Agricultural Soil Science and the Remediation of Oil and Brine Spills

Kerry SubletteCenter for Applied Biogeosciences

University of Tulsa

Remediation of Oil and Brine Spills

• Typical bioremediation process for oil:– Fertilizer

• Provide N and P for hydrocarbon degraders– Bulking agent

• Increase O2 and water infiltration– Tilling

• Mixing• Aeration

– Control pH and moisture to the extent possible

Remediation of Oil and Brine Spills

• Typical elements of brine spill remediation:– Drainage control

• So the salt has somewhere to go– Organic matter

• Increases permeability to water and mobilize salt

– Tilling• Mixing• Improving permeability

– Gypsum• Combat sodicity

Remediation vs. Restoration• How do we define the remediation endpoint?

– Reduction in concentration of contaminants (hydrocarbons, brine)• Regulatory limit• Risk to human health or environmental receptors• Land use

• Remediation is not restoration– Both the original spill and the remediation process disrupt soil

ecology• Disruptions in N and P cycling• Reduced diversity of soil microbes and invertebrates• Loss of vegetation

– All levels of ecosystem affected• Producers (plants)• Consumers (bugs, worms, mites, nematodes, etc.)• Decomposers (microbes)

• What constitutes restoration?– It depends

• Land use• Landowner wishes (within reason)• Restoring ecosytems

Remediation vs. Restoration• We need to start thinking about remediation and

restoration together- what should we do differently?

Remediation vs. Restoration• Who can help us with this? Who else

– works to grow something in the soil– strives to maximize yield– is careful to maintain soil fertility so that the soil remains productive?

• When we do bioremediation– our crop is a functioning

community of hydrocarbon-degrading microbes

– our “yield” is rapid and efficient removal of hydrocarbon

– next season’s crop is a restored plant communityand functioning soil ecosystem

• Lessons learned will also have application in the remediation of brine spills

Some good advice from the ag industry

• Fertilizers and salinity• Surface crusting• Soil compaction• Gypsum and soil

nutrients• Letting the weeds talk

What the ag industry knows about fertilizers and salinity

• Fertilizers increase soil salinity• Excess fertilizer application reduces yield and

increases runoff of N and P• Practical limits to amount of fertilizer added to the

soil in a single application– Soil salinity prior to fertilizing– Tolerance of the crop– Form of the fertilizer

• Rule-of-thumb for N, maximum application of 3-4 lbs/1000 ft2

Fertilizer salt index

• The fertilizer salt index is a relative measure of the salinity produced by a fertilizer in soil water– Sodium nitrate is the standard against which all

other fertilizer are compared• Salt index (SI) for NaNO3 = 100

• The partial salt index is a relative salt index per unit weight of nutrient (one unit = 20 lbs of N, P2O5, or K2O)

• The SI cannot predict amount of fertilizer that will do injury to plants (or microbes); it is for comparison of fertilizers only

Salt indices of common fertilizers

Fertilizer SI Fertilizer SIAmmonium nitrate

(33% N)104 Gypsum 8

Urea(46%)

71 Calcium nitrate (15.5% N) 65

Ammonium sulfate(21% N)

88 Monoammonium phosphate (MAP) (11% N)

26

Diammonium phosphate (DAP) (18% N)

29 Triple super phosphate(45% P2O5)

10

Muriate of potash 32

Partial salt indices of common fertilizers per unit nutrient (20 lbs of nutrient)

Fertilizer Nutrient PSI Fertilizer Nutrient PSI

Ammonium nitrate

N 3.06 Gypsum 0.25

Urea N 1.62 Calcium nitrate N 4.20

Ammonium sulfate

N 3.25 Sodium nitrate N 6.08

Diammoniumphosphate

(DAP)

P2O5 0.46 Monoammoniumphosphate

(MAP)

P2O5 0.10

Muriate of potash

K2O 1.94 Triple super phosphate

P2O5 0.22

An illustration of the problem

Soil impacted with light crude is to be bioremediated. The total TPH inventory is found to be 5600 kg and the total spill area is 12,000 ft2 (about 2% TPH). How much N should be applied for effective in situbioremediation?

• An often quoted EPA recommendation is C:N:P:K of 100:10:1:1 (weight ratio)– Predicts a N requirement of 450 kg – Equivalent to about 82 lbs/1000 ft2

– 27 times the rule-of-thumb

An illustration of the problem

• A more reasonable approach taken by most practioners has been split additions of N, like an initial C:N of 150:1 followed by monitoring– Predicts a N requirement of 5.5 lbs N/1000 ft2

which still may be too high• Lesson- be judicious in fertilizer application

and monitor soil salinity along with N, P concentrations

• Rule-of-thumb: 3- 4 lbs/1000 ft2

higher SI lower SI

What the ag industry knows about surface crusting

Effect of rain on soil infiltration and oxygen transfer

• Rain drops strike the soil surface at about 20 mph

• Soil aggregates are separated due to beating of rain drops

• Surface soil macropores fill with soil particles forming a surface crust and reducing infiltration

• Anaerobic zone produced under the surface crust

• Reduced soil infiltration also causes surface flow and erosion

Type of rainfall

Intensity(inches/hr)

Relative energy impacting the

soilDrizzle 0.001 1.0

Light rain 0.004 5.5

Moderate rain 0.15 28

Heavy rain 0.59 154

Excessive rain 1.7 1454

Cloudburst 3.9 1500

Energy transfer to soil during rainfall

What types of soils tend to form surface crusts?

• Tendency to form crusts– High silt or clay content– Low organic matter concentrations and

weak aggregates– Small aggregates more susceptible to rain

Preventing crusting

• High concentrations of decaying organic matter in the soil

• Light surface dressing or mulch of organic matter– Too much and you limit oxygen transfer

• Coordinate cultivation with rainfall events• Larger aggregates and greater surface

roughness (chisel plough for cultivation)

Choice of cultivation equipment can have a dramatic effect on surface crusting

0 10 20 30 40 50 60 70 80 90

Accumulated rainfall (mm)100 mm = 4 inches

Infiltra

tion

rat

e (m

m/h

)

0 1

0 2

0 30

40

50

60 7

0

Chisel plough

Mouldboard + diskDisk

harrow

Surface dressing of organic matter reduces erosion

What the ag industry knows about soil compaction

• Soil compaction causes– Poor aeration and

oxygen transfer– Waterlogging– Excessive runoff and

erosion– Excessive soil

strength limiting root growth during revegetation

Bulk soil density

Low Medium High

Effect of soil compaction plant roots

Soil that plant roots cannot effectively penetrate will not support significant biodegradation of hydrocarbon

The effects of soil compaction maypersist for decades

Historic bison wallow (from the 19th

century) in tallgrass prairie in Oklahoma

Field capacity

Soil-tire interface pressure for an 18.4R38 tire

Properly inflated

Excessive inflation; greater potential for compaction

Depth of soil compaction from tire loads

Radial tires perform better in terms of reducing load on soil

Preventing soil compaction

• Add organic matter• Limit vehicular traffic• Keep out livestock• Cultivate at proper soil

moisture content• Use wider tires with

minimum inflation• Distribute loads• Monitor soil impaction

with soil penetrometer

Facilitating the movement of salt in soil for brine spill remediation

• Increasing permeability to water in the spill area– Mechanical loosening of the soil– Soil amendments

• Organic matter• Gypsum

• What does gypsum do?– Improves soil structure by displacing Na+ from

clays and promoting aggregation of clay particles

– Improved soil structure results in better infiltration rates

What the ag industry knows about gypsum

• Gypsum is used in the ag industry as a source of calcium and sulfur for crops– Typical application rates 1-2 tons/acre but highly dependent on crop

• Gypsum applications for remediation of brine spills can be tens of tons/acre

• Large gypsum applications can reduce soil fertility– Increasing Ca+2 in soil solution decreases uptake of K+ and

Mg+2 by plants– Ca+2 causes release of K+ and Mg+2 from soil and loss by

leaching – effect is increased by irrigation– Sulfate reduces uptake of molybdenum– Gypsum interferes with the humification process (formation

of stable soil organic matter)– Gypsum increases immobilization of P (effect compounded if

CaCO3 present)• Applied P can induce Zn+2 deficiency by reducing Zn+2 uptake• Zn+2 application can reduce uptake of Cu+2 and Mn+2

What the ag industry knows about gypsum

• Presence of high gypsum concentrations in soil makes fertilizer additions less effective– Need management of both macro and

micronutrients in gypsum applied soils – soil and leaf analysis recommended

What the ag industry knows about biological indicators of the restorationof soil health and fertility

• During revegetation pay attention to the weeds that pop up

• The weeds that grow on your site can signal adverse growing conditions in the soil such as:– Too little water– Too much water– Low N– High N– Too much shade– Compaction– Low pH– General low fertility

Barnyard grass-

poor drainage

Birdsfoot trefoil-drought, low

nitrogen

Common chickweed-too shady

Prostrate knotweed-compaction

Conclusions

• Careful attention to bioremediation and brine remediation practices can not only increase the efficiency of the remediation process but also lead to successful restoration an impacted site– Being careful about fertilizer applications– Coordinating rain events with cultivation– Using chisel ploughs for cultivation– Incorporating lots of organic matter in the soil– Keeping livestock off the sites– Carefully monitoring soil nutrients when gypsum is used– Monitoring salinity and compaction– Topdressing with hay