Groundwater Cleanup Activity Overview


Table of Contents


The California Department of Toxic Substances Control (DTSC)The department within the California Environmental Protection Agency in charge of the regulation of hazardous waste from generation to final disposal. DTSC oversees the investigation and cleanup of hazardous waste sites. and the U.S. Department of the Interior (DOI)The United States department charged with conservation and development of natural resources. The U.S. Department of the Interior uses sound science to manage and sustain America’s lands, water, wildlife, and energy resources, honors our nation’s responsibilities to tribal nations, and advocates for America’s island communities. are the lead governmental agencies responsible for the environmental investigation and cleanup of the Topock Project Site (Site). These agencies oversee the Pacific Gas and Electric Company’s (PG&E's) actions to protect the Colorado River and to clean up soil and groundwaterWater beneath the Earth’s surface that flows through soil and rock openings (aquifers). contamination in the vicinity of the PG&E Topock Compressor Station (Station). Environmental investigation and groundwater monitoring have been under way at the Site since 1997. The plumeA body of contaminated groundwater. The movement of a groundwater plume can be influenced by such factors as local groundwater flow patterns, the character of the aquifer in which the groundwater is contained, and the density of contaminants. of affected groundwater (containing mainly hexavalent chromiumHexavalent chromium is a form of chromium. Chromium is a metal naturally found in rocks, soil, and the tissue of plants and animals. Hexavalent chromium can be found naturally at low concentrations, but it is also used in industrial products and processes and is a known carcinogen. On May 28, 2014, the California Department of Public Health adopted a new California drinking water standard at 10 parts per billion for hexavalent chromium.) lies beneath federally owned lands, and lands owned by PG&E, BNSF Railroad, and the Fort Mojave Indian Tribe. To view the current groundwater monitoring locations, click on the map below. To view the most recent plume maps based on quarterly groundwater data, visit the Resource Conservation Recovery Act (RCRA) Facility Investigation/Remedial Investigation (RFI/RI) page or the Groundwater and Surface Monitoring page.


Map of Topock Compressor Station and surrounding area and composite plume

(Click on image above for larger view)

Resource Conservation and Recovery Act Facility Investigation/Remedial Investigation

PG&E has submitted three volumes of the Resource Conservation and Recovery Act Facility Investigation/Remedial Investigation (RFI/RIAn investigation that occurs in the corrective action process following a Facility Assessment under RCRA and/or a Site Inspection under CERCLA. It is an in-depth study designed to gather data needed to determine the nature and extent of contamination at a site.) report for the Site. These studies include Volume 1 for site background and history, and Volume 2 for groundwater, surface water, hydrogeological characterization, river-sediment, and pore water. Volume 1 was completed in August 2007. A revised final Addendum to Volume 1 was completed on May 30, 2014. The RFI/RI Volume 2 - Hydrogeologic Characterization and Results of Groundwater and Surface Water Investigation was completed in February 2009. DTSC and DOI both approved the report in February 2009. An Addendum to the RFI/RI Volume 2 Report was completed in June 2009 and was approved by both DTSC and DOI in June 2009. PG&E has also submitted a draft of the third volume of the RFI/RI Report on the soil investigation. Please refer to the investigation page for additional discussion on the RFI/RI Reports Volume 3.

Human and Ecological Risk Assessment for Groundwater Contamination

In December 2008, DTSC and DOI approved the Revised Risk Assessment Work Plan (RAWP) for the Site. In 2009, PG&E prepared the first addendum to the RAWP, and the addendum was approved in December 2009.

In November 2009, PG&E completed a Human and Ecological Risk Assessment of Groundwater report at the Site. This study used standard models and assumptions to estimate potential risks associated with the known groundwater plume contamination. The result of the Risk Assessment defined and recommended cleanup goals for the Site. The Final Groundwater Risk Assessment was approved by the agencies in December 2009.

Corrective Measure Study/Feasibility Study

A Corrective Measures Study/Feasibility Study (CMS/FS) Report for contamination in groundwater was prepared by PG&E to address groundwater contamination associated with past releases from the Station to the Bat Cave Wash (designated as Solid Waste Management Unit [SWMU] 1/Area of Concern [AOC] 1), previous injection well PGE 8 (designated as SWMU 2), and the East Ravine (designated as AOC 10). The report identified and evaluated cleanup options (or remedial alternatives) for the groundwater contamination and recommended a cleanup approach.

The Final CMS/FS Report for groundwater was approved by the agencies (DTSC and DOI) in December 2009.

PG&E will prepare another Corrective Measure Study/ Feasibility Study (CMS/FS) for soil contamination after the completion of the Soil RFI/RI volume 3 report of the soil investigation.

In Situ Pilot Tests

PG&E conducted both a floodplain reductive zone in situ pilot test (ISPT), as well as an upland reductive zone ISPT for groundwater contamination. The purpose of these ISPTs was to evaluate the efficacy of using food-grade reagent mixture to remove hexavalent chromium from groundwater using chemical reduction Typical chemical reduction/oxidation process (sometimes referred to as Redox) reactions chemically convert hazardous contaminants to nonhazardous or less toxic compounds that are more stable, less mobile, and/or inert. Redox reactions involve the transfer of electrons from one compound to another. Specifically, one reactant is oxidized (loses electrons) and one is reduced (gains electrons).to form stable, insoluble trivalent chromium.

The floodplain tests and monitoring began in May 2006, with monitoring completed in June 2014. The upland tests began in March 2008, with monitoring completed in June 2014. Post-test monitoring of the wells in the floodplain ISPT demonstrated that hexavalent chromium continued to be reduced in the contaminated groundwater test areas. All post-test monitoring was completed in June 2014.

Groundwater Remedy Selection

Before a final remedy was selected based on the groundwater CMS/FS report, DTSC evaluated the potential environmental impacts of the remedial alternatives and the proposed remedy in a draft Environmental Impact Report (EIR) pursuant to the California Environmental Quality Act (CEQA). In addition to the draft EIR, DTSC also prepared a draft Statement of Basis A document which describes the basis for DTSC's proposed remedy and cleanup standards.that concurred with PG&E’s recommended alternative as the preferred remedy and explained the rationale for the selection. Based on the feedback received, DTSC adopted the proposed remedy and certified a Final EIR, and its mitigation measures, on January 31, 2011.

DOI underwent a parallel process for groundwater remedy selection. DOI prepared a Proposed Plan that identified the preferred alternative selected by DOI and explained the rationale for the selection. DOI finalized the Groundwater Record of Decision in December 2010.

Based on the evaluations conducted in the CMS/FS report, the potential impacts assessment of the EIR, and input from stakeholders, DTSC and DOI concurred with PG&E on the use of in-situ treatment with fresh water flushing as the final remedy The final cleanup action proposed for managing contaminants at a project site.for the groundwater contamination associated with SWMU 1/AOC 1 and AOC 10.

In May 2015, DTSC determined that the preparation of a Subsequent EIR (SEIR) is required to evaluate potential environmental impacts resulting from design details of the selected groundwater remedy (In situ TreatmentTreatment of contamination in place. with Freshwater FlushingMoving of fresh water through the well system to push the plume through an In-Situ Reduction Zone located along National Trails Highway.) that were added or modified since the approval of the conceptual Groundwater Remediation Project in the 2011 Final Groundwater Remedy EIR and the 2013 Addendum to the EIR. DTSC issued a Notice of Preparation announcing this decision. The public comment period began on May 5 and ended on June 4, 2015. In addition, DTSC held public meetings on May 19 and 20, 2015, where the local agencies, members of the public, and Native American Tribes learned more about the Project and provided comments to help scope the environmental issues to be addressed in the Draft Subsequent EIR for the groundwater remedy. All comments received were considered in the preparation of the Draft SEIR. On January 12, 2017, DTSC posted a notice of availability of the draft SEIR, a 47-day public comment period, and two open houses/public hearings on the Draft SEIR. Comments received during the January 12, 2017 through February 27, 2017 comment period were responded to and incorporated into the Final Subsequent EIR for the Groundwater Remedy, which was certified on April 24, 2018. 

Corrective Measure/Remedial Design

Design and implementation of the selected groundwater remedy of in-situ treatment with fresh water flushing includes design and construction of the remedy, followed by operations, maintenance, and monitoring to assure the remedy is performing as designed. To guide that process, PG&E prepared the Groundwater Corrective Measures Implementation/Remedial Design (CMI/RD) Work Plan for SWMU 1/AOC 1 and AOC 10, including a sequence of steps and submittals to design and implement the remedy. With extensive stakeholder, Tribal, and agency coordination, the design was developed over time in increasing levels of detail from a 30% preliminary design to a 60% intermediate design and onto a 90% pre-final and 100% final stages of review and approvals. That sequence began with PG&E preparing the Basis of Design/Preliminary (30%) Design for submittal on November 18, 2011. On April 5, 2013, PG&E submitted the Basis of Design Report/Intermediate (60%) Design to DOI and DTSC. The Intermediate (60%) Design Report included comments received on the 30% design and presented a design that has a higher (60%) level of detail.

The final remedy requires a supply of freshwater. On January 28, 2013, PG&E submitted a Final Implementation Plan for Evaluation of Alternative Freshwater Sources in the Topock Remediation Project Area, which incorporated comments from regulatory agencies, Tribal Nations, and stakeholders. On September 4, 2013, DTSC and DOI approved the Final Implementation Plan for the freshwater sources, and field work began on October 2, 2013. A Summary of Findings associated with the Evaluation of Alternative Freshwater Sources in the Topock Remediation Project Area was completed mid-July 2014. An addendum to the above-mentioned report was included as an appendix in the Pre-Final 90% Design that was submitted on September 8, 2014. Comments received on the 90% Design were reviewed and considered, and agency responses to the comments were attached to the Final (100%) Design documents.

The Final (100%) Design for the groundwater remedy was submitted on November 18, 2015. An errata was submitted on November 18, 2016 and an addendum to the flow and solute transport model was submitted on January 9, 2017. DOI conditionally approved the Final (100%) Design on April 3, 2018 and DTSC conditionally approved it on April 24, 2018.

Groundwater Remedy

Simplified for illustration purposes, the map below shows a bird’s eye view of the groundwater remedy and its major components. Those components include the in-situ reactive zone (IRZ) along National Trails Highway; the extraction wells along the river and in the East Ravine; the upland recirculation injection wells for water that is extracted, amended with carbon, and reinjected at the IRZ; and the fresh water injection wells that will help push the plume toward and through the IRZ. Not shown on this map is some of the other supporting infrastructure and the extensive network of monitoring wells that are used to constantly monitor the plume and effectiveness of the remedy.

Map showing the monitoring locations at the site and sampling frequency

In-situ or “in place” treatment is an effective method to clean-up environmental contamination without first removing the contaminant out of its existing location. PG&E will use this in-situ method to safely remove the hexavalent chromium from groundwater while maintaining the water as a regional resource. The illustration below zooms into the microscopic space between soil particles to show what happens during the approved in-situ treatment. The selected remedy involves both a biological and chemical process which begins by injecting a food source, or “reagent” into the affected groundwater to stimulate the growth of naturally occurring bacteria within the soil. The food source currently being used at the site is an alcohol, but could also be provided as sugars or oils. The biological activity of the bacteria creates conditions that convert hexavalent chromium to trivalent chromium, a naturally abundant substance. Once converted, trivalent chromium leaves the groundwater and becomes part of the surrounding soil. Although the converted trivalent chromium will not likely revert back to hexavalent chromium, the changes in subsurface conditions that convert the hexavalent chromium to trivalent are temporary and will return to baseline conditions after the injections of reagent end.

Illustration showing a zoomed in view of the microscopic space between soil particles to show what happens during the approved in-situ treatment

For the freshwater flushing component of the groundwater remedy, injection wells located around the hexavalent chromium groundwater plume will pump freshwater into the ground. The freshwater will push the contaminated groundwater through the IRZ for treatment. Below is an illustration of how the groundwater plume is pushed through the IRZ. Fresh water for flushing will be supplied from wells in Arizona.

Illustration of how the groundwater plume is pushed through the IRZ

Corrective Measure/Remedial Action Implementation

In November 2015, PG&E submitted the Construction/Remedial Action Workplan (C/RAWP) in conjunction with the Final (100%) Design. The C/RAWP provided a roadmap to guide implementation of the approved Final (100%) Design.

Because of the extensive footprint of remedial components and the critical need to monitor and protect sensitive biological and cultural resources during all aspects of construction, implementation of the Final (100%) Design is proceeding in two phases. Phase 1 began in October 2018 and focuses on establishing the in situ reactive zone (IRZ) along National Trails Highway (NTH), including installation of pipelines, electrical systems, control systems, process management tanks and buildings, and numerous injection, extraction, and monitoring wells. Specifically, Phase 1 infrastructure included construction of 42 remediation wells (for injection and/or extraction) and 74 monitoring wells for measuring water levels and quality, as well as a network of over 68,000 linear feet of water conveyance piping and over 46,000 feet of electrical conduits that connect the remediation wells to the power supply system, the carbon amendment building, and the produce water conditioning system.

With concurrence from DTSC and DOI, operation of the NTH IRZ began on December 22, 2021. As required with the startup and operation of the NTH IRZ, the Interim Measure 3 (IM-3) groundwater extraction and treatment system ceased operations and is in layup mode to eventually be decommissioned. IM-3 had operated continuously and successfully since 2005 as an interim measure until a final remedy could be determined, designed, and implemented. During operation, the IM-3 groundwater extraction and treatment system has extracted and treated over 1,000,000,000 gallons of water and removed 8,470 pounds of chromium from August 1, 2005 through December 21, 2021.

With the primary remedial components, which are the NTH IRZ and its associated monitoring wells, constructed and operating, Phase 2 of remedy construction began in March 2022 as shown in the summary schedule which can be downloaded here. Phase 2 focuses on installing remaining components, including freshwater injection wells and supporting conveyance lines for the fresh water flushing component of the remedy. The freshwater injection wells are to be located primarily to the west (upland) of the groundwater plume. They will pump fresh water into the groundwater aquifer to help push water and contaminants in the plume through the reactive zone for treatment. Additional extraction wells and injection wells for in-situ remediation will also be installed.

Coordination with Tribal Nations and Stakeholders

Due to the diverse interests of this project, regulatory agencies, Tribal Nations, and other stakeholders meet regularly to exchange information and gather input as part of the Consultative Workgroup (CWG)A group consisting of stakeholders and multiple state and federal agencies that have an interest in the cleanup of a contaminated site, and meet regularly to discuss actions and make decisions., the Technical Workgroup (TWG)A focused stakeholder subgroup of the Consultative Work Group (CWG) where various stakeholders and their consultants discuss technical project related issues in greater detail which are then reported back to the CWG., the Clearinghouse Task Force (CTF)A group formed to develop and implement processes and tools to improve communications and enhance Topock stakeholder understanding of project technical and regulatory information., and the Topock Leadership Partnership (TLP)Forum that enables senior officials to provide input to the regulatory agencies on the direction of actions necessary to complete the Topock project.

The CWG, established by DTSC in March 2000, consists of agencies, Tribal Nations, and other entities that have an interest in protecting the Colorado River and the surrounding environment. The goal of the CWG is to allow timely input on proposed activities and decisions to be made. In addition to the CWG, the regulatory agencies and PG&E occasionally conduct independent outreach to the public, governmental representatives (including federal, state, county, and city elected officials and staff), and leaders and staff of Tribal Nations. The CWG generally meets about three times per year.

The TWG is a subgroup of the CWG. The TWG meets to deliberate on specific technical issues of the Project in greater detail and then report back to the CWG with the results. All CWG members are invited to send staff to participate in the TWG. Technical areas of discussion include geochemistry, hydrogeology, statistics for investigation, modeling and engineering design, human health and ecological risk assessments, remediation alternatives, and remedial design for the Project. The frequency of TWG meetings is dependent on Project needs but in general between monthly to quarterly.

The TLP was created as a result of an understanding that a forum was needed to enable senior officials of Tribes and stakeholder groups to provide input to the regulatory agencies and PG&E on the direction of actions necessary to complete the Project. The purpose of the TLP is to exchange information, views, and opinions on various proposed actions to ensure timely development, selection, and implementation of the groundwater and soil remedy for the Site. The intent is to provide a senior-level perspective of each participant’s interest, and gain understanding of differing points of view that could be considered before critical decisions are made by the lead regulatory agencies. The TLP has met several times since 2008, prior to critical Project decisions.

A subgroup of the TLP is the CTF. The CTF was formed to develop tools and implement ideas to improve communications and enhance stakeholder understanding of the technical and regulatory processes of the Project. The goal is to foster timely and effective project management, and early collaboration with Tribal Nations and stakeholders, and to inform state and federal agencies on issues and concerns prior to decision making on the Project.

In addition to these meeting venues, PG&E, DTSC and DOI continue to be actively engaged in consultation with Tribal Nations regarding the potential impacts of the project to the Tribes' Traditional Cultural Property (TCP) as determined and established by the Bureau of Land Management.