5 research outputs found
Altitude of the Potentiometric Surface in the Mississippi River Valley Alluvial Aquifer, Spring 2018
The Mississippi River Valley alluvial (MRVA) aquifer is an important surficial aquifer in the Mississippi Alluvial Plain (MAP) area. The aquifer is generally considered to be an unconfined aquifer (fig. 1; Clark and others, 2011), and withdrawals are primarily used for irrigation (Maupin and Barber, 2005). These groundwater withdrawals have resulted in substantial areas of water-level decline in parts of the aquifer. Concerns about water-level declines and the sustainability of the MRVA aquifer have prompted the U.S. Geological Survey (USGS), as part of the USGS Water Availability and Use Science Program and with assistance from other Federal, State, and local agencies, to undertake a regional water-availability study to assess the characteristics of the MRVA aquifer, including the potentiometric-surface altitude of the MRVA aquifer for spring 2018, and to provide information to water managers to inform their decisions about resource allocations and aquifer sustainability. The purpose of this report was to present a potentiometric-surface map for the MRVA aquifer using manually measured groundwater-altitude data and daily mean or maximum groundwater-altitude data from wells measured generally in spring 2018, which is after water levels have substantially recovered from pumping in the previous irrigation season and before pumping begins for the next irrigation season, and using the altitude of the top of the water surface in rivers in the area, hereinafter referred to as “surface-water altitude,” generally on April 10, 2018, from streamgages in the area. The term “potentiometric surface” is used in this report because it is applicable for maps of the groundwater-altitude surface in unconfined, semiconfined, and confined aquifers (Lohman, 1972). In this report, the maps of the MRVA aquifer’s groundwater surface are termed potentiometric-surface maps as opposed to water-table maps because, although the MRVA aquifer generally exhibits characteristics of unconfined conditions, where surface-water features may or may not be hydraulically connected, it also exhibits characteristics of confined or semiconfined conditions in some areas at least during part of the year. The location of these areas, where the aquifer is confined or semiconfined, is not well understood or defined (Arthur, 1994; Kleiss and others, 2000).
Datasets used attache
Altitude of the Potentiometric Surface in the Mississippi River Valley Alluvial Aquifer, Spring 2018
The Mississippi River Valley alluvial (MRVA) aquifer is an important surficial aquifer in the Mississippi Alluvial Plain (MAP) area. The aquifer is generally considered to be an unconfined aquifer (fig. 1; Clark and others, 2011), and withdrawals are primarily used for irrigation (Maupin and Barber, 2005). These groundwater withdrawals have resulted in substantial areas of water-level decline in parts of the aquifer. Concerns about water-level declines and the sustainability of the MRVA aquifer have prompted the U.S. Geological Survey (USGS), as part of the USGS Water Availability and Use Science Program and with assistance from other Federal, State, and local agencies, to undertake a regional water-availability study to assess the characteristics of the MRVA aquifer, including the potentiometric-surface altitude of the MRVA aquifer for spring 2018, and to provide information to water managers to inform their decisions about resource allocations and aquifer sustainability. The purpose of this report was to present a potentiometric-surface map for the MRVA aquifer using manually measured groundwater-altitude data and daily mean or maximum groundwater-altitude data from wells measured generally in spring 2018, which is after water levels have substantially recovered from pumping in the previous irrigation season and before pumping begins for the next irrigation season, and using the altitude of the top of the water surface in rivers in the area, hereinafter referred to as “surface-water altitude,” generally on April 10, 2018, from streamgages in the area. The term “potentiometric surface” is used in this report because it is applicable for maps of the groundwater-altitude surface in unconfined, semiconfined, and confined aquifers (Lohman, 1972). In this report, the maps of the MRVA aquifer’s groundwater surface are termed potentiometric-surface maps as opposed to water-table maps because, although the MRVA aquifer generally exhibits characteristics of unconfined conditions, where surface-water features may or may not be hydraulically connected, it also exhibits characteristics of confined or semiconfined conditions in some areas at least during part of the year. The location of these areas, where the aquifer is confined or semiconfined, is not well understood or defined (Arthur, 1994; Kleiss and others, 2000).
Datasets used attache
Quality of water from shallow wells in urban residential and light commercial areas in Lafayette Parish, Louisiana, 2001 through 2002 /
"National Water-Quality Assessment Program."Shipping list no.: 2004-0256-P.Includes bibliographical references (p. 24-27).Mode of access: Internet
Methane and Benzene in Drinking-Water Wells Overlying the Eagle Ford, Fayetteville, and Haynesville Shale Hydrocarbon Production Areas
Water
wells (<i>n</i> = 116) overlying the Eagle Ford,
Fayetteville, and Haynesville Shale hydrocarbon production areas were
sampled for chemical, isotopic, and groundwater-age tracers to investigate
the occurrence and sources of selected hydrocarbons in groundwater.
Methane isotopes and hydrocarbon gas compositions indicate most of
the methane in the wells was biogenic and produced by the CO<sub>2</sub> reduction pathway, not from thermogenic shale gas. Two samples contained
methane from the fermentation pathway that could be associated with
hydrocarbon degradation based on their co-occurrence with hydrocarbons
such as ethylbenzene and butane. Benzene was detected at low concentrations
(<0.15 μg/L), but relatively high frequencies (2.4–13.3%
of samples), in the study areas. Eight of nine samples containing
benzene had groundwater ages >2500 years, indicating the benzene
was
from subsurface sources such as natural hydrocarbon migration or leaking
hydrocarbon wells. One sample contained benzene that could be from
a surface release associated with hydrocarbon production activities
based on its age (10 ± 2.4 years) and proximity to hydrocarbon
wells. Groundwater travel times inferred from the age-data indicate
decades or longer may be needed to fully assess the effects of potential
subsurface and surface releases of hydrocarbons on the wells