GLA_Att.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.

Arizona Department of Environmental

Quality (ADEQ)

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?

Offeror Response:

GeoLogic’s Quality Management Plan (QMP) will govern quality assurance/quality control (QA/QC). GLA’s standard process for reviewing proposals and technical documents is summarized in the QMP Figure shown below.

With the exception of routine monitoring reports (essentially a transmittal of environmental data), reports are reviewed for editorial content by a technical editor. The report is then reviewed by a designated senior technical staffer focusing on content including calculations and appropriateness of conclusions and recommendations.

Engineering deliverables are reviewed by a

Professional Engineer with licensure in the state during the second level of review. Finally, the report is reviewed by the Principal-in-

Charge. This process will be slightly modified for Arizona Department of Environmental

Quality (ADEQ) projects, because we understand that ADEQ will review draft reports before reports are put in final form. Therefore, this process will be implemented for both the draft and final reports. Routine monitoring reports are checked against laboratory reports by administrative and support staff.

GLA has not provided deliverables to verify completion of the QA process in the past, but we can prepare a checklist (with input from

ADEQ, if desired) to serve this purpose. If

ADEQ does find a quality issue, we encourage

ADEQ to reach out to the Principal-in-Charge, who performs the highest level of review.

Principal level staff are always available to

ADEQ, particularly regarding issues related to safety, quality assurance, and responsiveness.

Arizona Department of Environmental

Quality (ADEQ)

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?

Offeror Response:

The primary criterion for determining if soil vapor extraction (SVE) system operations can be terminated is whether remediation goals have been achieved. Remediation goals include clean-up of soil to appropriate soil remediation levels and protection of groundwater from potential future impacts from residual contamination in the vadose zone (A.A.C. R18-

7-203). A secondary criterion is whether residual soil gas concentrations have been reduced to sufficient levels to address the potential risk of vapor intrusion to indoor air. Closure evaluations are made after operational data indicate that the system was effective at addressing the vadose zone source and a period of pulsed operations has been employed at the site.

SVE closure determinations are made using multiple lines of evidence including SVE system operations and performance monitoring, an understanding of the conceptual site model (CSM), and supporting data from subsurface performance monitoring points and post operational sampling results. Applicable system performance monitoring data include:

emissions stack testing showing negligible or asymptotic levels; minimal rebound observed upon system re-start during pulsed operations; or pulsed venting downtime periods greatly exceeding pulsed operational periods. Due to the inherent limitations in collecting volatile organic compound data from soils, it is recommended to use soil vapor concentrations and calculate equivalent soil concentrations to compare to post operation vadose zone conditions to the selected closure criteria for soils. ADEQ provides default values for input variables in making such calculations.

Closure criteria include soil remediation levels (SRLs) promulgated pursuant to the “Soil Rule” (A.A.C. R-18-7-203 et.

seq.), including Groundwater Protection Levels (GPLs). A site-specific determination can be made to use residential SRLs, non-residential SRLs (with an appropriate Declaration of Environmental Use Restriction or “DEUR”), or site-specific risk-based levels provided that GPLs are met. Pursuant to the Soil Rule, if residential SRLs are used for contaminants other than designated know human carcinogens, remediation levels at a 1 x 10-5 risk level may be used unless the current or intended future use of the property is a child care facility or school where children under the age of 18 can reasonably be expected to be in frequent, repeated contact with the soil.

Observed soil gas concentrations can also be used to screen for the potential risk of soil gas to indoor air vapor intrusion by multiplying the observed soil gas concentrations by an attenuation factor and comparing the residential to U.S.

Environmental Protection Agency “Regional Screening Levels” for Composite Worker Indoor Air health-based screening levels.

Arizona Department of Environmental

Quality (ADEQ)

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.

Offeror Response:

See next page

Table 1. Proposed Groundwater Performance Monitoring Program

Field Field Field Field Field Field Field Field Calculation Laboratory

Well Location Baseline (pre-injection)

30/60/90 Days Post-Injection

Quarterly (Q2- Q4)

Solinist Meter (or equivalent)

YSI Pro Plus (or equivalent)

YSI Pro Plus (or equivalent)

YSI Pro Plus (or equivalent)

YSI Pro Plus (or equivalent)

YSI Pro Plus (or equivalent)

Method 8008 by Hach

Colorimeter

Method 8008 by Hach

Colorimeter

(Total Iron - Ferrous Iron)

200.7 rev 4.4/6010B

Injection Wells IW-01 Source X X X X X X X X X X X X X IW-02 Source X X X X X X X X X X X X X

Performance Wells PW-01 10 ft upgradient X X X X X X X X X X X X X PW-02 10 ft downgradient X X X X X X X X X X X X X PW-03 20 ft downgradient X X X X X X X X X X X X X PW-04 30 ft downgradient X X X X X X X X X X X X X

(continued...)

Field Laboratory Laboratory Laboratory Laboratory Laboratory Laboratory Laboratory Laboratory Laboratory Field Laboratory Laboratory

Well Location Method 8008 by Hach Colorimeter

200.7 rev

4.4/6010B EPA 8260B EPA 300.0 EPA 300.0 EPA 310.2

EPA

415.1/9060/SM

5310D

EPA

415.1/9060/SM

5310D

ASTM

D1945/RSK-175 EPA 8015B

Visual inspection/Inte rface probe

CENSUS ®

qPCR (or equivalent)

HPLC/UV or Ion chromataogrp hy

Injection Wells IW-01 Source X X X X X X X X X X X X X IW-02 Source X X X X X X X X X X X X X

Performance Wells PW-01 10 ft upgradient X X X X X X X X X X X X X PW-02 10 ft downgradient X X X X X X X X X X X X X PW-03 20 ft downgradient X X X X X X X X X X X X X PW-04 30 ft downgradient X X X X X X X X X X X X X x = Well sampled for indicated parameter VFA = Volatile Fatty Acids. (Acetic Acid, Propionic Acid, Butyric Acid, Pyruvic Acid, Lactic Acid; n-Pentanoic Acid, i-Pentnaoic Acid, n-Hexanoic Acid, i-Hexanoic Acid by ion chromatography)

Dechlorinating bacteria

(Dehalococcoi VFAsTotal

Manganese

Dissolved Manganese

(filtered) VOCs Nitrate Sulfate

Total Alkalinity (as CaCO3)

Total Organic Carbon

Dissolved Organic Carbon

(filtered)

Methane/Ethane /Ethylene/CO2

Total Petroleum

Hydrocarbon- Emulsion

Dissolved Oxygen pH Specific

Conductivity Temperature Oxidation/ Reduction

Potential (mV) Total Iron

Field/Laboratory

Sampling Frequency Ferrous Iron

(Fe2+)

Ferric Iron

(Fe3+) Dissolved Iron

(filtered)

Water Level/Water

Column

Arizona Department of Environmental

Quality (ADEQ)

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.

Offeror Response:

GLA and its subsidiaries have implemented monitored natural attenuation (MNA) at a number of sites. A notable Clear

Creek success was the closure of a voluntary remediation site after active remedial measures were utilized and subsequently discontinued. The post-remediation monitoring demonstrated sustained reduction in chlorinated volatile organic compounds (CVOC) concentrations. Clear Creek demonstrated and concluded, and ADEQ concurred, that remediation efforts ensured the protection against the loss or impairment of current and reasonably foreseeable uses of groundwater at the site in accordance with the requirements of A.R.S. §49-175.B and the rules adopted pursuant to A.R.S.

§49-282.06.

An MNA remedy, or component of a remedy, may be appropriate in instances where: (1) adequate source control measures are in place, (2) clear and significant reductions in contaminant mass and/or concentrations are observed at appropriate monitoring points, (3) the conceptual site model (CSM) indicates that concentration reductions are meaningful and not a consequence of unintended or misunderstood plume migration, and (4) there is minimal risk, such as migration to a potential receptor or formation of more toxic by-products.

MNA is typically thought of in terms of destructive reduction of contaminants (e.g., degradation). However, Arizona’s aquifers generally have minimal levels of organic carbon and are typically aerobic—factors that limit the natural degradation of CVOCs. Nevertheless, MNA for CVOCs is a viable alternative in deep Arizona alluvial aquifers. While abiotic degradation is possible, such as in contact with iron bearing minerals, chlorinated solvent plumes in Arizona typically are dominated by the parent compounds (e.g., trichloroethylene [TCE] or tetrachloroethylene [PCE]), with low levels of degradation by-products (e.g., cis 1,-2-DCE) observed. U.S. Environmental Protection Agency guidance recognizes that other mechanisms, such as dispersion, dilution and volatilization, fall within the overall definition of natural attenuation. These mechanisms play a significant role in natural attenuation of contaminants in Arizona aquifers.

The lines of evidence used to evaluate MNA’s effectiveness include:

• Contaminant mass loss vs. time and space: including statistical tools such as Mann-Kendall analysis to evaluate the statistical significance of concentration trends, mass balance calculations, mass flux evaluations across a target interval, and an understanding of fate and transport mechanisms that show a plume is stable or shrinking.

• Geochemical conditions: e.g., field parameters, such as dissolved oxygen, oxidation-reduction potential, pH, dissolved iron, total organic carbon, sulfate, methane, etc., which provide insight as to whether the right conditions exist to support MNA and whether MNA is occurring.

• Presence of iron-bearing minerals: this is particularly important in Arizona groundwater basins where organic carbon concentrations are low and abiotic processes play a significant role.

Lesser used lines of evidence, to be used judiciously as they tend to be less conclusive and not necessarily applicable to all sites, include:

• Isotope Analysis to identify biotic or abiotic degradation processes

• Molecular Biological tools

• Microcosm Studies in the field or laboratory

Low-flow sampling approaches allow for the collection of monitoring data in addition to chlorinated solvent concentrations, such as hydrogeochemical parameters, that may be useful in evaluating MNA particularly when biodegradation of CVOCs is a consideration. Low-flow sampling can also provide supporting information on CVOC concentrations if there are concerns regarding inadequate through-flow or stagnant water in a monitoring well. However, passive monitoring may be appropriate under appropriate conditions or in cases where mass flux monitoring may be utilized.

Arizona Department of Environmental

Quality (ADEQ)

Pertinent References

In Situ Treatment Performance Monitoring: Issues and Best Practices (15 pp) April 2018, EPA 542-F-18-002

Calculation and Use of First-Order Rate Constants for Monitored Natural Attenuation Studies – Ground water Issue (PDF)

(28 pp, 752 KB) (EPA/540/S-02/500) November 2002 – Abstract

Guidance for Monitoring Passive Groundwater Remedies Over Extended Time Scales, Fritz, B.G., M.J. Truex, V.L.

Freedman, C. Bagwell, R.J. Cameron, J. Counts, L.E. Martino, K.C. Picel, J. Quinn, and E.Y. Yan. Pacific Northwest

National Laboratory, 66 pp, 2020

Development of a Quantitative Framework for Evaluating Natural Attenuation of 1,1,1-TCA, 1,1-DCA, 1,1- DCE, and 1,4-

Dioxane in Groundwater: Danko, A., D. Adamson, C. Newell, J. Wilson, B. Wilson, D. Freedman, and C. Lebron. ESTCP

Project ER-201730, 360 pp, 2021

Chapelle, F.H., Novak, John, Parker, John, Campbell, B.G., and Widdowson, M.A., 2007, A framework for assessing the sustainability of monitored natural attenuation: U.S. Geological Survey Circular 1303, 35 pp.

Interstate Technology and Regulatory Council In Situ Bioremediation Team, 2002. A Systematic Approach to In Situ

Bioremediation in Groundwater Including Decision Trees for In Situ Bioremediation of Nitrates, Carbon Tetrachloride, and

Perchlorate, 158 pp.

Interstate Technology and Regulatory Cooperation Workgroup, In Situ Bioremediation Subgroup, 1998. Technical and

Regulatory Requirements for Enhanced In Situ Bioremediation of Chlorinated Solvents in Groundwater, 122 pp.

Interstate Technology and Regulatory Cooperation Work Group, In Situ Bioremediation Work Team, 1998. General

Protocol for Demonstration of In Situ Bioremediation Technologies, 54 ppp

Naval Facilities Engineering Command, 2002. Remedy Selection and Optimization Considerations for Monitored Natural

Attenuation, fact sheet, 6 pp.

Stroo, H.F., C.H. Ward, eds, 2010. In Situ Remediation of Chlorinated Solvent Plumes, SERDP and ESTCP Remediation

Technology Monograph Series. Springer Publishing.

Suthersan, S.S., C.C. Lutes, P.L Palmer, F. Lenzo, F.C. Payne, D.S. Liles, J.Burdick, 2002. Final: Technical Protocol for

Using Soluble Carbohydrates to Enhance Reductive Dechlorination of Chlorinated Aliphatic Hydrocarbons, Prepared for

Air Force Center for Environmental Excellence, Brooks AFB, Texas, 172 pp.

US EPA, 1999. Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and underground Storage tank Sites, Directive 9200.4-17P. 32 pp.

US EPA, 2000. Biochlor Natural Attenuation Decision Support System, EPA/600/R-00/008 54 pp.

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.

www.epa.gov/superfund/health/conmedia/gwdocs/protocol.htm.

Wiedemeier, T.H., M. J. Barden, P.E. Haas, W. Z. Dickson, 1991, Designing Monitoring Programs to effectively evaluate the Performance of Natural Attenuation in Practical handbook of environmental site characterization and groundwater monitoring, second edition / edited by David M. Nielsen. p. 573-637

Wiedemeier, T.H., M.J. Barden, W.Z. Dickson, and D. Major, Multiple Lines of Evidence Supporting Natural Attenuation:

Lines of Inquiry Supporting Monitored Natural Attenuation of Chlorinated Solvents. U.S. Department of Energy, WSRC-

TR-2003-00331, 2005.

Wiedemeier, T.H., J.T. Wilson, D.H. Kampbell, R.N. Miller, and J.E. Hansen, Technical Protocol for Implementing Intrinsic

Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Ground Water, US Air

Force Center for Environmental Excellence, Brooks Air Force Base, San Antonio, TX, 1995.

https://archive.epa.gov/ada/web/pdf/10004674.pdf https://clu-in.org/download/techfocus/na/PNNL-30441.pdf https://clu-in.org/download/techfocus/na/ER-201730-Final-Report.pdf https://clu-in.org/download/techfocus/na/ER-201730-Final-Report.pdf https://cluin.org/download/techfocus/na/Remedy-Selection-MNA-Fact-Sheet.pdf

Arizona Department of Environmental

Quality (ADEQ)

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?

Project team staff has utilized in situ oxidation by potassium permanganate delivery by injection wells, injection of whey solution by direct-push points, injection of molasses solution by dedicated wells and direct-push points, soil excavation backfill with percarbonate (oxygenation), emulsified vegetable oil treatment by injection wells, injection of colloidal liquid milled activated carbon, treatment with sulfidated microscale zero-valent iron (smZVI), and bioaugmentation with dehalococcoides sp. using colloidal activated carbon as a substrate. Staff are currently implementing excavation backfill with smZVI to ensure reagent delivery in low-permeability clay at an active site.

These technologies are successful when applied in coarse-grained aquifers and can be problematic if applied to clay-dominant water-bearing zones. Reagent specification and loading can be quantified in advance but reagent delivery is key to the overall program success. In situ technologies have been perceived as low-cost solutions and misapplied in clay environments where reagent delivery is non-uniform or where injection is rejected altogether by the formation. In situ technologies have also been applied to address one contaminant only to leave a more recalcitrant contaminant behind

(i.e., 1,4 dioxane). Injections have failed where low-cost pilot-scale injection testing would have demonstrated that subsurface permeability is just too low. In situ technology has the greatest potential for success where applied with appropriate data quality objectives (DQOs) in mind at a well-characterized project site.

In situ technology programs can be successfully designed to address a variety of DQOs. Appropriate DQOs are essential to develop suitable expectations for program success. Complete contaminant reduction to non-detect values may not be an appropriate goal where significant mass reduction alone is appropriate and reasonable. Similarly, simple and successful pilot-scale reagent delivery in a focused area could be a program goal that allows for a measured scale-up to address a larger area. Plume control by cut-off wall (i.e., colloidal carbon injection) is also a common program goal but must be applied where groundwater flow and contaminant transport are predictable or controllable over the long term.

A project site conceptual model developed with appropriate site characterization data is important to the overall treatment plan design and implementation. Essential, basic site characterization data include subsurface lithology, groundwater velocity, groundwater flow direction, depth-to-water, water column height per well, and baseline groundwater geochemical data. Baseline data include dissolved oxygen, pH, oxidation-reduction potential, cations/anions, dissolved gases, and related parameters. Baseline groundwater geochemical data are important advance data required to determine what candidate in situ technology is appropriate for a given project. Reductive technologies may not be appropriate for a well-oxygenated, aerobic, or continually recharging system that would be relatively difficult to convert to anaerobic. Sensitive receptors such as adjacent properties are also key site characterization data, for example, where vinyl chloride potentially produced by enhanced reductive dechlorination may impact indoor air quality.

In addition, contaminant data are essential since significantly elevated concentrations can be problematic for some in situ technologies more successful with lesser impacted sites. In addition, a complete characterization of groundwater contaminant species is also critical to ensure trace compounds or potentially recalcitrant co-contaminants are not ignored and left behind in treatment such as 1,4 dioxane, perchlorate, hexavalent chromium, or other metals. Potential metals mobilization should also be considered. Of course, some contaminants can be addressed with anaerobic treatment (e.g., chlorinated volatile organic compounds) while others cannot (e.g., benzene).

Arizona Department of Environmental

Quality (ADEQ)

Mass flux testing combined with potable water injection testing provide site characterization data used to optimize the reagent delivery program. Pre-treatment potable water confirmation injection testing is important to ensure the subsurface can actually accept the pre-specified reagent volume at the target depths. The potable water injection testing is also used to develop the injection point radius-of-influence so the full-scale injection grid can be appropriately spaced with overlapping treatment zones to optimize reagent delivery.

Mass flux testing developed and described by Annable et al (2005) and Hatfield et al (2004) is applied to identify discrete subsurface zones where contaminant transport is predominant. This allows reagent delivery to be optimized and focused on the key zones that need to be targeted for treatment. Mass flux testing also helps identify zones where reagent delivery is not needed and cost-savings can be realized.

Clear Creek’s recent (2010-2020) use of in situ technologies provides insight regarding the potential limitations that may be encountered. Clear Creek implemented an in situ mass reduction field-scale pilot test utilizing PlumeStop® colloidal activated carbon as a substrate and augmented bioremediation for enhanced reduction dichlorination (ERD) utilizing

BioDeclor Innoculum Plus (BDI-Plus™). The objective of the project was to reduce mass in a localized area with high concentrations of TCE that represented a significant source for a soil gas to indoor air vapor intrusion pathway. Pre-design site characterization work included the use of an Enviroflux Passive Flux Meter™ to vertically profile the predominant contamination migration pathways. Because the wells used for the project were located in City right-of-way, closure of the project was required by the City to allow for new utilities to be installed by the City through the test area. Immediate reductions in observed TCE concentrations were achieved after the initial application of PlumeStop®. Demonstration of

ERD was observed through the reduction in TCE concentrations in downgradient monitor wells, formation of degradation daughter products (through ethene), reduced dissolved oxygen levels and negative oxidation reduction potential, as well as formation of methane and carbon dioxide. Although a reduction in TCE concentrations was observed, the overall mass reduction rate did not achieve project target levels. Additionally, limited reductions were observed in overlying soil gas likely due to the partial source strength TCE concentrations achieved in groundwater. Project limitations include relatively high hydraulic gradients in the test area and the continued influx of contaminant mass and oxygenated water through the test area. However, post-completion monitoring indicates that some level of ERD continued for several years after project closure potentially attributed to the use of a slow reacting electron donor supplement and/or endogenous biomass decay

(Adamson and Newall, 2009). Other project limitations included physical access constraints that limit the ability to install the necessary infrastructure to scale-up an in situ project and achieve the necessary contact with impacted media in an urban environment.

References:

Adamson, David & Newell, Charles. (2009). Support of Source Zone Bioremediation through Endogenous Biomass Decay and Electron Donor Recycling. Bioremediation Journal - BIOREMEDIAT J. 13. 29-40. 10.1080/10889860802690539.

Annable, M.D., K. Hatfield, J. Cho, H. Klammler, B. Parker, J. Cherry, and P.S.C. Rao, 2005. Field-Scale Evaluation of the

Passive Flux Meter for Simultaneous Measurement of Groundwater and Contaminant Fluxes. Environmental Science and

Technology, 39, 7194-7201.

Hatfield, K., M. Annable, J. Cho, P.S.C. Rao, and H. Klammler, 2004. A direct passive method for measuring water and contaminant fluxes in porous media. Journal of Contaminant Hydrology, 75, 155-181.

Arizona Department of Environmental

Quality (ADEQ)

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?

The Air Force Center for Environmental Excellence (AFCEE) MAROS software includes several statistical evaluation tools that allow for the evaluation of temporal trends at a site, including potential spatial distribution of trends, potential data gaps or potential redundant wells in an existing monitoring network, and monitoring frequency. Use of MAROS is only appropriate at sites that have been adequately characterized and have a sufficient (i.e., statistically significant) data set available for assessment. Depending on the available data set, an initial data reduction step may be necessary to fit within the constraints of MAROS (up to 200 wells and 40 sampling events for MAROS 3.0). Monitoring optimization can be performed using the sampling location modules to identify redundant wells, and a sampling frequency module to determine the lowest sampling frequency for each sampling location. A data sufficiency module allows for evaluation of the clean-up status at each sampling location and the importance or significance of the concentration trend at that location. The center’s mass of the plume can be evaluated with MAROS to determine if it is increasing or decreasing and whether it is moving over time. The sampling location and frequency evaluations support the optimization of the monitoring program, both in terms of locations and frequency, such that adequate but not excessive monitoring is conducted to support a determination of whether compliance with remedial objectives is being met. A plume movement analysis supports an assessment of whether the remedy is protective or if mass is moving towards a potential point of exposure (e.g., a municipal or agricultural well) in sufficient quantities to represent a potential risk. A Mann-Kendall test can be used to evaluate statistical trends in individual wells to evaluate the adequacy of MNA. Linear regression analyses can be used to estimate time to achieve compliance levels.

Statistically driven monitoring optimization methods have been developed by GLA staff, including temporal and spatial optimizations that have led to dramatic savings in cost, safety exposure hours, and greenhouse gas emissions due to monitoring activities. While these analyses can be performed to some degree in the AFCEE MAROS software, the software requires upgrades due to bugs and errors. A new release is expected to be available in late 2024 or early 2025.

The new version will retain some of the limitations of the previous versions, including the two-dimensional analysis of plumes. GLA staff have used the methodologies and clear logic presented in the AFCEE MAROS software and developed proprietary tools that can perform analyses on large datasets (hundreds or thousands of wells over tens of years of sampling events, with multiple contaminants of concern) in three dimensions (3D) and with clear graphical outputs. Steps to the monitoring optimization include: 1) a 3D plume stability analysis with graphical outputs of plume footprints, center of mass, and plume mass and volume changes over time, 2) a spatial optimization that identifies the minimum well network needed to replicate plume conditions compared with the full monitoring network, and 3) a sampling frequency analysis that recommends the minimum sampling required for each well based on temporal changes in concentrations.

In the case of the large tetrachloroethylene (PCE) plume, the ten-year dataset would be analyzed for plume stability, including overall mass and volume changes, plume footprint changes, and changes in the center-of-mass of the plume over the ten-year period. Then, a baseline plume would be interpolated using the most recent dataset and a spatial optimization would be performed to identify the wells needed for long-term monitoring, with additional consideration for retaining downgradient wells and wells used for remediation evaluation. Then, a sampling frequency optimization would be performed using Mann-Kendall trends and rates of change to recommend the minimum frequency needed based on historical concentration changes. The recommendations for the optimized program would be communicated in a short technical memo, including plume maps, mass and volume graphs, well network comparison figures, time-series plots, and tables of recommended sampling for each well.