USGS

 

Geohydrology of a Deep-Aquifer Monitoring-Well Site at Marina, Monterey County, California

By R. T. Hanson, Rhett R. Everett, Mark W. Newhouse, Steven M, Crawford, M. Isabel Pimentel, and Gregory A. Smith

 

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02-4003

Sacramento, California 2001

Prepared in cooperation with the Monterey County Water Resources Agency


PDF Version of Report

To view PDF documents, you must have the Adobe Acrobat Reader (free from Adobe Systems) installed on your computer. (download free copy of Acrobat Reader).

This report may be downloaded as two large files or as a set of smaller files.


Complete Text (11 MB PDF)

Appendixes (7.2 MB PDF)


Set of smaller files. Includes cover, report text (which contains tables 1 and 2, and figures 9, 10, 12, and 13), remaining figures, and appendixes.
Cover
(644 KB)
Text
(412 KB)
Appendix 1 &
Table A1.1
(260 KB)
Figure A1.1
(Cores 1&2)
(772 KB)
Figure A1.1
(Cores 3&4)
(980 KB)
Figure A1.1
(Cores 5&6)
(792 KB)
Figure A1.1
(Cores 7&8)
(712 KB)
Figure A1.1
(Cores 10&11)
(844 KB)
Figure A1.1
(Cores 12&13)
(844 KB)
Figure A1.1
(Cores 14&15)
(928 KB)
Figure A1.1
(Cores 16, 18& 19)
(1.3 MB)
Appendixes 2 & 3
(236 KB)
Figure 1
(1.1 MB)
Figure 2
(1.2 MB)
Figure 3
(712 KB)
Figure 4
(Cores 1-6)
(1.6 MB)
Figure 4
(Cores 7-13)
(1.4 MB)
Figure 4
(Cores 14-19)
(1.3 MB)
Figure 5
(956 KB)
Figure 6
(600 KB)
Figure 7
(956 KB)
Figure 8
(460 KB)

Abstract

In 2000, a deep-aquifer system monitoring-well site (DMW1) was completed at Marina, California to provide basic geologic and hydrologic information about the deep-aquifer system in the coastal region of the Salinas Valley. The monitoring-well site contains four wells in a single borehole; one completed from 930 to 950 feet below land surface (bls) in the Paso Robles Formation (DMW1-4); one 1,040 to 1,060 feet below land surface in the upper Purisima Formation (DMW1-3); one from 1,410 to 1,430 feet below land surface in the middle Purisima Formation (DMW1-2); and one from 1,820 to 1,860 feet below land surface in the lower Purisima Formation (DMW1-1). The monitoring site is installed between the coast and several deep-aquifer system supply wells in the Marina Coast Water District, and the completion depths are within the zones screened in those supply wells. Sediments below a depth of 955 feet at DMW1 are Pliocene age, whereas the sediments encountered at the water-supply wells are Pleistocene age at an equivalent depth.

Water levels are below sea level in DMW1 and the Marina Water District deep-aquifer system supply wells, which indicate that the potential for seawater intrusion exists in the deep-aquifer system. If the aquifers at DMW1 are hydraulically connected with the submarine outcrops in Monterey Bay, then the water levels at the DMW1 site are 8 to 27 feet below the level necessary to prevent seawater intrusion. Numerous thick fine-grained interbeds and confining units in the aquifer systems retard the vertical movement of fresh and saline ground water between aquifers and restrict the movement of seawater to narrow water-bearing zones in the upper-aquifer system.

Hydraulic testing of the DMW1 and the Marina Water District supply wells indicates that the tested zones within the deep-aquifer system are transmissive water-bearing units with hydraulic conductivities ranging from 2 to 14.5 feet per day. The hydraulic properties of the supply wells and monitoring wells are similar, even though the wells are completed in different geologic formations.

Geophysical logs collected at the DMW1 site indicate saline water in most water-bearing zones shallower than 720 feet below land surface and from about 1,025 to 1,130 feet below land surface, and indicate fresher water from about 910 to 950 feet below land surface (DMW1-4), 1,130 to 1,550 feet below land surface, and below 1,650 feet below land surface. Temporal differences between electromagnetic induction logs indicate possible seasonal seawater intrusion in five water-bearing zones from 350 to 675 feet below land surface in the upper-aquifer system.

The water-chemistry analyses from the deep-aquifer system monitoring and supply wells indicate that these deep aquifers in the Marina area contain potable water with the exception of the saline water in well DMW1-3. The saline water from well DMW1-3 has a chloride concentration of 10,800 milligrams per liter and dissolved solids concentration of 23,800 milligrams per liter. The source of this water was determined not to be recent seawater based on geochemical indicators and the age of the ground water. The high salinity of this ground water may be related to the dissolution of salts from the saline marine clays that surround the water-bearing zone screened by DMW1-3. The major ion water chemistry of the monitoring wells and the nearby MCWD water-supply wells are similar, which may indicate they are in hydraulic connection, even though the stratigraphic layers differ below 955 feet below land surface.

No tritium was detected in samples from the deep monitoring wells. The lack of tritium suggest that there is no recent recharge water (less than 50 years old) in the deep-aquifer system at the DMW1 site. The carbon-14 analyses of these samples indicate ground water from the monitoring site was recharged thousands of years ago.

Table of Contents

Abstract

Introduction

Description of Study Area

Land and Water Use

Geohydrology of The Salinas Valley

Approach to Investigation

Acknowledgments

Geohydrologic Description of DMW1

Geologic Data

Geophysical Data

Paleontologic Data

Hydrostratigraphy of DMW1 Site

Hydraulics

Water-Level Measurements

Hydraulic Properties

Water Chemistry

Chemical Characteristics of Water from Monitoring and Supply Wells

Source, Age, and Movement of Ground Water

Seawater Intrusion and Saline Ground Water

Summary and Conclusions

References Cited

Appendix 1: Cuttings and Core Descriptions for the DMW1 Monitoring Site

Appendix 2: Paleontologic Analyses for the DMW1 Monitoring Site

Appendix 3: Water-Chemistry Data for the DMW1 Monitoring Wells and Core Pore Waters


Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This information provides tools to help make PDF files accessible. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by a number of common screen-reading programs that synthesize text as audible speech. In addition, an accessible version of Acrobat Reader 5.0 for Windows (English only), which contains support for screen readers, is available. These tools and the accessible reader may be obtained free from Adobe at Adobe Access.

 



Water Resources of California




U.S. Department of the Interior, U.S. Geological Survey
Persistent URL: http://pubs.water.usgs.gov/wri024003
Page Contact Information: GS Pubs Web Contact
Last modified: Thursday, September 01 2005, 02:22:10 PM
FirstGov button  Take Pride in America button