# APPLICATION OF AN ELECTRO-DIALYSIS(EDR) PROCESS TO REMEDIATE A BRINEIMPACTED AQUIFER

A.Joseph Reed, ARCADIS G&M Inc. Alan J. Reed Jr., ARCADIS G&M Inc.



# ABSTRACT

ARCADIS G&M, Inc., is in the process of remediating a produced brine plume
that extends for a distance in excess of one mile from the source. The plume is located in an erosional channel carved in clays, which has been filled with sands and gravels. Although groundwater can be obtained from the aquifer throughout the area, the erosional channel contains the most permeable gravels and produces a preferential flow path for the groundwater. The brine plume has been contained in the long sinuous
erosional channel.

To remediate the site after delineation, ARCADIS designed a membrane treatment system approach with Ionics, Inc. using an electro-dialysis reversal (EDR) process. An EDR unit was leased from Ionics, and the system was tested for approximately 4 months to determine the ec onomics of operation and to evaluate the potential for remediation of the aquifer.

The pilot test proved the method to be economically and physically feasible, and a 280-gallon per minute treatment system is in the process of being built for full scale implementation. The remediated water will be of high quality, averaging approximately 500 milligrams per liter total dissolved solids. This water will be injected back into the aquifer for resource reclamation, and used fo r pasture irrigation and stock water. The landowner is pleased with the restora tion and conservation of the resource



### .

# INTRODUCTION

This paper discusses the applicability of the EDR process for the remediation of fresh groundwater impacted by the release of o il field produced brine water. It addresses the treatment of high volumes of water pumpe d to contain the migration of the brine plume, as well as the time and volume of produc tion needed to effectively remediate the impact.

The situation in the study area includ es several sources of brine releases, including brine disposal pits, injection well failure, and pipeline breaks. The resultant groundwater plume is nearly two miles long with chloride concentrations up to 8,000 milligrams per liter (mg/L). The plume is defi ned within a narrow erosional channel in
bedrock which contains clean sands and gravels, has relatively low gross saturated thickness and chlorides tending to be con centrated at the base of the aquifer.

The EDR process is an effective remedy for removal of salts from the impacted water which reclaims approximately 80 per cent of the produced water, 20 percent by volume being a wastewater stream. The fresh water from the system may be utilized for re-inject into the freshwater aquifer as recharge or for hydrologic control around the plume to help prevent unwanted migration. It can also be utilized for crop irrigation, direct discharge or sold as fresh water. Wastewater from the process can be sent to oil field disposal wells that can handle the redu ced volume or be used in oil field secondary recovery operations.



# BACKGROUND

On July 28, 2001, a pilot test was initiated in the project area to test the applicability of electro-dialysis reversal (EDR) technology for treating groundwater containing elevated levels of the chloride i on and total dissolved solids (TDS). The pilot test was concluded on December 5, 2001 with the final collection of field data to be used for evaluating the pilot test.

The main goals of the pilot test included determining the technical feasibility of using EDR technology for treating the chloride plume, and comparing the economic and environmental benefits of using EDR technology to capture, contain and remediate the effected groundwater versus a traditional pump and dispose system. An additional goal of the pilot test was to determine operationa l and design parameters for a full-scale EDR treatment unit should the technology prove to be economical.

Technical issues evaluated during the pilot test included the following:

• Can EDR technology be utilized to treat groundwater containing chloride ion concentrations up to 1,500 milligrams per liter (mg/L) and total dissolvedsolids up to 3,000 mg/L in the blended feed water to the system and produce a product water that at least meets the State of Texas secondary drinking water standards of 300 mg/L chloride a nd 1,000 mg/L TDS. The preferential goal for the product water was to meet the United States Environmental Protection Agency (USEPA) secondary drinking water standards of 250 mg/L chloride and 500 mg/L TDS;

• Can EDR technology recover at least 80 percent of the produced chloride impacted water (e.g. produce a waste stream of less than 20 percent requiring disposal). The current pump and dispose system has no treatment component, and all of the produced water is wasted through disposal;

• Is EDR technology capable of operating in a remote setting with minimum on-site supervision and op eration and maintenance;

• Can capture zones be created during the p ilot test and can the chlorides in the production wells and nearby monitor wells be reduced during the pilot test;

and

• If all of the above conditions can be met, what is an appropriate full-scale EDR system design and estimated timeframe to remediate the impacted groundwater to as close to Texas secondary drinking water standards as possible.

Economic issues evaluated during the pilot test included the following:

• The costs of operation and maintena nce of EDR technology versus a traditional pump and dispose system for remediating the chloride plume; and

• The time to remediate the chloride plum e as currently defined to as close to State of Texas secondary drinking water standards as practical for chloride
and TDS.

Environmental issues evaluated during the pilot test included the following:

• The applicability of utilizing EDR technology to restore an aquifer containing elevated levels of the chlori de ion and TDS to a useable drinking water source; and

• The ability of EDR technology to recover at least 80 percent of the produced chloride-impacted groundwater at a sufficient quality to return it to the aquifer or provide beneficial uses such as irrigation of pasture or farm land,
and stock water.

# HYDROGEOLOGY

As discussed above, a recent evaluation of the area groundwater revealed a chloride ion groundwater plume existing in the study area. Figure 1 shows the extent of the chloride plume in February 2001. The ch loride plume is contained in gravels of the aquifer. The aquifer characteristically cont ains a heterogeneous deposition of clay, silt, sand and gravel. However, in the area of this study, the aquifer contains a basal, clean, coarse gravel which does not contain clay or fine-grained material of any significance. These gravels are deposited on top of clays, in an erosional channel which trends northwest to southeast. Figure 3 is a structure contour map showing the base of the aquifer. The map shows the described erosi onal channel. The gravels range from less than 10 to greater than 30 feet in thic kness and yield significant quantities of water considering the thickness of the gravels. Ve rtical specific conductance testing indicates that the bulk of the chloride plume mass gene rally exists at the base of the gravels.

The hydraulic gradient of the aquifer in the study area generally trends in a northwest to southeast direction. Figure 2 is a potentiometric map of the aquifer in the study area in February 2001. The gross satur ated thickness of the aquifer in the study area ranges from approximately 12 feet in ar eas outside the defined erosional channel to approximately 36 feet within the defined erosional channel. Based on various publications and groundwater sampling conducte d within the study area, the background water characteristically contains less than 300 mg/L of chloride, and less than 1,000 mg/L
of TDS.

Documented sustained well yields in the study area range from approximately 10 to 80 gallons per minute (gpm), depending on well construction, gross saturated thickness, and thickness of gravel section in the aquifer. Well yields are based on pumping tests conducted in the study area, a nd current production records from a number of wells within the study area.



# PILOT PROJECT

EDR Treatment Concept

EDR is an advanced water treatment process based on electro-dialysis (ED). ED/EDR is based on the principles governing the behavior of an ionic solution when it is subject to direct current (DC) potential. In ED, alternating anion and cation permeable membranes (called anion transfer and cation transfer membranes) are placed in layers with an anode on one side of the assembly and a cathode on the other. When a current is applied to the system, water within one group of channels is “de-ionized”. Cations migrate through the cation transfer membrane towards the cathode, and the anions migrate through the anion transfer membrane towards the anode. In the adjacent channels, the membranes do not allow migration in the direction the ions are drawn (cations cannot migrate through the anion me mbrane and anions cannot migrate through the cation membrane). Thus, alternating channe ls are formed of deionized product water
and ion-rich concentrate stream.The ED stack contains two distinct flow channels, one for feed water and one for concentrate recycle. This allows concentrate to be recycled and only feed water to flow through demineralizing channels. The concentr ation of ions in the concentrate are the limiting factor only to the extent that very hi gh ion concentrations lead to precipitation which will foul membranes. Therefore, some concentrate is continuously blown down to waste and made-up with feed water.

The EDR process is a refinement of the ED process allowing continuous operation without regular chemical cleaning. In EDR, the electrical polarity and thus the demineralized and concentrate flow passages are automatically reversed 2 to 4 times every hour. The reversal process has five major effects on the operation of a membrane
stack:

• Polarization films are broken up two to four times each hour, thus preventing polarization scale;

• Freshly precipitated scale and seeds of scale are broken up and flushed to waste before they can grow or cause damage;

• Slime and similar formations on membrane surfaces are broken up by electrically reversing the direction of colloidal particle movement;

• The entire complex of practical probl ems associated with the need for continuous feed of acids or complex chemicals is minimized; and

• The electrodes are automatically clean ed with acid formed during anodic operations.

At reversal, automatically operated valves switc h the inlet and outlet streams so that the incoming feed water flows into the new demineralization compartments and the recycle concentrate stream flows into the new concentrating compartments.

The manner in which the membrane stack is arranged is called staging. The ultimate goal of staging is to increase pr oduct water purity. There are two types of staging: electrical and hydraulic. In electrical staging, another pair of electrodes is added to the system and feed water passes between more than one set of electrodes, which can be set to different currents and voltages. In hydraulic staging, water passes through a separate set of hydraulic channels. The con cept of staging leads to great flexibility in system design with standard components. Fo r example, if 75 percent demineralization is required, then sufficient stages are installed to give the required 75 percent. In systems where greater production volume is required, additional lines of treatment may be used. These lines will be connected in parallel. Generally, each line in an installation will contain the same number of hydraulic and electrical stages.

A conductivity monitor is installed in the outlet stream to open a product diversion valve arrangement that will send the product water to final storage if it meets the specified conductivity requirements. It is sent to waste via the Off Specification Product (OSP) line if the product water c onductivity exceeds the maximum allowable conductivity determined by the system product water requirements.

## EDR Pilot Test Design and Operation

The pilot test was designed to treat a representative portion of the chloride plume. Monitor wells MW-20, MW-21, MW-22 and MW -25 were selected for use as recovery wells for the pilot test, because they were located generally in the center of the chloride plume, and because they were located within the described erosional channel. Because
the bulk of the chloride mass was located at or near the base of the aquifer gravels within the erosional channel, the recovery wells for the system were completed with pumps designed to produce the groundwater at relatively low flow rates in order to maximize the production of chloride impacted groundwater while minimizing the production of fresh groundwater. Pumping tests conducted on monitor wells MW-11, MW-13, MW-19 and MW-20 indicated that these wells could safely yield between 40 and 60 gpm. Based on this information, monitor wells MW- 20 and MW-21 were designed to produce approximately 25 gpm, and monitor wells MW-22 and MW-25 were designed to produce approximately 35 gpm for a total system design flow of approximately 120 gpm to the EDR pilot test treatment facility.



### Ionics, Incorporated provided a se mi-trailer mounted Aquamite XX EDR unit rated for a product flow rate of 200 gpm at 80% recovery (approximately 250 gpm feed rate). The EDR unit contained two sets of membrane stacks, each rated at 100 gpm product flow (approximately 125 gpm feed rate at 80% recovery). For the pilot test, only one set of memb rane stacks was utilized, and the design feed flow rate to the system was be tween 120 and 125 gpm. During operation of the EDR pilot treatment facility, product water and wastewater streams were produced. The product water stream was used to irrigate approxi mately 5 acres of pastureland. The wastewater stream was discharged to a deep injection system.



## Data Collection

On July 21, 2001, groundwater levels were measured in 30 wells in the vicinity of the chloride plume to provide a baseline for fluid levels in the aquifer prior to initiation of the EDR pilot test. Figure 2 shows a pot entiometric map of the aquifer based on the July 21, 2001 fluid level measurements. Between July 23, 2001 and August 2, 2001, groundwater samples were collected from 14 we lls along a portion of the chloride plume. The samples were collected and analyzed for chloride to provide a baseline for chloride ion concentrations in the aquifer at the beginning of the EDR pilot test. On July 28, 2001 the EDR pilot test was initiated. During the course of the pilot test groundwater levels were measured bi-weekly. Groundwater samples were collected from 14 wells along a portion of the chloride plume once per month in August, September and October during the pilot test, and final samples were collected on December 4-5, 2001. In addition to the groundwater fluid level and water quality data, EDR system operational data was also collected during the pilot test. Operational data was collected using a SCADA system and verified with field observa tions. The SCADA system was utilized to remotely observe real-time operation of the system, and to log critical operational parameters. Operational data collected included the following:Production Wells MW-20, MW-21, MW-22 and MW-25 :

• Water production rate and totalized data from client supplied Haliburton meters;

• Line pressure data from client supplied Murphy switches; and

• Power consumption data from deduct meters placed by the local power company
at each well. EDR System Feed Water Parameters :

• Flow rate and totalized data for water supplied to the feed water tank using a client provided Haliburton meter;

• Feed water tank level and temperature data from client supplied instrumentation;

• Flow rate and totalized data using a T hornton Instruments meter and an Ionics supplied flow sensor;

• Temperature of the feed water supplied to the EDR system using an Ionics supplied sensor;

• Conductivity of the feed water supplied to the EDR system using standard EDR instrumentation and an Ionics-supplied sensor; and

• Line pressure for the feed water supplied to the EDR system using an Ionics supplied sensor. EDR System Product Water Parameters :

• Flow rate and totalized data using a Thornton Instruments meter and Ionicssupplied flow sensor for the treated (produced) water;

• pH of the product water using an Ionics-supplied sensor;

• Conductivity of the product water using standard EDR instrumentation and an Ionics-supplied sensor; and

• Line pressure for the product water discharged from the EDR system using an Ionics supplied sensor. EDR System Wastewater Parameters :

• Flow rate and totalized data using a client supplied Haliburton meter for wastewater pumped from the wastewater holding tank to a client water disposal tank;

• Waste tank level data from client supplied instrumentation; and

• Line pressure for the wastewater pumped from the wastewater tank to the water disposal tank. Miscellaneous EDR System Operational Parameters :

• Power consumption data from a deduct meter placed by the local power

company;

• Operating time using a cumulative hour meter;

• Stack voltage and current for each of the three membrane stacks using Ionics instrumentation;

• Stack inlet and outlet pressure using Ionics instrumentation;

• Stack power draw using Ionics instrumentation;

• Dilute flow using Ionics instrumentation;

• Brine makeup flow using Ionics instrumentation;

• Electro flow using Ionics instrumentation;

• Electrode inlet pressure using Ionics instrumentation;

• Sand filter inlet and outlet pressure using Ionics instrumentation;

• Water recovery as a ratio of the produced water flow to the feed water flow (percent); and

• Rejection / Cut as a ratio of the TDS in the produced water to the feed water (percent).

# RESULTS

The EDR pilot test was an overall success based on an evaluation of the data generated and results achieved as measured ag ainst the technical goals, economic issues
and environmental benefits established for evaluating the pilot test. The following sections provide a discussion of the technical, economic and environmental issues evaluated and results achieved during the pilot test.



## Technical Feasibility

The technical feasibility of the EDR treatment concept as applied to the remediation of groundwater containing elev ated chlorides and TDS at this site was evaluated based on four main categories: 1) hydraulic capture and reduction of chloride levels within the plume; 2) treatment of the produced groundwater to meet secondary drinking water standards; 3) reclamation of 80% of the produced water; and 4) the ability of EDR technology to operate in a remote setting.

Data indicate that the pumping of wells MW-20, MW-21, MW-22 and MW-25 created a localized water table depression in the vicinity of these wells of up to 6 feet by the end of the pilot test period in December 2001. The pumping of these wells reduced fluid levels by approximately 0.5 feet in monitor wells approximately 1,000 feet away during the pilot test. Based on this information, it is apparent that the radius of influence from the pumping of the four wells during the p ilot test captured the elevated chlorides in the section of the plume addressed by the pilot. A review of chloride levels shows a
decline in chloride concentrations in production wells MW-21, MW-22 and MW-25 of between 150 mg/L (MW-21) to over 600 mg/L (MW-22) during the pilot test (Figure 4). Figure 5 indicates the quality of feed water from the four pilot wells over the life of the pilot test.

Records from sampling events conducted dur ing the pilot test show that feed water TDS concentrations ranged from a high of 3,040 mg/L at the beginning of the pilot test to a low of 1,830 mg/L at the end of the pilot test, and feed water chloride concentrations ranged from a high of 1,350 mg/L at the beginning of the pilot test to a low of 943 mg/L at the end of the pilot test. Product water TDS levels during the pilot test ranged between 390 mg/L and 670 mg/L, and product water chloride levels ranged between 162 mg/L and 271 mg/L. These product water TDS and chloride levels meet State of Texas secondary drinking water st andards of 1,000 mg/L TDS and 300 mg/L chloride. Product water samples from many of the sampling events conducted during the pilot test indicated that USEPA secondary dr inking water standards of 500 mg/L TDS and 250 mg/L chloride were met during the pilot test (see Figures 6 and 7).

A technical goal of the pilot test was to reclaim 80% of the water produced during the pilot test. During the pilot test period, a total of approximately 18.35 million gallons of water was pumped and treated by the EDR system. Of the total volume pumped, approximately 78% (14.28 million gallons) was reclaimed and used forirrigation. During certain operational periods during the pilot test, up to 81% recovery
was observed.

The ability of the EDR system to operate in a remote setting was also evaluated during the pilot test. The system was set up with remote monitoring capability to allow for data collection of various system f unctions and to access the system to check performance. Because of the remote setting, th ere was no plant operator stationed at the site, and the remote monitoring capability was u tilized extensively to monitor the system. During the pilot test, the EDR system operated without significant adjustments on average 84% of the time. Much of the down time documented can be attributed to power spikes and failures (usually resulting from thunderstorms) that occurred during weekend periods or when staff was not available to restart the system, and when a pump failed in one of the production wells. It is anticipated that a new model unit will be more reliable, and can be programmed to restart after power failures.



## Economics

An economic evaluation was conducted at the conclusion of the pilot test period using site-specific factors including powe r costs to pump groundwater to the EDR treatment system, operate the EDR system and pump wastewater to a disposal system; disposal cost for the wastewater; chemical cost for antiscalent; EDR system maintenance costs including membrane accrual; water sampling and monitoring costs; and project management.

Another factor in the economic evaluation was the timeframe for cleanup. The cleanup time matters because operation and main tenance costs can greatly affect the total cost of the project and are dependent on the time required for completion of the project. For purposes of the economic evaluation, a five-year remediation goal was used. The five-year remediation timeframe was establis hed based on an estimate of the volume of groundwater to be pumped for remediation of the elevated chloride plume.

From the economic evaluation, for this site, it was concluded that costs for operating the EDR system were comparable to the costs for pumping groundwater directly to disposal. The major reason that ED R is comparable in cost is that the waste stream is reduced by at least 80 percent as compared with the direct disposal option, and disposal cost is significant. The use of EDR is even more economical if the cost of the
EDR unit is distributed over more than one re mediation project. The effective life of the EDR unit is about 20 to 25 years, (not including the membranes, the cost of which is included in O&M). If a project site can be remediated in less than 12 1⁄2 years, then the cost of the unit can be apportioned to additional sites, reducing the capital cost of the equipment per site.



## Environmental Benefits

It is apparent from the pilot test that pumping groundwater to capture, contain
and remediate elevated chlorides is a viable so lution in this project area. This conclusion
is reached based on the reduction of chlorides not ed in the pilot test area. There are twomain problems with producing groundwater to remediate the elevated chloride plume at this site using traditional pump-and-dispose systems: 1) the groundwater resource is wasted through injection to deep disposal we lls; and 2) the timeframe for remediation is affected by volume of water that can be pumped to disposal. Utilizing EDR technology alleviates both problems. First, the use of EDR technology allows for preservation of the natural resource by reclaiming approximately 80% of the elevated chloride water. The treated water can be re-injected into the fresh water aquifer, used for irrigation, and/or used for stock watering. In addition, a gr eater volume of water may be produced (which will reduce remediation time) and still meet disposal capacity limitations.



## Full Scale System Design Considerations

With the success of the p ilot test, the site was evaluated to determine an appropriate size unit to remediate the entire defined area chloride plume in the most economical manner. Based on the area encomp assed by the elevated chloride plume and estimated volume of groundwater required to pump for containment and remediation, a 280 gpm (feed rate) EDR unit was recommended for design. Using the 280 gpm design rate, it was estimated that remediation of the elev ated chloride areas to as close to state of Texas secondary drinking water standards for chloride and TDS as practical may require approximately 3 to 5 years.

Approximately 13 production wells (producing between 10 and 35 gallons per minute each) are planned for the remediation system. The EDR treatment plant is designed to allow for two 140-gpm sets of memb rane stacks that can be isolated. By isolating the stacks, the feed water volume can be reduced as certain areas of the site are remediated, and less water is required to be produced. Also, as the site is remediated, certain wells may be put on a pulse cycle to allow for flushing of residual chlorides remaining in the dewatered portion of the aquifer.

The EDR treatment system is designed to treat the produced groundwater to at least State of Texas secondary drinking water standards. The wastewater from the treatment process will continue to be dispo sed through deep injection. The product water from the treatment process will be used for approximately eight months out of each calendar year to irrigate approximately 30 acres of land seeded with range grass. During the remaining four months, it is planned to inject the water into three injection wells completed in the aquifer.



# CONCLUSIONS

In summary, the EDR pilot test conducted at the project site was a success as evaluated against the following criteria:

• EDR technology can be utilized to treat groundwater containing chloride ion levels up to 1,500 mg/L and TDS up to 3,000 mg/L and produce a product
water that at least meets the State of Texas secondary drinking water standard of 300 mg/L chloride and 1,000 mg/L TDS. Depending on the circumstances, the technology may al so allow treatment meeting USEPA secondary drinking water standard of 250 mg/L chloride and 500 mg/L TDS.• During the pilot test, the EDR system recovered approximately 78% of the water delivered to the treatment plant. It is anticipated that at least 80% of water can be recovered with a new model system.

• EDR treatment plants are robust systems that are capable of operating in a remote setting with minimum on-s ite supervision and operation and maintenance. During the pilot test, the EDR system remained in operation without supervision approxima tely 84% of the time. When the system failed, it was most commonly the result of powe r failures or surges that shut the system down. A new model system can be programmed to restart after such power interruptions.

• The pilot test proved that low flow groundwater produced from a number of wells in the elevated chloride plume was effective in capturing and containing the plume. In addition, three of the production wells showed significant reduction in chloride levels during the pilot test.

• A full-scale EDR system design was prep ared from the pilot test data and based on a 3 to 5-year estimated timeframe for remediation of the elevated chloride plume to as close to Texas secondary drinking water standards as practical.

• The costs of operation and maintena nce of EDR technology versus a traditional pump and dispose system for remediating the chloride plume are comparable because of the relatively hi gh costs for disposal of produced groundwater containing elevated chlorides.

• Based on the successful pilot test, a new 280 gpm EDR system will be designed and installed to complete the remediation at the subject site.Figure 1. M a p of Chlorid e PlumeFigure 2. Potentiom e tri c Map of the AquiferFigure 3. Structure Contour Map Show ing Base of the Aquifer0 20 0 40 0 60 0 80 0 10 00 12 00 14 00 16 00 18 00

J u l

- 0 1 A u g

- 01 S e p

- 01 O c t

- 01 N o v

- 01 D e c

- 01 J a n-0 2



### S a m p le D a t eChloride Levels (mg/L)

MW

- 2 0

MW

- 2 1

MW

- 2 2

MW

- 2 5

Figure 4. Decline in Chlor i de Concentrations in F our Pilot Wells0 500 1000 1500 2000 2500 3000 3500

J u l- 01 Aug- 01 Sep- 01 O c t- 01 Nov- 01 Dec

- 01 J an- 02 

### Sa m p le D a teSample Levels (mg/L)

Chlor i des

TD S

Figure 5. Qualit y of Feed Water Fro m Four Pilot Wells0 50 10 0 15 0 20 0 25 0 30 0

Ju l

- 0 1 A u g-01 S e p-01 Oc t-01 N o v-01 D e c-01 Ja n-02



### S a mp le D a teChloride Levels (mg/L)

ED R Pr od uc t ( + )

ED R Pr od uc t (

- )

Figure 6. Pr oduct Water Chloride Lev e ls0 10 0 20 0 30 0 40 0 50 0 60 0 70 0 80 0

J u l

- 01 A u g- 0 1 S e p

- 01 O c t

- 01 No v

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Sa mp le D a t eTDS Levels (mg/L)

E D R P r od uc t ( + )

E D R P r od uc t (

- )

Figure 7. Pr oduct Water TDS LevelsEDR Unit at Pilot Project SiteEDR Me m b r a ne StacksTypical Irrigation SprinklerTypical Prod uction Well