1. Introduction
1.1. Purpose
2. Site Setting
3.1. LNAPL Recovery
4.1. LNAPL Properties
4.2. LNAPL Distribution
4.3. LNAPL Recoverability
4.4. LNAPL CSM Summary
6. Vapor Phase
8.1. Remediation Management Area No. 1
8.2. Remediation Management Area No. 2
8.3. Remediation Management Area No. 3
8.4. Remediation Management Area No. 4
8.5. Remediation Management Area No. 5
8.6. Remediation Management Area No. 6
8.7. Remediation Management Area No. 7
8.8. Remediation Management Area No. 8
8.9. Remediation Management Area No. 9
8.10. Remediation Management Area No. 10
9. References
Tables
Figures
Figure 1-1. Site Layout
Figure 2-1 North Olive Lithology Compare
Figure 2-2 North Market Lithology Compare
Figure 2-3 Isometric Compare
Figure 2-4. North Olive Stratum Extent And Isopach
Figure 2-5. Rand Stratum Extent And Isopach
Figure 2-6. Epa Stratum Extent And Isopach
Figure 2-7. Main Silt Extent And Isopach
Figure 3-1. Total Petroleum Hydrocarbons Recovered Since 1978
Figure 3-2. Vapor Collection System Layout And Production Well Locations
Figure 4-1. LNAPL Characterization And Viscosity Results
Figure 4-2. Benzene Effective Solubility And Dissolved Phase Concentrations
Figure 4-3. Laser Induced Fluorescence Boring And LNAPL Sample Locations
Figure 4-4. Three Dimensional LNAPL Distribution
Figure 4-5. LNAPL Thickness In The Rand Stratum, Low Groundwater
Condition, January 2006
Figure 4-6. LNAPL Thickness In The Rand Stratum, Low Groundwater
Condition, March 2015
Figure 4-7. LNAPL Thickness In The Rand Stratum, Average Groundwater
Condition, April 2007
Figure 4-8. LNAPL Thickness In The Rand Stratum, Average Groundwater
Condition, July 2017
Figure 4-9. LNAPL Thickness In The Rand Stratum, High Groundwater
Condition, July 2008
Figure 4-10. LNAPL Thickness In The Rand Stratum, High Groundwater
Condition, January 2016
Figure 4-11. LNAPL Thickness In The Main Sand Stratum, Low Groundwater
Condition, January 2006
Figure 4-12. LNAPL Thickness In The Main Sand Stratum, Low Groundwater
Condition, March 2015
Figure 4-13. LNAPL Thickness In The Main Sand Stratum, Average
Groundwater Condition, April 2007
Figure 4-14. LNAPL Thickness In The Main Sand Stratum, Average
Groundwater Condition, July 2017
Figure 4-15. LNAPL Thickness In The Main Sand Stratum, High Groundwater
Condition, July 2008
Figure 4-16. LNAPL Thickness In The Main Sand Stratum, High Groundwater
Condition, January 2016
Figure 4-17. Fluid Level Saturations For Soil Cores
Figure 4-18. Schematic Diagram Of Dual Optimal LNAPL Response Model
Figure 5-1. Saturated Thickness North Olive Stratum, Low Groundwater
Conditions, March 2015
Figure 5-2. Saturated Thickness North Olive Stratum, High Groundwater
Conditions, January 2016
Figure 5-3. Saturated Thickness Rand Stratum, Low Groundwater Conditions,
March 2015
Figure 5-4. Saturated Thickness Rand Stratum, High Groundwater Conditions,
January 2016
Figure 5-5. Potentiometric Surface Map Main Sand Stratum, Low Groundwater
Conditions, March 2015
Figure 5-6. Potentiometric Surface Map Main Sand Stratum, Average
Groundwater Conditions, July 2017
Figure 5-7. Hydraulic Head Analysis, Monitoring Point Mp-079d (Zone 1)
Figure 5-8. Hydraulic Head Analysis, Monitoring Point Mp-053c (Zone 5)
Figure 5-9. Hydraulic Head Analysis, Monitoring Point Mp-085d (Zone 6)
Figure 5-10. Detailed Potentiometric Surface Map Main Sand Stratum,
January 2016
Figure 5-11. Detailed Potentiometric Surface Map Main Sand Stratum,
April 2016
Figure 5-12. Detailed Potentiometric Surface Map Main Sand Stratum,
July 2016
Figure 5-13. Detailed Potentiometric Surface Map Main Sand Stratum,
October 2016
Figure 5-14. Historical Dissolved Phase Constituents Of Concern, Shallow
Hydrostratigraphic Units (2006 - 2008)
Figure 5-15. Dissolved Phase Constituents Of Concern, Shallow
Hydrostratigraphic Units (2013 - 2018)
Figure 5-16. Dissolved Phase Constituents Of Concern, Deep
Hydrostratigraphic Units (2013 - 2018)
Figure 5-17. Dissolved Phase Natural Attenuation Indicators, Shallow
Hydrostratigraphic Units (2013 - 2018)
Figure 5-18. Dissolved Phase Natural Attenuation Indicators, Deep
Hydrostratigraphic Units (2013 - 2018)
Figure 5-19. Dissolved Phase Constituents Of Concern And
Hydrogeochemical Indicator Summary Versus Distance
Figure 5-20. Assimilative Capacity Through Centerline
Figure 6-1. Vapor Intrusion Conceptual Site Model
Figure 6-2. Structures With Historical Fire And Odor Complaints
Figure 6-3. Typical Soil Vapor Extraction Wellhead Completion Detail
Figure 6-4. Typical Wellhead, Stinger, And Flowrate Measurement Device
Details For New And Modified Extraction Wells
Figure 6-5. Effectiveness Monitoring Network And Lines Of Section
Figure 6-6. Typical Stinger Detail
Figure 6-7. Total Volatile Petroleum Hydrocarbon Mass Recovery Rate By
SVE Effectiveness Zone
Figure 6-8. Distribution Of Benzene In Soil Vapor Under Low And High River
Stage (2004-2005)
Figure 6-9. Distribution Of Isopentane In Soil Vapor Under Low And High
River Stage (2004-2005)
Figure 6-10. River Stage Triggered Event Summary (2007 - 2011)
Figure 6-11. River Stage Triggered Event Summary (2012 - 2017)
Figure 6-12. Structures That Have Been Monitored And Mitigated
Figure 6-13. Select Constituents Of Concern Versus Total Volatile Petroleum
Hydrocarbons In Indoor Air
Figure 6-14. Vapor Intrusion Pathway Decision Flowchart
Figure 7-1. Site-Specific Attenuation Factors
Figure 8-1. Proposed Remediation Management Areas
Appendices
Appendix A
Appendix B
Appendix C
Appendix D
Appendix E
Appendix F
Appendix G
Appendix H
Appendix I
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Conceptual Site Model, March 2018
Hartford Petroleum Release Site
7. DATA GAPS IN THE CONCEPTUAL SITE MODEL
Following compilation and evaluation of the historical and more recent data collected at the Hartford Site, there were some limitations identified within the existing data sets. These limitations were identified as data gaps within the CSM. These data gaps will need to be resolved via the collection of additional data to answer the essential questions that remain. This section described the data gaps that were identified following a review of the data presented within the preceding three sections and the proposed activities that will be taken to resolve these data gaps within the CSM.
7.1. NATURE OF LNAPL IN EFFECTIVENESS ZONE 1
As described in Section 4.2.5, the LNAPL thickness within monitoring well HMW-046C appears to be increasing under confined conditions over the past 15 years of monitoring. In addition, LNAPL was first measured in multipurpose monitoring point MP-078D in 2014 and has since been measured within this monitoring point under various hydraulic conditions. Monitoring well HMW-046C and monitoring point MP-078D are located in the northwest portion of Effectiveness Zone 1 along North Old St. Louis Road between West Rand Avenue and West Arbor Streets. Changes in the LNAPL morphology within the northwest portion of Effectiveness Zone 1 was previously identified as a data gap and described within the revised Summary of Lines of Evidence Indicating a Potential Alternate Source of Petroleum Hydrocarbons beneath Soil Vapor Extraction System Effectiveness Zone 1 (212 Environmental 2016d).
In order to resolve this gap in the CSM, additional LNAPL samples are proposed to be collected from select monitoring locations in Effectiveness Zone 1 (wells HMW-045C, HMW-046C, and HMW-047C, and multipurpose monitoring points MP-078D, MP-079C, and MP-080C) for comparison to LNAPL samples collected in other monitoring locations across the Hartford Site (which may include wells HMW-044C and HMW-048C, as well as monitoring points MP-029D, MP-038C, and MP-039C). The additional LNAPL samples would be analyzed for physical properties (e.g., density, viscosity, vapor pressure, and carbon fraction range) and an expanded list of paraffins, isoparaffins, aromatics, naphthenes, and olefins. In addition, the LNAPL samples would be analyzed for additives including oxygenates (e.g., methyl tert-butyl ether, tert- butyl alcohol, etc.) and methyl lead additives (e.g., tetraethyl lead, tetra methyl lead, etc.), as well as petroleum related biomarkers. Finally, compound specific isotopic analyses will be considered as another means of differentiating LNAPL types. A letter work plan will be prepared describing data quality objectives, specific sampling procedures, and analytical methods and will be provided in a separate submittal.
7.2. DISSOLVED PHASE LIMIT IN EFFECTIVENESS ZONE 1
As described in Section 5.3.3, the dissolved phase plume appears to be stable beyond edge of the LNAPL smear zone. However, while monitoring locations are present and sampled along nearly the entire edge of the smear zone, there is a gap in the monitoring network between West Arbor and West Birch Streets in the northwest portion of Effectiveness Zone 1. To address this data gap, Apex proposes to install two additional groundwater monitoring wells west of North Old St. Louis Road, the first would be located to the south of West Rand Avenue and the second would be located to the north of West Arbor Street. Both wells would be installed within the Village of Harford right of way. The two proposed monitoring wells be screened within the Main Sand stratum and incorporated into the existing groundwater monitoring network and sampled in accordance with the Dissolved Phase Investigation Work Plan (Trihydro 2013).
7.3. CHRONIC RISK EXPOSURE TO VOLATILE PETROLEUM HYDROCARBONS
As described in 6.4.2, while the comparison values developed for the Hartford Site are appropriate for evaluating acute residential inhalation exposure to volatile petroleum hydrocarbons over short duration events, they are not appropriate for evaluating chronic risks for residential or commercial receptors. Furthermore, data to evaluate longer term inhalation risks has not been collected at the Hartford Site. To address this data gap, Apex proposes to collect long-term passive samples, as was described in the draft Combined Effectiveness Monitoring Workplan dated October 7, 2016 (212 Environmental 2016b). A passive sampler is a device that contains a sorbent material within an inert container that has openings of a known size, which allow for volatile and semivolatile organic constituents to easily pass through and be absorbed at a steady uptake rate. Passive samplers are small and can be deployed in both ambient air, as well as installed in the subsurface for the collection of sub-slab and deeper soil vapor samples. Passive samplers offer several advantages over short duration grab samples including:
Collecting passive samples over extended timeframes allows for a more accurate means of assessing chronic inhalation risk rather than biasing sample collection during worst case conditions (e.g., river stage triggered events), as typically performed via collection of grab samples which is more appropriate for acute risk determination. The time-weighted concentrations reported from the passive samplers deployed in indoor air, outdoor air, and soil vapor can be used to evaluate the vapor intrusion pathway into a structure, as well as potential inhalation risks based on a comparison to chronic generic screening levels, such as the USEPA Vapor Intrusion Screening Levels (USEPA 2018).
In order to assess potential alternate sources of volatile petroleum hydrocarbons within indoor air during future assessment of chronic risk, the estimated attenuation rate from sub-slab soil vapor to indoor air within each structure will be compared to the USEPA default attenuation factor (3.0E-3). As described in Section 6.1, the soil vapor to indoor air attenuation factor provides the best single line of evidence to indicate whether vapor intrusion may be the cause of volatile constituents detected in indoor air. The recommended USEPA default attenuation factor for soil vapor to indoor air (including deeper soil vapor and sub-slab soil vapor) was developed using data collected from nearly 2,000 paired indoor air and soil vapor samples with varying lithology across a range of seasonal conditions (USEPA 2012). These samples were primarily collected from residential structures and as such are representative of typical preferential pathways (i.e. sewer lines) that are present in residential structures.
To validate the use of the USEPA default attenuation factor, site-specific attenuation factors were calculated using analytical data from 13 structures (14 paired indoor air and sub-slab soil vapor samples collected at the Hartford Site between 2016 and 2017). As previously described in Section 6.4.3.1, these samples were collected when there was an exceedance of a sub-slab soil vapor or indoor air action level. There were an additional three structures that were sampled between 2016 and 2017 that were not included in this evaluation because: (1) there was a source of the volatile petroleum hydrocarbons identified inside the structure (129 West Birch Street), (2) the sub-slab soil vapor and indoor air samples were not collected at the same time (135 West Forest Street), or (3) the sub-slab soil vapor sample was not representative of conditions due to startup of an adjacent vapor extraction well (101 East Birch Street). Site specific attenuation factors were only calculated for those constituents of concern that exceeded the indoor air comparison values in at least one structure between 2016 and 2017, including hexane, butane, and isopentane.
The site specific attenuation factors are summarized on Table 7-1 and shown graphically on Figure 7-2. The range of calculated site-specific attenuation factors was between 8.0E-6 and 6.2E-2. The calculated attenuation factors were less than the USEPA default attenuation factor, meaning more attenuation is occurring at the Hartford Site than is represented by the USEPA default attenuation factor, with the exception of hexane measured within 610 North Old St. Louis Road, for the sample collected in February 2017. The average site-specific attenuation factor was 2.6E-3, which means there is nearly 10 times more attenuation occurring within the residences at the Hartford Site compared to the USEPA default attenuation factor. Based on this evaluation, use of the USEPA recommended default attenuation factor is a conservative value that can be used at the Hartford Site when evaluating the vapor intrusion pathway.