8560-0006_HillAFB_OU_10_SS109_PMR4_Draft_9MAY19.pdf

Hill Air Force Base, Utah

Draft

Operable Unit 10 – Site SS109 Performance Monitoring Report #4

MAY 2019

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1. REPORT DATE (DD-MM-YYYY)

09-05-2019

2. REPORT TYPE

Draft

3. DATES COVERED (From - To)

MAR 2018 – MAY 2019

4. TITLE AND SUBTITLE

Operable Unit 10 – Site SS109 Performance Monitoring Report #4 Hill Air Force Base, Utah

5a. CONTRACT NUMBER

FA8903-09-D-8560-0006

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

EA Engineering, Science, and Technology, Inc., PBC

5d. PROJECT NUMBER 6236906 5e. TASK NUMBER 5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

2363 N. Hill Field Road, Suite 104 Layton, Utah 84041

8. PERFORMING ORGANIZATION

REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) Air Force Civil Engineer Center 2261 Hughes Avenue, Suite 163 JBSA Lackland Air Force Base, Texas 78236-9853

AFCEC

11. SPONSOR/MONITOR’S REPORT

NUMBER(S)

12. DISTRIBUTION/AVAILABILITY STATEMENT

13. SUPPLEMENTARY NOTES

14. ABSTRACT

This Performance Monitoring Report documents progress toward meeting the performance objectives detailed in the Operable Unit (OU) 10 Optimized Exit Strategy Performance Plan. The report includes the results of baseline and post-injection enhanced reductive dechlorination performance monitoring conducted at OU 10 Site SS109 from March 2018 through March 2019. Data from this period of performance monitoring indicate that tetrachloroethene concentrations in Performance Monitoring Wells U9-12-006 and U10-175 have decreased by approximately 94 percent and 99 percent, respectively, from baseline concentrations. In addition, the trichloroethene (TCE) concentration at Performance Monitoring Well (U10-181) has decreased by 98 percent from the baseline concentration. Soil vapor methane concentrations greater than the lower explosive limit (50,000 parts per million) persist in the immediate vicinity of U10-519. Soil gas purging and methane monitoring is ongoing in that area.

15. SUBJECT TERMS

Performance Monitoring Report, optimized exit strategy, optimization, carbon substrate, enhanced reductive dechlorination, treatability study, tetrachloroethene, TCE, methane, soil gas

16. SECURITY CLASSIFICATION OF: 17. LIMITATION

OF ABSTRACT

18. NUMBER

OF PAGES

19a. NAME OF RESPONSIBLE

PERSON

Sandra Staigerwald

a. REPORT

UNCLASSIFIED

b. ABSTRACT

UNCLASSIFIED

c. THIS PAGE

UNCLASSIFIED

SAR 128 19b. TELEPHONE NUMBER (include area code)

(385) 393-4982

Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18

D R A F T

Hill Air Force Base

Performance-Based Remediation

Operable Unit 10 – Site SS109 Performance Monitoring Report #4

Hill Air Force Base Contract No: FA8903-09-D-8560

Task Order 0006

Prepared for:

Air Force Civil Engineer Center 2261 Hughes Avenue, Suite 163

JBSA Lackland Air Force Base, Texas 78236-9853

Prepared by:

2363 N. Hill Field Road, Suite 104 Layton, Utah 84041

MAY 2019

OPERABLE UNIT 10 – SITE SS109 PERFORMANCE MONITORING REPORT #4 DRAFT

HILL AIR FORCE BASE, UTAH MAY 2019

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Contents

Page

Table .............................................................................................................................................................. i Figures .......................................................................................................................................................... ii Appendices .................................................................................................................................................... ii Acronyms and Abbreviations ...................................................................................................................... iii

1.0 Introduction ................................................................................................................................... 1-1

1.1 Purpose of the Report ...................................................................................................... 1-1

1.2 Objectives ........................................................................................................................ 1-1

1.3 Report Organization ......................................................................................................... 1-2

2.0 Remedial Progress and Status ....................................................................................................... 2-1

2.1 Overview of Site Advancement ....................................................................................... 2-1

2.1.1 Enhanced Reductive Dechlorination Implementation ........................................ 2-1

2.1.2 Enhanced Reductive Dechlorination Monitoring ............................................... 2-1

2.1.3 Data Quality Evaluation ...................................................................................... 2-2

2.1.4 Soil Gas Monitoring............................................................................................ 2-2

2.1.5 Remedial Action-Operations Monitoring Well Network Optimization.............. 2-3

2.2 Performance Model Update ............................................................................................. 2-4

2.2.1 Enhanced Reductive Dechlorination Performance (Groundwater)..................... 2-4

2.2.2 Enhanced Reductive Dechlorination Performance (Soil Gas) ............................ 2-6

2.3 Continual Improvement Efforts ....................................................................................... 2-6

2.3.1 Enhanced Reductive Dechlorination Improvement ............................................ 2-6

2.3.2 Compliance with Decision Documents and Plans .............................................. 2-7

2.3.3 Five-Year Review Deficiencies Corrected ......................................................... 2-7

3.0 Performance Summary .................................................................................................................. 3-1

4.0 References ..................................................................................................................................... 4-1

Table

2-1 Baseline and Performance Monitoring Field Parameters and Sample Results

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Figures

1-1 Location Map 1-2 Treatment Areas for the PCE and Shallow TCE Plumes 2-1 On-Base PCE Treatment Area 2-2 Off-Base PCE Treatment Area 2-3 TCE Treatment Area 2-4 On-Base PCE Treatment Performance Plots 2-5 Off-Base PCE Treatment Performance Plots 2-6 Shallow TCE Treatment Performance Plots for Well U10-181

Appendices

A Analytical Data Tables B Data Quality Evaluation C Soil Gas Monitoring Results

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Acronyms and Abbreviations

- Value was not measured or not recorded < Less than µg/L Microgram(s) per liter

AFB Air Force Base

B Analyte is detected in an associated blank bgs Below ground surface BQAPP Basewide Quality Assurance Project Plan

DCE Dichloroethene DO Dissolved oxygen

EA Engineering, Science, and Technology, Inc. (prior to 12 December 2014) or

EA Engineering, Science, and Technology, Inc., PBC (12 December 2014 and thereafter) ERD Enhanced reductive dechlorination EVO Emulsified vegetable oil ft Feet(foot)

IC Institutional control

J Estimated value. The analyte was present, but the reported value may not be precise JBSA Joint Base San Antonio

LEL lower explosive limit

MCL Maximum Contaminant Level mg/L Milligram(s) per liter MNA Monitored natural attenuation mV Millivolt(s)

OES Optimized exit strategy ORP Oxidation reduction potential OU Operable Unit

PBR Performance-Based Remediation PCE Tetrachloroethene PMR Performance Monitoring Report ppmv Part(s) per million by volume

RA-O Remedial action-operation RD/RAWP Remedial Design/Remedial Action Work Plan RG Remediation goal ROD Record of Decision

SVE soil vapor extraction

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TCE Trichloroethene TOC Total organic carbon TS Treatability Study

U Not detected. The analyte was analyzed for but not detected above the method detection limit.

UB Analyte is not detected at or above the indicated concentration due to blank contamination.

UJ Estimated detection limit. The result was estimated and may be a false negative due to related quality control problems.

VC Vinyl chloride VOC Volatile organic compound

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1.0 Introduction

The Air Force Civil Engineer Center has contracted EA Engineering, Science, and Technology, Inc., PBC (EA) to perform remedial actions at multiple Operable Units (OUs) and underground storage tank sites at Hill Air Force Base (AFB) under Performance-Based Remediation (PBR) Contract No. FA8903-09-D- 8560, Task Order 0006. Pursuant to the Comprehensive Environmental Response, Compensation, and Liability Act, cleanup at Hill AFB is being conducted under a Federal Facility Agreement between the Utah Department of Environmental Quality, U.S. Environmental Protection Agency, and Hill AFB.

This Performance Monitoring Report (PMR) #4 has been prepared for OU 10 Site SS109 located in the western portion of Hill AFB in Utah (Figure 1-1). The primary contaminants of concern in groundwater at OU 10 are tetrachloroethene (PCE), trichloroethene (TCE) and daughter products cis-1,2-dichloroethene (DCE) and trans-1,2-DCE. The nature and extent of contamination is documented in more detail in the Remedial Investigation, Feasibility Study, and Feasibility Study Report Supplement (CH2M HILL 2009a; CH2M HILL 2009b; EA 2014). The selected remedies at OU 10 include enhanced reductive dechlorination (ERD) targeted treatment (biobarriers), monitored natural attenuation (MNA), and institutional controls (ICs) for the PCE and Shallow TCE Plumes and MNA and ICs for the Deep TCE Plume. The PCE and Shallow TCE Plumes and associated treatment areas and performance monitoring wells are shown on Figure 1-2.

An ERD treatability study (TS) was initiated on-Base in 2014 to evaluate the effectiveness of treating PCE and TCE (EA 2015a). Additional injections were performed in this area as part of the full-scale ERD implementation in 2015 and 2016.

1.1 Purpose of the Report

This report documents progress toward meeting performance goals provided in the Final OU 10 Optimized Exit Strategy (OES) Performance Plan (EA 2015b). The purpose of the report is to demonstrate remedy performance. The report includes the results of post-injection ERD performance monitoring conducted at the site from March 2018 through March 2019. Performance monitoring data collected for groundwater and soil gas prior to March 2018 are documented in PMR #1 (EA 2016a), PMR #2 (EA 2017), and PMR #3 (EA 2018a). Actual performance data are compared to the performance models described in the Final OU 10 OES Performance Plan (EA 2015b). The report graphically presents measured contaminant concentrations against the performance model curves.

1.2 Objectives

The OU 10 Feasibility Study Supplement Report (EA 2014) showed that without active treatment, remedial timeframes for the PCE and Shallow TCE Plumes would be greater than 50 years. With active treatment in targeted areas at the PCE Plume and Shallow TCE Plume, remedial timeframes could be reduced considerably and life-cycle costs also reduced. For the Deep TCE Plume, Feasibility Study modeling demonstrated that active treatment would provide no benefit in reducing the remedial timeframe.

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The Record of Decision (ROD) for OU 10 (Hill AFB 2015) was signed in 2015 and the selected and implemented remedies included the following:

• PCE Plume – In situ treatment for mass removal by biodegradation, MNA to monitor plume stability/attenuation, and ICs to prevent groundwater exposure until Maximum Contaminant Levels (MCLs) are achieved.

• Shallow TCE Plume – In situ treatment for mass removal by biodegradation, MNA to monitor plume stability/attenuation, and ICs to prevent groundwater exposure until MCLs are achieved.

• Deep TCE Plume – MNA to monitor plume stability/attenuation and ICs to prevent groundwater exposure until MCLs are achieved.

The Minimum Performance Objectives for OU 10 are remedy in place and OES. An Interim Remedial Action Completion Report (EA 2015c) documenting remedy in place has already been approved.

An OES Performance Plan (EA 2015b) was developed to lay out the path to achieving site closeout.

The following PBR performance standards were identified in the OU 10 OES Performance Plan to reduce life-cycle costs and advance the site toward closeout (EA 2015b):

• Reduce PCE concentrations in the PCE Plume treatment areas by 90 percent in the selected biobarrier performance wells.

• The original OES goal was to reduce TCE concentrations in the Shallow TCE Plume treatment area (two separate streets – 200 West and 600 North) by 75 percent in the selected biobarrier performance wells. Because of the accumulation of methane in one of the biobarrier transects (200 West), the USAF prefers that no further substrate injections be performed. Without the ability to affect the 200 West biobarrier with contingency injections, a new performance goal (discussed further in Section 2.3.1) was established as a 75 percent TCE reduction at Performance Monitoring Well U10-181 only (600 North biobarrier). Performance Monitoring Well U10-020 (200 West biobarrier) will continue to be monitored but will have no TCE reduction goal.

• Optimize long-term management by reducing the average number of annual samples collected at the beginning of the Period of Performance by approximately 40 percent by the end of the Period of Performance.

1.3 Report Organization

This report is organized as follows:

• Section 1.0 – Introduction. Presents a brief description of the basis of work and a summary of the purpose and document organization.

• Section 2.0 – Remedial Progress and Status. Describes remediation performance and optimization activities conducted during the period of reporting.

• Section 3.0 – Performance Summary. Summarizes site optimization status and treatment performance.

• Section 4.0 – References. Lists the references used in preparing this document.

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• Appendix A – Analytical Data Tables. Contains tabulated analytical data results from two performance monitoring events conducted during August 2018 and January 2019.

• Appendix B – Data Quality Evaluation. Includes data quality evaluation reports for samples collected during the two groundwater sampling performance monitoring events conducted during August 2018 and January 2019.

• Appendix C – Soil Gas Sampling Analytical Results. Contains tabulated methane data and time series graph for soil gas sampling results during the reporting period of March 2018 through March 2019.

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DAVIS COUNTY

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RIVERDALE

CLINTON

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FIGURE 1-1

LOCATION MAP

OPERABLE UNIT 10 – SITE SS109 PERFORM ANCE M ONITORING REPORT #4

HILL AIR FORCE BASE, UTAH

0 25 5012.5 M iles

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LEGEND

OU10 Plum e Con c en tration s (µg/L):

Coun ty Boun dary M un ic ipa l Boun dary Hill Air Forc e Base Boun dary

PCE Plum e Con c en tration (μg/L) (2016 - 2017)

Sha llow TCE Plum e Con c en tra tion (μg/L) (2016 - 2017)

Deep TCE Plum e Con c en tration (μg/L) (2016 - 2017)

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5 - 10 10 - 100

100 - 1,000

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Plum e c on tours b ased on the c on c en tration s of groun dwa ter sa m ples collected durin g Ja n uary 2016 - M arc h 2017.

Acronym(s) and Abbreviation(s):

µg/L = M ic rogra m (s) per liter OU = Opera b le Un it PCE = Tetra c hloroethen e TCE = Tric hloroethen e V OC = V olatile orga n ic com poun d Note(s):

Geogra phic da ta for the study area were projec ted usin g c oordin a te system W orld Geodetic System 1984 Un iversa l Tra n sverse M erc ator Zon e 12N.

DAVIS-WEBER CANAL

Shallow TCE

PCE

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CLINTON SUNSET

CLEARFIELD

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1200 AREA

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1 inc h equa ls 600 feet

FIGURE 1-2

TREATMENT AREAS FOR THE PCE AND SHALLOW TCE PLUMES

OPERABLE UN IT 10 – SITE SS109 PERFORMAN CE MON ITORIN G REPORT #4

HILL AIR FORCE BASE, UTAH

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Sha llo w Gro und wa ter Flo w Direc tio n

So urc e Area Plum e Bo und a ry, Da shed W here Inferred

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U10-157U10-167

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U10-508

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MAP INDEX

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Extent Source(s):

Im a gery fro m ESRI o nline m a p servic e, Digita lGlo b e, 2017.

Acronym(s) and Abbreviation(s):

µg/L = Mic ro gra m (s) per liter PCE = Tetra c hlo ro ethene RG = Rem ed ia tio n go a l TCE = Tric hlo ro ethene Note(s):

Geo gra phic d a ta fo r the stud y a rea were pro jec ted using c o o rd ina te system W o rld Geo d etic System 1984 Universa l Tra nsverse Merc a to r Z o ne 12N .

0 1.5 3 Miles

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2.0 Remedial Progress and Status

2.1 Overview of Site Advancement

2.1.1 Enhanced Reductive Dechlorination Implementation

Implementation of the targeted in situ treatment with biobarriers, in addition to MNA and ICs, as described in the OU 10 Remedial Design/Remedial Action Work Plan (RD/RAWP) (EA 2015d) began in April 2015, with the construction activities completed by August 2015. The evaluation of progress toward the original performance goals (90 percent reduction in PCE concentrations in the selected PCE Plume treatment area performance wells and 75 percent reduction in TCE in the selected Shallow TCE Plume treatment area performance wells) began following injection of the carbon substrate. The revised performance goal for shallow TCE is discussed further in Section 2.3.1.

Additional injections were performed in 2016 at each treatment area in an attempt to improve substrate distribution within the aquifer and improve treatment reductions. The 60 Percent Slow Release Substrate – Small Droplet Emulsified Vegetable Oil Substrate product from Terra Systems was used for the injections. In March 2017, injections were performed in two new wells along 200 West using the same type of Terra Systems substrate used for the 2016 injections. Locations of the injection wells are illustrated on Figures 2-1 through 2-3.

2.1.2 Enhanced Reductive Dechlorination Monitoring

Groundwater performance monitoring was conducted to assess the effectiveness and progress of subsurface injections. Performance monitoring results from the baseline event and first four post-injection sampling events are documented in PMR #1 (EA 2016a). Performance monitoring results from the fifth through the eighth sampling events are documented in PMR #2 (EA 2017). Performance monitoring results from the ninth and tenth sampling events are documented in PMR #3 (EA 2018a).

Performance monitoring conducted during this reporting period included collection of water level measurements, water quality parameters, and groundwater samples during the following events:

• Eleventh post-injection sampling event – August 2018

• Twelfth post-injection sampling event – January 2019.

For evaluation purposes, performance monitoring data were compared with baseline data as detailed in the OU 10 OES Performance Plan (EA 2015b). The sampling frequency and performance indicators were selected to monitor performance of each ERD biobarrier in reducing PCE and TCE concentrations in groundwater and to collect adequate representative data to support decision making and system optimization.

Semi-annual groundwater samples were collected from Wells U9-12-006, U10-020, U10-133, U10-172, U10-175, U10-181, U10-182, U10-198, and U10-214. The locations of these monitoring wells are illustrated on Figure 1-2 and Figures 2-1 through 2-3. Performance Monitoring Wells U9-12-006 and U10-175 were used to monitor treatment performance for the on-Base and off-Base PCE Plumes, respectively. As discussed in Section 2.2.1, the revised performance model utilizes TCE concentrations in Performance Monitoring Well U10-181 to monitor treatment performance for the Shallow TCE Plume.

The remaining downgradient ERD monitoring wells were used to monitor groundwater conditions in the treatment zone, but were not part of the performance calculation.

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Groundwater elevation and field geochemical parameters (temperature, pH, conductivity, oxidation reduction potential, turbidity, and dissolved oxygen) were measured in accordance with the OU 10 RD/RAWP (EA 2015d). Groundwater samples for laboratory analysis were collected in accordance with the OU 10 RD/RAWP (EA 2015d). Groundwater monitoring field parameters and analytical groundwater monitoring results are presented in Table 2-1 for all monitoring events since the baseline sampling round. Analytical data tables from the two groundwater performance monitoring events (in August 2018 and January 2019) are included in Appendix A.

2.1.3 Data Quality Evaluation

Evaluation of 100 percent of the chemical data was performed using methods in the PBR Work Plan, which is Attachment 2 of the Quality Program Plan for Performance-Based Remediation (Hill AFB 2013), and the Basewide Quality Assurance Project Plan (BQAPP) (Hill AFB 2014) as a guide for data quality. The assessment of data included reviewing (1) chain-of-custody documentation; (2) holding-time compliance; (3) required quality control samples at the specified frequencies; (4) flagging for method blanks; (5) laboratory control spiking samples; (6) surrogate spike recoveries for organic analyses;

(7) matrix spike and matrix spike duplicate samples on a site and location basis; (8) internal standard areas and retention times; and (9) initial and continuing calibration information and other method-specific criteria as documented in the data quality evaluation included in Appendix B.

The BQAPP completeness goal of 95 percent was met for all analytes. Out of approximately 1,270 normal and FD data points, 26 final results were qualified as estimated due to QC exceedances related to calibration, field duplicate, holding time, laboratory control sample, and matrix (approximately

2.1 percent); and 9 results were affected by laboratory or field blanks (approximately 0.7 percent). This meets the completeness goal stated in the BQAPP for the project and indicates that the quality of the laboratory program and field procedures is sufficient to meet the project data quality objectives. Based on the data quality evaluation, the data were found to be of acceptable quality and can be used in the project decision making process. The completeness summary is presented in Appendix B, Table B-9.

Evaluation of 100 percent of the chemical data was performed using the BQAPP as a guide for data quality. No systematic protocol errors were identified based on the QC program set up or during the monitoring of the field or laboratory efforts.

2.1.4 Soil Gas Monitoring

A baseline (or pre-treatment) soil gas sampling event was conducted in April and May 2015 prior to substrate injections. Since that time, monthly soil gas samples were collected through May 2017 from five soil gas probes (U10-194, U10-508, U10-519, U10-525, and U10-570). The locations of these soil gas probes are illustrated on Figure 1-2 and Figures 2-1 through 2-3. From May 2015 through May 2017, data collected from these soil gas probes showed that all health-related constituents (volatile organic compounds [VOCs], hydrogen sulfide, and methane) remained below site-specific screening levels listed in Table 6-10 of the OU 10 RD/RAWP (EA 2015d).

The May 2017 soil gas monitoring event concluded the 2 years of soil gas monitoring specified in the OU 10 RD/RAWP (EA 2015d). However, because additional substrate injections were performed at two wells near soil gas probe U10-519 (Figure 2-3), it was agreed with the U.S. Air Force (USAF) that quarterly soil gas monitoring would be performed in this area until Winter 2018.

Eafp\departments\Federal\6236900 AFCEE WERC09\6236906 Hill AFB PBR 2-3

High methane concentrations initially detected in September 2017 are still present (above the lower explosive limit [LEL] of 50,000 ppmv) in the immediate vicinity of soil gas probe U10-519 along 200 West and approximately 590 North in Clearfield City. A methane purge test work plan describing the use of a portable soil vapor extraction (SVE) system was prepared and approved in 2018 (EA 2018b). A one-day purge event using two SVE vent wells was initiated in August 2018 and was successful at reducing methane concentrations to below the LEL at U10-519 (EA 2018c). Following documentation of the purge test and Air Force approval to continue, one-day purge tests have been performed approximately every 3 to 4 weeks since November 2018. Appendix C, Table 1 includes all the methane data for soil gas probes along with the SVE vent wells as part of the purge test events.

Indoor air monitoring for methane was performed at the two residential homes adjacent to U10-519 (U10-8237 and U10-8052) in February and March 2019. Traces of methane were detected around gas appliances. No methane attributed to soil vapor intrusion into the residence was detected in either home.

These are the same homes that were monitored for methane in September 2017 when high methane at U10-519 was initially detected.

Methane data for this reporting period are discussed in Section 2.2.2.

2.1.5 Remedial Action-Operations Monitoring Well Network Optimization

In January 2016, optimization of remedial action-operation (RA-O) groundwater monitoring was performed for the plumes at OU 10. Optimization of RA-O groundwater monitoring at OU 10 consisted of both geostatistical and qualitative evaluations of the RA-O groundwater monitoring well network (EA 2016b). The optimization resulted in a 25 percent reduction in the number of wells or intervals within long-screened wells that are used to monitor groundwater at OU 10, based on the 2014 monitoring well network, plus a reduction in the sampling frequency for some wells.

The optimization of the OU 10 RA-O groundwater monitoring represents an overall reduction in the average number of groundwater VOC samples collected annually, from 377 samples in 2012 (as shown in Table 5-1 of the OU 10 Performance Standard Verification Plan [Hill AFB 2012]) to 151 samples in Operating Year 2018 (as shown in Table A-1 of the April 2017 – March 2018 OU 10 – Site SS109 Annual RA-O Report [EA 2018d]). This is an approximately 60 percent reduction, even after considering that new monitoring wells were added to the OU 10 monitoring network as part of the selected remedy (EA 2015d).

This overall reduction consists of the average reduction in the number of groundwater VOC samples collected per year, which includes the results of optimizing the number of wells and the sampling frequency. It should be noted that the number of wells sampled at OU 10 in any given year varies because some wells are sampled only every 2 or 4 years. To accurately represent the number of samples collected over the long term, the average number of samples collected annually is calculated over a 4-year period. This was accomplished by prorating the number of samples for each monitoring well in both Table 5-1 of the OU 10 Performance Standard Verification Plan (Hill AFB 2012) and Table A-1 of the April 2017 – March 2018 OU 10 – Site SS109 Annual RA-O Report (EA 2018d). The proration was based on the sampling frequency for each well as follows:

• Quarterly: 4 (i.e., 4 samples per year)

• Semi-annually: 2

• Annually: 1

• Every 2 years: 0.5

• Every 4 years: 0.25

Eafp\departments\Federal\6236900 AFCEE WERC09\6236906 Hill AFB PBR 2-4

This method resulted in an average of 377 samples collected annually over a 4-year period, based on the 2012 monitoring network and sampling frequencies, and an average of 151 samples collected annually over a 4-year period, based on the 2018 monitoring network and sampling frequencies.

2.2 Performance Model Update

2.2.1 Enhanced Reductive Dechlorination Performance (Groundwater)

The performance of each ERD biobarrier was evaluated by calculating reductions in the PCE and TCE concentrations from performance monitoring wells downgradient of each biobarrier. A detailed discussion of baseline concentrations and projected reductions in PCE and TCE for the OU 10 Plume treatment areas are included in the OU 10 OES Performance Plan (EA 2015b). The performance goal at OU 10 is to reduce PCE concentrations in the selected PCE Plume treatment area performance wells by 90 percent. For the Shallow TCE Plume, the performance goal was a 75 percent reduction from the mean TCE concentration in groundwater from Performance Monitoring Wells U10-020 and U10-181 by 2020.

Although concentrations of TCE have been reduced, concentrations have fluctuated beyond the potential process improvement and into the contingency range (EA 2017). At the injection row along 200 West, poor substrate distribution and preferential flow paths have been observed. Substrate is thought to have entered the vadose zone via a preferential flow path during a March 2017 injection event, leading to methane generation. As a result, the USAF has indicated they prefer the contingency measure of additional substrate injections not be performed in this area. Therefore, the revised goal is 75 percent reduction by 2020 at Performance Monitoring Well U10-181 only (located at the 600 North transect) compared to 2015 baseline concentrations. Groundwater TCE concentration monitoring will continue at Performance Monitoring Well U10-020. Performance as measured against this revised goal is discussed below.

2.2.1.1 Primary Contaminants of Concern Enhanced Reductive Dechlorination Baseline Performance

Indicator Projection

On-Base PCE Plume Treatment Area. For the on-Base PCE Plume treatment zone (Figure 2-1), Performance Monitoring Well U9-12-006 was used to establish the performance model. Although Well U10-198 also will be used to monitor performance of the biobarrier, it is not being used as part of the performance calculation because of the low initial concentration of PCE. The treatment goal for the on-Base PCE Plume is to reduce the PCE concentration in Well U9-12-006 to 9 micrograms per liter (µg/L).

Off-Base PCE Plume Treatment Area. For the off-Base PCE Plume treatment zone (Figure 2-2), Performance Monitoring Well U10-175 was used to establish the performance model. Although Well U10-214 also will be used to monitor performance of the biobarrier, it is not being used as part of the performance calculation because of the low initial concentration of PCE. The treatment goal for the off-Base PCE Plume is to reduce the PCE concentration in Well U10-175 to 11 µg/L.

Shallow TCE Plume Treatment Area. For the Shallow TCE Plume treatment zone (Figure 2-3), the concentration of TCE in Performance Monitoring Well U10-181 was used to establish the performance model for the TCE biobarrier (EA 2015b). The treatment goal for the Shallow TCE Plume is to reduce the TCE concentration in Well U10-181 to 28 µg/L.

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2.2.1.2 Primary Contaminants of Concern Enhanced Reductive Dechlorination Actual Performance Indicator Values

On-Base PCE Plume Treatment Area. The baseline (or pre-treatment) concentration for the on-Base PCE Plume treatment area is represented by the March 2014 PCE concentration in Performance Monitoring Well U9-12-006 because the ERD TS was implemented at this location after March 2014 (EA 2014). This baseline PCE concentration was 90 µg/L. In January 2019, PCE concentrations at U9-12-006 measured 5.5 µg/L, which represents an overall PCE concentration reduction of 94 percent compared with the pre-treatment March 2014 concentration and exceeds the treatment reduction goal of 90 percent to 9 µg/L or less. Time-series graphs of the PCE concentrations and percent reductions for Performance Monitoring Well U9-12-006 are presented on Figure 2-4.

Off-Base PCE Plume Treatment Area. The baseline concentration for the off-Base PCE Plume treatment area is represented by the May 2015 PCE concentration of 107 µg/L in Performance Monitoring Well U10-175. During August 2018 and January 2019, PCE concentrations at U10-175 remained less than 1 µg/L, which represents an overall PCE concentration reduction of over 99 percent compared with the pre-injection Spring 2015 baseline and exceeds the treatment reduction goal of 90 percent to 11 µg/L or less. Time-series graphs of the PCE concentrations and percent reductions for Performance Monitoring Well U10-175 are presented on Figure 2-5.

Shallow TCE Plume Treatment Area. The OES performance goals for the Shallow TCE Plume were originally represented by the average TCE concentration in Performance Monitoring Wells U10-020 and U10-181. The performance goal has been revised to a 75 percent TCE reduction by 2020 at Performance Monitoring Well U10-181 only. Performance Monitoring Well U10-020 will continue to be monitored but not included in the performance goal calculation. The baseline TCE concentration for U10-181 is represented by May 2015 data, when the TCE concentration was 112 µg/L. As of January 2019, the TCE concentration in U10-181 has decreased to 1.7 µg/L. This represents an overall TCE concentration reduction of approximately 98 percent compared to the May 2015 baseline concentration and exceeds the treatment reduction goal of 75 percent to 28 µg/L or less. Time-series graphs of the TCE concentrations and percent reductions for Performance Monitoring Well U10-181 are presented on Figure 2-6.

2.2.1.3 Daughter Product Enhanced Reductive Dechlorination Performance Indicator Values

Concentrations of PCE/TCE degradation products (cis-1,2-DCE, trans-1,2-DCE, and vinyl chloride [VC]) are expected to increase in performance monitoring wells during the ERD treatment process.

Cis-1,2-DCE concentrations were detected above baseline values in Wells U9-12-006, U10-020, U10-172, U10-175, U10-198, and U10-181 during the reporting period. Cis-1,2-DCE, trans-1,2-DCE, and VC concentrations have been detected over several sampling events at one well (U10-181), with the most recent January 2019 concentrations of 85 µg/L, 0.92 J µg/L, and 1.3 J µg/L, respectively.

Cis-1,2-DCE, trans-1,2-DCE, and VC concentrations are included in Table 2-1.

2.2.1.4 Water Quality Enhanced Reductive Dechlorination Performance Indicator Values

Total organic carbon (TOC) is monitored to evaluate the distribution and consumption of the injected carbon substrate. A TOC threshold of 20 milligrams per liter (mg/L) is used as a general indication that geochemical conditions conducive for ERD treatment of PCE and TCE have been created at OU 10.

Baseline (or pre-treatment) TOC concentrations were less than 2 mg/L in Performance Monitoring Wells U10-175, U10-020, and U10-181. In January 2019, TOC concentrations were greater than 20 mg/L in one well, U10-181, measuring 250 mg/L. Methane concentrations remained elevated from baseline values in the majority of the performance monitoring wells. Similarly, elevated ferrous iron and low oxidation reduction potential (ORP) and dissolved oxygen (DO) values were measured at most of the

Eafp\departments\Federal\6236900 AFCEE WERC09\6236906 Hill AFB PBR 2-6 performance wells, indicating anaerobic conditions have persisted in those wells. TOC and methane concentration results are included in Table 2-1.

Groundwater geochemical data from each treatment zone indicate that multiple carbon substrate injections created anaerobic conditions conducive for ERD. DO and ORP have remained relatively low in most wells and continue to provide the anaerobic groundwater conditions necessary for successful ERD. Additionally, the reduction in sulfate and nitrate and the production of methane all strongly indicate that effective anaerobic conditions persist for dechlorination of PCE and TCE in each treatment zone. As expected, metals concentrations including arsenic, manganese, and ferrous iron have increased above baseline concentrations in response to the geochemically reducing conditions created by the substrate injections. Table 2-1 presents the results for each analyte and field parameter for each sampling event.

2.2.2 Enhanced Reductive Dechlorination Performance (Soil Gas)

As discussed in Section 2.1.4, elevated (above the LEL) soil vapor methane concentrations persist beneath the road in the immediate vicinity of U10-519. Ongoing monitoring was performed during the reporting period at U10-519, U10-525, U10-250, U10-251, U10-252, U10-253, U10-254, U10-8237, and U10-8052 (Figure 2-3). Elevated methane concentrations (above the LEL) were measured during the reporting period at soil gas probe U10-519 and SVE vent wells U10-255 and U10-256, which are located approximately 5 feet directly north and south of U10-519, respectively. An overall decrease in methane concentrations has been observed at each location following initiation of the purge events, and methane rebound between events has decreased significantly. However, methane concentrations greater than the LEL continue to be measured at U10-519, U10-255, and U10-256. Increased frequency of purge events, approximately every 5 to 7 days, are planned to start in April 2019 and last for approximately 1 to 2 months. The increased frequency will allow for oxygen levels to remain above 5 percent and increase the methane degradation rate. Purge events thereafter will continue in accordance with recommendations made in the Operable Unit 10 – Off-Base Trichloroethene/Enhanced Reductive Dechlorination Treatment Area Soil Vapor Methane Purge Test Results Summary Technical Memorandum, Hill Air Force Base, Utah (EA 2018c). Methane data for the soil gas sampling events are provided in Appendix C, Table C-1.

Time-series plots of methane data for each purge event for U10-519, U10-255, and U10-256 are provided in Appendix C, Figure C-1, Figure C-2, and Figure C-3, respectively.

2.3 Continual Improvement Efforts

2.3.1 Enhanced Reductive Dechlorination Improvement

Contaminant concentrations in the TCE treatment area have been reduced to below the OES goal in performance monitoring well U10-181. No further process improvements are required for the TCE plume.

For the PCE treatment areas, PCE concentrations have been reduced by greater than 94 percent on-Base and 99 percent off-Base, relative to baseline concentrations and exceeding the OES performance goal.

No further process improvements are required for the PCE plume.

Soil gas purging and monitoring for methane will be performed approximately every 1 to 3 weeks in the area along 200 West until methane readings fall below the lower explosive limit.

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2.3.2 Compliance with Decision Documents and Plans

OU 10 is managed in compliance with the OU 10 ROD (Hill AFB 2015) and RD/RAWP (EA 2015d), which includes the following remedies to address groundwater contamination. The status of each remedy also is noted.

Remedy (summarized) Status PCE Plume – In situ treatment for mass removal by biodegradation, MNA to monitor plume stability/attenuation, and ICs

In Compliance

Shallow TCE Plume – In situ treatment for mass removal by biodegradation, MNA to monitor plume stability/attenuation, and ICs

In Compliance

Deep TCE Plume – MNA to monitor plume stability and ICs In Compliance ICs to prevent completion of potential exposure pathways In Compliance Five-year review of remedial actions In Compliance

2.3.3 Five-Year Review Deficiencies Corrected

The 2018 Five-Year Review did not identify deficiencies for OU 10.

TABLE 2-1

Baseline and Performance Monitoring Field Parameters and Sample Results Operable Unit 10 – Site SS109 Performance Monitoring Report #4, Hill Air Force Base, Utah

Location Monitoring

Well Analyte

Measurement/ Analysis Method Units

Sampling Event Results

Pre-Injection Baseline(1)

First Post- Injection

July 2015(1)

Second Post- Injection

September 2015(1)

Third Post- Injection

December 2015(1)

Fourth Post- Injection March

2016(1)

Fifth Post- Injection

August 2016(1)

Sixth Post- Injection

November 2016(1)

Seventh Post- Injection February/

March 2017(1)

Eighth Post- Injection

May 2017(1)

Ninth Post- Injection

October 2017(1)

Tenth Post- Injection February

2018(1)

Eleventh Post- Injection

August 2018(1)

Twelfth Post- Injection

January 2019(1)

On-Base

PCE

Treatment Area

U10-133

29-Apr-15 7-Jul-15 17-Sep-15 21-Dec-15 17-Mar-16 2-Aug-16 17-Nov-16 2-Mar-17 16-May-17 4-Oct-17 26-Feb-18 08-Aug-18 31-Jan-19 39-41 ft bgs 39-41 ft bgs 33-35 ft bgs 33-35 ft bgs 33-35 ft bgs 33-35 ft bgs 33-35 ft bgs 33-35 ft bgs 33-35 ft bgs 33-35 ft bgs 33-35 ft bgs 33-35 ft bgs 33-35 ft bgs

TOC SW 9060A mg/L 0.562 J 0.836 J 0.587 J 0.454 J 0.735 J 0.664 0.767 0.52 0.802 0.701 0.813 0.86 J 1 B

PCE

SW 8260B

µg/L 5.91 5.40 1.48 2.08 2.55 2.91 1.8 2.68 2.24 2.08 2.72 2.1 1.6 TCE µg/L 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 1 U 1 U cis-1,2-DCE µg/L 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 1 U 1 U trans-1,2-DCE µg/L 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 1 U 1 U

VC µg/L 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 1.5 U 1.5 U Methane RSK-175 µg/L 0.208 J 0.0454 J 0.189 0.108 U 0.0776 J 0.0773 J 0.0788 J 0.174 J 0.193 U 0.169 J 0.26 J 5 U 5 U Ethene µg/L 0.456 U 0.408 U 0.239 U 0.222 U 0.236 U 0.225 U 0.282 J 0.355 U 0.371 U 0.426 U 5 U 5 U 5 U

Arsenic, dissolved SW 6020A mg/L 0.0017 J 0.00181 B 0.00162 J 0.00159 J 0.00170 J 0.00181 J 0.00157 J 0.0016 J 0.00157 0.00155 0.00148 0.0015 J 0.0013 J Manganese, dissolved mg/L 0.000763 UB 0.002 UB 0.002 UB 0.00158 B 0.00172 B 0.00204 B 0.004 UB 0.00325 B 0.0017 B 0.001 UB 0.001 UB 0.0035 U 0.0035 U

Ferrous Iron HACH(2) mg/L < 0.03 0.04 0.10 0.38 0.38 0.11 0.08 0.03 0.02 0.02 0.0 1.05 0.02 Sulfate E300 mg/L 18.0 25.7 20.7 21.7 23.3 24.6 26 B 26.2 26.2 26.4 27.3 31 24 Sulfide E376.2 mg/L 0.0141 J 0.0250 U 0.0262 0.0250 U 0.0530 J 0.0164 J 0.0371 J 0.025 U 0.025 U 0.025 U 0.025 U 4 U 4 U

Nitrate-N E353.2 mg/L 3.72 3.79 3.93 2.44 2.38 B 2.63 B 1.7 B 2.2 B 1.96 2.07 2.63 1.8 1.2 B

DO

YSI

mg/L 2.3 3.1 3.0 4.5 2.5 2.57 3.2 4.7 4.33 5.0 3.6 3.6 2.61

ORP mV 210 310 161 28.5 199 35 132.0 144.8 100.7 35.6 145 112.6 71.5 pH 6.90 7.24 7.28 7.27 7.32 7.44 7.4 7.25 7.23 7.3 7.0 7.0 7.1

U10-198

16-Apr-15 7-Jul-15 22-Sep-15 21-Dec-15 15-Mar-16 4-Aug-16 16-Nov-16 28-Feb-17 18-May-17 4-Oct-17 27-Feb-18 08-Aug-18 30-Jan-19 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs

TOC SW 9060A mg/L 0.944 J 3.58 1.89 0.89 J 1.16 0.955 1.06 0.795 1.42 2.48 2.93 2.8 3

PCE

SW 8260B

µg/L 13.80 10.40 1.29 4.53 5.48 3.31 3.38 5.48 3.69 4.74 1.07 4.2 3.3 TCE µg/L 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.18 J 0.5 U 0.18 J 0.5 U 0.27 J 0.28 J cis-1,2-DCE µg/L 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.23 J 2.11 1.3 1 U trans-1,2-DCE µg/L 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 1 U 1 U

VC µg/L 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 1.5 U 1.5 U Methane RSK-175 µg/L 0.0495 J 0.0377 J 0.0527 J 0.483 16.6 27.4 269 197 264 3940 1400 3200 5100 J Ethene µg/L 0.349 U 0.484 U 0.198 U 0.186 U 0.217 U 0.256 U 0.234 U 0.396 U 0.379 U 1.56 U 5 U 5 U 5 U

Arsenic, dissolved SW 6020A mg/L 0.000904 J 0.00093 B 0.00163 J 0.00172 J 0.00175 J 0.0027 0.00241 0.00213 0.00239 0.0608 B 0.0179 B 0.026 0.013 Manganese, dissolved mg/L 0.0441 0.207 B 0.653 B 0.691 B 0.728 B 1.01 B 0.718 B 0.494 B 0.451 B 0.502 B 0.387 B 0.2 0.0055 B

Ferrous Iron HACH(2) mg/L < 0.03 1.6 < 0.03 0.67 0.24 0.06 0.14 0.0 0.02 1.96 1.71 2.92 0.02 Sulfate E300 mg/L 13.4 24.4 19.1 12.8 18.4 20.8 B 20.9 B 18.6 B 12.5 B 14.9 8.83 4.7 J 3.6 J Sulfide E376.2 mg/L 0.0250 U 0.0282 0.0152 J 0.0250 U 0.027 0.025 U 0.025 U 0.00905 J 0.025 U 0.025 U 0.0739 4 U 4 U

Nitrate-N E353.2 mg/L 7.29 3.54 4.64 B 6.96 8.51 13.7 9.57 B 6.49 4.36 B 0.603 0.0852 0.5 UJ 0.26 J

DO

YSI

mg/L 0.73 3.0 0.11 0.84 5.6 1.6 0.0 2.87 3.72 2.6 2.5 1.1 1.57

ORP mV 222 272 99.8 -138 52.6 20.9 -157.9 46.4 42.8 -143 -145 -19.2 78.2 pH 8.01 7.70 8.33 7.85 8.10 7.91 8.1 7.82 7.80 7.3 7.5 6.1 7.23

U9-12- 006(3)

11-Mar-14 7-Jul-15 22-Sep-15 21-Dec-15 15-Mar-16 4-Aug-16 16-Nov-16 28-Feb-17 18-May-17 4-Oct-17 26-Feb-18 08-Aug-18 31-Jan-19 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs 32-34 ft bgs

TOC SW 9060A mg/L ‒ 7.62 1.63 6.14 2.45 6.83 6.37 8.68 4.11 3.49 4.04 2.7 1.6 B

PCE

SW 8260B

µg/L 90 14.8 15.6 15.6 14.4 15.8 10.3 13.3 11 9.59 7.92 7.7 5.5 TCE µg/L 7.8 0.5 U 0.17 J 0.31 J 0.380 J 0.47 J 0.85 1.77 1.6 2.45 2.95 2.9 3 cis-1,2-DCE µg/L 0.2 U 0.5 U 0.5 U 0.85 1.11 0.21 J 0.57 1.52 1.59 1.96 1.97 2 0.44 J trans-1,2-DCE µg/L 0.2 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 1 U 1 U

VC µg/L 0.8 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 1.5 U 1.5 U Methane RSK-175 µg/L ‒ 24.1 58.2 328 660 982 2,540 971 J 1880 7920 13000 6300 4600 Ethene µg/L ‒ 0.445 U 0.2 U 0.195 U 0.217 U 0.233 0.725 U 0.385 U 0.425 U 2.42 U 5 U 5 U 5 U

Arsenic, dissolved SW 6020A mg/L ‒ 0.0166 B 0.00457 0.0342 0.0920 B 0.0857 0.274 0.374 0.4 0.331 B 0.42 0.240 0.094 Manganese, dissolved SW 6020A mg/L ‒ 1.21 B 0.831 B 0.773 B 1.06 B 0.887 B 1.03 B 0.994 B 0.906 B 1.05 B 1.1 B 0.770 0.42

Ferrous Iron HACH(2) mg/L 0.09 0.06 < 0.03 2.4 3.3 2.96 2.11 3.3 1.41 2.42 2.94 3.3 0.76 Sulfate E300 mg/L ‒ 20.0 B 21.5 13.9 18.4 9.87 B 5.24 B 2.3 B 5.65 B 4.15 4.51 9.4 5 Sulfide E376.2 mg/L ‒ 0.00817 J 0.0250 U 0.00938 J 0.0250 U 0.0825 0.0702 0.33 0.00903 J 0.0166 J 0.00971 J 4 U 4 U

Nitrate-N E353.2 mg/L ‒ 0.684 0.922 B 0.126 0.0127 0.194 0.0762 B 0.0315 0.0215 B 0.01 U 0.142 0.5 UJ 0.5 UB

DO

YSI

mg/L 3.1 0.11 0.50 1.4 0.20 0.23 0.0 0.21 0.43 3.1 0.9 0.3 0.33

ORP mV 118 -39.5 104 -63.1 -140 -186.3 -161.3 -188.3 -124.3 -138.1 -148 -102.8 -127.6 pH 7.13 7.17 6.91 7.02 7.21 7.12 7.2 7.0 6.95 7.0 6.6 6.7 6.98

Baseline and Performance Monitoring Field Parameters and Sample Results Operable Unit 10 – Site SS109 Performance Monitoring Report #4, Hill Air Force Base, Utah

Location Monitoring

Well Analyte

Measurement/ Analysis Method Units

Sampling Event Results

Pre-Injection Baseline(1)

First Post- Injection

July 2015(1)

Second Post- Injection

September 2015(1)

Third Post- Injection

December 2015(1)

Fourth Post- Injection March

2016(1)

Fifth Post- Injection

August 2016(1)

Sixth Post- Injection

November 2016(1)

Seventh Post- Injection February/

March 2017(1)

Eighth Post- Injection

May 2017(1)

Ninth Post- Injection

October 2017(1)

Tenth Post- Injection February

2018(1)

Eleventh Post- Injection

August 2018(1)

Twelfth Post- Injection

January 2019(1)

Off-Base

PCE

Treatment Area

U10-172

20-May-15 9-Jul-15 17-Sep-15 16-Dec-15 14-Mar-16 2-Aug-16 16-Nov-16 28-Feb-17 17-May-17 2-Oct-17 22-Feb-18 02-Aug-18 31-Jan-19 24-27 ft bgs 24-27 ft bgs 24-27 ft bgs 24-27 ft bgs 24-27 ft bgs 24-27 ft bgs 24-27 ft bgs 24-27 ft bgs 24-27 ft bgs 24-27 ft bgs 24-27 ft bgs 24-27 ft bgs 24-27 ft bgs

TOC SW 9060A mg/L 3.08 3.76 5.24 1.75 4.06 3.62 4.54 2.7 6.45 3.35 1.46 8.8 B 7.7 B

PCE

SW 8260B

µg/L 4.40 4.56 3.57 2.90 3.68 2.65 1.49 1.16 0.46 J 0.19 J 0.5 U 1 U 1 U TCE µg/L 11.3 10.5 10.1 11.8 13.1 12.1 10.1 14.7 13.4 10.3 9.17 1.7 1.8 cis-1,2-DCE µg/L 9.27 9.45 7.43 8.05 10.40 9.6 10.7 9.32 7.16 6.31 7.92 18 17 trans-1,2-DCE µg/L 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.17 J 0.21 J 1 U 0.21 J

VC µg/L 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 0.5 U 1.5 U 1.5 U Methane RSK-175 µg/L 3240 1760 4,240 8,050 8,820 3,870 7,130 1,570 2,780 8460 11000 6800 3300 Ethene µg/L 2.63…