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