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Guidance on Evaluating the Vapor Intrusion 4

Pathway through the Collection of Soil Gas 5

Data at Sites Enrolled in the Brownfield 6

Projects Voluntary Oversight and Assistance 7

Program 8

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DoR External Review 11

DRAFT 12

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Tennessee Department of Environment and Conservation 15

Division of Remediation 16

*Date When Final* 17

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ACKNOWLEDGEMENTS 18

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DISCLAIMER 25

This document presents technical recommendations of the Tennessee Department of 26 Environment and Conservation (TDEC) Division of Remediation (“DoR” or “Division”) based 27 on the current understanding of potential vapor intrusion into indoor air from subsurface 28 vapor sources. This guidance document does not impose any requirements or obligations 29 on TDEC, local or tribal governments, or the regulated community. Rather, the sources of 30 authority and requirements for addressing subsurface vapor intrusion are the relevant 31 statutes and regulations. Decisions regarding a particular situation should be made based 32 upon statutory and regulatory authority. TDEC decision-makers retain the discretion to 33 adopt or approve approaches on a case-by-case basis that differ from this guidance 34 document, where appropriate. 35

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TABLE OF CONTENTS 45

ACKNOWLEDGEMENT......................................................................................................................... 46

DISCLAIMER.......................................................................................................................................... 47

TABLE OF CONTENTS.......................................................................................................................... 48

EXECUTIVE SUMMARY......................................................................................................................... 49

1.0 INTRODUCTION............................................................................................................................ 50

1.1 Intended Use of this Technical Guidance....................................................................... 51

1.2 Overview of This Guidance ............................................................................................. 52

2.0 SCOPING AND PLANNING………………………............................................................................... 53

2.1 Early Scoping and Voluntary Party Considerations...................................................... 54

2.2 Vapor Intrusion Investigation Planning Considerations……………………………………….. 55

3.0 SAMPLING AND CHARACTERIZATION…………......................................................................... 56

3.1 Sub-Slab Soil Gas Data…………………………………………………………………………………………. 57

3.2 Exterior Soil Gas Data…………………………………………………………………………………………… 58

3.3 Indoor Air Data ……………………………………………………………………………………………………. 59

3.4 Passive Vapor Sampling Devices…………………………………………………………………………… 60

4.0 RISK ANALYSIS……………………………………………………………………………………………………………….. 61

4.1 Screening Level Comparison for Soil Gas……………………………………………………………… 62

4.2 Residential vs. Commercial Screening………………………………………………………………….. 63

5.0 VAPOR INTRUSION MITIGATION ............................................................................................. 64

5.1 Determining if Vapor Mitigation is Required………………………………………………………… 65

5.2 Selecting a General Vapor Mitigation Strategy.............................................................. 66

6.0 POST-INSTALLATION VAPOR INTRUSTION MITIGATION SYSTEM REQUIREMENTS……. 67

6.1 Verification Sampling……………………………………………………………………………………………. 68

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6.2 Verification Sampling Report Submittals and Schedule………………………………………… 69

6.3 Alternatives to Indoor Air Verification Sampling…………………………………………………… 70

6.4 Passively Vented Systems Conversion to Active……………………………………………………. 71

6.5 Operation and Maintenance………………………………………………………………………………… 72

6.5.1 Monitoring Emissions…………………………………………………………………………….. 73

6.5.2 Permitting………………………………………………………………………………………………. 74

6.6 Required VIMS Related Submittals ………………………………............................................. 75

6.7 Decommissioning………………………………………………………………………………………………… 76

REFERENCES ....................................................................................................................................... 77

APPENDIX A Acronyms……………………………………………………….……………………..……………………….. 78

APPENDIX B Calculating Vapor Intrusion Screening Levels using the EPA Vapor 79 Intrusion Screening Levels (VISL) Calculator…………………………………………………………………….. 80

APPENDIX C Determining Vapor Intrusion Risk using the USEPA VISL Calculator…………. 81

LIST OF TABLES 82

Table 3-1 Recommended Minimum Number of Sub-Slab Soil Gas Samples......................……… 83

LIST OF FIGURES 84

Figure 5-1 Existing Buildings Mitigation Risk Criteria…………………………………………………………….. 85

Figure 5-2 New Construction Mitigation Risk Criteria……………………………………………………………. 86

Figure 6-1 Idealized Verification Sampling and O&M Timeline………………………………………………. 87

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EXECUTIVE SUMMARY 93

This technical guidance document presents TDEC-DoR’s current understanding of how to 94 identify and address vapor intrusion (VI) risk at sites enrolled in the Brownfield Projects 95 Voluntary Oversight and Assistance Program (VOAP). 96

One of the main purposes of this guidance document is to promote a protective, streamlined 97 process that can be applied consistently across the State of Tennessee at sites enrolled in 98 the VOAP. This guidance document intentionally focuses on one line of evidence to guide 99 decision making in the VOAP context: soil gas data - either sub-slab soil gas in the case of an 100 existing building, or exterior soil gas in the case of a new construction. It has been the 101 experience of the VOAP that by focusing on soil gas data, mitigation decisions can be made 102 on a relatively rapid time frame that can often be compatible with VOAP Brownfield 103 development project timelines. It is also our experience that mitigation decisions based on 104 soil gas are protective, defensible, and transparent. It is expected that while this guidance 105 does not explicitly call for the development and presentation of a Conceptual Site Model 106 (CSM), it is recommended that the investigator develop a CSM through planning and scoping 107 and refine it as more information becomes available. While this guidance focuses on soil gas 108 collection in the context of existing or planned buildings there may be a need to collect soil 109 gas data from other areas of a site, as well as data from other media, to more fully develop 110 the VI CSM. 111

1.0 INTRODUCTION 112

1.1 Intended Use of this Technical Guidance 113

This Vapor Intrusion Technical Guidance Document was prepared by TDEC DoR staff from 114 the Central Office and Regional Environmental Field Offices. An external comment period 115 was held between #/#/21 and #/#/21. All received comments were considered and 116 appropriate changes were incorporated into the document. This guidance establishes a 117 state-wide TDEC-DoR process for identifying and addressing environmental contamination 118 associated with the vapor intrusion (VI) pathway so that human health is adequately 119 protected at Brownfield projects being addressed under the Voluntary Cleanup, Oversight 120 and Assistance Program (VOAP). The document is intended to be used by environmental 121 professionals already familiar with general VI concepts. 122

Vapor intrusion is the general term given to migration of hazardous vapors from any 123 subsurface vapor source, such as contaminated soil or groundwater, into an overlying 124 building or structure. 125

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1.2 Overview of This Guidance 126

Subject matter areas that are discussed in this guidance include: 127

• Scoping and Planning (Chapter 2) 128 • Sampling and Characterization (Chapter 3) 129 • Risk Analysis (Chapter 4) 130 • Vapor Intrusion Mitigation (Chapter 5) 131 • Post Vapor Intrusion Mitigation System Verification Sampling, Operation and 132

Maintenance, and System Decommissioning (Chapter 6) 133 134

2.0 SCOPING AND PLANNING 135

While determining when VI mitigation is required at a VOAP Brownfield project is a primary 136 goal of this guidance, remediation of potential VI source mass should always be considered 137 as a more permanent option for addressing vapor intrusion risk at VOAP sites. 138

2.1 Early Scoping and Voluntary Party Considerations 139

A voluntary party (VP) may enroll a Brownfield project into the VOAP with the intention of 140 ensuring that the project property is safe for its intended use. This guidance presents a 141 process for identifying and addressing environmental contamination associated with the VI 142 pathway. Therefore, if the process described in this guidance is followed, end users of VOAP 143 Brownfield projects should be adequately protected from VI risks, and liability protections 144 associated with the VI pathway can be obtained by VOAP participants that successfully 145 complete the program and execute a Brownfield Voluntary Agreement (BVA). 146

Prior to program entry, most VOAP Brownfield projects already have had a Phase I and a 147 Preliminary or Limited Phase II Environmental Site Assessment (ESA) produced for the 148 project property. If the site history and any other available information from the Phase I and 149 Phase II ESA data is reviewed and does not indicate the possibility of a complete VI pathway, 150 and the TDEC-DoR project manager (PM) agrees, then the VI investigation does not need to 151 continue. For the purposes of the liability implications addressed in a BVA for this scenario, 152 no VI related contamination is identified and therefore there is no VI related contamination 153 to address. 154

If the likelihood of a VI pathway has not been eliminated in early project scoping, the 155 expectation is that soil gas data will be collected and risk will be calculated based on collected 156 data, and an appropriate mitigation strategy will be determined for the project, based on the 157 calculated risk. Note that after project scoping and planning, and prior to beginning a VI 158

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investigation involving soil gas sampling, a VI workplan should be submitted to the PM for 159 review and approval. 160

2.2 Vapor Intrusion Investigation Planning Considerations 161

The Division considers soil gas data—either sub-slab soil gas in the case of an existing 162 building, or exterior soil gas in the case of a new construction—to be the type of 163 environmental data that is most useful in identifying and addressing the VI pathway. 164

Therefore, the collection and analysis of soil gas data will be the primary line of evidence 165 discussed in this guidance. While comprehensive site-specific VI investigations are often 166 conducted through a multiple lines of evidence approach, a streamlined approach focusing 167 on quantitative soil gas data as a primary line of evidence is presented here. By focusing on 168 soil gas data, the VI pathway can be investigated in a relatively expeditious manner so that 169 potential current and future VI risk can be determined relatively quickly, and appropriate 170 mitigation strategies can be rapidly integrated into a Brownfield project. 171

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Existing Buildings 174

Sub-slab soil gas collected from beneath a potentially impacted building of interest will 175 provide the primary line of evidence for making VI risk-based mitigation determinations for 176 existing buildings. Collecting this type of soil gas sample allows for quantitative analysis of 177 volatile organic compounds (VOCs) directly below the slab of a building and enables 178 estimates of current and future exposure and risk to building occupants from indoor air 179 concentrations estimated by using default attenuation factors. Note that when existing 180 buildings are the subject of a VI investigation, indoor air samples should be collected along 181 with sub-slab soil gas samples as a supplemental line of evidence and to gage current 182 exposure to any building occupants. 183

Favorable indoor air results are often presented to DoR along with elevated sub-slab soil gas 184 results to make the argument that a building slab is in such good condition that it is 185

Plan to collect soil gas data and use it as the primary line of evidence to assess the VI pathway at VOAP Brownfield project sites.

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preventing vapor intrusion from occurring. While this may be true at the time the argument 186 is being made, concrete slabs may degrade over time and new slab penetrations can occur 187 as the needs of a building change. It is unrealistic to expect a building slab to remain static 188 over time, and it is impractical to control or monitor the integrity of a slab for decades, as is 189 sometimes proposed. Therefore, current favorable indoor air monitoring results cannot be 190 extrapolated into the future with any certainty. 191

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For existing buildings, it is also possible that the existence of preferential pathways may 193 require preferential pathway vapor sampling. Preferential pathways into buildings include, 194 but are not limited to, sewer lines, electrical conduits, gas lines, and bedding or fill material 195 under the building. There may also be natural features, such as karst geology, that could 196 potentially create preferential VI pathways into buildings. 197

New Construction 198

For new construction, exterior soil gas should be collected in the projected footprint of a 199 planned building. This data will be the primary line of evidence for planned buildings and will 200 be used to predict exposure and risk to future occupants.. 201

For either case—existing buildings or new construction—any required VI mitigation efforts 202 may have to continue well into the future, with appropriate land use controls established to 203 ensure that the VI mitigation measures are maintained over time.. 204

3.0 SAMPLING AND CHARACTERIZATION 205

For the vapor sampling described in this guidance (sub-slab, exterior, and indoor air) it is 206 expected that time-integrated samples will be collected in evacuated stainless steel or silica-207 lined canisters that are prepared to be under negative pressure relative to the environment 208 and are certified by the laboratory to be clean and leak free. Collected air samples are 209

For existing buildings, mitigation decisions will be primarily based on sub-slab soil gas data as opposed

to indoor air data. Indoor air samples will often be needed to assess current risks but will be of limited use in determining the need to mitigate sub-slab

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typically analyzed via the TO-15 (EPA 1999) method. Indoor air samples are often collected 210 using six-liter canisters with a sample collected over a 24-hour period in residences or over 211 an 8-hour period (or workday equivalent) in commercial and industrial settings when using 212 these devices. Sub-slab and exterior soil gas samples can be collected over a much shorter 213 sampling duration. 214

3.1 Sub-Slab Soil Gas Data 215

When an existing building is being renovated or rehabilitated as part of a VOAP Brownfield 216 project, sub-slab soil gas data will be the primary line of evidence used to make risk-based 217 mitigation decisions for the structure. Soil gas directly below a building slab represents the 218 primary source concentrations that may impact indoor air. Therefore, the collection of sub-219 slab soil gas from a building can provide the most relevant data for determining the need for 220 vapor mitigation. 221

The minimum number of sub-slab soil gas collection locations will be based on the square 222 footage of a building’s footprint and are presented below in Table 3-1. Sample collection 223 should be biased toward potential contaminated areas (e.g., suspect source locations such 224 as near former drycleaner machines or waste storage areas) and may increase the number 225 of samples above the minimum. After the initial round of sub-slab soil gas is collected, 226 additional samples may be necessary to adequately delineate sub-slab soil gas impacts. 227

Table 3-1 Minimum Number of Sub-Slab Soil Gas (SSSG) Samples* 228

Square footage of building Number of SSSG Samples Up to 1,500 2 1,501 to 5,000 3 5,001 to 10,000 4 10,001 to 20,000 5 20,001 to 50,000 6 50,001 to 250,000 8 250,001 to 1,000,000 10 > 1,000,000 12+

(*Note Table 3-1 is also basis for number of exterior soil gas samples and indoor air verification samples) 229

3.2 Exterior Soil Gas Data 230

For VOAP Brownfield projects that involve new construction, exterior soil gas will be 231 considered the primary line of evidence for making mitigation decisions for planned 232 buildings. Exterior soil gas samples should be collected in the planned footprint of new 233

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buildings, also using Table 3-1 and the square footage of the planned building as the basis 234 for determining the appropriate number of samples. 235

There may be other practical reasons for collecting exterior soil gas at a VOAP Brownfield 236 project beyond the perimeter of planned building footprints; for example, delineating 237 potential vapor intrusion implications of an exterior source. 238

3.3 Indoor Air Data 239

While this guidance does not consider indoor air as a primary line of evidence necessary to 240 make VI mitigation decisions, there are important reasons for collecting it at VOAP sites. If 241 the VOAP Brownfield project involves an existing building, collecting indoor air samples can 242 confirm current complete exposure pathways, i.e., indoor sampling can verify the existence 243 of a vapor intrusion pathway and characterize exposures and risks current at the time of 244 sampling. In extreme cases, it may be necessary to relocate workers or conduct immediate 245 mitigation measures. When mitigation is required in new construction or in existing 246 buildings, indoor air sample collection will be the primary means of verifying mitigation 247 system effectiveness. 248

3.3 Passive Vapor Sampling Devices 249

Although passive (diffusion) samplers have been less commonly used to quantify indoor air 250 concentrations, their use may grow because of recent demonstrations that they can yield 251 results comparable to those obtained using evacuated canisters and a recognition that they 252 may be less intrusive for some building owners and occupants and more convenient for field 253 staff. Passive samplers are also capable of being deployed for longer durations than 254 evacuated canisters, thereby providing a more economic means of obtaining average indoor 255 air concentrations over longer periods of exposure. These factors make them good 256 candidates for use when indoor sampling is needed at VOAP sites. 257

However, there are still data quality limitations when deployed in the sub-slab environment 258 or the soil column. Currently passive soil gas sampling is mostly used by DoR staff in the 259 initial site characterization phases of an investigation. Passive sampling limitations in 260 generating quantitative data suitable for risk assessments also limit the ability to make risk-261 based decisions regarding mitigation requirements. 262

4.0 RISK ANALYSIS 263

Risk analysis of collected soil gas data will involve a screening step where concentrations of 264 detected VOCs are compared to risk-based soil gas screening levels. The result of this 265 comparison is the list of Chemicals of Potential Concern (COPCs) for the project. This will be 266

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followed by a risk calculation step for each COPC. The USEPA’s VISL Calculator can be used 267 for both steps. During screening it is important to know if the laboratory reporting limits 268 have been raised. Laboratory reporting limits can be raised for several reasons, for example, 269 due to elevated concentrations of an analyte that can mask the presence of other analytes. 270 Chemical concentrations reported as non-detect (ND) present a point of uncertainty and 271 must be taken into consideration if the laboratory reporting limits are above initial screening 272 levels. If the detection limit (DL) is above the initial screening value(s), then it is suggested 273 that half the DL is used as the screening concentration. 274

4.1 Screening Level Comparison for Soil Gas 275

Initial screening will be completed using soil gas screening levels based on an excess lifetime 276 cancer risk (CR) of 1E-06 and a non-cancer hazard quotient (HQ) of 0.1. 277

TDEC-DoR uses the EPA Vapor Intrusion Screening Level (VISL) calculator (https://epa-278 visl.ornl.gov/cgi-bin/visl_search) to screen analytes and develop a list of COPCs associated 279 with VI. A quick guide on finding/calculating screening values by using the EPA VISL calculator 280 can be found in Appendix B. 281

Note that the list of screening values can be extensive at early site screening and can 282 comprise most of the TO-15 analyte list due to the number of VOCs that are typically found 283 to be present at low/trace concentrations in soil gas samples. 284

4.2 Residential vs. Commercial Screening 285

The selection of residential and/or commercial screening values will in part depend on the 286 planned land use of the project. If residential or mixed-use development is planned for the 287 project, residential screening levels should be used. Residential screening levels should also 288 be used when sensitive receptors are expected to be present on a recurring basis in certain 289 non-residential scenarios, such as children attending a daycare or a school. If 290 commercial/industrial use is planned for the project and land use restrictions are, or will be, 291 established that restrict residential use and other uses that involve sensitive receptors, then 292 commercial screening levels can be used. The VOAP program considers land use restrictions 293 as the primary means of controlling future land-use. 294

When the screening concentration of a particular VOC is less than or equal to a screening 295 value, the VOC is considered “screened out”. Screened out VOCs do not need to be carried 296 forward to the risk calculation phase. VOCs that do not screen out comprise the list of COPCs 297 for the site. The maximum concentration detected in soil gas (either exterior or sub-slab) for 298 each COPC is used to predict indoor air risk using the VISL Calculator and the default 299

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exposure variables and attenuation factor used in the calculator. See Appendix C for 300 additional info. 301

5.0 VAPOR INTRUSION MITIGATION 302

5.1 Determining if Vapor Mitigation is Required 303

Indoor air carcinogenic risk for each individual COPC is calculated using the VISL Calculator, 304 as described in Appendix C, and if the resultant cumulative carcinogenic risk is greater than 305 1E-05, mitigation is required. Non-carcinogenic risk (hazard quotients) for COPCs is also 306 calculated using the VISL Calculator, and if the sum of the hazard quotients (hazard index) is 307 greater than 1.0, then vapor mitigation is required. Note that if the hazard index is greater 308 than 1.0, target organs can be researched, and hazard indices can be calculated based on 309 grouped chemicals that share the same target organ. Consulting a risk assessor during this 310 step is recommended. The list of VOCs that significantly contribute to exceedances of 1E-05 311 or an HI of 1.0 are considered the Contaminants of Concern (COCs) for the site. These are 312 the VOCs that are driving the need to mitigate and that will be the focus of post-installation 313 verification monitoring 314

5.2 Selecting a General Vapor Mitigation Strategy 315

The two broad categories of vapor mitigation can be described as active or passive. Active 316 mitigation of the VI pathway involves interception, dilution, or diversion of soil gas entry into 317 a building using mechanical means that are powered by electricity. The performance of 318 active mitigation systems is quantifiable by measurement of vacuum, area of influence, flow 319 rates, mass flux, etc. Passive mitigation of the VI pathway involves interception, dilution, 320 diffusion, or diversion of soil gas entry into a structure without the use of electrically powered 321 mechanical means. Passive mitigation strategies physically block the entry of vapors into a 322 building and/or rely on natural mechanisms, such as chemical diffusion and thermal- or 323 wind-induced pressure gradients to divert VOCs and soil gas around the building (e.g., to 324 riser pipes). For the purposes of this guidance, a passive system is defined as a system that 325 employs a VOC-resistant vapor barrier into its design. 326

Both types of systems can be effective mitigation solutions to elevated soil gas 327 concentrations, although in general terms, active systems are considered more effective. 328 Passive strategies can have a high degree of success in new construction scenarios due in 329 part to the relative ease of incorporating passive systems into the design and construction 330 of new buildings. 331

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For existing buildings, as stated above, active mitigation is required when cumulative 332 carcinogenic risk is greater than 1.0E-5 carcinogenic risk or a hazard index is greater than 333 1.0. If vapor mitigation is required at an existing building, an active system will be required. 334 Retro-fitting an existing building with a passive system is not considered technically feasible. 335

For new construction, if mitigation is required but the calculated cumulative carcinogenic risk 336 does not exceed 1E-04 and a hazard index of 3.0, a passive system is considered acceptable 337 if it is designed to have the capacity to become active in case follow up verification sampling 338 demonstrates poor system effectiveness. When passive systems are installed during building 339 construction, contingency plans for converting to an active system should be part of system 340 design. See Figures 5-1 and 5-2 below for a pictorial representation of the above-described 341 risk criteria concepts. 342

For all systems, whether passive or active, permanent sub-slab monitoring points should be 343 installed. For active systems these points will be used to monitor the induced negative 344 pressure field in the sub-slab environment which is a key component to verification and O&M 345 inspections. For passive systems, they will be installed in case the system needs to go active 346 in the future. For both active and passive systems, the sampling points can be used to collect 347 post-installation sub-slab soil gas concentration data should that information be necessary 348 to obtain as part of verification sampling/O&M activities or possible decommissioning 349 activities described below, 350

Figure 5-1 Existing Buildings Mitigation Risk Criteria 351

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Figure 5-2 New Construction Mitigation Risk Criteria 354

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Intrinsically safe building design can also be an effective method of addressing vapor 356 intrusion risks. For example, a building designed with a highly ventilated area, such as an 357 open parking garage constructed at ground level, can prevent vapors from entering occupied 358 upper floors that may be present above the parking garage. However, proposed building 359 design should not be used as rationale for not collecting soil gas data. If intrinsically safe 360 building design is selected as the mitigation strategy, this may need to be reflected in 361 institutional controls such as a Notice of Land Use Restrictions. 362

Also note that adjustment of an HVAC system is not considered an adequate stand-alone 363 vapor mitigation technology and is therefore not considered a vapor intrusion mitigation 364 system for the purposes of this guidance. However, adjustments to a building’s HVAC are 365 encouraged with the goal of increasing indoor positive pressure and maximizing the 366 effectiveness of any required VI mitigation system (VIMS) that has been installed. 367

6.0 POST-INSTALLATION VAPOR INTRUSION MITIGATION SYSTEM REQUIREMENTS 368

6.1 Verification Sampling 369

After a required VIMS is installed, there will be a period of verification sampling to evaluate 370 the performance of the system and to confirm that it is performing as intended. Typically, 371 this will consist of four quarters of indoor air sampling that can focus on the COCs as 372 analytes. Sampling will begin a minimum of 60 days after system startup. Alternative 373 sampling schedules and sampling methodologies can be considered. 374

6.2 Verification Sampling Report Submittals and Schedule 375

Following each system verification sampling event, a report documenting the sampling event 376 and results will be provided to DoR. This report will also include required Operation and 377

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Maintenance (O&M) inspection data (described below in Section 6.5). Indoor air verification 378 sampling will be conducted using an appropriate analytical method according to a schedule 379 that has been approved by DoR. When four quarters of indoor air verification sampling 380 results confirm the VIMS is effectively mitigating vapor intrusion risk, verification sampling 381 can end with DoR approval and the system can be considered commissioned. Otherwise, 382 additional verification sampling will be required according to a schedule approved by DoR. 383 While the typical verification sampling period is expected to be one year of quarterly 384 samples, it can last longer or be required on a more frequent basis if verification sampling 385 results exceed indoor air target concentrations or due to other site-specific factors, including 386 but not limited to source strength, proposed, or intended future land use, and potentially 387 exposed sensitive populations. In general, if verification sampling extends beyond the initial 388 year of quarterly sampling events, verification sampling will continue until there are at least 389 two consecutive quarterly sampling events that meet indoor air target concentrations. 390

6.3 Alternatives to Indoor Air Verification Sampling 391

Sometimes indoor air verification sampling may be impractical using SUMMA canisters in 392 newly occupied buildings, and it may be more practical to demonstrate VIMS effectiveness 393 by alternative sampling methodologies such as sampling with passive sampling devices, or 394 by other sampling strategies. It is important to discuss alternative verification sampling 395 procedures with the assigned VOAP Project Manager early in the planning process so that 396 alternative sampling concepts can be included in the VIMS work plan (discussed below), and 397 any necessary sampling ports can be incorporated into system and building design with 398 agreed upon target concentrations and monitoring parameters. 399

6.4 Passively Vented Systems Conversion to Active 400

Any required passively vented system should be designed to accommodate conversion to an 401 active system, should verification sampling results fail to confirm the passive VIMS is 402 effectively mitigating vapor intrusion risk. Decision criteria for requiring the conversion of a 403 passive system to an active system should be detailed in the VIMS work plan discussed 404 below. 405

6.5 Operation and Maintenance 406

Operation and Maintenance inspection reports will be required for both active and passive 407 systems. Inspections will occur concurrently with verification sampling during the verification 408 sampling period, and then annually when the verification period has ended, and the system 409 is commissioned. Inspections will, at a minimum: 1) Use field instrumentation (e.g., PID) to 410 document any elevated indoor air VOC concentrations; 2) Check floor integrity for holes, 411

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gouges, and cracks; and 3) For active systems employ a micromanometer to collect pressure 412 field measurements through permanent sub-slab monitoring points to ensure a minimum 413 vacuum of -0.004 inches of water is being met at all monitoring point locations. Spot repairs 414 for minor issues should be performed in accordance with the manufacturer’s instructions. 415 When floor coatings are part of a mitigation system, O&M inspections to evaluate the floor 416 coating integrity will be performed quarterly during the verification sampling period and 417 then annually after that period ends. 418

O&M records will be maintained in the owner/operator's files, and a system O&M annual 419 report documenting the O&M inspections will be submitted to DoR within 60 days of each 420 inspection. DoR should be notified within 48 hours if any system issues are identified that 421 are outside of normal operating parameters. The measures implemented to address system 422 issues discovered during O&M will be transmitted to DoR within 48 hours. 423

Figure 6-1 Idealized Verification Sampling and O&M Timeline 424

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6.5.1 Monitoring Emissions 426

For required active systems, emission rates will be calculated based on soil gas 427 concentrations and the cubic feet per minute (CFM) rating of the blowers planned for the 428 system. If prospective emissions are below 1,000 lbs./yr., then the emissions are considered 429 insignificant according to the definition of “insignificant activity” or “insignificant emissions 430 unit” contained in Rule 1200-03-09-.04(2)(a). No monitoring of system emissions will be 431 necessary. 432

If emissions are predicted to be greater than 1,000 lbs./yr., then post-installation emissions 433 monitoring may be required by the VOAP PM. If such monitoring occurs, a yearly emission 434 rate will be predicted based on the collected emissions monitoring data. If emissions are still 435 predicted to be greater than 1,000 lbs./yr., granular activated carbon (GAC) filtering may be 436 required. 437

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6.5.2 Permitting 439

In general, the installation of a VIMS on sites enrolled in the VOAP will be considered a clean-440 up activity conducted under the purview of DoR. Therefore, the following permit exemption 441 is applicable, and construction or operating permits required through the Division of Air 442 Pollution Control will not be necessary. 443

68-212-222. Permit exemption -- On site clean-up activities. 444

“No state or local permits shall be required for clean-up activities which are conducted entirely on site and 445 in accordance with this part; provided, that such clean-up activities meet the standards that would apply 446 if such permits were required.” 447

Contacting the local air pollution control programs at counties where the State’s permitting 448 authority is delegated to a local jurisdiction is recommended (i.e., Davidson, Hamilton, Knox, 449 and Shelby counties). 450

6.6 Required VIMS Related Submissions 451

Before a required VIMS is installed, the following submittals are required as part of the VIMS 452 work plan: 453

1) A summary of the site data used to predict the vapor intrusion risk at a site. 454

2) The calculated vapor intrusion risk used to determine the vapor mitigation strategy 455 proposed for the site. 456

3) A post VIMS installation verification sampling plan that presents site COCs and 457 discusses planned pressure field monitoring for active systems and indoor air 458 sampling along with indoor air target concentrations for COC verification monitoring. 459 Typically, the number of proposed indoor verification air samples should also be 460 based upon the square footage of the building footprint (Table 3-1). If an alternative 461 indoor air sampling strategy will be used this must be thoroughly explained. If a 462 passive system is installed, indoor air target concentrations should be included that 463 will determine when a passive system should be converted to active (i.e., blowers or 464 fans will be installed). 465

4) An O&M plan with a proposed schedule. 466

5) A description of land use restrictions, either planned or already established, that will 467 provide for the maintenance and continued operation of the VIMS. 468

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6) VIMS Design Plans - While DoR is requiring design submittals they will not be formally 469 reviewed or approved. DoR will however identify any issues that call into question the 470 ultimate performance of the system and its ability to meet indoor air target 471 concentrations used in verification sampling. 472

7) Predicted COC yearly emission rates for active systems. 473

6.7 Decommissioning 474

Unless active remediation of VI source mass occurs while a required system is in place and 475 functioning, it will be assumed that the system will run in perpetuity. If remediation of source 476 mass occurs while the system is operating there may be an opportunity, as determined on a 477 site-specific basis, to demonstrate that remediation has eliminated the actionable vapor 478 intrusion risk. DoR can then be approached with a decommissioning proposal. Each proposal 479 will be reviewed on a site-specific basis. A key component to any decommissioning proposal 480 will most likely involve sub-slab soil gas sampling through permanent sub-slab monitoring 481 points to indicate if remediation has reduced levels of soil gas to acceptable levels. 482

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REFERENCES 483

U.S. Environmental Protection Agency. 2015. OSWER Technical Guide for Assessing And 484 Mitigating The Vapor Intrusion Pathway From Subsurface Vapor Sources To Indoor Air. 485 OSWER Publication 9200.2-154. Office of Solid Waste and Emergency Response, 486 Washington, DC. https://www.epa.gov/sites/production/files/2015-09/documents/oswer-487 vapor-intrusion-technical-guide-final.pdf 488

U.S. Environmental Protection Agency. 2015. OSWER Technical Guide for Assessing 489 Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites. EPA 510-R-15-001. 490 Office of Underground Storage Tanks, Washington, DC. 491 https://www.epa.gov/sites/production/files/2015-06/documents/pvi-guide-final-6-10-15.pdf 492

U.S. Environmental Protection Agency. 2012. EPA’s Vapor Intrusion Database: Evaluation 493 and Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds 494 and Residential Buildings. EPA 530-R-10-002. Office of Solid Waste and Emergency 495 Response, Washington, DC. https://www.epa.gov/sites/production/files/2015-496 09/documents/oswer_2010_database_report_03-16-2012_final_witherratum_508.pdf 497

U.S. Environmental Protection Agency. 2002. Guidance on Choosing a Sampling Design for 498 Environmental Data Collection. EPA QA/G-5s. Office of Environmental Information, 499 Washington, DC. https://www.epa.gov/sites/production/files/2015-06/documents/g5s-500 final.pdf 501

U.S. Environmental Protection Agency, 2021. Regional Screening Levels for Chemical 502 Contaminants at Superfund Sites. https://www.epa.gov/risk/regional-screening-levels-rsls 503

U.S. Environmental Protection Agency, 2021. Vapor Intrusion Screening Level Calculator 504 https://www.epa.gov/vaporintrusion/vapor-intrusion-screening-level-calculator 505

U.S. Environmental Protection Agency (EPA). 2009c. Risk Assessment Guidance for 506 Superfund (RAGS), Volume I: Human Health Evaluation Manual (Part F, Supplemental 507 Guidance for Inhalation Risk Assessment). Office of Superfund Remediation and 508 Technology Innovation, Washington, D.C. OSWER 9285.7-82, EPA-540-R-070-002. 509 https://www.epa.gov/sites/production/files/2015-09/documents/partf_200901_final.pdf 510

Tennessee Department of Environment and Conservation. 2008. Technical Guidance 511 Document -018. Division of Underground Storage Tanks, Nashville, TN. 512 https://www.tn.gov/content/dam/tn/environment/underground-storage-513 tanks/documents/tgds/ust_guidance_tgd-018.pdf 514

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Tennessee Department of Environment and Conservation. 2006. Environmental 515 Assessment Guidelines. Division of Underground Storage Tanks, Nashville, TN. 516 https://www.tn.gov/content/dam/tn/environment/underground-storage-517 tanks/documents/ust_environmental-assessment-guidelines.pdf 518

New Jersey Department of Environmental Protection. 2018. Vapor Intrusion Technical 519 Guidance. Version 4.1. Site Remediation and Waste Management Program, New Jersey. 520 https://www.nj.gov/dep/srp/guidance/vaporintrusion/vit_main.pdf?version_4.1 521

Massachusetts Department of Environmental Protection (MADEP). 2016. Vapor Intrusion 522 Guidance. Boston, MA. WSC#-16-435. https://www.mass.gov/doc/wsc-16-435-vapor-523 intrusion-guidance-site-assessment-mitigation-and-closure/download 524

Georgia Environmental Protection Division (EPD). 2020, Guidance for Evaluating the Vapor 525 Intrusion Exposure Pathway. External Review DRAFT. Land Protection Branch. Atlanta, 526 Georgia. 527 https://epd.georgia.gov/document/document/lpb2020vaporintrusionguidancedraftextrvwp528 df/download 529

Interstate Technology & Regulatory Council (ITRC). 2014. Petroleum Vapor Intrusion: 530 Fundamentals of Screening, Investigation, and Management. Interstate Technology and 531 Regulatory Council, Vapor Intrusion Team, Washington, D.C. 532 http://itrcweb.org/PetroleumVI-Guidance 533

Interstate Technology & Regulatory Council (ITRC). 2007a. Vapor Intrusion Pathway: A 534 Practical Guideline. ITRC Vapor Intrusion Team, Washington, D.C. VI-1. 535 http://www.itrcweb.org/documents/VI-1.pdf 536

Interstate Technology & Regulatory Council (ITRC). 2007b. Vapor Intrusion Pathway: 537 Investigative Approaches for Typical Scenarios. ITRC Vapor Intrusion Team, Washington, 538 D.C.VI-1A. http://www.itrcweb.org/documents/VI-1A.pdf 539

ITRC (Interstate Technology & Regulatory Council). 2020. Technical Resources for Vapor 540 Intrusion Mitigation. Washington, D.C.: Interstate Technology & Regulatory Council, VIM 541 Team. https://vim-1.itrcweb.org/ 542

California Environmental Protection Agency. 2011. Guidance For The Evaluation and 543 Mitigation of Subsurface Vapor Intrusion to Indoor Air (Vapor Intrusion Guidance). 544 Department of Toxic Substances Control, California. https://dtsc.ca.gov/wp-545 content/uploads/sites/31/2018/01/Final_VIG_Oct_2011.pdf 546

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547

California Environmental Protection Agency. 2011. Vapor Intrusion Mitigation Advisory. 548 Final. Revision 1. Department of Toxic Substances Control, California. 549 https://dtsc.ca.gov/wp-content/uploads/sites/31/2016/01/VIMA_Final_Oct_20111.pdf 550

California Environmental Protection Agency. Department of Toxic Substances Control. Los 551 Angeles Regional Water Quality Control Board. San Francisco Regional Water Quality 552 Control Board. 2015. Advisory – Active Soil Gas Investigations. California. 553 https://dtsc.ca.gov/wp-554 content/uploads/sites/31/2021/03/VI_ActiveSoilGasAdvisory_FINAL.pdf 555

556

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APPENDIX A - ACRONYMS 557

Conceptual Site Model CSM 558

Brownfield Projects Voluntary Cleanup, Oversight and Assistance Program VOAP 559

Brownfield Voluntary Agreement BVA 560

Cancer Risk (Excess Lifetime) CR 561

Chemicals of Potential Concern COPCs 562

Contaminants of Concern COCs 563

Cubic Feet per Minute CFM 564

Detection Limit DL 565

Division of Remediation DoR or “Division” 566

Environmental Site Assessment ESA 567

Granular Activated Carbon GAC 568

Hazard Quotient HQ 569

Non-Detect ND 570

Operation and Maintenance O&M 571

Project Manager PM 572

Sub-Slab Soil Gas SSSG 573

Tennessee Department of Environment and Conservation TDEC 574

Vapor Intrusion VI 575

Vapor Intrusion Mitigation System VIMS 576

Vapor Intrusion Screening Level VISL 577

Volatile Organic Compounds VOCs 578

Voluntary Party VP 579

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Appendix B - Calculating Vapor Intrusion Screening Levels using the EPA Vapor 580 Intrusion Screening Level (VISL) Calculator 581

1) Select a hazard quotient of 0.1 and a target risk of 1E-06. 582 2) Select the applicable exposure scenario (Resident or Commercial) for the current land 583

use and/or for the potential future land use scenario. 584 3) Predict indoor air concentrations, and risk, from media concentrations. Select “No”. 585 4) Select Screening Level Type as “Default”. 586 5) Groundwater Temperature (°C): Leave as default (25). 587 6) Search and select Individual detected chemicals, or search for all detected chemicals. 588

Make sure the chemical has the correct Chemical Abstracts Service (CAS) number. 589 7) Hit the “Retrieve” button at bottom of page – generates next page. 590 8) Scroll down to Resident (or Commercial if selected) Vapor Intrusion Screening Levels 591

(VISL). 592 9) Scroll over and find Target Indoor Air, Sub-Slab and Near-source Soil Gas (considered 593

equivalent to exterior soil gas) Concentration 594 10) These are the VISL numbers to screen detected volatiles against for the data that has 595

been collected during the site investigation so far. 596

597

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Appendix C - Determining Vapor Intrusion Risk using the USEPA VISL Calculator 598

1) Select a hazard quotient of 1.0 and a target risk of 1E-05. 599 2) Select the applicable exposure scenario (Resident or Commercial) for the current land 600

use and/or for the potential future land use scenario. 601 3) Predict indoor air concentrations, and risk, from media concentrations. Select “Yes”. 602 4) The Select Medium option will become available. Select “Site Sub-slab or Near-source 603

Soil Gas Concentration (Csg)” 604 5) “Default” will be selected as Screening Level Type. 605 6) Leave Database hierarchy defaults selected as the Source for chemical physical 606

properties and toxicity values. 607 7) Groundwater Temperature (°C): Leave as default (25). 608 8) Select COPCs as the Individual Detected Chemicals. 609 9) Hit the “Retrieve” button at bottom of page – generates next page. 610 10) Enter the maximum detected soil gas concentration for each COPC. 611 11) Scroll down to bottom of page and hit “Retrieve” again. 612 12) The retrieved page will include Vapor Intrusion Risk in the third table presented. 613 13) Scroll over and find VI Carcinogenic Risk CR, and VI Hazard HQ. 614 14) Carcinogenic Risk and Hazard Quotients will be listed for individual COPCs and will be 615

summed for all COPCs. 616

617