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Irrigation with Reclaimed Water: Implications for Groundwater Recharge by
Rebecca Singer
Dr. Sally Brown
Why Reuse? Fresh Water Use in WA State
• 5.6 bil-gal/day
• 63% for irrigation
This decreases groundwater levels
Low Groundwater levels =
Low Stream Flows
What if…
We reuse the 200 mil-gal of wastewater
treated each day?
This may provide nutrients for irrigation
while providing groundwater recharge
In turn, improve stream flows
Determining Suitability for Recharge
Did the Soil Change the Water
OR did the water change the
soil?
Public Use
Irrigation
Thermo-electric
Industry Other
A Green House Study
Three Types of Water
1. Membrane Bioreactor
(MBR)
2. Sand Filter (SF)
3. Tap (Control)
Two Types of Soil
1. Alderwood Sandy Loam
(Forest)
2. Earlmont-Snohomish Silt
Loam (Agriculture
Source Water Characteristics
Source water influenced…
pH Agriculture soil pH=5.5
• Source water
influenced leachate pH
Forest Soil pH=3.9
•Source water
influenced leachate
pH as irrigation rate
increased
Soil influenced… Metals Source Water generally met criteria for all metals EXCEPT arsenic,
even tap water had higher As concentrations than WA State GW limit.
Ag Leachate: All leachates higher than source waters but
showed potential to decrease with time.
Forest Leachate: All leachate higher than state limit. Tap
water leachate was higher than tap source.
Soil influence As leaching for both soil types
under all water types and irrigation rates.
State Limit
Agriculture Leachate Forest Soil Leachate
Source Water n Rep50 (ng/L) %potency
Control 9 .02 +/-.03
MBR 9 0.11 +/- .05
SF 9 307 +/- 147
Regulated Metals Drinking
water MCL (EPA 2012)
Ground water Quality criteria (WAC 173-200)
Source Waters
Control MBR SF
mg L-1
Arsenic 0.01 0.00005 0.00047 0.00084 0.00110
Lead 0.015 0.05 0.00085 0.00020 0.00003
Soil also influenced…
EDCs •MBR and control source waters were similar and close to
detection limit.
•MBR and Control Leachate similar to source waters
•SF Source water had very high EDC activity
•SF Leachate significantly lowered
via filtration
Soil appears to reduce EDC
potency in water
SF EDC potency reduced 86% in Agriculture Soil. The same trend occurred in the Forest soil leachate
Three Irrigation Rates
1. 1X- 2.5cm or 250m3ha-1
2. 2X- 5.0cm or 500m3ha-1
3. 4X- 10cm or 1000m3ha-1
Each column was assigned one water
Type and on rate. Leachate was
collected within 24hrs of irrigation.
Columns were watered for 4 months.
Grass was planted after 2 months
Biomass was measured at the end
of the study for the Agriculture soil.
Nutrient
Nutrient
Limit (EPA 012) (WAC 173-
200) Source Water
Control MBR SF
mg L-1
Nitrate 10 0.041±.03 3.22±.6 5.67±3.3
*Ammonia and phosphate were low in both source water
and leachate
Nitrate: All leachates for both soils were above standards.
•Forest soil leachate NO3 decreased with increased rate
and increased over time for all rates
•Ag soil leachate lower than forest leachate but remained
above standards.
So, should we use reclaimed water
for irrigation?
Yes!
All leachate met EPA MCL for drinking water except nitrate.
Nitrate will leach under any irrigation water or rate
All leachate met WA State Ground Water Quality except
arsenic and nitrate
Both As and NO3 leached under all water types and rates
*The characteristics in the leachate waters are what
we would find under natural conditions or irrigation
with potable water
Special Thanks to King County for funding this project. To my committee members: Dr. Sally Brown, Susan Kaufman-Una and Dr. Darlene Zabowski To all those who supported and helped me through this research