Electrokinetic Based Soil Desalinization System AchievesDesalinization System Achieves

Closure at a Brine Contaminated Site

Christopher J. Athmer, P.E. Terran Corporation

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Environmental Issues for B i S illBrine Spills

• Chloride and Sodium do not breakChloride and Sodium do not break down any further… Must be removed or dilutedor diluted.

• Sodium exchanges with calcium in the soil leaving the land barrensoil leaving the land barren.

• Chloride percolates to the water table i h i i iwith precipitation.

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Electrokinetic Remediation ?Electrokinetic Remediation ?

• Application of direct current (DC) electricityApplication of direct current (DC) electricity to the soil

P l i d l t d i k t f• Polarized electrodes invoke movement of pore water and ions contained in the pore water even in low permeability soilswater, even in low permeability soils

• Effective in saturated and unsaturated soils

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ElectrokineticsElectrokinetics• Electroosmosis – Movement of pore water

and contaminants toward the cathodeand contaminants toward the cathode

Electromigration Migration of ionic• Electromigration – Migration of ionic species toward respective electrodes (anions toward anode cations toward cathode) bytoward anode, cations toward cathode) by electrical attraction

• Transport rates proportional to voltage gradient

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Principles of ElectrokineticsElectroosmosis = Water Transport from anode to cathodeElectromigration = Ion Transport to the opposite electrode

Soil ParticleSoil Particle

A d

- - - - - -

-+Soil Particle

--

++ + + ++ + +-

- ++ + WaterAnode

-- -----

Cathode

S il P ti l-

+ ++++ +++- - - -++ Velocity

Profile

Soil ParticleSoil Particle

Soil Particle

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Electrokinetic ApplicationsElectrokinetic Applications• Environmental Remediation

– Heavy Metals (lead, chrome)

– Organic Solvents (with in-situ ZVI)

Oth ( i it t ISCO bi d t )– Others (arsenic, nitrate, ISCO, bio-amendments)

• Dewatering/Stabilization

• Desalinization

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EK Desalinization Application

B i

Electromigration

Brine

+ -

Electroosmosis

Na+Cl- Salt inSolution

Rate of ion migration (electromigration) is proportional to voltage gradient and ionic mobility plus electroosmosis flow and anyAnode + Cathode -mobility plus electroosmosis flow and any bulk convectional flow.

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Cost Effective DesignCost Effective Design

• Readily available equipment and parts (lowest costs)y q p p ( )

• Electrodes are installed like miniature wells

– Slotted 1” PVC well screen (24 cathodes, 69 anodes)

DSA i i i l d– DSA wire wrapping as primary electrode

– Backfill annulus with cathodic backfill material (example-Loresco SWS®)p

– Installed with hydraulic push (Geoprobe®) or small drill rig

• Extraction (siphon) equipment is multi head peristaltic• Extraction (siphon) equipment is multi-head peristaltic pumps operated on timers – extremely low flow.

• Passive as possible operation

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EK Desalinization ProcessEK Desalinization Process480 Volt

AC Line Feed

Brine ToteMulti-head Peristaltic

Brine Discharge Pump

Siphon tubes

Anode buss feed

Cathode buss feed(DC)

+-

Pumps

Rectifier

Na+ Electrodes arranged

Cl-

Pore Water

in hexagonal grid

Anode(multiple)

Cathode(multiple)

Pore Water

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Demonstration Site Description:Prairie pothole region in North DakotaSaturated clay/silt (10-8) high organic, Fe, Mn, Mg, SO4

~500 bbl process water release from pipeline leakEnvironmentally sensitive areaEnvironmentally sensitive areaElevated chloride to 10 feet deepEK Desalinization utilized as mass removal option

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First action was to isolate the small slough from larger, begin pumping g g , g p p gaffected water from the small slough, and excavate contaminated soil around release point and above the sloughrelease point and above the slough.

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What a muck hole !(effectively a swamp bottom)

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Site Layout

7

1

19

13

8

3

2

16

10

4

22

20

14

15

9

23

21

24

Tra

iler

Tra

iler

17

16

11

12

5

4

18 6

Highest area of salt contamination was treated with an array of 24 hexagonal units

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Area was covered with geofabric, g ,geogrid, and cover rock to confine the contaminated soil and create a firm working surface Surface materialsworking surface. Surface materials were removed at completion. TERRAN

Installation was accomplishedInstallation was accomplished using a Geoprobe rig

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Installing the EK systemInstalling the EK system

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Site after completed installation

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Operations To DateOperations To Date

System began operations June 2 2016System began operations June 2, 2016System shut down for winter October 13, 2016

Restarted May 11, 2017Shut down for winter October 2, 2017

Restarted May 4, 2018Shut down for winter September 29, 2018

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Site Overall Electrical ConductanceBased on Rectifier Output

35

40

25

30

moh

s)

Conductance should decrease as salt ions are removed from the soil.

As chloride and sodium are removed, the soil conductivity should decline

20

m C

on

du

ctan

ce (

m

10

15

Syst

em

0

5

005/14/16 08/13/16 11/12/16 02/11/17 05/14/17 08/13/17 11/12/17 02/11/18 05/14/18 08/13/18 11/12/18

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Site Current Mapping

Current measurements were made at each electrode during operations help identify bad electrodes and general operating uniformity. (Readout is amps/100)

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Soil Sampling Locations

Matched samples collectedMatched samples collected before and during operations (6 locations, 2 depths, n=12)

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Operations Summary

– First summer (2016) operations went well: Removal after 1st summer was 41%.

– Poor electrode operations during second summer contributed to lower rates July 2017 interim samplescontributed to lower rates. July 2017 interim samples showed 47% removal. Conductance and EM surveys confirmed reductions.

– Results for November 2017 sampling indicated a regress to only 25% removal ????.

• 2017 was a dry year and water was brought in to• 2017 was a dry year and water was brought in to hydrate the electrodes and a reverse-pulse was attempted.

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Operations Summary

– For the 3rd summer (2018), the electrode conductors were l d d ti t h threplaced and operations went much smoother.

• November 2018 results show an overall 68% removal –very close to the target of 70-80%.

• Site Closure was granted by the North Dakota Department of Health.

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Chloride Soil Data

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Lessons LearnedLessons Learned• Improved electrode connections

• Low levels of chlorine gas generated at anode (expected)

h l d• Choose materials and pump equipment wisely (better grade pump tubing)

N d d i llh d• Needed to upsize wellhead generator to handle jack pump and rectifier

Water addition at anodes ma be necessar• Water addition at anodes may be necessary during dry periods

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ConclusionsConclusions

• EK desalinization worked at the demonstration site.

• Site closure from ND Dept of Health!

• If it works at the Connie site, it can work at most any site.

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Many Thanks!Many Thanks!

• To Oasis Petroleum for believing in this process g pand allowing the trial at this site

• To US Fish and Wildlife Service and the North Dakota Dept of Health for guidance and support

• Habitat Management; American Engineering and Testing; Vertex; Stealth Energy Group; and OneCor for site support

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