WSP01544

• File Number: 8170
• Description: Arkansas Basin Water Quality Issues
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 1/1/1996
• Author: Bradford Austin
• Title: Report to the Commissioner of Agriculture - Colorado Department of Agriculture - Ground Water Monitoring Activities - Arkansas River Valley Alluvial Aquifer - 1994-1995
• Water Supply Pro - Doc Type: Report/Study

0288

In addition to the inorganic constituents, all of the groundwater samples collected
were analyzed for selected pesticides. A listing of pesticides was compiled for analysis
based on those substances that have recently been, or are currently being utilized in the
Arkansas River Valley according to agricultural officials there. Budget restrictions would
not allow testing for all pesticides used in the study area. To reduce the analysis cost, each
pesticide was weighted according to its chemical properties of persistence and mobility in
the environment, amount of active ingredient used per acre, and the amount of acreage
within the study area that the pesticide was used on. Pesticides were then selected according
to their fmal score and the ability of the laboratory to detect their presence.

GROUND WATER MONITORING RESULTS

The results from this sampling program have been entered into the CDPHE
Groundwater Quality Data System, a database specifically designed and maintained by the
WQCD to store ground water quality data. Reports may be generated from the database on
ground water quality in any area of the state from all data sources available. A complete
printout of all water quality data from this survey is provided in Appendix A.

Analysis of the laboratory results indicates that ground water in portions of the study
area has been impacted by nitrates and certain pesticides. The major inorganic contaminant
of concern is nitrate. Nineteen (19) of the one hundred thirty nine (\39) wells sampled (14%)
showed nitrate levels in excess of the EPA standard for drinking water (10 mgIL) (Figure 2).
One hundred twelve (112) wells (SO%) tested positive for nitrate but were below the EPA
standard. Eight (8) wells (6%) tested below the detection level of 0.5 mgIL.

Nitrate below
detedion level
of 0.5 mglL

80%

18 10 -19.9
mg/L

1 39.1 mg/L

"

.,' ,l

14%

. ~,

Nitrate present at
0.5 - 9.9 mgIL

Nitrate exceeds
Drinking Water Standard
of 10 mgIL

Cobrado Dept. He8llh 1994

<

FIGURE 2 - Nitrate levels in Arkansas Valley wells Chart showing distribution of
nitrate levels in the Arkansas River Vallev alll\vial aquifer, 1994.

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