UNITED STATES DEPARTMENT OF THE INTERIOR 
GEOLOGICAL SURVEY
Analytical results for 38 water samples 
from a hydrogeochemical survey of the U.S. Virgin Islands
By 
J.B. McHugh and R.E. Tucker^
Open-File Report 88-514
This report is preliminary and has not been reviewed for conformity with 
U.S. Geological Survey editorial standards and stratigraphic nomenclature, 
Any use of trade names is for descriptive purposes only and does not imply 
endorsement by the USGS.
*U.S. Geological Survey, DFC, Box 25046, MS 973, Denver, CO 80225
1988
CONTENTS
Page 
Introduction................................................................ 1
Study Area.................................................................. 1
Sample Collection........................................................... 1
Analytical Methods.......................................................... 1
Results..................................................................... 2
References Cited............................................................ 2
ILLUSTRATIONS 
Figure 1. 
Index map of the study area...................................... 3
Figure 2. Sample location map of St. Croix Island.......................... 4
Figure 3. 
Sample location map of St. John Island........................... 5
TABLES
Table 1. 
Analytical methods used for water analyses,
U.S. Virgin Islands.................................................... 6
Table 2. 
Chemical analyses for 38 water samples from the
U.S. Virgin Islands.................................................... 7
INTRODUCTION
A hydrogeochemical study was conducted in the U.S. Virgin Islands on the 
islands of St. John and St. Croix. Thirty-eight water samples were collected, 
twenty-nine samples from St. John and nine samples from St. Croix. The nine 
samples from St. Croix were collected in November 1984. The samples from St. 
John were collected in January 1985 except for the last seven samples which 
were collected in August 1986.
The purpose of the study was to examine the concentration of metals and 
anions in water to determine the hydrogeochemical characteristics associated 
with mineralization on St. John and St. Croix Islands (Tucker and others, 
1985; Alminas and Tucker, 1987; Tucker, 1987). The samples were analyzed for 
15 metal ions, silica, and five anions along with pH and specific 
conductance. The study was funded by the USGS Virgin Islands project.
STUDY AREA
The U.S. Virgin Islands are located in the Greater Antilles Island arc 
some 40 mi east of Puerto Rico (fig. 1). 
The major islands include St. 
Thomas, St. John, and St. Croix. There are about 50 smaller islands in the 
study area concentrated near St. Thomas and St. John.
St. John is 7 mi long, on the average is 3 mi wide, and contains some 
12,000 acres. The topography is mountainous with the highest elevation of 
1,277 ft on Bordeaux Mountain. The island has a very irregular coastline with 
many bays and offshore islets. 
St. Croix, the largest of the U.S. Virgin 
Islands, is 22 mi long and 6 mi wide with 54,000 acres. St. Croix is 
characterized by regular coastline and two adjacent islands. The topography 
is more subdued with the highest point of 1,165 ft on Mt. Eagle. Streams on 
these two islands are intermittent and discharge into the sea.
The climate in the Virgin Islands is maritime tropical. The average 
annual rainfall at higher elevations is 50-60 in and at lower elevations 20-30 
in. 
There is no well-defined wet or dry season. The temperature is generally 
constant between 80 and 85°F.
The vegetation is generally not native to the islands and consists of 
thorny brush and Hurricane grass in the formerly cleared areas. The uncleared 
portions of the more mountainous areas are covered by dense tropical forest 
with a few large trees and a dense undergrowth of brush and vines.
SAMPLE COLLECTION
Thirty-eight water samples were collected from the study area. At each 
site, a 60-ml sample was filtered through a 0.45-um membrane filter into an 
acid-rinsed polyethylene bottle, and then acidified with reagent grade 
concentrated nitric acid to a pH of less than 2. 
A 500-ml untreated sample 
was also collected in a clean polyethylene bottle.
ANALYTICAL METHODS
Water temperature and pH were measured at the sample site. All other 
analyses were completed at the U.S. Geological Survey laboratory in Denver, 
Colorado.
Calcium, magnesium, sodium, potassium, lithium, silica, zinc, copper, 
molybdenum, silver, arsenic, vanadium, iron, manganese, and aluminum were 
determined using the filtered-acidified sample. Alkalinity, sulfate,
chloride, fluoride, nitrate, uranium, and specific conductance were determined 
using the untreated sample. Alkalinity measures the total acid-neutralizable 
constituents in water and is generally due to the presence of carbonate and 
bicarbonate ions. A complete list of analytical methods used and a reference 
for each are listed in table 1.
RESULTS
Figures 2 and 3 are maps showing the location of each sample on the 
islands of St. Croix and St. John respectively. All the samples were 
collected from springs or streams except as noted. Sample numbers SC01, SJ75, 
SJ86, SJ87, and SJ88 are estuary water samples. Sample numbers SC06, SJ64, 
SJ81, SJ82, and SJ83 are rainwater samples. The rainwaters were collected off 
of building roofs.
The analytical results of the 23 constituents that were determined for 
these samples are shown in table 2 along with the latitude and longitude for 
each sample location. Duplicate samples were collected at sites SJ67-68, 
SJ72-73, and SJ82-83. The results of the charge balance shown in table 2 for 
the 38 samples show good accuracy of analyses. 
Ionic solutions are 
electrically neutral. By comparing the sum of the charges for cations against 
anions, accuracy of analyses can be checked. Twenty-one of the samples are 
within 5 percent, fifteen samples are between 5-10 percent, and two samples 
are between 10-15 percent of electrical neutrality.
The high salt content of the estuary water samples from the sea causes 
interferences in the analytical procedure which give high copper, silver, and 
molybdenum values.
REFERENCES CITED
Alminas, H.V., and Tucker, R.E., 1987, Lead, tin, and precious-metals
mineralization in the U.S. Virgin Islands: Society of Mining Engineers
annual meeting, preprint number 87-108. 
Fishman, J.J., and Pyen, G., 1979, Determination of selected anions in water
by ion chromatography: U.S. Geological Survey Water Resources
Investigations 79-101, 30 p. 
Orion Research, Inc., 1978, Analytical methods guide, 9th ed.: 
Cambridge,
Massachusetts, 48 p. 
Perkin-Elmer Corporation, 1976, Analytical methods for atomic-absorption
spectrophotometry: Norwalk, Connecticut, Perkin-Elmer Corporation,
586 p. 
____1977, Analytical methods for atomic-absorption spectrophotometry, using
the HGA graphite furnace: Norwalk, Connecticut, Perkin-Elmer
Corporation, 208 p.
Scintrex Corporation, 1979, UA-3 Uranium Analyzer: Toronto, Canada, 45 p. 
Skougstad, M.W., Fishman, M.J., Fruedmann, L.C., Erdmann, D.E., and Duncan,
S.S., 1979, Methods for determination of inorganic substances in water
and fluvial sediments: Techniques of Water Resources Investigations of
the U.S. Geological Survey, chapter Al, 26 p. 
Tucker, R.E., 1987, A geochemical study of St. John, U.S. Virgin Islands:
Colorado School of Mines, Ph.D. dissertation, 405 p. 
Tucker, R.E., Alminas, H.V., and Hopkins, R.T., 1985, Geochemical evidence for
metallization on St. Thomas and St. John, U.S. Virgin Islands: U.S.
Geological Survey Open-File Report 85-297, 46 p.
69*
66
63
60
DOMINICAN 
REPUBLIC
GREATER ANTILLES
VIRGIN ISLANDS
ATLANTIC OCEAN
STUDY AREA
a***
^ST. CROIX
Q ST. MARTIN
^ 
ANTIGUA
o 
r^&
CARIBBEAN 
SEA
GUADELOUPE
MARTINIQUE
01
VENEZUELA
Figure 1. 
Index map of the study srea
100 
50
100
100
MILES
100
200
KILOMETERS
200
3OO
50'
17° 40
64*50'
40'
0 
2 
4 
68 
KILOMETERS
Figure 2. 
Sample location map of St. Croix Island.
64P 50'
46'
42
- _ t«*T6B
BOVOCOAP 
POINT
CARIBBEAN SEA
18'21'3
19'
MILES 
1 
.5 
0
Figure 3. 
Sample location map of St. John Island
TABLE 1. Analytical methods used for water analyses, U.S. Virgin Islands
Constituents
Method
Reference
Alkalinity
Sulfate, chloride, 
and fluoride
Uranium
Specific conductance
Calcium, magnesium, 
sodium, potassium, 
silica, lithium, 
aluminum, iron, 
manganese, and zinc
Arsenic, silver, 
vanadium, copper, 
and molybdenum
Gran's plot potentiometric 
titration
Ion chromatography
Laser-excited fluorescence
Conductivity bridge
Flame atomic-absorption 
spectrophotometry
nameless atomic-absorption 
spectrophotometry
Orion Research, 
Inc. (1978).
Fishman and Pyen 
(1979).
Scintrex Corp. 
(1979).
Skougstand et al. 
(1979), p. 545.
Perkin-Elmer Corp. 
(1976).
Perkin-Elmer Corp, 
(1977).
Table 2. 
CHEMICAL ANALYSES FOR SB WATER SAMPLES FROM THE u.s. VIRGIN ISLANDS
[N, not detected? <, detected but below the limit of determination shown; >, determined to be greater than the value shown.)
Sample
LATITUDE
LONSITUD
CACMG/L)
MG(MG/L)
NA(WG/L)
K(MG/L)
LKUG/L)
SI02(MG/
ALK(MG/L
sroi
SC02
SC03
sco4
SCP5
SC06
SCO?
SC08
SC09
SJ60
SJ61
SJ62
SJ63
SJ64
SJ65
SJ66
SJ67
SJ68
SJ69
SJ70
SJ71
SJ72
SJ73
SJ74
SJ75
SJ76
SJ77
SJ78
SJ79
SJ80
SJ81
SJ82
SJ83
SJ84
SJ85
SJ86
SJ87
SJ88
17 46
17 44
17 46
17 45
17 44
17 46
17 44
17 44
17 44
18 21
18 20
18 19
18 19
18 21
18 19
18 19
18 19
18 19
18 19
18 2P
18 20
18 19
18 19
18 19
18 19
18 20
18 20
18 21
18 21
18 21
18 21
18 21
18 21
18 20
18 ?0
18 20
18 19
18 21
43
27
53
3
1^
10
25
23
7
29
54
46
22
14
32
'55
55
55
51
4
38
43
43
17
26
32
49
34
22
7
14
16
16
36
31
IB
15
18
64 45
64 42
64 46
64 52
64 51
64 44
64 51
64 50
64 50
64 44
64 46
64 47
64 46
64 45
64 45
64 45
64 45
64 45
64 46
64 43
64 43
64 43
64 43
64 42
64 45
64 45
64 44
64 44
64 44
64 44
64 45
64 45
64 45
64 44
64 45
64 42
64 45
64 45
10
4
34
20
41
15
9
54
1
23
37
0
53
41
31
57
54
54
44
38
26
15
15
37
58
34
33
2
11
38
41
41n
58'
34
27
30
40
580.0
37.0
70.0
90.0
115.0
2.7
82.0
102.0
90.0
15.0
122.0
70.0
103.0
2.6
71 .0
46.0
52.0
52.0
118.0
2.9
6.8
53.0
53.0
5.1
610.0
83.0
41.0
11.0
11.0
15.0
1.2
.5
.6 .
79.0
79.0
410.0
410.0
410.0
1,040.0
17.0
27.0
18.0
18.0
2.2
25.0
26.0
?5.0
11.0
51.0
48.0
46.0
1.9
44.0
31.0
41.0
41.0
84.0
4.6
7.9
66.0
66.0
5.8
1,1?0.0
50.0
39.0
5.1
5.8
16.0
.6
.1
.2
43.0
44.0
1,060.0
1,060.0
1,060.0
10,000
60
140
55
55
22
66
63
93
150
140
300
320
18
180
300
220
220
310
57
66
560
560
68
11,000
360
220
32
36
180
3
2
5
210
280
11,400
11,400
11,200
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.5
.3
.3
.0
.0
.0
.0
.0
390
7
3
2
2
2
1
1
4
3
3
7
1
7
4
3
3
1
1
3
6
6
3
420
8
3
5
3
5
3
5
440
450
440
.00
.20
.80
.50
.30
.90
.30
.40
.30
.20
.20
.10
.70
.30
.70
.20
.60
.70
.10
.30
.00
.90
.80
.90
.00
.40
.60
.20
.30
.20
.40
.92
.84
.30
.50
.00
.00
.00
190
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
<4
200
<4
<4
<4
<4
<4
<4
<2
<2
<2
<2
155
155
155
1.7
?8.0
?2.0
23.0
27.0
<1.0
23.0
24.0
?5.0
27.0
41 .0
27.0
26.0
<1.0
20.0
?5.0
29.0
29.0
39.0
26.0
20.0
27.0
27.0
24.0
1 .5
40.0
35.0
23.0
21.0
30.0
<1.0
1.0
<1.0
33.0
40.0
2.0
2.0
2.0
143.0
208.0
295.0
240.0
240.0
4.9
315.0
394 .0
240.0
177 .0
396.0
473.0
628.0
5.5
377 .0
 526.0
483.0
416.0
586 .0
9.0
35.0
36T-.0
357.0
75.0
143.0
643.0
452.0
78.0
65.0
213.0
3.9
2.0
4.0
680.0
707 .0
147.0
134.0
148.0
Table 2. .CHEMICAL ANALYSES FOR 38 WATER SAHPLES FROM THE u.s. VIRGIN ISLANDS continued
Sample
2,070.0
11.0
31.0
10.0
16.0
CL(MG/L)
20,200.0
75.0
145.0
74.0
102.0
F(MG/L)
9.00
.22
N03(HG/L
ZN(UG/L)
66
10
9
10
11
CtKUG/L)
45.0 
5.4 
2.0 
1.5 
1.1
MCKUG/L)
5,5 
<1.0 
<1.0 
<1.0 
<1 .0
AGUJG/L)
1.60 
<.02 
<.02 
<.0?
5.0
9.0 
17.0 
30.0 
lfi.0
36.0
75.0
77.0
139.0
150.0
.03
3.00
17
8
10
7 
fi
1.0 
1.2 
1 .4 
1.2 
2.2
.0 
.0
.0
<.02 
<.02 
.03 
<.02 
<. 02
29.0 
31.0 
93.0 
4.0 
?7.0
248.0 
338.0 
359.0 
35/0 
277.0
.46
2.00
.04
10.00
10
6
6
8
6
1 .9 
2.0 
3.2 
1 .0 
4.5
.0 
.0
02
02
06
02
02
20..0
16.0
16.0
66.0
8.0
285.0
250.0
242.0
409.0
80.0
.40 
.01 
.40 
.52 
.08
5
4
4
11
17
2.0 
1.9 
1.4 
2.5 
10.0
.0 
.0
.0
<.02
<.02
<.0?
.02
.03
12.0
111.0
114.0
6.0
2 ,300.0
29.0
36.0
4.0
2.0
29.0
98.0
827.0
706.0
76.0
21,400.0
343.0
195.0
27.0
46.0
199.0
.12
.85
2.00
.13
6.00
.70
<.01
.07
.09
18
9
7
6
25
5
9
6
4
4
16.0
3.0
2.3
2.3
45.0
2.0 
<1.0 
5.0 
3.0 
1.5
1 .0
1.0 
1 .0 
1 .0
5.5
.0 
.0
.0 
.0
.06
.05
.05
<.02
1.70
.03 
<.02 
.03 
.02 
.0?
1.0
.6
2.0
13.0
17.0
6.0
2.9
5.8
270.0
315.0
,01
,02 
,01 
,20
,30
.4
120
80
26
22
1 .0 
2.0 
7.2 
1.6 
1.5
1 .5 
1 .0 
1 .2
,02 
02 
,02 
,02 
R2
2 ,100.0
2,000.0
1 ,900.0
21,600.0
21,900.0
21,300.0
13.00
12.00
12.00
60
35
40
20.0
20.0
20.0
16.0
17.0
16.0
40
40
2.40