Loading...
HomeMy WebLinkAboutDERR-2024-010078 Technical Memorandum Date: June 17, 2024 To: Leigh Anderson, Project Manager Division of Environmental Response & Remediation Utah Department of Environmental Quality 195 North 1950 West Salt Lake City, Utah 84114-4840 From: Brad Glisson, Assistant Vice President, Project Manager WSP USA Environment & Infrastructure Inc. RE: Potential Risk Associated with 1,4-Dioxane in Groundwater Former General Electric (GE) Facility at 130 East 1100 North North Salt Lake, Utah VCP No. C102 This technical memorandum evaluates the potential human health risk associated with the presence of 1,4-dioxane in groundwater at and directly downgradient of the Site through 1) the identification of potential receptors and exposure routes and 2) the comparison of measured concentrations of 1,4-dioxane in groundwater to risk-based screening criteria. The results of the evaluation indicate there is no potential for adverse human health risk associated with exposure to 1,4-dioxane in shallow groundwater. General Background 1,4-Dioxane was widely used as a stabilizer for chlorinated solvents such as 1,1,1- trichloroethane (TCA) and is often found at solvent release sites. 1,1,1-TCA was identified as an ozone-depleting material in 1995 in accordance with the Montreal Protocol and production declined significantly along with the use of 1,4-dioxane as a solvent stabilizer (USEPA, 2017; ITRC, 2021a). Recent studies have also demonstrated that 1,4- dioxane is a relatively common contaminant in association with trichloroethylene (TCE) in groundwater, independent of the presence of 1,1,1-TCA. (USEPA Region 5, 2019). The US Environmental Protection Agency (USEPA) has not established a maximum contaminant level (MCL) for 1,4-dioxane. The drinking water equivalent for 1,4-dioxane is 1 milligram per liter (mg/L) or 1,000 micrograms per liter (µg/L), with a lifetime health advisory of 0.2 mg/L (200 µg/L) in drinking water (USEPA, 2018). USEPA has calculated a Regional Screening Level (RSL) of 0.46 µg/L for residential use of tap water based on a 1E-06 lifetime excess cancer risk. The residential tap water RSL based on noncancer hazard (HQ=1) is 57 µg/L (USEPA, 2024a). State standards for 1,4-dioxane in drinking water and/or groundwater range from 0.3 µg/L (Massachusetts and Vermont) to 200 µg/L (Iowa). Utah is one of eight states with no established drinking water standard or Technical Memorandum Potential Risk Associated with 1,4-Dioxane in Groundwater Former GE Facility, VCP No. C102 June 17, 2024 2 screening criterion for 1,4-dioxane. The World Health Organization has a suggested drinking water threshold of 50 µg/L (ITRC, 2021b). Evaluation of Potential Receptors and Exposure Routes 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 based on the 2023 Zoning Map, 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 off-site downgradient properties to the west, are zoned 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 current water well search on the Utah Division of Water Rights well log dataset (2024) indicates that four well borings were started east of the mobile home park in 2009. Three wells were completed, one to a finished well depth of 70 feet with a well intake depth at 50 feet, one to a finished well depth of 65 feet with a well intake depth of 45 feet, and the third well was installed to a finished well depth of 50 feet with a well intake depth of 50 feet. The well log records for these three wells identify them as “test” wells and the wells were abandoned in September 2023. Six well logs were identified within approximately one-half mile downgradient of the Site. Three wells were located generally southwest of the Site, including: (1) a nonproduction well (Holly Energy) bored to 280 feet but not completed with no finished well depth or well intake depth noted; (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; and (3) a well (Bountiful East Stake) finished to 221 feet, with a water intake depth of 211 feet. A fourth well, identified as an irrigation well owned by Lynn Trenbeath, is located to the west and was installed to 157 feet with a well intake depth of 147 feet. The remaining two locations are associated with the municipal well located approximately 200 feet west of the Site. The one location is identified as a boring to 320 feet that was subsequently abandoned. The remaining well, the municipal well, is identified to have a finished well depth of 300 feet with a well intake depth of 180 feet. There are 22 monitoring wells 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). Based on data collected at the Site from 2017 Technical Memorandum Potential Risk Associated with 1,4-Dioxane in Groundwater Former GE Facility, VCP No. C102 June 17, 2024 3 through April 2024, the average depth to water is 7.80 ft below TOC. 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). Two deep soil borings were advanced near the Site’s western property boundary in September 2023 to complete vertical delineation of on-site subsurface geologic soil conditions and to evaluate for the presence of a deeper water bearing zone. Prior to installation of the borings, WSP first completed a review of available soil boring logs from wells located on adjoining properties to evaluate the deeper lithologic soil conditions. These logs identify the presence of a clay layer extending from as shallow as 5 ft to 100 + ft-bgs. The results of the vertical delineation assessment conducted near the Site boundary indicated soil conditions consisted of approximately 20 feet of predominantly clay soil with no water bearing zone at depth. In addition, there was no evidence of volatile organic compounds at depth (WSP, 2023). There is no potential for residential exposure to the shallow groundwater as the properties downgradient of the Site are located in industrial/commercial use and there are no known residences within one-half mile of the Site. There is no use of shallow groundwater on-site or directly downgradient; therefore, there is no potential for industrial or commercial worker exposure to 1,4-dioxane in 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. 1,4-Dioxane is considered a volatile compound, and the only potentially complete exposure pathway is considered to be worker exposure to 1,4-dioxane that has volatilized from groundwater to indoor air. As discussed in the following section, concentrations of 1,4- dioxane in shallow off-site groundwater are well below the corresponding USEPA Vapor Intrusion Screening Levels (VISLs) protective of both residential and industrial receptors. The Site is currently vacant, and the on-site building is not currently occupied. Therefore, there are no current receptors or complete exposure pathways on the Site. A draft environmental covenant and Site Management Plan have been developed, and when finalized, will restrict groundwater use for monitoring purposes only and will restrict the property to industrial/ commercial use only. These restrictions will eliminate the potential for on-site direct contact exposure to 1,4-dioxane in shallow groundwater through its use as a potable water supply. Future worker exposure to 1,4-dioxane volatilizing to indoor air is considered the only potentially complete on-site exposure pathway; however, concentrations in on-site groundwater are also below the VISLs protective of both residential and industrial receptors. Potential Risk Associated with 1,4-Dioxane The risk associated with potential exposure to 1,4-dioxane in groundwater is discussed below for both on-site and directly downgradient, off-site groundwater. Technical Memorandum Potential Risk Associated with 1,4-Dioxane in Groundwater Former GE Facility, VCP No. C102 June 17, 2024 4 On-Site Groundwater Since monitoring of on-site groundwater for the presence of 1,4-dioxane began in 2021, detections have ranged from 0.14 µg/L (MW-14, September 2021) to 132 µg/L (MW-3, December 2023). Based on the April 2024 monitoring event, analytical results for 1,4- dioxane in on-site groundwater ranged from non-detect (14 monitoring wells) to 17.9 µg/L (MW-3). Along the western property boundary (MW-15 through MW-19) concentrations ranged from non-detect at the method detection limit (MDL) of 0.597 µg/L (MW-15 and MW-16) to 4.05 µg/L (MW-18). The on-site 1,4-dioxane data are well below the corresponding VISLs for both residential and industrial properties of 2,860 µg/L and 12,500 µg/L, respectively (USEPA, 2024b; TR=1E-06), indicating that with the environmental covenant in place, there will be no potential for adverse exposure to 1,4- dioxane in on-site groundwater. Off-Site Groundwater Two monitoring wells were installed off-site on the 3D Storage property in 2022 to total depths of 20 feet with depth to water in April 2024 of 4.39 feet from top of casing (ft TOC) and 6.65 ft TOC, respectively (offsite A-1 and offsite A-2). 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. During the five quarters of groundwater monitoring conducted at the off- site wells A-1 and A-2, detections of 1,4-dioxane ranged from 1.0 µg/L (offsite A-2 in September 2022) to 5.76 µg/L (offsite A-1 in December 2023). Off-site wells A-3 through A-12 were installed in 2024 to complete the delineation of 1,4- dioxane in off-site groundwater. The 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 new monitoring wells installed on the immediately downgradient properties. 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 1. These results indicate 1,4-dioxane was detected at 3.35 µg/L in well A-2 but was non-detect in the remaining off-site wells at the MDL of 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 1) and represent an acceptable cancer risk of 1E-06 based on residential use of off-site groundwater as a potable water supply. This was confirmed through use of the risk-calculation mode of the USEPA on-line RSL calculator and an assumed groundwater concentration of 0.597 µg/L. The resulting cumulative cancer risk is 1.3E-06, which, per USEPA risk assessment practice, would round to 1E-06. Thus, using the MDL of 0.597 µg/L, the off-site properties are delineated to the acceptable 1E-06 cancer risk level. The MDL (0.597 µg/L) is also well below the acceptable noncancer hazard level of 57 µg/L as well as the residential and industrial VISLs (2,860 µg/L and 12,500 µg/L, respectively). The one detection of 1,4-dioxane of 3.35 µg/L (off-site A-2) is below the Technical Memorandum Potential Risk Associated with 1,4-Dioxane in Groundwater Former GE Facility, VCP No. C102 June 17, 2024 5 midpoint of the acceptable cancer range for residential use of groundwater of 4.6 µg/L (equal to a residential cancer risk of 7E-06) and is also less than the acceptable noncancer hazard level and VISLs. Shallow groundwater at and in the vicinity of the Site is not used as a source of potable water supply and there are no off-site residential receptors immediately downgradient of the Site. Communication with the City of North Salt Lake has indicated drinking water is obtained from the confined aquifer at depths of approximately 80 to 130 feet bgs, and the water quality is not currently impacted by 1,4-dioxane or any VOCs, and based on the vertical delineation studies, is unlikely to be impacted in the future. The groundwater quality of the North Salt Lake Municipal Well located approximately 200 feet to the west of the Site is routinely monitored and according to the North Salt Lake water department representatives there have been no issues identified with the Site related constituents of concern (COCs). Conclusion The evaluations presented above demonstrate that: (1) The non-detect data associated with off-site wells A-3 through A-12 bound the presence of 1,4-dioxane in groundwater at the MDL of 0.597 µg/L; thus, off-site concentrations of 1,4-dioxane have been delineated; (2) The off-site data at the MDL equate to an acceptable cancer risk of 1E-06 based on residential exposure to 1,4-dioxane in groundwater used as a potable water supply; (3) There is no potential for adverse risk associated with exposure to 1,4-dioxane in either on-site or off-site groundwater because: • There is no use of shallow groundwater as a source of drinking water supply on or near the Site. • The municipal well located to the immediate west of the Site is located in a separate confined aquifer, with the water-bearing zone identified as 80 to 130 feet below ground surface (bgs). • Review of available well boring logs located on adjoining properties identified the presence of a clay layer extending from as shallow as 5 ft to 100 + ft-bgs; • The off-site property(s) to the west and northwest are used for industrial/commercial purposes in accordance with their zoning designations. There are no known residential receptors within one-half mile of the Site in a downgradient direction; • The only potentially complete exposure pathway is considered to be worker exposure to 1,4-dioxane that has volatilized from groundwater to indoor air. Measured concentrations of 1,4-dioxane in both on-site and off-site shallow groundwater are well below both the residential and industrial VISLs; and • The potential for exposure to 1,4-dioxane in on-site groundwater will be eliminated through the environmental covenant to be placed on the Site and the Site Management Plan. Technical Memorandum Potential Risk Associated with 1,4-Dioxane in Groundwater Former GE Facility, VCP No. C102 June 17, 2024 6 Based on the information presented above, there is considered to be no potential for adverse risk associated with exposure to 1,4-dioxane in shallow groundwater at, and directly downgradient of the Site. Technical Memorandum Potential Risk Associated with 1,4-Dioxane in Groundwater Former GE Facility, VCP No. C102 June 17, 2024 7 References City of North Salt Lake, 2023. Zoning Map, adopted February 21. ITRC, 2021a. Fact Sheet: History of Use and Potential Sources - 1,4-Dioxane, March. ITRC, 2021b. Fact Sheet: Regulatory Framework - 1,4-Dioxane, February. USEPA, 2019. Memorandum entitled “Procedures for Addressing Potential 1,4-Dioxane Contamination at Region 5 Superfund Remedial Sites”, from Douglas Ballotti, Director, Superfund & Emergency Management Division to Remedial Project Managers, December 12. USEPA, 2017. Technical Fact Sheet – 1,4-Dioxane, Office of Land and Emergency Management, EPA 505-F-17-011, November. USEPA, 2018. 2018 Edition of the Drinking Water Standards and Health Advisories Tables, Office of Water, March. USEPA, 2024a. Regional Screening Level (RSL) Summary Table (TR=1E-06; HQ=1), May. USEPA, 2024b. Vapor Intrusion Screening Level Calculator (TR=1E-06; HQ=1), May. 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. WSP USA Environment & Infrastructure, Inc., (WSP) 2023. Memorandum from WSP to General Electric Company on Exploratory Soil Boring Findings, October 5, 2023. FIGURE 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.FIGURE1 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. 1,4-DIOXANE TECHNICAL MEMORANDUM Approximate GE Parcel Boundary Off-Site Monitoring Well Location 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.