• Related Pages
  • Equus Beds Groundwater Recharge Project
  • Equus Beds Site Map
  • Equus Beds Groundwater Quantity
  • Equus Beds Surface-Water Quantity
  • Equus Beds Water Quality
  • Equus Beds Recharge
  • Equus Beds Publications

Equus Beds Water Quality

Water Quality - Baseline

• Baseline (before artificial recharge) sampling and during demonstration phase defined the constituents of concern (>5% of samples exceed water quality standards) for artificial recharge;
• Surface water: (Little Arkansas River site at Highway 50 near Halstead and at Sedgwick Kansas)
• Chloride, atrazine, bacteria, sodium, and maganese
• Groundwater:
• Chloride, sulfate, nitrate, arsenic, iron, manganese, and sodium
• A number of organic compounds have been detected, but no concentrations exceed water-quality standards.
• Chloride has moved about 3 miles in past 45 years
• Little Arkansas River near Halstead exceeds 250 mg/L 27% of time
• 8% of groundwater in area exceeds 250 mg/L (SDWR)-- near Burrton and along the Arkansas River
• Sulfate exceeds 250 mg/L (SDWR) in 18 percent of shallow and 13% of deep  groundwater
• Nitrate exceeds 10 mg/L (MCL)  in about 9% of shallow groundwater- little nitrate in deep groundwater
• Arsenic exceeds 10 ug/L (MCL)
• In surface water about 14% of time usually during low flow
• In shallow groundwater in 10% wells and 6% of area
• In deep groundwater in 34%  of wells and 35% of area
• Atrazine concentrations in the Little Arkansas River exceed 3 ug/L 27% (MCL – as annual average) of the time mostly in late spring through early fall.
• Atrazine is detected in 55% of shallow wells indicating infiltration from field application– none exceed MCL.
• Coliform and E. Coli are detected in all surface water samples.
• Total coliform was detected in 95% of shallow index wells and 87% of deep index wells.
• Viral indicators are detected in surface water

Concentrations and load estimates for select locations of the Little Arkansas River indicate that the sources of the loads of chloride and fecal coliform bacteria are upstream of Highway 50. The concentrations and load estimates also indicate that atrazine loads are distributed throughout the basin. For further information refer to “Regression Analysis and Real-Time Water-Quality Monitoring to Estimate Constituent Concentrations, Loads, and Yields in the Little Arkansas River, South-Central Kansas, 1995-99.” In addition, hourly estimates of concentrations and loads for these sites from 1999 to today are available at http://nrtwq.usgs.gov/ks/

Expected effects of artificial recharge

• Will increase water levels and storage in the aquifer.
• Will slow down movement of chloride.
• As water levels increase, concentrations of some metals may temporarily increase until reaches geochemical equilibria.
• Recharge of oxygenated water will decrease concentrations of metals—as long as it remains oxygenated.

Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer, South Central Kansas, 1995-2004, were defined using simple mixing, solute-transport, and theoretical geochemical models. Simple mixing and solute-transport models indicated that about 75% of the water in the diversion well at Halstead originates from the nearby stream. Geochemical modeling indicated that if fully oxygenated water is injected in the aquifer, chemical precipitation of calcite and iron oxyhydroxide are likely and may reduce the efficiency of the injection wells.

Water-quality changes  after Phase 1 recharge

• Water-quality Data Compilation for 2011
• Table 1: Inorganics, nutrients & bacteria
• Table 2: Trace elements
• Table 3: Dissolved pesticides and herbicides (Schedule 2003)
• Table 4: Dissolved pesticides (Schedule 2060)
• Table 5: Volatile organic compounds
• Table 6: Radionuclides
• Table 7: Organochlorine and organophosphate pesticides
• Table 8: Acid and base/neutral organic compounds
• Water-quality Data Compilation for 2006-2011
• Table 1: Inorganics, nutrients & bacteria
• Table 2: Trace elements
• Table 3: Dissolved pesticides and herbicides (Schedule 2003)
• Table 4: Dissolved pesticides (Schedule 2060)
• Table 5: Volatile organic compounds
• Table 6: Radionuclides
• Table 7: Organochlorine and organophosphate pesticides
• Table 8: Acid and base/neutral organic compounds
• The Equus Beds Aquifer Storage and Recovery (ASR) Project Phase I began in 2006 “to inject groundwater into the Equus Beds Aquifer for the purpose of storage and later recovery of the groundwater and to form a hydraulic barrier to a known brine plume” (Kansas Underground Injection Control Area Permit Class V Injection Well, Kansas Permit No. KS-05-079-001). The project diverts water from the Little Arkansas River through bank storage (diversion) wells, completed adjacent to the stream, when flow in the Little Arkansas River exceeds base flow (base flows can be found in the “Surface-Water Quantity” section above). The diverted water is artificially recharged into the Equus Beds aquifer through injection wells and recharge basins. The following link provides more information on the Equus Beds Aquifer Storage and Recovery (ASR) Project Phase I. Equus Beds Aquifer Storage and Recovery Project Phase 1.
• There are 37 monitoring wells associated with the Equus Beds Aquifer Storage and Recovery (ASR) Project Phase I and all were sampled during the sampling period of August 11 – 25, 2008. The following are constituents that exceeded their Maximum Contaminant Level (MCL) or Secondary Drinking Water Regulation (SDWR) followed by the number of wells in which the level was exceeded:
• Arsenic (10 micrograms per liter MCL), 3
• Iron (300 micrograms per liter SDWR), 14
• Manganese (50 micrograms per liter SDWR), 30
• Total dissolved solids (500 milligrams per liter SDWR), 4
• Sulfate (250 milligrams per liter SDWR), 1
• As of September 2009, artificially recharged water has reached the monitoring wells at RB-2, RRW3, and RRW4
• Decreasing trends in several constituents at monitoring wells closest to recharge locations
• Calcium
• Sodium
• Chloride
• Sulfate
• Dissolved Solids
• Iron
• Arsenic (only for wells of recharge basin which predominately used treated river water)
• Most notable in wells from southern part of recharge area where initial concentrations were largest
• The following link is a summary table of selected data that exceeded their respective water-quality criteria in samples collected for the Equus Beds Aquifer Storage and Recovery (ASR) Project Phase I from August 2006 through August 2008. Data summary for Project Phase I. The summary includes the water-quality criteria, number of samples collected, minimum, maximum, average, median, percentage of detected compounds, percentage of samples exceeding the water-quality criteria as well as the percentage of replicate samples exceeding the water-quality criteria for each compound.

Water-quality changes  after Phase 2 recharge

• Water-quality Data Compilation for 2011
• Table 1: Inorganics, nutrients & bacteria
• Table 2: Trace elements
• Table 3: Dissolved pesticides and herbicides (Schedule 2003)
• Table 4: Dissolved pesticides (Schedule 2060)
• Table 5: Volatile organic compounds
• Table 6: Radionuclides
• Table 7: Organochlorine and organophosphate pesticides
• Table 8: Acid and base/neutral organic compounds
• Water-quality Data Compilation for 2010-2011
• Table 1: Inorganics, nutrients & bacteria
• Table 2: Trace elements
• Table 3: Dissolved pesticides and herbicides (Schedule 2003)
• Table 4: Dissolved pesticides (Schedule 2060)
• Table 5: Volatile organic compounds
• Table 6: Radionuclides
• Table 7: Organochlorine and organophosphate pesticides
• Table 8: Acid and base/neutral organic compounds
• Average concentration before Phase 2 recharge
• Data summary for Project Phase 2

Statistical information on all sites sampled from February 1995- December 2010 as part of the Equus Beds Groundwater Recharge Project:

• Abbreviations and definitions associated with the statistical summaries
• Little Arkansas River at Highway 50 near Halstead, KS
• Little Arkansas River near Sedgwick, KS
• Diversion well site near Halstead, KS
• Halstead recharge site near Halstead, KS
• Monitoring wells near Halstead recharge site
• Sedgwick recharge site near Sedgwick, KS
• Monitoring wells near Sedgwick recharge site
• Background wells
• Areal Index Assessment Network
• Aquifer-Storage and Recovery (ASR) prototype wells
• Local well field at Wichita, KS
• Miscellaneous surface-water sites
• ASR Phase I sites surface-water sites
• ASR Phase II sites surface-water sites

Aquifer Storage and Recovery Project Phase I site maps:

• RRW-1
• RRW-2
• RRW-3
• RRW-4
• RB-1
• RB-2

All sites sampled from August 2006 - March 2010 as part of the Equus Beds Aquifer Storage and Recovery (ASR) Project Phase I:

• Table 1: Inorganics, nutrients & bacteria
• Table 2: Trace elements
• Table 3: Pesticides
• Table 4: Volatile organic compounds
• Table 5: Radionuclides
• Table 6 & 7: Acid & Base/Neutral compounds

What controls the water quality?

• Chloride- proximity to Burrton and Arkansas River and gradient
• Arsenic, iron, and manganese—presence in aquifer materials, distribution of clays, chemically reducing conditions, and areas of larger declines
• If oxygenated water is recharged into reducing aquifer, concentrations of dissolved arsenic, iron and manganese will decrease because these will precipitate from solution
• Nitrate, atrazine, bacteria, viral indicators– controlled by runoff and agricultural land use

Why is Arsenic an issue in the Equus Beds Aquifer?

1. There is an EPA Maximum contaminant level (MCL) of 10 micrograms per liter (ppb). Before 2006, the criterion was 50 ppb. Annual samples are required. If the criterion is exceed, then quarterly are required. The MCL is the annual average of the collected samples.
2. Background concentrations (before recharge) for arsenic exceeded 10 ppb in a number of wells and in the Little Arkansas River.
3. Arsenic is naturally present in the aquifer sediments.
4. Arsenic is controlled by the geochemistry of the aquifer material and the oxygen conditions in the aquifer.

Arsenic concentrations in groundwater in the United States, 2000, in micrograms per liter

http://www.epa.gov/safewater/arsenic/index.html
http://water.usgs.gov/nawqa/trace/pubs/geo_v46n11/fig3.html

BASELINE (1995-2005) Arsenic concentrations in shallow groundwater (well less than 80 feet deep)

• Arsenic concentrations exceed 10 ppb in 6% of the study area
• Arsenic concentrations  exceeding 10 ppb  are associated with low (no) oxygen, clays, and areas of water-level declines

Average arsenic concentrations in shallow wells, 1995-2005, in micrograms per liter

BASELINE (1995-2005) Arsenic concentrations in deep groundwater

• Concentrations exceed 10 ppb in 35 % of deep groundwater
• Concentrations are controlled by low (no) oxygen, more clay, and possibly thicker aquifer

Average arsenic concentrations in deep wells, 1995-2005, in micrograms per liter

Arsenic in surface water

Computed dissolved arsenic concentration in the Little Arkansas River at Highway 50 near Halstead, KS

When streamflow exceeds 57cfs, arsenic doesn’t exceed 10 ppb
Therefore, arsenic in treated surface water is not a problem for artificial recharge
From 1999-2008, Arsenic

Duration curve of dissolved arsenic in the Little Arkansas River at Highway 50 near Halstead, KS, 1999-2008

10 ppb about 15% of time

Arsenic variability is much greater than chloride variability.

General Geochemical controls for Arsenic

• Minerals important for recharge and geochemistry
• Calcite (calcium carbonate)
• Pyrite (iron sulfide) (can contain arsenic)- Sources
• Iron hydroxides (both source and sink)
• Controls
• Clays
• Oxygen (oxidation-reduction potential or Eh)
• Concentrations

Natural geochemical process of arsenic concentrations in an aquifer

• Controlled by:
• Sources–clay-rich areas have more pyrite (and arsenic)
• Oxygen(or lack of oxygen); more oxygen = less dissolved arsenic
• Infiltrating water quality and receiving aquifer quality
• What does this mean in the aquifer?
• Dewatered areas oxygenate and destabilize arsenic-containing pyrites
• Arsenic and iron are dissolved or leached
• As a result of increasing oxygen concentrations from either dewatering or the recharge of oxygenated water, amorphous iron oxides (hydroxides, oxyhydroxides) may form.
• Dissolved arsenic species can be scavenged by or sorb to the surfaces of precipitated iron oxide species, and are, therefore, removed from groundwater
• In summary, a new equilibrium is reached in the aquifer that is primarily controlled by oxygen availability

Arsenic Summary

• Before recharge, natural arsenic concentrations exceed the MCL of 10 ppb in 35% of deep groundwater, 6% of shallow groundwater, and in the Little Arkansas River 15% of the time since 1999.
• Arsenic concentrations exceeding 10 ppb are associated with low (or no) oxygen, areas with more clay in the aquifer and areas where water levels have declined and are now recovering.
• Increases in arsenic can be minimized by maintaining similar oxygen levels between the aquifer and recharge water.
• If oxygen-rich water is recharged;
• iron and calcite likely will precipitate and may coat the aquifer materials,
• arsenic concentrations in the aquifer water will decrease if oxygen is maintained,
• the overall water quality in the aquifer will improve with respect to arsenic.