Perchlorate Monitoring Results 

Henderson, Nevada to the Lower Colorado River 

December 2005 Report 

Compiled by: 

US Environmental Protection Agency, Region 9 

Waste Management Division 

75 Hawthorne St. 

San Francisco, CA 94105 

Based on Monitoring Data from 

• Nevada Division of Environmental Protection 

• Southern Nevada Water Authority 

• Metropolitan Water District (MWD) of Southern California 

• Tronox (formerly Kerr McGee) 

Perchlorate Monitoring Report February 6, 2006 
PERCHLORATE MONITORING RESULTS:


HENDERSON, NEVADA TO THE LOWER COLORADO RIVER


TABLE OF CONTENTS


I. EXECUTIVE SUMMARY ................................................... 1


1. Introduction and Purpose .................................................. 1


2. Summary of Surface Water and Groundwater Quality Trends ..................... 1


3. Recent Developments and Current Status ...................................... 2


4. Monitoring Locations ..................................................... 4


5. Perchlorate Monitoring Trends for 2005 at Each Monitoring Location. . . . . . . . . . . . . . . .4


II MONITORING DATA ...................................................... 7


1. Total Perchlorate Mass Removal by Tronox .................................. 7


2. Perchlorate Mass Loading in Las Vegas Wash at North Shore Road . . . . . . . . . . . . . . . . 10


3. Groundwater on Tronox Property Above Slurry Wall ........................... 11


4. Groundwater on Tronox Property Below Slurry Wall (M-100) .................... 11


5. Groundwater at Athens Road Wells (ART-8) .................................. 12


6. Groundwater Below Athens Road Wells (ARP - 3) ............................. 12


7. Groundwater at Seep Area (PC-97) ......................................... 13


8. Las Vegas Wash Downstream of Seep Area (LW 5.3) ........................... 14


9. Las Vegas Wash at North Shore Road ....................................... 14


10. Lake Mead at Las Vegas Bay (LVB 2.7/LVB 3.5) ............................. 15


11. Lake Mead at Saddle Island (AMSWTF Raw Water) .......................... 15


12. Colorado River Below Hoover Dam (Willow Beach) .......................... 16


13. Colorado River at the Colorado River Aqueduct at Lake Havasu ................. 16


APPENDIX A: MAPS ......................................................... 17


1. Southern California, Southern Nevada and Western Arizona ..................... 17


2. Las Vegas Wash and Lake Mead Perchlorate Monitoring Locations ................ 18


3. Lake Mead and Lower Colorado River Perchlorate Monitoring Locations ........... 19


APPENDIX B: BACKGROUND ................................................ 20


1. Discovery and Magnitude of the Perchlorate Problem ........................... 20


2. Status of Applicable Perchlorate Standards ................................... 20


3. Tronox Control Strategy and Current Status .................................. 21


4. AMPAC’s Control Strategy and Current Status ................................ 22


5. Estimated Travel Times and Flushing Times .................................. 22


6. Perchlorate Monitoring Trends for 2004 at Each Monitoring Location . . . . . . . . . . 23


7. Perchlorate Monitoring Trends for 2003 at Each Monitoring Location . . . . . . . . . . . . . . 25


Perchlorate Monitoring Report February 6, 2006 
PERCHLORATE MONITORING RESULTS


HENDERSON, NEVADA TO THE LOWER COLORADO RIVER


I. EXECUTIVE SUMMARY 

1. Introduction and Purpose 

This report summarizing perchlorate monitoring results in Henderson, Las Vegas Wash, Lake 

Mead and the Lower Colorado River has been compiled to measure the effectiveness of 

perchlorate remediation efforts in Henderson, Nevada, and to keep interested agencies and others 

informed on the latest perchlorate monitoring data. It is designed to present an overview of the 

data so that all parties have the same information. It does not include all of the monitoring data 

available, just a manageable set of the most representative data. Please refer to Appendix B: 

Background for details about the perchlorate problem, applicable standards, Tronox’s 

(formerly Kerr McGee) control strategy, AMPAC’s (American Pacific Corp; referred to as 

PEPCON in previous reports) control strategy and travel times/flushing times. 

This report will allow agencies to assess the effectiveness of control elements, track progress of 

control efforts and their downstream benefits, and more accurately predict perchlorate 

concentrations at downstream locations. 

Several agencies have contributed data to this report, including the Nevada Division of 

Environmental Protection (Las Vegas Wash at North Shore Road and the Lower Colorado River 

at Willow Beach), Southern Nevada Water Authority (LasVegas Wash downstream of the seep, 

Lake Mead/Las Vegas Bay and Lake Mead/Saddle Island) and Metropolitan Water District 

(MWD) of Southern California (Colorado River Aqueduct). Tronox has also contributed 

substantial data to this report (ground water monitoring and mass removal data at the Slurry 

Wall, Athens Road and the Seep Area). 

This report addresses only the perchlorate releases from Tronox and AMPAC in Henderson, 

Nevada and their impacts on Las Vegas Wash, Lake Mead and the lower Colorado River. There 

are many other perchlorate releases throughout the United States which have created their own 

separate and distinct perchlorate plumes. This report does not address any of these other 

releases. 

2. Summary of Surface Water and Groundwater Quality Trends 

• Monthly averages are presented where more than one sample per month is collected. 

• Ground water and surface water concentrations show significant seasonal variability. 

•	 Ground water concentrations are declining as a result of Tronox’s capture and control efforts 

at three locations: slurry wall on Tronox property, Athens Road about half way to Las Vegas 

Wash, and seep area near Las Vegas Wash. Ground water extraction wells in these three 

locations are removing approximately 1700 to 2000 pounds of perchlorate per day. 

Perchlorate Monitoring Report 1 February 6, 2006 
•	 Surface Water concentrations in Las Vegas Wash, Lake Mead and the Lower Colorado River 

have declined by 85%, 70% and 60%, respectively, since seep capture and treatment began 

in November 1999. Additional decreases may occur in 2006 due to improved capture at 

Athens Road (continuous capture began on October 22, 2002) and the seep area wellfield 

(continuous wellfield operation with 4 wells began on 10/22/02; 5 more wells were 

added on 3/24/03, and a 10th well began operation in July 2005). 

•	 In the last 2 years, concentrations of perchlorate at Saddle Island (AMSWTF Raw Water) in 

Lake Mead have ranged from 2 to 8 ppb which is below the recently adopted US EPA 

reference dose drinking water equivalent level (DWEL) of 24.5 ppb, but at times greater than 

California’s Public Health Goal of 6 ppb. 

•	 Average perchlorate concentrations in Lake Mead were probably higher than expected in 

2002, 2003 and 2004 because a 5 year long drought resulted in less water entering Lake Mead 

and lowered the Lake level about 90 feet between January 2000 and December 2004. This 

resulted in about a 44% decrease in the Lake volume. During 2005 the Lake level rose 13-

14 feet to 1137.5 feet. If the drought continues/reemerges in 2006 and beyond, perchlorate 

concentrations in Lake Mead may not decline as much as expected. The intake depth of the 

AMSWTF was lowered from 1050 to 1000 feet on June 29, 2004, which would be expected 

to decrease perchlorate concentrations somewhat. 

•	 Peak levels of surface water concentrations at the Colorado River Aqueduct near Parker Dam 

have declined gradually, but steadily from 9 ppb to less than 4 ppb since seep capture began 

in November 1999. Gradual declines in peak levels are expected to continue in 2006. 

•	 In the last 2 years, concentrations of perchlorate at the Colorado River Aqueduct near Parker 

Dam have ranged from non-detect (ND = 2 ppb) to 5.6 ppb, which is below the recently 

adopted US EPA reference dose drinking water equivalent level (DWEL) of 24.5 ppb. Since 

June 2002, all of the monthly samples have been at or below California’s Public Health Goal 

of 6 ppb. In 2004 nine of the twelve monthly samples were non-detect (ND = 4 ppb). In 

2005 all twelve monthly samples were less than 4 ppb. 

3. Recent Developments and Current Status 

This is the eighth and last in a regular series of reports on the progress of the perchlorate 

cleanup in Henderson, Nevada. This report has evolved over time to best suit the needs of the 

interested parties. Given the significant decreases in perchlorate releases that have been 

achieved and the associated decreases in drinking water concentrations in Lake Mead and 

the Colorado River, we don’t believe that future reports of this type are necessary. The 

data will continue to be collected by the respective parties, but they will not be compiled 

into a single report. Anyone interested in the data collected in the future should visit the 

Nevada Division of Environmental Protection (NDEP) website [www.ndep.nv.gov] (for 

North Shore Road or Willow Beach data) or contact Todd Croft of NDEP at 702 486-2850 

ext 230. At the NDEP homepage, scroll down near the bottom of the page and click on 

“Southern Nevada Perchlorate Cleanup Project.” 

Perchlorate Monitoring Report 2 February 6, 2006 
The ground water and surface water systems included in this report are complex systems, 

and the data at each sampling location are influenced by many factors, including 1) natural 

variability, 2) seasonal variability, 3) Lake Mead water levels and flow dynamics, 4) Colorado 

River flow dynamics, and 5) ground water flow dynamics, etc. As such, it is important to 

remember that one data point does not constitute a trend, and that water quality improvements 

will not necessarily occur in a steady, straight-line fashion. 

In January 2002 EPA proposed a new reference dose for perchlorate of 0.00003 mg/kg, with a 

associated drinking water equivalent level of 1 ppb. This reference dose would have replaced 

the provisional reference dose DWEL of 4-18 ppb, but it was never finalized. In order to 

resolve disagreements about how to interpret the health effects data, the National Academy 

of Sciences (NAS) reviewed the health effects data for perchlorate and issued their report to EPA 

on January 10, 2005. The NAS recommended a perchlorate reference dose of 0.0007 mg/kg. On 

February 18, 2005 EPA adopted a perchlorate reference dose of 0.0007 mg/kg/day, which can be 

used to calculate a drinking water equivalent level (DWEL) of 24.5 ppb, assuming that all 

perchlorate exposure comes from drinking water, and using standard adult body weight and 

water consumption estimates. On January 26, 2006 EPA’s Office of Solid Waste and 

Emergency Response (OSWER) issued “Assessment Guidance for Perchlorate,” which 

recommends using 24.5 ppb as a starting point for evaluation of federal cleanup sites. EPA 

is currently working to determine whether or not a national drinking water regulation for 

perchlorate would present a meaningful opportunity for health risk reduction. California 

adopted a perchlorate Public Health Goal of 6 ppb on March 11, 2004 and is expected to adopt a 

state MCL for perchlorate in 2006. 

In 2003 Kerr McGee constructed a new fluidized bed reactor (FBR), biologically based 

perchlorate treatment plant to replace the existing ion exchange units. The Plant Ion Exchange 

Units (12) began operating in October 2002, while the Wash Ion Exchange Units (3) began 

operating in November 1999. The new FBR plant was in startup/shakedown mode from 

December 2003 through September 2004 and became fully operational in November 2004. The 

perchlorate concentration and mass discharged from the new treatment plant have decreased to 

less than 18 ppb and less than 0.21 pounds per day, respectively, based on a flow of 1000 gallons 

per minute. The Plant Ion Exchange Units have not operated since March 2004; the Wash Ion 

Exchange Units have not operated since June 2004. All ion exchange units were 

decommissioned by Tronox during the fall of 2005, but the units still remain on-site. 

In 2003 McGinley and Associates conducted a perchlorate modeling effort for the Nevada 

Division of Environmental Protection for the portion of Las Vegas Wash impacted by perchlorate 

releases to the Wash itself and to the Las Vegas Wash gravels. Assuming 90% or better capture 

of all perchlorate sources to Las Vegas Wash, the modeling predicted that perchlorate mass 

loading at North Shore Road would decline to 100 pounds per day or less by October 2004. This 

would represent about a 90% reduction from the amount of perchlorate entering Las Vegas Wash 

prior to any controls (about 900 to 1000 pounds per day; initial perchlorate controls began in 

November 1999). In late 2003 the North Shore Road mass loading was in the 250 to 280 pounds 

Perchlorate Monitoring Report 3 February 6, 2006 
per day range, slightly higher than predicted by the McGinley and Associates modeling. In late 

2004, the mass loading was generally in the 110 to 140 pounds per day range (when not 

influenced by rainfall events). In late 2005, the mass loading has generally been in the 100 to 

150 pounds per day range, a decrease of about 85% from pre-control amounts. NDEP and 

EPA are considering whether to have McGinley and Associates refine their 2003 

perchlorate modeling efforts to provide a better predictive tool that includes the effect of 

two more years of operation of the Tronox Athens Road extraction wells, as well as the 

AMPAC extraction wells which are scheduled to begin operation in February 2006. 

4. Monitoring Locations 

There are eleven monitoring locations referenced within this report that extend from Tronox’s 

property in Henderson, Nevada to the Colorado River Aqueduct near Parker Dam on the Lower 

Colorado River. The monitoring locations are indicated below and are shown on the three maps 

in Appendix A. 

• Groundwater on Tronox Property Above Slurry Wall (collected by Tronox) 

• Groundwater on Tronox Property Below Slurry Wall (M-100) (collected by Tronox) 

• Groundwater at Athens Road Wells (ART-8) (collected by Tronox) 

• Groundwater Below Athens Road Wells (ARP-3) (collected by Tronox) 

• Groundwater at Seep Area (PC-97) (collected by Tronox) 

• Las Vegas Wash Downstream of Seep Area (LW 5.3) (collected by SNWA) 

• Las Vegas Wash at North Shore Road (collected by NDEP) 

• Lake Mead at Las Vegas Bay (LVB 2.7/LVB 3.5) (collected by SNWA) 

• Lake Mead at Saddle Island (AMSWTF Raw Water) (collected by SNWA) 

• Colorado River Below Hoover Dam (Willow Beach) (collected by NDEP) 

• Colorado River at Colorado River Aqueduct at Lake Havasu (collected by MWD) 

5. Perchlorate Monitoring Trends for 2005 at Each Monitoring Location 

The following summaries are based solely on 2005 data; they do not reflect any changes 

that may have occurred in 2006. 

A. Mass Loading in Las Vegas Wash at North Shore Road 

-Has declined slightly in 2005 to about 120 lbs/day.


-Has ranged from 100-160 lbs/day from April through December 2005.


-Further declines to less than 100 lbs/day may occur in 2006.


-Annual average declined by 16% from 170 lbs/day in 2004 to 142 lbs/day in 2005.


B. Ground Water on Tronox Property Above Slurry Wall 

-Has declined slightly from 1,500,000 - 1,800,000 ppb (1500 - 1800 ppm) to 1,200,000 -

Perchlorate Monitoring Report 4 February 6, 2006 
1,500,000 ppb (1200 - 1500 ppm).


-Monitoring location reflects perchlorate source area; not likely to decrease significantly for


many years


C. Ground Water on Tronox Property Below Slurry Wall (M-100) 

-Has declined about 85% since slurry wall installed in October 2001 

-Currently about 130,000 to 180,000 ppb (130 to 180 ppm); has been relatively steady at this 

level for the last two years. 

D. Ground Water at Athens Road Wells (ART-8) 

-Steady at about 400,000 ppb (400 ppm), as expected 

-Not likely to decrease for many years 

E. Ground Water Below Athens Road Wells (ARP-3) 

-Has declined about 80% since Athens Road Wells began continuous operation in October 2002


-Results somewhat erratic; there could be a “stagnant zone”(a nearly flat gradient with low flows)


just below Athens Road Wells


-Currently about 70,000 to 120,000 ppb (70 to 120 ppm)


F. Ground Water at Seep Area (PC-97) 

-Has declined more than 95% since Athens Road Wells began continuous operation in October


2002


-Currently about 2,000 ppb (2 ppm)


G. Las Vegas Wash Downstream of Seep Area (LW 5.3) 

-Has declined about 75% to 80% since Athens Road Wells began continuous operation in


October 2002


-Currently about 60 to 100 ppb


H. Las Vegas Wash at North Shore Road 

-Perchlorate concentrations declined about 50% in 2004 to about 140 ppb; concentrations


remained at 130 to 140 ppb in 2005.


-Further declines to less than 100 ppb may occur in 2006


I. Lake Mead at Las Vegas Bay (LVB 2.7/LVB 3.5) 

-Seasonal variation from 10 - 100 ppb over the last six years; peaks in spring/summer; valleys in 

fall/winter; range for 2005 was 7 to 24 ppb. 

Perchlorate Monitoring Report 5 February 6, 2006 
-On 12/16/03 sampling location moved to LVB 3.5 due to low water elevations in Lake Mead 

-No clear trend (except seasonal variation) from 2000 to 2003; summer time peaks in 2004 and 

2005 show decreases of about 65% and 75%, respectively, compared to 2002. 

J. Lake Mead at Saddle Island (AMSWTF Raw Water) 

-Concentrations began to decline in late 2003; declines continued in 2004 and 2005.


-Monthly average concentrations ranged from 2.4 ppb to 3.9 ppb from May through November


2005, the seven lowest values in more than 6 years of data.


-November and December 2003 monthly average peaks were both 10.5 ppb, about 35% lower


than previous 3 year’s peaks (2000, 2001 and 2002).


-November and December 2005 monthly averages were 2.6 and 6.3 ppb, respectively. The two


month average (4.5 ppb) is 57% lower than the November/December 2003 average of 10.5 ppb.


-2005 annual average was 3.8 ppb, a decrease of 60% from the 2003 annual average of 9.8 ppb,


and a decrease of 70% from the 2000 annual average of 13.1 ppb.


-On June 29, 2004 the intake depth was lowered from 1050 feet to 1000 feet, which would be


expected to decrease perchlorate concentrations.


K. Colorado River Below Hoover Dam (Willow Beach) 

-Peak concentrations have gradually declined from about 10 ppb to about 4 ppb since seep


capture began in November 1999


-Concentrations declined to 1.8 ppb in July, 1.9 ppb in August and 1.9 ppb in September 2005,


the 3 lowest values ever measured at this location.


-Annual average concentrations have declined from 6.5 ppb in 2000 to 2.4 ppb in 2005 (a 63 %


decrease); further declines are expected in 2006.


-Modeling conducted for MWD predicted that concentrations would reach 2 ppb by the end of


2005; the average for the last 6 months of 2005 was 2.1 ppb.


L. Colorado River at Colorado River Aqueduct 

-Peak concentrations have gradually declined from 9 ppb to less than 4 ppb since seep capture


began in November 1999


-In 2005 all twelve monthly samples were less than 4 ppb.


-Annual average concentrations have declined from 6.4 ppb in 2000 to less than 4 ppb in 2004 


and 2005 (about a 50% decrease).


-Modeling conducted for MWD predicted that concentrations would reach 2 ppb by the end of


2005; in November and December 2005 the concentrations were 2 ppb and non-detect,


respectively (method detection limit = 2 ppb).


Perchlorate Monitoring Report 6 February 6, 2006 
II MONITORING DATA 

1. Total Perchlorate Mass Removal by Tronox 

Table 1. : Perchlorate Removed by Tronox (formerly Kerr McGee), Henderson, Nevada. 

1. 

(near LVW) 

(lbs/day) 

2. Athens Road 

Wells (midpoint) 

(lbs/day) 

3. 

Wells 

(lbs/day) 

4. Total 

(lbs/day) 

Total 

Tons 

Removed 

per/month 

October 

2002* 

495 331 1402 2228 34.5 

Seep Area On Site CTL 

November 

2002 

December 

2002 

January 

2003 

February 

2003 

March 

2003** 

April 

2003 

May 

2003 

June 

2003 

July 

2003*** 

August 

2003 

September 2003 

October 

2003 

370 769 1003 2142 33.1 

422 1001 1146 2569 38.5 

208 1164 1292 2664 41.3 

335 1074 1467 2876 44.6 

570 783 1060 2413 33.8 

485 806 1067 2358 36.5 

713 713 1033 2460 36.9 

703 729 1148 2581 40.0 

686 907 1098 2691 40.4 

594 755 1034 2383 36.9 

463 741 921 2125 32.9 

416 770 937 2123 31.8 

Perchlorate Monitoring Report 7
 February 6, 2006 
November 

2003 

337 713 949 1999 30.0 

December 

2003 

317 735 915 1967 30.5 

January 

2004 

305 689 953 1947 30.2 

February 

2004 

312 630 894 1836 26.6 

March 

2004 

221 743 932 1895 29.4 

April 

2004 

151 733 849 1733 26.0 

May 

2004 

122 740 835 1697 26.3 

June 

2004 

157 755 1053 1965 29.5 

July 

2004 

195 794 968 1958 30.4 

August 

2004 

201 767 914 1882 29.2 

September 2004 

169 835 974 1978 29.7 

October 

2004 

262 799 1026 2088 32.4 

November 

2004 

167 814 1032 2013 30.2 

December 

2004 

123 811 901 1835 28.4 

January 

2005 

142 775 1008 1926 29.8 

February 

2005 

143 648 991 1782 25.0 

March 

2005 

157 781 979 1917 29.7 

Perchlorate Monitoring Report 8 February 6, 2006 
April 

2005 

145 787 987 1919 28.8 

May 

2005 

152 756 982 1890 29.3 

June 

2005 

151 793 985 1929 28.9 

July 

2005 

154 769 1077 2000 31.0 

August 

2005 

135 800 1109 2044 31.7 

September 2005 

85 807 1140 2032 30.5 

October 

2005 

99 797 1077 1973 30.6 

November 

2005 

111 773 1089 1973 29.6 

December 

2005 

121 725 1137 1984 30.8 

*Athens Road Extraction Wells begin full time operation on 10/22/02.


**Five new seep area extraction wells begin operation on 3/24/03.


***As expec ted, Seep Area mas s capture b egan to de cline in July 20 03 as a resu lt of Athens Ro ad mass ca pture. 


These d eclines are ex pected to continue thro ughout 2006. 

Perchlorate Monitoring Report 9 February 6, 2006 
2. Perchlorate Mass Loading in Las Vegas Wash at North Shore Road 

•	 Measures total perchlorate load in Las Vegas Wash entering Lake Mead; measures overall 

effectivness of perchlorate remediation efforts in Henderson, Nevada. 

•	 Mass loading declined in 2000 after seep capture began in November 1999, and declined further in 

2003, 2004 and 2005 after Athens Road Wells began operation in October 2002. 

•	 During the last seven months of 2003 mass loadings ranged from 250 to 325 lbs/day, a substantial 

decrease from amounts in 2002 and early 2003. 

• During the last nine months of 2005 mass loadings ranged from 100 to 160 lbs/day. 

• Further declines may occur in 2006. 

Perchlorate Monitoring Report 10 February 6, 2006 
3. Groundwater on Tronox Property Above Slurry Wall 

! Measures perchlorate source concentrations


! Concentrations show gradual declining trend since October 2002


4. Groundwater on Tronox Property Below Slurry Wall (M-100) 

! Measures effectiveness of slurry wall/extraction well capture system.


! Extraction wells began operating in January 1999; slurry wall completed in September 2001.


! Concentrations declined about 85% after September 2001; concentrations have been in the


130-180 ppm range for the last two years. 

Perchlorate Monitoring Report 11 February 6, 2006 
5. Groundwater at Athens Road Wells (ART-8) 

! Measures plume concentrations at Athens Road, about midway between the Tronox plant site and 

Las Vegas Wash 

! This groundwater is being extracted and treated; the goal is “virtually complete capture.” 

6. Groundwater Below Athens Road Wells (ARP - 3) 

! Measures effectiveness of Athens Road extraction well capture system and downstream effects. 

! Concentrations have declined about 80% since October 2002. 

Perchlorate Monitoring Report 12 February 6, 2006 
7. Groundwater at Seep Area (PC-97) 

! Measures plume concentrations at seep area.


! Shows combined effect of Athens Road and seep area extraction wells.


! Concentrations have declined more than 95% since October 2002.


Perchlorate Monitoring Report 13 February 6, 2006 
8. Las Vegas Wash Downstream of Seep Area (LW 5.3) 

! Measures perchlorate “daylighting” from Las Vegas Wash gravels, near Historic Lateral. 

! Concentrations may decline further in 2006. 

9. Las Vegas Wash at North Shore Road 

! Measures total perchlorate concentration in Las Vegas Wash entering Lake Mead. 

! Concentrations declined in 2000 after seep capture began in November 1999, and declined further in 

2003, 2004 and 2005 after Athens Road Wells began operation in October 2002. 

! Further declines may occur in 2006. 

Perchlorate Monitoring Report 14 February 6, 2006 
10. Lake Mead at Las Vegas Bay (LVB 2.7/LVB 3.5) 

! Measures perchlorate concentrations in Las Vegas Bay; sampling location moved to LVB 3.5 in 

December 2003 due to declining water levels in Lake Mead. 

! Concentrations began to decline in 2000 after seep capture began in November 1999. 

! Declining Lake Mead surface elevations (years 2000 to 2004) may have resulted in increased 

perchlorate concentrations. 

11. Lake Mead at Saddle Island (AMSWTF Raw Water) 

! Measures perchlorate concentrations in Las Vegas Valley drinking water supply. 

! Concentrations began to decline in 2000 after seep capture began in November 1999. 

! Destratification of water in Lake Mead in November/December each year causes seasonal peaks in 

perchlorate concentrations; 2003 seasonal peak was about 35% lower than in previous three years. 

! Declining Lake Mead surface elevations (years 2000 to 2004) may have resulted in increased 

perchlorate concentrations 

! Intake depth lowered from 1050 feet to 1000 feet on June 29, 2004. 

! Metho d Detec tion Limit = 0.2 ppb beginning in May 2005 (M DL = 4 ppb previously). 

Perchlorate Monitoring Report 15 February 6, 2006 
12. Colorado River Below Hoover Dam (Willow Beach) 

! Measures perchlorate concentrations in water entering Lower Colorado River 

! Concentrations have declined more than 60% since seep capture began in November 1999. 

! Concentrations declined to less than 2 ppb in July, August and September 2005. 

! Method Detection Limit (MDL) = 1 ppb beginning in November 2004 (MDL = 4 ppb prior to 

December 2002; 2 ppb from December 2002 to October 2004) 

13. Colorado River at the Colorado River Aqueduct at Lake Havasu 

! Measures perchlorate concentrations at Southern California drinking water supply. 

! Peak concentrations have shown gradual decline since seep capture began in November 1999. 

! In 2005, 11 of the 12 monthly samples were non-detect; all concentrations less than 4 ppb. 

! Method Detection Limit (MDL) = 2 ppb since Nov. 2005; non-detect samples graphed at MDL. 

! California Public Health Goal (PHG) = 6 ppb. 

Perchlorate Monitoring Report 16 February 6, 2006 
APPENDIX A: MAPS 

1. Southern California, Southern Nevada and Western Arizona 

Perchlorate Monitoring Report 17 February 6, 2006 
2. Las Vegas Wash and Lake Mead Perchlorate Monitoring Locations 

Perchlorate Monitoring Report 18 February 6, 2006 
3. Lake Mead and Lower Colorado River Perchlorate Monitoring Locations 

Perchlorate Monitoring Report 19
 February 6, 2006 
APPENDIX B: BACKGROUND 

1. Discovery and Magnitude of the Perchlorate Problem 

•	 In mid - 1997 the Metropolitan Water District of Southern California discovered perchlorate 

in the lower Colorado River due to a more sensitive test method, and traced the contamination 

to Lake Mead and the Las Vegas Wash. Ultimately, the source of the perchlorate was traced 

to the Kerr McGee (now Tronox) Chemical Plant in Henderson, Nevada. 

•	 Since 1997 the Nevada Division of Environmental Protection and the US Environmental 

Protection Agency have been working closely with Kerr McGee/Tronox to achieve source 

control and reduce perchlorate releases to Las Vegas Wash as quickly as possible. 

•	 Kerr McGee Chemical Company (KMCC) - perchlorate production was initiated in 1945; full 

commercial production of ammonium perchlorate began in 1951 under prior 

owners/operators; Kerr McGee acquired the property in 1967; name changed to Tronox in 

November 2005. 

•	 Perchlorate contaminated ground water from the Kerr McGee/Tronox plume flows north 

about 3 miles from Tronox to Las Vegas Wash. Tronox is the most significant source of 

perchlorate entering LVW; prior to controls, the Tronox plume released about 900 to 1000 

pounds per day (average) to Las Vegas Wash (LVW). 

•	 These perchlorate releases to Lake Mead and the Lower Colorado River have impacted the 

drinking water supply of 15 to 20 million people in Arizona, southern California, southern 

Nevada, Tribal nations and Mexico. 

•	 In the last 2 years, concentrations of perchlorate at Saddle Island (AMSWTF Raw Water) in 

Lake Mead have ranged from 2 to 8 ppb which is below the recently adopted US EPA 

reference dose drinking water equivalent level (DWEL) of 24.5 ppb, but at times greater than 

California’s Public Health Goal of 6 ppb. 

•	 In the last 2 years, concentrations of perchlorate at the Colorado River Aqueduct near Parker 

Dam have ranged from non-detect (ND = 2 ppb) to 5.6 ppb, which is below the recently 

adopted US EPA reference dose drinking water equivalent level (DWEL) of 24.5 ppb. Since 

June 2002, all of the monthly samples have been at or below California’s Public Health Goal 

of 6 ppb. In 2004 nine of the twelve monthly samples were non-detect (ND = 4 ppb). In 2005 

all twelve monthly samples were less than 4 ppb. 

•	 This report addresses only the perchlorate releases from Tronox and AMPAC in Henderson, 

Nevada and their impacts on Las Vegas Wash, Lake Mead and the lower Colorado River. 

There are many other perchlorate releases throughout the United States which have created 

their own separate and distinct perchlorate plumes. This report does not address any of these 

other releases. 

2. Status of Applicable Perchlorate Standards 

•	 In 1992 EPA adopted a federal provisional reference dose drinking water equivalent level 

(DWEL) of 4-18 ppb. 

•	 In January 2002 EPA proposed a new reference dose for perchlorate of 0.00003 mg/kg, with 

an associated drinking water equivalent level of 1 ppb, but this reference dose was never 

finalized. In order to resolve disagreements about how to interpret the health effects 

Perchlorate Monitoring Report 20 February 6, 2006 
data, the National Academy of Sciences (NAS) reviewed these data for perchlorate and issued 

their report to EPA on January 10, 2005. The NAS recommended a reference dose of 0.0007 

mg/kg. 

•	 On February 18, 2005 EPA adopted a perchlorate reference dose of 0.0007 mg/kg/day, which 

can be used to calculate a drinking water equivalent level (DWEL) of 24.5 ppb, assuming 

that all perchlorate exposure comes from drinking water, and using standard adult body 

weight and water consumption estimates. 

•	 On January 26, 2006 “Assessment Guidance for Perchlorate” was issued by EPA’s 

Office of Solid Waste and Emergency Response (OSWER), which recommends using 

24.5 ppb as a starting point for evaluation of federal cleanup sites. 

•	 EPA is currently working to determine whether or not a national drinking water 

regulation for perchlorate would present a meaningful opportunity for health risk 

reduction. 

•	 In November 2002 the state of California proposed a Public Health Goal (PHG) for 

perchlorate of 2-6 ppb and adopted a final PHG of 6 ppb on March 11, 2004. 

• California expects to adopt a drinking water standard for perchlorate in 2006. 

• The state of Nevada uses a perchlorate “provisional action level” of 18 ppb. 

3. Tronox Control Strategy and Current Status 

• Control Strategy: capture and treat perchlorate at three locations: 

" On Tronox property where perchlorate is most concentrated, 

" At Athens Road about midway between Tronox and Las Vegas Wash where there is a 

narrow subsurface channel that makes effective capture possible, and 

" Near Las Vegas Wash where capture will have the most immediate impact on reducing 

releases to Las Vegas Wash. 

• Current Status: 

"	 On Tronox property - source control achieved in October 2001; slurry wall (1700 feet 

long & 60 feet deep) and 22 extraction wells captured an average of 1050 pounds per day 

in 2003, 940 in 2004 and 1050 pounds per day in 2005 (“virtually complete capture”). 

"	 At Athens Road - 8 extraction wells began regular operation in October 2002; they 

captured an average of 790 pounds per day in 2003, 760 in 2004 and 770 pounds per day 

in 2005 (an estimated 90 - 98% of the mass flow). 

"	 Near Las Vegas Wash - seep and 10 extraction wells capture an estimated 70 - 90% of the 

mass flow. As expected, mass removal rates at this location have decreased significantly 

due to perchlorate removal by the upstream wells at Athens Road (from about 700 lbs/day 

in April/May/June 2003 to about 85 - 135 lbs/day in August through December 2005). 

•	 Water Treatment - A total of 1000 gpm of water captured from the three locations is treated 

using a biologically-based fluidized-bed reactor (FBR), then discharged back to LVW. The 

FBR treatment plant was in startup/shakedown mode for most of 2004, but successfully 

completed a 30-Day Performance Test in October/November, and is now fully operational. It 

has a treatment capacity of about 1000 gpm and removes about 99.99% of the perchlorate. 

The perchlorate concentrations in the treatment plant effluent are less than 18 ppb (1000 gpm 

at 18 ppb equates to about 0.21 pounds per day of perchlorate to Las Vegas Wash). The FBR 

Perchlorate Monitoring Report 21 February 6, 2006 
has replaced the previously used ion exchange treatment units. 

•	 Summary - engineered controls are in place and removing 1700-2000 pounds (almost 1 ton) 

per day of perchlorate from the Tronox plume that flows towards Las Vegas Wash. As of 

December 31, 2005, these control systems have removed more than 1800 tons of perchlorate 

from the environment. 

4. AMPAC’s Control Strategy and Current Status 

The former AMPAC perchlorate plant also has a plume of perchlorate, but it is smaller and much 

less concentrated than the Tronox plume. However, the AMPAC plume is being investigated 

and will be remediated. 

•	 AMPAC conducted an In-Situ Bioremediation Pilot Study from December 2002 to April 

2003; the pilot was successful, reducing perchlorate concentrations from about 500 ppm to 

less than 2 ppb. During 2003 and 2004 AMPAC conducted additional investigation of the 

nature and extent of their perchlorate plume. 

•	 Nevada Division of Environmental Protection (NDEP) is requiring that AMPAC install a 

remediation system at the leading edge of its plume by February 2006. 

•	 The next step would be to install a full scale system at the middle or source of the plume in 

2007. 

5. Estimated Travel Times and Flushing Times 

It takes time for ground water and surface water to travel from one point to the next (travel time). 

Even after a source of perchlorate is reduced or eliminated, it takes time for clean water to flush 

out the contaminated ground water or surface water (flushing time). 

•	 Athens Road to Las Vegas Wash - travel time is estimated to be 7 months; flushing time to 

reach 4 ppm is estimated to take 28 to 49 months (4 to 7 travel times) 

•	 Las Vegas Wash Gravels - travel time is estimated to be 6 months; flushing time is estimated 

to take 18 to 42 months (3 to 7 travel times) 

•	 Lake Mead - flushing time is likely to be several years; the average residence time of Boulder 

Basin (the lower part of Lake Mead) is about 10 months. 

•	 Lower Colorado River (below Hoover Dam) - travel time from Hoover Dam to Colorado 

River Aqueduct intake is estimated to be 3 months; flushing time estimated to be about 1 year; 

MWD had a contractor investigate this issue - their final report of flushing time estimates was 

issued on March 25, 2004. 

•	 In late 2003 Flow Science conducted a perchlorate modeling effort for the Metropolitan Water 

District of Southern California to estimate how long it would take Colorado River perchlorate 

concentrations to reach target levels under various perchlorate control strategies and 

hydrological conditions. Their final report was dated March 25, 2004. Assuming 90% 

capture of all perchlorate sources to Las Vegas Wash (and based on the modeling results from 

the October 20, 2003 McGinley and Associates report prepared for the Nevada Division of 

Environmental Protection), the modeling predicts that perchlorate concentrations at the 

Colorado River Aqueduct intake will reach 4 ppb by mid 2004 and 2 ppb by mid to late 2005. 

The 2004 and 2005 annual average concentrations at this location were less than 4 ppb. In 

November 2005 the method detection limit (MDL) for this sampling location was 

Perchlorate Monitoring Report 22 February 6, 2006 
changed from 4 ppb to 2 ppb. 

6. Perchlorate Monitoring Trends for 2004 at Each Monitoring Location 

The following summaries are based solely on 2004 data; they do not reflect any changes that 

may have occurred in 2005. 

A. Mass Loading in Las Vegas Wash at North Shore Road 

-Has declined about 50% in 2004 to about 130 lbs/day


-Has ranged from 110-170 lbs/day between May through December 2004


-Further declines to less than 100 lbs/day expected in 2005


-Annual average declined by more than 50% from 374 lbs/day in 2003 to 170 lbs/day in 2004.


B. Ground Water on Kerr McGee Property Above Slurry Wall 

-Has declined slightly from 1,500,000 - 1,800,000 ppb (1500 - 1800 ppm) to 1,300,000 -


1,500,000 ppb (1300 - 1500 ppm).


-Monitoring location reflects perchlorate source area; not likely to decrease significantly for many


years


C. Ground Water on Kerr McGee Property Below Slurry Wall (M-100) 

-Has declined almost 90% since slurry wall installed in October 2001 

-Currently about 110,000 to 130,000 ppb (110 to 130 ppm) 

D. Ground Water at Athens Road Wells (ART-8) 

-Steady at about 400,000 ppb (400 ppm), as expected 

-Not likely to decrease for many years 

E. Ground Water Below Athens Road Wells (ARP-3) 

-Has declined about 80% since Athens Road Wells began continuous operation in October 2002


-Results somewhat erratic; there could be a “stagnant zone” (a nearly flat gradient with low flows)


just below Athens Road Wells


-Currently about 90,000 ppb (90 ppm)


F. Ground Water at Seep Area (PC-97) 

-Has declined about 95% since Athens Road Wells began continuous operation in October 2002 

-Currently about 3,000 ppb (3 ppm) 

Perchlorate Monitoring Report 23 February 6, 2006 
G. Las Vegas Wash Downstream of Seep Area (LW 5.3) 

-Has declined about 75% to 80% since Athens Road Wells began continuous operation in October


2002


-Currently about 60 to 90 ppb


H. Las Vegas Wash at North Shore Road 

-Perchlorate concentrations have declined about 50% in 2004 to about 140 ppb 

-Further declines to less than 100 ppb expected in 2005 

I. Lake Mead at Las Vegas Bay (LVB 2.7/LVB 3.5) 

-Seasonal variation from 10 - 100 ppb over the last five years; peaks in spring/summer; valleys in


fall/winter


-On 12/16/03 sampling location moved to LVB 3.5 due to low water elevations in Lake Mead


-No clear trend (except seasonal variation) from 2000 to 2003; summer time peak in 2004 shows a


decrease of about 60% compared to 2002 and 2003.


J. Lake Mead at Saddle Island 

-Concentrations began to decline in late 2003; declines continued in 2004


-Monthly average concentrations ranged from 4.2 ppb to 4.7 ppb between July through November


2004, the five lowest values in more than 5 years of data


-November and December 2003 monthly average peaks were both 10.5 ppb, about 35% lower


than previous 3 year’s peaks (2000, 2001 and 2002)


-November and December 2004 monthly averages were 4.7 and 7.2 ppb, respectively. The two


month average (6.0 ppb) is more than 40% lower than the November/December 2003 average of


10.5 ppb.


-2004 annual average was 5.6 ppb, a decrease of about 40% from the 2003 annual average of 9.8


ppb, and a decrease of almost 60% from the 2000 annual average of 13.1 ppb.


-On June 29, 2004 the intake depth was lowered from 1050 feet to 1000 feet, which would be


expected to decrease perchlorate concentrations.


K. Colorado River Below Hoover Dam (Willow Beach) 

-Peak concentrations have gradually declined from about 10 ppb to about 6 ppb since seep capture


began in November 1999


-Concentrations declined to 2.8 ppb in August, 2.5 ppb in September and 2.0 ppb in October


2004; the 3 lowest values ever measured at this location


-Annual average concentrations have declined from 6.5 ppb in 2000 to 3.8 ppb in 2004 (about a


40% decrease).


-Further declines expected in 2005


Perchlorate Monitoring Report 24 February 6, 2006 
L. Colorado River at Colorado River Aqueduct 

-Peak concentrations have gradually declined from 9 ppb to less than 6 ppb since seep capture


began in November 1999


-In 2004 nine of the twelve monthly samples were non-detect (ND = 4 ppb)


-Annual average concentrations have declined from 6.4 ppb in 2000 to less than 4 ppb in 2004


(about a 50% decrease)


-Modeling conducted for MWD predicts that concentrations will reach 2 ppb by the end of 2005.


7. 2003 Perchlorate Monitoring Trends at Each Monitoring Location 

The following summaries are based solely on 2003 data; they do not reflect any changes that 

occurred in 2004. 

A. Mass Loading in Las Vegas Wash at North Shore Road 

-Has declined about 50% in 2003 to about 275 lbs/day


-Has “leveled off” at 250-280 lbs/day in October/November/December 2003


-Further declines to about 100 lbs/day expected in 2004


B. Ground Water on Kerr McGee Property Above Slurry Wall 

-Steady at 1,500,000 - 1,800,000 ppb (1500 - 1800 ppm), as expected


-Monitoring location reflects perchlorate source area; not likely to decrease for many years


C. Ground Water on Kerr McGee Property Below Slurry Wall (M-100) 

-Has declined about 80% since slurry wall installed in October 2001 

-Currently about 160,000 ppb (160 ppm) 

D. Ground Water at Athens Road Wells (ART-8) 

-Steady at 400,000 - 450,000 ppb (400 - 450 ppm), as expected 

-Not likely to decrease for many years 

E. Ground Water Below Athens Road Wells (ARP-3) 

-Has declined 50% - 60% since Athens Road Wells began continuous operation in October 2002


-Results erratic; there could be a nearly flat gradient with low flows just below Athens Road


Wells


-Currently about 220,000 ppb (220 ppm)


Perchlorate Monitoring Report 25 February 6, 2006 
F. Ground Water at Seep Area (PC-97) 

-Has declined about 90% since Athens Road Wells began continuous operation in October 2002 

-Currently about 10,000 ppb (10 ppm) 

G. Las Vegas Wash Downstream of Seep Area (LW 5.3) 

-Has declined about 75% since Athens Road Wells began continuous operation in October 2002 

-Currently about 80 to 90 ppb 

H. Las Vegas Wash at North Shore Road 

-Perchlorate concentrations have declined about 50% to 60% in 2003 to about 200 - 270 ppb 

-Further declines to about 100 ppb expected in 2004 

I. Lake Mead at Las Vegas Bay (LVB 2.7) 

-Seasonal variation from 20 - 100 ppb; “peaks” in spring/summer; “valleys” in fall/winter


-No clear trend (except seasonal variation) during last 3 years


-On 12/16/03 sampling location moved to LVB 3.5 due to low water elevations in Lake Mead


J. Lake Mead at Saddle Island 

-Concentrations appear to be declining in late 2003; further declines expected in 2004


-Monthly average concentrations declined to 5.9 ppb in September and 6.6 ppb in October 2003,


the 2 lowest values in more than 4 years of data


-November and December monthly average peaks were both 10.5 ppb, about 35% lower than


previous 3 years peaks (2000, 2001 and 2002)


-2003 annual average was 9.8 ppb, about the same as 2001 (10.4 ppb) and 2002 (9.9 ppb); lower


lake levels have likely prevented decreases in annual average concentrations


K. Colorado River Below Hoover Dam (Willow Beach) 

-Peak concentrations have gradually declined from about 10 ppb to about 7 ppb since seep capture


began in November 1999


-Concentrations declined to 3.4 ppb in September and 3.0 ppb in October 2003; the 2 lowest


values ever measured at this location


-Further declines expected in 2004


L. Colorado River at Colorado River Aqueduct 

-Peak concentrations have gradually declined from 9 ppb to less than 6 ppb since seep capture


began in November 1999


-Recent concentrations have ranged from non-detect (ND = 4 ppb) to 6 ppb


Perchlorate Monitoring Report 26 February 6, 2006 
-Annual average concentration has declined from 6.4 ppb in 2000 to 4.8 ppb in 2003 (a 25%


decrease)


-Further declines expected in 2004


Perchlorate Monitoring Report 27
 February 6, 2006