10/12/88 Special - Laserfiche WebLink

Home

42. 43. 44. 45. 46. Sampling data collected during the Remedial Investigation (RI) and Interim studies Report (ISR) demonstrated that the landfill facility has resulted in local contamination of groundwater by volatile organic compounds (VOC's). Nineteen specific VOC's were observed consistently in the unconsolidated sand aquifers located downgradient of the landfill site. VOC contamination is reaching groundwater within the Upper Sand and tunnel valley aquifers. These aquifers are bounded by the Grantsburg till and St. Lawrence Formation bedrock aquitards (p. 35, EIS). The pathway of release has been the percolation of leachate through the unlined bottom of the landfill and then through the unsaturated sands. The source of leachate generation is believed to be water infiltration through mixed municipal solid waste (garbage) deposited in the landfill since its inception. The bedrock aquifers appear not to be affected. Near surface soils beyond the WMMI landfill property line, local air quality and nearby surface water bodies have not been affected by the contamination (p.35, EIS). The contaminant plume originating at the landfill follows the direction of regional groundwater flow towards the south- southeast, until it encounters a tunnel valley and the local bedrock high located on the west edge of the Hunters Hill's subdivision. At this point the plume has deflected with a southern lobe flowing to the south and slightly west, following the higher pe---meabi!ity sediments of the tunnel valley. North of the bedrock high the plume margin has reached only as far as monitoring well number 35BB, which is located 200 feet east of Sunfish Lake Blvd. at the southern end of Sunfish Lake (p.36, E~S) . The contaminant plume extends approximately 2,500 feet southeast of the limits of fill placement, and is roughly 2,500 feet in width at its broadest point. The area of the plume with ~he highest concentrations (above !,000 ug/!) of the contamination is located ir~.ediate!y southeast of the landfill and extends to 1,600 feet from ~he landfill. Maxin"-.n total VOC concentrations are cbse_-ved to be approximately 3,000 ug/! in an area of the tunnel valley a~aifer ir-n-e~iate!y east cf the fill area. Ethyl ether and tetrahydrofuran (THF) appear to be ~he predominant compounds in the groundwater east cf the landfill while halogenated VOC's appear to be predominant in the groundwater souuh of the fill area (p.36, EiS). 'That the response action which has been approved by the MPCA (resulting from ~ne 1985 consent order) to address ground water ~-=~ ~ has five basic components: c ........... a._on - A final cover system with surface ~anoff controls and a double barrier to limit infiltrauicn cf water. - A groundwater f!o~ barrier well system to restrict migration of contaminants from the site. - A ground water recovery we!! system to capture and treat contamination that has already migrated from the site. 6