Abstract  Beginning in November 2013 General Mills began testing and then mitigating buildings where there was a potential for vapor intrusion. As this first stage of the work, building testing and mitigation moves toward completion, the next stage of the project, soil gas contamination source response is beginning. On June 16, 2014 General Mills submitted a draft plan to the MPCA to begin this additional work. The MPCA reviewed the plan and sent comments back to General Mills. General Mills revised the work plan, which MPCA received on August 20, 2014. The MPCA reviewed and approved the plan in September 2014. The work plan and the MPCA’s response letter are below. (Older versions of the work plan are below under “site information.”)

Abstract  Ground water contaminated by the chlorinated organic compounds trichloroethene (TCE), cis-dichloroethene (DCE), and vinyl chloride (VC) has been found in the surficial aquifer beneath the Naval Aviation Depot at the U.S. Naval Air Station, Jacksonville, Florida. The affected area is designated Operable Unit 3 (OU3) and covers 134 acres adjacent to the St. Johns River. Site-specific ground-water flow modeling was conducted at OU3 using MODFLOW, and solutetransport modeling was conducted using MT3DMS. Simulations using a low dispersivity value, which resulted in the highest concentration discharging to the St. Johns River, gave the following results. At 60 years traveltime, the highest concentration of TCE associated with the Area C plume had discharged to St. Johns River at a level that exceeded 1×103 micrograms per liter (µg/L). At 100 years traveltime, the highest concentration of TCE associated with the Area D plume had discharged to the river at a level exceeding 3×103 µg/L. At 200 years traveltime, the Area B plume had not begun discharging to the river. Simulations using a first-order decay rate halflife of 13.5 years (the slowest documented) at Area G caused the TCE to degrade before reaching the St. Johns River. If the ratio of the concentrations of TCE to cis-DCE and VC remained relatively constant, these breakdown products would not reach the river. However, the actual breakdown rates of cis-DCE and VC are unknown. Simulations were repeated using average dispersivity values with the following results. At 60 years travel time, the highest concentration of TCE associated with the Area C plume had discharged to St. Johns River at a level exceeding 4×102 µg/L. At 100 years travel time, the highest concentration of TCE associated with the Area D plume had discharged to the river at a level exceeding 1×103 µg/L. At 200 years traveltime, the Area B plume had not begun discharging to the river. “Pump and treat” was simulated as a remedial alternative. The concentration of TCE at Area B trended rapidly downward; however, one isolated pocket of TCE remained because of the low-permeability sediments present at this area. The concentration of TCE at Area C trended rapidly downward and was below 1 µg/L in about 16 years. The concentration of TCE at Area D also trended rapidly downward and was below 1 µg/L in about 18 years.

Abstract  The United States Environmental Protection Agency (U.S. EPA), Office of Pollution Prevention and Toxics (OPPT), identified and chose trichloroethylene (TCE) for risk evaluation as part of its Existing Chemicals Management Program under the Toxics Substances Control Act (TSCA). TCE is a volatile organic compound (VOC) that is classified as a human carcinogen.  Its consumption in the U.S. is 255 million pounds (lbs) per year. TCE is widely used in industrial and commercial processes, and also has some limited uses in consumer products. Main Conclusions of this Risk Assessment This risk assessment identifies cancer risk concerns and short‐term and long‐term non‐cancer risks for workers and occupational bystanders at small commercial degreasing facilities and dry cleaning facilities that use TCE‐based solvents and spotting agents, respectively. EPA/OPPT also identifies short‐term non‐cancer risks for consumers and residential bystanders from the use of TCE‐containing solvent degreasers and spray-applied protective coatings.