INTRODUCTION

Great Sand Dunes National Monument and Preserve 

is located on the eastern side of the San Luis Valley in 

south-central Colorado. The monument covers 60.4 square 

miles in Saguache and Alamosa Counties and lies at the 

base of the Sangre de Cristo Mountains, where a unique 

combination of climate, topography, and hydrology has 

created and maintained the Nation’s tallest inland sand 

dunes. The Sangre de Cristo Mountains, which rise to more 

than 14,000 feet to the north and east of the dunes, are the 

source of several streams that flow around the dunes and 

eventually recharge the aquifer beneath the valley. Sand 

Creek and Medano Creeks are the largest of the streams in 

the monument that originate in the Sangre de Cristo Mountains; several ephemeral streams flow into Sand Creek and 

Medano Creek. 

Maintaining the high surface-water quality in the 

Great Sand Dunes National Monument and Preserve is 

identified as a critical issue by the National Park Service. 

Additionally, the National Park Service has indicated a 

desire to pursue an Outstanding Waters Designation, which 

offers the highest level of water-quality protection available 

under the Clean Water Act and Colorado regulations. This 

designation is designed to prevent any degradation from 

existing conditions (Chatman and others, 1997). Assessment is needed to evaluate whether the water quality of the 

streams in the monument meets the requirements for an 

Outstanding Waters Designation. 

Historically, prospecting and mining activities have 

occurred in the watersheds of Sand and Medano Creeks; 

currently, however, there is no mining activity in those 

watersheds. In addition, the camping and recreation that 

occur upstream from the monument on national preserve 

lands and water activities that occur in Medano Creek 

during the summer are a potential source of human-waste 

contamination. 

The U.S. Geological Survey (USGS), in cooperation 

with the National Park Service, investigated the water 

quality at 15 sites (fig. 1) from February 1999 through 

September 2000 to identify baseline water-quality conditions and to determine if the water met standards to qualify 

for the Outstanding Waters Designation. This report 

describes current water-quality conditions in streams in the 

This is the Title for Fact Sheet Investigation of Water Quality in the Great Sand Dunes 

National Monument and Preserve, Saguache County, 

Colorado, February 1999 through September 2000: 

Qualifying for Outstanding Waters Designation

—By Sheryl A. Ferguson

Great Sand Dunes National Monument and Preserve

U.S. Department of the Interior

U.S. Geological Survey WRIR 02–4196

January 2003

Supersedes December 2002 version
Denver

Colorado

Springs

Pueblo

Alamosa Study area

(1)

Six Mile Road

0

0 1 2 3 KILOMETERS

1 2 3 MILES

106°

37°48'

37°42'

105°30'

Perennial stream.—no exceedances

 of instream standards

Perennial stream.—exceedance

 of instream standard for manganese

Ephemeral stream.—no exceedances

 of instream standards

Spring

Interdunal pond.—exceedance of

 instream standard for manganese

Site name and number (see table 1)

EXPLANATION

C O L O R A D O

150

Garden Creek (12) Buck Creek (4)

Sawmill Canyon (11)

Medano Creek at the

 Park Boundary (3)

Medano Creek 

 below Mosca 

 Creek (7)

Little Medano Creek 

 at Mouth (9)

Cold Creek (8)

Castle Creek (10)

Sand Creek at 

the Monument 

 Boundary (2)

Sand Creek 

 at the Baca 

 Grant (1)

West Elk

Spring Pond

(15)

Mosca Creek (6)

Morris Gulch Spring (14)

Medano Creek below

 Garden Creek (5)

Mosca Spring (13)

GREAT

SAND DUNES

NATIONAL

MONUMENT

AND PRESERVE

SAGUACHE COUNY

ALAMOSA COUNY

HUERFANO COUNY

Monument

Boundary

Sangre de Cristo

Mountains

Sand Creek

Medano Creek

monument and compares the water-quality data to 

Colorado instream standards to assist the State of 

Colorado Water Quality Control Commission in the 

determination of qualification for Outstanding Waters 

Designation. 

CRITERIA FOR OUTSTANDING WATERS 

DESIGNATION

Currently (2002), the State of Colorado, Water 

Quality Control Commission, has assigned the streams 

in the monument the following use classifications: (a) 

Cold Water Aquatic Life–Class 1, (b) Recreation Class 

2–secondary contact, (c) Domestic Water Supply, and 

(d) Agriculture. The classification of Cold Water 

Aquatic Life indicates that the waters presently 

support a wide variety of cold-water species. Recreation Class 2 indicates that waters are suitable for 

limited human contact, such as fishing and other 

streamside recreation, but not for ingestion. Domestic 

Water-Supply use is defined as suitable for potable 

water supplies that will meet Colorado drinking-water 

standards upon standard treatment, and Agricultural 

use is defined as suitable for irrigation of crops and 

would not be hazardous either to livestock or as 

drinking water (Colorado Department of Public Health 

and Environment, 2001a). 

Specific waters may be designated as 

Outstanding Waters if the State of Colorado Water 

Quality Control Commission determines that (1) the 

existing quality for each of the 12 parameters listed 

below is equal to or better than that specified for the 

protection of Cold Water Aquatic Life–Class 1, Recreation Class 1, and Domestic Water-Supply uses; 

(2) the waters constitute an outstanding natural 

resource based on the fact that the waters are a significant attribute of a National Monument; (3) the waters 

have exceptional recreational or ecological significance and have not been modified by human activities 

in a manner that substantially detracts from their value 

as a natural resource; and (4) the waters require protection in addition to that provided by the combination of 

water-quality classification standards and the protection afforded water under Colorado Department of 

Public Health and Environment (CDPHE) guidelines 

(Colorado Department of Public Health and Environment, 2001a). Recreation Class 1 indicates that the 

waters are suitable or intended to become suitable for 

recreational activities when the ingestion of small 

quantities of water is likely to occur. The 12 waterquality parameters identified by the CDPHE for determining Outstanding Waters Designation are pH, 

dissolved oxygen, fecal coliform bacteria, un-ionized 

ammonia and nitrate, and dissolved cadmium, copper, 

lead, manganese, selenium, silver, and zinc (Colorado 

Department of Public Health and Environment, 

2001b). 

DATA COLLECTION

Water-quality samples were collected using 

USGS protocols (Wilde and others, 1998) for analysis 

of selected water-quality properties and constituents 

by the USGS National Water-Quality Laboratory 

(table 1). Dissolved oxygen and pH were measured 

onsite, and instantaneous streamflow measurements 

Figure 1. Location of study area, sampling sites, and indication of sites that meet or exceed instream standards.
 Table 1. Selected water-quality data for the Great Sand Dunes National Monument, Colorado, 1999–2000

[mg/L, milligrams per liter (equivalent to parts per million); μg/L, micrograms per liter (equivalent to parts per billion); col/100 mL, colonies per 100 milliliters; n/a, not applicable E, estimated value; MRL, 

minimum reporting level; <, less than; >, greater than; %, percentage; Bold number, exceedance of instream standard [note: 15th and 85th percentiles used to determine exceedance of instream standard for 

pH; 15th percentile used to determine exceedance of instream standard for dissolved oxygen; geometric mean used to determine exceedance of instream standard for fecal coliform; 85th percentile used to determine exceedances of instream standards for other constituents (Colorado Department of Public Health and Environment, 2001b)]

Statistical

parameters

pH

(standard units)

Dissolved 

oxygen 

(mg/L)

Fecal 

coliform 

bacteria 

(col/100 mL 

water)

Un-ionized 

ammonia 

(mg/L)

Nitrate 

(mg/L)

Dissolved 

cadmium 

(μg/L)

Dissolved 

copper 

(μg/L)

Dissolved 

lead 

(μg/L)

Dissolved 

manganese

(μg/L)

Dissolved 

selenium 

(μg/L)

Dissolved 

silver

(μg/L)

Dissolved 

zinc

(μg/L)

PERENNIAL STREAMS

Sand Creek at the Baca Grant—Site 1

Number of samples 4 4 4 4 4 4 4 4 4 4 4 4Percentage less than MRL n/a n/a n/a 100% 50% 100% 25% 100% 50% 100% 100% 75%Minimum value 7.8 6.3 21 n/a <0.05 <0.05 0.7 <1.0 E1.6 <1.0 <0.20 7.4Maximum value 8.1 8.3 210 <0.001 .13 <.14 1.4 <1.0 7.0 <2.4 <.20 <2085th percentile value 7.8–8.1 6.4 9.1 <.001 .10 <.10 1.2 <1.0 5.9 <1.8 <.20 <20Instream standard 6.5–9.0 >6.0 200 0.02 10.0 .74 2.5 .48 50 17 .01 33

Sand Creek at the Monument Boundary—Site 2

Number of samples 5 5 5 6 6 5 5 5 6 5 5 5Percentage less than MRL n/a n/a n/a 100% 50% 100% 40% 100% 67% 100% 100% 80%Minimum value 7.3 7.9 <1 <.001 <.05 <.05 .5 <1.0 E1.5 <1.0 <.2 <1.0Maximum value 8.1 14.0 36 <.001 .08 <.14 2.1 <1.0 6.8 <2.4 <.2 <2085th percentile 7.5–8.0 8.1 1 <.001 .07 <.14 1.7 <1.0 4.8 <2.4 <.2 <20Instream standard 6.5–9.0 >6.0 200 0.02 10.0 .86 3.0 .60 50 17 .01 39

Medano Creek at the Park Boundary—Site 3

Number of samples 27 26 24 8 8 8 8 8 9 8 8 8Percentage less than MRL n/a n/a n/a 88% 75% 100% 75% 100% 0% 100% 100% 75%Minimum value 7.2 6.0 <1 <.001 <.05 <.05 .5 <1.0 6.0 <1.0 <.2 <1.0Maximum value 8.2 11.8 15 .001 .09 <.14 <1.3 <1.0 15.1 <2.4 <.2 <2085th percentile 7.5–8.0 7.1 1.2 <.001 .07 <.14 <1.3 <1.0 12.5 <2.4 <.2 <20Instream standard 6.5–9.0 >6.0 200 0.02 10.0 1.0 3.7 .79 50 17 .01 48

Buck Creek—Site 4

Number of samples 27 25 25 8 8 8 8 8 8 8 8 8Percentage less than MRL n/a n/a n/a 100% 100% 100% 88% 100% 0% 100% 100% 88%Minimum value 7.2 5.9 <1 <.001 <.05 <.05 <.5 <1.0 7.2 <1.0 <.2 <1.0Maximum value 8.2 9.0 E140 <.001 <.05 <.14 .70 <1.0 386 <2.4 <.2 <2085th percentile 7.6–7.9 7.0 1.0 <.001 <.05 <.14 <1.3 <1.0 201 <2.4 <.2 <20Instream standard 6.5–9.0 >6.0 200 0.02 10.0 2.4 9.5 2.7 50 17 .08 124

Medano Creek below Garden Creek—Site 5

Number of samples 21 19 19 7 7 6 6 6 6 6 6 6Percentage less than MRL n/a n/a n/a 100% 71% 83% 50% 100% 67% 100% 100% 83%Minimum value 7.2 5.8 21 <.001 <.05 <.05 <.5 <1.0 E1.2 <1.0 <.2 <1.0

Maximum value 8.2 10.5 16001 <.001 .08 .39 1.6 <1.0 7.0 <2.4 <.2 <2085th percentile 7.6–8.1 6.4 20.8 <.001 .08 <0.20 1.4 <1.0 5.2 <2.4 <.2 <20Instream standard 6.5–9.0 >6.0 200 0.02 10.0 1.0 3.6 .78 50 17 .01 48
PERENNIAL STREAMS—Continued

Mosca Creek—Site 6

Number of samples 27 26 25 8 8 8 8 8 8 8 8 8Percentage less than MRL n/a n/a n/a 100% 88% 100% 62% 100% 38% 100% 100% 75%Minimum value 7.7 7.2 <1 <.001 <.05 <.05 <.5 <1.0 E1.2 <1.0 <.2 <1.0Maximum value 8.2 10.5 62 <.001 .07 <.14 1.3 <1.0 3.6 <2.4 <.2 <2085th percentile 7.8–8.2 7.9 1 <.001 <.05 <.14 1.3 <1.0 3.0 <2.4 <.2 <20Instream standard 6.5–9.0 >6.0 200 0.02 10.0 1.9 7.4 2.0 50 17 .05 96

Medano Creek below Mosca Creek—Site 7

Number of samples 26 25 25 7 7 7 7 7 7 7 7 7Percentage less than MRL n/a n/a n/a 86% 86% 100% 57% 100% 14% 100% 100% 88%Minimum value 7.3 5.7 21 <.001 <.05 <.05 <.5 <1.0 E2.3 <1.0 <.2 3.3

Maximum value 8.4 9.8 2500 .001 .08 <.14 3.2 <1.0 16.3 <2.4 <.2 2085th percentile 7.8–8.1 6.8 47 <.001 <.05 <.14 1.5 <1.0 15 <2.4 <.2 <20Instream standard 6.5–9.0 >6.0 200 0.02 10.0 1.4 5.2 1.2 50 17 .02 68

EPHEMERAL STREAMS

Cold Creek—Site 8

Number of samples 2 2 0 2 2 2 2 2 2 2 2 2Percentage less than MRL n/a n/a n/a 100% 50% 100% 50% 100% 100% 100% 100% 50%Minimum value 7.9 8.8 n/a <.001 .01 <.05 E.75 <1.0 E1.6 <1.0 <.2 3.0Maximum value 7.9–8.0 9.8 n/a <.001 <.05 <.14 1.7 <1.0 <2.2 <2.4 <.2 <2085th percentile2 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a

Instream standard 6.5–9.0 >6.0 n/a 0.02 10.0 1.1 4.0 .88 50 17 .02 52

Little Medano Creek at Mouth—Site 9

Number of samples 4 4 0 4 4 4 4 4 4 4 4 4Percentage less than MRL n/a n/a n/a 100% 25% 100% 75% 100% 0% 100% 100% 50%Minimum value 7.8 7.2 n/a <.001 <.05 <.05 <1.3 <1.0 3.5 <1.0 <.2 2.3Maximum value 8.0 9.6 n/a <.001 .10 <.14 1.5 <1.0 14 <2.4 <.2 <2085th percentile 7.9–8.0 7.4 n/a <.001 .09 <.14 1.4 <1.0 13 <2.4 <.2 <12Instream standard 6.5–9.0 >6.0 n/a 0.02 10.0 1.1 3.8 .83 50 17 .01 50

Castle Creek—Site 10

Number of samples 2 2 0 2 2 2 2 2 2 2 2 2Percentage less than MRL n/a n/a n/a 100% 50% 100% 50% 100% 50% 100% 100% 50%Minimum value 8.1 7.7 n/a <.001 <.05 <.05 <1.3 <1.0 2.6 <1.0 <.2 4.6Maximum value 8.1 7.9 n/a <.001 .06 <.14 2.7 <1.0 <3.0 <2.4 <.2 <2085th percentile2 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a

Instream standard 6.5–9.0 >6.0 n/a 0.02 10.0 1.4 5.3 1.3 50 17 .03 70

 Table 1. Selected water-quality data for the Great Sand Dunes National Monument, Colorado, 1999–2000 (Continued)[mg/L, milligrams per liter (equivalent to parts per million); μg/L, micrograms per liter (equivalent to parts per billion); col/100 mL, colonies per 100 milliliters; n/a, not applicable E, estimated value; MRL, 

minimum reporting level; <, less than; >, greater than; %, percentage; Bold number, exceedance of instream standard [note: 15th and 85th percentiles used to determine exceedance of instream standard for 

pH; 15th percentile used to determine exceedance of instream standard for dissolved oxygen; geometric mean used to determine exceedance of instream standard for fecal coliform; 85th percentile used to determine exceedances of instream standards for other constituents (Colorado Department of Public Health and Environment, 2001b)]

Statistical

parameters

pH

(standard units)

Dissolved 

oxygen 

(mg/L)

Fecal 

coliform 

bacteria 

(col/100 mL 

water)

Un-ionized 

ammonia 

(mg/L)

Nitrate 

(mg/L)

Dissolved 

cadmium 

(μg/L)

Dissolved 

copper 

(μg/L)

Dissolved 

lead 

(μg/L)

Dissolved 

manganese

(μg/L)

Dissolved 

selenium 

(μg/L)

Dissolved 

silver

(μg/L)

Dissolved 

zinc

(μg/L)
EPHEMERAL STREAMS—Continued

Sawmill Canyon—Site 11

Number of samples 1 1 0 1 1 1 1 1 1 1 1 1Value 8.00 8.8 n/a <.001 <.05 <.05 2.1 <1.0 <3.0 <1.0 <.2 <2085th percentile2 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a

Instream standard 6.5–9.0 >6.0 n/a 0.02 10.0 1.4 5.4 1.3 50 17 .03 71

Garden Creek—Site 12

Number of samples 2 2 0 2 2 2 2 2 2 2 2 2Percentage less than MRL n/a n/a n/a 100% 100% 100% 50% 100% 100% 100% 100% 50%Minimum value 7.8 7.6 n/a <.001 <.05 <.05 <.67 <1.0 <3.0 <1.0 <.2 3.1Maximum value 7.8 9.0 n/a <.001 <.05 <.14 1.7 <1.0 <3.0 <2.4 <.2 <2085th percentile2 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a

Instream standard 6.5–9.0 >6.0 n/a 0.02 10.0 1.3 4.8 1.1 50 17 .02 63

SPRINGS

Mosca Spring—Site 13

Number of samples 16 15 16 3 3 3 3 3 3 3 3 3Percentage less than MRL n/a n/a n/a 100% 100% 67% 0% 100% 100% 100% 100% 100%Minimum value 7.0 6.7 <1 <.001 <.05 .07 1.3 <1.0 E1.8 <1.0 <.2 E8.0Maximum value 7.7 8.4 17 <.001 <.05 <.1 2.0 <1.0 <3.0 <1.0 <.2 <2085th percentile 7.6 7.1 1.0 <.001 <.05 <.1 1.8 <1.0 E2.7 <1.0 <.2 <20Instream standard 6.5–9.0 >6.0 200 0.02 10.0 2.1 8.3 2.3 50 17 .06 109

Morris Gulch Spring—Site 14

Number of samples 25 24 23 7 7 7 7 7 7 7 7 7Percentage less than MRL n/a n/a n/a 100% 100% 100% 100% 100% 0% 88% 100% 71%Minimum value 7.4 5.9 <1 <.001 <.05 <.05 <1.3 <1.0 5.6 1.1 <.2 4.3Maximum value 8.4 10.4 390 <.001 <.05 <.14 <1.3 <1.0 17 <2.4 <.2 <2085th percentile 8.14 7.0 1.1 <.001 <.05 <.14 <1.3 <1.0 13 <2.4 <.2 <20Instream standard 6.5–9.0 >6.0 200 0.02 10.0 2.9 12 3.6 50 17 .13 155

INTERDUNAL POND

West Elk Spring Pond—Site 15

Number of samples 7 6 0 7 7 7 7 7 7 7 7 7Percentage less than MRL n/a n/a n/a 57% 86% 100% 86% 100% 0% 86% 100% 71%Minimum value 6.9 10.2 n/a <.001 <.05 <.05 .5 <1.0 3.9 1.1 <.2 1.0Maximum value 9.5 18.9 n/a .025 .05 <.14 <1.3 <1.0 150 <2.4 <.2 <2085th percentile 8.60 10.7 n/a .007 <.05 <.14 <1.3 <1.0 116 <2.4 <.2 <20Instream standard 6.5–9.0 >6.0 n/a 0.02 10.0 1.6 6.3 1.6 50 17 .04 82

1Based on nonideal count.285th percentile value not given for samples sizes less than 3.

 Table 1. Selected water-quality data for the Great Sand Dunes National Monument, Colorado, 1999–2000 (Continued)[mg/L, milligrams per liter (equivalent to parts per million); μg/L, micrograms per liter (equivalent to parts per billion); col/100 mL, colonies per 100 milliliters; n/a, not applicable E, estimated value; MRL, 

minimum reporting level; <, less than; >, greater than; %, percentage; Bold number, exceedance of instream standard [note: 15th and 85th percentiles used to determine exceedance of instream standard for 

pH; 15th percentile used to determine exceedance of instream standard for dissolved oxygen; geometric mean used to determine exceedance of instream standard for fecal coliform; 85th percentile used to determine exceedances of instream standards for other constituents (Colorado Department of Public Health and Environment, 2001b)]

Statistical

parameters

pH

(standard units)

Dissolved 

oxygen 

(mg/L)

Fecal 

coliform 

bacteria 

(col/100 mL 

water)

Un-ionized 

ammonia 

(mg/L)

Nitrate 

(mg/L)

Dissolved 

cadmium 

(μg/L)

Dissolved 

copper 

(μg/L)

Dissolved 

lead 

(μg/L)

Dissolved 

manganese

(μg/L)

Dissolved 

selenium 

(μg/L)

Dissolved 

silver

(μg/L)

Dissolved 

zinc

(μg/L)
SITE NUMBER

FECAL COLIFORM–

GEOMETRIC MEAN,

COLONIES PER 

100 MILLILITERS 

WATER

Perennial streams

State instream standard for 

Outstanding Waters 

Designation = 200 colonies 

per 100 milliliters

1 2 3 4 5 6 7 13 14

1

50

220

100

150

200

Springs

were made using standard measurement techniques 

(Rantz and others, 1982). Water-quality and fecal 

coliform samples were collected many times from 

February 1999 through September 2000 at 15 sites on 

the Great Sand Dunes National Monument and 

Preserve (fig. 1). Samples were collected at seven sites 

located on perennial streams and five sites on ephemeral streams. In addition, two springs and one interdunal pond were sampled. Interdunal ponds are areas 

where water accumulates in depressions in the sand 

sheets. The data are published in the USGS annual 

data report (Crowfoot and others, 1999, 2000). 

Samples were collected during varied streamflow 

conditions. Measurements of instantaneous streamflow at the time of sampling ranged from less than 

0.1 cubic foot per second (ft3/s) at several of the 

smaller tributaries to 76 ft3

/s in Sand Creek. 

WATER-QUALITY CONDITIONS AND 

COMPARISON TO COLORADO 

INSTREAM STANDARDS

A water-quality standard defines the allowable 

concentration of various water-quality constituents and 

establishes the criteria necessary to maintain and 

protect water quality. Water-quality standards for some 

constituents are fixed values; standards for other 

constituents are calculated values. The calculated standards are computed using the average hardness at each 

site in an equation determined by the CDPHE Water 

Quality Control Commission. Determination of 

exceedances are made for each site using the 15th and 

85th percentiles of the data for pH, the 15th percentile 

of the data for dissolved oxygen, the geometric mean 

of the data for fecal coliform, and the 85th percentile 

of the data for other constituents. Concentrations of 

many constituents were less than the minimum 

reporting level (MRL), the smallest measured concentration of a constituent that may be reliably reported 

using a given analytical method (Timme, 1995). 

Field Measurements

Many chemical and biological reactions in 

surface water depend directly or indirectly on the pH 

and the amount of oxygen present in the water. The pH 

of water directly affects physiological functions of 

plants and animals, and it is, therefore, an important 

indicator of the health of a water system. Measurements of pH ranged from 6.9 to 9.5, and the 15th and 

85th percentile values at each site met the instream 

standard (table 1). Dissolved oxygen is necessary in 

aquatic systems for the survival and growth of many 

aquatic organisms (Wilde and others, 1998). The 

instream standard for dissolved oxygen concentrations 

is a minimum of 6 milligrams per liter (mg/L). 

Prolonged exposure to dissolved oxygen concentrations less than 6 mg/L may be harmful to aquatic biota. 

Dissolved oxygen concentrations during the study 

ranged from 5.7 to 18.9 mg/L, and the 15th percentile 

of the data at each site met the Colorado instream standard (table 1). 

Fecal Coliform

Fecal indicator bacteria are used to assess the 

quality of water, and the concentration fecal indicator 

bacteria is a measure of water safety for body-contact 

recreation or for consumption. Wastes from warmblooded animals contribute a variety of intestinal 

bacteria that are pathogenic to humans (Wilde and 

others, 1998). Water samples were collected and 

Figure 2. Geometric mean and instream standard for fecal coliform data 

for Outstanding Waters Designation. (Note: Current instream standard 

for fecal coliform is 2,000 colonies per 100 milliliters water.)
0

250

50

100

150

200

85TH PERCENTILE OF 

DISSOLVED MANGANESE

CONCENTRATIONS, IN 

MICROGRAM PER LITER

SITE NUMBER

State instream standard

for dissolved manganese 

0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

Perennial streams Ephemeral streams Springs

Interdunal

Pond

analyzed for fecal coliform bacteria from the perennial 

streams and springs approximately weekly and four to five 

times at Sand Creek at the Monument Boundary (site 2, fig. 

1) and Sand Creek at the Baca Grant (site 1, fig. 1) from 

May 1999 through the first week in September 2000. 

Bacteria data were not collected from sites on ephemeral 

streams or the interdunal pond. Exceedances of the instream 

standard for fecal coliform are determined by comparing the 

geometric mean of the data for each site to the Colorado 

instream standard. The instream standard for fecal coliform 

is 2,000 colonies per 100 milliliters (col/100 mL) of sample 

water under the current classification; however, under 

Outstanding Waters Designation, the instream standard for 

fecal coliform would be 200 col/100 mL of sample water 

(fig. 2). 

During the study period, only one fecal coliform 

bacteria sample from Medano Creek below Mosca Creek 

(site 7, fig. 1) exceeded 2,000 col/100 mL and the geometric 

mean for that site did not exceed the instream standard 

(fig. 2). Although some individual measurements of fecal 

coliform concentrations were greater than 200 col/100 mL 

of sample water, the geometric mean of the data did 

not exceed the instream standard of 200 col/100 mL. 

All of the samples that had concentrations greater than 

200 col/100 mL were collected during the summer, which is 

also the peak visitor season at the monument.

Nutrients 

Nitrogen is a nutrient that is essential for plant 

growth; however, excessive nutrient concentrations in water 

can accelerate the growth of algae and other aquatic plants. 

Also, high levels of un-ionized ammonia can be toxic to 

fish. More than 90 percent of samples analyzed for unionized ammonia had concentrations less than the MRL. 

The 85th percentile of the data did not exceed the chronic 

instream standard of 0.02 mg/L at any site. More than 

75 percent of samples analyzed for nitrate had concentrations less than the MRL. The 85th percentile of the data for 

nitrate was 0.1 mg/L or less at all sites and did not exceed 

the instream standard of 10 mg/L. 

Trace Elements

Trace elements occur naturally in water, generally at 

concentrations less than 1,000 micrograms per liter (μg/L), 

and may be derived from the weathering of rocks or 

acquired as the water moves through an aquifer or a stream 

channel. Nearly all dissolved cadmium and selenium and 

all dissolved lead and silver concentrations measured 

during the study were less than the MRL, and the 85th 

percentile values for those constituents were less than the 

MRL. Therefore, those constituents are considered to meet 

the chronic instream standards set by the CDPHE (Philip 

Hegeman, Colorado Department of Public Health and Environment, oral commun., 2001). 

More than 60 percent of the analyses for dissolved 

copper were below the MRL, and the chronic instream standard was not exceeded at any site (table 1). The chronic 

instream standard for dissolved manganese (50 μg/L) was 

exceeded by the 85th percentile of the data at Buck Creek 

(site 4, fig. 3) and West Elk Spring Pond (site 15, fig. 3). 

Dissolved manganese concentrations at Buck Creek ranged 

from 7.2 to 386 μg/L, and the 85th percentile of the data 

was 201 μg/L. Dissolved manganese concentrations at West 

Elk Spring Pond ranged from 3.9 to 150 μg/L and the 85th 

percentile of the data was 116 μg/L. These higher dissolved 

manganese concentrations may be a result of geological or 

possible oxidation-reduction processes occurring in the 

water. Most of the dissolved zinc concentrations were less 

than the MRL; the highest concentration greater than the 

reporting limit was an estimated value of 8.0 μg/L. 

Figure 3. Instream standard for Outstanding Waters Designation and 

85th percentile of dissolved manganese data.
Printed on recycled paper

SUMMARY AND SIGNIFICANT RESULTS

Concentrations of the 12 water-quality parameters for determining Outstanding Waters Designation 

did not exceed Colorado instream standards at most 

sites. The chronic instream standard for dissolved 

manganese was exceeded at two sites, and those 

exceedances likely are related to weathering of 

geologic materials or oxidation-reduction processes. 

Therefore, based on a comparison of the data collected 

during this study to instream water-quality standards 

established by the CDPHE, the existing water-quality 

criteria for determining Outstanding Waters Designation in the Great Sand Dunes National Monument and 

Preserve are being met.

• Instream standards of the 15th and 85th percentiles 

for pH and the 15th percentile for dissolved 

oxygen were not exceeded at any site during the 

study period.

• Most un-ionized ammonia concentrations were less 

than the minimum reporting level, and none 

exceeded the instream standard of 0.02 mg/L. 

• The instream standard of 10 mg/L for nitrate was 

not exceeded at any site during the study period.

• The geometric mean of fecal coliform bacteria data 

did not exceed either the current CDPHE 

instream standard of 2,000 col/100 mL water or 

the Outstanding Waters Designation instream 

standard of 200 col/100 mL water at any site. A 

few samples collected during the summer months 

had measurements greater than 200 col/100 mL, 

and may be related to stream use by monument 

visitors.

• The chronic instream standards for dissolved 

cadmium, copper, lead, silver, zinc, and selenium 

were not exceeded.

• Exceedances of the instream standard for dissolved 

manganese occurred at two sites: West Elk Spring 

Pond and Buck Creek. 

REFERENCES

Chatman, M.L., Sharrow, D., Valdez, A.D., 1997, Water 

resources management plan, Great Sand Dunes 

National Monument, Colorado: National Park Service, 

Water Resources Division, 197 p.

Colorado Department of Public Health and Environment, 

Water Quality Control Commission, 2001a, The basic 

standards and methodologies for surface water 

(5 CCR 1002–31), Regulation No. 31.

Colorado Department of Public Health and Environment, 

Water Quality Control Commission, 2001b, Classifications and numeric standards for Rio Grande Basin, 

Regulation No. 36.

Crowfoot, R.M., Unruh, J.W., Ritz, G.F., Steger, R.D., and 

O’Neill, G.B., 1999, Water resources data—Colorado, 

Water Year 1999, Volume 1: U.S. Geological Survey, 

Water-Data Report CO–99–1, 499.

Crowfoot, R.M., Unruh, J.W., Steger, R.D., and O’Neill, 

G.B., 2000, Water resources data—Colorado Water 

Year 2000, Volume 1: U.S. Geological Survey, 

Water-Data Report CO–00–1.

Rantz, S.E., and others, 1982, Measurement and computation of streamflow—v. 1, Measurement of stage and 

discharge: U.S. Geological Survey Water-Supply Paper 

2175, 284 p.

Timme, P.J., 1995, National Water Quality Laboratory 1995 

services catalog: U.S. Geological Survey Open-File 

Report 95–352, p. 92. 

Wilde, F.D., Radtke, D.B., Gibs, Jacob, and Iwatsubo, R.T., 

1998, National field manual for the collection of waterquality data: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 9, chaps. 

A1–A5.

For additional information, please contact:

Subdistrict Chief

U.S. Geological Survey

Water Resources Division

201 W. 8th Street, Suite 200

Pueblo, CO 81003

Telephone: (719) 544-7155, ext. 106

Photographs by Michael G. Rupert