Soil Excavation at MDT Swan Lake Facility

2026-11-03

Preliminary Activities Submit Proposal as Work Plan for DEQ and PTRCB review . Conduct literature review . Review the June 30 , 2022 Remedial Investigation Report and the May 2023 Remedial Investigation Report . Review the Ferndale one - time landfarm application and permit . Coordination activities associated with communications with Aaron Anderson at MDT , Reed Miner at DEQ , and Steve Opp with the USFS . Excavation Activities Part of the Excavation Activities will occur on National Forest System Lands administered by the USFS . Coordinate with Steve Opp of the Forest Service when specific dates are scheduled . Excavate shallow impacted subsurface soils in the source delineated by MW8 / SB5 , SB6 and SB7 . Excavation is anticipated to extend 5 to 7 feet bgs in depth . Excavation activities should be conducted during a period of low water to minimize groundwater infiltration into the excavation pit . It is recommended to start excavation in the southwest corner and proceed to the northeast . Screen soil with Photoionization Detector utilizing a heated headspace method . There will be some clean overburden in the southwest corner . Prepare to separate as much as 250 loose cubic yards of clean overburden during the excavation process . Separate clean overburden to use as backfill . MDT will provide a Grizzly Screen to filter out larger rocks and boulders from the excavation . Excavated soil may need to be screened twice to separate larger rocks and boulders . Screened rocks and boulders may be used as backfill . Anticipate some groundwater infiltration into the excavation boundary . No dewatering activities are approved during excavation activities . Excavate in a strategic manner to minimize the disruption of groundwater on excavation activities . Transport impacted soil to a one - time landfarm facility at the MDT Ferndale facility . Contractor will present their excavation estimates based on a loose cubic yards unit cost . Please provide the costs for handling and screening material , to be divided between clean overburden to be placed back in the excavation and contaminated soil to be hauled to the one - time landfarm . Assuming a 25 % swell , base your bid on the excavation of 750 loose cubic yards of contaminated soil and 250 loose cubic yards of overburden . Actual volumes will be determined in the field . Remove the defunct septic tank if it interferes with excavation activities . The defunct septic tank appears to be assembled from treated timbers . Timbers will need to be disposed at a Class II Landfill . Contractor will inspect the defunct septic tank and have it pumped if sludge is present prior to the excavation . Itemize costs for sludge removal separately if they prove to be unnecessary . Collect confirmation soil samples . One composite sample is necessary per sidewall on every sidewall . Budget to collect a second sample per headwall on the following criteria : A discrete soil sample is determined necessary for contamination left in place . One sample as necessary to be used for direct contact criteria . One surface ( 0 - 2 ) sample . Analyze soil samples for Volatile Petroleum Hydrocarbons ( VPH ), Extractable Petroleum Hydrocarbons ( EPH ) screen . Fractionate EPH with Polycyclic Aromatic Hydrocarbons ( PAH ) if the Total Extractoble Hydrocarbon ( TEH ) value exceeds 200 ppm . Submit all soil samples to DEQ - approved laboratory for analytical services . All analytical invoices will be paid directly by MDT . Validate data , including the collection of duplicates , equipment , and trip blanks per DEQ guidance . Mix 1760 lbs of a dry powder Oxygen Releasing Compound ( ORC ) into the backfill . Utilize calcium peroxide , similar to ORC - A . Backfill the excavation in 6 - inch lifts and compact each lift to at least 95 % of the proctor . Provide compaction testing as needed . Provide construction oversight during excavation and backfilling activities . Excavation contractors and oversight personnel are required to have current 40 - HAZWOPER training with current 8 - hour refresher training . Submit a Cleanup Report to DEQ and MDT following cleanup activities and groundwater monitoring . The cleanup Report will follow the DEQ PTCS Cleanup Report Expectations guidance document . Reminder : this includes updating the RCP and completing applicable DVSFs . Landfarm Activities Review the Ferndale one - time landfarm application and permit ( attachment A ). Properly prepare the landfarm site at 13114 MT Highway 83 . Characterize soil hauled to landfarm by collecting one five - point composite sample per 200 cubic yards deposited at landfarm . Samples will be analyzed for VPH , EPH , and 8270 for SVOCs . During excavation activities , soil may be deposited on landfarm site , but deposited soil must be spread to a 6 ” lift within one week of completion of excavation activities . Place a berm along the southwest corner of the landfarm as necessary to control surface runoff . The berm may be placed following placement of soil as to facilitate the actual landfarm size . Till landfarm soil approximately 3 months after soil is spread . Till soil once prior to first snowfall in late fall and once in late spring post snowmelt . Continue with landfarm maintenance through 2026 and 2027 . Sample soil in Fall 2026 . Collect five - point composite samples per 200 cubic yards . Samples will be analyzed for VPH , EPH ( fractionate with PAH if necessary ), and 8270 for SVOCs . Annual Sampling event will native soil beneath landfarm soil to verify no leaching has occurred . Soil samples will be collected from 1 - 3 feet beneath native surface and analyzed for VPH , EPH ( fractionated with PAHs if necessary ), and 8270 for SVOCs . Validate all laboratory analytical data using DEQ ’ s Data Validation Summary Form ( DVSF ) found online under the Guidance dropdown at the Petroleum Tank Cleanup Section ( PTCS ) webpage . Contractor will obtain utility locates as necessary to complete the work . Post Excavation Groundwater Monitoring It is anticipated that MW - 8 will be destroyed by excavation . MW - 8 will need to be reinstalled . The replacement well should be 2 ” diameter with a screened interval from 4 - 14 ’ bgs . It will be completed with a flush mounted monument . Utilize a liquid tight cap and properly seal well annulus to prevent any potential corridors from surface water to groundwater . Measure static water levels , purge and sample the monitoring wells within 30 days of completion of excavation . Sampling should use a low - flow sampling methodology as outlined in DEQ guidance . Preserve samples in appropriate containers as directed by the lab .

Montana

2026-04-29