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Characterization of and Temporal Changes in Groundwater Quality of the Upper Black Squirrel Creek Basin, El Paso County, Colorado, 2018–20

Scientific Investigations Report 2022-5061
Prepared in cooperation with Upper Black Squirrel Creek Ground Water Management District
By: , , and 
https://doi.org/10.3133/sir20225061

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Abstract

In 2018–20, the U.S. Geological Survey, in cooperation with Upper Black Squirrel Creek Ground Water Management District, sampled 48 wells for Phase III of a multiphase plan investigating groundwater quality in the alluvial aquifer of the Upper Black Squirrel Creek Basin (UBSB), El Paso County, Colorado. Results for samples collected from October to December each year were used to assess spatial and temporal changes in groundwater quality and to differentiate sources of nitrate. Groundwater was predominantly classified as mixed-cation and mixed-anion water type in the aquifer, with variable chemistry along the periphery. Concentrations of constituents in groundwater were generally less than regulatory standards, except for nitrate in four wells. Isotopes of nitrogen and oxygen in nitrate identified four different potential sources or processes affecting nitrate in the alluvial aquifer: naturally occurring nitrate from soils, nitrate from animal and (or) human waste, and an unknown source, along with evidence of denitrification. Pharmaceutical compounds and personal-care products were detected in seven wells, with three wells having multiple detections. Stable isotopes of water indicated variability in seasonality of recharge throughout the UBSB alluvial aquifer. Nitrate concentrations from the 1984 study and the 1996 study were compared to the more recent concentrations in the 2013 study and the 2018–20 study. The northern one-third of the UBSB alluvial aquifer had a statistically significant increase in nitrate concentration from the 2013 study to the 2018–20 study, but no change was shown from the 1984 study to the 1996 study. The opposite was found true for the southern two-thirds of the UBSB alluvial aquifer with no statistically significant difference in nitrate concentration from the 2013 study to the 2018–20 study. Analysis of temporal changes indicated an increase in median and maximum nitrate concentrations from the 2013 study to the 2018–20 study throughout the UBSB alluvial aquifer. Continued sampling of wells in the UBSB would be beneficial to better determine temporal changes in groundwater quality, characterize human effects on water quality, and understand characteristics of the alluvial aquifer pertaining to sustainability of the resource.

Suggested Citation

Kisfalusi, Z.D., Bauch, N.J., and Bern, C.R., 2022, Characterization of and temporal changes in groundwater quality of the Upper Black Squirrel Creek Basin, El Paso County, Colorado, 2018–20: U.S. Geological Survey Scientific Investigations Report 2022–5061, 43 p., https://doi.org/10.3133/sir20225061.

ISSN: 2328-0328 (online)

ISSN: 2328-031X (print)

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Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Methods
  • Groundwater Quality 2018–20
  • Temporal Changes in Groundwater Quality
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Characterization of and temporal changes in groundwater quality of the Upper Black Squirrel Creek Basin, El Paso County, Colorado, 2018–20
Series title Scientific Investigations Report
Series number 2022-5061
DOI 10.3133/sir20225061
Year Published 2022
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Colorado Water Science Center
Description viii, 43 p.
Country United States
State Colorado
County El Paso County
Online Only (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details