The science and implementation of
chemical amendment of coal seam
water as an irrigation resource
David Macfarlane & Scott Dalzell
Irrigation Australia Conference – Gold Coast
5 June 2014
GLNG CS Water Irrigation Footprint
GAS FIELD AND PIPELINE
RSGPA
Irrigation Footprint-Fairview
GAS FIELD AND PIPELINE
RSGPA
Irrigation Footprint - Roma
GAS FIELD AND PIPELINE
RSGPA
CS Water as an Irrigation Resource
• CS water salts are predominantly NaCl and
NaHCO3
• In Santos GLNG footprint this generally varies
from 2000 to 12,000 microsiemens (µS)/cm in EC
or about 1300 to 8000 mg/L salinity
• Fairview Project Area has EC median / range of
3670 µS/cm / 1900-11,000 µS/cm and SAR
median / range of 143/ 75 to 268
• Roma Shallow Gas Project Areas has EC median
/ range of 3620 µS/cm / 2180-10,000 µS/cm and
SAR median / range of 106 / 84-179.
Current & Potential Commercial CS
Water Treatment Options
• Reverse Osmosis with micro-filtration &/or ion exchange front ends
• Chemical amendment process 1: Associated Water Amendment
Facilities (AWAF) adding prescribed quantities of sulphuric acid and
micronised gypsum
• Chemical amendment process 2: AWAF treatment of raw CS
water + RO permeate blends
• Chemical amendment process 3: Land Amendment Irrigation
(LAI) involving suitable quality CS water and suitable soils and soil
surface addition of prescribed quantities of sodium bentonite
sulphur prills and agricultural gypsum
• Chemical amendment process 4: Potential to blend IX filtrate or
RO permeate with up to 8000 µS/cm CS water and utilise via LAI
Major soils and variability in an irrigation area
Treating CS water with an AWAF
• Influent water ranges from 2000-3400 µS/cm EC with SAR up to 130
• Up to 400 L/ML 98% sulphuric acid is applied to reduce bicarbonate
alkalinity from ~1000 mg/L to 200 mg/L & reduce pH from 8-9 to 5.3
• Acidified water is stored for 1-2 days and then dosed with micronised
gypsum (<35 microns) to reduce irrigation water SAR and maintain
SAR/EC balance for structurally/hydraulically stable soils
• Current AWAFs have output ECs of 3000 to 4000 µS/cm have safe
target SARs of 18-30
AWAF chemistry:
• Acid dosing: 2NaHCO3 + H2SO4 ==> Na2SO4 + 2H2O + 2CO2
• Every mole of sulphuric acid used generates 2 moles CO2
• SAR reduction using calcium only: SAR = [ Na ] / SQRT { ( [Ca]) /
2 } where concentrations are in milliequivalents per litre.
Commercial use of chemical
amendment of CS water
Santos GLNG has built 3 AWAF facilities at the Fairview field:
• AWAF1 – 10 ML/d capacity
• AWAF2 – 2 ML/d capacity
• AWAF3 – 4 ML/d capacity
Designed plant CS water amendment capacities:
Parameter
pH
Feed CS Water Amended CS water
8.5-9.2
5.8-6.7
Alkalinity (mg CaCO3/L)
700-1100
120-280
SAR
100-150
20-30
2200-2900
2700-3400
EC (µS/cm)
Plan of AWAF 1 – 10 ML/d
Micronised
gypsum silos &
batching plant
Control room &
irrigation pump
station
2 x 5 ML storage tanks
Ozonation unit
Filters &
pumps
degassing tanks
Acid
dosing
intake
Sludge
tank
AWAF Drip and Pivot Irrigation
Drip CWG planting
Drip CWG at 36 months
Planting leucaena twin rows
Drip CWG at 2 months
Drip tube laying 1 m space
Leucaena after 3 months
Drip CWG at 14 months
Drip irrigated leucaena &
Leucaena after 5 months with
AWAF drip &pivot irrigation
• 217 ha of AWAF pivot irrigation – pivots 10-50 ha
• Rhodes grass/leucaena pastures or fertilised Rhodes grass pastures
• Systems are designed to apply 6-10 ML/ha/yr over 5-6 years
• 72 ha drip irrigated Rhodes grass/leucaena drip lines 1 m apart, up to
4 ML/ha/yr over 5 yrs
• Standard baseline application of 3 t/ha gypsum prior to irrigation
• Pastures fertilised with N, P, & S
• Expected levels of production are: >4 LSU/ha (1 LSU = 400 kg steer)
producing >1000 kg beef/ha/yr
• 1075 ha Chinchilla White Gum on Springwater and 200 ha CWG on
Fairview with surface and sub-surface, 4 m tree row spacing and
expected marketable sawlog yield yr 25 of 250 m3/ha
AWAF Applied Research 2009-2011
• Investigation of United States experience of chemical amendment
• Required acid dosing for specific bicarbonate levels in treated water
• Target soil solution Na, Ca, bicarbonate requirements following irrigation
for sustainable soil condition
• Pre- and post-treatment bicarbonate dynamics in CS water
• Periodic land amendment gypsum requirements to protect against high
rainfall
• Engineering integrity limits of sulphuric acid dosing
• Gypsum solubility and CS water pH relationships and optimum dosing
rates
• Gypsum vs gypsum + Mg SO4 for SAR control in hypermagnesic soils
• Managing the hydroscopicity of micronised gypsum
• Periodic acid flushing to avoid calcium salts in drip lines and emitters
• Variability in emitter output
• TDS conversions for CS water for salinity loading calculations
LAI – US Experience
• LAI implemented in >95 irrigation projects since 1999
• Typical Powder River Basic CS water quality:
• Salinity 2500-3600 µS/cm;
• SAR 40-80;
• GPS precision spreading of gypsum and sulphur required
• overlapping S drops soil pH to 3 → strips poor lucerne
growth
• Apply 2-5 ML/ha in summer over 7-9 yr period
• For average 3 m deep clay loam soil under LAI
• SAR ranged from 6-18 and averaged 10-12;
• EC ranged from 4-5 dS/m
• Lower costs/ML treated than for RO or Ion Exchange (e.g.
Higgins Loop) water treatment systems
Land Amendment Irrigation - US
Gypsum and sulphur applied twice in 7
mth growing season with gps tractors.
8 yr old LAI lucerne - hydraulic
conductivities tested at 3 depths/6 months.
8 yr old lucerne on LAI clay loams in better
condition than adjacent river water pivots.
LAI occurs on clay loams & light clays on
slopes up to 6-8%
Requirements for commercial LAI
•
•
•
•
•
Soil hydraulic conductivity >40 mm/day
Soil depth >1.5 m and starting profile salinity <1 dS/m
CSG water applied EC <4000 µS/cm
Target crops have high yield/water use salinity thresholds
If reach trigger values (≤ 75% threshold) reached provide salinity
flushing irrigations – do not restrict water use of the crop pump
• Peripheral non-irrigated buffers of deep rooted perennial species
up to 100 m width required
• No major aquifer within 35 m below root zone and separated by
stratigraphies of 15-20% porosity
• Minimum area of 50 ha / block, up to 4 x 50 ha blocks within 2 km
of each other sufficient to attract a reliable land amendment
contractor
Good potential LAI soils
Red Kandosol
Yellow Kandosol
Tenosol
Deep A Chromosol
Reduced potential LAI soils
Dermosol
Vertosol
Shallow A horizon
Chromosol
Managing CS water with Pivot LAI
1. Regularly apply small amounts of S-bentonite on poorly buffered
soils to prevent fluctuations in soil pH
2. Induce leaching (~10-15% leaching fraction) to maintain soil rootzone salinity within acceptable limits
3. Leaching irrigation applied during winter when crop ET demand
is low likely to most effective
4. Field observations of soil hydraulic conductivity backup routine
soil chemistry monitoring
5. Continuous/periodic environmental monitoring  adaptive
management  prevents adverse impacts on soil/water
resources
LAI can be implemented on long-term, large-scale centralised, or
medium term decentralised or short-term local appraisal irrigation
projects where water quality is suitable.
Root zone impacts AWAF vs LAI
Tested Kandosols and Red Vertosols dominant soils
Would LAI leave soils in the same or better
condition than AWAF system ?
Tested 36 ML/ha of AWAF CS water of
3000-3200 µS/cm…….
Key findings:
LAI surface applied gypsum and S left
soils in better SAR condition than AWAF
Whole profile salinity of LAI was 5% higher
than for AWAF systems
Profile sodicity of LAI and AWAF soils
similar
S bacteria may take time to increase in
soils – S may need to be applied 3 times in
first year then twice / yr thereafter
Large intact soil cores at UQ
Soil impacts of LAI - after 9ML/ha LAI & 400
mm rainfall
Parameter
Kandosol- HIGH
POTENTIAL
Dermosol –
REDUCED
POTENTIAL
Water infiltration – unsaturated flow @ 9
ML/ha
40 mm/hr
15 mm/hr
Deep drainage (mm)
84
1
∆ Root Zone SAR
117.6
18.724.3
∆ Root Zone EC fc (dS/m)
0.32.83
9.215.6
∆ Root Zone pH
6.76.4
8.747.85
∆ Root Zone Ca (mM)
0.160.5
1.112.7
∆ Root Zone Mg (mM)
0.532.54
10.3728.9
∆ Root Zone S (mM)
0.184.25
1.266.51
∆ Root Zone Al (mM)
0.010.03
0.020.01
∆ Root Zone EC/100 mm rain leaching (dS/m)
-0.05
+0.4
∆ Root Zone SAR/100 mm leaching rainfall
-3.5
-2.3
Estimated ML/ha to 7 dS/m ECse threshold
35 ML/ha
15-20 ML/ha
Comparing AWAF, AWAF + extra gypsum, LAI
and local bore water irrigation systems
IR6(3) comparative trial key data
Current comparative field trial
AWAF 1 water – 2800 µS/cm,
SAR 21
AWAF 1 water + gypsum @
514 kg gypsum/ML/ha
Dam water – 300 µS/cm, SAR
<1
Raw CSG water 2900 µS/cm
and SAR 123 + 514 kg
gypsum/ML/ha & 210 kg
S/ML/ha
Irrigation started May 2013 – finished January 2014 with 7 ML/ha applied
No differences in yield observed between treatments under irrigation.
No significant differences in infiltration with 7 ML/ha – local farmers agree no
difference in surface soil condition
Recent analyses suggest 50-200 ha commercial non-central / remote field area
gathering system – storages - LAI treatment has total cost of approximately 50% cost
of contracted relocatable Reverse Osmosis treatment and waste management and
that LAI can reduce short term appraisal water CS water management to ≤ 40%
trucking cost to suitable storage.
Using broad scale soil association/land resource
maps to focus LAI soils reconnaissance
Environmental impacts-AWAF vs LAI vs ROP systems
Parameter
LAI pivot
Rhodes/leucaena
AWAF trees – drip
AWAF Rhodes/
leucaena - drip
ROP pivot
Rhodes/leucaena
1. Energy usage
low
moderate
moderate
high
2. Waste management
status at project end
All salt within top 6mbgl
All salt within top 6mbgl
All salt within top 6mbgl
CS salt within 3 mbgl +
RO brine deep injected
3. Soil structure /
SAR/EC balance
Stable all rainfall events
Stable & needing extra
gypsum -high rainfall yrs
Stable & needing extra
gypsum -high rainfall yrs
Stable & needing extra
gypsum -high rainfall yrs
5. Soil hyd.cond
80-100% baseline
> 80% baseline
80-100% baseline
> 80% baseline
6. Surface water
Nil impact expected
Nil impact over 5 yrs
Nil impact expected
Nil impact over 5 yrs
7. Ground water
Nil impact
Nil impact
Nil impact
Nil impact
8. Weed
flora/ecological
diversity
Nil weed impact under
Leucaena Code, nil
impact native veg
Nil weed impact, nil
impact native veg,
wildlife corrodors
Nil weed impact under
Leucaena Code, nil
impact native veg
Nil weed impact under
Leucaena Code, nil
impact native veg
9. Productivity –
irrigation vs dryland
X 20-25 beef
production if median
rain + 5-6 ML/ha/yr
20% increase
merchantable volume
X 20-25 beef production if
median rain + 5-6
ML/ha/yr
X25-30 beef production
if median rain + 8
ML/ha/yr
10.Productivity - postirrigation
Post-irrigation vs
baseline Rhodes
similar, if +leucaena x3
Post-irrigation vs
baseline CWG similar
Post-irrigation
Leucaena/Rhodes vs
baseline Rhodes x3
Post-irrigation
Leucaena/Rhodes vs
baseline Rhodes x3
Management of environmental
risks of chemical amendment
Environmental risks/ mitigation:
1. Fail to maintain sustainable soil chemical conditions / real time soil
monitoring and periodic soil & analysis, use proven salinity / sodicity
/water balance modelling, treat water or amend soils for
stoichiometrically correct levels of calcium and sulphuric acid entering
system for bicarbonate and SAR management
2. Increase soil salinity / regular monitoring, develop soils with low-moderate
starting salinity, adequate hydraulic conductivity, manage irrigation
practice & crop selection for target water / salt leaching fractions beyond
root-zone
3. Movement of CS water salinity beyond the irrigation environment impacting
surface water or groundwater / regular monitoring, irrigation application &
buffer management controls, sub-root zone unsaturated zone being >35
m deep of 15-20% porosity, conservative 2-D seepage modelling,
adaptive irrigation management
Total costs - centralised CS water management
Assumptions: 10 ML/d, 10 yrs operation with CAPEX written off, gathering
system cost $31 M, standard irrigation and monitoring CAPEX & OPEX /ha
Parameter
LAI + Forages
AWAF + CWG
AWAF +
Forages
ROP + brine
injection + forages
Gathering, Storage
Treatment and
monitoring CAPEX
54
73
67
100
Treatment+irrigation
+monitoring OPEX
28
27
21
100
TOTAL COST index
48
62
50
100%
TOTAL COST
INDEX less
gathering system
37
57
42
100%
Comparative process risks of LAI vs AWAF as
chemical amendment water treatment systems
Process
Risk
Sulphuric
acid/
Sbentonite
Current AWAF design
LAI
Sulphuric acid from Townsville every
20 days – higher truck
movements >safety risk
S-bentonite trucked 2-3 times per
year from Brisbane – < truck
movement safety risk & low cost
onsite storage
98% sulphuric acid (33% S @ $300/t
delivered) high hazard product –
human safety and engineering risk
to stainless steel and PVC
components
Dry storage of S-bentonite (90% S
@ $600/t delivered) which is a low
hazard product – endloader bucket
must not create sparks possible
ignition
Gypsum
Micronised gypsum @ $400/t has
flowability/hydroscopic challenges
and requires steep coned silos,
fluidised air supply for regular flow
&uniform dosing
3-6 months field requirement for
agricultural gypsum @ $180/t is
easily spread with S-bentonite.
Generally use 1-1.2 tonnes
gypsum/ML
Reliability
of input
supply
Low supply chain risk with multiple
local suppliers. If wet weather stops
acid delivery it also stops irrigation.
If Brisbane S-bentonite supply lost,
costs and delivery lead times from
Geelong or overseas would
Santos GLNG business benefits
Chemical amendment of CS water delivers the following benefits:
1. Flexibility in CS water management planning
2. Reduced water treatment costs
3. Shorter lead time to beneficial CS water use accelerates field
development
4. Least cost centralised and decentralised water treatment options for
commercial and appraisal irrigation projects for suitable water quality
5. LAI offers enhanced process safety and reliability over AWAF and ROP
+ brine injection systems based on 5.7 years Fairview experience
6. Superior environmental outcomes - best practice LAI vs best practice
AWAF and ROP irrigation system management will consistently reduce
the risk of soil structural degradation by maintaining superior soil
EC/SAR balance in surface soil