BPM006010_Solicitation_Attachment_12_-_Method_of_Approach.pdf

Request for Proposal

Solicitation No. BPM006010

ASRAC Assessment and Remediation of Hazardous Substances

Arizona Department of Environmental Quality (ADEQ)

1110 W. Washington Street Phoenix, AZ 85007

Solicitation Attachment – Method of Approach | Revision No. 1 | Revised 11-22

Attachment 12 – Method of Approach

The Offeror shall provide a narrative response to each section that demonstrates their understanding of the Scope of Work requirements and describes the company’s overall method of approach for providing the Service(s) stated in this Solicitation.

Offeror shall provide a response either after each question or in a separate document entitled: “Attachment - Method of Approach.” If a separate document is used, please clearly designate each section and double-check to ensure that each question has been answered. If any information provided is considered CONFIDENTIAL by Offeror, the information must be specifically included in the Confidential Information Designation Attachment and related documentation to be assessed for confidential treatment under A.A.C. R2-7-103.

Responses shall be limited to one (1) page per question. Response to Question #5 may be up to two (2) pages, in font size 10 pt or greater.

Questions and Responses provided on the following pages.

Question 1: Describe your company’s quality control/quality assurance process for reviewing proposals and technical documents prior to submission to ADEQ. What deliverables can ADEQ review to verify QA was completed? If ADEQ finds a quality issue, who, other than the PM, is the point of contact for a remedy?

Solicitation Attachment – Method of Approach | Revision No. 1 | Revised 11-22 Page 1 of 1 for Question 1

Question 1, Tetra Tech Response: Tetra Tech recognizes the success of our company depends on the quality of the services that we provide for our clients. Tetra Tech’s quality assurance (QA) program serves as a guide to ensure that project quality objectives are met. The QA program is based on principles, requirements, and guidance provided in the American National Standards Institute (ANSI) and the International Standards Organization (ISO) 9001:2000 Standards and applies to all personnel who are responsible for activities that may affect the quality of data, products, and performance of project work.

Tetra Tech’s QA program provides the necessary guidance and sets forth requirements to accomplish the following objectives:

• To maintain quality and consistency across all aspects of technical and administrative work functions.

• To provide and document training activities vital to the corporation and/or project.

• To ensure the overall effectiveness of program management and technical services.

• To ensure that all measurements are adequately documented, complete, verifiable, and scientifically and legally defensible.

• To ensure an acceptable level of work performance through quality assessment and review of product deliverables.

• To maintain documentation of all project activities to provide traceability of all data and work products.

Tetra Tech’s QA Program requires detailed project plans, often in the form of a work plan, to be developed and approved by the client before initiating project-related activities. Project performance is compared to the initial work plan and closely monitored by the project manager to identify when changes or variances occur. Communication with the client ensures that events requiring a change in scope, schedule, budget, and level of quality are addressed in an organized and agreeable manner.

Tetra Tech requires that all technical deliverables undergo a documented, independent peer review prior to delivery to the client by a staff member with at least equal experience and capabilities as the primary author. Tetra Tech encourages project managers and program managers to solicit client feedback throughout the course of the project. All client observations are viewed as a potential opportunity for quality improvement.

Tetra Tech routinely provides training to familiarize personnel with technical, administrative, and project-related requirements and guidelines, as well as the provisions of the QA Program. Training to familiarize employees with the policy, philosophy, and requirements of the QA Program is provided to all personnel within one year of employment and every two years thereafter.

Tetra Tech has two levels of project management training that all project managers are required to participate in within 6 months of becoming a Tetra Tech Project Manager. Project-specific training requirements are determined by the Project Manager, Program Manager, or office manager and provided to project personnel as needed to meet specific goals on a given project. Tetra Tech recognizes that procuring quality goods and services positively impacts projects rendering rework and delays unnecessary, which reduces costs and builds client confidence.

The proper maintenance and control of all measuring and test equipment (M&TE), including field tools and monitoring instrumentation, as well as other M&TE used to obtain data, is outlined in Tetra Tech’s QA Program. M&TE is calibrated in accordance with the manufacturer’s recommendations for the anticipate conditions in which it will be used. Requirements for equipment use and calibration are included in project-specific plans to assist field crew in the use of the equipment.

Tetra Tech’s QA Program sets forth a uniformed system of records management to ensure that documents considered as records are properly assembled, filed, controlled, maintained, and stored until disposition or transfer to the client. Every office has a central location where all project records, including electronic files, are maintained. The systems ensures that all files are easily retrievable, protected from damage and loss, and turned over to the client or destroyed at the appropriate time. Tetra Tech takes steps to guarantee that software used or developed by personnel produces technically defensible outputs, meets clients’ requirements, and is used by personnel trained in the program. All Tetra Tech-developed software for internal or client use is accompanied by a hardcopy or online user guide or developed to be so intuitive that a typical user can function with minimal instruction.

Tetra Tech’s Quality Assurance Director or designee at each office location performs periodic QA assessments to monitor compliance. Tetra Tech develops standard operating procedures (SOPs) and best management practices (BMPs) at the discretion of managers in key areas of cooperation in order to document repetitive tasks so that the tasks yield comparable outputs when implemented by different individuals at different times. The QA Program prohibits deviation from SOPs/BMPs without appropriate documentation. Each SOP/BMP is peer reviewed and approved by the Quality Assurance Director prior to implementation. Tetra Tech reviews newly implemented SOPs/BMPs annually and well-established SOPs/BMPs every three years to ensure that work governed by the SOPs/BMPs is compliant with current industry practices and requirements.

Question 2: Describe the methods and criteria your company would propose for confirming that a soil vapor extraction system located at a former dry cleaner in downtown Phoenix could be turned off and demobilized from the site. Consider both vapor and direct exposure. How does the Arizona “Soil Rule” apply at closure?

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Question 2, Tetra Tech Response: Termination criteria for a soil vapor extraction system (SVE) are typically established during the feasibility study and documented in a Record of Decision (ROD), in compliance with the Arizona Administrative Code (A.A.C) Title 18, Chapter 7, commonly known as the "Soil Rule”, including but not limited to: (1) A.A.C. R18-7- 203(A), which provides for establishing Soil Remediation Levels (SRLs) or using pre-determined SRLs; (2) A.A.C. R18- 7-203(B)(1), which provides for remediated soil protectiveness of groundwater and associates further to ADEQ’s 1996/2020 guidance pertaining to Groundwater Protection Levels (GPLs); and (3) A.A.C. R18-7-203C, which associates to ADEQ's 2017 Soil Vapor Sampling Guidance and the Soil Phase Partitioning calculation provided in ADEQ’s 2020 updated to the GPL Model workbook. It is essential to adhere to the latest regulatory guidance and ensure that all criteria are met before demobilizing the SVE system.

An SVE system is typically constructed to 1) remove/reduce the mass of volatile organic compounds (VOCs) that are contaminants of concern (COCs) for soil and/or soil vapor, and/or 2) prevent receptor exposure from COCs at concentrations greater than their corresponding remedial goals. The termination criteria under these two primary scenarios are outlined as follows:

Scenario 1 – SVE for Mass Removal/Reduction Purpose Only: Termination criteria for an SVE system primarily focused on mass removal or reduction should be based on the attainment of asymptotic performance indicators. These may include trend analysis of SVE system influent concentrations, mass removal rates, and rebound analysis. Any residual risk to human, ecological, and groundwater receptors should be addressed by complementary remedial measures, such as vapor mitigation systems.

Scenario 2 – SVE for Soil Remediation and Exposure Prevention: For an SVE system designed to prevent exposure of COCs to receptors, termination criteria should consider multiple exposure pathways:

• Direct Exposure to Human Receptors (Dermal, Ingestion): The termination criteria should align with the residential or non-residential SRLs (if utilizing non-residual SRLs, must consider requirements of a Declaration of Environmental Use Restriction). Alternatively, if site-specific risk-based remediation levels are sought and approved (which applies to soil only, not groundwater), A.A.C. R18-7-206 applies. In cases where soil data is unavailable, soil vapor concentrations may be used in conjunction with ADEQ's three-phase partitioning model equation, as presented in the 2020 ADEQ GPL Model in the “Soil Phase Partitioning Calc” Excel worksheet, and also described in Section 6 of ADEQ’s Soil Vapor Sampling Guidance (2017). This allows for the calculation of a soil-solid concentration from discrete soil vapor samples.

The calculated total contaminant concentrations in soil need to be evaluated against the SRLs and GPLs (GPLs are further detailed below under “Leaching to Groundwater”) to determine whether an SVE system can be terminated for direct exposure.

• Vapor Intrusion Pathway (Inhalation): Soil vapor concentrations should be evaluated against applicable regulatory screening levels to determine whether the SVE system can be terminated and demolished in consideration of the vapor intrusion pathway. The EPA OSWER Technical Guidance for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air (June 2015) can be used to support this determination. Evaluation against applicable indoor air screening levels may include: Pending/future ADEQ indoor air screening levels, EPA Vapor Intrusion Screening Levels (VISLs), and EPA Regional Screening Levels (RSLs).

Seasonal variations in soil vapor concentrations should be considered, and potential offsite migration of any residual soil vapor plume should be assessed. Since the site is in downtown Phoenix, and human receptors are expected at surrounding properties, available soil vapor concentration data should be evaluated for potential offsite migration. This includes the potential for subsurface utilities, such as sewers, to act as preferential migration pathways.

• Leaching to Groundwater: Compliance with Aquifer Water Quality Standards (AWQS) outlined in A.A.C. R18-11- 406 is essential for closure. Total concentrations in soil must be protective of groundwater (per A.A.C. R18-7- 203(B)(1)), either based on the default GPLs from the 1996/2020 guidance, or calculated GPLs using ADEQ's approved 2020 GPL Model methodology. In the case of lacking soil-solid concentration data, soil concentrations in equilibrium with soil vapor concentrations can be calculated using the aforementioned three-phase partitioning model equation.

• Exposure to Ecological Receptors: An ecological risk evaluation should be performed to ensure that remaining contaminants do not adversely impact ecological receptors, particularly in areas adjacent to sensitive habitats or water bodies such as an abutting greenway or feeder wash to the Salt River.

Throughout the termination process, adherence to all regulatory requirements and ADEQ guidance is paramount to ensure the safe and effective closure of the SVE system.

Question 3: Provide a table for a sampling and analysis plan for the implementation of an in situ enhanced reductive dechlorination program for a period of 12 months.

Assume the program includes two injection wells (IW-01 and IW-02), four performance monitoring wells (one well [PW-01] located 10-feet upgradient of the injection wells with the remaining three wells located 10- [PW-02], 20- [PW-03], and 30-feet [PW-04] downgradient of the injection wells), and one injection utilizing emulsified vegetable oil. Sample and analysis plan should include what parameters are to be collected for the design of the implementation and for remedy performance monitoring.

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Question 3, Tetra Tech Response:

Question 4: Describe the multiple lines of evidence necessary to evaluate monitored natural attenuation (MNA) in a typical Arizona aquifer and your experience with the viability of MNA in the deep aquifers of Arizona (focusing on chlorinated solvents), including the limits on MNA in our hydrogeologic settings? Provide key references where appropriate (does not count against page limit).

Describe why low-flow sampling would be preferable over passive sampling in MNA evaluation.

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Question 4, Tetra Tech Response: Multiple lines of site-specific evidence are necessary to assess the feasibility and efficacy of relying on monitored natural attenuation (MNA) as a remediation approach. Our experience indicates that deep basin-fill aquifers in Arizona (AZ) are more aerobic than originally postulated due to inherent low organic carbon content rendering their natural condition non-conducive to the reductive dechlorination processes needed for chlorinated volatile organic compound (CVOC) biodegradation in a reasonable time frame without some component of active remediation. Key experiences and evidence that are relevant when evaluating MNA in these aquifers include:

1. Hydrogeological Setting Analysis: Understanding the geological and hydrological characteristics of the aquifer, including its depth, permeability, porosity, groundwater flow rates, vertical gradients (natural and pumping induced), and flow direction, is crucial. Our experience in conducting hydrogeological investigations in AZ aquifers indicates that a robust hydrogeologic conceptual site model (CSM) is paramount to support MNA characterization. This typically includes the design and sampling of monitor wells, aquifer testing, and groundwater flow modeling to define the contaminant flow field.

2. Contaminant Plume Characterization: Detailed characterization and delineation of the CVOC plume is essential to determine its extent, concentration gradients, and potential migration pathways. A trend of decreasing CVOC mass and/or concentration over time should be demonstrated at adequate monitoring points. Appropriate selection of sampling and analysis techniques, such as collecting field parameters for general chemistry and lab samples for aquifer characterization and contaminant analysis, is pertinent.

3. Biogeochemical Processes: Assessing if biogeochemical processes are occurring within the aquifer that can contribute to CVOC degradation is important. These processes can be limited in AZ aquifers and testing for and evaluating microbial activity, redox conditions, and geochemical reactions involved in natural attenuation processes is relevant.

4. Long-Term Monitoring: Establishing a baseline and longer-term monitoring programs to track changes in CVOC concentrations and aquifer geochemistry over time is critical for assessing the effectiveness of MNA. Experience in designing and implementing monitoring programs, including the selection of monitoring well locations and placement of screens and sampling frequencies, is critical for a reliable data set.

5. Regulatory Compliance: Understanding regulatory requirements and guidelines related to MNA implementation is essential. Experience in navigating applicable regulatory frameworks such as maximum contaminant levels (MCLs) versus public health goals and effectively communicating with regulatory agencies is valuable for ensuring concurrence with the monitoring strategy and overall compliance and necessary approvals.

Low-flow sampling can be preferable over passive sampling in MNA evaluation for several reasons:

• Representative Sampling: Low-flow sampling allows for the collection of groundwater samples under controlled conditions, ensuring that samples are representative of in-situ conditions. In contrast, passive sampling may not provide representative samples as it relies on the diffusion of contaminants into sampling devices over time and retrieval of passive devices may introduce oxygen and impact results.

• Greater Control Over Sample Collection: Low-flow sampling provides greater control over the sample collection process, including the ability to purge wells to remove stagnant water and contaminants before sampling. This helps minimize the risk of sample contamination and ensures more accurate results.

• Real-Time Monitoring: Low-flow sampling allows for real-time monitoring of key parameters such as groundwater flow rates, pH, and oxidation-reduction potential during sample collection. This information can be used to assess the effectiveness of sampling and ensure consistency between sampling events.

• Regulatory Acceptance: Low-flow sampling is generally widely accepted by regulatory agencies for groundwater monitoring purposes due to its well-established protocols and documented effectiveness. Using low-flow sampling can help ensure regulatory compliance and facilitate the approval process for MNA projects.

Overall, low-flow sampling can provide a more reliable and accurate method for evaluating MNA compared to passive sampling, particularly in complex hydrogeological settings like those found in AZ aquifers. However, combining passive sampling with in-situ continuous monitoring via down-well multiparameter sondes that measure water level, quality (e.g., temperature, conductivity, pH/ORP, dissolved oxygen, turbidity, chloride, and nitrate) and flow can deliver accurate data cost-effectively and provide reliable results for MNA decision-making in the correct settings. (REFERENCES ON NEXT PAGE)

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Question 4, Tetra Tech References:

ITRC. 2010 “Use and Measurement of Mass Flux and Mass Discharge (itrcweb.org)” Technology Review.

Parker, B. L., S. W. Chapman, and M. A. Guilbeault. 2008. “Plume Persistence Caused by Back Diffusion from Thin Clay Layers in a Sand Aquifer Following TCE Source Zone Hydraulic Isolation,” Journal of Contaminant Hydrology 102(1–2):

86–104.

Ricker, J. A. 2008. “A Practical Method to Evaluate Groundwater Contaminant Plume Stability,” Ground Water Monitoring and Remediation 28(4): 85–94.

USEPA. 2001a. Monitored Natural Attenuation: USEPA Research Program—An EPA Science Advisory Board Review.

EPA-SAB-EEC-01-004. Review by USEPA Science Advisory Board Environmental Engineering Committee. Monitored Natural Attenuation: USEPA Research Program - An EPA Science Advisory Board Review (clu-in.org)

Wiedemeier, T. H., H. S. Rifai, C. J. Newell, and J. T Wilson. 1999. Natural Attenuation of Fuels and Chlorinated Solvents in the Subsurface. New York: Wiley.

Wiedemeier, T. H., M. A. Swanson, D. E Moutoux, E. K. Gordon, J. T. Wilson, B. H. Wilson, D. H. Kampbell, P. E. Haas, R. N. Miller, J. E. Hansen, and F. H. Chapelle. 1998. Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water. EPA/600/R-98/128. TECHNICAL PROTOCOL FOR EVALUATING NATURAL

ATTENUATION EPA/600/R-98/128

https://maf-1.itrcweb.org/wp-content/uploads/2020/11/MASSFLUX1.pdf https://clu-in.org/download/remed/eec01004.pdf https://clu-in.org/download/remed/eec01004.pdf https://semspub.epa.gov/work/06/668746.pdf https://semspub.epa.gov/work/06/668746.pdf

Question 5 (RESPONSE to this Question may be up to two (2) pages): Describe the in situ technologies you have used and provide a critical evaluation of successes and failures. What would useful data quality objectives be for the various in situ technologies you have used (plume control, source remediation, mass reduction)? What site characterization data and steps are needed to fully evaluate the applicability of specific in situ technologies?

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Question 5, Tetra Tech Response:

Selecting the correct in situ technology for a site starts with a robust Conceptual Site Model (CSM) and defining Remedial Objectives (ROs). The four major components of a robust CSM for a site are as follows:

1. Delineation of contaminants of concern (COCs) in soil, groundwater, and soil vapor.

2. Full understanding of geological and hydrogeological information.

3. Full understanding of geochemical, biogeochemical, and biological parameters (i.e., field and laboratory parameters).

4. Identification of exposure pathways, transport mechanisms, and receptors.

Additional data-gap investigation might be necessary to complete the remedial design, depending on the selected remedy.

For example, if In Situ Chemical Oxidation (ISCO) is chosen, Soil Oxidant Demand samples (soil) should be collected if a treatability study has not been completed, to calculate the amendment dosing for a field pilot study.

Below are reviews of several in situ technologies we have used to target chlorinated and petroleum hydrocarbons, and hexavalent chromium impacted groundwater:

In Situ Bioremediation (ISB): Anaerobic ISB is a process where microorganisms use the COCs for cellular respiration, enhanced with the addition of nutrients and electron donors. Sometimes, COC-specific degrading microorganisms are added to the target treatment area to improve treatment. ISB technologies reduce or eliminate toxicity, mobility, or volume of COCs by implementing a process that alters, bonds with, isolates, or completely destroys the COCs. Monitored Natural Attenuation (MNA) is a form of intrinsic bioremediation whereby indigenous microorganisms degrade COCs without the use of amendments.

• Remedial Objectives for Anaerobic ISB: Source mass reduction, prevent COC migration off-site above applicable criteria, and mitigate existing off-site COCs above regulatory criteria.

• Successes and Lessons Learned: Injections can be completed by gravity and low pressures (<30 pounds per square inch (psi)) in most sandy and silty sand formations through injection wells or direct push injection points. Radius of influence based on chemical parameters was an average of 15 feet. Daylighting occurred at the annular seal of wells that were not properly sealed during installation. Potable water with high oxygen did not affect the performance results of the target bacteria.

In Situ Chemical Reduction (ISCR): ISCR involves the addition of reductants that convert COCs to water, carbon dioxide, or nontoxic substances, or alter, bond with, or isolate the COCs. Reductants are added to the subsurface to promote abiotic and biotic degradation processes. Reductants include electron donors (sugars, vegetable oils, and other organic substrates), ferrous iron, and zero-valent iron (ZVI). The ISCR biotic processes are anaerobic and stimulate microorganisms to use COCs for cellular respiration with the addition of nutrients and electron donors. The ISCR abiotic chemical reduction process uses ferrous iron or ZVI to promote rapid chemical reactions that completely mineralize the COCs.

• Remedial Objectives for Anaerobic ISCR: Prevent COC migration off-site above applicable criteria and mitigate existing off-site COCs above regulatory criteria.

• Successes and Lessons Learned: Injections were completed at pressures ranging from 50 to 250 psi in most sandy and silty sand formations through direct push injection points. Radius of influence based on chemical parameters was an average of 20 feet. Daylighting occurred at the annular seal of previous soil borings that were not properly sealed during installation. Performance monitoring indicated that potable water with high oxygen did not affect the performance results of the target bacteria. One direct push technology (DPT) injection crew can inject approximately 3,500 to 4,500 gallons of amendment at treatment depths of 20 to 10 feet below ground surface (ft bgs) or eight DPT points with treatment depths of 20 to 10 ft bgs in one ten-hour day.

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(Question 5 continued)

In Situ Chemical Oxidation (ISCO): ISCO involves the addition of reagents that mineralize COCs to water, carbon dioxide, or nontoxic substances. The typical reagents used for remediation are Fenton’s reagents or sodium persulfate oxidants. The selection of which reagent to use will depend on the CSM. The oxidants are added to the subsurface to promote oxidation of groundwater COC by the hydroxyl or sulfate radicals produced.

• Remedial Objectives for In Situ Chemical Oxidation: Source area COC mass reduction (i.e., LNAPL and DNAPL), prevent COC migration off-site above applicable criteria, and mitigate existing off-site COC above criteria.

• Successes and Lessons Learned: Injections can be completed by gravity and low pressures (<30 psi) in most sandy and silty sand formations through injection wells or direct push injection points. Radius of influence based on chemical parameters was an average of 15 to 20 feet. In formations with high Darcy velocity, a fast kinetics reagent should be selected to maximize oxidation and limit flushing the reagent out of the target treatment zone.

In Situ Metal Stabilization: This alternative involves injections of amendments to immobilize hexavalent chromium Cr(VI). The injections target the saturated zone within the source area, serving as the primary ongoing source to the Cr(VI) groundwater plume. The amendment used was a nontoxic highly soluble reagent that chemically reduces Cr(VI) to stable (low solubility) trivalent chromium Cr(III) oxyhydroxides by the reaction of CrO4

2- with iron oxide (Fe(II)).

• Remedial Objectives for In Situ Metal Stabilization: Prevent COC migration off-site above applicable regulatory criteria.

• Successes and Lessons Learned: Injections were completed at pressures ranging from 50 to 75 psi in most sandy and silty sand formations through injection wells or direct push injection points. Radius of influence based on chemical parameters was an average of 20 feet. Daylighting occurred at the annular seal of previous soil borings that were not properly sealed during installation. Depending on the selected amendment, the precipitation of Cr(VI) minerals or other byproduct minerals may reduce the water-bearing unit permeability. Walkley-Black analysis should be evaluated to understand the natural attenuation factor associated with the soils.

Question 6: ADEQ is focusing more on statistical techniques to both monitor long term performance of remedies, including MNA and optimize remediation and monitoring programs. Describe how the Air Force Center for Environmental Excellence (AFCEE) MAROS process can be used for these types of programs. What steps and metrics would you use to optimize a monitoring well network on a large PCE plume over a ten year period that includes both MNA and pumping from existing production wells for municipal or agricultural use?

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Question 6, Tetra Tech Response - Utilizing AFCEE MAROS Process:

The AFCEE MAROS process is a systematic approach designed to optimize remediation strategies and monitoring programs by integrating statistical techniques and environmental data analysis. Key steps include:

1. Data Collection and Characterization: Gather comprehensive data on the contaminants of concern (COC) plume, hydrogeological characteristics, and existing remediation efforts. This includes historical monitoring data, groundwater flow patterns, aquifer properties, and information on existing extraction/production wells.

2. Model Development and Calibration: Develop site-specific models to simulate groundwater flow, COC transport, and the performance of existing remediation systems. Calibrate the models using available site data.

3. Scenario Analysis and Optimization: Utilize calibrated models to conduct scenario and optimization analyses.

Evaluate remediation/monitoring strategies to identify a cost-effective and efficient approach to attain cleanup.

4. Decision Support System: Implement a decision support system that incorporates statistical techniques to analyze monitoring data in real-time. This allows for adaptive management, where remediation and monitoring strategies can be adjusted based on changing site conditions and new information.

Steps to Optimize a PCE Plume Monitoring Well Network:

Given the likely site heterogeneity, the role of matrix diffusion in enhancing COC persistence, and the ten-year timeframe for the PCE plume scenario, the optimization of the well network should be approached systematically:

1. Baseline Assessment: Conduct a comprehensive baseline assessment of the existing monitoring well network, including well locations, depths, screen intervals, and sampling frequencies. Evaluate the adequacy of the network in capturing spatial and temporal variations in groundwater quality.

2. Hydrogeological Characterization: Update the hydrogeological conceptual model based on current data.

Identify preferential flow paths, areas of high COC concentration, and potential receptors (e.g., supply wells).

3. Optimization Criteria: Establish optimization criteria based on project objectives, regulatory requirements, and technical feasibility. These criteria may include coverage of the plume, spatial resolution, cost-effectiveness, and minimization of data redundancy.

4. Statistical Analysis, Modeling and Simulation: Utilize Mann-Kendall plume stability methodology to demonstrate the plume stability condition (expanding, stable, or decreasing) and track the progress of remediation efforts. Use modeling to simulate groundwater flow and COC transport over the ten-year period. Incorporate MNA processes and pumping from existing production wells into the modeling framework. Evaluate the impact of different monitoring well configurations on the effectiveness of assessing MNA and COC removal.

5. Sensitivity Analysis: Conduct sensitivity analyses to assess the influence of key parameters (e.g., well spacing, screen lengths, sampling frequencies) on the performance of the monitoring network. Identify critical factors that drive monitoring network optimization.

6. Optimization Strategies: Explore various optimization strategies, such as adding new monitoring wells, relocating existing wells, converting injection wells to monitoring wells, adjusting sampling frequencies, or implementing innovative monitoring technologies (e.g., multilevel samplers, passive diffusion samplers).

7. Cost-Benefit Analysis: Perform a cost-benefit analysis to compare the expected costs of implementing different monitoring well network configurations against the anticipated benefits in terms of improved remediation efficiency and reduced long-term monitoring costs.

8. Adaptive Management Plan: Develop an adaptive management plan that outlines protocols for periodic review and adjustment of the monitoring network based on data, model predictions, and changes in site conditions.

Metrics for Optimization:

Key metrics for evaluating the effectiveness of the monitoring well network optimization process include:

• Plume Coverage: High percentage of the plume area adequately covered by monitoring wells.

• Data Density: Spatial and temporal density of monitoring data within the plume.

• Data Quality: Reliability and accuracy of monitoring data obtained from the network.

• Early Detection Capability: Ability to detect changes in groundwater quality and COC concentrations early.

• Cost Efficiency: Cost-effectiveness of the monitoring network in terms of data collection and analysis.

• Compliance: Degree to which the monitoring network meets regulatory and performance standards.