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 economics 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 for pasture irrigation and stock water. The 

landowner is pleased with the restoration 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 oil field produced brine water. It addresses 

the treatment of high volumes of water pumped to contain the migration of the brine 

plume, as well as the time and volume of production needed to effectively remediate the 

impact. 

The situation in the study area includes 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 defined within a narrow erosional channel in 

bedrock which contains clean sands and gravels, has relatively low gross saturated 

thickness and chlorides tending to be concentrated 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 percent 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 reduced 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 ion 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 operational 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 dissolved 
solids 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 and 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 operation and maintenance; 

• Can capture zones be created during the pilot 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 maintenance of EDR technology versus a 

traditional pump and dispose system for remediating the chloride plume; and 

• The time to remediate the chloride plume 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 chloride 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 chloride plume is contained in gravels of the 

aquifer. The aquifer characteristically contains 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 erosional channel. The gravels range from less 

than 10 to greater than 30 feet in thickness and yield significant quantities of water 

considering the thickness of the gravels. Vertical specific conductance testing indicates 

that the bulk of the chloride plume mass generally 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 saturated thickness of the aquifer in the study 

area ranges from approximately 12 feet in areas outside the defined erosional channel to 

approximately 36 feet within the defined erosional channel. Based on various 

publications and groundwater sampling conducted 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, and 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 membrane and anions cannot migrate through 

the cation membrane). Thus, alternating channels 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 concentration of ions in the concentrate are the 

limiting factor only to the extent that very high 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 problems associated with the need for 

continuous feed of acids or complex chemicals is minimized; and 

• The electrodes are automatically cleaned with acid formed during anodic 

operations. 

At reversal, automatically operated valves switch 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 product 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 concept of staging leads to great flexibility in 

system design with standard components. For 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 conductivity 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 semi-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 membrane stacks was utilized, and the design 

feed flow rate to the system was between 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 approximately 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 potentiometric 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 wells 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 observations. 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 Thornton 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 against 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 elevated 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 pilot 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 during 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 standards 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 drinking 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 for 
irrigation. 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 functions and to access the system to check 

performance. Because of the remote setting, there was no plant operator stationed at the 

site, and the remote monitoring capability was utilized 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 power 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 maintenance 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 established 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 EDR 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 remediation 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 solution in this project area. This conclusion 

is reached based on the reduction of chlorides noted in the pilot test area. There are two 
main 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 wells; 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 greater 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 pilot 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 encompassed 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 elevated 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 membrane 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 disposed 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 also 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-site supervision and operation and 

maintenance. During the pilot test, the EDR system remained in operation 

without supervision approximately 84% of the time. When the system failed, 

it was most commonly the result of power 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 prepared 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 maintenance of EDR technology versus a 

traditional pump and dispose system for remediating the chloride plume are 

comparable because of the relatively high 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. Map of Chloride Plume 
Figure 2. Potentiometric Map of the Aquifer 
Figure 3. Structure Contour Map Showing Base of the Aquifer 
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Figure 4. Decline in Chloride Concentrations in Four Pilot Wells 
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Figure 5. Quality of Feed Water From Four Pilot Wells 
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Figure 6. Product Water Chloride Levels 
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Figure 7. Product Water TDS Levels 
EDR Unit at Pilot Project Site 
EDR Membrane Stacks 
Typical Irrigation Sprinkler
Typical Production Well