Evaluation of Remedy Completeness at the General Mills/Henkel Corp Superfund … · 2017. 3....

EVALUATION OF REMEDY COMPLETENESS AT

THE GENERAL MILLS/HENKEL CORP. SUPERFUND SITE

Issued: 14 March 2017 Prepared for: General Mills, Inc.

GSI Environmental Inc. 2211 Norfolk, Suite 1000, Houston, Texas 77098-4054 tel. 713.522.6300

March 2017 EVALUATION OF REMEDY COMPLETENESS AT THE GENERAL

MILLS/HENKEL CORP. SUPERFUND SITE

Table of Contents

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1.0 INTRODUCTION ...................................................................................................... 11.1 Personal qualifications and experience ............................................................................ 11.2 Summary of my involvement with the Facility ................................................................. 21.3 Summary of key findings ................................................................................................... 2

2.0 SITE HISTORY AND OVERVIEW ........................................................................... 4

3.0 DETAILED FINDINGS ............................................................................................. 53.1 Based on the large amount of new information since 2013, the conceptual model of

environmental impacts associated with the Facility must be updated to correctly show only limited historical impacts. ............................................................................... 5

3.2 There are multiple sources of TCE and other chlorinated solvents not associated with the Facility ................................................................................................................... 8

3.3 The waste material associated with the Facility had a unique fingerprint that was distinct from other sources of TCE in the vicinity. ........................................................ 12

3.4 The soil and groundwater impacts associated with the historical disposal of waste at the soil absorption pit were limited to the immediate vicinity of the pit. ..................... 17

3.5 The high concentrations of petroleum and chlorinated solvents detected in Monitoring Well 106 installed at the former disposal site were an artifact of drilling and not indicative of aquifer contamination. .................................................................. 19

3.6 Available investigation results show no current or historical DNAPL impacts at the Facility. ............................................................................................................................... 24

3.7 The pump and treat remediation system successfully remediated groundwater impacts associated with the Facility by 1991. ................................................................ 27

3.8 Considering both current and historical information, it is clear that upgradient sources of TCE in groundwater were already impacting the Facility and areas further downgradient in the 1980s. .............................................................................................. 31

3.9 There is no “clean area” or “area of lower TCE” separating the upgradient sources from the area of the Facility. ............................................................................................ 32

3.10 All necessary response actions at the General Mills/Henkel Superfund Site have been completed. ................................................................................................................ 39

4.0 CITED REFERENCES ........................................................................................... 39

March 2017 EVALUATION OF REMEDY COMPLETENESS AT THE GENERAL

MILLS/HENKEL CORP. SUPERFUND SITE

Table of Contents

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Tables Table 1: Summary of Investigations at Properties Upgradient from the Facility That Have

Detected TCE in Shallow Groundwater ..................................................................... 12Table 2: Testimony of Former GMI Employees Regarding Solvents Used at 2010 E

Hennepin Research Laboratory Between 1947 and 1962 ........................................ 13Table 3: Average Concentration of Chlorinated Solvents in GMI Source Soil Samples ...... 18Table 4: Percentage of TCE in Soil and Water Samples Collected within 20 ft of the Former

Soil Absorption Pit Compared to Samples Collected Greater than 20 ft from the Former Soil Absorption Pit ......................................................................................... 19

Figures Figure 1: Revised Conceptual Model of TCE Plume in the 1980s Based on Currently

Available Information .................................................................................................. 7Figure 2: Revised Conceptual Model of the Current TCE Plume .............................................. 8Figure 3: TCE Concentrations in the Glacial Drift Aquifer and in Sub-slab Samples ........... 10Figure 4: Area of GSI Evaluation of MPCA Investigation/Remediation Sites ........................ 11Figure 5: VOC Contamination in Soil in the Vicinity of the Former Soil Absorption Pit:

1980s Investigation Results ..................................................................................... 16Figure 6: Illustration of Contamination from Unsaturated Soil Being Smeared Around the

Borehole During the Installation of Monitoring Well 106 in March 1983 .............. 21Figure 7: Illustration of Borehole Contamination at Monitoring Well 106 and the

Dissipation of the Contamination over the Three Sample Events in 1983 .......... 22Figure 8: VOC Concentrations Measured in Water Samples Collected from Well 106 ......... 23Figure 9: Results from 2014 Investigation of TCE in Glacial Drift Aquifer Showing Vertical

Distribution Inconsistent with DNAPL from Former Soil Absorption Pit ............. 27Figure 10: Chlorinated Solvent Concentrations in Recovered Groundwater Sent to the On-

site Treatment System: 1985 to 1996 ...................................................................... 29Figure 11: Investigation Results for Locations DP-72 to DP-76 .............................................. 34Figure 12: TCE Concentrations in Groundwater and Sub-slab Vapors in the Vicinity of the

Facility ........................................................................................................................ 36Figure 13: Overlay of MPCA TCE Concentration Figure and TCE Sub-slab Vapor

Concentration Data ................................................................................................... 38 Attachments Attachment A Resume of Thomas E. McHugh, Ph.D., D.A.B.T.

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EVALUATION OF REMEDY COMPLETENESS AT THE GENERAL MILLS/HENKEL CORP. SUPERFUND SITE

1.0 Introduction 1.1 Personal qualifications and experience I, Thomas E. McHugh, am a Principal Toxicologist and environmental scientist with GSI Environmental Inc., (GSI) with over 20 years of experience in toxicology and environmental science and engineering, specializing in the areas of human and ecological risk assessment, environmental site investigation, and corrective action design. I received a B.S. in Biochemistry and Environmental Science from Rice University, an M.S. in Environmental Engineering from Stanford University and a Ph.D. in Toxicology from the University of Washington. I am a Diplomate of the American Board of Toxicology. During my years in the environmental industry, I have worked on hundreds of environmental risk assessment, environmental site investigation, and remediation projects. I have also worked on a large number of projects related to environmental chemical exposure. In addition to work on corrective action projects at industrial facilities nationwide, I helped develop and implement risk-based corrective action policies and procedures for the Texas Commission on Environmental Quality (TCEQ) and other regulatory agencies. I have participated in numerous workgroups developing regulatory guidance documents on various environmental issues. I have worked on a number of projects related to vapor intrusion including field investigations and model development. I have been the principal investigator (PI) for four vapor intrusion research projects funded by the Department of Defense through their Environmental Security Technology Certification Program (ESTCP). Through these projects, I have developed improved methods to assess vapor intrusion and to distinguish between vapor intrusion and indoor sources of volatile organic compounds (VOCs). I am the lead author on several peer-reviewed journal articles, peer-reviewed conference proceedings, and technical documents on vapor intrusion. I have developed and taught several training classes on vapor intrusion. I have extensive experience conducting environmental training programs. I developed training courses on vapor intrusion, the Texas Risk Reduction Program (TRRP), and other topics related to environmental risk assessment and have taught these courses to thousands of environmental professionals. I have conducted a large number of training programs in the U.S., Europe, and Asia, including ASTM RBCA training, “RBCA Tool Kit” software training, and vapor intrusion training. I served as President of the Ethical, Legal, and Social Issues Specialty Section of the Society of Toxicology. A true and correct copy of my resume that accurately sets forth my qualifications is provided in Attachment A of this report.

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1.2 Summary of my involvement with the Facility In early 2013, I was retained by General Mills, Inc. to provide a review and analysis of General Mill’s response to environmental conditions at the former General Mills, Inc. facility (Facility, or East Hennepin Site) located at 2010 East Hennepin Avenue, Minneapolis, Minnesota and the contaminants in groundwater both upgradient and downgradient of the Facility. I have been asked to evaluate claims related to third-party litigation and also to evaluate completeness of regulatory remediation requirements at the Facility. In 2013 and 2014, I led an effort to evaluate the presence or absence of upgradient sources of trichloroethylene (TCE) that could be contributing to the persistent groundwater impacts in the vicinity of the Facility. My staff and I identified a large number of sites northeast of the Facility where environmental investigations had been completed under Minnesota Pollution Control Agency (MPCA) regulatory oversight. With the assistance of MPCA staff, we obtained copies of available investigation reports and data. By combining the investigation results across sites, we identified a coherent TCE plume originating northeast of the Anne Gendein Trust property and extending into the Como neighborhood. Subsequent investigation activities conducted on behalf of General Mills and the MPCA have further confirmed the coherence of this large TCE plume. As part of my engagement, I was also asked to evaluate the nature of the solvent waste generated by General Mills during the period of on-site disposal activities from the 1940s to 1962. My review of available employee testimony combined with a review of the original early 1980s source area investigation results at the Facility provided an improved understanding of the complex nature and unique fingerprint of this waste. This, in turn, has supported an evaluation of remedy effectiveness and remedy completeness that distinguishes between the contribution of General Mills waste and upgradient sources of TCE. 1.3 Summary of key findings For my evaluation, I have reviewed reports and investigation results for the site covering the time period from 1980 to present, I have obtained and reviewed publically available information from the MPCA, and I have compiled investigation results from these sources and conducted independent analyses of these data. The key findings of my evaluation include the following:

1) From 1981 to 2013, site investigation and response actions were planned and implemented based on a conceptual model that did not account for the presence and impacts of upgradient sources of TCE. The original site conceptual model was based on the assumption that the Facility was the source of the TCE plume identified in the vicinity of the Facility and downgradient of the Facility. Over time,

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the persistence of this large TCE plume led to an assumption that the Facility was a strong source of TCE and that TCE dense non-aqueous phase liquid (DNAPL) was likely present at the Facility. It is important to note that these assumptions were based solely on the presence and persistence of the large TCE plume and were not supported by any primary evidence regarding the use or disposal of TCE at the Facility. These assumptions are not supportable when considered in the context of all currently available information concerning historical activities at the Facility and the presence of upgradient sources of TCE. This report summarizes the original conceptual model and presents an updated model that reflects the large amount of recently obtained information.

2) There are multiple sources of TCE and other chlorinated solvents that are not associated with the Facility, including important sources located upgradient (i.e., northeast) of the Facility.

3) The solvent waste disposed at the Facility from the 1940s to 1962 was a complex mixture dominated by petroleum solvents that also included a number of different chlorinated solvents. TCE was a minor component of the General Mills waste; other chlorinated solvents were present in higher amounts. The General Mills waste material had a unique fingerprint that was distinct from the upgradient source of TCE. We have used this unique fingerprint to evaluate the effectiveness of the General Mills remedy. Specifically, the removal of other chlorinated solvents such as 1,1,1-trichloroethane (1,1,1-TCA) and chloroform down to non-detectable concentrations in groundwater at the Facility demonstrates that all TCE associated with the Facility has also been removed from groundwater.

4) The soil and groundwater impacts associated with the historical disposal of waste at the soil absorption pit were limited to the immediate vicinity of this disposal location.

5) The high concentrations of petroleum and chlorinated solvents detected in Monitoring Well 106 were an artifact of drilling and not indicative of aquifer contamination.

6) DNAPL is not present at the Facility and was not present historically. 7) The pump and treat remediation system operated by General Mills from 1985 to

2010 successfully remediated the chlorinated solvent groundwater impacts associated with the Facility by 1991. The chlorinated solvents associated with the General Mills waste, including any TCE disposed at the Facility, are no longer detectable. No additional remediation is required to address impacts associated with the Facility. All detectable TCE in groundwater is associated with other sources.

8) Considering both current and historical information, it is clear that upgradient sources of TCE in groundwater were already impacting the Facility and areas further downgradient in the 1980s.

9) There is no “clean area” of “area of lower TCE concentration” separating the upgradient sources from the area of the Facility. The distribution of TCE within the Glacial Drift aquifer provides no evidence of on-going impacts associated with the Facility.

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Together, these analyses support the overall finding that all necessary remedial actions at the Facility have been completed. A detailed discussion of the basis for these findings is presented in this report. I am available to provide additional information concerning these findings. 2.0 Site History and Overview Site activities: Historical site activities have been summarized as follows (Barr, 2014):

From approximately 1930 until the 1970s, General Mills and later General Mills Chemicals, Inc. operated a technical center and research laboratory at the Site. Laboratory wastes reportedly were disposed in a disposal area in the southeast portion of the Site. In 1977, Henkel, Inc. acquired General Mills Chemicals, Inc. and with it, the facility at 2010 East Hennepin Avenue. The former disposal area was used to manage wastes at the facility in a manner that was generally consistent with industry practices at the time. It reportedly consisted of three empty 55-gallon drums that were perforated, stacked one on top of another, and constructed with the bottom of the deepest drum about 10 to 12 feet below the ground surface. The disposal area reportedly was used until approximately 1962. Site characterization work associated with the former disposal area began in 1981. The drums were reportedly excavated in 1981, and the bottom of the excavation is believed to have been about 12 feet deep (Barr, 1983).

1980s Facility investigation: In 1981, General Mills reported the solvent disposal site to the Minnesota Pollution Control Agency (MPCA) and the United States Environmental Protection Agency (USEPA) (General Mills, 1981). Site investigations conducted from 1981 to 1984 identified soil contamination in the vicinity of the former disposal area as well as contaminated groundwater in the vicinity of the Facility. Shallow geology and hydrogeology: Surficial soils in the vicinity of the Facility consist of a heterogeneous distribution of fill material and peat deposits. The peat is underlain by an alluvial sand interval 30 to 40 feet (ft) in thickness that varies between fine and medium-grained sizes with gravel in some areas. This interval is underlain by fine-grained (clay) glacial till up to 10 ft in thickness that is present in some areas and absent in others. Beneath the glacial till are the Decorah Shale, present across much of the area, and the Platteville Limestone (Barr, 1983). Three water-bearing units were identified during the site characterization process. From shallow to deep, these units include the alluvial sand and glacial till interval (collectively referred to as the Glacial Drift aquifer) and the Carimona and Magnolia members of the Platteville Formation (Barr, 1983). More recently, the Carimona formation has been described as part of the Decorah Shale (Mossler 2008). Additional deep bedrock aquifers are present below these formations.

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Response activities: In 1984, General Mills and the MPCA signed a Consent Order specifying site management activities. This Consent Order included a Remedial Action Plan specifying pump and treat as the remedial technology to be used to address groundwater contamination (MPCA, 1984). This groundwater pump and treat system was installed and began operation in 1985 (Barr, 2012). The groundwater pump and treat system operated from 1985 to 2010. This system initially consisted of five groundwater extraction wells completed in the Glacial Drift aquifer and one groundwater extraction well completed in the Carimona formation. In 1992, the Carimona well was replaced by two extraction wells screened in the Magnolia member of the Platteville formation. The groundwater pumping system was shut down in 2010 and groundwater monitoring has continued to the present time (Barr, 2012). Additional site investigation activities: Following the identification of vapor intrusion risks at residences in the vicinity of the Facility, in 2013 to 2015, General Mills conducted additional site investigation activities at the General Mills Source Area, at other locations on the Facility, and at locations in the vicinity of the Facility (Barr, 2015). The results of these investigations combined with other investigation results compiled from reports submitted to the MPCA by other parties have supported the development of a revised conceptual model for the source of TCE in the vicinity of the Facility. Establishment of the Southeast Hennepin Area Groundwater and Vapor Site: Based on investigation results from General Mills and other parties, in 2016, the MPCA established the Southeast Hennepin Area Groundwater and Vapor Site. This site was added to the state Permanent List of Priorities on August 24, 2016 (MPCA, 2016). The MPCA is leading efforts to evaluate and mitigate vapor intrusion risks at this site. In addition, the MPCA is conducting additional site investigation activities to identify the TCE source area(s). Terminology: For the purpose of this report, I am using the following terminology to refer to specific areas of interest in this matter.

Former General Mills, Inc. Facility (Facility): The property parcel at 2010 East Hennepin Avenue formerly owned by General Mills.

Soil Absorption Pit: The engineered structure consisting of buried drums located at the south end of the Facility used for on-site disposal of solvent waste from the 1940s until 1962.

The General Mills Source Area: The area of solvent waste contamination in soil identified in the early 1980s in the immediate vicinity of the Soil Absorption Pit.

The Como Neighborhood: The neighborhood between East Hennepin Ave and Elm Street SE impacted by the large TCE plume.

3.0 Detailed Findings 3.1 Based on the large amount of new information since 2013, the

conceptual model of environmental impacts associated with the

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Facility must be updated to correctly show only limited historical impacts.

In the early 1980s, General Mills reported historical on-site disposal practices in accordance with regulatory reporting requirements. It was the only party in the immediate area to do so. As a result, the Facility was the only known source of subsurface chlorinated solvent contamination during the initial site investigation conducted in the early 1980s. In the absence of information concerning other sources, the groundwater impacts identified during this investigation were managed as if they were attributable exclusively to the Facility. Although numerous other sources of TCE have been identified in recent years, in the early 1980s, the Facility was thought to be the only source. Based on this conceptual model, the pump and treat remediation system was designed to address groundwater impacts at, and downgradient of, the former disposal area. During the operation of this pump and treat system, the changes in TCE concentration in groundwater were assumed to reflect progress in remediation of source material in the former disposal area. Slower than anticipated progress in reducing TCE concentrations was assumed to indicate a significant TCE source area at the Facility. This assumption was based solely on the persistence of the TCE plume in the Glacial Drift aquifer. There never has been any direct evidence of significant use or disposal of TCE at the Facility. In addition, there never has been any evidence of DNAPL at the Facility. In recent years, subsequent to the shut-down of the pump and treat remediation system, a large amount of additional information has been obtained concerning conditions at the Facility and sources of TCE not associated with the Facility. Based on this new information, this report presents an updated conceptual model for environmental impacts in the area. Updating the conceptual model is consistent with standard practice (e.g., ASTM, 2014; NJDEP, 2011). Several key elements of the revised conceptual model are discussed in detail in subsequent sections of my report, below. Figure 1 and Figure 2 present the current conceptual understanding of solvent waste source areas at the Facility and upgradient of the Facility in the 1980s and today, respectively.

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Figure 1: Revised Conceptual Model of TCE Plume in the 1980s Based on Currently Available Information

Key Point: The revised conceptual model indicates that an extensive TCE plume associated with upgradient sources had already impacted the Glacial Drift aquifer in the vicinity of the Facility in the 1980s. The General Mills waste material was an LNAPL (i.e., less dense than water) and was a complex mixture of petroleum and chlorinated solvents that included only small amounts of TCE. The impacts associated with the General Mills waste were limited to soil and shallow groundwater in the immediate vicinity of the soil absorption pit. The high concentrations of TCE in the deep Glacial Drift aquifer and underlying bedrock can only be explained by upgradient sources.

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Figure 2: Revised Conceptual Model of the Current TCE Plume

Key Point: The revised conceptual model indicates the continued presence of the extensive TCE plume associated with upgradient sources. Although TCE concentrations in the vicinity of the Facility are much lower than in the 1980s, the general distribution is the same with the highest TCE concentrations present in the upgradient areas. The complex mixture of chlorinated solvents associated with the General Mills source is no longer detectable even in the immediate vicinity of the soil absorption pit. 3.2 There are multiple sources of TCE and other chlorinated solvents not

associated with the Facility Within the general vicinity of the Facility, detectable concentrations of TCE are widespread

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within the Glacial Drift aquifer (see Figure 3). At many of these locations, such as areas upgradient of the Facility, a simple evaluation of potential transport pathways from the Facility demonstrates that the TCE cannot be associated with the Facility. In other words, the highest concentrations of TCE in the Glacial Drift aquifer are located ½ mile or more upgradient (northeast) of the Facility. There is no plausible transport mechanism by which TCE could migrate from the Facility to these upgradient locations. Groundwater flow within the Glacial Drift aquifer is from the northeast to the southwest (Barr, 2012). This has consistently been the direction of groundwater flow since the time of the initial investigations in the 1980s (Barr, 1984). High concentrations of TCE have been detected in the Glacial Drift aquifer at several locations northeast (upgradient) of the Facility (see Figure 3). Based on the groundwater flow direction, migration of chemicals from these upgradient locations is to the southwest (downgradient) towards the Facility. This simple analysis suggests on-going transport of TCE from these upgradient sources to the Facility, the vicinity of the Facility, and downgradient of the Facility. At large number of properties located northeast of the facility, property owners or other parties have conducted environmental investigations under MPCA supervision and independently from General Mills (GMI) (see Figure 4). For sites located upgradient of the Facility, we contacted the MPCA to request review of publically available investigation reports. We reviewed MPCA’s files to identify locations where concentrations of TCE and other chlorinated solvents have been detected and reported in groundwater. A number of different parties have documented the presence of TCE and other chlorinated solvents in groundwater at properties located upgradient from the Facility (see Table 1). The combined investigation results document a widespread and continuous area of dissolved TCE in the Glacial Drift aquifer that originates at least ½-mile upgradient from the Facility. The Facility is located along the northwest edge, about half way between the currently-identified upgradient extent of the TCE and the downgradient end (see Figure 3. Based on the groundwater flow direction and the documented distribution of TCE within the Glacial Drift aquifer, it is clear that TCE has migrated and is continuing to migrate from source(s) located upgradient of the Facility. This on-going migration of TCE is responsible for the continued presence of TCE in groundwater at the Facility, adjacent to the Facility to the southeast (i.e., cross-gradient from the Facility), and downgradient of the Facility.

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Figure 3: TCE Concentrations in the Glacial Drift Aquifer and in Sub-slab Samples

Notes: 1) Figure shows most recent concentration measured at each investigation location between 1990 and December 2016. 2) MPCA SE Hennepin Area Site outline from MPCA (2017). Key Point: Available groundwater monitoring data show an extensive and continuous plume of TCE in the Glacial Drift aquifer originating at least ½ mile upgradient from the Facility.

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Figure 4: Area of GSI Evaluation of MPCA Investigation/Remediation Sites

Key Point: A large number of MPCA-oversight investigation sites are present upgradient of the Facility. The investigation results from these sites provide an improved understanding of TCE concentrations in the Glacial Drift aquifer.

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Table 1: Summary of Investigations at Properties Upgradient from the Facility That Have Detected TCE in Shallow Groundwater

Site MPCA Project No.

Maximum TCE concentration

(year)

Approx. Distance from Former General

Mills Facility East Hennepin Auto Service, 2100 E Hennepin

LEAK 2477 24 ug/L (1994)

<100 ft

Frank’s Auto Repair, 2314 E Hennepin

LEAK 17726 1,620 ug/L (2009)

1000 ft

Hennepin Square, 2021 E Hennepin

LEAK 5026 / VP6700

0.79 ug/L (1992)

<100 ft

Anne Gendein Trust, 359 Hoover

LEAK6600 / VP13270, VP13271

3,600 ug/L (2001)

1,500 ft

Office Warehouse, 2301 Traffic

VP27480 2.7 ug/L (2011)

800 ft

Property, 2400 Traffic VP22300, 22301, 22302

41 ug/L (2006)

2,000 ft

Sears, 2700 Winter St NE LEAK7043, 7905 290 ug/L (1995)

2,000 ft

Ameripride, 700 Industrial Blvd NE

VP24750 / LEAK16906

7.2 ug/L (2009)

3,000 ft

Northwestern Warehouse, 3255 Spring St NE

VP13100, 13101 610 ug/L (2000)

2,500 ft

Note: Table summarizes sites east and northeast of the Facility where TCE has been detected in groundwater. LEAK project numbers are for sites in the Petroleum Remediation Program (PRP). VP project numbers are for sites in the Voluntary Investigation and Cleanup (VIC) Program. 3.3 The waste material associated with the Facility had a unique

fingerprint that was distinct from other sources of TCE in the vicinity. From around 1947 to 1962, a wide variety of petroleum solvents and chlorinated solvents were disposed in a soil absorption pit comprised of three perforated 55-gallon drums stacked on top of each other with the base buried approximately 10 to 12 ft below ground surface (bgs). Although there was no clear documentation regarding the precise nature of the mixture of solvents disposed in the absorption pit, information on disposal practices is available from depositions of several employees who worked at the Facility during the 1940s, 1950s, and 1960s. These depositions, obtained during the late 1990s as part of litigation between General Mills and its insurance carriers, indicate that the waste organic solvents being generated consisted primarily of chemicals other than TCE. As summarized in Table 2, depositions of the research chemists indicated that they used primarily petroleum solvents including kerosene or other petroleum mixtures and some individual petroleum compounds such as toluene and xylenes. Those who used chlorinated solvents indicated that they used a variety of chlorinated solvents other than TCE including 1,1,1-trichloroethane (1,1,1-TCA), ethylene dichloride (also known as 1,2-dichloroethane or 1,2-DCA), and chloroform. Some employees recall small amounts of

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TCE being available on-site, but none recalled more than occasional use of this solvent (Depositions and Deposition Excerpts from General Mills vs. Travelers Indemnity). Table 2: Testimony of Former GMI Employees Regarding Solvents Used at 2010 E Hennepin Research Laboratory Between 1947 and 1962

Employee (Years at Facility)

Source of Testimony

Summary of Testimony Regarding Use of Solvents in Research Laboratory

Charles Berry (1934 to 1962)

Deposition on 7 July 1998

• Solvents used: petroleum ether, 1,2-DCA, benzene, pyridine, and alcohols.

• “I don’t think I ever used trichloroethylene [TCE]” Don Floyd (1943 to 1984)

Deposition on 8 July 1998

• Used primarily hydrocarbon solvents: Skelly-Sol B, higher boiling ketones, aromatic hydrocarbons such as benzene, toluene, xylenes, mineral spirits.

• Used chlorinated solvents, but not often: chloroform, carbon tetrachloride.

Arthur Sveum Deposition on 8 July 1998

• Used kerosene and toluene • Remembered TCE being around but does not recall using

it. Robert Nordgren (1939 to 1980)

Deposition on 13 October 1998

• Did not use a lot of chlorinated solvents in his work. Didn’t work with chlorinated solvents very much at all.

Dave Chatterton (1958 to 1985)

Deposition on 14 October 1998

• Worked with methyl chloride [chloromethane], 1,2-DCA, 1,1,1-TCA, carbon tetrachloride

• Used 1,2-DCA in fats chemistry Ronald Swanson (part time 1956 to 1964; full time 1964 to 1986)

Deposition on 7 January 1999

Solvent use from Mid 1950s to early 1960s: • Used mostly Skellysolve B, also Skellysolve C and smaller

amount of Skellysolve F (all petroleum solvents). • Used a lot of acetone and kerosene. • Used a lot of 1,1,1-trichloroethane (1,1,1-TCA), some

chloroform • Does not recall using trichloroethene (TCE) • Does not know anyone who used TCE or

tetrachloroethene (PCE) In addition to employee depositions, the mixture of chemicals disposed at the Facility can be characterized by the results of chemical analysis of soil samples collected above the groundwater. The results of soil testing conducted in the early 1980s are consistent with the employee depositions, providing additional evidence that TCE was a minor component of the waste solvents disposed at the Facility. At the Facility, groundwater is typically encountered at a depth of approximately 20 ft bgs. Contamination detected within the saturated zone (i.e., at a depth of 20 ft or greater below ground) could be either i) associated with an on-site source and/or ii) could originate from an upgradient source that migrated beneath the site with the natural flow of groundwater. Contamination detected in soil above the water table is much more likely to be associated with an on-site source because soil conditions above the water table are not affected by the flow of groundwater

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from upgradient locations. If the material disposed on-site migrated down to the water table, then the soil and water testing conducted at the soil water interface in the immediate vicinity of the disposal location also provides characterization of the disposed materials. The available soil and water test results from the vicinity of the soil absorption pit at the Facility indicate that the mixture of chemicals disposed at the Facility are very different from those found in the widespread area of dissolved TCE in groundwater that originates upgradient from the Facility (as discussed in Section 3.2). Soil testing in the vicinity of the soil absorption pit was conducted in 1981 and 1983 as part of the initial site investigation. In 1981, three soil borings were completed in the immediate vicinity of the soil absorption pit (Soil Exploration Company, 1981). At each boring, a soil sample was collected at a depth of 14.5 – 16 ft bgs. These were the only samples from these borings that were below the bottom of the soil absorption pit but above the water table. The samples contained primarily a variety of different petroleum hydrocarbons. However, eight different chlorinated solvents were also detected: 1,1-dichloroethane, chloroform, 1,2-dichloroethane, 1,1,1-TCA, carbon tetrachloride, 1,1,2,2-tetrachloroethane, chlorobenzene, and TCE (Soil Exploration Company, 1981, Tables 5 and 6). In all three samples, TCE was a minor component of the chlorinated solvents, representing less than 10% of the mass of chlorinated solvents detected. As a percentage of total analytes (including petroleum hydrocarbons), the amount of TCE in the samples was less than 2% of the total analyzed constituents. At each of these three soil boring locations, an additional sample was collected at a depth of 19.5 to 21 ft bgs. Groundwater was encountered at a depth of approximately 20 ft bgs, so these samples could have been affected by contamination in groundwater (i.e., migrating from sources upgradient of the Facility). However, based on their close proximity to the soil absorption pit, they are more likely to be representative of the mixture of chemicals disposed on site. Compared to the shallower samples, these samples contained a higher proportion of chlorinated solvents relative to petroleum hydrocarbons. However, TCE was still a minor component of the chlorinated solvent mixture, again representing less than 10% of the mass of chlorinated solvents detected and typically less than 5% of the total analyzed constituents. In 1983, monitoring well 106 was installed in the immediate vicinity of the soil absorption pit (Barr, 1983). A soil sample was collected from a depth of 20 – 22 ft bgs during the installation of the monitoring well on March 28, 1983. The well was installed at a depth of 20 – 25 ft bgs. The soil sample was analyzed for only three petroleum hydrocarbons (benzene, toluene, and xylenes) and four chlorinated solvents (chloroform, PCE, 1,1,1-TCA, and TCE). All of the petroleum hydrocarbons and all of the chlorinated solvents except 1,1,1-TCA were detected in the sample. TCE represented 39% of the total mass of the chlorinated solvents analyzed and 31% of the mass of all constituents analyzed. However, the laboratory report indicated that the sample contained several additional unidentified chemicals; thus the TCE as a percentage of all chemicals in the sample was actually lower. Water samples were collected from the well on April 15, 1983 and April

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28, 1983. The two water samples collected from this well were analyzed for only three petroleum hydrocarbons (benzene, toluene, and xylenes) and nine chlorinated solvents (1,1-dichloroethane, chloroform, 1,2-dichloroethane, 1,1-dichloroethene, trans-1,2-dichlorethene, 1,1,1-TCA, 1,1,2,2,-tetrachloroethane (second sample only), TCE, and PCE). All of these chemicals were detected in at least one of the two water samples, however, the concentration of benzene, 1,1,2,2-tetrachloroethane, and PCE could not be determined in the second sample because the laboratory instrument used to test the samples could not separate these compounds from other compounds that were also present in the sample. In the two water samples, TCE represented 26% and 28%, respectively, of the total mass of chlorinated solvents quantified in these samples, and less than 8% of the total mass of analytes measured including petroleum hydrocarbons. The locations of soil borings and groundwater samples in the vicinity of the soil absorption pit are shown in Figure 5. Except for soil boring 101, which contained only trace levels of contaminants, no other samples were collected within 20 ft of the soil absorption pit within a depth range from below the base of the pit (12 ft bgs) to the top of the water table (20 ft bgs). Monitoring well 107 was installed close to the absorption pit but was screened well below the top of the water table at a depth of 34 – 39 ft bgs. Additional soil borings installed more than 20 ft but less than 50 ft from the absorption pit showed only trace levels of constituents (i.e., soil borings 5, 6, 10, 11, and 102). These data demonstrate that the impacts associated with the soil absorption pit were confined to a very small area within 20 ft of this pit (see Figure 5).

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Figure 5: VOC Contamination in Soil in the Vicinity of the Former Soil Absorption Pit: 1980s Investigation Results

Notes: 1) Map shows early (i.e., 1981 and 1983) soil investigation locations in the vicinity of the former soil absorption pit. 2) Soil samples were collected at multiple depths in each boring. The inset tables show the results from the sample with the highest overall VOC concentration collected from any depth at that boring location. All boring locations included a sample collected at the water table (20-21.5 ft bgs). 3) The pie chart shows the average composition of soil samples collected from the 14.5 to 22 ft bgs range, from borings within 20 ft of the former soil absorption pit. Key Point: The early 1980s investigation showed that impacts associated with the historical disposal of GMI solvent waste were limited to within 20 ft of the former soil absorption pit. The impacts were defined by a complex mixture of petroleum and chlorinated VOCs. TCE was only a small component of this mixture.

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In summary, the soil and water samples collected in the immediate vicinity of the soil absorption pit in 1981 and 1983 consistently show:

• A predominance of petroleum solvent constituents over chlorinated solvents • A complex mixture of chlorinated solvents with only small amounts of TCE

Although these 1980s samples confirm that the solvent waste disposed at the site was mostly petroleum, the quantified compounds underrepresent the proportion of petroleum solvent in the original waste material for the following reasons:

• Based on deposition testimony, most of the petroleum solvents used in the research laboratory were complex mixtures containing 10s to 100s of individual petroleum compounds (e.g., kerosene, Skellysolve). The laboratory analysis of the soil and water samples quantified only a small fraction of these compounds. Therefore, the laboratory results account for only a fraction of the petroleum solvents in the soil and water samples.

• The 1980s investigations were conducted approximately 35 years after the start of on-site disposal and 20 years after the end of this disposal. Biodegradation and other break-down processes would have destroyed much of the petroleum solvent waste (and likely a smaller portion of the chlorinated solvent waste) during this time period.

Together, the 1990s insurance deposition testimony and the analytical results from the 1980s site investigation activities confirm that the waste solvent material disposed at the soil absorption pit was a complex mixture of mostly petroleum solvents with a smaller amount of several different chlorinated solvents. Chlorinated solvents in the waste material included, at a minimum, 1,1-dichloroethane, chloroform, 1,2-dichloroethane, 1,1-dichloroethene, trans-1,2-dichlorethene, 1,1,1-TCA, 1,1,2,2-tetrachloroethane, TCE, and PCE. TCE was a minor component, as discussed further in Section 3.4. 3.4 The soil and groundwater impacts associated with the historical

disposal of waste at the soil absorption pit were limited to the immediate vicinity of the pit.

As discussed in Section 3.3 of this report, the waste solvent material disposed at the soil absorption pit was a complex mixture of mostly petroleum solvents with a smaller amount of several different chlorinated solvents. Chlorinated solvents in the waste material included, at a minimum, 1,1-dichloroethane, chloroform, 1,2-dichloroethane, 1,1-dichloroethene, trans-1,2-dichlorethene, 1,1,1-TCA, 1,1,2,2,-tetrachloroethane, TCE, and PCE. Based on the results of the soil testing, at least three chlorinated VOCs (1,1,1-TCA, chloroform, and 1,1,2,2-tetrachloroethane) were present in the GMI waste in greater amounts than TCE (see Table 3). This complex mixture of solvents was apparent in soil samples collected from within 20 ft of the soil absorption pit and in the initial water samples collected from Well 106.

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Table 3: Average Concentration of Chlorinated Solvents in GMI Source Soil Samples

Chlorinated VOC Average Concentration (mg/kg) 1,1,1-trichloroethane (1,1,1-TCA) 205 mg/kg (8 x higher than TCE) Chloroform 71 mg/kg (3 x higher than TCE) 1,1,2,2-tetrachloroethane 29 mg/kg (1.1 x higher than TCE) TCE 26 mg/kg 1,2-dichlorethane 8.9 mg/kg

Note: Source soil samples defined as source area soil samples containing greater than 1 mg/kg total chlorinated VOCs.

In contrast to the soil and water samples collected within 20 ft of the soil absorption pit, water samples collected further away were dominated by TCE. Well A, located 50 ft southwest of the absorption pit, was analyzed for six chlorinated solvents in 1981 (1,1-dichloroethane, chloroform, 1,2-dichloroethane, 1,1,1-TCA, 1,1,2,2,-tetrachloroethane, and TCE) and nine chlorinated solvents in 1983 (1,1-dichloroethane, chloroform, 1,2-dichloroethane, 1,1-dichloroethene, trans-1,2-dichlorethene, 1,1,1-TCA, 1,1,2,2,-tetrachloroethane, TCE, and PCE). This well contained 94% TCE in 1981 and 87% TCE in 1983. Well 2, located 125 ft southwest of the soil absorption pit, was analyzed in 1982 for 11 chlorinated solvents (1,1-dichloroethane, chloroform, 1,2-dichloroethane, 1,1-dichloroethene, trans-1,2-dichlorethene, 1,1,1-TCA, 1,1,2,2,-tetrachloroethane, methylene chloride, carbon tetrachloride, TCE, and PCE). TCE was 94% of the total mass of chlorinated solvents detected. Five other Glacial Drift monitoring wells were sampled in 1982: Wells B, 1, 3, 4, and 5, located 250 ft to 1050 ft from the soil absorption pit. Wells B and 1 are located northeast of the pit while Wells 3, 4, and 5 are located southwest of the pit. These wells were analyzed for six chlorinated solvents (1,1-dichloroethane, chloroform, 1,2-dichloroethane, 1,1,1-TCA, 1,1,2,2-tetrachloroethane, and TCE). Two of the wells (Wells 1 and 4) contained only trace levels of chlorinated solvents. The remaining three wells (Well B, Well 3, and Well 5) contained 95%, 61% and 99% TCE, respectively. Well 107, screened in the Glacial Drift aquifer below the zone of soil contamination associated with the absorption pit, was analyzed in 1983 for nine chlorinated solvents (1,1-dichloroethane, chloroform, 1,2-dichloroethane, 1,1-dichloroethene, trans-1,2-dichlorethene, 1,1,1-TCA, 1,1,2,2,-tetrachloroethane, TCE, and PCE). This well contained 97% TCE. The difference between chemical composition of sample results close to the pit versus those further away is summarized in Table 4. As indicated in the table (and also discussed in Section 3.3), TCE was only a small percentage of the chlorinated solvents detected in the samples collected within 20 ft of the former soil absorption pit, and an even smaller percentage of total solvents when petroleum hydrocarbons are considered. In contrast, for the samples collected further from the soil absorption pit, TCE represented the overwhelming majority of the chlorinated solvents detected (typically greater than 90%). This indicates that i) while a wide variety of chlorinated solvents and wastes were disposed in the soil absorption pit, the area of impact was limited to the immediate vicinity of the

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former pit, and ii) contaminated groundwater outside of the local area around the pit was impacted by a source unrelated to disposal at the pit. Table 4: Percentage of TCE in Soil and Water Samples Collected within 20 ft of the Former Soil Absorption Pit Compared to Samples Collected Greater than 20 ft from the Former Soil Absorption Pit

Well or Soil Boring

Sample Type

Sample Depth (Depth

bgs)

Distance from

Absorption Pit

Sample Date

Number of Chlorinated

Solvents Analyzed

Percent TCE**

Samples located within 20 ft of the former soil absorption pit Boring #2 Soil 14.5 – 16 ft 2 ft 6/2/1981 8 9% Boring #3 Soil 14.5 – 16 ft 15 ft 6/2/1981 8 6% Boring #4 Soil 14.5 – 16 ft 18 ft 6/3/1981 8 6% Boring #2 Soil 19.5 – 21 ft 2 ft 6/2/1981 8 7% Boring #3 Soil 19.5 – 21 ft 15 ft 6/2/1981 8 9% Boring #4 Soil 19.5 – 21 ft 18 ft 6/3/1981 8 6% Well 106 Soil 20 – 22 ft 3 ft 3/28/1983 4 39% Well 106 Water 20 – 25 ft 3 ft 4/15/1983 8 26% Well 106 Water 20 – 25 ft 3 ft 4/28/1983 9 28%

Samples located greater than 20 ft from the soil absorption pit Well 107 Water 34 – 39 ft 3 ft * 4/28/83 9 97% Well A Water 2.5 – 12.5 ft 50 ft 6/24/81 6 94% Well A Water 2.5 – 12.5 ft 50 ft 4/28/83 9 87% Well 2 Water 16 – 26 ft 125 ft 4/5/82 11 94% Well B Water 16.6 – 26.6 ft 250 ft 12/17/82 6 95% Well 3 Water 13.5 – 23.5 ft 400 ft 4/5/82 6 61% Well 5 Water 14 – 24 ft 1050 ft 4/5/82 6 99% Note: * = Well 107 is located within 20 ft of the soil absorption pit but is screened below the zone of affected soil at a depth of 34 to 39 ft bgs. ** Percent TCE is TCE as a percentage of the total concentration of chlorinated solvents in the sample. The value does not account for petroleum hydrocarbons or other constituents which would serve to further decrease the percent TCE.

In summary, the impacts associated with disposal of waste solvents at the former soil absorption pit were confined to areas located close to the disposal sites. As discussed in more detail in Section 3.8, below, it is now clear that high concentrations of TCE detected in groundwater away from the soil absorption pit were (and are) attributable to sources unrelated to the Facility. 3.5 The high concentrations of petroleum and chlorinated solvents

detected in Monitoring Well 106 installed at the former disposal site were an artifact of drilling and not indicative of aquifer contamination.

Monitoring Well 106 was installed in March 1983 as part of the initial site investigation efforts. This well was installed at the south end of the Facility at the location of the former absorption pit and was screened across the water table with a screened interval of 20-25

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ft bgs. Water samples collected from this well in April 1983 showed concentrations of several VOCs including TCE that were anomalously high, much higher than those measured subsequently in that well and much higher than those measured at any other monitoring well installed and sampled in the 1980s. A review of all available information concerning the installation and sampling of this well indicate that the VOC concentrations measured in these samples were an artifact of drilling through impacted soils and were not indicative of aquifer contamination. Specifically, when the well was drilled, a small amount of soil contamination from the unsaturated zone appears to have been carried downwards and smeared along the outer edge of the well borehole (see Figure 6). Water flowing from the aquifer into the monitoring well dissolved this contamination resulting in contaminant concentrations in the collected water samples that were much higher than contaminant concentrations in the aquifer outside of the well (see Figure 7, left panel). Because the drilling transported only a small amount of contamination from the unsaturated zone, the effect of this contamination began to dissipate within only a few weeks (see Figure 7, middle and right panels and Figure 8). The first water sample collected from Well 106 on April 14, 1983, only 16 days after the well was installed, contained VOC concentrations ranging from 2,300 ug/L for PCE to 62,000 ug/L for benzene, including 7,200 ug/L TCE. The second sample collected from the well on April 28, 1983, only 14 days later, contained VOCs ranging from 1,400 ug/L for 1,1,1-TCA to 18,000 ug/L for benzene, including 2,400 ug/L TCE. These concentrations represented a 50% to 80% decrease in concentration compared to the first sample event, consistent with the rapid dissipation of the contamination carried down from the unsaturated soil. A third water sample, collected 9 months after the well was installed, further supports this interpretation. This water sample was collected from Well 106 on December 12, 1983. The sample was analyzed only for TCE and showed a TCE concentration of only 560 ug/L, a 92% decrease compared to the initial result. This rapid decrease in VOC concentrations measured in three samples collected from Well 106 over nine months confirms that the VOCs in Well 106 were an artifact of drilling and were not indicative of contaminant concentrations within the Glacial Drift aquifer.

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Figure 6: Illustration of Contamination from Unsaturated Soil Being Smeared Around the Borehole During the Installation of Monitoring Well 106 in March 1983

Key Point: The installation of Well 106 involved drilling though impacted soil in the unsaturated zone. The drill rig carried a small amount of this material down to the water table and smeared it on the outside of the Well 106 borehole.

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Figure 7: Illustration of Borehole Contamination at Monitoring Well 106 and the Dissipation of the Contamination over the Three Sample Events in 1983

Key Point: The impacted soils smeared on the outside of the Well 106 borehole dissipated over time resulting in a large reduction in the concentration of TCE measured in the well across the three sample events in 1983. Well 106 was not sampled after 1983.

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Figure 8: VOC Concentrations Measured in Water Samples Collected from Well 106

Note: Benzene and PCE were detected in the April 28 sample but could not be quantified by the laboratory due to co-elution with other compounds. The sample collected 12/12/83 was analyzed only for TCE. Key Point: All of the VOCs measured in Well 106 showed a large decrease in concentration from March 14, 1983 (16 days after well installation) to March 28, 1983 (30 days after well installation). These unusually large decreases in concentration over a short period of time provide additional evidence that the high VOC concentrations were an artifact of drilling though contamination in the unsaturated zone. This explanation of Well 106 results is consistent with data from the well and, further, the occurrence of cross-contamination was not unusual in the early 1980s. Nationally, widespread efforts to delineate and remediate soil and groundwater contamination associated with historical waste management and accidental releases began in the early 1980s. During this time, there was a limited understanding of the measures required to obtain groundwater samples that were truly representative of aquifer contamination. In June 1983, the American Petroleum Institute published Groundwater Monitoring and Sample Bias in order to address a number of common errors in characterizing groundwater contamination. Among other common problems, this document highlights the dangers of drilling through shallow soil contamination when installing a monitoring well. This document states:

Considerable difficulty or uncertainty in sample integrity can arise if the augers bore through deposits that contain adsorbed or precipitated contaminants or contain contaminants in an

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immiscible phase. As the augers bore through this zone, a small but significant mass of contaminated material may adhere to the auger bit or to the lead augers. The potential for this to occur is greatest in cohesive clayey deposits. If the contaminated material adhering to the augers is moved downward in the borehole where the intake zone of the installation is to be located, and if this contaminated material is smeared on the wall of the hole or is otherwise deposited in this zone, water samples drawn from this installation may be contaminated because of contact of the water with this material as it is drawn from the groundwater zone through the borehole zone into the installation. This potential cause of sample contamination is difficult to diagnose in the field and it is difficult to develop methods that will provide assurance that the potential for contamination is entirely avoided. (API, 1983, pg 37-38)

Well 106 was plugged and abandoned in 2003. In 2014, General Mills installed a new well (Well 311GS) at the location of former Well 106 (i.e., at the location of the former soil absorption pit). This new well was screened over approximately the same interval (i.e., across the top of the Glacial Drift aquifer). Water samples collected from Well 311GS further confirm that Well 106 was not representative of aquifer contamination. Chloroform, 1,1,1-TCA, and 1,2-DCA, which were detected at concentrations of 15,000 ug/L, 2,800 ug/L, and 1,400 ug/L in Well 106, were all non-detect (<1 ug/L) in Well 311GS. TCE concentrations, however, were up to about 80 ug/L in Well 311GS. This is consistent with on-going migration from upgradient locations that exhibit higher concentrations of TCE. In summary, the high concentrations of benzene, TCE, and other VOCs in the water samples collected from Well 106 were an artifact of drilling though contaminated soil and were not representative of actual aquifer contamination. This type of artifact was not uncommon in the early 1980s. 3.6 Available investigation results show no current or historical DNAPL

impacts at the Facility. Before the current understanding of upgradient sources, the persistence of the TCE plume in the Glacial Drift aquifer led to speculation that DNAPL might be present at the Facility in the vicinity of the soil absorption pit. However, there was no primary evidence of DNAPL waste. Based on the employee depositions and soil investigation results discussed in Section 3.3 of this report, it is clear that the General Mills waste was mostly petroleum with a small amount of chlorinated solvents. This mixture was less dense than water (i.e., an LNAPL, not a DNAPL). Extensive environmental investigations have also shown an absence of DNAPL at the Facility. Since 1981, environmental impacts at the Facility have been extensively investigated through the collection of over 96 soil samples from 36 locations and 399 groundwater samples from 38 locations. None of these investigation results suggest the current or historical presence of TCE DNAPL within the Glacial Drift aquifer at the Facility. In fact, the following evaluations indicate that DNAPL is not present at the Facility:

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• Waste Generated at the Facility Was Not a DNAPL: As discussed in Section 3.3 of this report, the waste generated at the former General Mills research laboratory and disposed in the soil absorption pit was composed mostly of petroleum solvents with a small amount of chlorinated solvents. Although chlorinated solvents, in their pure form, are more dense than water (i.e., a DNAPL), a mixture of mostly petroleum solvents with a small amount of chlorinated solvents is less dense than water (i.e., an LNAPL). The low density of the waste is further demonstrated by the results of the 1980s site investigation. This investigation showed that the highest contaminant concentrations in soil were found at the top of the Glacial Drift aquifer. In other words, when waste disposed at the soil absorption pit reached the Glacial Drift aquifer, it pooled at the top of the water table, as expected for an LNAPL, rather than migrating downwards through the aquifer as would be expected for a DNAPL (see Figure 1).

• No Visual Evidence of DNAPL: DNAPL was not observed in soil cores collected from any of the 58 different investigation locations completed at the Facility for the purpose of collecting soil or groundwater samples.

• Low TCE Concentrations in Groundwater: High concentrations (above 1% of solubility; Newell and Ross, 1992) of dissolved TCE (or another chlorinated solvent) may indicate that DNAPL is present at a site even when it is not directly observed. TCE has a solubility of 1,280,000 ug/L. Thus, the presence of TCE at a concentration above 12,800 ug/L can be an indirect indicator of nearby TCE DNAPL. Out of the 399 groundwater samples collected from the Facility since 1981, TCE has never been measured at a concentration above 1% of solubility. Excluding the two non-representative samples collected from Well 106 (discussed in Section 3.5), the highest concentration of TCE measured in a groundwater sample collected from the Facility was 2,400 ug/L in Well BB, a well screened in a rock aquifer below the Glacial Drift aquifer. The highest concentration of TCE measured in a groundwater sample collected within the Glacial Drift aquifer at the Facility was 1,600 ug/L in Well B (approximately 0.1% of solubility). This well is located 250 ft upgradient from the soil absorption pit and is screened within the shallow portion of the Glacial Drift aquifer. As such, even if DNAPL has been released from the soil absorption pit, it is unlikely that a shallow well at this location would have been impacted by such a release. The historical maximum concentrations of TCE measured in Wells B and BB are both lower than TCE concentrations measured at several upgradient monitoring locations such as Well 301GD (see Figures 1 and 2). Thus, these concentrations are consistent with the migration of TCE from an upgradient source.

• MIP Investigation Did Not Indicate DNAPL: In 2014, as part of the supplemental investigation of the former soil absorption pit, Barr Engineering used a Membrane Interface Probe (MIP) to evaluate the presence of DNAPL near the former soil absorption pit. A MIP provides a continuous reading of contaminant levels through the entire depth of an aquifer at the investigation location. The presence of DNAPL at any depth causes a clear spike in instrument response at that depth. The MIP investigation conducted by Barr provided no evidence of DNAPL at the investigation locations (Barr, 2015).

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• Vertical and Lateral Distribution of TCE is Not Consistent with Disposal of DNAPL in the Soil Absorption Pit: In 2014, as part of the supplemental investigation of the former soil absorption pit conducted by Barr Engineering, groundwater samples were collected at several depths within the Glacial Drift aquifer. Specifically, groundwater samples were collected directly above clay layers present within the Glacial Drift aquifer. If TCE DNAPL had been disposed in the absorption pit, this DNAPL would have pooled on top of clay layers as it migrated downwards through the Glacial Drift aquifer. This would have resulted in much higher dissolved TCE concentrations at the top of these clay layers compared to other depths within the aquifer. As shown in Figure 9, TCE concentrations within the Glacial Drift aquifer near the former soil absorption pit show low variation with depth regardless of clay layers. Although TCE concentrations are somewhat higher at clay layers, the concentrations observed are not consistent with current or former DNAPL.

At all depths within the aquifer, the highest TCE concentrations measured on the Facility during this 2014 investigation program were found at the upgradient property line, approximately 200 ft upgradient of the former soil absorption pit. This distribution of TCE is not consistent with a DNAPL release at the former soil absorption pit but it is consistent with the continued migration of TCE onto the Facility from upgradient sources.

The extensive investigations of the Facility all showing an absence of DNAPL provide strong evidence that DNAPL is not present at the Facility. Although some historical site investigation reports suggest or speculate that DNAPL may be present at the Facility, these documents were written within the context of the old site conceptual model without knowledge of strong upgradient TCE sources. Without knowing about these upgradient TCE sources, the presence of DNAPL at the Facility was used as a possible explanation for the long-term persistence of TCE in groundwater despite the operation of the pump and treat remediation system from 1985 to 2010. Since the time of those historical speculations, there have been additional investigations both at the Facility and upgradient of the Facility. The investigations at the Facility provided further documentation that DNAPL, in fact, is not present there. The investigations upgradient of the Facility document the presence of upgradient sources of TCE and provide a clear explanation for why TCE remains in groundwater. Throughout the Glacial Drift aquifer, TCE concentrations are generally higher at the bottom of the aquifer just above the bedrock than within the shallow portion of the aquifer. This distribution is consistent with a DNAPL source area located somewhere north of East Hennepin Avenue.

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Figure 9: Results from 2014 Investigation of TCE in Glacial Drift Aquifer Showing Vertical Distribution Inconsistent with DNAPL from Former Soil Absorption Pit

Key Point: TCE concentrations show low variation with depth in the Glacial Drift aquifer, consistent with an absence of DNAPL in the former General Mills Source Area. TCE concentrations are highest at the up-gradient edge of the Facility, consistent with on-going migration of TCE from upgradient sources onto the Facility.

3.7 The pump and treat remediation system successfully remediated groundwater impacts associated with the Facility by 1991.

General Mills operated a groundwater pump and treat system from 1985 to 2010 that recovered groundwater from the vicinity of the former soil absorption pit and areas downgradient of the Facility. This system initially consisted of five groundwater extraction wells completed in the Glacial Drift aquifer and one groundwater extraction well completed in the deeper Carimona aquifer. In 1992, the Carimona well was replaced by two extraction wells screened in the Magnolia member of the Platteville formation. Three of

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the Glacial Drift groundwater extraction wells (Well 111, 112, and 113) were located near the downgradient end of the TCE plume. Groundwater recovered from these extraction wells was discharged into the city sanitary sewer system. The remaining Glacial Drift extraction wells (Well 109 and 110) and the Platteville extraction wells were located on or near the Facility. From 1985 to 1992, the groundwater recovered from these wells was pumped to a treatment system located at the southern end of the Facility and then discharged to the sewer system after treatment. In 1992, when the Carimona well (Well 108) was replaced with two Magnolia wells (MG-1 and MG-2), the groundwater from Wells 109 and 110 was sent to the treatment system while the groundwater from MG-1 and MG-2 was discharged to the sewer system without treatment. From 1985 to 2010, remediation progress was evaluated by monitoring contaminant concentrations in the combined flows from Wells 111, 112, and 113 and the combined flows from Wells 108, 109, 110 (or, after 1992, just Wells 109 and 110). Contaminant concentrations in the individual groundwater extraction wells were not monitored separately until 1998. Although TCE was a primary focus for evaluation of progress in remediation, the groundwater recovered by the pump and treat system was also monitored for other chlorinated solvents, specifically 1,1-dichloroethane, 1,2-dichloroethane, 1,2-dichloroethene (cis & trans), 1,1,2,2-tetrachloroethane, 1,1,1-TCA, and PCE. As discussed in Sections 3.3 and 3.4 of this report, several of these chlorinated VOCs were detected at concentrations greater than TCE in soil samples collected from the immediate vicinity of the soil absorption pit. In contrast, 1,1-dichloroethane, 1,2-dichloroethane, and 1,1,1-TCA are either not detected in upgradient wells or are detected at low concentrations (i.e., < 70 ug/L). These three chlorinated solvents have chemical properties that are reasonably similar to those of TCE such that the pump and treat remediation system installed by General Mills would have similar effectiveness for all four compounds. As a result, the three chlorinated solvents other than TCE can be used to accurately track progress in remediation of groundwater impacts associated with the Facility while avoiding the confounding effects caused by other sources of TCE. The pump and treat system monitoring results for the time period of 1985 to 1996 clearly demonstrate that this system successfully remediated groundwater impacts associated with the Facility and that these impacts were remediated by 1991.1 Figure 10 shows the concentrations of 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-TCA, and TCE in recovered groundwater sent to the on-site treatment system from 1985 to 1996. These data reflect the constituent concentrations in the combined flows from Wells 108, 109, and 110 from 1985 to 1992 and the combined flows from Wells 109 and 110 after Well 108 was taken out of service.

1 After 1991, 1,1-dichloroethane, 1,2-dichloroethane, and 1,1,1-trichloroethane were not detected at concentrations greater than 5 ug/L. Because TCE was a minor component of the waste material from the Facility, this indicates that the maximum TCE impacts associated with the Facility were also less than 5 ug/L (and likely much less than 5 ug/L) after 1991.

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Figure 10: Chlorinated Solvent Concentrations in Recovered Groundwater Sent to the On-site Treatment System: 1985 to 1996

Key Point: As discussed in Section 3.4, 1,1,1-TCA was present in the General Mills waste in concentrations approximately 8 times higher than TCE. 1,1-dichloroethane and 1,2-dichloroethane were also significant components of the General Mills waste. In the water recovered by the pump and treat system, the concentrations of these three constituents decrease by approximately 90% from 1985 to 1996 and were consistently less than 5 ug/L after 1991. In contrast, TCE concentrations decreased by only about 60% from 1985 to 1996 This demonstrates that the pump and treat system remediated the General Mills source area by 1991 but continued to capture TCE originating from other (i.e., upgradient) sources after that time.

As can be seen in Figure 10, the initial concentration of 1,1-dichloroethane, 1,2-dichloroethane, and 1,1,1-TCA in the recovered groundwater ranged from approximately 10 ug/L to 30 ug/L. These three constituents reflect groundwater impacts associated with the Facility. The initial concentrations of TCE were far higher, approximately 1200 ug/L. Based on our current understanding of the Facility waste material and other sources of

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TCE, the vast majority of this TCE is clearly attributable to sources other than the Facility. From 1985 to 1996, the concentrations of 1,1-dichloroethane, 1,2-dichloroethane, and 1,1,1-TCA consistently decreased over time. Concentrations of all three constituents were generally less than 2 ug/L after 1992 reflecting decreases in concentration of over 90%. In contrast, TCE concentrations decreased less (approximately 60%) and remained much higher than the Facility constituents. This pattern with TCE is consistent with on-going impacts from other sources. From 1985 to 1997, VOC concentrations were monitored only for the combined flows from source area wells (Wells 108,109 and 110) and the combined flows from the downgradient wells (Wells 111, 112, and 113). Beginning in 1998, VOC concentrations in the Glacial Drift groundwater extraction wells were monitored individually. From 1998 to present, the monitoring results from Wells 109 and 110 consistently show that TCE concentrations were lower in Well 109 (located in the Facility at the former soil absorption pit) than in Well 110 (located approximately 500 ft southeast of the Facility property line). Typically, TCE concentrations in Well 110 have been about twice as high as those in Well 109. These data further confirm that the chlorinated solvent contamination associated with the soil absorption pit was remediated prior to 1998 (when monitoring in individual wells started) and that the TCE being recovered after that time originated from an off-site source. During its operational period, this pumping system recovered approximately 6 billion gallons of groundwater and removed more than 7,000 pounds of TCE from the subsurface (Barr, 2014). However, based on my review of the annual monitoring reports and other historical site documents, during the operational period, the groundwater pumping system extracted much lower amounts of the chlorinated solvents associated with the General Mills waste such as 1,1,1-TCA (approximately 140 pounds). As discussed above, General Mills waste was a mixture of solvents consisting mostly of petroleum hydrocarbons, but including a number of different chlorinated solvents. TCE represented only a small percentage of the waste solvents disposed. The disparity between the composition of the waste material disposed at the Facility and the composition of contaminants in the groundwater recovered by the pumping system indicates the vast majority of TCE recovered by the pump and treat system from 1985 to 2010 originated from sources other than the Facility. In 2014, additional soil and groundwater testing was conducted in the vicinity of the former soil absorption pit as part of efforts to understand the source of TCE. The 2014 investigation results from the absorption pit area confirm that the chlorinated solvents associated with historical disposal at the soil absorption pit have been fully remediated. With the exception of PCE, TCE, and their associated degradation products, none of the chlorinated solvents associated with the General Mills waste were detected in any soil or groundwater sample collected in this area. The concentrations of TCE and 1,2-dichloroethylene (1,2-DCE) currently detected in groundwater samples from this area are lower than those detected at upgradient and cross-gradient sample locations, consistent with the on-going impacts from other sources.

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In summary, the unique fingerprint of the General Mills waste supports an evaluation of remedy effectiveness despite the confounding presence of upgradient sources of TCE.

• The TCE was a minor component (likely less than 10%) of the chlorinated solvents in the General Mills solvent waste.

• The pump and treat system removed the mixed chlorinated solvent waste from the former General Mills disposal area.

• Except for TCE and its degradation product, cis-1,2-DCE, none of the chlorinated solvents associated with the General Mills waste are detectable in the former source area or in monitoring wells in the immediate vicinity of the source area. This demonstrates that, in the absence of an upgradient source of TCE, TCE and cis-1,2-DCE would also not be detectable in this area.

The complete remediation of chlorinated solvents such as 1,1,1-TCA proves that the smaller amount of TCE present in the General Mills waste has also been fully remediated. Thus, no further actions are needed to address these historical impacts. 3.8 Considering both current and historical information, it is clear that

upgradient sources of TCE in groundwater were already impacting the Facility and areas further downgradient in the 1980s.

Based on the recently-obtained information concerning other sources of TCE in the vicinity of the Facility, it is now clear that the high concentrations of TCE detected in groundwater at locations more than 20 ft from the former soil absorption pit were not associated with the Facility. Investigation results obtained since 2013 clearly document the presence of strong sources of TCE in the Glacial Drift aquifer (and deeper aquifers) at locations upgradient of the Facility. For example, Well 301GD contains TCE concentrations as high as 4,690 ug/L. As shown in Figure 3 above, available investigation results show a continuous plume of TCE-contaminated groundwater originating more than ½ mile upgradient of the Facility and extending more than ½ mile downgradient of the Facility. The Facility is located on the northwest side of this long plume near the midpoint between the upgradient and downgradient ends. In the 1980s, most of the monitoring wells exhibiting the highest concentrations of TCE were located upgradient or cross-gradient of the soil absorption pit. For example, Wells B and BB, located 250 ft upgradient from the soil absorption pit, contained 1,600 ug/L and 2,200 ug/L of TCE, respectively (see Figure 1). In addition, Well WW and Well 8, located over 350 ft and 800 ft cross gradient from the soil absorption pit, respectively, both contained TCE at concentrations of 2,300 ug/L. Based on the groundwater flow direction from northeast to southwest in the vicinity of the Facility and the absence of DNAPL at the Facility (as discussed in Section 3.6), the TCE in these four wells could not have been associated with historical waste disposal at the pit. In the context of currently available information, these historical investigation results clearly indicate that the upgradient sources of TCE were already present in the 1980s and were the primary cause of TCE

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contamination in groundwater at and downgradient of the Facility at that time. 3.9 There is no “clean area” or “area of lower TCE” separating the

upgradient sources from the area of the Facility. In their November 2015 response to the Vapor Intrusion Pathway Investigation Report, the MPCA suggested that the current distribution of TCE within the shallow portion of the Glacial Drift aquifer provides evidence of on-going impacts associated with the Facility. Specifically, the MPCA states that:

“Elevated (>100 μg/L) TCE concentrations in the shallow glacial drift up-gradient (northeast) of the Site do not extend onto the Site or into the central area investigated by GMI. An area of elevated TCE in groundwater is present in the shallow glacial drift directly down-gradient (southwest) of the Site in the central area consistent with a TCE release from the Site. (MPCA, 2015)”

In reaching this conclusion, the MPCA does not appear to consider the following factors:

• The distribution of TCE within the deeper portions of the Glacial Drift aquifer shows that high concentrations of TCE from upgradient sources do extend into the Central Area.

• The high spatial variability in the distribution of TCE within the shallow portion of the Glacial Drift aquifer makes it difficult to draw conclusions based on TCE concentrations measured at one or two individual wells over a short period of time.

• TCE concentrations measured in sub-slab samples provide additional information concerning the distribution of TCE within the shallow Glacial Drift aquifer and these data demonstrate continuously high TCE concentrations extending from the upgradient sources into the Central Area.

Each of these points is addressed in more detail below: The distribution of TCE within the deeper portions of the Glacial Drift aquifer: The deeper monitoring wells in the Glacial Drift aquifer show a continuous area of TCE > 100 ug/L extending from upgradient of the Facility into the Central Area. Examples include: Well 306GD (Max TCE = 740 ug/L), Well 309GD (Max TCE = 250 ug/L), Well 313GD (Max TCE = 540 ug/L). TCE concentrations are lower at the deep well installed at the former GMI disposal area (Well 311GD, TCE = 172 ug/L), demonstrating that the GMI source area is not an on-going source of TCE. Within the core of the plume, no deep monitoring wells suggest that the TCE concentrations drop below 100 ug/L until the toe of the plume southwest of Well 315GD. High spatial variability in the shallow Glacial Drift aquifer: TCE concentrations within the shallow portion of the Glacial Drift aquifer exhibit high spatial variability that is unrelated to contributions from different sources. For example, along 23rd Ave SE, TCE

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concentrations in the shallow portion of the Glacial Drift aquifer were measured at five different locations over a distance of approximately 150 ft (See sample points DP-72 to DP-76; Figure 11). At four of these five locations (DP-73, DP-74, DP-75, and DP-76), TCE concentrations at the top of the aquifer were less than 10 ug/L; however, at DP-72, TCE concentrations were 181 ug/L. In contrast, TCE concentrations at the bottom of the Glacial Drift aquifer were very high at all five locations (761 ug/L to 1210 ug/L) demonstrating that all five sample locations were within the TCE plume emanating from upgradient sources. Based on these investigation results, the location of Wells 306GS and 306GD were moved from their originally planned location (at DP-76) to match the location of DP-72, the location with the higher concentrations (Barr, 2015). Other areas with multiple shallow Glacial Drift sample locations clustered within a small area also show similar high levels of variation in TCE concentration (e.g., Frank’s Auto site).

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Figure 11: Investigation Results for Locations DP-72 to DP-76

Key Point: There is much greater variation in TCE concentrations within the shallow portion of the Glacial Drift aquifer compared to the deeper portion of the Glacial Drift aquifer. A single monitoring well or investigation point in the shallow portion of the Glacial Drift aquifer may not detect high concentrations of TCE present within close proximity of the investigation location.

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As a result of this high spatial variability within the shallow Glacial Drift aquifer, in areas where only a single well or sample point has been installed, it is clear that that single observation location is not representative of the range of TCE concentrations in that immediate area. For example, Well 312GS (and temporary point DP-19 installed earlier at the same location) is the only shallow monitoring point located within a 300 ft radius of the intersection of Talmage and 22nd Ave SE (see Figure 12). Based on all of the available data, the TCE plume emanating from the upgradient sources almost certainly runs through this area. Even though TCE has been detected at a maximum concentration of 63.5 ug/L in this well, it is almost certain that higher concentrations of TCE are present within the shallow portion of the Glacial Drift aquifer in the vicinity of this well.

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Figure 12: TCE Concentrations in Groundwater and Sub-slab Vapors in the Vicinity of the Facility

Key Point: Considered together, the groundwater and sub-slab results indicate a continuous area of high TCE concentrations in the Glacial Drift aquifer extending from the upgradient sources into the Como neighborhood.

TCE concentrations in sub-slab samples: In general, the TCE concentrations in shallow groundwater are well correlated with the TCE concentrations measured in sub-slab samples collected from overlying residences. Although clay layers or other barriers may prevent TCE vapors from reaching the sub-slab at some locations, the detection of higher concentrations of TCE vapors in sub-slab samples provides strong evidence that higher concentrations of TCE are also present in groundwater in this immediate area. This strong connection between groundwater and sub-slab concentrations has been observed at

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other vapor intrusion sites such as the Redfield Rifle site in Colorado where the distribution of 1,1-DCE in sub-slab soil gas provided a greatly improved understanding of the extent of contamination in groundwater (Folkes et al., 2009). Thus, at this site, sub-slab TCE vapor concentrations can be used to provide an improved understanding of TCE concentrations within the shallow portion of the Glacial Drift aquifer in areas with few monitoring wells. Specifically, TCE concentrations in sub-slab samples collected from residences along 23rd Ave SE and 22nd Ave SE demonstrate a continuous area of elevated TCE within the shallow Glacial Drift within the area identified in the November 2015 MPCA letter as an area of lower TCE concentration (see Figure 13).

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Figure 13: Overlay of MPCA TCE Concentration Figure and TCE Sub-slab Vapor Concentration Data

Note: Blue contours are TCE isoconcentration contours for the shallow Glacial Drift aquifer shown in Figure 1 of MPCA, 2015. Key Point: The sub-slab results provide evidence of TCE > 100 ug/L within the shallow Glacial Drift aquifer within the area shown on the MPCA map as containing less than 100 ug/L TCE. After considering all available data concerning the distribution of TCE within the Glacial Drift aquifer and accounting for the inherent variability in its spatial distribution, there is no evidence of any current contribution originating from the Facility.

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3.10 All necessary response actions at the General Mills/Henkel Superfund Site have been completed.

As detailed above, within the Glacial Drift aquifer, the chlorinated solvents associated with the Facility have been fully remediated and are no longer detectable. Petroleum impacts are limited to a single monitoring well (Well 311GS) installed at the former General Mills source area. No further remediation is required to address impacts associated with the Facility. Impacts associated with the Facility do not contribute to the need for on-going vapor intrusion mitigation at properties in the vicinity of the Facility. No other exposure control or mitigation measures are needed to address impacts associated with the Facility. 4.0 Cited References American Petroleum Institute (1983). Groundwater Monitoring and Sample Bias. API Publication 4367, Washington, D.C. ASTM (2014). Standard Guide for Developing Conceptual Site Models for Contaminated Sites (ASTM E-1689-95 (2014)). ASTM International. Barr (1983). Site Characterization Study and Remedial Action Plan, General Mills Solvent Disposal Site, 2010 East Hennepin Avenue, Minneapolis, MN. Barr Engineering, June 1983. Barr (1984). Water Treatment Feasibility Study, Groundwater Pump-Out System, General Mills East Hennepin Avenue Site, Minneapolis, MN. Barr Engineering, August 1984. Barr (2012). Groundwater Pump-out System Shutdown Summary Report and 2011 Annual Report, East Hennepin Avenue Site, Minneapolis, MN. Barr Engineering, March 2012. Barr (2014). Vapor Intrusion Pathway Investigation and Feasibility Study Work Plan: Sampling and Monitoring Work Plan, August 2014. Barr (2015). Vapor Intrusion Pathway Investigation Report, July 2015. Deposition Excerpts from General Mills vs. Travelers Indemnity Folkes D, Wertz W, Kurtz J, Kuehster T. (2009). Observed Spatial and Temporal Distributions of CVOCs at Colorado and New York Vapor Intrusion Sites. Groundwater Monitoring & Remediation. Vol. 29, No. 1, 70-80. General Mills. (1981). Voluntary Notification of Contamination at Site. General Mills, Inc. Minneapolis, Minnesota, 6/12/1981.

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Mossler, J.H. (2008). Paleozoic Stratigraphic Nomenclature for Minnesota, Minnesota Geological Survey Report of Investigations 65, ISSN 0076-9177. MPCA (1984). Response Order by Consent between Minnesota Pollution Control Agency and General Mills Inc., Executed 10/23/1984. MPCA (2015). Letter Re: Minnesota Pollution Control Agency Response to the Vapor Intrusion Pathway Investigation Report for the General Mills/Henkel Corporation Site; Site ID#: SR3. November 3, 2015. MPCA (2016). Letter Re: Request for Approval of Site Listing and Delisting on the State Superfund List of Priorities. August 24, 2016. MPCA (2017). “Figure 1: Proposed Existing Wells and Temporary Well Locations for SE Hennepin,” map issued 1/18/2017. Newell, C.J., and R.R. Ross, 1992. Estimating Potential for Occurrence of DNAPL at Superfund Sites. U.S. Environmental Protection Agency. R.S. Kerr Office of Solid Waste Publication: 9355.4-07FS. NJDEP (2011). Technical Guidance for Preparation and Submission of a Conceptual Site Model. December 16, 2011 Soil Exploration Company (1981). Study of Subsurface Contamination, Henkel Corporation, 2010 East Hennepin Ave, Minneapolis, MN.

March 2017

EXPERT REPORT AND DECLARATION OF THOMAS E. MCHUGH, Ph.D., D.A.B.T.

ATTACHMENTS

Attachment A Resume of Thomas E. McHugh, Ph.D., D.A.B.T.

March 2017

EVALUATION OF REMEDY COMPLETENESS AT THE GENERAL MILLS/HENKEL CORP.

SUPERFUND SITE

ATTACHMENT A

Resume of Thomas E. McHugh, Ph.D., D.A.B.T.

March 2017

Thomas E. McHugh, Ph.D., D.A.B.T. Biographical Summary Dr. McHugh is an environmental consultant with GSI Environmental, in Houston, Texas. He is a Diplomate of the American Board of Toxicology and has over 20 years of experience in the environmental industry with academic research and private consulting organizations. He has been a Principal with GSI Environmental since 2003. He received a B.A. in Biochemistry and Environmental Science from Rice University (1990), an M.S. in Environmental Engineering from Stanford University (1993), and a Ph.D. in Toxicology from the University of Washington (1997). Dr. McHugh has extensive project experience in environmental site investigation, site restoration, and human health and ecological risk assessment. He has developed training classes on a number of topics including the Texas Risk Reduction Program (TRRP) and was a member of the government/industry workgroup that developed the Ecological Risk Assessment Guidance for Remediation Sites in Texas. Dr. McHugh served as the principal investigator (PI) for a number of research projects funded by the Department of Defense and other funding organizations. He is the lead author on several peer-reviewed journal articles, peer-reviewed conference proceedings, and technical documents on vapor intrusion and other topics related to environmental site investigation and remediation.

Education Ph.D., Toxicology, University of Washington, 1997

M.S., Environmental Engineering, Stanford University, 1993

B.A., Biochemistry and Environmental Science, Rice University, 1990

Professional Background Vice President, GSI Environmental Inc. (formerly Groundwater Services, Inc.), Houston, Texas, 2003 to

present

Toxicologist and Environmental Scientist, GSI Environmental Inc., Houston, Texas, 1997 to present

Research Assistant, University of Washington, Seattle, Washington, 1993 to 1997

Environmental Scientist, Groundwater Services, Inc., Houston, Texas, 1990 to 1992

Professional Affiliations Diplomate, American Board of Toxicology (2002 to present); Recertification completed in 2007, 2012, and

2017

Air and Waste Management Association

National Ground Water Association; Certified Ground Water Professional (CGWP, 2008 to 2012)

Society of Toxicology; President of Ethical, Legal, Social Issues Specialty Section (2007-2008)

Thomas E. McHugh, Page 1 of 10

Project Experience Vapor Intrusion

Evaluation of Sewers and Utility Tunnels as Preferential Pathways for Volatile Organic Compound Migration into Buildings, Various Locations. Principal Investigator for a three-year DoD funded research project to develop and validate a reliable protocol to evaluate sewer and utility tunnel preferential pathways. Protocol includes initial desktop screening to identify sites that may have preferential pathways, procedures for field investigation of sewers, and methods to investigate the interaction between sewers and buildings.

Vapor Intrusion Investigation, Industrial Building, Utah. Developed and implemented vapor intrusion sampling program for an industrial building used for management of hazardous waste management. Sampling program utilized real-time analysis of indoor air samples using a field portable HAPSITE GC/MS. Real-time results were used to identify and remove indoor sources of VOCs to reduce or eliminate the impact of these indoor sources on the samples collected for off-site laboratory analysis. After the initial investigation, the building depressurization to evaluate the effect of variable building pressure on vapor intrusion.

Vapor Intrusion Investigation, Railroad Facilities, Montana. Developed and implemented vapor intrusion sampling program for multiple railroad facility sites in Montana. Sampling program utilized real-time analysis of indoor air samples using a field portable HAPSITE GC/MS. Real-time results were used to identify and remove indoor sources of VOCs to reduce or eliminate the impact of these indoor sources on the samples collected for off-site laboratory analysis.

Validation of Tools to Distinguish Between Vapor Intrusion and Indoor Sources of VOCs, Various Locations. Principal Investigator two three-year DoD funded research project to validate vapor intrusion investigation methods that distinguish between vapor intrusion and indoor sources of VOCs. Innovative tools include compound-specific stable isotope analysis (CSIA) and on-site VOC concentration analysis using a HAPSITE field-portable GC/MS.

Vapor Intrusion Investigation, Petroleum Storage Tank Farm, Montana. Developed and implemented vapor intrusion sampling program for 20 homes overlying crude oil/condensate plume originating from near-by tank farm. Sampling program includes sub-slab soil gas, indoor air, and ambient air. Data evaluation utilized multiple lines of evidence including distribution of VOCs below and within residences, comparison of VOC and radon attenuation factors, hydrocarbon fingerprinting, and analysis of VOCs known to originate from indoor sources.

Validation of New Tools to Better Manage Vapor Intrusion Liability, Air Force Center for Engineering and the Environment. Demonstrated a suite of investigation tools that will provide the U.S. Air Force with a scientifically defensible method to i) discriminate between indoor and subsurface sources of VOCs in buildings and ii) document biotic and abiotic destructive processes occurring in the vadose zone that prevent/minimize vapor intrusion impacts. Application of these tools to vapor intrusion sites will be documented in a technical report that will allow the Air Force to better manage their potential vapor intrusion liability.

BioVapor Software Tool, American Petroleum Institute. Developed user-friendly Excel-based version of the Indoor Vapor Intrusion with Oxygen-Limited Biodegradation model presented in DeVaull, 2007. This is the first publically-available, user-friendly vapor intrusion model that can be used to evaluate the vapor intrusion risk associated with petroleum hydrocarbons accounting for oxygen-limited biodegradation.

Soil Gas Investigation, Former Petroleum Refinery, Mexico City. Conducted a soil gas investigation at a former petroleum refinery site being redeveloped as a city park. Used on-site analysis to obtain real-time understanding of the distribution of petroleum hydrocarbon vapors in soils. Results were used to evaluate vapor intrusion risk and identify the need for remediation and/or land use controls.

Vapor Intrusion Best Practices, Major Oil Company. Developed “Best Practices” guidance documents for evaluation of the vapor intrusion pathway, collection and analysis of soil gas and sub-slab samples, and collection and analysis of indoor air samples at corrective action sites. These guidance documents are used to ensure that project managers, consultants, and contractors evaluate the vapor intrusion pathway in a consistent and protective manner at company sites.


Protocol for Tier 2 Evaluation of Vapor Intrusion at Corrective Action Sites, Various Locations. Principal Investigator for four-year DoD funded research project to develop and validate Tier 2 and Tier 3 investigation protocols for the evaluation of vapor intrusion.

Petroleum Vapor Intrusion Database, American Petroleum Institute. Compiled and analyzed database of petroleum hydrocarbon measurements in groundwater, soil, soil gas, indoor air, and ambient air to obtain a better understanding of site-specific factors contributing to the presence or absence of vapor intrusion impacts at petroleum hydrocarbon corrective action sites.

Detailed Field Investigation of Vapor Intrusion Processes, Various Locations. Conducted three-year DoD-funded research project on vapor intrusion processes at three DoD facilities. Identified site characteristics contributing to the occurrence of vapor intrusion impacts. Validated cost-effective vapor intrusion investigation methods.

Vapor Intrusion Exposure Pathway, American Petroleum Institute. Developed new model for evaluation and screening of the groundwater-to-indoor air exposure pathway. Model provides a significant advantage over the commonly used evaluation model (i.e., the Johnson Ettinger Model) by providing a mass balance in groundwater rather than considering groundwater to be an infinite source of volatile chemicals. In addition, provided technical evaluation of the 2001 Draft USEPA Vapor Intrusion Guidance.

Toxicology and Risk Assessment

Human Health and Ecological Risk Assessment, Former Military Facility, Dallas, Texas. Completed a Tier 2 ecological risk assessment lake sediments impacted by operations of a former military facility. The study evaluated the risk to sediment benthics and wildlife associated with metals and PCBs in lake sediments. Used advances analytical methods to evaluate metals bioavailability. Evaluated risk to human health associated with PCBs in fish.

Risk Management Software Tool, Major Oil Company. Developed Microsoft Access-based software tool to evaluate and track environmental risks associated with a large portfolio of industrial properties. Tool is used to manage overall portfolio risk and to track reduction in risk over time.

Ecological Risk Assessment, Former Industrial Site, Longview, Texas. Completed a Tier 2 ecological risk assessment for recycling facility. The study evaluated risk to ecological receptors associated with exposure to lead in soil, surface water, and sediment.

Ecological Risk Assessment, State Superfund Site, Houston, Texas. Completed a Tier 2 ecological risk assessment for former metals processing facility. The study utilized site-specific measurements of metal bioavailability in soil and included food-chain analyses for estimation of exposures to higher-level receptors.

Wetlands Evaluation, Chemical Manufacturing Facility, Gulf Coast, Texas. Evaluated presence of wetlands and U.S. Army Corps jurisdictional issues associated with abandoned borrow pits in an undeveloped portion of a chemical manufacturing facility.

Barite Risk Assessment, Energy Services Company, Houston, Texas. Conducted a risk assessment comparing the toxicity of barite (used in drilling mud) to soluble barium compounds. Based on this analysis, the TCEQ agreed to classify barite a chemical that it not a human health concern. Developed and validated a procedure to distinguish between soluble barium and barite in environmental soil samples.

Ecological Risk Assessment, Former Pesticide Plant, Houston, Texas. Completed a Tier 2 ecological risk assessment for soils impacted by chlorinated pesticides. The study included food-chain analyses for estimation of exposures to higher-level receptors. Risk assessment resulted in the development of clean-up standards for the protection of ecological receptors utilizing the uplands habitat adjacent to the facility.

Baseline Risk Assessment for RFI Units, Chemical Manufacturing Facility, Gulf Coast, Texas. Completed base-line risk assessment for former waste management units at a chemical manufacturing facility as part of the RCRA Facilities Investigation (RFI) process for the facility. Evaluation was completed to determine if corrective action measures were needed at the former waste management units to protect human health and the environment, and included an ecological risk assessment.


Ecological Risk Assessment, Pipeline Company, Greenville, Texas. Completed a Tier 2 ecological risk assessment on a creek impacted by 500,000 gallons of oxygenated gasoline released from a pipeline break. The study included food-chain analyses for estimation of exposures to higher-level receptors. Risk assessment found no remediation required in creek due to the natural rapid decrease in gasoline constituent concentrations in creek sediments over time.

TNRCC Ecological Risk Assessment Workgroup, Austin, Texas. Member of a state government and industry workgroup which developed guidance for conducting ecological risk assessments for remediation sites in Texas.

Risk-based Decision Making Performance Study, Five States. Conducted an evaluation of the impact of Risk-Based Decision Making (RBDM) on the performance of corrective action program in five pilot states. The study, funded by the USEPA through ASTM, involved development of program performance measures and analysis of state program databases to determine the impact of RBDM on risk reduction, program efficiency, and cost control.

Baseline Risk Assessment, Major Oil Company, Louisiana. Completed baseline risk assessment for a bayou and associated wetlands that have previously received discharges from an adjacent chemical manufacturing facility. Report summarized potential risk associated with occasional recreational use of the bayou and consumption of resident biota. Adult and child lead models developed by the USEPA were utilized to assess potential risks from lead exposure.

Environmental Engineering

Development and Validation of a Time-Integrated Groundwater Sampler. Developed and validated a new type of sampler for measurement of VOC concentrations in groundwater. The sampler can be deployed in a monitoring well for up to three months and measures the average constituent concentration in the monitoring well over the deployment time period. Patent pending, application number 15/157,013.

Development of Improved Groundwater Monitoring Methods, Various Locations. Principal Investigator for three-year research project sponsored by the Department of Defense to obtain a better understanding of the causes of variability in groundwater monitoring results and to develop improved sampling methods to reduce monitoring variability.

Corrective Measures Study, Chemical Manufacturing Facility, Gulf Coast, Texas. Completed Corrective Measures Study (CMS) in accordance with Texas Risk Reduction Rules, Standard 3. CMS identified stabilization and containment for historic waste management units and associated affected soils and natural attenuation for affected groundwater as the preferred remedies.

Radioactive Material License Renewal Application, Chemical Manufacturing Facility, Gulf Coast, Texas. Completed application for renewal of a Radioactive Materials License (RML) subject to state and federal regulations for on-site disposal of low-level radioactive waste associated with chemical manufacturing. The application included a modeling evaluation of potential radiological impacts associated with the disposal units in accordance with state and federal regulations.

Risk Prioritization Study of Petroleum Hydrocarbon Sites, Major Oil Company, Torrance, California. Compiled database of 300 petroleum hydrocarbon sites based on questionnaires completed by site contractors. Incorporated the ASTM Risk-Based Corrective Action (RBCA) framework to rank sites based on relative risk to human health. Identified site where natural attenuation was the preferred remedy.

Full Scale In situ Biotreatment System, Gas Processing Plant, Wexford, Michigan. Analyzed design basis information and utilized the OASIS/BIOPLUME modeling system to design a full scale in situ bioremediation system for remediation of dissolved BTEX plume. Coordinated system construction and installation. Provided analysis of performance and operation data.

Dense Non-Aqueous Phase Liquid (DNAPL) Dissolution Study, MOTCO Superfund Site, La Marque, Texas. Contributed to the development of a conceptual design for management of DNAPL contaminated portions of site. Project included design and evaluation of field scale study of the dissolution of soluble components of DNAPL. Compared field results to computer model predictions and used results to refine computer model. Developed cost effective long-term containment strategy.


Course Development and Training

Vapor Intrusion. Developed and taught 1-day seminar on vapor intrusion covering: conceptual model, soil gas sampling, indoor air sampling, petroleum vapor intrusion, state and USEPA guidance, and innovative vapor intrusion investigation methods.

Field Investigation Method to Distinguish Between Vapor Intrusion and Indoor Sources of VOCs. Developed and taught ½-day seminar on vapor intrusion investigation methods. Course focusing on investigation tools and data interpretation methods to distinguish between vapor intrusion and indoor sources of VOCs.

Evaluation of Background at Vapor Intrusion Sites. Developed and taught 90-minute seminar on indoor air investigations and identification of background sources of VOCs for the U.S. Navy’s spring 2011 RITS seminar series. Seminar was presented to Navy project managers, contractors, and regulators in six cities within the United States.

BioVapor, 1-D Vapor Intrusion Model with Aerobic Biodegradation. Developed and taught half-day training class on the BioVapor model. Key topics included: Overview of the BioVapor Model, BioVapor Model Features, Calculational Bases, and Model Inputs/Outputs, BioVapor Demonstration, and Example Case Studies.

Vapor Intrusion Webinar. Developed and taught half-day web-based training class on vapor intrusion for the project managers and consultants at a major oil company. Key topics included: vapor intrusion conceptual model, vapor intrusion pathway screening, collection of soil gas samples, collection of indoor air samples, data interpretation, and vapor intrusion mitigation.

Management of Large and Dilute Groundwater Plumes. Developed and taught 90-minute seminar on management of large and dilute groundwater plumes for the U.S. Navy’s spring 2008 RITS seminar series. Seminar was presented to Navy project managers, contractors, and regulators in six cities within the United States.

Texas Risk Reduction Program (TRRP) Guidance and Policy. Developed and taught one-day training course on TRRP guidance and policy. Key topics included: land use classification, groundwater classification, laboratory data validation, ecological risk assessment, total petroleum hydrocarbons, monitored natural attenuation, and non-aqueous phase liquids, and the use of state mandated report forms.

Texas Risk Reduction Program (TRRP) Regulations. Developed and taught two-day training course on the Texas Risk Reduction Program regulations. Key topics included: overview of the TRRP rule, applicable program areas, comparison to former Risk Reduction Rules, affected property assessment, PCL development, remedy standards, and response actions.

Texas Risk Reduction Program Software. Developed and taught one-day training course on use of TRRP software package for calculation of PCLs under TRRP. Key topics included calculation of PCLs and understanding how land use, application of institutional controls, and other site-specific factors impact PCL values.

Risk-Based Corrective Action Training. Developed and taught two-day training course on Risk-Based Corrective Action (RBCA). Key topics included: overview of corrective action, environmental fate and transport, development of site-specific clean-up standards, remedy selection, monitored natural attenuation, and the use of RBCA software.

Natural Attenuation. Developed and taught one-day training course on the application of natural attenuation to corrective action sites. Key topics included: overview of natural attenuation, primary, secondary, and option lines of evidence for evaluation of natural attenuation, and the use of software for evaluation of natural attenuation.

ASTM Course on Remediation by Natural Attenuation. Taught two-day ASTM training course on remediation by natural attenuation.

ASTM Tier 2 RBCA Toolkit Training. Taught one-day training course on the use of the RBCA Toolkit software for development of site-specific clean-up standards for corrective action sites.


ASTM Course on Risk-Based Corrective Action. Taught two-day training course on Risk-Based Corrective Action

Litigation Support

Contaminated Groundwater Site, Minnesota. Testified concerning the likely sources of TCE in soil, groundwater, and air. Testified regarding the evaluation and mitigation of vapor intrusion.

Petroleum E&P Sites, South America. Testified concerning the potential for adverse human health effects associated with exposure to petroleum contamination at oil well sites and oil production facilities in South America.

Contaminated Groundwater Site, Indiana. Testified concerning the potential for adverse human health effects associated with exposure to low concentrations of vinyl chloride in drinking water.

Pipeline Site, Texas. Testified concerning the potential human health and ecological impacts associated with a release of water-based drilling mud.

Agricultural Site, Missouri. Testified concerning the potential for volatile chemicals to migrate from livestock operation to adjacent farm property. Evaluate health risks associated with potential chemical exposure.

Metals-Affected Soils Site, Montana. Testified concerning potential toxicity of and exposure mechanisms for metals in soil and volatile organics in groundwater at a site in Montana.

Contaminated Groundwater Site, Illinois. Testified concerning hazards associated with dissolved vinyl chloride present in groundwater. Evaluated ingestion exposures and vapor intrusion exposures.

Leaking Underground Storage Tank Site, Texas. Testified concerning timing of a gasoline release from former underground storage tanks and the likelihood of achieving state remediation requirements.

Contaminated Property, Texas. Testified concerning potential toxicity of and exposure mechanisms for chlorinated solvents present at a contaminated site in north Texas. Also testified concerning the obligations to investigate and remediate contaminated properties in Texas.

Diesel Plume, North Dakota. Testified concerning human health impacts of an LNAPL diesel plume underlying a small town in North Dakota. Vapor intrusion was identified as the key potential exposure concern. Used multiple lines of evidence to distinguish between background indoor air impacts and diesel vapor intrusion. Determined that no vapor intrusion impact occurred.

Pipeline Break, Texas. Testified concerning human health and ecological impacts associated with a release for oxygenated gasoline from a pipeline into an adjacent creek and drinking water reservoir. Evaluation included gasoline fate and transport, exposure potential, health impact, and remedy selection.

Pesticide Plant, Texas. Testified concerning human health and ecological risks associated with chlorinated pesticides present in soils adjacent to a former pesticide manufacturing facility. Evaluation included the development of clean-up standards for the protection of human health and ecological receptors.

Landfill Permit Hearing, Texas. Testified regarding the potential health risks associated with a Type IV (Construction and Inert Material) Landfill. Testimony also addressed the toxicity of waste material accepted by the landfill and the adequacy of site operating procedures to prevent unacceptable exposure to the materials.

Representative Publications McHugh, T, Loll, P., Eklund, B., “Recent Advances in Vapor Intrusion Site Investigations”. Journal of

Environmental Management. In Press, On-line February 22, 2017. Doi: 10.1016/j.jenvman.2017.02.015 Connor, J.A., Walker, K., Molofsky, L., Baca, E., Gie, E. and McHugh, T., Comment on “Impact to

Underground Sources of Drinking Water and Domestic Wells from Production Well Stimulation and Completion Practices in the Pavillion, Wyoming, Field”. 2016. Environmental Science & Technology, 50(19), pp.10769-10770.

Molofsky, L.J., Richardson, S.D., Gorody, A.W., Baldassare, F., Black, J.A., McHugh, T.E. and Connor, J.A., Effect of Different Sampling Methodologies on Measured Methane Concentrations in Groundwater


Samples. Groundwater. Volume 54, Issue 5, September/October 2016, Pages 669–680. doi: 10.1111/gwat.12415.

Molofsky, L.J., Connor, J.A., McHugh, T.E., Richardson, S.D., Woroszlyo, C. and Alvarez, P.J., 2016. Environmental Factors Associated With Natural Methane Occurrence in the Appalachian Basin. Groundwater., 2016. Volume 54, Issue 5, September/October 2016, pp 656-668.

Beckley, L., McHugh, T., Philp, R.P., “Utility of Compound-Specific Isotope Analysis for Vapor Intrusion Investigations”, Ground Water Monitoring and Remediation, Volume 36, Issue 4. On-line 30 Sept. 2016. doi: 10.1111/gwmr.12185.

McAlary, T., McHugh, T. et al., “Comments and Corrections to: “The Emperor’s Old Clothes: An Inconvenient Truth About Currently Accepted Vapor Intrusion Assessment Methods,” and “Emperor’s Old Clothes Revisited,” Two Recent Editorials by Mark Kram”. Letter to the Editor, Groundwater Monitoring and Remediation. Volume 36, No. 3 /Summer 2016. doi: 10.1111/gwmr.12166.

McHugh, T.E., Kulkarni, P.R., and Newell, C.J., “Time Vs. Money: A Quantitative Evaluation of Monitoring Frequency Vs. Monitoring Duration”, Groundwater, Volume 54, Issue 5, September/October 2016, Pages 692–698, DOI: 10.1111/gwat.12407.

McHugh, T.E., Kulkarni, P.R., Beckley, L.M., Newell, C.J., and Zumbro, M., “Negative Bias and Increased Variability in VOC Concentrations Using the HydraSleeve in Monitoring Wells”, Groundwater Monitoring and Remediation, Volume 36, Issue 1, Winter 2016, Pages 79–87, DOI: 10.1111/gwmr.12141

McHugh, T.E., Molofsky, L., Connor, J.A. “Comment on ‘Characterization of Marcellus Shale Flowback Water’ “, Environmental Engineering Science, 2016, Volume 33, Number 1. DOI: 10.1089/ees.2015.0330.

Kulkarni, P.R., McHugh, T.E., Newell, C.J., Garg, S. “Evaluation of Source-Zone Attenuation at LUFT Sites with Mobile LNAPL”, Soil and Sediment Contamination: An International, Journal, Accepted author version posted online: 22 Jul 2015.

McHugh, T.E., Rauch, S.R., Paquette, S.M., Connor, J.A., Daus, A.D., “Life Cycle of Methyl tert-Butyl Ether in California Public Water Supply Wells”, Environmental Science and Technology Letters, 2015, Volume 2, pp. 7 – 11.

Connor, J.A., Kamath, R., Walker, K.L., McHugh, T.E., “Review of Quantitative Surveys of the Length and Stability of MTBE, TBA, and Benzene Plumes in Groundwater at UST Sites”. Groundwater, 53(2) pp. 195-206. March/April 2015.

Beckley L., Gorder, K., Dettenmaier, E., Rivera-Duarte, I., and McHugh, T., On-Site Gas Chromatography/Mass Spectrometry (GC/MS) Analysis to Streamline Vapor Intrusion Investigations” Environmental Forensics, 15:234–243, 2014.

Adamson, D.T., McHugh, T.E., Rysz, M.W., Landazuri, R., Seyedabbasi, M.A., Haas, P.E., Newell, C.J. “On-Site Vapor-Phase Analysis as a Novel Approach for Monitoring Groundwater Wells”. Groundwater Monitoring and Remediation, Vol. 34, No. 2, pp. 42-59. 2014

McHugh, T.E., Kulkarni, P.R., Newell, C.J., Connor, J.A., and Garg, S., “Progress in Remediation of Groundwater at Petroleum Sites in California”, Groundwater, 52(6) pp. 898–907, November/December 2014.

McHugh, T.E., Beckley, L., Bailey, D., “Influence of Shallow Geology on Volatile Organic Chemical Attenuation from Groundwater to Deep Soil Gas” Groundwater Monitoring and Remediation, Groundwater Monitoring and Remediation, Vol. 33, No 3, pp 92-100, Summer 2013.

Klisch, M., Kuder, T., Philp, R.P., McHugh, T.E., “Validation of Adsorbents for Sample Preconcentration in Compound-Specific Isotope Analysis of Common Vapor Intrusion Pollutants”, Journal of Chromatography A, Vol.1270, pp 20-27, 2013.

McHugh, T.E., Newell, C.J., Landazuri, R., Molofsky, L.J., Adamson, D.T., “Influence of Seasonal Vertical Temperature Gradients on No Purge Sampling of Wells”, Remediation Journal, Vol. 22, No. 4., Autumn 2012.


Eklund, H., Beckley, L., Yates, V., McHugh, T., “Overview of State Approaches to Vapor Intrusion”, Remediation Journal, Vol. 22, No. 4, Autumn 2012.

McHugh, T.E., Beckley, L., Gorder, K., Dettenmatier, E., Rivera-Duarte, I., Brock, S., MacGregor, I., “Evaluation of Vapor Intrusion Using Controlled Building Pressure”, Environmental Science and Technology, April 9, 2012, Vol. 46, pp 4792-4799.

Kamath, R., Connor, J.A., McHugh, T.E., Nemia, A., Le, M.P., Ryan, A.J., “Use of Long-Term Monitoring Data to Evaluate Benzene, MTBE, and TBA Plume Behavior in Groundwater at Retail Gasoline Sites”, Journal of Environmental Engineering, Vol. 138, pp. 458-469. April 2012. (This paper won the 2013 ASCE Wesley W. Horner Award.)

McHugh, T.E., Kuder T., Fiorenza S., Gorder K., Dettenmaier E., Philp P., “Application of CSIA to Distinguish Between Vapor Intrusion and Indoor Sources of VOCs”, Environmental Science and Technology, July 15, 2011, Vol. 45, No. 14, pp 5952-5958.

McHugh, T.E., Beckley, L.M., Liu, C.Y., Newell, C.J., “Factors Influencing Variability in Groundwater Monitoring Data Sets”, Ground Water Monitoring and Remediation, Volume 31, Issue 2, pages 92–101, Spring 2011.

McHugh, T.E., Davis R., DeVaull G.E., Hopkins H., Menatti J., and Peargin T., “Evaluation of Vapor Attenuation at Petroleum Hydrocarbon Sites: Considerations for Site Screening and Investigation”, Soil and Sediment Contamination: An International Journal, November/December 2010, Vol. 19, No. 6., pp 725-745.

McHugh, T.E., Gorder, K., “Methods to distinguish between vapor intrusion and indoor sources of VOCs at residences near Hill AFB, Utah, USA” Chapter 11 in Vapor Emission to Outdoor Air and Enclosed Spaces for Human Health Risk Assessment: Site Characterization, Monitoring and Modeling, Editors: Sabrina Saponaro, Elena Sezenna and Luca Bonomo (Politecnico di Milano, Italy), Nova Publishers, Fall 2010.

McHugh, T.E., McAlary, T., “Important Physical Processes for Vapor Intrusion: A Literature Review” in Proceedings of AWMA Vapor Intrusion Conference (San Diego, CA, January 28-30, 2009).

McHugh, T.E., Hammond, D.E., Nickels, T., Hartman, B., “Use of Radon Measurements for Evaluation of VOC Vapor Intrusion”, Environmental Forensics, Vol. 9 No. 1, p. 107, March 2008.

McHugh, T.E., Nickels, T.N., Brock, S., “Evaluation of Spatial and Temporal Variability in VOC Concentrations at Vapor Intrusion Investigation Sites” in Proceedings of Vapor Intrusion: Learning from the Challenges (Providence, RI, September 26-28, 2007).

Connor J.A., F. Ahmad, and T.E. McHugh. 2006. “Evaluation of Vapor Intrusion from Subsurface Diesel Plume Using Multiple Lines of Evidence”, Proceedings of Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Assessment, and Remediation Conference, Houston, Texas, 6-7 November 2006

McHugh, T.E., and Connor, J.A. “Selection of Effective Technologies for Management of Contaminated Lands,” in Simeonov, L. and Chirila, E. (ed.), Chemicals as Intentional and Accidental Global Environmental Threats, Springer Publishers, The Netherlands, 2006.

McHugh, T.E., and Connor, J.A. “Evaluating Health Risks and Prioritising Response Actions for Contaminated Lands,” in Simeonov, L. and Chirila, E. (ed.), Chemicals as Intentional and Accidential Global Environmental Threats, Springer Publishers, The Netherlands, 2006.

Newell, C.J., and McHugh, T.E. “The Use of Models for the Evaluation of Chemical Attenuation in the Environment,” in Simeonov, L. and Chirila, E. (ed.), Chemicals as Intentional and Accidential Global Environmental Threats, Springer Publishers, The Netherlands, 2006.

McHugh, T.E., de Blanc, P.C., and Pokluda, R.J. “Indoor Air as a Source of VOC Contamination in Shallow Soils Below Buildings” Soil and Sed. Contam., Vol. 15, No. 1, pp. 103-122, January 2006.

McHugh, T.E. Ahmad, F. Connor, J.A. “Empirical Analysis of Groundwater-to-Indoor-Air Exposure Pathway Based on Measured Concentrations at Multiple Groundwater Impact Sites” Env. Forensics. Vol. 5, No. 1, pp. 33-44, March 2004.


McHugh T.E., Connor J.A., Ahmad F., Newell C.J., “A Groundwater Mass Flux Model for Groundwater-To-Indoor-Air Vapor Intrusion”, Paper H-09, in: V.S. Magar and M.E. Kelley (Eds.), In Situ and On-Site Bioremediation—2003. Proceedings of the Seventh International In Situ and On-Site Bioremediation Symposium (Orlando, FL; June 2003). ISBN 1-57477-139-6, published by Battelle Press, Columbus, OH, www.battelle.org/bookstore.

Connor, J.A., and T.E. McHugh, “Impact of Risk-Based Corrective Action (RBCA) on State Corrective Action Programs”, Human and Ecological Risk Assessment, CRC Press, Volume 8, Number 2, April 2002.

Connor, J.A., R.L. Bowers, and T.E. McHugh, “RBCA Toolkit: Comprehensive Risk-Based Modelling System for Soil and Groundwater Cleanup,” in Linders, J.B.H.J. (ed.), Modelling of Environmental Chemical Exposure and Risk, Kluwer Academic Publishers, The Netherlands, 2001.

Connor, J.A., R.L. Bowers, T.E. McHugh, and J. P. Neven, “Software Guidance Manual, RBCA Tool Kit for TRRP”, Groundwater Services, Inc., 2001

York, J. L., L. C. Maddox, P. Zimniak, T. E. McHugh, and D. F. Grant, “Reduction of MTT by Glutathione S-Transferase”, Biotechniques, Volume 25, pp. 622-8, October, 1998.

Van Ness, K. P., T. E. McHugh, T. K. Bammler, and D. L. Eaton, “Identification of Amino Acid Residues Essential for High Aflatoxin B1-8,9-Epoxide Conjugation Activity in Alpha Class Glutathione S-Transferase through Site-Directed Mutagenesis”, Toxicology and Applied Pharmacology, Volume 152, pp. 166-174, September, 1998.

McHugh, T. E., W. M. Atkins, J. K. Racha, K. L. Kunze, and D. L. Eaton, “Binding of the Aflatoxin-glutathione Conjugate to Mouse Glutathione S-Transferase A3-3 is Saturated at Only One Ligand per Dimer”, The Journal of Biological Chemistry, Volume 271, pp. 27470-74, November 1, 1996.

Chiang C., P. Petkovsky, M. Beltz, S Rouse, T, Boyd, C. Newell, T. McHugh, “An Enhanced Aerobic Bioremediation System at a Central Production Facility - System Design and Data Analysis”, Proceedings of the Conference on Petroleum Hydrocarbons and Organic Chemicals in Ground Water, National Ground Water Association, Houston, Texas, November, 1993, pp. 661-678.

Newell, C.J., J.A. Connor, D.K. Wilson, and T. E. McHugh, “Impact of Dissolution of Dense Non-Aqueous Phase Liquids (DNAPLs) on Ground Water Remediation”, Proceedings of the Conference on Petroleum Hydrocarbons and Organic Chemicals in Ground water, National Water Well Association, Houston, Texas, November, 1991.

Representative Conference Presentations McHugh, T.E., O’Neill, H., Newell, C., Molofsky, L. A Long-Duration Time-Integrated Sampler for

Groundwater Monitoring. Tenth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, May 2016.

McHugh, T.E., Kulkarni, P.R., Newell, C.J., Time versus Money: A Quantitative Approach to Selection of Groundwater-Monitoring Frequency. Third International Symposium on Bioremediation and Sustainable Environmental Technologies, Miami, Florida, May 18-21, 2015.

McHugh, T.E., Rauch, S.R., Paquette, S.M., Connor, J.A., and Daus, A.D., The Lifecycle of MTBE in Public Water Supply Wells in California. Third International Symposium on Bioremediation and Sustainable Environmental Technologies, Miami, Florida, May 18-21, 2015.

McHugh, T.E., Beckley, L.M., State-of-the-Practice: Innovative Tools for Evaluating Vapor Intrusion Risk. Third International Symposium on Bioremediation and Sustainable Environmental Technologies, Miami, Florida, May 18-21, 2015.

McHugh, T.E., Distinguishing Between Vapor Intrusion and Indoor Sources of Volatile Organic Compounds. REMTEC. Westminster, Colorado, March 2-4, 2015.

McHugh T.E., High Bias and Analytical Uncertainty of the Massachusetts APH and Other TPH Methods for Indoor Air and Sub-Slab Soil Gas Samples. 28h Annual International Conference on Soils, Sediments, and Water, Amherst, MA, October 15-18, 2012.


McHugh T.E., Kulkarni, P., Newell, C, Garg, S., Mass Discharge Data from Multiple Hydrocarbon Sites: Attenuation Mechanisms and Impact of Remediation. Eight International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, May 2012.

McHugh T.E., Beckley L, Chadwick B., Rivera-Duarte I., MacGregor, I., “Use of Building Pressure Control During Sample Collection to Reduce the Impact of Temporal Variability in Vapor Intrusion”, International Symposium on Bioremediation and Sustainable Environmental Technologies, Reno, Nevada, June 2011.

McHugh T.E., Newell C., Gorder K., “Less is More! Surprising Results from a Detailed Statistical Evaluation of Actual Long-Term Groundwater Monitoring Data”, International Symposium on Bioremediation and Sustainable Environmental Technologies, Reno, Nevada, June 2011.

McHugh T.E., “Use of CSIA to Distinguish Between Vapor Intrusion and Indoor Sources of VOCs” AMWA Vapor Intrusion Specialty Conference, September 2010.

McHugh T.E., “Causes of Variability in Groundwater Monitoring Data” Seventh International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, May 2010.

McHugh T.E., “Use of CSIA to Distinguish Between Vapor Intrusion and Indoor Sources of VOCs” Seventh International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, May 2010.

McHugh T.E., “Improved Investigation Methods to Distinguish Vapor Intrusion from Indoor Sources of VOCs”, The AFCEE Technology Transfer Conference (San Antonio, Texas, April 2010).

McHugh T.E., “Improved Investigation Methods to Distinguish Vapor Intrusion from Indoor Sources of VOCs”, The Federal Remediation Technology Roundtable General Meeting (Washington, DC, November 10, 2009).

McHugh T.E., Rysz, M., Adamson, D.T., Newell, C.J., “Vapor Phase Monitoring of Groundwater Wells: Results of Laboratory Validation Study”, The International In Situ and On-Site Bioremediation Symposium (Baltimore, MD, May 5-8, 2009).

McHugh T.E., DeVaull, G., Hopkins, H., “BioVapor: A 1-D Vapor Intrusion Model with Oxygen-Limited Aerobic Biodegradation”, National Tanks Conference (Sacramento, CA, March 30 - April 1, 2009).

McHugh T.E., “Vapor Intrusion: Investigation of Buildings”, Workshop: Soil Gas and Housing - How are the two connected? (Vingsted Center, Denmark, Monday, March 9, 2009).

McHugh T.E., McAlary, T., “Important Physical Processes For Vapor Intrusion: A Literature Review”, AWMA Vapor Intrusion Conference (San Diego, CA, January 28-30, 2009).

McHugh, T.E., T.N. Nickels, S Brock, K. Gorder, “Evaluation of Vapor Intrusion Impacts Using Induced Building Depressurization”, Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, May 2008.

McHugh T.E., Nickles, T.N., Gorder, K., Brock, S., “Evaluation of Spatial and Temporal Variability at Vapor Intrusion Sites”, 2008 AFCEE Technology Transfer Workshop, March 25-28, 2008.

McHugh, T.E., T.N. Nickels, S Brock, K. Gorder, “Evaluation of Vapor Intrusion Impacts Using Induced Building Depressurization”, The SERDP and ESTCP Partners in Environmental Technology Technical Symposium and Workshop, December 2007.

McGinty, J., McHugh, T.E., Higgins, E.A. 2007. Barium Sulfate: A Protocol for Determining Higher Site-Specific Barium Cleanup Levels. 2007 SPE E&P Environmental and Safety Conference held in Galveston, Texas.

McHugh, T.E., S. Maberti, et. al, “The Use of Empirical Data to Evaluate the Impact of Biodegradation on Petroleum Hydrocarbon Vapor Intrusion”, Vapor Intrusion: The Next Great Environmental Challenge - An Update, Los Angles, California, September 13-15 2006.

McHugh, T.E., “Indoor Air as a Source of VOC Contamination in Shallow Soil Below Buildings”, Southeast Asia Environmental Forensics Conference, Taipei, Taiwan, September 19-20, 2005.


McHugh, T.E.., “Vapor Intrusion Investigation Methods”, API Petroleum Vapor Intrusion Workshop, Costa Mesa, CA, August 17, 2005.

McHugh, T.E., J.A., Connor, “Methods for Characterization of Exposure to Volatile Chemicals Due to Vapor Intrusion, 2005 NGWA Ground Water and Environmental Law Conference, Baltimore, MD, July 21-22, 2005.

McHugh, T.E., J.A., Connor, “Methods for Characterization of Background Indoor Air and Subsurface Vapor Intrusion”, Fourth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, May 2004.

McHugh, T. E., P. C. DeBlanc, J. A. Connor, “A Mass Flux Model for Evaluation of the Groundwater-to-Indoor-Air Exposure Pathway”, NGWA Petroleum Hydrocarbons Conference, Atlanta, GA, November 6-8, 2002.

Connor, J.A., F. Ahmad, T. E. McHugh, P. C. DeBlanc, C. J. Newell, R. J. Pokluda, “Development of Simple Screening Criteria for the Indoor Air Exposure Pathway”, RCRA National Conference, Washington, DC, January 15-18, 2002.

McHugh, T.E., J.A., Connor, R.S. Lee, “Weight-of-Evidence Screening Criteria for Ecological Risk Assessment of Metals”, Society of Environmental Toxicology and Chemistry 22nd Annual Meeting, Baltimore, Maryland, November 14-18, 2001.

McHugh, T.E., J.A., Connor, “Impact of Risk-Based Decision Making on LUST Programs in Five States”, Second International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, May 2000.

McHugh, T. E., J. A. Connor, M. W. Malander, “Use of Human Health, Ecological, and Other Risk Drivers to Prioritize Remediation of Contaminated Sites”, Society of Environmental Toxicology and Chemistry 20th Annual Meeting, Philadelphia, PA, November 11-15, 1999.

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