Hydrogeologic Analysis of the Delphi Corporation Site, Wyoming Michigan Mark Bryson, Emily Daniels, Sara Nagorsen, Kirk Perschbacher, Joe Root, Jason Stewart, Alex Snider, and John Vogelzang (Student Scholarship Day Poster Geo 440 Geohydrology Fall 2006 Dr. Peter Riemersma) Introduction The Delphi Corporation is located in nearby Wyoming, Michigan (See Figure 1) and has received recent media attention, one reason it was selected as a focus for our class project in Geohydrology (Geo 440). We analyzed data from soil borings, monitoring wells, pump tests and groundwater samples collected by consultants at the site General Motors constructs a spark plug facility on what used to be agricultural fields 1987 Groundwater found to be contaminated with a variety of chemicals. Leaking underground storage tanks likely source for main organic contaminants of concern (like TCE) Delphi Corporation takes over facility 2005 Grand Rapids Press Article highlights unhappy homeowners living above contaminated groundwater plume Objectives 1.To identify the subsurface lithology at the site 2.To identify the direction of groundwater flow 3.To identify the migration of contaminated groundwater plumes 4.To estimate the groundwater flow velocity at the site (3.2 feet per day – not shown on poster) Subsurface Lithology The subsurface lithology at the Delphi site consists of a sandy unconfined aquifer containing lens of clay overlying bedrock (See Figures 3, 4 and 5). Note that the depth to bedrock and the resulting thickness of the sand aquifer is highly variable. The axis of a probable east-west channel is visible in Figure 4 near MW325 as the bedrock appears eroded in this location and contains coarse sand and gravel channel lag sediment. The bedrock high and reduced thickness of the aquifer in the vicinity of MW 201 and MW110 (Figure 5) will affect the hydraulic gradient at the site (see Figure 6) Figure 1 Location of Delphi Site in Wyoming Michigan. Figure 2 Location map showing well locations, geologic cross-sections. Figure 4 North-south geologic cross-section. Figure 3 East – west geologic cross-section. Figure contaminant plume map showing concentrations of total volatile organic compounds. Figure 6 Water table elevation and groundwater flow map for January Figure 9 Concentrations of cis-1,2, Dichloroethene in August 2004 (yellow is lower, red is higher). Figure 8 Concentrations of TCE in August Figure 10 Concentrations of vinyl chloride in August Figure 5 North-south geologic cross-section. Groundwater Flow and Contaminant Plume Migration Groundwater flow at the Delphi site is to the north. A high hydraulic gradient results in the region of the “thin” aquifer (Figure 5), similar to the increased water velocity observed in rivers where the channel narrows. Figure 7 illustrates that a narrow plume of contaminates have moved in the direction of groundwater flow and have migrated off-site. Degradation of TCE TCE degrades into cis 1,2, DCE which further degrades into vinyl chloride. Figures 8, 9 and 10 provide a snapshot in time of TCE and it’s biodegradation products. Note that the Drinking Water Maximum Concentration Limit for TCE is 5 ppb and for vinyl chloride is 2 ppb. Highlights 1.Identification of sand and gravel channel eroded into bedrock. 2. Increase in hydraulic gradient attributed to sudden thinning of aquifer over bedrock high. 3. Illustrates offsite migration of narrow contaminant plume and delineates distribution of TCE and degradation products. Source of raw data is Haley and Aldritch reports