continuous record, indicate that runoff increases from approximately 2.1 ft3/s (cubic feet per second) upstream from the landfill to 2.7 ft3/s downstream from the landfill, although the drainage area down-stream is only 11 percent greater than the drainage area upstream. A water-budget estimate based on available streamflow and climatic data indicates that Sandy Brook below the landfill gains about 80 million gallons per year from sources outside the drainage-basin boundary. Possible sources include the lower aquifer north or west of the landfill area and the fractured bedrock northwest of Sandy Brook. Specific conductance of water in Sandy Brook increases downstream from the landfill. In September 1993, specific conductance was 184 liS/cm (microsiemens per centimeter at 25 degrees Celsius) upstream from the landfill and 496 uS/cm downstream from the landfill. Continuous monitoring of specific conductance in Sandy Brook shows that the downstream increase is less during periods of stormflow because of dilution. Electromagnetic terrain-conductivity surveys, results of ground-water chemical analyses, and changes in streamwater quality have been used to identify areas of likely ground-water contamination. The specific conductance of ground water exceeds 2,000 uS/cm in some areas near the landfills. This compares to specific conductances of less than 200 uS/cm in water from most shallow wells that are considered to represent background water quality. Ground water in the upper aquifer east of Sandy Brook and in the lower aquifer west of Sandy Brook has been affected by leachate flowing from the landfill areas. The extent of contamination in bedrock, if any, is unknown. Water levels measured in 16 wells were used to help determine the direction of ground-water flow. The electromagnetic terrain-conduct surveys and stream specific-conductance data sup port the interpretation that water in the upper aqui fer flows radially away from the two disposal areas east of Sandy Brook towards Sandy Brook and other small surface-water bodies in the area. West of Sandy Brook, ground water under the third dis posal area moves in the lower aquifer northeast and southeast towards Sandy Brook, where it discharges to the stream.

Maine↗
USGS1994

Yields of bedrock wells in Massachusetts

Six to seven percent of the population of Massachusetts obtains its water from domestic bedrock wells. Additional public, commercial, industrial, and domestic supplies from bedrock will be needed in the future. Information about the factors that are related to large well yields is needed. The factors associated with well yields were identified by use of statistical analysis of reported data from 4,218 bedrock wells. The median reported yield of all bedrock wells was 7 gallons per minute, and the median depth was 170 feet. Wells in valleys and lowlands had the largest median yield--I0 gallons per minute. The median well yield on hilltops and slopes was 6 gallons per minute. In valleys and lowlands, significant increases in well yields corresponded to increasing thickness of overburden. On hilltops and slopes, only small increases in well yield corresponded to increases in overburden thickness. Increases in well diameter corresponded to significant increases in well yields for all well locations, depths, and use categories. The common assumptions that fractured crystalline rocks generally yield only small quantities of water to wells and that the fractures that yield water to wells pinch out or are closed because of lithostatic pressure at depths greater than 300 to 400 feet may be in error. Analysis of well data indicates that the median yield of all bedrock wells decreased as well depth increased to 400 feet and increased slightly with well depths greater than 600 feet. The median yield of bedrock wells located in valleys and lowlands reached 50 gallons per minute at depths of 600 to 700 feet. The median yield of wells located on hilltops and slopes reached 15 gallons per minute at depths of 600 to 700 feet. Carbonate bedrock, with a median well yield of 25 gallons per minute, seemed to be the most productive bedrock type. A reported yield of 1,700 gallons per minute from an industrial well completed in carbonate bedrock is the largest reported yield from a bedrock well in Massachusetts. Yield of wells in sedimentary rocks of the Connecticut Valley increased significantly at depths greater than 400 feet, indicating that this bedrock type may have some primary permeability. Commercial or industrial wells had a median yield of 30 gallons per minute. These wells appear to be preferentially sited, large in diameter, and deeper than average to maximize potential well yields. The median reported bedrock well yield and depth have changed over time. The median yield of about 20 gallons per minute for 1920-40 decreased to 6 gallons per minute for 1970-80. Well depth increased from 128 feet for 1950- 60 to 250 feet for 1980-90. The period during which well depths began to increase coincides with a change in bedrock-well drilling methods from cable tool to air rotary with percussion. Four methods of testing the yield of domestic bedrock wells were evaluated: air injection, evacuation and recovery, constant-discharge, and instantaneous discharge or recharge. A constant-discharge test best satisfied the criteria established to evaluate the testing methods. Further data collection and evaluation are needed for the systematic characterization and appraisal of the bedrock aquifers of Massachusetts. Specific elements include (1) improved and expanded collection and storage of well data, (2) detailed hydrogeologic evaluations of apparent high yield bedrock areas, (3) an evaluation of the relation between the vertical distribution of hydraulic properties measured during well drilling to actual hydraulic properties, (4) an evaluation of the effect of well diameter on well yield, and (5) areal evaluations to characterize the quality of water in bedrock.

Water-Resources Investigations Report↗
USGS1986

Exploration for areas suitable for ground-water development, central Connecticut Valley lowlands, Massachusetts

Drilling and geophysical borehole logs for a 25-sq-mi section of the Connecticut River valley lowlands area of Amherst, Hadley, and Sunderland, Massachusetts, indicate that the area is mostly underlain by fine-grained lacustrine deposits. Nine test wells ranging in depth from 100 to 303 ft completely penetrate the unconsolidated valley fill. Geophysical logs indicate that the lacustrine deposits grade from clay to slightly coarser silt or fine sand with increasing depth. Seismic-refraction surveys indicate bedrock surfaces ranging from 138 to 476 ft below land surface. Interpretation of a continuous seismic-reflection profile on 10.8 mi of the Connecticut River indicates some areas where coarse deposits may underlie the fine-grained lake deposits. These deposits appear to range in thickness from 0 to 165 ft. Bedrock surfaces with elevations down to 190 ft below sea level also were indicated. Water is presently being withdrawn from limited and irregularly distributed sand and gravel deposits for municipal supplies. These deposits may be continuous with previously mapped surficial ice-contact sand and gravel deposits. Areas that are most favorable for future groundwater exploration are mainly in the southern part of the area, between the Connecticut River and the Holyoke Range. (USGS)

Water-Resources Investigations Report↗