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To address both soil and groundwater 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 of the underlying soils was conducted between May 2019 and January 2020. Following the submission of the semi-annual report documenting project status for the second half of 2019, a meeting between DAI and WDNR personnel was held on January 21, 2020. The outcome of the meeting was that further chemical treatment would not be required and that installation of the proposed sub-slab depressurization (SSD) system should be completed. The SSD system in the 2410 and 2412 tenant spaces was being installed during the first semi-annual period of 2020. The SSD system startup was initiated on August 10, 2020, and the first verification vacuum testing was performed on August 24, 2020.
A Remedial Construction Report (Construction Report) dated September 8, 2020, was submitted to WDNR to document the chemical treatment of Perc contaminated soils and confirmation sampling results, as well as the final design and operation of the sump water treatment system and the final design and startup performance testing of the SSD system. The Construction Report was approved in a letter dated November 23, 2020, but WDNR required that another round of sub-slab vapor sampling and confirmation vacuum testing be completed before Case Close Out could be requested. The first round of the additional sampling and verification testing was performed in December 2020; a second round is planned for early February 2021.
Additionally, the sump water treatment system within the Ace Hardware building has continued to operate successfully throughout the second semi-annual 2020 period. Required monthly discharge samples demonstrate that all contaminants the sump water (including Perc), are reduced in concentration to levels well below the permitted discharge limits, and generally below the method detection limits. Electronic reporting of the discharge sample results is completed monthly, as required under WPDES permit WI-0046566-07.
Two (2) quarterly groundwater sampling events were also conducted during the second semi-annual 2020 reporting period to assess the groundwater concentration of Perc in MW-5. The third quarter sampling was performed on July 14, 2020, with results provided in the Quarterly Groundwater Sampling Report dated July 31, 2020, and the fourth quarter groundwater sampling was performed on October 12, 2020, and the results were provided in the Quarterly Groundwater Sampling Report dated November 20, 2020.
The quarterly sampling results continue to show that the Perc concentrations in the area of MW-5 remain at concentrations above the Enforcement Standard (despite additional chemical injection in August 2019), with only a modest decline in groundwater concentration. The results of the most recent groundwater sampling from October 2020 indicate a Perc concentration in MW-5 that is generally consistent with the three (3) previous quarters. Within the last year, the Perc concentrations have remained stable, and the Trichloroethene concentrations remain below the Preventative Action Limit. Another quarterly sampling event is planned for January 2021 and the sampling results will be submitted in a quarterly report. A second quarter sampling will be scheduled.
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