This document summarizes a study evaluating passive managed aquifer recharge in the Mississippi River Valley Alluvial Aquifer of northeast Arkansas. Overpumping has caused severe groundwater declines in the aquifer. Common managed aquifer recharge methods like surface spreading and direct injection are difficult due to a confining clay layer. The study is testing infiltration galleries as a potential recharge method. Preliminary results from geophysics, sampling, and modeling indicate galleries could recharge 35-130 liters per minute. Pilot galleries will be constructed and monitored to evaluate recharge rates, water quality impacts, and feasibility of wider implementation.

1. Passive Managed Aquifer Recharge in
the Mississippi River Valley Alluvial
Aquifer of Northeast Arkansas
Soil and Water Conservation Society National Conference
30 July 2019
Ian Godwin, MS student
Arkansas State University
Michele L. Reba, PhD, PE
Delta Water Management Research Unit

2. STUDY AREA – MISSISSIPPI RIVER VALLEY
Acres of Irrigated Land in 2012 (USDA NASS) Lower Mississippi River
Basin (LMRB)
• Over 8 million acres of
irrigated cropland
• ~60% in Arkansas
• #1 rice producing state
• #3 cotton producer
• #10 soybean producer
• 8 Bgal/day groundwater
used for irrigation in AR
MRVA Aquifer

3. USGS MERAS Model
MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER
Clay
Fine
Sand
Med.
Sand
Coarse
Sand
Gravel
Clay
Surface
~40 – 50 m
PUMPING
RECHARGE

4. OVERPUMPING AND GROUNDWATER DECLINES
CACHE
RIVER
GRAND
PRAIRIE
2007 2038(Clark et al., 2011)
Projected future declines in groundwater elevation

5. WATER CONSERVATION ACTIONS
2015
Location of
Reservoirs
CACHE
GRAND
PRAIRIE
Yaeger, M.A., M.L. Reba, J.H. Massey, and M.A. Adviento-Borbe. Applied Engineering in Agriculture. 33(6): 869-878. DOI: 10.13031/aea.12352. 2017.
Yaeger, M., J.H. Massey, M.L. Reba, and M.A. Adviento-Borbe. Agricultural Water Management. 208:
373-383. DOI: 10.1016/agwat.
2018.06.040. 2018.

6. • Surface clay layer limits annual recharge
• Severe drawdown  thick unsaturated zone = storage space
• Managed aquifer recharge (MAR) – putting water back into ground
• Common MAR methods not easy in the Arkansas Delta
GROUNDWATER RECHARGE
Water SourceDrawdown
• High land value
• High sediment load in
surface water
• Confining clay layer

7. GROUNDWATER RECHARGE
Water SourceInjection Well
DIRECT INJECTION
• High treatment costs
• High energy costs for
pumping
Drawdown
• Surface clay layer limits annual recharge
• Severe drawdown  thick unsaturated zone = storage space
• Managed aquifer recharge (MAR) – putting water back into ground
• Common MAR methods not easy in the Arkansas Delta

8. GROUNDWATER RECHARGE
SURFACE SPREADING Water SourceSpreading Basin
• Land out of production
• High rate of sediment
and algal clogging
• Surface confining unit
Drawdown
• Surface clay layer limits annual recharge
• Severe drawdown  thick unsaturated zone = storage space
• Managed aquifer recharge (MAR) – putting water back into ground
• Common MAR methods not easy in the Arkansas Delta

9. • Trenches excavated to permeable material
• Filled with gravel, sand or other porous media
• Internal plumbing connected to surface source
INFILTRATION GALLERIES
Water SourceGallery
Enviro-Utilities, Inc.
Drawdown
• Completely sub-surface
• Inexpensive materials
• Design may slow clogging
• Can be used in conjunction
with reservoirs (source)

10. • Do the proper conditions exist?
• How much water can galleries recharge?
• Will water quality improve during infiltration?
INFILTRATION GALLERIES
Water SourceGallery
Enviro-Utilities, Inc.
Drawdown

11. • Ideal site: thin confining clay + permeable aquifer
• Focus on center of Cache CGA cone of depression
• Mapping using 400+ well drilling logs
• Clay thickness extremely variable (3 – 15m)
• 5 reservoirs with known water chemistry chosen
• Areas with thin clay (< 5m) do exist
DO THE PROPER CONDITIONS EXIST?
MAPPING

12. • Ideal site: thin confining clay + permeable aquifer
• Electrical resistivity surveying (ERS)
• Surveyed areas immediately around reservoirs
• Upper aquifer is high resistivity, increases
downward…coarse material?
GEOPHYSICS
DO THE PROPER CONDITIONS EXIST?

13. • Ideal site: thin confining clay + permeable aquifer
• Direct-push probe collected samples down to 8-10m
• Samples analysis: grain-size distribution, moisture,
FT-IR, ions and trace metals
• Upper aquifer is quartz-dominated silty find sand,
estimated K ≈ 1 m/d
SAMPLING
DO THE PROPER CONDITIONS EXIST?
Depth (m)

14. • Infiltration modeling with VS2D
• Designed around results of geophysics and sample
analysis
• Small galleries (15 x 1.5 m trench)
• 30 m unsaturated zone (typical)
• Unable to maintain saturated plume
• Recharge rate: 35 – 130 Lpm (average of 82)
• One season = 14.35 acre-feet  5 – 7 acres of rice
HOW MUCH CAN WE RECHARGE?
Simulation of infiltration plume

15. CAN WE IMPROVE WATER QUALITY?
• Infiltration column experiments
• Simulation of infiltration from gallery
• Testing media:
• Aquifer-like silty sand
• Gallery fill material (gravel)
• Testing parameters:
• Glyphosate and quinclorac
• Nitrate, ammonium, phosphate
• Major cation/anion, changes to CEC
• TSS, TDS, salinity, DO, temperature
• Still in progress

16. CAN WE IMPROVE WATER QUALITY?
• Gravel fill significantly reduces TSS,
TDS, and DO levels
• Upper 1.5m of aquifer sand reduces
TSS by ~85 - 90%

17. • Pilot site near Weiner, AR
• ~ 3.5m of surface clay  gallery excavated to 4.5m
• Two small parallel galleries to be constructed
• 15m long, 1.5m wide trench
SITE SELECTION AND DESIGN
Construction in Fall 2019

18. • Operated in non-production
season (Oct – Apr)
• Fully automated
Continuous water quality
monitoring:
1. Source
2. In-gallery
3. Upper aquifer (lysimeters)
4. Groundwater (monitoring
wells)
OPERATION AND MONITORING
RESERVOIR
SURFACE CLAY
MRVAA SAND
WATER TABLE
1
2
3
4
SIDE VIEW

19. • USGS MAP air-borne geophysical survey
• High resolution at depth  help to identify best places
for MAR
• Wider implementation  what would the impact be?
• Operation of pilot galleries
• Evaluation of recharge rate, clogging rate, groundwater
quality protection
• Isotope tracer study
NEXT STEPS

20. THANK YOU
The land owners and producers who have agreed to support this study
USGS, Ryan Adams and Wade Kress for helping with ERS Surveys
Shawn Brewer, P.E., Chris King, P.G., and Tim Kresse, P.G.
NRCS for funding this and other water conservations projects in the region
Cotton Inc. Core funding 13-786
The Geological Society of America for funding support
Yin-Lin “Jack” Chiu, Jonathon Delp, Geoffrey Payne, Patrick Leppold, and Cameron
Green from USDA DWMRU for assisting with field work