Abstract

Iso-GenTM technology for groundwater remediation was put into the field in January 2000 at a fuel storage terminal in San Jose, California. The objective was to evaluate the effectiveness of the technology in lowering boundary hydrocarbon contamination at the facility. The site was selected for remediation to demonstrate the effectiveness of the Iso-Gen ™ technology in low permeability carbonate-rich marine-clay formations.

Iso-Gen™ technology from H2O Technologies Limited uses electrolysis to disassociate water into hydrogen and oxygen and generate a particularly stable-in-solution form of dissolved oxygen (DO). The stable DO is available for microbes to utilize and degrade methyl tertiary-butyl ether (MTBE) and other petroleum hydrocarbons and additives. Furthermore, the Iso-Gen™ technology uses vertical recirculation mechanisms to distribute the DO laden groundwater throughout the aquifer without pumping any water to the surface.

The remediation site is large (~10 acres) consisting of bulk-storage tanks, a pipeline-terminal center, and truck-filling facilities. The principal chemical of concern (COC) is MTBE with significant concentrations of other petroleum hydrocarbons present in groundwater including benzene along with some separate phase hydrocarbons interior to the facility. COCs in groundwater originate at the central loading rack, the pipeline terminal, and at the bulk tanks and extend 800 feet downgradient in a relatively narrow plume that is approximately 150 feet wide.

The initial remedial program involved five Iso-Gen™ downhole units located laterally across the width of the MTBE affected areas in existing monitoring wells. Detailed observation points were placed at four foot centers around two of the five initial application points to evaluate the changes in reduction-oxidation potential (Redox), DO, and COCs.

Measured concentrations of DO were low prior to system startup in January 2000. Concentrations of DO were around 1 part per million (ppm). MTBE concentrations in the area of the remediation wells were in the range of 0.1 ppm to 1.0 ppm. After 11 months of operation there were large reductions in MTBE in the areas downgradient of the test wells. The piezometer array downgradient of boundary application well 19 shows an average reduction of 86% over an area 16 feet in diameter. This does not include the even greater reduction in the application well itself but is only based on the distant observation piezometer. Benzene concentrations decreased around the Iso-Gen™ remediation wells with an average decrease of 77% in the first 11 months of operation over an area 16 feet in diameter adjacent to well 19.

Further remediation and testing is being conducted with an additional array of five Iso-GenTM downhole units beginning October 2001.

INTRODUCTION TO SITE

The 10-acre site is an operating fuel terminal located in the City of San Jose, California. It consists of bulk-storage tanks, a pipeline-terminal center, and truck-filling facilities. The elevation of the site is approximately 75 feet above mean sea level. Surface topography at the site slopes gently westward. West of the site is an operating solvent recycling facility.

Seventy groundwater monitoring and groundwater extraction wells have been installed on- and off-site. The site is underlain primarily by clay and silt to depths of approximately 5 to 15 feet below ground surface (bgs). The surficial clay is underlain in places by a coarse-grained unit of poor to well graded sand, with gravels to 1-½ inches in diameter. These coarse grained deposits form channels, which trends southeast-northwest beneath the terminal and the adjacent solvent-handling facility. These shallow deposits of clay and sand channels are underlain by more uniform moderate to high plasticity clays to an approximate depth of 70 feet bgs.

Groundwater beneath the site is located at a depth ranging from approximately 15 to 20 feet bgs. The groundwater flow direction at the site appears to be west-northwest at an average gradient of 0.004 ft/ft. The hydraulic conductivity for coarse-grained channel deposits at the site, based upon previously collected pump test data, ranges from 0.11 to 0.43 feet per day. This denotes a groundwater velocity of approximately 0.65 feet/year to 2.6 feet/year. Much lower permeability deposits (i.e. marine clays) are present near well 19.

The principal chemical of concern is MTBE. A groundwater plume of dissolved MTBE originates at the central bulk tanks, loading rack, and pipeline terminal and extends approximately 800 feet downgradient in a relatively narrow plume that is approximately 150 feet wide. Previous work at the site suggests that there are multiple release points at the facility with the principal one being in the area of the pipeline terminal.

DESCRIPTION OF THE DEMONSTRATION STUDY

The Iso-Gen™ technology was applied to five existing wells at the site to test its effectiveness in controlling boundary concentrations of MTBE and other hydrocarbons in a mixed plume condition.

The Iso-Gen™ technology consists of: an Iso-Gen™ Controller with an AC voltage rectifier/transformer unit, and an Iso-Gen™ Downhole Unit consisting primarily of an electrolysis cell, circulation pump, and diffuser tube. Downhole Units were installed in wells A-3, 10, 19, E-6, and E-7 and powered off of two separate controllers.

A Downhole Unit draws groundwater in via the pump at the bottom, then the water is pumped through the electrolysis cell, through a chamber that allows oxygen to go into solution and then DO laden water is distributed back into the well through the diffuser tube. A portion of the water exits the well through the screened section, while the remaining portion re-circulates to the bottom of the well.

The Iso-GenTM units began operation on January 4, 2000. Prior to initiation of the Iso-GenTM study background groundwater data were collected from geoprobe borings in the vicinity of wells 10, 19, E-6 and E-7 in November 1999. In July 2000, two arrays of ¾-inch-diameter observation points were installed downgradient of Iso-GenTM wells E-7 and 19, five observation points near each well (e.g. 19-4, 19-8, etc., where four and eight indicate the distance in feet from well 19).

Quarterly groundwater samples were collected after July 2000 from the observation points and the Iso-Gen™ wells to monitor the concentration trends of the COCs, oxidation-reduction potential, and to evaluate in-situ dissolved oxygen.

RESULTS OF STUDY

Baseline Dissolved Oxygen (DO) concentrations in the Iso-GenTM wells and grab samples from geoprobe borings were approximately 1 to 1.5 milligrams per liter (mg/l) prior to initiation of the demonstration study. Positive effects from the electrolysis process are observed by an increase in DO concentrations in the Iso-Gen™ wells. Based on the weekly field parameters collected during the demonstration study, the DO concentrations in Iso-Gen™ wells 10, 19, A-3, E-6, and E-7 have been between approximately 5 ppm and 10 ppm during operation. DO concentrations in the ten Iso-Gen™ observation points have increased from 1 to 3 ppm above background and range up to 3.4 ppm as much as 12 feet away at observation points 19-12 and E7-12.

Baseline concentrations of MTBE in and around Iso-Gen™ wells were as high as 1,520 ppb prior to the Iso-GenTM demonstration study. Positive effects from Iso-GenTM on COCs are indicated best by the overall decrease in concentrations of TPHg, TPHd, benzene, and MTBE in the Iso-Gen™ and observation wells.
Data show an overall decrease in contaminant concentrations in each of the wells. MTBE in the observation wells within an 8-foot radius of well 19 decreased by an average of 86%. Benzene in these same wells reduced by an average of 77%.

Oxidation reduction potential for the site was not measured prior to the onset of this study. Values of ORP taken 9 months after startup to 11 months after startup show a general but small upward trend from a range of –25 to –63 mV to a range of –13 to +28 mV indicating the system/is generally reductive.

DISCUSSION OF RESULTS

Based upon the data collected during this study, the Iso-Gen™ system is capable of producing high levels of dissolved oxygen (10-15 ppm) in the Iso-Gen™ wells and appears to be capable of affecting an area 12 feet in radius in the fine grained units around well 19 and E-7.

A strong and broad general decrease in contaminant concentrations in Iso-Gen™ and Iso-Gen™ monitoring wells has been observed suggesting the Iso-Gen™ can be effective at reducing concentrations of hydrocarbons in groundwater. The Iso-GenTM system was not consistently operating from April to May 2000 or from approximately 90 to 160 days into the test due to a lack of routine inspection and pump maintenance. This corresponds with the unexpected rise in concentrations at Iso-GenTM well 19 and observation point 19-4 during this period. The system returned to continuous operation in late May 2000.

During the study, well E-7 showed a significant increase in concentrations of TPHd. This is attributed to the migration of contaminants in the vicinity of well 13 down-gradient to well E-7. It is believed that operation of a groundwater extraction system at the adjacent facility may have sped plume migration. Well E-7 continues to be monitored on a quarterly basis to determine if the Iso-Gen™ systems installed in that well is effective in reducing the dissolved TPHd concentrations in the presence of free-phase providing information on the sufficiency of the rate of oxygen application to the aquifer.

ADDITIONAL ISO-GENTM REMEDIAL STUDIES

A benchmarking study has been developed placing five additional Iso-Gen™ downhole units into an extensive array of application and monitoring wells. The new units were installed in August 2001 into wells on 20-foot centers to observe the impacts of use of solid-stem packers, the fluid recirculation dynamics, and subsequently the changes in ORP, the DO in groundwater and further COC reductions. The observation well network is on 5 to 10-foot centers and will be used to check on a variety of testing protocols including comparison to diffusive emitters for introducing gaseous oxygen to groundwater. These results are expected in 2002.

John Lambie is Executive Vice President of Environmental H2O, LLC in Milwaukie, OR; John Orolin is Head Research and Development for H2O Technologies in Milwaukie, OR; Tim Buschek is a Staff Hydrogeologist with Chevron Research and Technology Company in Richmond, CA; Rusty Benkosky is a Senior Project Manager with SECOR International Incorporated in Sacramento, CA; Bob Cochran is a Project Manager with Chevron Environmental Management Company in San Ramon, CA.
   

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