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Home My WebLink AboutDERR-2024-005487EarthTouch, Inc. 3135 North Fairfield Road, Suite D, Layton, Utah 84041 Tel: 801-771-2800 EarthTouch, Inc. 3135 North Fairfield Road, Suite D Layton, Utah 84041 22-Mar-2024 cjhowell@utah.gov Mr. Christopher Howell, PG Environmental Scientist Utah Department of Environmental Quality Division of Environmental Response & Remediation Voluntary Cleanup Program / Brownfields Section 195 North 1950 West (Street) Salt Lake City, Utah 84116 RE: Summary of Remedial Actions at the former Antimony Mill Site located in Antimony Canyon roughly 5.5 miles to the east-southeast of the town of Antimony in Garfield County, Utah. Reference: Voluntary Cleanup Program (No. C106) Dear Mr. Howell: On 25-Sep-2023, the Utah Department of Environmental Quality (DEQ), Division of Environmental Response & Remediation (DERR), Voluntary Cleanup Program/Brownfields Section accepted a Remedial Action Plan (RAP) prepared by EarthTouch, Inc. on behalf of The Richard William Davis Trust to excavate, transport, and disposed of residual high-grade ore, mill tailings, and metal-impacted soil related to the past operation of the Antimony Mill located in Antimony Canyon roughly 5.5 miles to the east-southeast of the town of Antimony in Garfield County, Utah (“subject property” or “site”). Previous investigations of the subject property identified roughly 21,000 square feet to 27,000 square feet in and around the former Antimony Mill impacted by antimony, arsenic, and thallium (contaminants of concern) to depths extending up to roughly 1-foot below ground surface (bgs). The former Antimony Mill was constructed within a roughly 5-acre patented mine claim identified as Claim 38B and located in Section 21, Township 31 South, Range 1 West, Salt Lake Base & Meridian (SLB&M) in Antimony Canyon to the east of Antimony in an unincorporated Garfield County, Utah. Claim 38B is bordered by other patented mine claims and lands administered by the Dixie National Forest along the eastern edge of the Escalante Ranger District. The impacted materials included yellow-colored residual ore piles adjacent to the former mill, grayish mill tailings with a texture of ‘flour’ and ‘sulfide odor’ (when wet) in areas adjacent to the former mill extending northwesterly along and across Forest Road 138 nearly to Antimony Creek; and underlying soils. Samples of ore piles and mill tailings were analyzed by Toxic Characteristic Leaching Procedure (TCLP) to generate a waste profile and based on analytical results were not considered hazardous waste. Proposed remedial actions included excavating/scrapping and removing/disposing of ore piles, mill tailings, and near-surface soil in and around the former mill with site-specific cleanup level based on a Utah DEQ/DERR Summary of Remedial Actions (VCP No.: C106) 2 Former Antimony Mill near Antimony, Utah ‘recreational use’ exposure model used by the US Forest Service and consistent with the US Bureau of Land Management (BLM) outline in the Screening Assessment Approaches for Metals in Soil at BLM Hazmat/AML [Abandoned Mine Lands] Sites Technical Memorandum. Based on a health risk assessment model included in the RAP, the site-specific cleanup levels (SSCLs) applied to remedial actions at the former Antimony Mill include: Contaminant of Concern Site-Specific Cleanup Level Antimony 470 mg/kg Arsenic 100 mg/kg Thallium 6.5 mg/kg Remedial actions were initiated in Oct-2023 and were performed in accordance with the RAP accepted by the Utah DEQ/DERR. At the outset of remedial actions, the ore piles to the south and southeast of the former mill and impacted soils in areas between Forest Road 138 and Antimony Creek were excavated, placed in dump-trucks, and transported to and disposed at the Garfield County Landfill. The excavated materials and bases of excavated areas were screened using a hand-held X-ray Fluorescence (XRF) unit to identify impacted media, perform a field assessment of excavated materials, and provide guidance for excavation activities with respect to the SSCLs. In general, the depths of excavations beneath and adjacent to the ore piles and areas of impacted soil between Forest Road 138 and Antimony Creek continued until field measurements using an XRF unit were more than 20% below the SSCLs prior to the collection of confirmation samples. After five days of excavation activities, field samples and confirmation samples confirmed the areas of the ore piles to the south and southeast of the former mill and mill tailings and impacted soil between Forest Road 138 and Antimony Creek were below the SSCLs. Initial excavation activities in the area between Forest Road 138 and Antimony Creek identified impacted media extending roughly 2 to 3 feet below a roughly 0.5- to 1-foot layer of ‘clean soil’ underlying an approximate 0.5 to 1-foot layer of impacted material on the surface. A somewhat linear area of impacted material was also identified extending east-southeasterly from the south (upper) part of the former mill to an ore pile; and was likely related to a former conveyor system in this portion of the site. Initial excavation activities adjacent to the former mill encountered increasing concentrations with depth beneath a roughly 0.5- to 1-foot layer of ‘clean soil.’ Exploratory excavations in an around the former mill were carried out in Nov-2023 and significant volumes of mill tailings were discovered with thicknesses ranging from 1 to 12 feet and completely filling areas of the rock-masonry superstructure of the former mill. In Nov-2023 and Dec-2023, mini-excavators and a front-loader were mobilized to the site and mill tailings within the rock-masonry superstructure of the former mill were removed with light- equipment and hand tools until rock-masonry floors or walls, or the country rock of cut-slope areas were exposed. In areas immediately to the east of the rock-masonry superstructure, the excavation continued to depths where XRF measurements suggested likely conformance with the SSCLs. Review of historical information suggested the area immediately to the east of the rock-masonry superstructure was likely a connective stairway between levels of the former mill within a wood-frame structure. At the completion of excavation activities, analyses of samples from exposed areas of the rock-masonry floors within the rock-masonry superstructure reported concentrations of contaminants of concern below the SSCLs. Areas where confirmation samples indicated residual concentrations of contaminants of concern below the SSCLs were covered with clean fill and areas between Forest Road 138 and Antimony Creek were reseeded with a mixture prescribed by the US Forest Service. Clean fill was transported to the site from quarry areas adjacent to the Garfield County Landfill at the beginning of remedial actions. Utah DEQ/DERR Summary of Remedial Actions (VCP No.: C106) 3 Former Antimony Mill near Antimony, Utah Remedial actions were suspended in the middle part of Dec-2023 due to decreasing temperatures and an inability to excavate impacted materials near the base of the former mill adjacent to Forest Road 138, which was frozen. Night-time temperatures in the last week of remedial actions in Dec-2023 typically ranged from 0 to 10 degrees Fahrenheit (F) with daytime temperatures rarely exceeding 35 degrees (F). Given the discovery of significant volumes of impacted material beneath ‘clean layers’ underlying the impacted material identified on the surface; remedial actions have thus far involved removing, transporting, and disposing of roughly 756 tons of impacted material at the Garfield Canyon Landfill and approximately 56 dump truck loads. The volume of impacted material removed/disposed greatly exceeds the estimates included in previous investigations of the subject property. Observations of field conditions suggest the physical setting at the former mill likely reflects a period of rapid deposition of ‘clean soil’ overlying the majority of impacted material with surficial areas of impacted material deposited through more ‘routine’ depositional events over a roughly 40- to 70-year period. The majority of cleanup at the former Antimony Mill has been completed. However, some areas with impacted materials remain, including areas near the base of the rock-masonry superstructure adjacent to and partially within Forest Road 138. The residual areas of impact are anticipated to be excavated, removed, and transported to the Garfield County Landfill, and disposed in May-2023 or Jun-2023, as weather and conditions permit. Photographs of the progress of remedial actions are attached to this memorandum. At the conclusion of remedial action, EarthTouch, Inc. will prepare and submit a Remedial Action Report (RAR) to the Utah DEQ/DERR on behalf of The Richard William Davis Trust summarizing remedial actions, evaluating field and laboratory data, and assessing the risk to human health and the environment. We appreciate the opportunity to provide the Utah DEQ/DERR with the memorandum summarizing ongoing remedial actions at the former Antimony Mill. Should you have any questions regarding this memorandum, please contact me at: 801.771.2800 or at bcox@earthtouchinc.com. Sincerely, EarthTouch, Inc. Brett Cox President / Senior Scientist ATTACHMENT Photograph(s) Utah Department of Environmental Quality Voluntary Cleanup Program (No.: C106) Former Antimony Mill Site Former Antimony Mill 5.5 Miles East of Antimony (Antimony), Garfield County, Utah 84712 Photograph 1 Description: Antimony Mill prior to remedial actions View: South Photograph 2 Description: Ore Pile to the south of the former mill View: West-northwest Photograph 3 Description: View from the south (upper) part of the mill prior to remedial actions View: North-northwest Utah Department of Environmental Quality Voluntary Cleanup Program (No.: C106) Former Antimony Mill Site Former Antimony Mill 5.5 Miles East of Antimony (Antimony), Garfield County, Utah 84712 Photograph 4 Description: Concrete foundation at base of the former mill View: South Photograph 5 Description: Initial excavation activities in and around the former mill View: South Photograph 6 Description: Initial excavation activities in and around the former mill View: South Utah Department of Environmental Quality Voluntary Cleanup Program (No.: C106) Former Antimony Mill Site Former Antimony Mill 5.5 Miles East of Antimony (Antimony), Garfield County, Utah 84712 Photograph 7 Description: Excavation of the upper parts of the mill following discovery of roughly 12 feet of mill tailings beneath a ‘clean layer’ of soil View: South Photograph 8 Description: Excavation of the upper parts of the mill following discovery of roughly 12 feet of mill tailings beneath a ‘clean layer’ of soil View: South Photograph 9 Description: Excavation of the upper parts of the mill following discovery of roughly 12 feet of mill tailings beneath a ‘clean layer’ of soil View: South-southeast Utah Department of Environmental Quality Voluntary Cleanup Program (No.: C106) Former Antimony Mill Site Former Antimony Mill 5.5 Miles East of Antimony (Antimony), Garfield County, Utah 84712 Photograph 10 Description: Rock-masonry floor and country wall exposure in cut-slope following removal of impacted material from the upper part of the former mill View: West Photograph 11 Description: Excavation of impacted material from the lower part of the former mill extending to a rock-masonry floor View: East Photograph 12 Description: Pocket of high-grade processed ore in the lower part of the former mill View: South Utah Department of Environmental Quality Voluntary Cleanup Program (No.: C106) Former Antimony Mill Site Former Antimony Mill 5.5 Miles East of Antimony (Antimony), Garfield County, Utah 84712 Photograph 13 Description: Rock-masonry superstructure of the lower and upper parts of the former mill following removal actions View: South-southeast Photograph 14 Description: Rock-masonry superstructure of the lower part of the former mill following removal actions View: Photograph 15 Description: Load-out of impacted material. View: West-southwest Utah Department of Environmental Quality Voluntary Cleanup Program (No.: C106) Former Antimony Mill Site Former Antimony Mill 5.5 Miles East of Antimony (Antimony), Garfield County, Utah 84712 Photograph 16 Description: Transport of impacted material View: West Photograph 17 Description: Removal actions in lower mill View: South Photograph 18 Description: Mill following removal actions View: South Utah Department of Environmental Quality Voluntary Cleanup Program (No.: C106) Former Antimony Mill Site Former Antimony Mill 5.5 Miles East of Antimony (Antimony), Garfield County, Utah 84712 Photograph 19 Description: Clean material placed in lower mill following confirmation sampling View: South Photograph 20 Description: Clean material placed in lower mill following confirmation sampling View: West Photograph 21 Description: Reseeded area between Forest Road 138 and Antimony Creek View: West Utah Department of Environmental Quality Voluntary Cleanup Program (No.: C106) Former Antimony Mill Site Former Antimony Mill 5.5 Miles East of Antimony (Antimony), Garfield County, Utah 84712 Photograph 22 Description: Residual foundation element and likely load-out in lower part of mill (at ground level) View: Northeast Photograph 23 Description: Remaining areas of impact along Forest Road 138 View: Southeast