DEPOSITION AND CHEMISTRY OF

BOTTOM SEDIMENTS IN COCHITI LAKE,

NORTH-CENTRAL NEW MEXICO

Prepared in cooperation with

PUEBLO DE COCHITI

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 99-4258

the
U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 99-4258

DEPOSITION AND CHEMISTRY OF 

BOTTOM SEDIMENTS IN COCHITI LAKE, 

NORTH-CENTRAL NEW MEXICO

Prepared in cooperation with the

PUEBLO DE COCHITI

By Jennifer T. Wilson and Peter C. Van Metre

Albuquerque, New Mexico

2000
iii

CONTENTS

Page

Abstract.................................................................................................................................................................................. 1

Introduction ........................................................................................................................................................................... 1

Purpose and scope ....................................................................................................................................................... 1

Methods ....................................................................................................................................................................... 3

Quality control............................................................................................................................................................. 3

Deposition of bottom sediment.............................................................................................................................................. 9

Sediment surveys ......................................................................................................................................................... 9

Core lithology, grain size, and organic carbon content ............................................................................................... 9

Estimating age of sediments and rates of deposition................................................................................................... 12

Chemistry of bottom sediments............................................................................................................................................. 12

Major elements ............................................................................................................................................................ 12

Trace elements ............................................................................................................................................................. 15

Organochlorine compounds......................................................................................................................................... 15

Polychlorinated biphenyls (PCB’s) ................................................................................................................... 15

DDT, DDD, and DDE........................................................................................................................................ 19

Polycyclic aromatic hydrocarbons............................................................................................................................... 20

Radionuclides .............................................................................................................................................................. 25

Conclusions ........................................................................................................................................................................... 28

References cited..................................................................................................................................................................... 30

FIGURES

1. Map showing contributing area of Cochiti Lake and location of sediment coring sites.......................................... 2

2-12. Graphs showing:

2. (A) Longitudinal profile of reservoir showing historical sedimentation and migration of sediment

front. (B) Suspended-sediment discharge of the Rio Grande at Otowi Bridge, N. Mex............................. 10

3. Grain size in a gravity core at site R1 (A) and box cores (B) and percentage of organic carbon in a

gravity core (C) and box core at site R1 (D) from Cochiti Lake ................................................................ 11

4. Major element concentrations in a gravity core and box core at site R1 from Cochiti Lake ........................... 13

5. Major element concentrations in box cores from Cochiti Lake ....................................................................... 14

6. Trace-element concentrations in a gravity core and box core at site R1 from Cochiti Lake............................ 16

7. Trace-element concentrations in box cores from Cochiti Lake........................................................................ 17

8. Concentrations of DDT and its metabolites in a gravity core (A) and box cores (B) from Cochiti Lake........ 21

9. Polycyclic aromatic hydrocarbon (PAH) concentrations (A-D), PAH sums (E), and the ratio of the sum

of 2- and 3-ringed PAH’s to total combustion PAH (F) in a gravity core from Cochiti Lake..................... 23

10. Polycyclic aromatic hydrocarbon (PAH) concentrations (A-D), PAH sums (E), and the ratio of the sum

of 2- and 3-ringed PAH’s to total combustion PAH (F) in box cores from Cochiti Lake ........................... 24

11. Uranium and thorium radionuclide activities in a gravity core from Cochiti Lake.......................................... 26

12. Uranium and thorium radionuclide activities in box cores from Cochiti Lake ................................................ 27

13. Plutonium activities in a gravity core (A and B) and box cores (C and D) from Cochiti Lake............................... 29
iv

TABLES

Page

1. Parameters analyzed for and their reporting levels in Cochiti Lake bottom-sediment samples.............................. 4

2. Polycyclic aromatic hydrocarbons (PAH’s) analyzed for, number of detections, and range and median

of concentrations, in micrograms per kilogram, in Cochiti Lake bottom-sediment samples ............................ 5

3. Counting and total errors of radionuclide analyses ................................................................................................. 8

4. Trace-element sediment-quality guidelines compared to concentration ranges, in micrograms per gram,

in Cochiti Lake gravity core .............................................................................................................................. 18

5. Concentrations of polychlorinated biphenals (PCB’s), in micrograms per kilogram, in Cochiti Lake gravity

core from site R1 and box cores from all sites .................................................................................................. 18

6. Organic sediment-quality guidelines compared to concentration ranges, in micrograms per kilogram,

in Cochiti Lake gravity core .............................................................................................................................. 20

CONVERSION FACTORS AND VERTICAL DATUM

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929—a geodetic datum derived from a general adjustment of the first-order level nets of the United States and

Canada, formerly called Sea Level Datum of 1929.

Multiply By To obtain

foot 0.3048 meter

ton 0.9072 metric ton
1

Deposition and Chemistry of Bottom Sediments

in Cochiti Lake, North-Central New Mexico

By Jennifer T. Wilson and Peter C. Van Metre

ABSTRACT

Bottom sediments were sampled at seven 

sites in Cochiti Lake in September 1996. Sediment 

cores penetrating the entire lacustrine sediment 

sequence were collected at one site near the dam. 

Surficial sediments were sampled at the near-dam 

site and six other sites located along the length of 

the reservoir. Analyses included grain size, major 

and trace elements, organochlorine compounds, 

polycyclic aromatic hydrocarbons (PAH’s), and 

radionuclides. Concentrations of trace elements, 

organic compounds, and radionuclides are similar 

to those in other Rio Grande reservoirs and are low 

compared to published sediment-quality 

guidelines. Most elements and compounds that 

were detected did not show trends in the ageestimated sediment cores with the exception of a 

decreasing trend in total DDT concentrations from 

about 1980 to 1992. The mixture of PAH’s 

suggests that the increase is caused by inputs of 

fuel-related PAH and not combustion-related 

PAH.

INTRODUCTION

Cochiti Lake is on the Cochiti Indian 

Reservation in north-central New Mexico (fig. 1). 

Storage of water from the Rio Grande and the Santa Fe 

River began in November 1973 (Borland and Ong, 

1995). The permanent pool elevation of approximately 

5,340 feet (ft) was reached in December 1975 

(Department of the Army, 1996). Cochiti Lake has a 

drainage area of approximately 38,600 square 

kilometers (km2), which includes 7,600 km2

 of closed 

basin in the San Luis Valley, Colo. A detailed 

description of the drainage area, including geology, 

soils, and climate, was published by the Department of 

the Army (1996). Cochiti Lake is used for flood 

control, sediment control, irrigation, and recreation 

(Ruddy and Hitt, 1990).

Los Alamos National Laboratory (LANL) has 

operated as a Federal facility since 1943. It is located 

on Pajarito Mesa on the east flank of the Jemez 

Mountains, within the drainage area of Cochiti Lake. 

Many activities and operations at LANL involve or 

produce liquids, solids, and gases that contain 

radioactive and (or) nonradioactive hazardous 

materials (Los Alamos National Laboratory, 1995). In 

1996, the U.S. Geological Survey (USGS), in 

cooperation with Pueblo de Cochiti, began a study to 

evaluate the chemistry of bottom sediments in Cochiti 

Lake.

Purpose and Scope

This report evaluates the occurrence and trends 

of major and trace elements and selected contaminants 

in the bottom sediments of Cochiti Lake. Gravity cores 

collected at a single site provided sediment samples for 

the analysis of the historical occurrences and trends of 

selected compounds, and box cores collected at six 

sites along the length of the reservoir provided 

sediment samples used to describe the spatial 

occurrence of selected compounds. Compounds 

studied include major and trace elements, 

organochlorine pesticides, polychlorinated biphenyls 

(PCB’s), polycyclic aromatic hydrocarbons (PAH’s), 

and several radionuclides. The study used reservoir 

paleolimnology following approaches used by the 

USGS National Water-Quality Assessment Program in 

other Rio Grande reservoirs (Van Metre and others, 

1996a) and elsewhere (Callender and Van Metre, 1997; 

Van Metre and others, 1997).
Figure 1. Contributing area of Cochiti Lake and location of sediment coring sites.

0 25 50 KILOMETERS

COLORADO

NEW MEXICO

ABIQUIU

RESERVOIR

Cochiti

Lake Jemez River

Rio

Chama

White Rock

Canyon

RIO GRANDE

107°

37°

36° x

Rio Grande at Otowi gaging station

Jemez Mts

Cochiti 

Pueblo

Cochiti

Recreation

Area

Tetilla Peak

Recreation 

Area

B5

B4

B3.5

B3

B2

B1

R1

Cochiti

Lake Cochiti Dam

106o20 ́ 106o15 ́

35o

35 ́

35o

40 ́

 EXPLANATION

 Sediment coring site

 

 Boat launch

B1

0 0.5 1 KILOMETER

Santa

Fe

River

ada

Cañ

de Cochiti

Rio Grande

Jemez Mts

Los Alamos National Laboratory

Cochiti Pueblo Santa Fe River

106°

COLORADO

Contributing area

of Cochiti Lake

NEW MEXICO

2
3

Methods

Bottom sediment cores were collected using a 

Benthos gravity corer (4 meters (m) long and 6.3 

centimeters (cm) in diameter) and a Wildco box corer 

(15 x 15 x 20 cm). Corers were lowered from a 15-ft 

aluminum A-frame on a custom-built pontoon boat. 

Bottom sediments were cored at seven sites in Cochiti 

Lake (fig. 1) in September 1996. The primary coring 

location, site R1, was located approximately 150 m 

northeast of Cochiti Dam in the right stream channel of 

the originally braided Rio Grande channel. The 

remaining six sampling sites (B1 through B5) were 

located along the length of the reservoir and included 

two sites with relatively shallow water depths near the 

inlet of the Rio Grande.

Five gravity cores (of varying lengths) and one 

box core were collected at site R1. Four gravity cores 

and the box core were extruded vertically and 

subsampled into discreet intervals on site. The fifth 

gravity core was split longitudinally and visually 

described in the field. The gravity core analyzed for 

major and trace elements was subsampled at 5-cm 

intervals along its 133-cm length. The gravity core 

analyzed for organic compounds, including 

organochlorines and PAH’s, was subsampled at 12-cm 

intervals from 0 to 120 cm. The gravity core analyzed 

for radionuclides was subsampled at 13-cm intervals 

from 0 to 156 cm. The gravity core for archiving was 

subsampled at 5-cm intervals along its 125-cm length. 

The box core analyzed for major and trace elements 

and organic carbon was subsampled at 2-cm intervals 

along its 18-cm length. A portion of the top 5 cm of this 

box core was analyzed for grain size, organochlorine 

compounds, PAH’s, and radionuclides.

At the other six sites (B1 through B5), only box 

cores were collected. Gravity cores were not collected 

at sites B1 through B5 because sedimentation has 

probably not been continuous since the date of 

impoundment, limiting the historical significance of 

gravity cores. Also, the sediments are more likely to be 

disturbed by flood events in these shallow, more 

upstream areas. At each of these six sites, three box 

cores were collected and the top 5 cm from each was 

composited for analysis. Samples were analyzed for 

grain size, major and trace elements, organochlorine 

compounds, PAH’s, and radionuclides.

Analyses of subsamples from the cores were 

analyzed at different laboratories. The USGS sediment 

laboratory in Iowa City, Iowa, conducted grain-size 

analyses by wet sieving the sand fraction and 

measuring silt- and clay-sized fractions using the pipet 

method (Guy, 1969). Analytical methods included the 

determination of percent organic carbon by a 

modification of the method in Hendricks and 

Eganhouse (1992); determination of major and trace 

elements by inductively coupled plasma-atomic 

emission spectrometry; determination of chromium, 

lead, and zinc by graphite-furnace atomic adsorption; 

determination of mercury by cold vapor atomic 

adsorption; and determination of selenium by hydride 

generation atomic adsorption spectrometry by the 

USGS National Research Program laboratory in 

Reston, Va. (Lichte and others, 1987; Fishman, 1993). 

Organic compounds were analyzed by the USGS 

National Water Quality Laboratory (NWQL) in 

Denver, Colo. Organochlorine compounds were 

extracted and analyzed using the procedures described 

by Foreman and others (1994) and the quantification 

procedures described by Wershaw and others (1987). 

PAH analyses followed the extraction and cleanup 

procedures of Furlong and others (1996) with selected 

ion monitoring for PAH’s by gas chromatography/mass 

spectrometry (Edward Furlong, U.S. Geological 

Survey, written commun., 1996). Radionuclides were 

analyzed by Quanterra Environmental Services in 

Richland, Wash. Analyses for 137Cs, 210Pb, and 226Ra 

were performed by gamma spectrometry and 234U, 

235U, 238U, 230Th, 232Th, 238Pu, and 239,240Pu by 

alpha spectrometry. Splits of samples from this core 

were provided to LANL for analysis of plutonium by 

mass spectrometry (Gallaher and others, 1999). 

Parameters analyzed for and their reporting levels are 

presented in tables 1 and 2.

Quality Control

Several samples were split at the various 

laboratories and analyzed in duplicate. The relative 

percent difference (RPD) is a measure of the 

variability in the values produced by the analytical 

method. RPD was calculated for each pair of duplicate 

samples by the equation: 

(1)

where sample 1 and sample 2 are the concentrations in 

duplicate samples.

RPD 100 x sample1 sample2 –

sample1 sample2 +

2 -------------------------------------------------- ⎝ ⎠ ⎛ ⎞

= -------------------------------------------------------
4

Table 1. Parameters analyzed for and their reporting levels in Cochiti Lake

bottom-sediment samples

[Reporting levels for organochlorine compounds vary for the volume of sample submitted for analysis. wt. %, weight 

percent; μg/g, micrograms per gram; μg/kg, micrograms per kilogram; PCB, polychlorinated biphenyl; PCN, 

polychlorinated naphthalene; pCi/g, picocuries per gram]

Parameter

Reporting

level Parameter

Reporting

level

Major elements wt. % Trace elements (continued) μg/g

Aluminum, Al 0.05 Uranium, U 2.0

Calcium, Ca 0.05 Vanadium, V 2.0

Iron, Fe 0.05 Yttrium, Y 2.0

Potassium, P 0.05 Ytterbium, Yb 2.0

Magnesium, Mg 0.005 Zinc, Zn 4.0

Sodium, Na 0.005 Organochlorine compounds μg/kg

Phosphorus, P 0.005 Aldrin 0.1 - 0.3

Carbon, organic 0.1 Chlordane 1.0 - 2.5

Carbon, total 0.1 DDD 0.1 - 0.3

Trace elements μg/g DDE 0.1 - 0.3

Silver, Ag 0.1 DDT 0.1 - 0.3

Arsenic, As 0.1 Dieldrin 0.1 - 0.3

Gold, Au 8.0 Endosulfan 0.1 - 0.3

Barium, Ba 1.0 Endrin 0.1 - 0.3

Beryllium, Be 1.0 PCB Aroclor 1242 1.0 - 3.0

Bismuth, Bi 0.1 PCB Aroclor 1254 1.0 - 3.0

Cadmium, Cd 0.1 PCB Aroclor 1260 1.0 - 3.0

Cerium, Ce 4.0 Gross PCN’s 1.0 - 3.0

Cobalt, Co 1.0 Heptachlor 0.1 - 0.3

Chromium, Cr 0.1 Heptachlor epoxide 0.1 - 0.3

Copper, Cu 1.0 Lindane 0.1 - 0.3

Europium, Eu 2.0 Methoxychlor 0.1 - 0.3

Gallium, Ga 4.0 Mirex 0.1 - 8.0

Mercury, Hg 0.02 Perthane 1.0 - 3.0

Holmium, Ho 4.0 Toxaphene 10 - 30

Lanthanum, La 2.0 Other organic compounds μg/kg

Lithium, Li 2.0 PAH’s (listed in table 2)

Manganese, Mg 4.0 Phenol 10

Molybdenum, Mb 1.0 p-cresol 10

Niobium, Ni 4.0 c8-alkyl-phenol 10

Neodymium, Nd 4.0 Radionuclides pCi/g

Nickel, Ni 2.0 Cesium-137, 137Cs 0.02

Lead, Pb 0.1 Lead-210, 210Pb 0.1

Antimony, Sb 0.1 Radium-226, 226Ra 0.4

Scandium, Sc 2.0 Uranium-234, 234U 0.01 - 0.04

Selenium, Se 0.1 Uranium-235, 235U 0.01 - 0.03

Tin, Sn 5.0 Uranium-238, 238U 0.01 - 0.04

Strontium, Sr 2.0 Thorium-230, 230Th 0.005 - 0.02

Tantalum, Ta 40.0 Thorium-232, 232Th 0.004 - 0.02

Thorium, Th 4.0 Plutonium-238, 238Pu 0.0002 - 0.002

Titanium, Ti 0.005 Plutonium-239, 240, 239,240Pu 0.0002 - 0.001
5

.

Table 2. Polycyclic aromatic hydrocarbons (PAH’s) analyzed for, number of detections, and range and medi

concentrations, in micrograms per kilogram, in Cochiti Lake bottom-sediment samples

PAH

Number of 

detections in 

gravity core

Concentration range in 

gravity core (and median)

Number of 

detections in box 

cores

Concentration range 

cores (and media

Naphthalene 9 BRL - 3.33 (2.14) 7 13.4 - 40.8 (21.C1-128 isomers 9 <10 - 25.9 (17.0) 7 40.9 - 185 (1042-Ethylnaphthalene 1 <10 - 12.7 (<10) 6 BRL - 4.65 (3.62,6-Dimethylnaphthalene 10 27.1 - 73.9 (44.9) 7 4.87 - 112 (25.61,6-Dimethylnaphthalene 9 BRL - 6.30 (3.94) 7 6.98 - 18.9 (15.9C2-128 isomers 10 38.1 - 88.0 (56.6) 7 24.6 - 167 (72.3Acenaphthylene 0 2 BRL - 1.51 (<101,2-Dimethylnaphthalene 0 6 BRL - 3.16 (2.1Acenaphthene 0 0C3-128 isomers 6 <10 - 12.6 (6.06) 7 14.4 - 45.9 (30.2,3,6-Trimethylnaphthalene 1 BRL - 0.460 (<10) 3 BRL - 1.96 (<109H-Fluorene 4 BRL - 1.94 (<10) 5 BRL - 3.94 (1.7C4-128 isomers 2 BRL - 5.31 (<10) 4 BRL - 30.2 (15.1-Methyl-9H-fluorene 6 BRL - 3.05 (1.60) 7 2.26 - 6.51 (4.4C1-166 isomers 8 BRL - 8.71 (5.58) 6 BRL - 16.9 (12.Dibenzothiophene 1 BRL - 1.15 (<10) 1 BRL - 1.16 (<10Phenanthrene 10 2.91 - 11.3 (5.40) 7 8.13 - 25 (16.0Anthracene 5 BRL - 1.92 (0.88) 6 BRL - 5.28 (1.8Acridine 1 BRL - 3.74 (<10) 0Phenanthridine 1 BRL - 6.74 (<10) 0

[PAH’s are listed in order of increasing molecular weight, and parent PAH’s are indicated in bold type. Ten gravity core in

and seven box core samples were submitted for analysis. BRL, below reporting level; <, less than]
6

9H-Carbazol 8 BRL - 2.50 (2.02) 4 BRL - 5.33 (3.2C5-128 isomers 0 4 <10 - 21.9 (10.2C2-166 isomers 1 BRL - 5.57 (<10) 1 BRL - 13.6 (<102-Methylanthracene 5 BRL - 1.78 (0.25) 5 BRL - 1.92 (1.44,5-Methylenephenanthrene 7 BRL - 1.94 (1.31) 1 BRL - 1.58 (<10C1-178 isomers 10 4.59 - 11.5 (7.48) 7 12.8 - 37.5 (24.41-Methylphenanthrene 10 1.09 - 2.45 (1.42) 7 7.34 - 20.6 (13.2C3-166 isomers 0 0C2-178 isomers 7 <10 - 12.0 (7.19) 7 27.5 - 76.1 (46.3Fluoranthene 10 4.64 - 12.8 (7.46) 7 2.92 - 10.8 (6.16Pyrene 10 4.38 - 13.8 (6.82) 6 BRL - 10.5 (5.9C3-178 isomers 3 BRL - 7.14 (<10) 6 <10 - 52.0 (27.8C4-178 isomers 0 01-Methylpyrene 3 BRL - 1.88 (<10) 0C1-202 isomers 10 12.4 - 21.9 (17.9) 5 <10 - 118 (28.1C2-202 isomers 8 BRL - 7.37 (5.02) 1 BRL - 4.4 (<10C5-178 isomers 1 BRL - 2.25 (<10) 5 BRL - 17.7 (13.Benz(a)anthracene 10 1.64 - 7.75 (2.43) 4 BRL - 3.80 (1.4Chrysene 10 3.43 - 9.16 (5.93) 7 1.59 - 8.06 (4.74C3-202 isomers 0 0C1-228 isomers 9 BRL - 7.3 (5.34) 3 BRL - 7.63 (<10

Table 2. Polycyclic aromatic hydrocarbons (PAH’s) analyzed for, number of detections, and range and medi

concentrations, in micrograms per kilogram, in Cochiti Lake bottom-sediment samples--Continued

PAH

Number of 

detections in 

gravity core

Concentration range in 

gravity core (and median)

Number of 

detections in box 

cores

Concentration range 

cores (and media
7

C4-202 isomers 0 0C5-202 isomers 0 0C2-228 isomers 5 BRL - 9.02 (2.21) 2 BRL - 13.2 (<10Benzo(b)fluoranthene 10 3.52 - 7.31 (5.24) 7 1.04 - 6.96 (1.67Benzo(k)fluoranthene 9 BRL - 10.4 (3.30) 4 BRL - 3.34 (1.0Benzo(e)pyrene 10 3.23 - 6.61 (5.24) 6 BRL - 6.94 (3.4Benzo(a)pyrene 10 1.74 - 10.2 (2.95) 3 BRL - 4.21 (<10Perylene 10 54.7 - 221 (157.5) 3 <10 - 23.8 (<10C1-252 isomers 5 BRL - 7.40 (1.40) 1C3-228 isomers 1 BRL - 4.76 (<10) 0C2-252 isomers 3 BRL - 6.64 (<10) 0C4-228 isomers 0 0Benzo(g,h,i)perylene 6 BRL - 3.62 (2.00) 1 BRL - 1.27 (<10Indeno(1,2,3-cd)pyrene 6 BRL - 9.58 (2.12) 1 BRL - 1.12 (<10Dibenzo(a,h)anthracene 3 BRL - 2.32 (<10) 0C3-252 isomers 0 0C4-252 isomers 0 0C5-228 isomers 1 BRL - 1.82 (<10) 0C5-252 isomers 0 0Coronene 1 BRL - 1.13 (<10) 0

Table 2. Polycyclic aromatic hydrocarbons (PAH’s) analyzed for, number of detections, and range and medi

concentrations, in micrograms per kilogram, in Cochiti Lake bottom-sediment samples--Continued

PAH

Number of 

detections in 

gravity core

Concentration range in 

gravity core (and median)

Number of 

detections in box 

cores

Concentration range 

cores (and media
8

Three sample intervals from the gravity core and 

one sample from the box core at site R1 were analyzed 

in duplicate for organic carbon. RPD for the four 

duplicate analyses of organic carbon ranged from 0 to 

0.78 percent, and the median was 0.36 percent.

One gravity core sample had duplicate analyses 

of major and trace elements. Thirty-nine major and 

trace elements were detected in both duplicate 

analyses, and 12 of these elements had identical 

concentrations (mostly two significant figures) in both 

analyses. The RPD for major elements ranged from 

0.26 percent for calcium to 0.76 percent for magnesium 

(median RPD = 0.39 percent for eight elements). The 

RPD for trace elements ranged from 0 percent for Ag, 

Ba, Bi, Cd, Hg, Mn, Mb, Nb, Sc, Sr, Y, and Yb to 4.5 

percent for antimony (median RPD = 0.29 percent for 

31 elements). The RPD for PAH compounds ranged 

from 0.0 percent for 4,5-methylenephenanthrene to 

68.0 percent for benzo(k)fluoranthene (median RPD = 

12.6 percent for 31 detections out of 64 reported PAH 

compounds). The duplicate sample for organochlorine 

pesticide analysis was ruined during preparation at the 

NWQL.

The NWQL analyzed method blanks, method 

spikes, certified reference material, and a duplicate 

sample for each batch of samples submitted for organic 

compound analysis. The results met established 

NWQL control limits (Pritt and Raese, 1992). 

Radionuclide results included counting errors and total 

errors for each sample. Counting error is the statistical 

uncertainty in the count contributed by background 

sources. Total error is the counting uncertainty plus the 

uncertainty in equipment calibration. These errors are 

reported in table 3. One interval from the gravity core 

and one box core sample had duplicate radionuclide 

analyses. The RPD for the gravity core duplicate 

ranged from 0.56 percent for 239,240Pu to 12.8 percent 

for 238Pu (median = 2.8 percent for seven 

radionuclides). The RPD of the box core duplicate 

ranged from 0.20 percent for 234U to 24 percent for 

238Pu (median = 0.62 percent for five radionuclides). 

Plutonium-238 had very low activity values, and even 

small differences in measured activities between 

duplicate analyses cause the RPD to be large.

Table 3. Counting and total errors of radionuclide analyses

[--, not reported]

Radionuclide

Number of 

samples

Range of 

counting error

Median 

counting error

Range of total 

error

Median total 

error

137Cs 13 0.066 - 0.110 0.079 0.079 - 0.120 0.095

210Pb 13 0.21 - 0.28 0.24 0.37 - 0.50 0.46

226Ra 13 0.14 - 0.20 0.18 0.18 - 0.25 0.23

238Pu 21 -- -- 0.00013 - 0.0029 0.00059

239,240Pu 21 -- -- 0.0014 - 0.0073 0.0033

230Th 21 0.092 - 0.21 0.11 0.14 - 0.21 0.19

232Th 21 0.086 - 0.18 0.11 0.13 - 0.19 0.17

234U 21 0.13 - 0.17 0.14 0.18 - 0.25 0.21

235U 21 0.019 - 0.039 0.030 0.020 - 0.040 0.030

238U 21 0.13 - 0.18 0.14 0.19 - 0.26 0.21
9

DEPOSITION OF BOTTOM SEDIMENT

Sediment Surveys

The Department of the Army, U.S. Army Corps 

of Engineers (USACE) periodically assesses reservoir 

sedimentation in Cochiti Lake. The elevation of the 

reservoir’s sediment surface, in feet above sea level, 

was available for surveys conducted in 1972 (before 

impoundment), 1976, 1979, 1981, 1986, 1991, and 

1998 (Department of the Army, 1996; and unpublished 

data). The USGS recorded depth to the sediment 

surface at each of the seven coring sites while 

collecting sediment cores. The reservoir’s water 

elevation during core collection was 1,628 m above sea 

level (Department of the Army, oral commun., 1996). 

Reservoir sediment-surface elevations during sampling 

in 1996 at each coring site were calculated and 

compared with previous sediment surveys to locate the 

sampling sites relative to historical sediment deposition 

and to assess the extent of sedimentation at each coring 

site over the past 5 years. A sediment front, marked by 

a sudden change from deep to shallow water depths, 

was profiled in the 1981, 1986, 1991, and 1998 

sediment surveys between 6 and 8 km upstream from 

the dam (fig. 2A). Bottom sediment coring sites B3, 

B3.5, and B4 were located along this sediment front in 

1996, as shown in figure 2A.

The USGS monitors suspended-sediment 

discharge at a gaging station on the Rio Grande at 

Otowi Bridge (station 08313000) about 27 km 

upstream from Cochiti Lake. The total suspendedsediment discharge, in tons per year (tons/yr), recorded 

at Otowi Bridge since the date of reservoir construction 

is compiled and illustrated in figure 2B. The total 

suspended-sediment discharge was typically about 1.5 

million tons/yr with a few exceptions. Years in which 

relatively high suspended-sediment discharge was 

recorded were typically followed by progradation of 

the sediment front in Cochiti Lake.

In the 5-year period between the 1981 and 1986 

sediment surveys, the crest of the sediment front built 

out, or prograded, approximately 0.5 km, resulting in 

an average progradation rate of 100 m/yr. The sediment 

front prograded from 1986 to 1991 and from 1991 to 

1996 at estimated average rates of 145 m/yr and

250 m/yr, respectively. The large total suspendedsediment discharges recorded at Otowi Bridge in 1991 

and 1995 have contributed to the greater rate of 

progradation in the 1991-96 period. The extremely 

high suspended-sediment discharge in 1995 coincides 

with a large progradation of the sediment front 

documented during 1996 core collection. A more 

recent sedimentation survey, performed by the USACE 

in 1998, shows the sediment surface at lower elevations 

near the crest than in 1996. The sediment front may 

have slumped or moved in the downstream direction 

from 1996 to 1998.

Core Lithology, Grain Size, and Organic 

Carbon Content

One gravity core from the primary coring 

location (R1) was visually described in the field. The 

core was 117 cm long and was the only gravity core 

that did not penetrate the prereservoir surface. 

Sediments were fine grained throughout the length of 

the core. The upper 25 cm of the core was dark 

yellowish brown (10YR 4/2; Geological Society of 

America, 1991) with a high water content and no 

visible benthic invertebrates. The core was of similar 

color and became firmer down to 73 cm. Below 73 cm, 

the sediment gradually became light tan (5YR 4/1) 

followed by a stiff, dark-yellowish-brown (5Y 4/1) 

zone at 91 to 93 cm. The sediment remained firm and 

the same color to the bottom of the core with the 

exception of a prominent dark-olive-black (5Y 2/1) 

zone at 108 to 112 cm.

Grain-size analyses at the primary coring 

location (R1) indicated sediments greater than 99 

weight percent silt and clay (less than 0.062 millimeter 

(mm)) along the full length of the core and a median of 

94 weight percent clay-sized particles (less than 0.004 

mm). The percentage by weight of clay-sized particles 

decreased slightly below 130 cm (fig. 3A). Grain-size 

analyses were also performed on the box cores of 

surficial sediments collected along the length of 

Cochiti Lake. The percentage of silt- and clay-sized 

particles has little variation along the length of the 

reservoir, ranging from 91.7 to 100 percent. Clay-sized 

particles decreased from 92.9 percent at primary coring 

location R1 to 26.2 percent at the farthest upstream 

sampling site, B5 (fig. 3B). This trend is typical in 

reservoirs because coarser grained sediments fall out of 

suspension first as water velocity slows in the upper 

part of the reservoir, whereas finer grained sediments 

stay in suspension longer and are transported farther 

down the reservoir.
Figure 2. (A) Longitudinal profile of reservoir showing historical sedimentation and migration of sediment front. The upper surface of each

 deposit determined during the sedimentation surveys conducted by the U.S. Army Corps of Engineers. The sediment-

 surface elevations calculated using data collected during the 1996 coring indicated by blue line. (B) Suspended-sediment

 discharge of the Rio Grande at Otowi Bridge, N. Mex. (U.S. Geological Survey streamflow-gaging station 08313000).

0 2 4 6 8

UPSTREAM DISTANCE FROM DAM, IN KILOMETERS

10 12 14

1,600

1,610

1,620

1,630

R1

B1

B2

B3

B3.5

B4 B5

ELEVATION, IN METERS

A

EXPLANATION

1979 sedimentation survey

1976 sedimentation survey

Prereservoir sediment (1972 survey)

Sediment coring site (1996)

Sediment eroded from 1996 to 1998

1998 sedimentation survey

1991 sedimentation survey

1986 sedimentation survey

1981 sedimentation survey

B1

TOTAL SUSPENDED-SEDIMENT

DISCHARGE, IN TONS PER YEAR

0 5,000,000 10,000,000

1972

1998

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

B

YEAR

WATER LEVEL

10
DEPTH IN CORE, IN CENTIMETERS

Figure 3. Grain size in a gravity core at site R1 (A) and box cores (B) and percentage of organic

 carbon in a gravity core (C) and box core at site R1 (D) from Cochiti Lake.

D

ORGANIC CARBON,

IN WEIGHT PERCENT

1.0 1.2 1.4

0

5

15

20

10

B

SILT- AND CL

AY-SIZED 

PARTICLES,

IN WEIGHT PERCENT

UPSTREAM DISTANCE FROM COCHITI DAM, IN KILOMETERS

0 1 2 3 4 5 6 7 8

20

40

60

80

100

C

0.8 1.0 1.2 1.4

0

20

40

60

80

100

120

140

A

Clay-sized 

particles

Silt- and 

clay-sized 

particles

EXPLANATION

DEPTH IN CORE, IN CENTIMETERS

SILT- AND CLAY-SIZED 

PARTICLES,

IN WEIGHT PERCENT

40

100

0

20

60

80

120

140

160

80 90 100

R1 B1

B2

B3

B4

B3.5 B5

11
12

Organic carbon was analyzed in a gravity core 

and box core from site R1. The percent organic carbon 

by weight ranged from 0.93 to 1.33 (fig. 3C), and the 

median was 1.07 percent in the full length of the gravity 

core. The box core from the same location had similar 

organic carbon concentrations as the corresponding 

upper portion of the gravity core. The box core 

concentrations ranged from 1.09 to 1.39 weight percent 

(fig. 3D), and the median was 1.31 percent. The weight 

percent organic carbon in the corresponding upper 

portion of the gravity core ranged from 0.99 to 1.33 

(fig. 3C), and the median was 1.19. The percent organic 

carbon was greatest in the upper portion of both the 

gravity and box cores. The decrease in organic carbon 

just below the sediment-water interface is typical of 

subaqueous sediments and is a reflection of early 

diagenesis with burial (Froelich and others, 1979). The 

sediment intervals below 40 cm had relatively stable 

organic carbon values (with one exception at 97.5 cm) 

(fig. 3C).

Estimating Age of Sediments and Rates of 

Deposition

Four of the five gravity cores penetrated to 

prereservoir material, as indicated by an abrupt 

transition from fine-grained (clay and silt), high watercontent sediment to a fine quartz sand with a low water 

content. The prereservoir boundary was at a mean 

depth of 138 cm and provides a date marker for 1975, 

when the reservoir was impounded at the elevation of 

the permanent pool.

Initially, sediment deposition dates were to be 

calculated using variations in 137Cs (half-life = 30.8 

years) and 210Pb (half-life = 22 years) activities with 

depth in the gravity core analyzed for radionuclides. 

However, the young age of Cochiti Lake limited their 

use, and deposition dates of core intervals were 

assigned on the basis of the average mass accumulation 

rate at site R1. Four of the five gravity cores collected 

at site R1 penetrated to prereservoir material, as 

indicated by an abrupt transition from fine-grained, 

high water-content sediment to a fine quartz sand with 

a low water content. The prereservoir boundary was at 

a mean depth of 138 cm and provides a date marker for 

1975, when the reservoir was impounded at the 

elevation of the permanent pool. Because the 

sedimentation rate in Cochiti Lake has varied greatly 

since its impoundment (fig. 2), using the average mass 

accumulation rate makes the sediment deposition dates 

assigned approximate values. An average mass 

accumulation rate of 2.74 grams (g)/cm2

/yr was 

calculated for the gravity core analyzed for major and 

trace elements using the measured porosity of each 

sampling interval and an assumed density of solids of 

2.5 g/cm3. The approximate dates were then 

extrapolated to the equivalent depth intervals in the 

other cores on the basis of relative differences in core 

lengths. Porosity data were not available for the other 

cores to allow extrapolation by equivalent mass. An 

average linear sedimentation rate of 6.6 cm/yr at site R1 

was calculated using all five gravity cores.

The average mass accumulation rate of 2.74

g/cm2

/yr was calculated for the major and trace 

elements in the gravity core using measured porosity 

and an assumed density of solids of 2.5 g/cm3. The 

dates were then extrapolated to the equivalent depth 

intervals in the other cores on the basis of relative 

differences in core lengths. An average linear 

sedimentation rate of 6.6 cm/yr at site R1 was 

calculated using all five gravity cores.

CHEMISTRY OF BOTTOM SEDIMENTS

Major Elements

The concentrations of major elements at site R1 

had little variability and showed no trends in the gravity 

core. Concentrations in the box core sediments also 

collected at site R1 were similar to those in the gravity 

core (fig. 4). An increase in concentrations of Al, Fe, 

Mg, and P in the downstream direction was indicated 

by box cores collected along the length of the reservoir 

(fig. 5). Ca, K, and Na decreased in concentration 

toward Cochiti Dam. Horowitz and Elrick (1987) 

demonstrated that many inorganic elements associate 

with particles smaller than 0.063 mm in size, which is 

comparable to silt- and clay-sized particles as 

measured by the USGS sediment laboratory. The 

percentage of silt- and clay-sized particles has little 

variation in the box cores collected along the length of 

Cochiti Lake (fig. 3B). The concentrations of major 

elements were normalized with respect to grain size by 

dividing the elemental concentration by the percentage 

of silt- and clay-sized particles to check whether 

concentration variations along the length of the 

reservoir are associated with the small variation in 

grain size. Normalization does not affect concentration 

variations (fig. 5) and normalization of other inorganic 

elements (trace elements and radionuclides) was not 

considered to be necessary.
Figure 4. Major element concentrations in a gravity core and box core at site R1 from Cochiti Lake.

MAJOR ELEMENT CONCENTRATION, IN WEIGHT PERCENT

Sodium

0 0.2 0.4 0.6 0.8

DEPTH IN CORE, IN CENTIMETERS

Magnesium

0 1 2 3

0

20

40

60

80

100

120

140

0 5 10 0 2 4 6

0

20

40

60

80

100

120

140

Aluminum

0 2 4

Calcium Iron Potassium

EXPLANATION

Gravity core

sample

Box core

sample

0 1 2 3

1996

1991

1986

1981

1976

ESTIM

ATED DEPOSITION DATE

0 0.1 0.2

Phosphorus 1996

1991

1986

1981

1976

ESTIM

ATED DEPOSITION DATE

13
0

5

10

0

0.05

0.10

0

2.5

5.0

0

0.025

0.05

0

1

2

0

0.01

0.02

0.002

0.001

0 0

0.1

0.2

UPSTREAM DISTANCE FROM DAM, IN KILOMETERS

0 2 4 6 8

Weight percent of major element

Weight percent of major element

normalized by percent silt- and

clay-sized particles

EXPLANATION

UPSTREAM DISTANCE FROM DAM, IN KILOMETERS

0 2 4 6 8

0

1

2

0

0.01

0.02

0

1.5

3.0

0

0.015

0.030

0

2

4

0

0.02

0.04

CONCENTR

ATION OF MAJOR ELEMENT, IN WEIGHT PERCENT

NORMALIZED CONCENTR

ATION OF MAJOR ELEMENT, IN WEIGHT PER

Aluminum

CENT

Iron

Magnesium

Phosphorus

Calcium

Potassium

Sodium

Figure 5. Major element concentrations in box cores from Cochiti Lake. Only the 0- to 2-centimeter interval

 of box core R1 is shown.

14

R1 B1 B2

B3 B4

B5 B3.5
15

Trace Elements

Concentrations of As, Cr, Cu, Li, Ni, and Zn 

showed small variations but no trends over their period 

of deposition in the gravity core from site R1. The 

concentrations of Pb and Se appear to have decreased 

with time (fig. 6); however, neither trend tested 

significantly at a 90-percent confidence interval 

(Spearman’s rank correlation coefficient = 0.86, pvalue = <0.00001 for lead; Spearman’s rank correlation 

coefficient = 0.63, p-value = 0.00047 for selenium).

Concentrations of As, Be, Co, Cr, Cu, Mn, Ni, 

Pb, Se, and Zn increased in the downstream direction. 

Barium concentrations decreased toward Cochiti Dam 

and U concentrations were variable. The 

concentrations of Be, Cr, Li, Mn, Ni, and U at site B3.5 

are noticeably lower than those at the adjacent box 

coring locations (fig. 7).

Table 4 compares trace-element concentrations 

in the Cochiti Lake gravity core to draft sedimentquality guidelines recommended by the Canadian 

Council of Ministers of the Environment (CCME) 

(1998) and Long and others (1995). Only elements that 

have guidelines are listed. These guidelines are not 

enforceable standards, but they provide a basis for 

comparison with the Cochiti Lake samples. The 

guidelines are based on numerous studies relating 

contaminant concentrations to measures of biological 

effects. CCME (1998) used a modification of the 

National Status and Trends Program approach to derive 

an interim sediment-quality guideline as the 

concentration below which adverse biological effects 

are rarely expected to occur. The probable-effect level 

was derived using the modified National Status and 

Trends Program approach and the spiked-sediment 

toxicity test approach to define the concentration above 

which adverse biological effects are expected to occur 

frequently (Canadian Council of Ministers of the 

Environment, 1998). Long and others (1995) separated 

concentrations whose “effects range-low” (ER-L) and 

“effects range-median” (ER-M). The 10th and 50th 

percentiles of concentrations associated with adverse 

biological effects, corresponding to ER-L and ER-M, 

respectively, define the guidelines.

The concentration ranges of As, Cr, Cu, Pb, Ni, 

and Zn in the gravity core are at or above thresholdeffect levels of at least one of the sediment-quality 

guidelines. All trace-element concentrations are below 

the probable-effect level. Although some of these 

concentrations are above threshold-effect levels, there 

is no evidence from this study that trace-element 

concentrations have been affected by anthropogenic 

activities.

Organochlorine Compounds

The organochlorine compounds detected in 

Cochiti Lake sediments include PCB’s and DDT and its 

metabolites DDD and DDE. Thirteen other 

organochlorine compounds were analyzed for but not 

detected, including chlordane and dieldrin (table 1). 

Organochlorine compounds are persistent in the 

environment, have low water solubility, and sorb 

strongly to particulate matter. Octanol-water partition 

coefficients for PCB’s, DDT, DDD, and DDE range 

from 105

 to 106 (Smith and others, 1988), indicating 

that these compounds will strongly partition into 

sediment organic matter. The octanol-water partition 

coefficient of a compound is the ratio of the 

compound’s concentration in a known volume of noctanol to its concentration in a known volume of water 

after equilibrium is reached (Smith and others, 1988). 

These compounds have been shown to be highly 

resistant to chemical breakdown in the natural 

environment (Smith and others, 1988; Alder and 

others, 1993) and are frequently detected in lake 

(Eisenreich and others, 1989) and reservoir (Van Metre 

and others, 1998) sediment cores.

Polychlorinated Biphenyls (PCB’s)

PCB’s were first synthesized in the laboratory in 

1929, and an estimated 5.94 x 108

 kilograms (kg) were 

produced from 1930 to 1974 (National Academy of 

Sciences, 1979). Annual PCB sales in the United States 

peaked at 36,530 metric tons in 1970 and declined to 

about one-half that amount by 1975 following the 1971 

voluntary ban on PCB use in open systems (Peakall, 

1975). In 1979 all new uses of PCB’s were banned 

(National Academy of Sciences, 1979). PCB’s were 

formulated and sold as Aroclors, which are complex 

mixtures of individual PCB compounds known as 

congeners. The analytical method used for this study 

quantified PCB’s relative to three Aroclor standards 

(Aroclor 1242, Aroclor 1254, and Aroclor 1260) 

(Wershaw and others, 1987).

Cochiti Lake was constructed a few years before 

the complete ban on PCB usage. However, PCB 

capacitors and transformers were still in use at LANL 

in 1993, and numerous PCB-contaminated items were 

in storage on the facility (Los Alamos National 

Laboratory, 1995, p. III-13). One or more Aroclors 

were detected in 7 of 10 samples from the gravity core 

from site R1 (table 5) and in 3 of 7 box core samples;
Figure 6.Trace-element concentrations in a gravity core and box core at site R1 from Cochiti Lake.

TRACE-ELEMENT CONCENTRATION, IN MICROGRAMS PER GRAM

DEPTH IN CORE, IN CENTIMETERS

Chromium

0 20 40 60 0

Copper

20 40 60

0

20

40

60

80

100

120

140

0 50 100

Lithium

0 10 20 30 40

Nickel

0

Selenium

0.2 0.4 0.6 0.8 0

Zinc

100 200

1976

1981

1986

1991

1996

0

Lead

20 40 60

1976

1981

1986

1991

1996

EXPLANATION

Gravity core sample

Box core sample

Arsenic

0

20

40

60

80

100

120

140

0 5 10

ESTIMATED DEPOSITION DATE

16
Figure 7.Trace-element concentrations in box cores from Cochiti Lake. Only the 0- to 2-centimeter interval of box

 core R1 is shown.

UPSTREAM DISTANCE FROM DAM, IN KILOMETERS

TR

ACE-ELEMENT CONCENTR

ATION, IN MICROGRAMS PER GRAM

1,400

1,200

1,000

UPSTREAM DISTANCE FROM DAM, IN KILOMETERS

EXPLANATION

Trace-element concentration

4

6

8

0

0 2 4 6 8

1

4

2

3

10

3.0

2.8

2.6

2.4

60

50

40

30

100

80

60

40

30

25

20

15

0.8

0.6

0.4

0.2

140

120

100

80

60

Arsenic

R1

B1

B2

B3

B4

B5

B3.5

Beryllium

Chromium

Lithium

Nickel

Selenium

Zinc

0 2 4 6 8

800

600

400

16

14

12

10

40

30

20

10

800

600

35

30

25

20

4.5

4.0

3.5

3.0

Barium

Cobalt

Copper

Manganese

Lead

Uranium

17
18

Table 4. Trace-element sediment-quality guidelines compared to concentration ranges,

in micrograms per gram, in Cochiti Lake gravity core

[CCME, Canadian Council of Ministers of the Environment; ISQG, interim sediment-quality guideline; PEL, 

probable-effect level; --, no guidelines defined; ER-L, effects range-low;

ER-M, effects range-median; median values are in parentheses]

Agency

Sedimentquality 

guideline Arsenic Cadmium

Chromium Copper Lead Nickel Zinc

CCME

(1998)

ISQG 5.9 0.6 37.3 35.7 35.0 -- 123

PEL 17.0 3.5 90.0 197 91.3 -- 315

Long and 

others

(1995)

ER-L 8.2 1.2 81 34 46.7 20.9 150

ER-M 70 9.6 370 270 218 51.6 410

Cochiti Lake 7.6 - 9.6 

(8.8)

0.3 - 0.5 

(0.4)

47 - 58 

(50)

32 - 42 

(35)

30 - 53 

(40)

27 - 30 

(28)

120 - 150 

(130)

Table 5. Concentrations of polychlorinated biphenyls (PCB’s), in micrograms per

kilogram, in Cochiti Lake gravity core from site R1 and box cores from all sites

[cm, centimeters; E, estimated; <, less than]

Sample name Middepth (cm) Aroclor 1242 Aroclor 1254 Aroclor 1260

Gravity core

COC.1 0-12 6 E1.9 <2.0 <2.0

COC.1 12-24 18 2.4 <2.0 <2.0

COC.1 24-36 30 <3.0 <3.0 <3.0

COC.1 36-48 42 <2.5 <2.5 <2.5

COC.1 48-60 54 2.2 <2.0 <2.0

COC.1 60-72 66 2.2 <2.0 <2.0

COC.1 72-84 78 1.4 1.2 1.2

COC.1 84-96 90 E0.97 E0.96 1.3

COC.1 96-108 102 1.2 1.1 1.0

COC.1 108-120 114 <2.0 <2.0 <2.0

Box cores

COC.R1 2.5 2.2 <2.0 <2.0

COC.B1 2.5 <2.0 <2.0 <2.0

COC.B2 2.5 <2.0 <2.0 <2.0

COC.B3 2.5 <1.0 <1.0 <1.0

COC.B3.5 2.5 1.3 1.7 <1.0

COC.B4 2.5 1.5 <1.0 <1.0

COC.B5 2.5 <1.0 <1.0 <1.0
19

all were at very low levels, however. Since completion 

of this study, the USGS NWQL has raised the reporting 

level for PCB Aroclors to 5.0 micrograms per kilogram 

(μg/kg) because of a change of equipment (Brooke 

Connor, U.S. Geological Survey, written commun., 

1997), which is greater than all detections in Cochiti 

Lake.

 Aroclor 1242 was the most commonly detected 

PCB in the gravity core (7 of 10 intervals). Aroclor 

1254 and 1260 had detectable concentrations in three 

sediment intervals deposited in the early 1980’s. 

Aroclor 1242 and 1254 were detected in three and one 

box cores, respectively (table 5). The maximum 

concentration of total PCB’s (the sum of Aroclors 

1242, 1254, and 1260) detected in Cochiti Lake 

sediments is well below sediment-quality guidelines 

(table 6). The magnitude of PCB concentrations and 

comparison to sediment-quality guidelines indicate 

that Cochiti Lake sediments are relatively 

uncontaminated with PCB’s. Cochiti Lake PCB 

concentrations are similar to those in other Rio Grande 

reservoirs (Van Metre and others, 1996a) and smaller 

than concentrations reported for urban reservoirs in 

Texas and Georgia (Van Metre and others, 1997). 

DDT, DDD, and DDE

The organochlorine pesticide DDT was first 

synthesized in 1874 and was used as an insecticide 

beginning in 1939 (U.S. Environmental Protection 

Agency, 1983). DDT usage peaked in the United States 

in the early 1960’s (Rapaport and others, 1985). Wide 

use of DDT on cotton, fruits, and vegetables continued 

in the United States until about 1970. DDT use was 

banned nationwide in 1972 (Smith and others, 1988). 

Occurrences of DDT and its metabolites, DDD and 

DDE, are common in reservoir bottom sediments (Van 

Metre and others, 1997). Agricultural and urban 

activities upstream from Cochiti Lake could have 

contributed DDT to the watershed.

DDD and DDE were present in all sediment 

intervals in the gravity core collected at site R1 (fig. 

8A). DDE had larger concentrations than DDD and 

DDT, composing 52 to 69 percent of total DDT (DDD 

+ DDE + DDT). Concentrations of DDT were detected 

in 6 of the 10 sediment intervals. Concentrations of 

DDD, DDE, and total DDT have statistically 

significant decreasing trends in the sediment deposited 

from about 1980 to 1992 (Spearman’s rank correlation 

coefficient = 0.93, p-value = 0.00086 for DDD and 

DDE; Spearman’s rank correlation coefficient = 0.90, 

p-value = 0.00201 for total DDT). The trends indicated 

by samples deposited from about 1980 to 1992 are 

similar to total DDT trends observed in many reservoirs 

(Van Metre and others, 1998) and lakes (Eisenreich and 

others, 1989). These metabolites have increased 

slightly from 1992 to the present. This increase could 

partly be the result of slightly higher organic carbon 

concentrations near the top of the core (fig. 3C); 

however, normalizing DDD and DDE to organic 

carbon does not reverse this trend. The recent increase 

also could result from the redistribution of sediments 

within the reservoir containing higher total DDT 

concentrations. Larger total DDT concentrations in two 

of the box core samples from the upstream part of the 

reservoir (sites B3.5 and B4, fig. 8B) suggest that this 

is possible.

DDD, DDE, and DDT were detected in all box 

core samples (fig. 8B). As with the gravity core, DDE 

had the largest concentrations, composing 56 to 66 

percent of total DDT. DDD and DDT had similar 

concentrations. Concentrations of total DDT were 

largest at the box coring location B4. Sites B3.5 and B4 

had greater total DDT and DDE values than those in the 

gravity core. These box cores were collected along the 

sediment front where the water depth changes from 

shallow, riverlike conditions to deep, lakelike 

conditions. A large portion of the sediment load carried 

by the Rio Grande drops out of suspension here as the 

water becomes deeper and the flow velocity slows. The 

deposition of sediment and associated sediment-bound 

contaminants in this area may contribute to the elevated 

total DDT concentrations at box coring locations B3.5 

and B4. Total DDT concentrations in these two samples 

(3.23 and 4.53 μg/kg, respectively) are below 

threshold-effect levels (table 6). As was the case for 

PCB’s, total DDT concentrations in Cochiti Lake 

sediments are similar to those in other Rio Grande 

reservoirs for comparable time intervals (Van Metre 

and others, 1996a) and smaller than those in urban and 

agricultural reservoirs in Texas and Georgia (Van 

Metre and others, 1997).
20

Polycyclic Aromatic Hydrocarbons

PAH’s are a group of organic compounds 

composed of two or more fused benzene rings with 

hydrogen atoms attached and side chains of alkyl 

groups possible. These chemicals are very 

hydrophobic, relatively unreactive, and sorb strongly to 

sediments. PAH’s are formed through pyrolysis (high 

temperature) reactions during the burning of wood, 

coal, oil, and petroleum products, and occur in 

uncombusted oil and petroleum products as well. They 

have both anthropogenic and natural sources, which 

include emissions from vehicles, power plants, and 

residential heating devices; used crankcase oil; crude 

oil; and forest fires. Some PAH’s are carcinogenic and 

(or) toxic to humans and aquatic life through multiple 

exposure pathways (Harvey, 1991). Concentrations of 

PAH’s increased in the environment during the 20th 

century in response to increased burning of fossil fuels 

(Hites and others, 1981). Urban areas, recreational 

areas, LANL, and forest fires within the watershed of 

Cochiti Lake could be historical contributors of PAH’s 

to the sediments stored in the reservoir.

Sixty-one PAH’s were analyzed for in the bottom 

sediments of Cochiti Lake. Fifteen of the 23 parent 

PAH’s and 17 of the 38 alkyl-homologs were detected 

in one-half or more of the gravity core samples (table 

2). Naphthalene alkyl-homologs containing one or two 

alkyl groups (C1-128 and C2-128 isomers, 

respectively) had the highest concentrations, with the 

exception of perylene, and were detected in 16 of 17 

samples from both the gravity and box cores. Alkylhomologs of phenanthrene/anthracene (C1-178 and 

C2-178 isomers) and fluoranthene/pyrene (C1-202 

isomers) also have high concentrations relative to the 

other PAH compounds. The concentration of perylene 

in the gravity core is especially high compared to other 

compounds. Perylene, though, is believed to form in 

place (LaFlamme and Hites, 1978) and is not 

considered a PAH contaminant from the drainage area.

Table 6. Organic sediment-quality guidelines compared to concentration ranges, in micrograms

per gram, in Cochiti Lake gravity core

[CCME, Canadian Council of Ministers of the Environment; ISQG, interim sediment-quality guideline, PEL, 

probable-effect level. --, no guidelines defined. ER-L, effects range-low. ER-M, effects

range-median. <, less than. Median values are in parentheses]

Agency

Sedimentquality 

guideline Total PCB Total DDT

Benz(a)-

anthracene

Benzo(a)-

pyrene

CCME

(1998)

ISQG 34.1 6.2 31.7 31.9

PEL 277 20.0 385 782

Long and others

(1995)

ER-L 23 1.6 -- --

ER-M 180 46 -- --

Cochiti Lake <3. 8 - 6.2 

(<6.1)

1.12 - 2.56

(2.00)

1.64 - 7.75 

(2.43)

1.74 - 10.2 

(2.95)

Agency

Sedimentquality 

guideline

FluoranthenePhenanthrene Pyrene Total PAH

CCME

(1998)

ISQG 111 41.9 53.0

PEL 2,355 515 875

Long and others

(1995)

ER-L -- -- -- 4,000

ER-M -- -- -- 45,000

Cochiti Lake 4.64 - 12.8 

(7.46)

2.91 - 11.3 

(5.40)

4.38 - 13.8 

(6.82)

134 - 240 

(190)
Figure 8. Concentrations of DDT and its metabolites in a gravity core (A) and box

 cores (B) from Cochiti Lake.

ORGANOCHLORINE

CONCENTRATION, IN

MICROGRAMS PER KILOGRAM

A

DEPTH IN CORE, IN CENTIMETERS

1996

1992

1988

1984

1980

0

20

40

60

80

100

120

0 1 2 3

0 1 2 3 4 5 6 7 8

5

0

1

2

3

4

B

ORGANOCHLORINE

CONCENTR

ATION, IN

MICROGRAMS PER KILOGRAM

UPSTREAM DISTANCE FROM DAM, IN KILOMETERS

R1 B1

B2

B3

B3.5

B4

B5

EXPLANATION

DDT

DDD

DDE

Total DDT

Nondetection

B1 Sediment coring site

ESTIMATED DEPOSITION DATE

21
22

PAH’s with the largest concentrations and the 

most detections in both the gravity core and box cores 

are shown in figures 9 and 10. The dominant 

compounds in the gravity core, naphthalenes with two 

alkyl groups (C2-128 isomers), have a statistically 

significant increasing trend in the sediments deposited 

since about 1988 (54 cm) (Spearman’s rank correlation 

coefficient = -0.90, p-value = 0.037). The other 

compounds most commonly detected had elevated 

concentrations in the early 1990’s relative to adjacent 

sample intervals (fig. 9A-D). Total PAH is the sum of 

all PAH compound concentrations (parent and alkylhomologs excluding perylene) measured in each 

sample. The amount of total PAH generally increased 

up to the most recently deposited sediments (fig. 9E). 

The amount of total PAH appears to increase with time 

(fig. 9E); however, this trend is not statistically 

significant (Spearman’s rank correlation coefficient = 

0.73, p-value = 0.024 for all except the bottommost 

sample).

Sediment-quality guidelines are available for 

five parent PAH’s and total PAH, none of which are 

exceeded by Cochiti Lake gravity core samples (table 

6). In fact, PAH concentrations in Cochiti Lake 

sediments are about two to four orders of magnitude 

smaller than those in urban lakes and reservoirs in 

Texas, Virginia, and Minnesota measured using the 

same methods as in this study (unpublished data).

The mixture of PAH compounds varies for 

PAH’s from different sources. Fuels (for example, 

crude oil) generally contain proportionally more low 

molecular weight (two and three ringed) PAH’s and 

more alkylated homologs than combustion products do 

(Hites and others, 1981; Eganhouse and Gossett, 1991). 

Conversely, combustion products are enriched in 

higher molecular weight parent PAH’s. Naphthalene 

and its alkylated homologs (two-ringed compounds) 

compose the greatest percentage of total PAH in the 

Cochiti Lake gravity core. This group accounts for 31 

to 57 percent of total PAH in the core (fig. 9E).

Various ratios of PAH’s have been used to 

evaluate sources of PAH’s to lake sediments (Hites and 

others, 1981). One such indicator is the ratio of the sum 

of 2- and 3-ringed PAH’s to the sum of combustion 

PAH’s. The sum of combustion PAH’s includes nine 

non-alkylated compounds (fluoranthene, pyrene, 

benz(a)anthracene, chrysene, benzofluoranthenes, 

benzo(e)pyrene, benzo(a)pyrene, benzo(g,h,i)perylene, 

and indeno(1,2,3-c,d)pyrene) that commonly 

contribute to PAH mixtures derived from the hightemperature burning of fuels (Prahl and Carpenter, 

1983). The ratio of the sum of 2- and 3-ringed PAH to 

the sum of combustion PAH’s decreases as combustion 

PAH’s become more dominant, often an indication of 

increased vehicle emissions. This ratio is larger than 

unity for sediments in the gravity core, ranging from 

1.4 to 4.4, and increases in the top portion of the core 

(fig. 9F). Ratio values greater than unity indicate that 

the PAH mixture does not have high-temperature 

combustion processes as its dominant source. 

Uncombusted fuels or lower temperature combustion 

processes may be contributing more to this mixture. 

Uncombusted fuels as the dominant source of PAH’s to 

the sediments is also indicated by the dominance of 

alkylated two-ringed compounds, such as napthalene 

and its alkylated homologs. In addition, PAH mixtures 

produced by the burning of wood and brush are 

dominated by benzo(a)pyrene and coronene (Freeman 

and Cattell, 1990), two compounds that do occur but 

are not prevalent in Cochiti Lake sediments. The peak 

in selected parent PAH’s, such as fluoranthene, pyrene, 

and chrysene, in about 1990 coincides with a low ratio 

of 2- and 3-ringed to combustion PAH’s, indicating a 

greater proportion of combustion sources in this part of 

the core.

The concentrations of the same 10 PAH 

compounds discussed for the gravity core do not 

exhibit a consistent spatial pattern for the box cores 

(fig. 10A-D). Several low molecular weight and alkylhomolog compounds had peak concentrations at site 

B4 (fig. 10A, B), which was similar to the DDT pattern 

(fig. 8B) and may be associated with the sediment 

front. The concentrations of the 4- and 5-ringed 

compounds and C2-128 isomers increased in the 

downstream direction (fig. 10A, C, D). Total PAH 

concentrations ranged from 245 (site B5) to 654 μg/kg 

(site B4, fig. 10E). All concentrations of PAH’s in box 

core sediments are below the sediment-quality 

guidelines shown in table 6.

The ratio of the sum of 2- and 3-ringed 

compounds to sum of combustion PAH’s decreased in 

the downstream direction (fig. 10F). Higher ratios in 

the upper reservoir indicate the dominance of fuelrelated sources; decreases in the lower part of the 

reservoir indicate a relative increase in combustion 

sources. Regardless, the ratio remains larger than unity 

along the length of the reservoir, indicating fuel-related 

sources as the dominant contributors of PAH’s to the 

surficial sediments in Cochiti Lake. Chemical 

differences in individual PAH’s may also affect this
PAH CONCENTRATION, IN MICROGRAMS PER KILOGRAM

DEPTH IN CORE, IN CENTIMETERS

PAH CONCENTRATION, IN MICROGRAMS PER KILOGRAM

0 5 10 15

0

0 20 40 60 80 100

20

40

60

80

100

120

A

C1-128 isomers

C2-128 isomers

Nondetection in gray

Phenanthrene

C1-178 isomers

B

0 5 10 15 20 25

1996

1992

1988

1984

1980

C

Fluoranthene

Pyrene

C1-202 isomers

0

0 2 4 6 8 10

20

40

60

80

100

120

D E

Chrysene

Benzo(b)fluoranthene

Benzo(e)pyrene

0 100 200 300

Total PAH

Sum of 2-ringed

compounds

1 2 3 4 5

1996

1992

1988

1984

1980

SUM OF 2- AND 3-RINGED PAH/

SUM OF COMBUSTION PAH

Figure 9. Polycyclic aromatic hydrocarbon (PAH) concentrations (A-D), PAH sums (E), and the ratio

 of the sum of 2- and 3-ringed PAH’s to total combustion PAH (F) in a gravity core from

 Cochiti Lake.

F

ESTIMATED DEPOSITION DATE

23
Figure 10. Polycyclic aromatic hydrocarbon (PAH) concentrations (A-D), PAH sums (E), and the ratio of the sum of 2- and 3-ringed PAH’s to

 total combustion PAH (F) in box cores from Cochiti Lake. Box core sampling locations are labeled above data points in (A).

PAH CONCENTRATION, IN MICROGRAMS PER KILOGRAM

0

200

150

100

50

A

C1-128 isomers

C2-128 isomers

C1-202 isomers

Nondetection

in gray

0

5

15

10

C

Fluoranthene

Pyrene

Nondetection in gray

UPSTREAM DISTANCE FROM DAM, IN KILOMETERS

0 2 4 6 8

0

800

600

400

200

E

Total PAH

Sum of 2-ringed

compounds

R1

B1

B2

B4

B3

B5

B3.5

PAH CONCENTRATION,

IN MICROGRAMS PER KILOGRAM

Phenanthrene

C1-178 isomers

B

0

40

30

20

10

0

2

4

6

8

10

D

Chrysene

Benzo(b)-

fluoranthene

Benzo(e)-

pyrene

Nondetection

in gray

0 2 4 6 8

5

30

25

20

15

10

UPSTREAM DISTANCE FROM DAM, IN KILOMETERS

F

SUM OF 2- AND 3-RINGED PAH/

SUM OF COMBUSTION PAH

B1 Sediment

coring site

24
25

ratio. One chemical factor that could affect this pattern 

is that the lower molecular weight PAH’s (2- and 3-

ringed compounds) have greater water solubilities than 

higher molecular weight PAH’s (Lucius and others, 

1992; Knox and others, 1993). Thus, a decrease in this 

ratio downstream could be caused by the preferential 

leaching of these lower molecular weight compounds 

as sediments are (gradually) transported downstream.

Radionuclides

 Ten radionuclides were analyzed for in the 

bottom sediments from Cochiti Lake. The 

radionuclides are 137Cs, 210Pb, 226Ra, 234U, 235U, 

238U, 230Th, 232Th, 238Pu, and 239,240Pu. Uranium234, 235U, and 238U were found at all depth intervals in 

the gravity core (fig. 11A, B). Uranium-234 and 238U 

have similar activities, ranging from 1.14 to 1.56 and 

1.19 to 1.59 picocuries per gram (pCi/g), respectively 

(fig. 11A). As observed elsewhere (Van Metre and 

others, 1996b), 235U had much lower activities than 

234U and 238U in bottom sediments, with 

concentrations from 0.024 to 0.088 pCi/g (fig. 11B). 

Thorium-230 and 232Th were also present in all 

samples from the gravity core at concentrations ranging 

from 1.40 to 1.79 and 1.12 to 1.57 pCi/g, respectively 

(fig. 11C). No trend was exhibited for these five 

naturally occurring radionuclides in the core (fig. 11AC).

Uranium-238, 235U, and 234U are naturally 

occurring isotopes found in rocks and may be 

important contaminants in uranium mining areas. 

Substantial uranium mining has not occurred upstream 

from Cochiti Lake; however, historical uranium 

releases by LANL into canyons draining into the Rio 

Grande are a concern. Naturally occurring uranium is 

dominated by the 238U isotope with minor amounts of 235U and 234U. The atom ratio of 238U/235U = 137.8 in 

naturally occurring uranium (Efurd and others, 1993). 

The ratio of 238U/235U can differentiate naturally 

occurring uranium from anthropogenically processed 

uranium. Natural uranium is processed to enrich 235U 

relative to 238U for nuclear fuel, significantly lowering 

the ratio of 238U/235U. The byproduct of processed 

uranium is depleted in 235U relative to 238U, increasing 

the ratio of 238U/235U. Enriched uranium may have 

ratios of 238U/235U lower than 0.06, whereas these 

ratios may be greater than 500 in depleted uranium 

(Gallaher and others, 1999). The atom ratio of 238U/

235U was calculated for each depth interval in the 

gravity core (fig. 11D). The number of atoms of 238U 

and 235U was calculated from the activity of the 

radionuclides using the following equation:

where N = number of atoms;

A = Activity, in disintegrations per minute 

(dpm; 1 pCi = 2.22 dpm);

λ = decay constant, which is 0.693/t1/2; and

t1/2 = half-life of the radionuclide.

The atom ratio of 238U/235U ranges from 99.7 to 331.8. 

The analytical total error associated with each sample 

(table 3) could account for the deviation of the 238U/

235U ratio from that of naturally occurring uranium 

with the exception of one sample. The sample 

deposited during the late 1980’s has a 238U/235U ratio 

of 331.8. Incorporating the total errors of 238U and 

235U lowered this sample’s ratio to 152.6. Depleted 

uranium could cause the ratio of 238U/235U to be 

greater than that of naturally occurring uranium in this 

sediment interval.

The activity of the U and Th radionuclides in the 

box cores is shown in figure 12. Van Metre and others 

(1996b) showed U and Th radionuclide activities to 

correlate positively with the percentage of silt- and 

clay-sized grains, so radionuclide activities in the box 

cores did not require normalization with respect to 

grain size. The activity of the U and Th radionuclides is 

similar to the activity of the samples collected in the 

gravity core (fig. 12A).

 Plutonium is a manmade element that is used in 

nuclear weapons and generates energy in nuclear 

reactors. LANL, situated northwest of Cochiti Lake, 

conducts nuclear technology research and has released 

plutonium to the environment in the form of airborne 

emissions and liquid effluents as a result of laboratory 

operations (Los Alamos National Laboratory, 1995). 

LANL was established in 1943 and its contribution of 

radionuclides to the environment has been extensively 

monitored and studied (Graf, 1994; Los Alamos 

National Laboratory, 1995). Graf (1994) reported the 

mean activities of 238Pu (0.0007 pCi/g) and 239,240Pu 

(0.0127 pCi/g) for northern Rio Grande Basin reservoir 

sediments (Rio Grande, Heron, El Vado, Abiquiu, and 

Cochiti Reservoirs) for 1982 through 1988. The Rio 

Grande, Heron, El Vado, and Abiquiu Reservoirs are 

located upstream from Cochiti Lake.

N A / = λ (2)
URANIUM ACTIVITY, IN PICOCURIES PER GRAM THORIUM ACTIVITY,

IN PICOCURIES PER GRAM

0 0.05 0.10 1.0 1.5 2.0

URANIUM ATOM RATIO

0 200 400

B C 1996

1991

1984

1976

ESTIMATED DATE OF DEPOSITION

D

238U/235U atom ratio

in each depth interval

238U/235U atom ratio

in naturally occurring 

uranium

230Th activity

232Th activity

234U activity

238U activity

235U activity

0

20

40

60

80

100

120

140

160

DEPTH IN CORE, IN CENTIMETERS

1.0 1.2 1.4 1.6

A

Figure 11. Uranium and thorium radionuclide activities in a gravity core from Cochiti Lake.

26
1.0

1.2

1.4

1.6

1.8

235U activity

EXPLANATION

234U activity

238U activity

 230Th activity

232Th activity

238U/235U atom ratio

238U/235U atom ratio

in naturally occurring 

uranium

RADIONUCLIDE ACTIVITY, IN PICOCURIES PER GRAM

Figure 12. Uranium and thorium radionuclide activities in box cores from Cochiti Lake.

0

0.02

0.04

0.06

0.08

0.10

B

1.0

1.2

1.4

1.6

1.8

C

0

100

200

400

UPSTREAM DISTANCE FROM DAM, IN KILOMETERS

0 2 4 6 8

300

D

A

R1

B1

B2

B3

B5

B3.5

27

B4
28

The activities of 238Pu in the Cochiti Lake 

gravity core were near the reported mean activity (Graf, 

1994) with the exception of a single sample deposited 

around 1985 (97.5 cm), which has an activity (0.004 

pCi/g) approximately five times greater than those in 

the other sediment intervals (fig. 13A). Plutonium-239, 

240 activities were more variable, with a peak around 

1989 to 1991 (58.5 to 71.5 cm) followed by a step 

decrease to activities below 0.01 pCi/g thereafter (fig. 

13B). Plutonium-239, 240 activities were at or below 

the mean activity reported by Graf (1994) except at the 

1989 to 1991 peak. LANL has collected surficial 

sediment samples yearly from Cochiti Lake since 1982. 

Both 238Pu and 239, 240Pu activities were greatest in 

sediments collected in 1989 (0.0025 and 0.0493

pCi/g, respectively) (Graf, 1994; Los Alamos National 

Laboratory, 1995). Decreasing trends in Pu in the 

gravity core appear graphically (fig. 13A, B), but the 

trends were not statistically significant (Spearman’s 

rank correlation coefficient = 0.54, p-value = 0.067 for 

238Pu; Spearman’s rank correlation coefficient = 0.48, 

p-value = 0.11 for 239, 240Pu).

Soils and river sediments collected between 

1978 and 1986 from areas in northern New Mexico and 

southern Colorado had mean activities of 0.006 pCi/g 

for 238Pu and 0.023 pCi/g for 239, 240Pu that were 

attributed to natural rock-forming minerals and 

worldwide fallout from atmospheric nuclear weapons 

tests (Purtymun and others, 1987). The 238Pu activities 

in all gravity core intervals were less than the 

worldwide fallout or natural activity (fig. 13A). In all 

but one interval (middepth of 71.5 cm), 239, 240Pu 

activities were less than the worldwide fallout or 

natural activity (fig. 13B).

Plutonium activities in box core sediment 

samples are shown in figures 13C and D. The largest 

plutonium activities were at coring location B2. 

Plutonium-238 activities in the box cores were similar 

to, or greater than, the mean activity reported for 

northern Rio Grande Basin reservoir sediments by Graf 

(1994). Only the box core collected at site B2 exceeded 

the worldwide fallout or natural activity of Purtymun 

and others (1987). Plutonium-239, 240 activities in all 

box core sediments were greater than the mean 

reservoir value of Graf (1994) and were similar to the 

mean worldwide fallout or natural activity (Purtymun 

and others, 1987). The 238Pu and 239, 240Pu activities in 

box core sample R1 were more than double the 

activities at the top of the gravity core. This difference 

could be indicative of small-scale variations in 

sediment chemistry (a 13-cm gravity core interval 

compared to a 5-cm, three-box-core composite sample) 

or an indication of analytical variability.

The Pu activities measured for this study are 

consistent with those measured and reported by Graf 

(1994) for northern Rio Grande Basin reservoirs, 

including Cochiti Lake and LANL (1995) for Cochiti 

Lake. They are similar to, or below, sediment activities 

reported by Purtymun and others (1987) for northern 

New Mexico and southern Colorado that were 

attributed to worldwide fallout or natural activity.

CONCLUSIONS

Anthropogenic contaminants in Cochiti Lake 

sediments showed no historical trends with the 

exception of a modest decreasing trend in total DDT for 

1980-92 and were at small concentrations relative to 

sediment-quality guidelines. The lack of trends implies 

few new additions of the sediment-bound compounds 

and elements measured for this study since storage in 

the reservoir began in 1973. Relatively small 

concentrations of hydrophobic contaminants including 

trace elements, organochlorine compounds, PAH’s, 

and naturally occurring radionuclides (U and Th) are an 

indication of limited effects by humans. High 

sedimentation rates, estimated to be about 6.6 cm/yr at 

the coring site near the dam and much greater at 

upstream sites based on sedimentation surveys, are 

partly responsible for the relatively “clean” sediments 

in the reservoir. Large inputs of sediment from 

undeveloped parts of the watershed dilute any 

anthropogenic inputs of contaminants from urban, 

industrial, and agricultural areas. 
Figure 13. Plutonium activities in a gravity core (A and B) and box cores (C and D) from Cochiti Lake. The Pu

 worldwide fallout and (or) natural activity level is greater than the maximum Pu activity value

 shown in (A) and does not appear on the graph.

 

238

238

0

0.008

0.006

0.004

0.002

R1 B1 B3

B4 B5

B3.5

B2

C

UPSTREAM DISTANCE FROM DAM, IN KILOMETERS

0 2 4 6 8

0.030

0.025

0.020

0.015

0.010

D

PLUTONIUM ACTIVITY, IN PICOCURIES PER GRAM

PLUTONIUM ACTIVITY, IN PICOCURIES PER GRAM

0 0.0025 0.0050 0 0.01 0.02 0.03

0 A

DEPTH IN CORE, IN CENTIMETERS

20

40

60

80

100

120

140

160

1996

1991

1984

1976

B

B1 Sediment coring site

EXPLANATION

238

239, 240

238

238

239, 240

239, 240

Pu activity

 Pu activity

Mean Pu activity in

northern Rio Grande Basin

reservoir sediments

(Graf, 1994)

Pu worldwide fallout and

(or) natural activity level

(Purtymun and others, 1987)

Mean Pu activity by

northern Rio Grande Basin

reservoir sediments

(Graf, 1994)

Pu worldwide fallout and

(or) natural activity level 

(Purtymun and others, 1987)

Pu worldwide

fallout and (or)

natural activity

= 0.004

238

29
30

REFERENCES CITED

Alder, A.C., Haggblom, M.M., Oppenheimer, S.R., and 

Young, Y., 1993, Reductive dechlorination of 

polychlorinated biphenyls in anaerobic sediments: 

Environmental Science & Technology, v. 27, p. 530-

538.

Borland, J.P., and Ong, K., 1995, Water resources data, New 

Mexico, water year 1994: U.S. Geological Survey 

Water-Data Report NM-94-1, 581 p.

Callender, E., and Van Metre, P.C., 1997, Reservoir sediment 

cores show U.S. lead declines: Environmental Science 

& Technology, v. 31, p. 424A-428A.

Canadian Council of Ministers of the Environment, 1998, 

Canadian sediment-quality guidelines for the protection 

of aquatic life--Introduction and summary tables, in

Canadian environmental quality guidelines, 1998: 

Canadian Council of Ministers of the Environment, 

Winnipeg.

Department of the Army, 1996, Cochiti Lake water control 

manual, Appendix C to Rio Grande Basin, Master water 

control manual: Department of the Army, Albuquerque 

District, Corps of Engineers, Albuquerque, N. Mex., 

185 p.

Efurd, D.W., Rokop, D.J., and Perrin, R.E., 1993, 

Characterization of the radioactivity in surface waters 

and sediments collected at the Rocky Flats Facility: Los 

Alamos National Laboratory Report LA-UR-93-4373, 

54 p.

Eganhouse, R.P., and Gossett, R.W., 1991, Historical 

deposition and biogeochemical fate of polycyclic 

aromatic hydrocarbons in sediments near a major 

submarine wastewater outfall in Southern California, in

Baker, R.A., ed., Organic substances and sediments in 

water: Boca Raton, Fla., Lewis Publishers, p. 191–220.

Eisenreich, S.J., Capel, P.D., Robbins, J.A., and 

Boubonniere, R., 1989, Accumulation and diagenesis 

of chlorinated hydrocarbons in lacustrine sediments: 

Environmental Science & Technology, v. 23, p. 1116–

1126.

Fishman, M.J., 1993, Methods of analysis of the U.S. 

Geological Survey National Water Quality Laboratory-

-Determination of inorganic and organic constituents in 

water and fluvial sediments: U.S. Geological Survey 

Open-File Report 93–125, 217 p.

Foreman, W.T., Connor, B.F., Furlong, E.T., Vaught, D.G., 

and Merten, L.M., 1994, Methods of analysis by the 

U.S. Geological Survey National Water Quality 

Laboratory--Determination of organochlorine 

insecticides and polychlorinated biphenyls in bottom 

sediment: U.S. Geological Survey Open-File Report 

94–140, 78 p.

Freeman, D.J., and Cattell, C.R., 1990, Woodburning as a 

source of atmospheric polycyclic aromatic 

hydrocarbons: Environmental Science & Technology, 

v. 24, p. 1581-1585.

Froelich, P.N., Klinkhammer, G.P., Bender, M.L., Luedtke, 

N.A., Heath, G.R., Cullen, D., Dauphin, P., Hammond, 

D., Hartman, B., and Maynard, V., 1979, Early 

oxidation of organic matter in pelagic sediments of the 

eastern equatorial Atlantic--Suboxic diagenesis: 

Geochimica et Cosmochimica Acta, v. 43, p. 1075-

1090.

Furlong, E.T., Vaught, D.G., Merten, L.M., Foreman, W.T., 

and Gates, P.M., 1996, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory-

-Determination of semivolatile organic compounds in 

bottom sediment by soxlet extraction, gel permeation 

chromatographic fractionation, and capillary-column 

chromatography/mass spectrometry: U.S. Geological 

Survey Open-File Report 95-719, 67 p.

Gallaher, B.M., Efurd, D.W., Rokop, D.J., and Benjamin, 

T.M., 1999, Plutonium and uranium atom ratios and 

activity levels in Cochiti Lake bottom sediments 

provided by Pueblo de Cochiti: Los Alamos National 

Laboratory Report, LA-13605-MS, 21 p.

Geological Society of America, 1991, The Geological 

Society of America rock color chart with genuine 

Munsell color chips: The Geological Society of 

America, Boulder, Colo., 8 p.

Graf, W.L., 1994, Plutonium and the Rio Grande--

Environmental change and contamination in the nuclear 

age: New York, Oxford University Press, 329 p.

Guy, H., 1969, Laboratory theory and methods for sediment 

analyses: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. C1, 58 p.

Harvey, R.G., 1991, Polycyclic aromatic hydrocarbons--

Chemistry and carcinogenicity: New York, Cambridge 

University Press, 396 p.

Hendricks, T., and Eganhouse, R.P., 1992, Modification and 

verification of sediment deposition models, final report: 

Southern California Coastal Water Research Project, 

Long Beach, Calif., 330 p.

Hites, R.A., LaFlamme, R.E., Windsor, J.G., Jr., Farrington, 

J.W., and Deuser, W.G., 1981, Polycyclic aromatic 

hydrocarbons in an anoxic sediment core from the 

Pettaquamscutt River (Rhode Island, U.S.A.): 

Geochimica et Cosmochimica Acta, v. 44, p. 873–878.

Horowitz, A.J., and Elrick, K.A., 1987, The relation of 

stream sediment surface area, grain size, and 

composition to trace element chemistry: Applied 

Geochemistry v. 2, p. 437–451.

Knox, R.C., Sabatini, D.A., and Canter, L.W., 1993, 

Subsurface transport and fate processes: Boca Raton, 

Fla., Lewis Publishers, 430 p.
31

LaFlamme, R.E., and Hites, R.A., 1978, The global 

distribution of polycyclic aromatic hydrocarbons in 

recent sediments: Geochimica et Cosmochimica Acta, 

v. 42, p. 289-303.

Lichte, F.E., Golightly, D.W., and Lamothe, P.J., 1987, 

Inductively coupled plasma-atomic emission 

spectrometry, in Baedecker, P.A., ed., Methods for 

geochemical analysis: U.S. Geological Survey Bulletin 

1770, p. B1–B10.

Long, E.R., MacDonald, D.D., Smith, S.L., and Calder, F.D., 

1995, Incidence of adverse biological effects within 

ranges of chemical concentrations in marine and 

estuarine sediments: Environmental Management, 

v. 19, no. 1, p. 81-97.

Los Alamos National Laboratory, 1995, Environmental 

surveillance at Los Alamos during 1993: LA-12973-

ENV.

Lucius, J.E., Olhoeft, G.R., Hill, P.L., and Duke, S.K., 1992, 

Properties and hazards of 108 selected substances--

1992 edition: U.S. Geological Survey Open-File Report 

92-527, 554 p.

National Academy of Sciences, 1979, Polychlorinated 

biphenyls: Washington, D.C., National Academy Press, 

182 p.

Peakall, D.B., 1975, PCB’s and their environmental effects: 

CRC Critical Reviews in Environmental Control, v. 5, 

no. 5, p. 469-508.

Prahl, F.G., and Carpenter, R., 1983, Polycyclic aromatic 

hydrocarbon (PAH)--Phase associations in Washington 

coastal sediment: Geochimica et Cosmochimica Acta, 

v. 47, p. 1013-1023.

Pritt, J.W., and Raese, J.W., 1992, Quality assurance/quality 

control manual--National Water Quality Laboratory: 

U.S. Geological Survey Open-File Report 92-495, 33 p.

Purtymun, W.D., Peters, R.J., Buhl, T.E., Maes, M.N., and 

Brown, F.H., 1987, Background concentrations of 

radionuclides in soils and river sediments in northern 

New Mexico, 1974-1986: Los Alamos National 

Laboratory Report LA-11134-MS.

Rapaport, R.A., Urban, N.R., Capel, P.D., Baker, J.E., 

Looney, B.B., Eisenreich, S.J., and Gorham, E., 1985, 

“New” DDT inputs to North America--Atmospheric 

deposition: Chemosphere, v. 14, p. 1167-1173.

Ruddy, B.C., and Hitt, K.J., 1990, Summary of selected 

characteristics of large reservoirs in the United States 

and Puerto Rico, 1988: U.S. Geological Survey OpenFile Report 90-163, 295 p.

Smith, J.A., Witkowski, P.J., and Fusillo, T.V., 1988, 

Manmade organic compounds in the surface water of 

the United States--A review of current understanding: 

U.S. Geological Survey Circular 1007, 92 p.

U.S. Environmental Protection Agency, 1983, Analysis of 

the risks and benefits of seven chemicals used for 

subterranean termite control: U.S. Environmental 

Protection Agency, Office of Pesticides and Toxic 

Substances, EPA-540/9-83-005.

Van Metre, P.C., Callender, E., and Fuller, C.C., 1997, 

Historical trends in organochlorine compounds in river 

basins identified using sediment cores from reservoirs: 

Environmental Science & Technology, v. 31, p. 2339-

2344.

Van Metre, P.C., Mahler, B.J., and Callender, E., 1996a, 

Water-quality trends in the Rio Grande/Rio Bravo Basin 

using sediment cores from reservoirs: U.S. Geological 

Survey Fact Sheet FS-221-96, 8 p.

Van Metre, P.C., Wilson, J.T., Callender, E., and Fuller, C.C., 

1998, Similar rates of decrease of persistent, 

hydrophobic and particle-reactive contaminants in 

riverine systems: Environmental Science & 

Technology, v. 32, p. 3312-3317.

Van Metre, P.C., Wirt, L., Lopes, T.J., and Ferguson, S.A., 

1996b, Effects of uranium-mining releases on groundwater quality in the Puerco River Basin, Arizona and 

New Mexico: U.S. Geological Survey Water-Supply 

Paper 2476, 72 p.

Wershaw, R.L., Fishman, M.J., Grabbe, R.R., and Lowe, 

L.E., eds., 1987, Methods for the determination of 

organic substances in water and fluvial sediments: U.S. 

Geological Survey Techniques of Water-Resources 

Investigations, book 5, chap. A3, 80 p.
J.T. Wilson and P.C. Van Metre—DEPOSITION AND CHEMISTRY OF BOTTOM SEDIMENTS IN COCHITI LAKE, 

NORTH-CENTRAL NEW MEXICO—U.S. Geological Survey Water-Resources Investigations Report 99-4258

U.S. Department of the Interior

U.S. Geological Survey, WRD

5338 Montgomery Blvd. NE, Suite 400

Albuquerque, NM 87109-1311

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