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Home My WebLink AboutDERR-2025-009159 Groundwater Remedial Action Plan Addendum -102 October 22 October 22, 2024 Ms. Leigh Anderson Utah Department of Environmental Quality Division of Environmental Response and Remediation 195 North 1950 West Salt Lake City, UT 84116 Re: Groundwater Remedial Action Plan Addendum Former General Electric Facility 130 East 1100 North North Salt Lake, Utah VCP No. C-102 WSP Project No. US-EI-WDP0033 Dear Ms. Anderson: WSP USA Environment & Infrastructure Inc. (WSP), on behalf of GE Vernova (GE) is providing this Groundwater Remedial Action Plan (RAP) Addendum for the former GE facility located at 130 East 1100 North, in North Salt Lake, Utah (Site). This document is an addendum to the Soil Remedial Action Plan (Soil RAP) (WSP, 2023a) that was approved by the Utah Department of Environmental Quality (UDEQ), Division of Environmental Response and Remediation (DERR) in March 2023 (UDEQ DERR, 2023a), and implemented at the Site in August 2023. As noted in the Soil RAP, the remedial action proposed for groundwater was to be provided under separate cover, and the Groundwater RAP is presented herein. GROUNDWATER RAP ADDENDUM Site-wide assessment activities are complete, and the horizontal and vertical nature and extent of impact to both soil and groundwater have been fully delineated. Soil impacts were confined to the Site, and the soil source areas were removed in 2023 during implementation of the Soil RAP. The Soil Remedial Action Closure Report (WSP, 2023b) was approved by the DERR in October 2023 (UDEQ DERR, 2023b). Groundwater impacts have been monitored since 2017 through the gauging and sampling of the 22 monitoring wells installed on the Site (MW-1 through MW-8 and MW-10 through MW- 23). In addition, at the request of the DERR, 12 additional monitoring wells were installed on the downgradient off-site properties. With the completion of the focused additional on-site investigations and installation of the additional off-site monitoring wells, groundwater impacts from site-related activities have been horizontally and vertically delineated to the residential 216 Centerview Drive, Suite 300, Brentwood, TN 37027 +1 (615) 333-0630 wsp.com Groundwater Remedial Action Plan Addendum -102 October 22 1E-06 acceptable cancer risk level. Figure 1 (Site Plan) and Figure 2 (Off-Site Well Locations) identify the locations of the groundwater monitoring wells. The constituents of concern (COCs) in groundwater, their location, and proposed remedy are discussed further below Objective The objective of the Groundwater RAP Addendum is to identify monitored natural attenuation (MNA) as the remedy selected to address the COCs in groundwater and to identify the groundwater performance objectives for the Site. Background The Site is owned by GE and comprises approximately 14.95 acres and includes two vacant buildings. It is located at 130 East 1100 North in North Salt Lake City, Davis County, Utah According to historical documents, General Motors Division built the facility in 1955 as a locomotive repair shop. General Motors sold the property in 1968 to Univac Guidance Systems, who operated at the Site until they sold the property to GE in 1971. GE utilized the Site for the cleaning, maintenance, and repair of transformers and electric motors until 2017 when it closed. Historical operations and previous environmental assessments are summarized in the Phase I Environmental Site Assessment (Amec, 2017), the Phase II Environmental Site Assessment Wood, 2020), the Site Characterization Work Plan (Wood, 2021), and the Human Health and Ecological Risk Assessment (HHERA) (Wood, 2022). Based on the assessments conducted at the Site, polychlorinated biphenyls (PCBs), total petroleum hydrocarbons (TPH), and arsenic were identified as COCs in soil. The soil removal action approved and executed in accordance with the Soil RAP addressed the PCBs and TPH in soil. Arsenic was determined to be well distributed in soil throughout the Site with elevated concentrations found at depths of generally greater than 10 feet below ground surface (bgs). Therefore, a soil removal action for arsenic was not practical or warranted, and the DERR agreed that arsenic in soil would be addressed through site and soil management, select engineering controls, and the future environmental covenant. Twenty-two monitoring wells have been installed on the Site (MW-1 through MW-8 and MW-10 through MW-23) constructed to depths that range from 9.5 ft below top of casing (ft below TOC) (MW-17) to 20.0 ft below TOC (MW-8) (Figure 1). Monitoring of these wells began in 2017, and a quarterly monitoring program was initiated in January 2022. Based on evaluation of the groundwater data collected at the Site, eight COCs were identified in groundwater including 1,1-dichloroethane (1,1-DCA), 1,1-dichloroethylene (1,1-DCE), cis-1,2- dichloroethylene (cis-1,2-DCE), 1,4-dioxane, trichloroethylene (TCE), arsenic, PCB-1254, and TPH- Groundwater Remedial Action Plan Addendum -102 October 22 DRO (at MW-7 only). The DERR previously approved the removal of PCBs from the site-wide groundwater monitoring program. TPH-DRO has been addressed through the removal of impacted soil in accordance with the Soil RAP, and as approved by the DERR in the Soil Remedial Action Closure Report. Due to the soil removal action, MW-7 required re-installation which was completed in August 2023. Three monitoring events have been conducted since soil RAP completion and re-installation of MW-7, and TPH-DRO concentrations have decreased from 1.1 milligrams per liter (mg/L) in December 2022 to 0.37 mg/L in April 2024. Based on these data, no further monitoring of TPH-DRO is warranted. For the purposes of the Groundwater RAP Addendum, therefore, the COCs in on-site groundwater include the five volatile organic compounds (VOCs) 1,1-DCA, 1,1-DCE, cis-1,2-DCE, 1,4-dioxane, TCE; and arsenic. Conceptual Site Model and Risk Evaluation The Site is currently vacant, and the on-site buildings are not currently occupied. Based on data collected at the Site from 2017 through April 2024, the average depth to water is 7.80 ft below TOC. Access to the Site building and storage areas is fenced and each monitoring well is capped and locked. Based on the current site conditions there are no current receptors or complete exposure pathways associated with groundwater at the Site. Land use within a 0.5-mile radius of the Site consists of industrial/commercial facilities to the north, west, and south. A mobile home park, Colonial Woods II Mobile Home Park, borders the Site to the east which is upgradient of the groundwater flow direction. The property to the west of the Site includes a railroad easement (4 tracks total), followed by 3D Storage property, a self-storage facility. Also, the North Salt Lake Municipal Well is located approximately 200 feet west of the Site boundary. There are no residential receptors located downgradient of the Site to the west and the closest downgradient residential district is approximately one (1) mile west of the Site (City of North Salt Lake, 2023). The Site, as well as the downgradient properties to the west, are zoned and used for manufacturing-distribution (MD) use. A residential development is located approximately one-half mile to the northwest of the Site across Highway 2600S. Property between the Site and the residential development is zoned Light Industrial/Business Park Zone (I-1) and is also in industrial/commercial use (Woods Cross City, 2021). A recent water well search on the Utah Division of Water Rights well log dataset (2024) did not identify any potable water wells other than the North Salt Lake Municipal Well located downgradient from the Site. A brief summary of the well logs identified include: Groundwater Remedial Action Plan Addendum -102 October 22 • Four well borings east of the mobile home park installed in 2009. Three wells were completed and the well log records identiﬁed them as “test” wells abandoned in September 2023. • Six well logs within approximately one-half mile downgradient of the Site. o (1) a nonproduction well (Holly Energy) bored to 280 feet but not completed; o (2) a well (no owner identiﬁed) installed to 390 feet with a well intake depth of 305 feet, a pump intake depth of 200 feet; o (3) a well (Bountiful East Stake) ﬁnished to 221 feet, with a water intake depth of 211 feet; o (4) an irrigation well owned by Lynn Trenbeath installed to 157 feet with a well intake depth of 147 feet; o (5) a boring associated with the municipal well located approximately 200 feet west of the Site that was installed to 320 feet and subsequently abandoned; and (6) the well log for the municipal well identiﬁed to have a ﬁnished well depth of 300 feet with a well intake depth of 180 feet. Groundwater flow at the Site is generally to the west/northwest and toward the municipal well; however, the municipal well is located in a separate confined aquifer, with the water- bearing zone identified as 80 to 130 feet below ground surface (bgs). At DERR’s request, two monitoring wells were installed off-site on the 3D Storage property in 2022 to further evaluate the potential horizontal migration of COCs in groundwater. The two wells, offsite A-1 and offsite A-2, were installed to total depths of 20 feet. During the sampling event in April 2024, depth to water in these wells was measured at 4.39 feet from top of casing (ft TOC) and 6.65 ft TOC, respectively. Groundwater on the 3D Storage property, as well as on the GE Site, is shallow in nature and there is no evidence of any connection to the deeper water bearing zone from which the municipal well draws water. To further evaluate the potential for vertical migration, WSP reviewed available soil boring logs from wells from the water well search. The review of the well logs identified the presence of a clay layer extending from as shallow as 5 ft to 100+ ft-bgs. At DERR’s request, and upon approval of the scope of work, two deep soil borings were advanced on-site near the western property boundary in September 2023 to complete vertical delineation of on-site subsurface geologic conditions and to evaluate for the presence of a deeper water bearing zone. The results of the vertical delineation indicated soil conditions consisted of approximately 20 feet of predominantly clay soil with no water bearing zone at depth. Soil samples collected at the terminus of the two borings were non-detect for VOCs (WSP, 2023c) indicating no vertical migration of COCs to the deeper water bearing zone associated with the municipal well. Groundwater Remedial Action Plan Addendum -102 October 22 Initial groundwater samples collected from the two off-site monitoring wells, A-1 and A-2, exhibited TCE concentrations higher than those detected in the on-site property boundary monitoring wells. To evaluate the possible presence of an off-site source of chlorinated VOCs (CVOCs) in groundwater downgradient from the Site, groundwater samples were collected from on-site well MW-3 (highest TCE concentration on-site) and offsite A-1 in March 2023 and submitted for stable isotope analysis (WSP, 2023d). The results of the isotope analysis show that the TCE detected at the downgradient offsite A-1 is less fractionated then the TCE detected at MW-3 indicating the samples are isotopically different. In addition, the results indicate the TCE at offsite A-1 is younger and likely due to a release that occurred more recently. The isotope data provide clear evidence that the TCE observed in offsite A-1 is from a separate off-site source and is unrelated to the TCE observed on the GE Site (WSP, 2023d). WSP has performed detailed Groundwater Plume Analytics® groundwater modeling since 2023 to obtain a better understanding of the overall stability of various constituent plumes at the Site. The Groundwater Plume Analytics® Services included the Ricker Method® Plume Stability Analysis, Center of Mass Movement Analysis, Spatial Change Indicator™ Analysis (US Pat. No. 10,400,583), and Molar Fractional Analysis. The Groundwater Plume Analytics® are being updated as new groundwater sampling event laboratory analytical data become available. The results of each Groundwater Plume Analytics® model are presented to the DERR under separate cover. Since the initial Groundwater Plume Analytics® were conducted in 2023, the results have demonstrated evidence of an off-site source of TCE, unrelated to the GE Site. This was demonstrated through comparison of the TCE concentrations at the property boundary (<0.3 to 3 ug/L; July 2022) to those reported for the off-site downgradient wells (22 to 74 µg/L, July 2022) which showed an increase in TCE concentrations off-site. In addition, the Groundwater Plume Analytics® demonstrated significantly different plume signatures with the on-site plume comprised largely of cis-1,2-DCE (67%) (a TCE biodegradation daughter product) while the off-site plume was comprised largely of TCE (72%) (a parent compound) (WSP, 2023e). The Groundwater Plume Analytics® also concluded that only low concentrations of CVOCs are migrating off-site in groundwater and these concentrations would be expected to attenuate or degrade to within acceptable concentrations immediately downgradient of the Site. The non- chlorinated VOC, 1,4-dioxane, however, was shown to have migrated off-site at low-level concentrations which were generally detected above the screening level of 0.46 µg/L (WSP, 2023e). Therefore, as discussed below, an additional assessment was conducted to delineate 1,4-dioxane in off-site groundwater. At the request of DERR, an additional off-site assessment was completed in April 2024 to complete the delineation of 1,4-dioxane in off-site groundwater. The proposed well locations were selected to demonstrate whether 1,4-dioxane was migrating further downgradient from the Site, or bound, i.e., delineated to acceptable levels, by the monitoring wells proposed to be installed on the immediately downgradient properties. Upon approval of the scope of work Groundwater Remedial Action Plan Addendum -102 October 22 and proposed off-site monitoring well locations by DERR, ten additional off-site wells were installed in March and April 2024, identified as A-3 through A-12. Off-site wells A-1 through A-12 were sampled during the April 2024 groundwater monitoring event with analytical results for 1,4-dioxane summarized on Figure 2. These results indicate 1,4- dioxane was non-detect in 11 of the 12 off-site wells including A-1 and A-3 through A-12. 1,4- Dioxane was detected at 3.35 µg/L in well A-2. These results were provided to DERR on June 19, 2024 in the April 2024 Additional Offsite Groundwater Delineation Report (WSP, 2024a). The laboratory method detection limit (MDL) for the off-site samples that were non-detect for 1,4-dioxane was 0.597 µg/L (i.e., at off-site wells A-1, and A-3 through A-12). The non-detect data at 0.597 µg/L delineate or bound the presence of 1,4-dioxane in off-site groundwater (Figure 2) and represent an acceptable cancer risk of 1E-06 based on residential use of off-site groundwater as a potable water supply. The information presented above indicates that the COCs in shallow groundwater do not have the potential to migrate vertically to deeper groundwater that is used as a source of potable water supply (i.e., the municipal well). Since the COCs, with the exception of arsenic, are volatile compounds, the only potentially complete migration pathway associated with the Site and downgradient locations is considered to be the potential for vapor intrusion from groundwater to indoor air. The information presented previously indicates there are no residential receptors downgradient in the immediate vicinity of the Site, and an environmental covenant, discuss further below, will be placed on the Site to preclude future residential development. Therefore, the only complete exposure pathway is considered to be the potential for worker exposure to constituents that may volatilize from groundwater to indoor air. This exposure pathway is considered a current/future exposure pathway for the off-site worker for potential exposure to 1,4-dioxane, the only site-related COC in off-site groundwater at concentrations of potential concern, volatilizing from groundwater to indoor air. On-site, this exposure pathway would be considered a future potential worker exposure pathway until the property is redeveloped. On-site, the potential for vapor intrusion is evaluated for all five volatile COCs in groundwater. To further evaluate this potential exposure pathway, the range of detection of the COCs in on- site groundwater, and of 1,4-dioxane in off-site groundwater, are presented in Table 1 in comparison to the USEPA Vapor Intrusion Screening Levels (VISLs) for both residential and industrial properties (TR=1E-06, HQ=1; USEPA, 2024). Groundwater Remedial Action Plan Addendum -102 October 22 TABLE 1 – GROUNDWATER DATA IN COMPARISON TO VISLS 01/2022 through 04/2024 (µg/L) VISL(1) (µg/L) VISL(1) (µg/L) Industrial? (Yes/No) VISL A-1 and A-2; Concentrations are below VISLs VISL at MW-2, MW-3, MW-11, MW-13, MW-17, MW-21(3) Units of micrograms per liter (µg/L) Notes: (1) USEPA VISLs based on a target cancer risk of 1E-06 and a target hazard quotient of 1. (2) Range for off-site data based on 4 events for off-site monitoring wells A-1 and A-2 and one collective event for A-1 through A-12. (3) An anomalous result from 2022 reported TCE at MW-21 at a concentration of 9.9 µg/L. TCE was non-detect in 11 other samples collected from this well. In summary, there is no potential for residential exposure to the on-site shallow groundwater as the Site is currently vacant and will have an environmental covenant to preclude future residential development. The downgradient properties are located in and currently used for industrial/commercial use. There are no known residences within one-half mile of the Site. In addition, there is no use of shallow groundwater on-site or directly downgradient; therefore, there is no potential for industrial or commercial worker exposure to shallow groundwater through its use as a potable water supply. The N. Salt Lake municipal well, as noted above, is associated with a water-bearing zone located 80 to 130 feet bgs. The only complete exposure pathway is considered to be the potential for worker exposure to constituents that may volatilize from groundwater to indoor air. Evaluation of the groundwater data as presented in Table 1, above, indicates that this pathway is not of concern for the off-site groundwater COC 1,4-dioxane. On-site, the pathway is of concern for TCE but only at locations associated with monitoring wells MW-2, MW-3, MW-11, MW-13, and MW-17 which are not located within the vicinity of the current on-site building. The one detection of TCE at 9.9 µg/L at MW-21 in August 2022 was preceded by five non-detect results and followed Groundwater Remedial Action Plan Addendum -102 October 22 by an additional six non-detect results. The observation from August 2022 (1 out of 12 samples) is considered an anomaly and TCE is considered non-detect at this location. A draft environmental covenant and Site Management Plan (SMP) have been developed, and when finalized and approved by DERR, will be recorded with Davis County. These administrative controls will restrict groundwater use to monitoring purposes only, restrict the property to industrial/ commercial use only and eliminate or control the potential for exposure to construction or future Site workers to any remaining on-site COCs. Similarly, these restrictions will eliminate the potential for on-site direct contact exposure to shallow groundwater through its use as a potable water supply. In addition, the environmental covenant will restrict the property to include the need for additional vapor assessment and/or potential vapor engineering controls, if future construction of a new building is planned near monitoring wells MW-2, MW-3, MW-11, or MW-17. Remedial Objective and Design The selected groundwater remedy for the Site is MNA. This remedy will work in conjunction with the implementation of engineering controls and the above referenced administrative controls including an environmental covenant and Site Management Plan in place for the Site. The overall remedial objective of the MNA is to bring individual COC concentrations to within the UDERR and USEPA acceptable cancer risk range of 1E-06 to 1E-04, or, for noncarcinogenic compounds, to achieve concentrations that equate to a hazard quotient less than or equal to 1. Proposed Performance Objectives The proposed performance objectives for the COCs in groundwater at the Site and their basis are summarized in Table 2 below. TABLE 2 – PROPOSED PERFORMANCE OBJECTIVES FOR ON-SITE GROUNDWATER Objectives (µg/L) Objectives 01/2022 through 04/2024 (µg/L) Units of micrograms per liter (µg/L) B= detected in the associated method blank C = Carcinogen Groundwater Remedial Action Plan Addendum -102 October 22 HQ = Hazard Quotient J = estimated concentration below the reporting limit but above the method detection limit MCL = Maximum Contaminant Level NC = Noncarcinogen Q = Sample was prepared and/or analyzed past holding time as deﬁned in the method. Concentrations should be considered minimum values. Upon DERR approval, the environmental covenant to be placed on the Site will preclude future residential development and, with the use of engineering and other site administrative controls placed upon the property, will also prevent the future use of on-site groundwater as a source of potable water supply. Based on these restrictions, the selection of performance objectives that are representative of either MCLs for public water systems, or risk-based screening criteria based on residential use of groundwater as a potable water supply are considered protective of future non-residential exposure where the groundwater direct contact exposure pathway is considered incomplete. The industrial VISLs were not selected as performance objectives as the environmental covenant will also restrict the property to include the need for additional vapor assessment and/or potential vapor engineering controls, if future construction of a new building is planned near monitoring wells MW-2, MW-3, MW-11, or MW- 17; thus, requiring a future evaluation of potential vapor intrusion for the majority of the Site. The selected performance objectives are discussed further below by COC, and the method for comparing Site data to the performance objectives is presented in the following section. • 1,1-DCA –This COC has both carcinogenic and noncarcinogenic properties. The USEPA Regional Screening Level (RSL) for residential use of tapwater (i.e., the Tapwater RSL) of 280 µg/L which is based on a target cancer risk of 1E-04 was selected as the performance objective for 1,1-DCA. This value is within the DERR’s acceptable cancer risk range and is less than the Tapwater RSL of 3,800 µg/L calculated based on the DERR’s acceptable hazard quotient (HQ) of 1. In addition, a MCL has not been established for 1,1-DCA. • 1,1-DCE – The MCL for 1,1-DCE in public water systems is 7 µg/L. 1,1-DCE is a noncarcinogen and the Tapwater RSL based on DERR’s acceptable hazard quotient of 1 is 280 µg/L. Therefore, as the on-site shallow groundwater is not a source of public water supply, 280 µg/L was selected as the performance objective for 1,1-DCE. • Cis-1,2-DCE – The MCL for cis-1,2-DCE in public water systems is 70 µg/L. This COC is a noncarcinogen and the Tapwater RSL based on DERR’s acceptable hazard quotient of 1 is 25 µg/L. Since 70 µg/L is the maximum concentrations allowed for public water systems, the Site performance objective does not need to be more restrictive as the environmental covenant will restrict potable use of groundwater. Therefore, the MCL of 70 µg/L was selected as the performance objective for cis-1,2-DCE. Groundwater Remedial Action Plan Addendum -102 October 22 • 1,4-Dioxane - This COC has both carcinogenic and noncarcinogenic properties. The Tapwater RSL of 46 µg/L which is based on a target cancer risk of 1E-04 was selected as the on-site performance objective for 1,4-dioxane. This value is within the DERR’s acceptable cancer risk range and is less than the Tapwater RSL of 57 µg/L calculated based on the DERR’s acceptable hazard quotient (HQ) of 1. An MCL has not been established for 1,4-dioxane. • TCE – The MCL for TCE in public water systems is 5 µg/L. This COC has both carcinogenic and noncarcinogenic properties. The Tapwater RSL of 49 µg/L which is based on a target cancer risk of 1E-04 was selected as the performance objective for TCE. This value is within the DERR’s acceptable cancer risk range and is higher than both the MCL and the Tapwater RSL of 2.8 µg/L calculated based on the DERR’s acceptable hazard quotient (HQ) of 1. The Site performance objective does not need to be more restrictive as the environmental covenant will restrict potable use of groundwater. • Arsenic –Concentrations of arsenic in groundwater are well distributed across the Site with ﬂuctuating concentrations in individual wells (low concentrations estimated below the laboratory reporting limit to higher concentrations that exceed the MCL), with no known or documented operational source other than the geologic setting. Therefore, the performance objective for arsenic is maintaining Site compliance with the institutional control that will prevent use of on-site groundwater as a source of potable water supply. • Off-site 1,4-dioxane - Based on the EPA Tapwater RSL for 1,4-Dioxane (0.46 µg/l), on-site and off-site groundwater was further evaluated as presented above in the Conceptual Site Model and Risk Evaluation. GE does not control the off-site property and cannot ensure no future use of groundwater as a drinking water source. Therefore, the off-site performance objective for 1,4-dioxane in groundwater is set to a concentration or detection limit equivalent to a 1E-06 residential cancer risk based on potable use of groundwater. Application of Performance Objectives Groundwater monitoring will continue to be conducted at the Site in accordance with the UDERR-approved groundwater monitoring program and Quality Assurance Project Plan (QAPP). Proposed modifications to the on-site groundwater monitoring program were submitted to the DERR dated July 19, 2024 (WSP, 2024b); GE is awaiting comments on the proposed modifications. The primary proposed on-site groundwater monitoring program modification included changing the frequency of monitoring to semi-annual, and to focus the sampling effort on select monitoring wells present at the Site. Groundwater Remedial Action Plan Addendum -102 October 22 With the selection of MNA as the groundwater remedy, long-term monitoring activities will be utilized to identify when groundwater concentrations meet the performance objectives included herein. Sampling of select VOCs will continue until the data indicate the performance objectives have been met. To evaluate Site-wide achievement of the performance objectives, a 95 percent upper confidence limit (UCL) will be calculated for each COC using the current version of USEPA’s ProUCL. The 95% UCL will be calculated using the conservative approach to only consider Site data from MW-2, MW-3, MW-4, MW-6, MW-11 through MW-13 and MW-15 through MW-19 from January 2022 to the present date. These wells are “focused” wells where VOCs remain of interest in groundwater. The selection of these wells conservatively eliminates utilizing groundwater sample results from consideration that are non-detect or have very low VOC concentrations (e.g., groundwater samples from monitoring wells MW-20 through MW-23). Further to the evaluate the Site groundwater performance objectives, individual concentrations of the COCs will be monitored at the boundary wells. (i.e., MW-15 through MW-19) and compared to the performance objectives. To support the evaluation of MNA at the Site, constituent concentrations will also be evaluated to determine concentrations trends (i.e., stable or decreasing). WSP proposes to complete the data evaluations on an annual basis using USEPA’s ProUCL, Groundwater Plume Analytics®, Mann-Kendall statistical tests, or similar data evaluations as appropriate. In support of the Groundwater RAP Addendum, GE also proposes to conduct two additional semi-annual groundwater monitoring events for off-site wells A-1 through A-12 to monitor the concentrations of 1,4-dioxane in off-site groundwater in relation to the established off-site performance objective. Only 1,4-dioxane will be monitored as GE has successfully demonstrated that the CVOCs detected in off-site groundwater are the result of an off-site source. This was demonstrated through Groundwater Plume Analytics® as well as the isotope analysis described above and in detail in previous correspondence. The off-site wells to be monitored will include A-1, A-2, A-3, A-5, and A-10. In support of DERR’s request regarding the presence of the off-site source of TCE, off-site wells A-1, A-2, and A-10 will also be monitored for TCE. Contingency Sampling If the data analyses described above identify the exceedance of a performance objective in a boundary well at the Site, the specific boundary well of interest will be re-sampled in the following month to determine if the analytical result accurately reflects groundwater conditions. If the laboratory analytical result still exceeds the performance objective, then GE will report the exceedance to the DERR and will evaluate potential corrective actions to be taken. If an exceedance of a performance objective is noted for an “interior well” (i.e., not a boundary well), the analytical result will be incorporated into the 95% UCL of the focused wells (MW-2, MW-3, MW-4, MW-6, MW-11 through MW-13 and MW-15 through MW-19). If the 95% UCL of the Groundwater Remedial Action Plan Addendum -102 October 22 focused wells exceeds a performance objective, the well in question will be resampled in the following month. If replacement of the analytical datapoint with the new result still results in a 95% UCL that exceeds a performance objective, GE will report the exceedance to the DERR and will evaluate future potential corrective actions to be taken, as deemed appropriate. Environmental Covenant An environmental covenant, when finalized, will be recorded on the deed to: • Restrict the property to industrial/commercial use only. • Restrict groundwater use to assessment and monitoring only • Manage impacted soils in accordance with the Environmental Covenant requirements and the SMP. • Evaluate whether environmental conditions pose a threat of vapor intrusion prior to construction of new building(s) and install a Vapor Mitigation System if appropriate. Final Report and Certificate of Completion The Soil RAP was successfully implemented in 2023 followed by DERR approval of the Soil Remedial Action Closure Report. With submittal of this Groundwater RAP Addendum, it is our understanding that Site will be “un-bifurcated”, i.e., brought back together so that final steps will address both soil and groundwater. The results of the groundwater sampling events conducted in support of the RAP will be documented in an annual groundwater monitoring report. We will also develop the Final Report that documents the activities conducted at the Site and request closure through a Certificate of Completion with continued monitoring of MNA as noted. Please contact Brad Glisson at brad.glisson@wsp.com if you have any questions or comments regarding this report. Respectfully submitted, WSP USA Environment & Infrastructure Inc. Bradley K Glisson, CHMM Sara B. Mathews, CHMM AVP - Project Manager AVP – Environmental Scientist Attachments: A – Figures B - References ATTACHMENT A FIGURES E 1100 North Ra i l r o a d T r a c k s Ra i l r o a d T r a c k s N M a i n S t r e e t 1100 North Municipal Well 40 E 1100 North North Salt Lake City MW-1 MW-15 MW-16 MW-17 MW-18 MW-3 MW-19 MW-4 MW-7 MW-2 MW-8 MW-22 MW-20 MW-21 MW-23 MW-6 MW-5 MW-14 MW-13MW-10 MW-11 MW-12 A2 A1 A10 A5 A6 A7 A3 A8 A11 A9 A4 A12 4283.77 4283.72 4285.87 4287.05 4288.41 <4284.05> <4285.15> 4288.65 4287.18 4287.70 4286.75 4286.49 4281.26 4281.85 4275.29 4276.84 4276.69 4272.48 4278.33 4280.45 4278.92 4278.95 4280.22 4275.21 4272.71 4271.73 4273.84 4270.39 4270.90 4274.45 4273.02 4270.53 4269.19 4268.99 42 7 6 42 7 7 42 7 8 42 7 9 42 8 0 428 1 42 8 2 428 3 428 4 428 5 428 6 428 7 428 8 427 7 427 5 4274 4273 42 7 2 42 7 1 42 7 0 42 6 9 42 7 0 427 1 42 7 2 42 7 3 42 7 4 42 7 5 428 8 42 8 7 42 8 6 42 8 5 42 8 4 42 8 3 42 8 2 42 8 1 42 8 0 427 9 42 7 8 DATE DESIGNED PREPARED REVIEWED APPROVED 04/24/2024 --- RLB CLIENT/PROJECT TITLE PROJECT NO.REV.FIGURE1 N P: \ I n d y O f f i c e \ G E U t a h \ S i t e W e s t . d w g - P S 0 4 - 2 4 - A p r . 2 4 , 2 0 2 4 2 : 0 2 p m APPROXIMATE SCALE IN FEET 0 140 280 CONSULTANT NAME WSP USA Environment & Infrastructure Inc. CONSULTANT LEGEND BG BG WDP0033.0006.02 SITE PLAN - WELL LOCATIONS 130 East 1100 North, North Salt Lake, Utah References: Google Earth Pro image dated 06/14/2022. Property parcels from Davis County Interactive Parcel Information App on their website. GROUNDWATER RAP ADDENDUM On-Site Monitoring Well Location Off-Site Monitoring Well Location Approximate GE Parcel Boundary E 1100 North Ra i l r o a d T r a c k s Ra i l r o a d T r a c k s N M a i n S t r e e t 1100 North Municipal Well 40 E 1100 North North Salt Lake City A12 A4 A9 A11 A8 A3 A7 A6 A5 A1 A2 A10 DATE DESIGNED PREPARED REVIEWED APPROVED 05/23/2024 --- RLB CLIENT/PROJECT TITLE PROJECT NO.REV.FIGURE2 N P: \ I n d y O f f i c e \ G E U t a h \ F i g u r e s f o r 1 s t Q t r 2 0 2 4 O f f - S i t e S a m p l i n g . d w g - 1 s t 2 4 1 4 D I O X - M a y . 2 3 , 2 0 2 4 1 2 : 2 4 p m APPROXIMATE SCALE IN FEET 0 100 200 CONSULTANT NAME WSP USA Environment & Infrastructure Inc. CONSULTANT LEGEND BG BG WDP0033.0006.02 GROUNDWATER ANALYTICAL MAP References: Google Earth Pro image dated 06/14/2022. Property parcels from Davis County Interactive Parcel Information App on their website. GROUNDWATER RAP ADDENDUM Approximate GE Parcel Boundary Off-Site Monitoring Well Location Off-Site 1,4-Dioxane CLIENT/PROJECT FORMER GENERAL ELECTRIC FACILITY 130 East 1100 North, North Salt Lake, Utah A-1 Result (µg/L) 4/2024 <0.597** 12/2023 5.76* 7/2023 3.1* 3/2023 2.8* 12/2022 5.2* 9/2022 1.3* A-2 Result (µg/L) 4/2024 3.35* 12/2023 5.06* 7/2023 4.2* 3/2023 5.0* 12/2022 5.1* 9/2022 1.0* A-10 Result (µg/L) 4/2024 <0.597** A-5 Result (µg/L) 4/2024 <0.597** A-6 Result (µg/L) 4/2024 <0.597** A-7 Result (µg/L) 4/2024 <0.597** A-3 Result (µg/L) 4/2024 <0.597** A-8 Result (µg/L) 4/2024 <0.597** A-9 Result (µg/L) 4/2024 <0.597** A-4 Result (µg/L) 4/2024 <0.597** A-11 Result (µg/L) 4/2024 <0.597** A-12 Result (µg/L) 4/2024 <0.597** Notes: 1. * - Result exceeds EPA Regional Screening Level (RSL) Limit of 0.46 μg/L. 2. J - Estimated value, ND - Not Detected, NS - Not Sampled, μg/L - micrograms per liter. 3. ** - Result reported above screening level of 0.46 μg/L. ATTACHMENT B LIST OF REFERENCES List of References Amec, 2017. Interim-Final Phase I Environmental Site Assessment, General Electric Facility, North Salt Lake, Utah, Amec Foster Wheeler Environment & Infrastructure, Inc., March 2017. City of North Salt Lake, 2023. Zoning Map, adopted February 21. US Environmental Protection Agency (USEPA), 2024. Vapor Intrusion Screening Level Calculator (TR=1E-06; HQ=1), May. Utah Department of Environmental Quality (UDEQ) Division of Environmental Response and Remediation (DERR), 2023a. Correspondence regarding Former General Electric VCP Site, North Salt Lake, Utah, providing acceptance of the Soil RAP under the VCP, dated March 1, 2023. UDEQ DERR, 2023b. Correspondence regarding GE North Salt Lake, Utah accepting several reports (S-RAP of Material Dumped by Third Party; CSIA Memorandum; Soil Remedial Action Closure Report, Groundwater Sampling Report for the July 2023 Offsite Sampling Event, and the Exploratory Soil Boring Memorandum), dated October 24, 2023. Utah Division of Water Rights, 2024. On-line search of water well records at: Utah Well Logs | Utah Well Logs | Utah’s State Geographic Information Database (AGRC), February 7, 2024. Woods Cross City, 2021. Zoning Map for Woods Cross City, Utah, last amended March 16, 2021. Wood Environment & Infrastructure Solution, Inc., (Wood), 2020. Phase II Environmental Site Assessment. Former General Electric Facility, 130 East 1100 North, North Salt Lake, Utah, February 2020. Wood Environment & Infrastructure Solution, Inc., (Wood), 2021. Site Characterization Work Plan, 130 East 1100 North, North Salt Lake, Utah, July 2021. Wood Environment & Infrastructure Solution, Inc., (Wood), 2022. Human Health and Ecological Risk Assessment Report, Former General Electric Facility, 130 East 1100 North, North Salt Lake, Utah, May 2022. WSP USA Environment & Infrastructure, Inc., (WSP), 2023a. Soil Remedial Action Plan, Former General Electric Facility, North Salt Lake, Utah, January 25, 2023. WSP, 2023b. Soil Remedial Action Closure Report, Former General Electric Facility, North Salt Lake, Utah, August 7, 2023. WSP, 2023c. Memorandum from WSP to General Electric Company on Exploratory Soil Boring Findings, October 4, 2023. WSP, 2023d. Memorandum from WSP to General Electric Company on CSIA Results, August 1, 2023. WSP, 2023e. Evaluation of Groundwater Monitoring Program 2017-2023 (Revision 1), Former General Electric Facility, North Salt Lake, Utah, October 2023. WSP, 2024a. April 2024 Additional Offsite Groundwater Delineation Report, Former General Electric Facility, North Salt Lake, Utah, June 19, 2024. WSP, 2024b. Proposed Modiﬁcation to the On-Site Groundwater Monitoring Program (Rev. 1), Former General Electric Facility, North Salt Lake, Utah, July 19, 2024.