App VI RI Report - Part 1.pdf

Bidding and Contract Document (R 8/17) Project Name: Chuck’s Corner Site File No. 761/15266.SAR

APPENDIX VI

REMEDIAL INVESTIGATION REPORT

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Project Num ember 2, 201

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461‐15

TABLE OF CONTENTS

1.0 INTRODUCTION

2.0 SITE CHARACTERIZATION AND CSM

2.1 Release/Source Information

2.2 Corrective Actions

2.3 General Site Characteristics

2.4 General Soil, Water and Surface Water Conditions

2.5 Hazardous Substances in Soil

2.6 Hazardous Substances in Groundwater

2.7 Hazardous Substances in Soil Gas

3.0 SITE CLASSIFICATION

4.0 RISK BASED CORRECTIVE ACTION (RBCA) EVALUATION

5.0 LNAPL ELEMENTS OF CONCEPTUAL SITE MODEL (CSM)

6.0 FEASIBILITY STUDY

6.1 Subsurface Conditions and Risks

6.2 Feasibility Study Assumptions

6.3 Technical Feasibility of Corrective Action Alternatives

6.4 Pilot Study Results

6.5 Costs of Feasible Alternatives

6.6 Corrective Action Recommendations

LIST OF APPENDICES

APPENDIX A: Figures

APPENDIX B: Soil Boring Logs & Well Construction Diagrams

APPENDIX C: Soil & Groundwater Results Tables

APPENDIX D: List of Samples with Concentrations Exceeding RBSLs

APPENDIX E: Laboratory Analytical Reports

APPENDIX F: LNAPL Tables

APPENDIX G: Feasibility Analysis Supporting Data

APPENDIX H: Pilot Test Supporting Data

COMMONLY USED ACRONYMNS

AMSL: Above mean sea level

BGS: Below ground surface

COC: Chemical(s) of concern

Csat: Soil saturation screening level

DWC/PC: Drinking water criteria/protection criteria

EPA: Environmental Protection Agency

GWVIIC/PC: Groundwater volatilization to indoor‐air inhalation criteria/protection criteria

GSIC/PC: Groundwater surface water interface criteria/protection criteria

LNAPL: Light non‐aqueous phase liquid

LUST: Leaking underground storage tank

MDEQ: Michigan Department of Environmental Quality

NREPA: Natural Resources and Environmental Protection Act

QAPP/SOP: Quality Assurance Project Plan and Standard Operating Procedures Manual

ROW: Right‐of‐way

RRD: Remediation and Redevelopment Division

SVIIC/P: Soil volatilization to indoor air criteria/protection criteria

TOC: Top of casing

UST: Underground storage tank

VOC: Volatile organic compound

Chuck’s Corner

Facility ID No. 00006430

Remedial Investigation Report

EnviroSolutions, Inc. 1 September 2016

1.0 INTRODUCTION

This Remedial Investigation (RI) Report is for the Chuck’s Corner leaking underground storage tank (LUST) Site (Facility ID No. 00006430). The Site is located at 15057 M‐115 Highway, Marion Michigan. Figure 1 in Appendix A illustrates the Site location.

The Michigan Department of Environmental Quality‐Remediation and Redevelopment Division (MDEQ‐RRD) retained EnviroSolutions, Incorporated (EnviroSolutions) to complete this RI Report to document corrective action activities conducted in response to Confirmed Release Number C‐ 1198‐98. To complete this RI Report, EnviroSolutions relied on data generated during historical site investigations. Table 1.1 provides a listing of data sources utilized to supplement the current investigation activities.

TABLE 1.1 ‐ Historical Data Sources

Name of Report Date Prepared by Relevant Data

Initial Assessment Report

(IAR)

February 22,2003 Michigan Consulting and Environmental, Inc.

(MC&E)

UST removal and initial site characterization data, soil data from former UST cavities

UST Triage Report September 25, 2013 Compliance, Inc.

(Compliance)

Soil and groundwater data adjacent and proximal to former USTs and fuel dispensing areas

Remedial Investigation Report

April 28, 2015 Global Environmental Engineering, Inc. (Global)

Additional source area characterization , off‐site investigation data, hydrogeological test data

MDEQ – Interoffice Communication

April 25, 2016 MDEQ – RRD: Geological Services Unit

Ground penetrating radar/electromagnetic survey of Four Corners Grill Property

Data gathered from these historical site investigations are incorporated throughout this RI Report text, figures, tables, and is referenced as appropriate. Corrective action activities conducted by EnviroSolutions consisted of performing the following activities:

Remedial Investigation;

Soil Gas Evaluation;

RBCA Evaluation;

Feasibility Study; and, Pilot Testing

The corrective action activities were conducted in accordance with EnviroSolutions Quality Assurance Project Plan and Standard Operating Procedures (QAPP/SOP) Manual and MDEQ approved work plan dated July 28, 2015. A focus of the work conducted by EnviroSolutions was to delineate the extent of environmental impact and fully characterize the release source area.

Table 1.2 provides a summary of the drilling program conducted by EnviroSolutions to

EnviroSolutions, Inc. 2 September 2016 accomplish this objective. For each sampling location, the table describes the purpose of the location, the drilling method used, as well as the laboratory analytical protocol(s) and supporting comments.

TABLE 1.2 – Remedial Investigation & Drilling Program Summary

Location Name

Purpose Drilling Method COCs & Soil

Analytical Protocol1 Comments

SB/MW‐

Provide vertical delineation of groundwater and characterize source area soil; use multiple casings to isolate and prevent downward spreading of VOC impacts;

installed to a total depth of 40 feet below ground surface (bgs)

Sonic Total VOCs2 per EPA Test Method 8260;

TPH‐GRO per EPA Test Method 8015

Well screen set at a depth of 35 feet to 40 feet bgs.

SB/MW‐

Provide soil delineation/characterization and verify/confirm vertical VOC delineation of groundwater at depth; installed to total depth of 40 feet bgs.

Sonic Total VOCs 2 per EPA

Test Method 8260;

fraction of organic carbon; grain‐size analysis

Well screen set at a depth of 30 feet to 35 feet bgs.

SB/MW‐

Provide soil type/lithology characterization;

total drilling depth of 15 feet bgs; confirm horizontal delineation of shallow groundwater impacts detected at MW‐113

Sonic Total VOCs 2 per EPA

Test Method 8260 Provides soil characterization for MW‐112 and MW‐113. Well screen set at a depth of 7 feet to 12 feet bgs.

SB/MW‐

116D

Provide horizontal delineation of deep groundwater impacts detected at MW‐115;

total drilling depth of 40 feet bgs.

Geoprobe/Hollow Stem Auger

Total VOCs2 per EPA Test Method 8260

Well screen set at a depth of 33 feet to 38 feet bgs.

SB/MW‐

Characterize groundwater in lower water bearing zone; total drilling depth of 40 feet bgs.

Geoprobe/Hollow Stem Auger

Total VOCs 2 per EPA

Test Method 8260 Well screen set at a depth of 35 feet to 40 feet bgs.

SB/MW‐

Provide soil delineation/characterization and verify/confirm horizontal VOC delineation of shallow groundwater impacts detected at MW‐113; drilled to a total depth of 20 feet bgs

Sonic Total VOCs 2 per EPA

Test Method 8260 Well screen set at a depth of 10 feet to 15 feet bgs.

1: COCs = Chemicals of concern; samples were collected into laboratory supplied/preserved containers. 2: VOCs = Volatile organic compounds

Table 1.3 provides a summary of the groundwater sampling and soil gas‐sampling program conducted by EnviroSolutions to characterize groundwater conditions at the site. For each sampling location, the table describes the purpose of the location, the timing used as well as the laboratory analytical protocol(s), and supporting comments.

TABLE 1.3 – Groundwater Sampling & Soil Gas Sampling Summary

Location Name

Purpose Timing COCs1 & Analytical

Protocol2 Comments

Select groundwater wells

Assess general groundwater chemistry and evaluate potential for in‐situ remediation alternative(s)

Initial sampling event

Nitrate, Iron (total & dissolved), sulfate, sulfide, chemical oxygen demand

2, fecal coliform3, total heterotrophs

3, total anerobes3

MW‐101, MW‐104S, MW‐105S, MW‐

106S, MW‐107, MW‐109S

EnviroSolutions, Inc. 3 September 2016

Location Name

Purpose Timing COCs1 & Analytical

Protocol2 Comments

Groundwater monitoring wells

Evaluate groundwater quality, collect low‐flow data, and subsurface groundwater flow characteristics

Initial sampling event and two‐ quarterly events

Total VOCs per EPA Test Method 8260

MW‐101, MW‐102, MW‐104S, MW‐

104D, MW‐105S, MW105D, MW‐

106S, MW‐106D, MW‐107, MW‐108,

MW‐109S, MW‐109D, MW‐110, MW‐

111, MW‐112, MW‐113; MW‐114,

MW‐115, MW‐116, MW‐117

Soil‐gas probe sampling

Evaluate seasonal fluctuations in sub‐slab soil gas concentrations

Initial sampling event and two‐ quarterly events

Total VOCs per EPA Test Method TO‐15

Assess vapor intrusion pathway using SS‐1 and SS‐2

Surface water

Evaluate potential for groundwater to impact surface water

Initial and final sampling event

Total VOCs per EPA Test Method 8260

Collect from the ditch, near the culvert and seeps, also near MW‐111 and MW‐113

1: COC = Chemicals of concern; samples collected into laboratory supplied/preserved containers. 2: Each sampling event includes QA/QC sampling (1‐duplicate per day; 1‐MS/MSD, 1‐field blank, and 1‐trip blank for VOCs only). 3: sampled at only three of six locations.

Groundwater sampling was also conducted to support corrective action pilot testing. A detailed discussion of the additional groundwater sampling is provided in Section 2.6 and Section 6. This soil and groundwater sampling, pilot testing data, historical site data, and other data obtained by EnviroSolutions combined to establish a comprehensive conceptual site model (CSM).

2.0 SITE CHARACTERIZATION AND CSM

2.1 Release/Source Information

A release was discovered when stained soils and vapors were observed during removal of a former UST system, which was comprised of five USTs (4 gasoline USTs and one diesel UST). A confirmed release (Confirmed Release Number C‐1198‐98) was reported to Michigan State Police, Fire Marshal Division, on December 2, 1998. Table 2 provides a summary of the current and historical USTs registered to the site.

TABLE 2.1 – Current and Historical UST Data Tank

ID

Tank Status

Capacity (in gallons)

Installation Date

Substance Stored

Tank Release Detection

Piping Release Detection

Piping Material

Piping Type

Constructio n Material

Impresse d Device

1 Removed from Ground

2000 Gasoline Inventory Control,Tank Tightness Testing

Line

Testing

Galvanized Steel

Suction:

Valve at Tank

Asphalt Coated or Bare Steel

No

2 Removed from Ground

4000 Gasoline Inventory Control,Tank

Automatic Line Leak Detectors

Galvanized Steel

Suction:

Valve at Tank

Asphalt Coated or Bare Steel

No

3 Removed from Ground

2000 Gasoline Inventory Control,Tank

Automatic Line Leak Detectors

Galvanized Steel

Suction:

Valve at Tank

Asphalt Coated or Bare Steel

No

EnviroSolutions, Inc. 4 September 2016

Tank

ID

Tank Status

Capacity (in gallons)

Installation Date

Substance Stored

Tank Release Detection

Piping Release Detection

Piping Material

Piping Type

Constructio n Material

Impresse d Device

4 Removed from Ground

4000 Gasoline Inventory Control,Tank Tightness Testing

Automatic Line Leak Detectors

Galvanized Steel

Suction:

Valve at Tank

Asphalt Coated or Bare Steel

No

5 Removed from Ground

2000 Kerosene Inventory Control,Tank Tightness Testing

Line Tightness Testing

Galvanized Steel

Suction:

Valve at Tank

Asphalt Coated or Bare Steel

No

6 Currently In Use

6000 1/1/1988 12:00:00

AM

Diesel SIR, Tank Tightness Testing, Inventory Control

Safe Suction, Automatic Line Leak Detectors

Galvanized Steel, Cathodically Protected

Suction:

No Valve At Tank

Cathodicall y Protected Steel

No

7 Currently In Use

12000 12/10/1998 12:00:00

AM

Gasoline SIR, Inventory Control

SIR,

Automatic Line Leak Detectors

APT,

Double Walled, Flexible Piping

Pressure Perma Tank, Asphalt Coated or Bare Steel, Fiberglass Reinforced Plastic, Double Walled

No

2.2 Corrective Actions

Historical corrective actions include the removal of five USTs. According to the IAR, before removal from the ground the residual contents of the five USTs were emptied, cleaned, and transported off‐site for disposal. The former UST cavities were backfilled with native soil and fill and no impacted soils or groundwater were remediated during the December 1998 UST removal activities.

2.3 General Site Characteristics

Physical Location: Please reference Figure 2 in Appendix A for depiction of the Site layout. The site is located at the southeast corner of the intersection of M‐115 Highway and M‐66 Highway in a rural area approximately five‐miles south of the Village of Marion, in Osceola County, Michigan.

The site property is triangular in shape and is bounded by M‐115 Highway to the northeast, Sunrise Lake Road to the south, and M‐66 Highway right‐of‐way (ROW) to the west. The site is accessed via paved entrance drives from M‐115 Highway in the northwest and northeast corners, and from Sunrise Lake Road in the southwest corner. The site elevation is approximately 1,115 feet above mean sea level (amsl). The site topography generally slopes moderately to the north‐northeast towards M‐115.

Current and Past Land Use: Chuck’s Corner operates as a retail gasoline station and convenience store. USTs containing gasoline (12,000‐gallon capacity) and diesel fuel (6,000‐gallon capacity) are currently present at the site. Based on State of Michigan UST registration records, the site has operated as a retail gasoline station since at least 1988, the listed date of installation for the 6,000‐ gallon capacity diesel UST. The release (C‐1198‐98) was from the former USTs cavities, which were located in the north central portion of the site, northeast and southeast of the current

EnviroSolutions, Inc. 5 September 2016 dispenser islands. The former UST cavity northeast of the current dispenser island is located within the M‐115 Highway ROW.

Dated aerial photographs available from Google Earth show the current convenience store building, a garage, and a residential dwelling present in 1998. The photographs show a shop building southeast of the garage (currently operated as P.R.I.C.E. Auto Repair) as constructed between 1998 and 2005. The photographs show the garage and shed structures located northwest of the residential dwelling as constructed between 2011 and 2015.

The property is serviced by a potable water well and septic system. Underground utilities in the investigation area include a natural gas line in the southern M‐115 Highway right‐of‐way (ROW), and storm water conveyance ditches in the northern and southern M‐115 Highway right‐of‐way.

Portions of this investigation involved work at the property directly to the north of the Site.

This property, (15806 M‐115 Highway) is also serviced by a potable water well and septic system and is currently operated as the Four Corners Grill. Based on historical data from the Central Michigan District Health Department’s Osceola Branch Office, this site appears to have formerly contained USTs. Ground penetrating radar (GPR), electro‐magnetic (EM), and drilling surveys of the Four Corners Grill property revealed the presence of subsurface anomalies consistent with the location of former UST(s).

Ownership and Zoning: According to Osceola County Department of Assessment records, 15057 M‐115 Highway is listed as owned by Jamie Kocur. The site is located in Middle Branch Township, which does not have zoning classifications.

Water Supply Wells: The MDEQ and GeoWebFace Water Well Viewer indicates the presence of 12 water supply wells within a one half‐mile radius of the site. A water supply well for the site is located near the south corner of the store building. However, there is no well log for the onsite water well. According to Mr. Jamie Kocur, the depth of the onsite well is approximately 100 feet below ground surface. Routine sampling and analysis of the on‐site water well have not indicated the presence of VOC contamination.

The nearest off‐site water supply well is located approximately 300 feet north of the current UST system, across M‐115 at the on the Four Corners Grill property. According to what appears to be the water well record for the Four Corners Grill property, the drinking water well at this site is completed at 44 feet bgs. Routine sampling and analysis of the water well have not indicated the presence of VOC contamination.

The MDEQ and GeoWebFace Water Well Viewer database also indicates the nearest wellhead protection area is a low vulnerability wellhead area located approximately five‐miles north of the site in the Village of Marion.

EnviroSolutions, Inc. 6 September 2016

2.4 General Soil, Water and Surface Water Conditions

Surface Soil: The United States Department of Agriculture Soil Survey of Osceola County Area, Michigan indicates the majority of the site (and area of investigation) as located within an area with surface soils mapped as Nester Loam, 6% to 12% slopes, moderately eroded. The soils are characterized as well drained silty clay loam, occurring on moraines and till plains.

Subsurface Geology: The MDEQ online database displays the site within a glacial land system classified as lacustrine fine sediments. According to The Quaternary Geology of Southern Michigan (Farrand and Bell, 1982), the surface sediments at the site are mapped as fine textured glacial till. Bedrock beneath the site is mapped as the Early Pennsylvanian Saginaw formation. The glacial drift thickness overlying bedrock in the site vicinity is mapped as being between 401 feet and 600 feet thick.

Native soils encountered during drilling were consistent with the published regional geology.

Beneath the surface cover (asphalt, concrete, gravel, or vegetation) clay, with locally varying sand, silt, gravel, and organic content was encountered. The observed sand content was higher in the on‐site soil borings, with clay or silty clay predominantly observed in the off‐site, northern portion of the investigation area. Organic soils were locally observed from near surface to a depth of approximately 12.0 below ground surface (bgs) feet in the northern portion of the site. The organic soils extended into the M‐115 Highway right‐of‐way, where a peat unit was observed from approximately 8.5 feet bgs to 12.0 feet bgs. Discontinuous silt and sand units, ranging from approximately 0.5 feet to 4.5 feet in thickness were observed. The total thickness of a sand unit observed from 38.0 feet bgs to 40.0 feet bgs (bottom of boring) in SB/MW‐114 is unknown. Soil boring logs and well construction diagrams available for the project are included in Appendix B. Figure 3 in Appendix A is a geologic transect map, and Figure 3a is a cross section diagram illustrating the site geology.

A grain‐size distribution analysis was conducted on two of the shallow discontinuous sand units encountered during drilling at SB/MW‐114. The sand unit encountered at 14 feet bgs and the unit encountered at 29 feet was analyzed. The grain size analysis indicated relatively consistent results. Both analyses indicated the presence of fine‐grained sand (greater than 58 percent) containing varying amounts of medium‐grained sand with at least 20 percent of the matrix comprised of silt and clay.

Groundwater: Saturated soils were encountered during subsurface investigation activities at depths ranging from approximately 5.0 feet to 38.0 feet bgs. Groundwater saturation was typically observed in discontinuous sand or silt units, or within the clay at horizons with higher silt or sand content. Table 1 in Appendix A provides a record of the depth to groundwater and groundwater elevations recorded for the project. These periodic groundwater‐gauging events show relatively stable depths to groundwater ranging from 1.65 feet to 14.99 feet below the top of casing (TOC).

EnviroSolutions, Inc. 7 September 2016

Groundwater elevation data from October 15, 2015, March 23, 2016, and May 11, 2016 was used to establish a gradient for the near surface groundwater. This data is presented in Appendix A, on Figures 4a, 4b, and 4c, respectively. The static water elevation data for the shallow groundwater zone indicates groundwater generally moves from the site in a north‐ northeasterly direction. However, groundwater elevation data from October 15, 2015 and March 23, 2016 depicts the movement of groundwater radially toward MW‐115S or northwesterly. These flow patterns are likely indicative of the relatively discontinuous nature of the shallow water‐bearing zone.

A deeper and potentially more continuous groundwater unit was encountered at depths ranging from approximately 25 feet to 36 feet bgs. Four monitoring wells (MW‐114, MW‐115, MW‐116D, and MW‐117) were screened in this unit. A groundwater contour map using the March 23, 2016 gauging data was developed and is presented in Appendix A on Figure 4d. This gradient suggests that groundwater in this deeper unit may flow radially away from MW‐

115. As observed on Figure 3c in Appendix A, in at least four locations across the site, monitoring wells were installed in clusters. Although not consistent at all locations, groundwater in the deeper unit generally had a lower hydraulic head than the other related cluster wells. This may suggest the presence of a vertically downward groundwater flow component, which would be consistent with the distribution of COCs detected in some of the deeper screened wells.

The October 2015 static water elevation data was used to calculate a groundwater gradient for the site. Based on the static water elevations between MW‐106S and MW‐109S, and MW‐102 and MW‐110, an average horizontal groundwater gradient value of 0.044 ft/ft was calculated. Data from aquifer performance testing (please reference Remedial Investigation Report dated April 28, 2015) calculated an average hydraulic conductivity value of 1.07 feet/day. Based on the site‐specific groundwater gradient and hydraulic conductivity values, and an assumed reference porosity value of 20%, the groundwater flow velocity is calculated as

0.24 feet/day.

Hydraulic Connection Between Groundwater and Surface Water: The nearest surface water body is the West Branch of the Middle Branch River, located approximately 750 feet north of the site. The elevation of the river at this location is approximately 1090 feet amsl. Based on the groundwater flow direction and static water elevation data from the investigation area (1096.84 feet amsl to 1110.03 feet amsl on October 19, 2015), hydraulic connection between the groundwater of concern and this surface water body is possible.

There is a storm water conveyance ditch/culvert in the southern M‐115 Highway right‐of‐way (ROW). In addition, there is a storm water conveyance ditch in the northern M‐115 Highway ROW. Based on the observed depth to groundwater near the ROW, there is a potential for these conveyances to function as preferential pathways for the migration of groundwater or COCs toward and into the drainage ditch. This was especially evident when air bubbles were found in the surface water during the hydrogen peroxide injection pilot test. This suggests the

EnviroSolutions, Inc. 8 September 2016 premise that there is hydraulic communication between the groundwater and the drain on the southern side of M‐115.

2.5 Hazardous Substances in Soil

Supporting Data: Based on the historical UST contents of leaded gasoline, unleaded gasoline, and diesel and generally consistent with MDEQ‐Storage Tank Division Operational Memorandum Number 14, June 12, 1998, soil samples were initially analyzed for the following COCs:

Benzene, toluene, ethylbenzene, xylenes (BTEX);

Methyl‐tertiary‐butyl‐ether;

Tri‐methylbenzene Isomers (TMBs);

1,2‐Dibromoethane (EDB);

1,2‐Dichloroethane;

Polynuclear Aromatic Hydrocarbons (PAHs); and, Lead

Analysis of soil and groundwater samples for PAHs and lead were discontinued based on detected concentrations in early sampling events. Soil and groundwater samples collected during recent investigation and sampling events were analyzed for the presence of volatile organic compounds (VOCs). Table 2, in Appendix C provides a summary of the soil analytical results for the project. Laboratory analytical reports for the most recent sampling events are included in Appendix E.

Remaining Soil Impact: Table A in Appendix D presents a list of samples with soil impacts exceeding various Part 213 Tier I Risk Based Screening Levels (RBSLs) and/or associated screening levels. COCs detected above soil saturation screening level (Csat) include Total Xylenes; 1,2,4‐Trimethylbenzene (TMB). COCs detected at concentrations exceeding Residential/Nonresidential Drinking water Protection (DWP) RBSLs include 1,2,4‐ Trimethylbenzene (TMB); 1,3,5‐TMB; Benzene; Ethylbenzene; Total Xylenes; Naphthalene; n‐ Propylbenzene; n‐Butylbenzene; sec‐Butylbenzene; and Toluene. COCs detected above Groundwater‐Surface Water Protection (GSIP) RBSLs include 1,2,4‐Trimethylbenzene (TMB);

1,3,5‐TMB; 2‐Methylnaphthalene; Ethylbenzene; Isopropylbenzene; Total Xylenes;

Naphthalene; Toluene; and, Phenanthrene.

Please note that that soil samples collected at depths of more than five feet below ground surface (bgs), were most likely saturated and therefore cannot be directly compared to the Risk Based Screening Levels (RBSLs). Soil screened at SB‐114 at 9 feet bgs indicated the presence of residual light non‐aqueous phase liquid (LNAPL) in the soil based on a gasoline‐range organic (GRO) analytical result at a concentration of greater than 0.5% saturation, however, had a “negative” reading for the Oil‐In‐Soil Test Kit. A “positive” reading for the Oil‐In‐Soil Test Kit was obtained for soil screened from SB‐114 at 13 feet bgs. However, the GRO analytical result

EnviroSolutions, Inc. 9 September 2016 had a concentration of just less than 0.5% saturation. Additional details pertaining to the presence of LNAPL is provided in Section 5.

Figure 5A and Figure 5B in Appendix A provides a depiction of the aerial extent of soil exceeding various RBSLs. Appendix A also contains Figure 3A, which is a cross section depicting the vertical extent of soil impact. The estimated extent of soil exceeding DWP RBSLs covers an area of approximately 14,000 square feet.

2.6 Hazardous Substances in Groundwater

Supporting Data: Groundwater data available for the site is provided on Table 3 in Appendix C.

The laboratory analytical reports for the most recent groundwater sampling events are included in Appendix D. During the investigation, groundwater was sampled from monitoring wells and from the drainage ditch, in the southern M‐115 ROW, near groundwater seeps, when present.

Mobile LNAPL: Mobile LNAPL has not been identified during any of the historical groundwater gauging events performed at the site. The depth to water observed during each event is provided on Table 3 in Appendix C.

Remaining Groundwater Impact: Table 2 in Appendix D presents a list of groundwater sampling locations with impacts that exceed various Part 213 Tier I RBSLs and/or associated screening levels during the March 2016 and May 2016 groundwater sampling events. COCs that exceed MDEQ Residential DW RBSLs include 1,2,4‐TMB; 1,3,5‐TMB, Benzene, Ethylbenzene, Total Xylenes, n‐Propylbenzene, n‐Butylbenzene, sec‐Butylbenzene, and Toluene. COCs detected above GSI RBSLs include 1,2,4‐TMB; 1,3,5‐TMB, 2‐MN, Ethylbenzene, Isopropylbenzene, Total Xylenes, Naphthalene, and Toluene. COCs that exceed the MDEQ Rule 57 Final Acute Value include 1,2,4‐TMB; Ethylbenzene; and, Toluene.

Figure 6 in Appendix A depicts the aerial extent of groundwater with exceedances various RBSLs. Appendix A also contains Figure 3B, which is a cross section depicting the vertical extent of groundwater impact. The estimated extent of groundwater exceeding DWP RBSLs, covers an area of approximately 20,000 square feet.

2.7 Hazardous Substances in Soil Gas

To evaluate risks associated with vapor intrusion, soil gas has been periodically monitored using two sub‐slab soil gas probes (SS‐1 and SS‐2) inside the Chuck’s corner convenience store building. Soil gas sampling procedures utilized by EnviroSolutions are included in the approved Work Plan and the QAPP/SOP for this project. Soil gas samples were collected from the probes and analyzed for the presence of VOCs using USEPA Method TO‐15.

A Soil Gas Analytical Results table (Table 4) is provided in Appendix D that compares soil gas analytical results to applicable screening levels. Soil gas analytical data sheets are provided in

EnviroSolutions, Inc. 10 September 2016

Appendix E. The soil gas results indicate that no samples analyzed exceed the MDEQ‐RRD Vapor Intrusion Shallow Soil Gas Screening Level for Nonresidential Land Use. The results for the October 2015 soil gas sampling did indicate an exceedance of the compound Bromomethane for the Vapor Intrusion Shallow Soil Gas Screening Level for Residential Land Use at SS‐1. However, previous and subsequent sampling at this location did not reveal exceedances.

3.0 SITE CLASSIFICATION

Based on investigation activities conducted, current Site conditions meet the Class 2 designation requirements, according to Remediation and Redevelopment Division Policy and Procedure Number RRD‐21, November 8, 2013. The Class 2 designation is based on the presence of multiple soil samples exceeding Csat concentrations. Although the extent of COCs in groundwater contaminated above DW RBSLs is defined, the proximity (i.e. within 120 feet and within the two year travel time of a drinking water well) of impacted groundwater to public water supply wells on site and on the adjoining downgradient property is also a concern.

4.0 RISK BASED CORRECTIVE ACTION (RBCA) EVALUATION

The results from the remedial investigation activities indicate soil and groundwater impacts extend off‐site. Soil impacts extend to the north off site into the M‐115 Highway right‐of‐way.

Groundwater impacts extend to the north off‐site into the M‐115 Highway right‐of‐way and exist on the northern adjoining property beyond the highway. The impacts on the adjoining property may, in part, be from a former UST system on the adjoining property.

Transport mechanisms for exposure pathways determined to be not relevant and the basis for that determination is listed below:

Direct Transport of Soil to Surface Water: The site is not adjacent to or relatively near a surface water body. It is unlikely impacted soil was transported into the nearby ditch.

Impacted soil at this site is covered by gravel or other impermeable pavement and would not contact surface water runoff. Therefore, soil from the site will not be directly transported to surface water and this pathway is not relevant.

Transport Mechanisms Associated with Impacted Sediment: This site is not adjacent to, or relatively near a surface water body. Groundwater in the ditch, bordering the site and M‐115, contained low levels of hydrocarbons. However, the release likely did not affect sediment and therefore this pathway is not relevant.

Endangered Species Exposure, Sensitive Habitat Exposure, or Other Ecological Concerns/Exposures (via transport mechanism of groundwater transport to surface water): The site is not near an endangered species habitat or other sensitive habitat and therefore this pathway is not relevant.

EnviroSolutions, Inc. 11 September 2016

The remaining transport mechanisms and exposure routes listed below, along with their associated RBSLs, are considered to be relevant:

Soil ingestion and dermal exposure;

Soil volatilization and indoor air inhalation;

Soil volatilization and ambient air inhalation;

Soil leaching to groundwater and relevant groundwater exposure pathways;

Soil particulate emission or dispersion and ambient air inhalation;

Groundwater transport and ingestion;

Groundwater volatilization and indoor air inhalation; and, Groundwater to surface water.

Soil concentrations were detected indicating residual LNAPL is present. Tier 1 RBSLs for several relevant pathways assume that LNAPL is not present and warrant further evaluation when LNAPL is present. These pathways include:

Soil ingestion and dermal exposure;

Soil volatilization and indoor air inhalation;

Soil volatilization and ambient air inhalation; and, Soil leaching to groundwater and relevant groundwater exposure pathways.

Additional detail for each of the above exposure pathways is discussed below.

Soil Ingestion and Dermal Exposure: Impacted soil at this site is covered by gravel or pavement and concentrations of COCs in soil do not exceed direct contact criteria. However the GRO testing indicates that LNAPL is present at >0.5% saturation and therefore, the pathway is relevant.

Soil Volatilization and Indoor Air Inhalation: The building is currently used as a retail gasoline station and convenience store, and is likely to continue so into the foreseeable future.

Concentrations of COCs in soil did not exceed applicable generic Part 213 Tier 1 residential RBSLs. However, due to the depth to water (i.e. less than three meters) and the presence of residual LNAPL, the use of the generic RBSLs exposure scenarios are not appropriate for the Site. Consequently, this pathway is being evaluated by use of sub‐slab soil gas monitoring. The soil gas monitoring results indicate that none of the samples analyzed exceed the MDEQ‐RRD Vapor Intrusion Shallow Soil Gas Screening Level for Nonresidential Land Use. The results for the October 2015 soil gas sampling did indicate an exceedance of the compound Bromomethane for the Vapor Intrusion Shallow Soil Gas Screening Level for Residential Land Use at SS‐1. Although previous and subsequent sampling at this location did not reveal exceedances, additional sampling is warranted.

EnviroSolutions, Inc. 12 September 2016

Soil Volatilization and Ambient Air Inhalation: Concentrations of COCs in soil did not exceed applicable generic Part 213 Tier 1 residential RBSLs and the impacts from the release are covered.

Soil Leaching to Groundwater: Concentrations of COCs in soil above generic Part 213 Tier I residential and non‐residential drinking water protection (DWP) RBSLs, groundwater‐surface water protection (GSIP) RBSLs, and Csat are present. Water wells are located on‐site and on the adjoining property to the north across Highway M‐115. The on‐site drinking water well is located approximately 60 feet up gradient from the impacted area, and is reportedly completed at a depth of approximately 100 feet bgs. According to the water well record available from MDEQ, the drinking water well on the northern adjoining property is completed at 44 feet bgs.

Based on proximity of the off‐site drinking water well to impacted groundwater, depth of completion, and downgradient location, the DWP exposure pathway is relevant. Although samples from the potable wells do not exceed drinking water RBSLs, routine monitoring of the drinking water wells is being conducted by the MDEQ.

Storm water conveyance ditches are located in the northern and southern ROW of Highway M‐

115. The closest surface water body, West Branch of the Middle Branch River, is located approximately 750 north of the site. Based on the depth of these ditches, the shallow depth to groundwater, and the extent of groundwater impacts, the GSIP exposure pathway is relevant.

However, additional sampling of the ditch is needed to complete the evaluation.

Groundwater Transport and Ingestion: Concentrations of COCs in groundwater exceed applicable generic Part 213 Tier 1 residential RBSLs. Water wells are located on‐site and on the adjoining property to the north across Highway M‐115. The on‐site drinking water well is located approximately 60 feet up gradient from the impacted area, and is reportedly completed at a depth of approximately 100 feet bgs. According to available information, the drinking water well on the northern adjoining property is completed at 44 feet bgs. Samples from the potable wells did not exceed drinking water RBSLs. Samples from the potable wells did not exceed drinking water RBSLs. Routine monitoring of the drinking water wells is being overseen by the MDEQ.

Groundwater Volatilization to Indoor Air Inhalation: Concentrations of COCs in groundwater did not exceed applicable generic Part 213 Tier 1 residential RBSLs. The results for soil gas samples collected during the project indicated results below MDEQ Nonresidential Vapor Intrusion Shallow Soil Gas Screening Levels. The results for the October 2015 soil gas sampling indicated the compound Bromomethane exceeded the MDEQ Residential Vapor Intrusion Shallow Soil Gas Screening Level. This pathway is relevant and will continue to be monitored through periodic soil gas sampling from the existing sub‐slab vapor pins.

Groundwater to Surface Water Transport: Concentrations of COCs in groundwater above generic Part 213 Tier I GSI RBSLs are present. The VOC concentrations in MW‐101, MW‐104S, and MW‐107 also exceeded the MDEQ Rule 57 Final Acute Value. Storm water conveyance

EnviroSolutions, Inc. 13 September 2016 ditches are located in the northern and southern right‐of‐way (ROW) of Highway M‐115. The closest surface water body, West Branch of the Middle Branch River, is located approximately 750 feet north of the site. Based on the depth of these ditches, the shallow depth to groundwater, and the extent of groundwater impacts, the GSIP exposure pathway is relevant.

Surface water samples were collected from the drainage ditch along the southern and northern M‐115 ROW and analyzed for the presence of VOCs. The VOCS in the surface water sample from the ditch along the southern M‐115 ROW were below the GSI RBSLs and non‐detectable in the sample from the ditch north of M‐115. However, additional sampling of the surface water/ groundwater seeps is needed to further asses this pathway.

5.0 LNAPL ELEMENTS OF CONCEPTUAL SITE MODEL (CSM)

The conceptual site model (CSM) presents information from site assessment activities and provides the current overall understanding of the site and release. The CSM will guide future corrective action activities. The CSM will be updated with new site assessment information as it becomes available.

Site assessment activities identified the extents of soil and groundwater impacts above the most restrictive generic Part 213 Tier 1 residential and non‐residential RBSLs. The estimated extent of soil exceeding DWP RBSLs, covers an area of approximately 14,000 square feet. The estimated extent of groundwater exceeding DWP RBSLs covers an area of approximately 20,000 square feet.

LNAPL Chemistry and Physical Characteristics: A release was reported when stained soils and vapors were observed during removal of a former UST system, which was comprised of five USTs (4 gasoline USTs and one diesel UST). Field observations, soil, groundwater, and soil vapor investigations indicated subsurface impacts characteristic of an unleaded gasoline release and the residual impact is characteristic of weathered gasoline

LNAPL Geometry, Groundwater, and Hydrogeologic Conditions: Figure 5B depicts the estimated extent of highly impacted or “source‐area” soil impacts. This includes an area of residual LNAPL, which has potentially been identified at four isolated locations during field activities (NE FLOOR 1; B1@9; B7@7.5; and SB‐114). Residual LNAPL has been delineated based on soil and groundwater analytical results from sample locations surrounding the former UST cavities. Mobile LNAPL has not been encountered. Investigation/delineation conducted indicates residual LNAPL present in soil appears in locations near the former tank cavities.

Residual LNAPL appears primarily in sand or silt lithology or within the clay at horizons with higher silt or sand content. A LNAPL Screening Results Summary table (Table 6) is provided in Appendix F.

Soil Gas Sampling/Screening: SS‐1 and SS‐2 were installed inside the Chuck’s Corner convenience store building. The soil gas monitoring results indicate that none of the samples

EnviroSolutions, Inc. 14 September 2016 analyzed exceed the MDEQ‐RRD Vapor Intrusion Shallow Soil Gas Screening Level for Nonresidential Land Use. The results for the October 2015 soil gas sampling did indicate an exceedance of the compound Bromomethane for the Vapor Intrusion Shallow Soil Gas Screening Level for Residential Land Use at SS‐1. However, previous and subsequent sampling at this location did not reveal exceedances. Ambient air was screened inside the garage area using a PID and no detections of VOCs were observed.

LNAPL Mobility and Stability: The extent of residual LNAPL appears to be limited near the former tank cavities based on concentrations of indicator compounds present in soil, groundwater, and soil gas samples. Based on available data, mobile LNAPL is not present at the site. Any residual LNAPL remaining is considered stable.

The following tables provide further CSM details, including specifics regarding indications of LNAPL presence. The following tables and CSM were developed in accordance with the ASTM standard Guide for Development of Conceptual Site Models and Remediation Strategies for Light Non Aqueous‐Phase Liquids Released to the Subsurface (standard E2531‐06).

TABLE 5.1 ‐ Maximum Concentrations in Soil Compound Sample Sample

Date Depth (feet bgs)1

Concentration

Soil (concentrations in µg/kg with exception of TPH concentrations in mg/kg)1

Benzene B6@7.5 7/1/2013 7.5 3,500

Toluene NE FLOOR 1 12/7/1998 8 140,000

Ethylbenzene SB‐114 9/29/2015 9 81,000

Xylenes SB‐114 9/29/2015 9 378,000

1,2,4‐TMB1 SB‐114 9/29/2015 9 230,000

1,3,5‐TMB1 SB‐114 9/29/2015 9 69,000

MTBE B6@15 7/1/2013 15 89

Naphthalene SE WW‐1 12/7/1998 5 83,000

2‐MN1 SE WW‐1 12/7/1998 5 69,000

Isopropylbenzene SB‐114 9/29/2015 9 8,500 n‐Butylbenzene GP‐102 7/14/2014 9 2,500 n‐propylbenzne SB‐114 9/29/2015 9 35,000 sec‐Butylbenzene SB‐114 9/29/2015 9 3,400

Styrene GP‐104 7/14/2014 10 130

Lead NE VSR‐B 12/7/1998 4 32,000

Acenaphthene GP‐102 7/14/2014 9 1,300

Anthracene GP‐101 7/14/2014 9 420

Phenanthere GP‐102 7/14/2014 9 2,500

Pyrene GP‐101 7/14/2014 9 540

TPH‐GRO

SB‐114 9/29/2015 9 6,700,000

Footnotes:

1. bgs = below ground surface, µg/kg = micrograms per kilogram, TPH = total petroleum hydrocarbons, mg/kg = milligrams per kilogram, ND

= Not detected above analytical detection limits, 2MN = 2‐methylnaphthalene, TMB = trimethylbenzene, PAH = polynuclear aromatic hydrocarbon, GRO = gasoline range organics, µg/L = micrograms per liter, ppbV = parts per billion by volume

EnviroSolutions, Inc. 15 September 2016

TABLE 5.2 ‐ Maximum Concentrations in Groundwater Compound Sample Sample

Date Screened Interval

Groundwater (concentrations in µg/L)1

Benzene MW‐104 3/22/2016 9‐14 1,400

Toluene MW‐101 3/22/2016 3‐8 5,900

Ethylbenzene MW‐101 3/22/2016 3‐8 1,400

Xylenes MW‐101 3/22/2016 3‐8 10,000

1,2,4‐TMB1 MW‐101 3/22/2016 3‐8 1,300

1,3,5‐TMB1 MW‐101 3/22/2016 3‐8 360

MTBE MW‐104D 3/22/2016 15‐20 30

Naphthalene MW‐105D 5/11/2016 15‐20 45

2‐MN1 MW‐102 3/22/2016 3‐8 44

1,2‐Dichloroethane MW‐114 3/23/2016 5‐10 27

2‐Butanone (MEK) VE‐1 3/15/2016 5‐10 8.8

2‐Propanone (acetone) VE‐1 3/15/2016 5‐10 13,000

Chloroform MW‐116 3/22/2016 10‐15 1.2

Isopropylbenzene MW‐105D 5/11/2016 15‐20 19 n‐Butylbenzene MW‐105S 5/11/2016 6‐11 4.6 n‐Propylbenzene MW‐101 3/22/2016 3‐8 110 sec‐Butylbenzene MW‐106S 3/22/2016 4.5‐9.5 8.8

Tetrahydrofuran VE‐1 3/15/2016 5‐10 30,000

Fluorene MW‐106S 8/27/2014 4.5‐9.5 1.6

Various Metals MW‐105S, MW‐ 106S, and MW‐107

3/22 and 5/16/2016

Various Detected but below criteria

Footnotes:

1. bgs = below ground surface, µg/kg = micrograms per kilogram, TPH = total petroleum hydrocarbons, mg/kg = milligrams per kilogram, ND = Not detected above analytical detection limits, 2MN = 2‐methylnaphthalene, TMB = trimethylbenzene, PAH = polynuclear aromatic hydrocarbon, GRO = gasoline range organics, µg/L = micrograms per liter, ppbV = parts per billion by volume

TABLE 5.3 ‐ Maximum Concentrations in Soil Gas Compound Sample Sample

Date Screened Interval

Soil Gas (concentrations in ppbV)1

Benzene SS‐1 5/11/2016 Sub Slab 15

Bromomethane2 SS‐1 5/11/2016 Sub Slab <9.5

Toluene SS‐2 5/11/2016 Sub Slab 810

Ethylbenzene SS‐2 5/11/2016 Sub Slab 66

Xylenes SS‐2 5/11/2016 Sub Slab 289

1,2,4‐TMB SS‐2 5/11/2016 Sub Slab 38

Chloroform SS‐2 5/11/2016 Sub Slab 31

2,2,4‐Trimethylpentane SS‐1 5/11/2016 Sub Slab 300

Tetrachloroethylene SS‐2 5/11/2016 Sub Slab 40

Footnotes:

1. bgs = below ground surface, TPH = total petroleum hydrocarbons, TMB = trimethylbenzene, ppbV = parts per billion by volume

2. Please note that on 10/20/2015 the concentration of bromomethane was 220 ppbV, which is greater than the MDEQ RRD Vapor Intrusion

Shallow Soil Gas Screening Level for Residential Land Use.

EnviroSolutions, Inc. 16 September 2016

TABLE 5.4 ‐ Indicators of LNAPL Presence LNAPL Indicator Yes No NA1

Known LNAPL release (gasoline) X

LNAPL observed in monitoring wells

a. Historically present X

b. Currently present X

c. Last LNAPL observation X

Visible LNAPL or other direct indicators in samples X

Fluorescence response in LNAPL range X

LNAPL constituents above Csat in soil X

LNAPL constituents near solubility limits in groundwater X

LNAPL constituents near volatility limits in soil gas X

TPH in soil and/or groundwater indicative of LNAPL X2

Organic Vapor Analyzer (OVA) and other Field Observations X

Field screening tests positive X

Footnotes:

1. NA = not analyzed or not applicable

2. TPH‐GRO of 6,700 mg/kg and 880 mg/kg detected in SB‐114 (9’ bgs) and SB‐114 (13’ bgs), respectively

3. Sudan IV dye tests

As shown in the above table, EnviroSolutions observed indicators of LNAPL at the site. The indicators of LNAPL included: visual and olfactory field observations, PID readings, elevated TPH concentrations in soil, and positive Sudan IV dye tests. Field observations and analytical results indicate the extent of residual LNAPL is limited and located in areas near the former tank cavities.

LNAPL/CSM Complexity/Adequacy Checklist: A LNAPL/CSM Complexity/Adequacy Checklist is provided in Appendix F that evaluates the complexity of the site and adequacy of the data used to develop the CSM. Risk at the site was considered to be low and the CSM was considered adequate.

6.0 FEASIBILITY STUDY

This Feasibility Study (FS) presents recommendations for corrective action intended to reduce current risks posed by the contamination and potential future risks. Ultimately, the goal of the recommended corrective action is to remediate the source area and achieve acceptable project completion (APC) in accordance with MDEQ guidelines and procedures. This FS was based upon historical data sources and data from the remedial investigation and discusses:

Subsurface conditions and risks;

FS Assumptions;

Technical feasibility of several corrective action alternatives;

Pilot study results;

Capital, annual, future and total costs for feasible alternatives; and, Corrective action recommendations.

EnviroSolutions, Inc. 17 September 2016

6.1 Subsurface Conditions and Risks

Site conditions presenting risks to human, health and the environment include the following.

A) Residual LNAPL exists on‐site and in the M‐115 ROW: Historical concentrations of COCs above Csat screening levels were detected in NE FLOOR 1, B1@9, and B7@7.5. Elevated PID readings, positive Sudan dye tests, indicator compound concentrations above Csat screening levels and gasoline range organic (GRO) concentrations (6,700 mg/kg) indicative of LNAPL were detected in SB‐114 in September 2015. Elevated concentrations of COCs, considered as “source area” contamination was also encountered in the following samples: NE Floor 2‐8’, SE SW 1‐5’, SE WW 1‐5’, SE WW 2‐ 5’, SE Floor 4‐8’, SE Floor 5‐8’, Dispenser 2‐4’, B6‐7.5’, B7‐7.5’, B8‐7.5’, B10‐5.5’, GP103‐ 10’, GP104‐10’, GP201‐9’ to 10’, GP202‐9’ to 10’. Mobile LNAPL has not been detected in monitoring wells. However, relatively high groundwater concentrations that may be indicative of “source area” contamination have been detected in wells MW‐101, MW‐ 104S and MW‐107.

The above sample locations include samples near the existing UST system and buildings and samples in the M‐115 right‐of‐way (ROW). Remediation of these areas is considered the primary focus of corrective actions for the site.

B) Vapor intrusion into the existing site building may present a risk and requires further evaluation Relatively high groundwater concentrations exist in MW‐101 (> 30,000 µg/L), which is near the existing building (MW‐101) and relatively high soil concentrations were detected in verification samples from the southeast UST excavation near the building (total COCs >200,000 µg/kg). The existing building is slab on grade construction. Sub slab soil gas samples were collected in August 2015, October 2015 and May 2016.

Numerous VOCs were detected in the sub‐slab samples at levels below Michigan’s non‐ residential shallow soil gas screening levels. Additional evaluation is required to confirm the vapor intrusion pathway does not present a risk.

C) Groundwater may discharge into a ditch that eventually drains to the West Branch of the Middle Branch River: The ditch along the south/west side of M‐115 drains through a culvert under the Chuck’s site driveways and pavement. Groundwater infiltrates into the culvert and flows to the ditch when groundwater elevations are high. This culvert is located within the source area and runs adjacent to impacted wells MW‐105S and MW‐

107. Water in the ditch, near the culvert under the site’s northwest drive, contained low levels of VOCs (below GSI criteria, including toluene). The ditch was only sampled in August 2015. Groundwater seeps have been observed near the culvert under the site’s northwest drive. These groundwater seeps may have been related to problems with the wastewater system at the site. This system was recently up‐graded. The ditch eventually drains across M‐66, then across M‐115 and to the River.

EnviroSolutions, Inc. 18 September 2016

D) Off‐site groundwater impacts: Groundwater concentrations in MW‐109S, MW‐113 (a shallow well) and MW‐115 (a deep well) located down gradient from the site, across M‐ 115, and on the Four Corners Grill property exceed Part 213 Tier 1 residential DW RBSLs.

During the initial stages of the site investigation, it was thought these concentrations migrated from the Chuck’s site across M‐115.