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
8. PROPOSED REMEDIATION MANAGEMENT AREAS
It is anticipated that various technologies may be employed within discrete portions of the Harford Site to achieve the proposed remedial objectives, remediation goals, and performance metrics described within the memo entitled, Proposed Multiphase Remedy Framework Remedial Objectives, Remediation Goals, and Performance Metrics (212 Environmental 2017c). Dividing the Hartford Site into remediation management areas will allow for more targeted and effective remedial technology selection and implementation, as a single remedial technology is not likely to be applicable across the entirety of the Hartford Site given the heterogeneity in the hydrogeologic setting and LNAPL source zones. The following data, described in detail within Sections 3 through 6 of this CSM, were considered in differentiating the proposed remediation management areas:
The proposed remediation management areas are depicted on Figure 8-1. A summary of the conditions, as they relate to the CSM, is provided in Table 8-1 and described within the remainder of this section. Once the remediation management areas have been agreed upon and the final end-points have been established, potentially viable remedial technologies will be identified for each of the remediation management areas via engineered options analyses. An example outline for an engineered option analysis is included in Appendix I.
Following completion of the engineered options analysis for a specific remediation management area, bench scale and pilot testing will be performed, as necessary, to confirm the effectiveness of selected remedial technologies in achieving agreed upon end-points. Next, implementation plans will be prepared for each remediation management area detailing the use of specific remedial technologies. These implementation plans will also provide the specifics including monitoring locations, constituents of concern, measurement methods, and frequency of monitoring that will be used to demonstrate progress towards each of the applicable remedial objectives, remediation goals, and performance metrics. Furthermore, specific end-points for selected technologies employed within each remediation management area will be established.
8.1. REMEDIATION MANAGEMENT AREA NO. 1
Remediation Management Area No. 1 (RMA-1) is designated as the area south of West Watkins Street on the western portion of the Hartford Site, south of the alley between East Watkins Street and East Maple Street on the eastern portion of the Hartford Site, and includes structures located along North Olive Avenue south of East Maple Street.RMA-1 is bound by Illinois State Route 3 to the west and North Olive Avenue to the east and extends to the southern boundary of the Hartford Site. LNAPL and dissolved phase petroleum hydrocarbons do not extend beneath this proposed remediation management area, as shown on Figure 8-1 and therefore there is no soil vapor source beneath this remediation management area, as shown on the figures in Appendix G.
8.2. REMEDIATION MANAGEMENT AREA NO. 2
Remediation Management Area No. 2 (RMA-2) is located along the western portion of the Hartford Site, and has been defined to the west by Illinois State Route 3, to the north by East Date Street, and to the south by West Watkins Street. The eastern boundary generally follows the extent of dissolved phase hydrocarbon impacts. RMA-2 includes the western portions of Effectiveness Zones 2 and 3 that were outside of the extent of the LNAPL smear zone and dissolved phase petroleum hydrocarbon plume as shown on Figure 8-1. There is not a soil vapor source beneath RMA-2, as shown on the figures in Appendix G.
8.3. REMEDIATION MANAGEMENT AREA NO. 3
Remediation Management Area No. 3 (RMA-3) is located immediately east of RMA-2 and has been defined to the east by North Market Street, to the north by the alley between West Elm Street and West Forest Street and to the south by West Watkins Street. The western boundary generally follows the extent of the dissolved phase hydrocarbon plume. RMA-3 includes the eastern portion of SVE Effectiveness Zone 3 that is within the current interpreted extent of dissolved phase petroleum hydrocarbons, as shown on Figure 8-1. Neither the North Olive stratum nor the Rand stratum are present beneath RMA-3 (Figure 2-4 and Figure 2-5), but rather the Main Silt grades into the deeper Main Sand stratum providing a direct hydraulic connection between the shallow and deeper hydrostratigraphic units.
Within RMA-3, LNAPL has not been detected within any monitoring location since January 2014. Since 2004 apparent LNAPL thicknesses were generally low with only four instances when LNAPL thickness exceeded 1.0-foot. Groundwater analytical data for dissolved phase constituents of concern is limited to two co-located monitoring wells (HMW-041B and HMW-041C) within RMA-3. Dissolved phase hydrocarbon concentrations have been consistently low (total constituents of concern below 1 mg/L) within these two monitoring locations screened in the Main Silt and Main Sand strata, respectively (Figure 5-15 and Figure 5-16).
Elevated TVPH concentrations are no longer observed in soil vapor samples collected beneath RMA- 3 (Appendix G-1-4 and Appendix G-2-4), even during river stage triggered events (Appendix G-1-3 and Appendix G-2-3). TVPH concentrations have decreased and generally remain below 100 ppmv. There are no structures that have had a completed vapor intrusion pathway based on in-home screening that has been conducted since 2013, as shown on Figure 6-12. There are four SVE wells operating in RMA-3 (wells HSVE-021, HSVE-031D, HSVE-033, and HSVE-034). These four SVE wells are operated in a cyclical fashion when the TVPH concentrations are measured above 100 ppmv.
8.4. REMEDIATION MANAGEMENT AREA NO. 4
Remediation Management Area No. 4 (RMA-4) is located immediately north of RMA-3 and is defined to the east by North Market Street and bound by the alleys to the north and south of West Elm Street. The western boundary of RMA-4 generally follows the current interpreted extent of the dissolved phase petroleum hydrocarbons. RMA-4 includes the southeastern portion of Effectiveness Zone 2 that is within the current interpreted extent of dissolved phase petroleum hydrocarbons. The North Olive stratum is only present beneath the western side of RMA-4 (Figure 2-4) and the Rand stratum is only present in the northeastern corner of the area (Figure 2-5). There are currently eleven structures within RMA-4, the majority of which are occupied residences.
LNAPL has been detected within five monitoring locations (HMW-019, MP-048B, MP-048C, MP- 087C, and MP-090C) installed in RMA-4 since 2013 with apparent LNAPL thicknesses ranging from 0.08 to 2.9 feet. These five monitoring locations are screened within either the Main Silt, Main Sand, or across both of these two hydrostratigraphic units. Within the Main Sand stratum, dissolved phase petroleum hydrocarbons concentrations are generally elevated with benzene concentrations ranging from 3.6 to 21.1 mg/L (Figure 5-16) over the past five years.
TVPH concentrations in soil vapor samples collected from the Rand and Main Silt stratum have generally been reported below 1,000 ppmv since 2014 with the exception of a single sample collected from monitoring point MP-048A during May 2017 (TVPH concentration measured at 39,650 ppmv). Monitoring point MP-048A is located on the northern boundary of RMA-4. There have been no structures with a completed vapor intrusion pathway within RMA-4 based on in-home screening conducted since 2013, as shown on Figure 6-12. Continuous operation of the SVE system remains necessary to control vapor migration in RMA-4.
8.5. REMEDIATION MANAGEMENT AREA NO. 5
Remediation Management Area No. 5 (RMA-5) is located immediately north of RMA-4 and is defined to the west by Illinois State Route 3, to the east by North Market Street, to the north by West Cherry Street and to the south by the alley south of West Date Street. RMA-5 includes the northern portion of Effectiveness Zone 2. There are currently 32 residential and commercial structures within RMA-5 including houses, an apartment complex, as well as the Village of Hartford Public Safety Building and Post Office.
The North Olive stratum underlies the majority of RMA-5, except the southeastern portion (Figure 2-4). The boundary for the Rand stratum generally trends from the northwest to the southeast of RMA-5 (Figure 2-5).
LNAPL has been detected within six monitoring locations (HMW-018, MP-038B, MP-038C, MP-039C, MP-043C, and MP-049C) screened in the Main Silt and Main Sand strata between 2013 and 2018 with the apparent LNAPL thicknesses ranging from 0.02 to 11.4 feet. Dissolved phase concentrations for constituents of concern were low or not detected for the limited data available for wells screened within the Rand stratum. Dissolved phase concentrations within the Main Sand stratum are higher on the eastern side of RMA-5, with benzene concentrations as high as 19 mg/L, while benzene concentrations on the western side have been reported between the reporting limit (0.002 mg/L) and 0.042 mg/L.
The distribution of volatile petroleum hydrocarbons in soil vapor is variable from the north to south end of RMA-5. Elevated TVPH concentrations (100,000 to 1,000,000 ppmv) were observed in soil vapor samples collected within the North Olive, Rand, and Main Silt strata beneath the northern portion of RMA-5, where it abuts RMA-6 along West Cherry Street as observed in November 2017 (Appendix G-1-4 and Appendix G-2-4). Elevated TVPH concentrations were only measured in soil vapor within the southern portions of RMA-5 during river stage triggered events, such as May 2017 (Appendix G-1-3 and Appendix G-2-3).
A single structure (516 North Delmar Avenue) within this proposed remediation management area has had a completed vapor intrusion pathway over the past five years, as shown on Figure 6-12. The vapor intrusion pathway has been incomplete within this structure since April 2014. The SVE wells within RMA-5 have largely been operable and continuous operation of the SVE system remains necessary to control the vapor intrusion pathway.
8.6. REMEDIATION MANAGEMENT AREA NO. 6
Remediation Management Area No. 6 (RMA-6) is located in the northwestern portion of the Hartford Site, and has been defined to the west by Illinois State Route 3, to the east by North Market Street, to the north by West Arbor Street, and to the south by West Cherry Street. RMA-6 includes the residential portions of SVE Effectiveness Zone 1. There are currently 21 residential structures located within RMA-6 along with one additional structure that is currently utilized as an office by Apex. The subsurface lithology within RMA-6 includes the North Olive, Rand, and Main Sand strata. The thickness of the North Olive stratum (Figure 2-4) beneath RMA-6 ranges from greater than 10 feet to less than 2 feet with the thickest portions of the stratum observed along the eastern boundary (North Delmar Avenue). The Rand stratum displays a uniform thickness beneath RMA-6 typically ranging from 4 to 6 feet (Figure 2-5).
Groundwater within the North Olive stratum is typically present for a short period following significant precipitation events and occasionally major flooding of the Mississippi River. Within the Rand stratum, groundwater has generally been measured in monitoring locations across RMA-6 across the range of hydraulic conditions, with the exception of the western edge of RMA-6 where monitoring locations are typically dry under low groundwater conditions. Groundwater within the Main Sand stratum has been under confined conditions even during low conditions, particularly along West Birch Street where confining conditions are ubiquitously present. Figure 5-7 shows the vertical hydraulic gradients within monitoring point MP-079D, which has frequently been coincident not only with the elevation of the Rand stratum, but also the overlying B-Clay.
Within RMA-6, LNAPL not been detected in the North Olive stratum and is present within a single monitoring location (MP-079B) screened within the Rand stratum over the past five years. However, LNAPL has frequently been detected within monitoring locations screened in the Main Sand stratum under both low and high groundwater conditions. LNAPL is most frequently detected within the two monitoring locations installed on West Birch Street (MP-079C and MP-080C). These two monitoring locations have exhibited some of the greatest apparent LNAPL thicknesses measured within the Main Sand stratum across the Hartford Site. LNAPL thicknesses are stable within the Main Sand stratum within RMA-6.
Dissolved phase petroleum hydrocarbons have been detected within the shallow hydrostratigraphic units beneath RMA-6; however, this is based upon limited samples collected between 2004 and 2018. Groundwater samples collected within the Main Sand stratum are reported with high concentrations of dissolved phase petroleum hydrocarbons with concentrations of benzene as high as 12 mg/L in MP-078D (Figure 5-16).
TVPH concentrations in soil vapor within the shallow stratum has changed very little over time beneath RMA-6 with concentrations as high as 1,000,000 ppmv in the Rand stratum and more than 100,000 ppmv in the North Olive stratum during effectiveness monitoring performed in May 2017 (Appendix G-1-3 and Appendix G-2-3) and November 2017 (Appendix G-1-4 and Appendix G-2-4). Nine of the 22 structures located in RMA-6 have had a completed vapor intrusion pathway, primarily during river stage triggered events, as shown on Figure 6-12. The SVE well network within RMA-6 has been largely operable and has been expanded to improve vapor recovery as part of the Effectiveness Zone 1 expansion (discussed in Section 6.2.1.3) and Effectiveness Zone 6 expansion (discussed in Section 6.2.1.4). Continuous operation of the SVE system, as well as intermittent operation of in-home mitigation systems, remain necessary to control the vapor intrusion pathway in the structures located in RMA-6.
8.7. REMEDIATION MANAGEMENT AREA NO. 7
Remediation Management Area No. 7 (RMA-7) is located in the northernmost portion of the Hartford Site, and is defined to the north by West Rand Avenue. It is defined to the south by: (1) West Arbor Street between Illinois State Route 3 and North Delmar Avenue and (2) West Cherry Street between North Delmar Avenue and North Market Street. The western boundary consists of:
(1) Illinois State Route 3 between West Rand Avenue and West Arbor Street and (2) North Delmar Avenue between West Arbor and West Cherry Street. The eastern boundary of RMA-7 is North Market Street. RMA-7 includes the non-residential portions of SVE Effectiveness Zone 1, including the Hartford Community Center and several small businesses.
The subsurface lithology beneath RMA-7 includes the North Olive, Rand, EPA, and Main Sand strata. The North Olive stratum is present beneath the entire area with unit thicknesses that range from 2 to 6 feet (Figure 2-4) and groundwater presence that is spatially and temporally variable (Figures 5-1 and 5-2). The Rand stratum is only present in the southern portion of RMA-7 and also contains groundwater that is spatially and temporally variable (Figure 5-3 and Figure 5-4). The EPA stratum is only present in the northeastern portion of RMA-7 (Figure 2-6), and there are currently no groundwater monitoring locations screened within the EPA stratum in RMA-7. Groundwater within the Main Sand stratum occurs under confined and unconfined conditions across various hydraulic conditions, that are influenced by the presence or absence of the Rand and EPA strata.
Within RMA-7, LNAPL has only been detected once in monitoring point MP-074 screened in the North Olive stratum over the past five years. LNAPL has been measured within seven monitoring locations (HMW-038C, HMW-045C, HMW-046C, HMW-047C, MP-035D, MP-036C, and MP-078D) screened within the Main Sand stratum with apparent LNAPL thicknesses ranging from 0.01 to 15.9 feet. Based on the trend analysis presented in Appendix D, LNAPL thicknesses in RMA-7 are generally stable, with the exception of an increasing trend in monitoring well HMW-046C located northwest of the Hartford Community Center.
Groundwater samples have been collected from two monitoring locations, including well HMW- 045B (screened in the Rand stratum) and well HMW-038C (screened in the Main Sand stratum) between 2013 and 2018. Concentrations of dissolved phase petroleum hydrocarbons were generally low within well HMW-045B with benzene concentrations reported at 0.018 mg/L. Within the Main Sand stratum, dissolved phase benzene was measured at a maximum concentration of 2.6 mg/L within well HMW-038C . This monitoring location is located along the western portions of RMA-7.
Similar to RMA-6, the distribution of volatile petroleum hydrocarbons in soil vapor has changed very little over time with TVPH concentrations measured as high as 1,000,000 ppmv in the Rand stratum and more than 100,000 ppmv in the North Olive stratum during effectiveness monitoring performed in May 2017 (Appendix G-1-3 and Appendix G-2-3) and November 2017 (Appendix G-1-4 and Appendix G-2-4). None of the structures have had a completed vapor intrusion pathway based on monitoring conducted since 2013, as shown on Figure 6-12. SVE wells located within RMA-7 have been largely operable and additional SVE wells were installed in 2015 to improve vapor recovery as part of the Effectiveness Zone 1 expansion (discussed in Section 6.2.1.3). Continuous operation of the SVE system remains necessary to control the vapor intrusion pathway in RMA-7.
8.8. REMEDIATION MANAGEMENT AREA NO. 8
Remediation Management Area No. 8 (RMA-8) is located in the northeastern portion of the Hartford Site, and is defined by East Rand Avenue to the north. The western boundary is located along North Market Street before extending down the alley located east of North Market Street. RMA-8 is bounded to the south by East Cherry Street and to the east by North Olive Avenue. RMA-8 includes the non-residential portions of Effectiveness Zone 6 and there is currently only a single commercial structure used as an office, garage, and gravel laydown yard.
The subsurface lithology beneath RMA-8 includes the North Olive, Rand, EPA, and Main Sand strata, which are all present beneath the majority of RMA-8. While the North Olive stratum ranges in thickness between 2 and 6 feet (Figure 2-4), the Rand stratum thickens toward the eastern boundary of RMA-8 to greater than 10 feet (Figure 2-5). The boundary of the EPA stratum generally coincides with the southern boundary of RMA-8. The presence of the low-permeability clays that define these three hydrostratigraphic units influence groundwater infiltration and result in confining conditions within the Rand, EPA, and Main Sand strata under average and high groundwater conditions.
LNAPL has not been detected within any groundwater monitoring locations screened within the North Olive stratum during the past five years in RMA-8. Within the Rand stratum LNAPL was detected a total of 17 times within four monitoring locations (HMW-048B, MP- 009D, MP-029B, and MP-029C) during the past five years. LNAPL thicknesses were generally less than 1 foot with a maximum thickness of 1.08 feet measured in monitoring location MP-009D in 2013. There are three monitoring locations (HMW-003, HMW-048C, and MP-085C) screened within the EPA stratum in RMA-8, two of these locations (HMW-048C and MP-085C) have contained LNAPL during the past five years. Monitoring well HMW-048C has frequently contained LNAPL with a maximum thickness of 17.7 feet measured in 2015. Within the Main Sand stratum, four monitoring locations (HMW-008, HMW-022, MP-029D, and MP-085D) have contained LNAPL with apparent thicknesses ranging from 0.01 to 13.8 feet. The thickest occurrence of LNAPL was measured at monitoring location MP-029D. Due to confined conditions observed within this area, LNAPL thicknesses are often exaggerated due to hydrostatic pressure between the LNAPL and the confining units.
Groundwater sampling within RMA-8 has been limited due to the frequently saturated conditions that occlude the well screens; however, based on the limited samples collected between 2013 and 2018, dissolved phase petroleum hydrocarbon concentrations within the shallow hydrostratigraphic units are generally low with benzene concentrations ranging from 2.78 mg/L to below the laboratory detection limit (0.002 mg/L). It should be noted that monitoring well HMW-048A has displayed a decreasing trend in benzene concentrations from 2.78 mg/L observed in 2014 to 0.23 mg/L observed in 2017.
TVPH concentrations in soil vapor samples collected from the shallow strata has changed very little over time within RMA-8 with concentrations as high as 1,000,000 ppmv in both the North Olive and Rand strata during effectiveness monitoring performed in May 2017 (Appendix G-1-3 and Appendix G-2-3) and November 2017 (Appendix G-1-4 and Appendix G-2-4). There has been one structure within RMA-8 with a completed vapor intrusion pathway (101 East Birch Street) based on in-home screening conducted since 2013, as shown on Figure 6-12. This structure, including three other residential structures, were demolished in 2017 and no residential structures remain in RMA-8. The persistence of TVPH concentrations in RMA-8 is likely attributed to limited mass recovery via the SVE system. The SVE wells screened within the Rand stratum are consistently occluded with groundwater. Three new SVE wells (HSVE-108, HSVE-110, and HSVE-111) and two existing SVE wells (HSVE-001D and HSVE-030S) were connected to the SVE system in June 2017 within RMA-8 (as described in Section 6.2.1.4), in an effort to improve vapor recovery within this portion of the Harford Site.
8.9. REMEDIATION MANAGEMENT AREA NO. 9
Remediation Management Area No. 9 (RMA-9) is located immediately south of RMA-8 and is defined by East Cherry Street to the north and East Elm Street to the south. RMA-9 includes the area between North Olive Avenue and the north-south oriented alley between North Olive Avenue and North Market Street. This remediation management area includes the southeastern portion of Effectiveness Zone 6 and the northeastern portion of Effectiveness Zone 5. There are currently four residential structures located within RMA-9.
The subsurface lithology beneath RMA-9 includes the North Olive, Rand, EPA, and Main Sand strata. The North Olive and Rand strata both range from 4 to 6 feet in thickness across the area (Figure 2-4 and Figure 2-5). The EPA stratum appears to be approximately 6 feet thick beneath RMA-9; however, this unit is only present along the eastern portion of the area (Figure 2-6). Despite the limited extent of the EPA stratum in RMA-9, subsurface hydraulic conditions within this area are similar to those observed in RMA-8 with confined conditions often present under average and high groundwater conditions.
LNAPL has been detected within two monitoring locations (MP-047A and MP-108B) screened within the North Olive during the past five years and three monitoring locations (MP-047B, MP-055B, and MP-108C) screened within the Rand stratum. The maximum apparent LNAPL thickness was reported at 3.7 feet within monitoring point MP-055B in 2015. LNAPL is frequently gauged within five monitoring locations (HMW-002, HMW-010, MP-042C, MP-047C, and MP-055C) screened within the Main Sand stratum over the past five years, with apparent LNAPL thickness ranging from 0.01 to 13.6 feet. Much like RMA-8, confined conditions observed within RMA-9 result in exaggerated apparent LNAPL thicknesses.
Groundwater analytical data from monitoring locations within RMA-9 are limited due to the frequently saturated conditions that occlude the screen interval combined with the frequent occurrence of LNAPL within the monitoring locations. There has been one monitoring location (MP- 042B) within RMA-9 that has been sampled during the past 5 years. This monitoring location is screened within the Rand stratum and contained a maximum benzene concentration of 2.29 mg/L (Figure 5-15).
TVPH concentrations in shallow soil vapor has changed very little over time within RMA-9 with concentrations as high as 1,000,000 ppmv in the Rand stratum and more than 100,000 ppmv in the North Olive stratum during effectiveness monitoring performed in May 2017 (Appendix G-1-3 and Appendix G-2-3) and November 2017 (Appendix G-1-4 and Appendix G-2-4). There has been one structure within RMA-9 with a completed vapor intrusion pathway (409 North Olive Avenue) based on routine in-home monitoring conducted since 2013, as shown on Figure 6-12. This structure was demolished in September 2017. The persistence of TVPH concentrations in RMA-9 is likely attributed to limited mass recovery via the SVE system within the northern half of RMA-9 due to the SVE wells screened within the Rand stratum remaining consistently occluded with groundwater. A new SVE well (HSVE-109) was connected within RMA-9 in June 2017, as discussed in Section 6.2.1.4, in an effort to improve SVE system operations within this portion of the Hartford Site. Continuous operation of the SVE system remains necessary to control the vapor intrusion pathway in RMA-9.
8.10. REMEDIATION MANAGEMENT AREA NO. 10
Remediation Management Area No. 10 (RMA-10) is also located immediately south of RMA-8 and is defined to the west by North Market Street, to the east by alley between North Market Street and North Olive Avenue, to the north by the alley between East Birch and East Cherry Streets, and to the south by East Elm Street. RMA-10 is located within the southwestern portion of Effectiveness Zone 6 and the northwestern portion of Effectiveness Zone 5. There are currently 15 residential structures within RMA-10, including one apartment building.
The lithology beneath RMA-10 includes the North Olive, Rand, and Main Sand strata. The North Olive is present across the area with the exception of the southwestern corner, and the Rand stratum is present across the entire area beneath RMA-10. The North Olive stratum is approximately 2 to 4 feet in thickness and the Rand stratum is approximately 4 to 8 feet in thickness. Groundwater within the shallow subsurface is spatially and temporally variable with dry conditions often observed in the shallow strata, and unconfined conditions within the Main Sand stratum.
LNAPL has not been detected within any groundwater monitoring locations screened within the North Olive stratum during the past five years in RMA-10. Within the Rand stratum, LNAPL has been detected within eight monitoring locations (MP-041B, MP-044C, MP-045B, MP-046B, MP-051C, MP- 052B, MP-053B, and MP-054B), with apparent LNAPL thicknesses ranging from 0.01 to 4.17 feet. Ten monitoring locations screened within the Main Sand stratum have frequently contained LNAPL during the past five years with apparent LNAPL thickness ranging from 0.01 to 12.26 feet. The maximum LNAPL thickness was measured within monitoring point MP-050C in January 2016.
Groundwater analytical data is limited within the shallow hydrostratigraphic units due to frequent dry conditions observed beneath RMA-10. Groundwater samples have not been collected from any of the monitoring locations screened within the North Olive or Rand stratum in the last five years. Within the Main Sand stratum, a single groundwater sample was collected (MP-051D). Dissolved benzene was reported at 24 mg/L within the groundwater sample collected from this location in 2017.
TVPH concentrations in soil vapor are generally elevated within the North Olive and Rand strata beneath RMA-10. Concentrations within the North Olive stratum (Appendix G-1-3 and Appendix G- 1-4) are generally less than 10,000 ppmv in the northern portion of the remediation management area and as high as 1,000,000 ppmv in the southern portion. TVPH concentrations have been as high as 1,000,000 ppmv throughout the Rand stratum (Appendix G-2-3 and Appendix G-2-4). There has been a single structure (119 East Date Street) with a completed vapor intrusion pathway within RMA- 10 based on routing monitoring conducted since 2013, as shown on Figure 6-12. This structure was demolished in September 2017. SVE wells within RMA-10 are generally operable and continuous operation of the SVE system remains necessary to control the vapor intrusion pathway in RMA-10.
8.11. REMEDIATION MANAGEMENT AREA NO. 11
Remediation Management Area No. 11 (RMA-11) is located immediately south of RMA-9 and RMA- 10 and is defined to the north by East Cherry Street and the south by the alley located between East Forest and Watkins Streets. RMA-11 includes the area between North Market Street and North Olive Street. This remedial management area includes the northern portion of Effectiveness Zone 4 and the southern portion of Effectiveness Zone 5 and structures within RMA-11 are generally residential.
The lithology beneath RMA-11 includes the North Olive, Rand, Main Silt, and Main Sand strata. The North Olive and Rand strata generally extend from the northwest corner to the southeast corner of RMA-11. Along the strata boundaries, the hydrostratigraphic units laterally grade into the Main Silt stratum. These shallow hydrostratigraphic units are frequently dry, and the Main Silt and Main Sand within this area are generally unconfined.
LNAPL has not been detected within any monitoring locations screened within the North Olive and shallow portions of the Main Silt strata during the past five years. Within the Rand and deeper portions of the Main Silt strata, LNAPL has been detected within two monitoring locations (MP-056B and MP-096C) within the past five years, with a maximum apparent LNAPL thickness of 2.78 feet measured within monitoring point MP-056B in 2014. Fifteen monitoring locations screened within the Main Sand stratum have frequently contained LNAPL during the past five years with apparent LNAPL thickness ranging from 0.01 to 13.22 feet.
Dissolved phase analytical data from the shallow hydrostratigraphic units is limited within RMA-11. Two collocated monitoring points (MP-056A and MP-056B) have been sampled during the past five years. Benzene was not detected within groundwater samples collected in the North Olive stratum (MP-056A). However, the groundwater sample collected from monitoring point MP-056B, screened within the Rand stratum, was reported with a dissolved phase benzene concentration of 3.13 mg/L. Dissolved phase petroleum hydrocarbon concentrations are significantly higher in the Main Sand stratum, within benzene concentrations that have ranged from 13 to 34 mg/L in the nine groundwater monitoring locations that have been sampled over the past five years.
TVPH concentrations in soil vapor are generally low within the shallow hydrostratigraphic units in the western and southern portion of RMA-11 (Appendix G-2-3 and Appendix G-2-4). TVPH concentrations are typically greater than 1,000 ppmv along the eastern side of RMA-11 within the North Olive and shallow portions of the Main Silt strata (Appendix G-1-2) and have been reported as high as 240,000 ppmv during river stage triggered events (Appendix G-1-3). TVPH concentrations have remained around 1,000,000 ppmv in vapor probe VMP-070M screened in the Rand stratum in the center of RMA-11.
Extraction well HSVE-112 was connected to the SVE system in June 2017 as part of the Effectiveness Zone 6 expansion (discussed in Section 6.2.1.4) to reduce elevated TVPH concentrations reported in samples collected from vapor monitoring probe VMP-070M. There was a single residential structure with a completed vapor intrusion pathway in RMA-11 (135 East Forest Street) based on in-home screening conducted since 2013, as shown on Figure 6-12. Well HSVE-112 is located near this structure. SVE wells within RMA-11 are generally operable and continued operation of the SVE system will be necessary to control the vapor intrusion pathway, particularly in the northern and eastern portions of RMA-11.
8.12. REMEDIATION MANAGEMENT AREA NO. 12
Remediation Management Area No. 12 (RMA-12) is located immediately south of RMA-11 and is defined to the west by North Market Street and to the east by North Olive Avenue and includes structures located along East Watkins Street bound by the alleys to the north and south of East Watkins Street. RMA-12 includes the central portion of Effectiveness Zone 4.
The subsurface lithology in RMA-12 consists mainly of the Main Silt and Main Sand strata with the North Olive stratum present on the eastern edge of RMA-12. LNAPL has not been detected in the North Olive, Main Silt or Main Sand strata in RMA-12 during the past five years. As a result, dissolved phase petroleum hydrocarbons concentrations tend to be lower within RMA-12 compared to the downgradient area, RMA-11. Benzene concentrations measured within groundwater samples collected from monitoring point MP-088C have ranged from 0.46 to 2.7 mg/L between 2016 and 2018.
TVPH concentrations in soil vapor are typically low (less than 100 ppmv) within the North Olive and Main Silt strata (Appendix G-1-4 and Appendix G-2-4) beneath RMA-12, even during river stage triggered events (Appendix G-1-3 and Appendix G-2-3). There are no structures that have had a completed vapor intrusion pathway based on in-home screening that has been conducted since 2013, as shown on Figure 6-12. The SVE wells within this remediation management area currently operate on a continuous basis, except for the extraction wells installed along East Watkins Street. These SVE wells are operated in a cyclical fashion when TVPH concentrations are measured above 100 ppmv. Pulsed (or cyclical) operation may be considered for the other portions of RMA-12.