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Background: To address Tetrachloroethylene (Perc) contamination identified in the area of a former dry cleaner (tenant spaces addressed as 2410-2412 10th Avenue) at the Sunrise Shopping Center facility, chemical treatment was conducted between May 2019 and January 2020. Additionally, a sub-slab depressurization (SSD) system installed in the 2410 and 2412 tenant spaces began continuous operation in 2020. No additional remedial actions are planned for this Site at this time. Groundwater sampling for per- and polyfluoroalkyl substances was approved as complete in a WDNR email dated November 7, 2022.
Quarterly Monitoring Well Sampling: Two (2) quarterly groundwater sampling events were conducted during the first semi-annual 2024 reporting period. Quarterly groundwater sampling for Perc was conducted at MW-5 on January 22nd April 25, 2024, with results provided in Quarterly Groundwater Sampling Reports dated February 29 and May 22, 2024. The most recent quarterly sampling results indicate that Perc concentrations remain above the Enforcement Standard, but continue to remain generally stable. Quarterly sampling will continue until a Case Closure Letter is issued for the Site.
Sump Water Treatment System Sampling: Three (3) sump water treatment systems were in operation within the Ace Hardware building during the January-June 2024 semi-annual period. As a result of a collapse of the discharge sewer leading from the building, the sump water from Sump #1 that discharged to permitted Outfall 001 needed to be re-routed. Sump #1 discharge was combined with the discharge from Sumps #2 and Sump #3, and beginning on May 22, 2024, all water has been discharged via permitted Outfall 011. A permit modification was submitted to the WDNR describing the change in discharge routing and notifying WDNR that the discharge to Outfall 001 ceased as of May 7, 2024.
Discharge sampling is completed monthly and the sample results are submitted electronically, as required. The results of the monthly sampling continue to show all contaminants in the treated effluent being reduced to levels well below the permitted discharge limits, and generally below the Limits of Detection (including Perc concentrations above the Enforcement Standards in sump influent samples). Therefore, the treatment systems continue to be effective in preventing any contaminants from discharging into the City of South Milwaukee stormwater sewer system and ultimately Lake Michigan. Additional remediation of the contaminated groundwater is not being proposed at this time since the existing groundwater recovery from the Ace Hardware building sumps has been effective in limiting further groundwater contaminant migration and reducing contaminant mass. Therefore treatment of the groundwater collected from the Ace Hardware sumps will be continued.
Vapor Sampling: At the request of WDNR, additional vapor intrusion investigations were initiated during the first semi-annual 2024. The sampling procedures were consistent with the protocol proposed in the Additional Vapor Investigation Work Plan dated January 18, 2024. The vapor sampling was initiated on March 25th by placing passive indoor air samplers inside the 2410 and 2412 tenant spaces, as well as within the Ace Hardware building. Vacuum readings were also collected at this time. Additionally, VOC canister samples were collected from the three (3) Ace Hardware sumps. Pressure readings indicated continued operation of the SSD system. The analytical results from this sampling event showed compliance for all samples collected in the Ace Hardware building and the 2412 tenant space. However, the passive air sample results collected in the 2410 tenant space were observed above the vapor action level. Therefore, modifications to the SSD system were undertaken, including increasing the fan size. Re-testing of the 2410 tenant space will be performed upon completion of the SSD system upgrades.
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