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In cooperation with the U.S. Air Force, Aeronautical Systems Center,
Environmental Management Directorate, Wright-Patterson Air Force Base, Ohio

Water-Level Variations and Their Effects on Tree Growth and Mortality and on the Biogeochemical System at the Phytoremediation Demonstration Site in Fort Worth, Texas, 1996–2003

By Christopher L. Braun1, Sandra M. Eberts1, Sonya A. Jones, and Gregory J. Harvey2 

1 U.S. Geological Survey.
2 Environmental Management Directorate, Wright-Patterson Air Force Base, Ohio.

U.S. Geological Survey
Scientific Investigations Report 2004–5107


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pdf (19.2 MB)


Contents

Abstract

Introduction

Purpose and Scope

Description of the Study Area

Acknowledgments

Methods

Water-Level Data

Factors Affecting Water-Level Variations

Aquifer Properties

Precipitation

Drawdown Induced by the Trees—Transpiration Effects

Irrigation

Effects of Water-Level Variations on Tree Growth and Mortality

Effects of Water-Level Variations on Ground-Water Biogeochemistry

Summary

References Cited

Appendix

Figures—Maps showing (a) lines of equal ground-water depths and (b) water-level altitude contours for

A–1.  
Aug. 17–22, 1996
A–2.  
Oct. 28, 1997
A–3.  
Feb. 11, 1998
A–4.  
June 22, 1998
A–5.  
Oct. 10, 2000
A–6.  
Jan. 8, 2001
A–7.  
July 12–13, 2001
A–8.  
Jan. 15–16, 2002
A–9.  
July 18–19, 2002
A–10.  
Jan. 14–15, 2003

Tables

A–1.  
Well-construction data
A–2.  
Trichloroethene concentrations from six sampling events
A–3.  
cis-Dichloroethene concentrations from six sampling events
A–4.  
Molar ratios of trichloroethene to cis-dichloroethene from six sampling events
A–5.  
Dissolved oxygen concentrations from six sampling events
A–6.  
Dissolved organic carbon concentrations from September 2000 sampling event
A–7.  
Quality-control results for trichloroethene (TCE), cis-dichloroethene (cis-DCE), and molar ratios of TCE to cis-DCE (TCE/cis-DCE) for four of six sampling events

Figures

1–5.  
Maps showing:
 
1.  
Location of study area, alluvial aquifer ground-water-flow directions, and trichloroethene (TCE) plume of October 2002
 
2.  
Land-surface altitudes in study area
 
3.  
Location of wells within the study area and location of low hydraulic conductivity zone
 
4.  
Location and relative diameter of existing trees, January 2003, and relations between mean tree diameter and ground-water depth (September 2000) and between mortality and ground-water depth (September 2000) within the whip plantation
 
5.  
Location and relative diameter of existing trees and location of trees stunted by beaver activity within the caliper plantation, January 2003
6.  
Graphs showing daily mean water-level altitudes for wells 513, 514, and 515, daily mean stream stage at Farmers Branch Creek, and monthly precipitation at Naval Air Station-Joint Reserve Base Carswell Field, November 1998–August 2002
7–11.  
Maps showing:
 
7.  
Estimated drawdown attributed to planted trees, June 22, 1998
 
8.  
Estimated drawdown attributed to planted trees, September 19–20, 2000
 
9.  
Lines of equal ground-water depths and (a) molar ratio of trichloroethene (TCE) to cis-dichloroethene (cis-DCE), and (b) dissolved oxygen concentrations, June 22, 1998
 
10.  
Lines of equal ground-water depths and (a) molar ratio of trichloroethene (TCE) to cis-dichloroethene (cis-DCE), and (b) dissolved oxygen concentrations, January 8, 2001
 
11.  
Lines of equal ground-water depths and (a) molar ratio of trichloroethene (TCE) to cis-dichloroethene (cis-DCE), and (b) dissolved oxygen concentrations, July 12–13, 2001
12.  
Boxplots showing distribution of (a) dissolved oxygen concentrations, September 2000–July 2002, and (b) molar ratios of trichloroethene (TCE) to cis-dichloroethene (cis-DCE), September 2000–July 2002 for selected ground-water depths
13.  
Map showing location and relative diameter of remaining trees within the whip plantation near well 516, graphs of dissolved oxygen concentration and molar ratio of trichloroethene (TCE) to cis-dichloroethene (cis-DCE) from well 516 samples for selected sampling events, and graph of monthly precipitation from the nearby Naval Air Station-Joint Reserve Base Carswell Field

Vertical Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).


Abstract

In 1996, a field-scale phytoremediation demonstration project was initiated and managed by the U.S. Air Force at a site in western Fort Worth, Texas, using a plantation of 1-year-old stems harvested from branches of eastern cottonwoods during the dormant season (whips) and a plantation of 1-year-old eastern cottonwood seedlings (calipers). The primary objective of the demonstration project was to determine the effectiveness of eastern cottonwoods at reducing the mass of dissolved trichloroethene transported within an alluvial aquifer. The U.S. Geological Survey conducted a study, in cooperation with the U.S. Air Force, to determine water-level variations and their effects on tree growth and mortality and on the biogeochemical system at the phytoremediation site. As part of the study, water-level and water-quality data were collected throughout the duration of the project.

This report presents water-level variations at periodic sampling events; data from August 1996 to January 2003 are presented in this report. Water levels are affected by aquifer properties, precipitation, drawdown attributable to the trees in the study area, and irrigation. This report also evaluates the effects of ground-water depth on tree growth and mortality rates and on the biogeochemical system including subsurface oxidation-reduction processes.

Overall, both whips and calipers showed a substantial increase in height, canopy diameter, and trunk diameter over the first 3 years of the study. By the fifth growing season (September 2000), the height of the calipers varied predictably with height decreasing with increasing depth to ground water. Percent mortality was relatively constant at about 25 percent in the whip plantation in January 2003 where ground-water levels were less than 10 feet below land surface during the drought in September 2000. The mortality rate increased where the ground-water levels were greater than 10 feet below land surface and approached 90 percent where ground-water levels were between 12 and 13 feet.

A decrease in molar ratio of trichloroethene to cis-dichloroethene was measured in ground water within and downgradient from the planted area over time. Decreases in these ratios appeared to be related to ground-water depth. The molar ratios of trichloroethene to cis-dichloroethene during the third growing season were relatively constant, between 3.0 and 4.0, in samples collected from wells across the site. By the end of the fifth growing season the lowest ratio was measured in areas where ground-water depth was less than 10 feet below land surface; these same areas had the lowest dissolved oxygen concentrations (0.93 to 1.7 milligrams per liter) and the highest dissolved organic carbon concentrations (1.6 to 1.8 milligrams per liter). This indicates that between the third and fifth growing seasons, a labile fraction of dissolved organic carbon had been introduced into the aquifer by the planted trees that was capable of stimulating reductive dechlorination of trichloroethene.

 


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