Ground Water: Cycle I Activities (1991 - 2001)

• Ground Water Study Design
• Study Unit Survey
• Land-Use Survey: Urban
• Land-Use Survey: Rice
• Low Intensity Phase Sampling

Ground Water Study Design

The study design for ground water focuses on assessing the water-quality conditions of major aquifers in the Study Unit with emphasis on the quality of recently recharged ground water associated with present and recent human activities. The sampling design is based on the need to examine ground-water quality at different spatial scales. Study-Unit Surveys are used, in conjunction with an analysis of available data, to broadly characterize ground-water quality across the Study Unit. Land-Use and Flow-Path Studies are done at intermediate and more local scales, respectively, to build an understanding of causal relations and processes. The Land-Use and Flow-Path Studies are directed, for the most part, toward the effects of human activities on ground-water quality. Low-Intensity Phase Sampling is intended to meet the objectives of trend assessment to identify, describe and explain current and future changes and trends in water quality.

Koterba , M.T., Wilde, F.D., Lapham, W.W., 1995, Ground-water data-collection protocols and procedures or the National Water-Quality Assessment Program: Collection and documentation of water-quality samples and related data: U.S. Geological Survey Open-File Report 95-399, 113 p.

Study-Unit Survey

The Sacramento subunit includes the deposits on the southeast side of the Sacramento Valley and has both the largest total ground-water use and the largest population in the study unit. Information on municipal ground-water use data is not available but is estimated to be one third of the total ground-water use. The valley aquifer in this subunit consists of heterogeneous alluvial fans deposited by streams draining the Sierra Nevada to the east, interfingering to the west with flood basin and channel deposits of the Sacramento River. In the north western part of the subunit, volcanic formations of the relict Sutter Buttes Volcano intrude the alluvial valley deposits, and deeper alluvial deposits are turned up around the volcanic formations. At the surface, alluvial fans from the eroded volcano surround the Buttes and interfinger with the alluvial deposits from the Sierra Nevada to the east and the Sacramento River to the west. Water levels range from near surface along rivers to greater than 150 feet below land surface in pumping depressions and along the valley edge.

In 1996, 29 domestic wells and 2 monitoring wells in the southeastern Sacramento Valley were sampled. This area was chosen because it had the largest amount of ground-water use in the Sacramento River Basin. The Sacramento subunit study area is about 4,400 square kilometers and includes intense agricultural and urban development. The wells sampled ranged from 14.9 to 79.2 meters deep. Ground-water samples from 31 wells were analyzed for 6 field measurements, 14 inorganic constituents, 6 nutrient constituents, organic carbon, 86 pesticides, 87 volatile organic compounds, tritium (hydrogen-3), radon-222, deuterium (hydrogen-2), and oxygen-18.

Data collected:
Thirty-one domestic and monitoring wells were sampled for major chemical constituents, nutrients, pesticides, volatile organic compounds, trace elements, and radon in 1996.
Click here for more information and data downloads .

Reference:
Dawson, B.M. , 2001, Ground-water quality in the southeastern Sacramento Valley aquifer, California: U.S. Geological Survey Water-Resources Investigations Report 2001-4125, 24 p.

Scott, J.C., 1990, Computerized stratified random site-selection approaches for design of a ground-water -quality sampling network: U.S. Geological Survey Water-Resources Investigations Report 90-4101, 109 p.

Land-Use Studies

Urban Land-use Study:

The purpose of the ground water Land-Use Studies was to assess the concentration and distribution of water-quality constituents in recently recharged ground water, and then to examine the natural and human factors affecting the quality of shallow ground water underlying various land uses.

The Sacramento Metro Area was selected for an urban land-use study because it is the only city in the study unit to meet the minimum population guidelines from VOC National Synthesis. The hydrogeologic framework consists of heterogeneous alluvial deposits eroded from the Sierra Nevada. Shallow ground water occurs at a wide range of depths, from near surface along the rivers to more than 30 meters in pumping depressions and along the valley edge. Perched water tables are known to exist in the area. The unsaturated zone in most of the Sacramento area is moderately to highly impermeable. Deposits along the Sacramento and American Rivers are permeable at the surface. Shallow ground water is possibly connected to surface waters that are used for public supply, but is not thought to be connected to deeper ground water used for public supply. No previous studies of shallow ground water have been done in the Sacramento area, except by private consultants at sites of point source contamination (e.g. McClellan Air Force base, Mather Air Force base, Aerojet Mfg.). The results of these studies are not currently publicly available. The occurrence of VOC's is not known in the shallow ground-water system in the Sacramento area except in connection with known point sources. VOC's have not been detected in the deeper ground-water that is used for drinking water supply, except in connection with point sources. The VOC methyl tert-butyl ether (MTBE) has not been sampled for but is in use in the Sacramento area. Moderate levels of arsenic and high levels of manganese have been detected in some areas, generally associated with reducing conditions in the aquifer. High levels of radon have also been detected in some wells. Pesticides have also been detected in some wells in the area.

In 1998, 19 wells were drilled and sampled. Ground-water samples were analyzed for field measurements, major ions, trace elements, stable isotopes, nutrients, dissolved organic carbon, pesticides, volatile organic compounds, tritium, and tritium/helium-3.

The above map shows the locations where wells were selected for the urban land use study. Areas outlined in blue fall within the time frame of having been developed between 5 and 25 years ago. These areas were defined using a combination of 1970's land use and 1990 U.S. Census data (Hitt, 1994). Unfortunately this process identified a large, undeveloped area in south Sacramento as urban. All areas were field checked before well sites were selected. Areas within the blue, shown in orange, allowed for well selection with a radius of 250 meters that had at least 75% area within the 5 to 25 year old region. Areas shown in yellow allowed for well selection with a radius of 250 meters that was entirely within the 5 to 25 year old regions. Therefore, the areas shown in yellow were given the highest priority for well selection.

Data collected:
Nineteen wells were sampled for major chemical constituents, nutrients, pesticides, volatile organic compounds, trace elements, and radon.
Click here for more information and data downloads .

Reference:
Shelton, J.L., 2005, Assessment of shallow ground-water quality in recently urbanized areas of Sacramento, California, 1998: U.S. Geological Survey Scientific Investigations Report 2005-5148, 51p.

Squillace, P.J. and Price, C.V., 1996, Urban Land-Use Study Plan for the National Water-quality Assessment Program: U.S. Geological Survey Open-File Report 1996-217, 19p.

Hitt, K.J., 1994, Refining 1970's land-use data with 1990 population data to indicate new residential development: U.S. Geological Survey Water-Resources Investigations Report 1994-4250, 15p.

Scott, J.C., 1990, Computerized stratified random site-selection approaches for design of a ground-water -quality sampling network: U.S. Geological Survey Water-Resources Investigations Report 90-4101, 109 p.

Rice Land-use Study:

A rice land-use study was chosen for an agricultural land-use study because rice is the largest acreage of land use in the Sacramento Study unit. The rice pesticide bentazon, which was in use until the late 1980's and has been banned for approximately 6 years, has been detected in wells in some rice areas while other rice pesticides such as molinate, carbofuran, and thiobencarb were not detected in the same wells. There is much state and local interest in studying the hydrogeologic and chemical processes in shallow ground-water in rice areas.

Rice is located on basin deposits and fine-grained alluvial deposits along either side of the Sacramento River. Shallow ground water occurs generally within 6 meters of land surface. There are 3 main areas of rice production. These areas were divided into 30 equal areas (approximately 10 wells per area) and 30 randomly located sites were selected for monitoring well installation. Samples were analyzed for the required NAWQA land-use constituents plus chloroflurocarbon compounds (CFCs) and Tritium/Helium-3 for age-dating. Volatile Organic compounds (VOCs) will not be sampled for as no VOCs are known to be associated with rice land use.

Data collected:
Twenty-eight wells were sampled for major chemical constituents, nutrients, pesticides, volatile organic compounds, trace elements, and radon.
Click here for more information and data downloads .

Reference:
Dawson, B.J., 2001, Shallow ground-water quality beneath rice areas in the Sacramento Valley, California, 1997: U.S. Geological Survey Water-Resources Investigations Report 2001-4000, 33p.

Scott, J.C., 1990, Computerized stratified random site-selection approaches for design of a ground-water -quality sampling network: U.S. Geological Survey Water-Resources Investigations Report 90-4101, 109 p.

Low-Intensity Phase Sampling

Five wells were chosen, for both the Rice and Urban land use studies (10 wells total), to be sampled on a quarterly basis from November 2003 to August 2004. These wells were sampled for major inorganics, nutrients and pesticides.