The Transport of MTBE through Groundwater in the Bootheel, an Alluvial Setting John Pate Department of Natural Resources, Missouri Geological Survey, Geological Survey Program, Environmental Geology Section, Subsurface Investigations and Waste Management Unit
What is MTBE? Physical and Chemical Properties Liquid Soluble in water Does not cling to soils Volatile organic compound (VOC) Flammable Colorless Taste and smells like turpentine Methyl tert-butyl ether (C " H $% O) Uses Fuel additive Octane enhancer Lower air pollution emissions Removes gallstones
History of MTBE Use Used in the United States since the 1979 as a replacement to lead in gasoline The Clean Air Act Amendments of 1990 Used at higher concentrations; up to 15 percent per volume, between 1992 to 2005 to meet oxygenate requirements of the Act EPA issued a Drinking Water Advisory, December 1997 20 to 40 ug/l Energy Policy Act of 2005 Switch from MTBE to ethanol
Santa Monica, California Population approximately 100,000 1995 high levels detected in city wells Charnock Well field shut down for 14 years 85% of potable was imported. Updated water treatment system Granular Activated Carbon filter Noteworthy Release Clean up and litigation cost more than $75 million 2008 Settlement = $423 million
Missouri Bootheel Mississippi Alluvial Plain Physiographical Region
Southeastern Lowlands Groundwater Province Qal - Quaternary System Alluvium sands, gravels and clays Up to 250 Feet Thick T - Tertiary System Wilcox Group and Midway Groups K - Cretaceous System Owl Creek and McNairy Formations
Chief aquifer in the area. May yield 3,000 gpm to wells in some localities. http://dnr.mo.gov/pubs/wr46.pdf
Missouri Well Construction Rules Definition of Alluvium 10 CSR 23-1.010(24)(A) Alluvium is a general term for clay, silt, sand, gravel or similar unconsolidated material deposited during comparative recent geologic time by a stream or body of running water as a sorted or semi sorted sedimentary deposit.
Missouri Well Construction Code Area 5 Bedrock (10 CSR 23-3.090(1)(A)) Set no less than eighty feet (80') of casing, extending not less than thirty feet (30') into bedrock Unconsolidated Material (10 CSR 23-3.090(5)(B)) No less than twenty feet (20') of casing shall be set above the screened or perforated interval of the well
Public Water Wells vs. Tanks Casing Depth (CD) (ft) 20 CD 80 80 CD 120 120 CD Unknown
Case Study
City Well 1 Depth of Well = 101 feet Casing Length = 66 feet Screen Length = 30 feet Highest MTBE Concentration = 35.5 ug/l Drilled in 1995 City Well 2 Depth of Well = 100 feet Casing Length = 77 feet Screen Length = 30 feet Highest MTBE Concentration = 2.12 ug/l Drilled in 2005 Site Facts
Site Facts Site Setting Thickness of alluvial sands and Gravels = 185 feet Shallow groundwater depth =23 to 24 feet City wells constructed to target zones of high hydraulic conductivity
85 to 105 feet: Sand and Pea Gravel
Identifying MTBE Zones Method 1 Install PVC 1 inch temporary monitoring wells Approximately 70 feet of riser Approximately 30 feet of screen Collect static water levels (SWL) Collect groundwater samples Method 2 Geoprobe SP16 Collect groundwater samples from varying depth intervals
Geoprobe SP16 Method http://geoprobe.com/sp16-groundwater-sampler
Feet
Feet
Feet
Findings Wider MTBE plume at a depth of 46 to 50 feet Close to original source MTBE transitions from shallow to a deeper groundwater zones Narrow MTBE plume at a depth 76 to 80 feet. Indicates a potential preferential pathway Approximate MTBE plume distance = 3,319 ft or 0.62 miles
Conclusion MTBE is soluble in water and does not cling to soils Can transition from shallow to deeper groundwater zones Plume narrows further from the source indicating a preferential pathway MTBE plume influenced by city wells completed in high hydraulic conductivity groundwater zones Drinking Water Advisory limit 20 to 40 ug/l Costly to clean up
Questions?