midessa ground water plume

INTERSECTION OF COUNTY RD 1290 & CR 128

The Site consists of three contaminated ground water plumes originating from an unidentified source(s). The contaminant plumes are located along County Road 1290, between Interstate 20 to the south, and Interstate Business 20 to the north, in the western part of Midland County. The Trinity and Ogallala aquifer is the only ground water source for drinking water in the site area. The water table is shallow as 19 feet below the ground surface in the Ogallala aquifer and the base of the lower Trinity aquifer is approximately 95 – 105 feet below ground surface. The Triassic red beds form the base of the aquifer. Ground water flow in the aquifer is generally to the south-southwest. The following site map illustrates the public and private water supply wells and the monitoring wells installed in June 2011. The extent of one or more volatile organic chemicals (VOCs) is illustrated in the colors of the respective plume areas for tetrachloroethene (PCE) as shown in purple, trichloroethene (TCE) as shown in green, cis-1,2-dichloroethene (cis-1,2-DCE) as shown in red, 1,4-dioxane as shown in blue, and 1,1-dichlorothene (1,1-DCE) as shown in yellow. The second round of monitoring well installation began the week of December 12th 2011, and resumed the week of January 2nd 2012. Sampling of the new wells was conducted the week of January 16th 2012 and January 30th 2012. Tetrachlorethene contamination was detected at all four of the new well locations on the south side of Interstate 20. Locations of the existing and recently installed monitoring wells are shown in the figure below. Ground water monitoring wells were also installed in June 2011 to provide data on the ground water flow direction, vertical and horizontal distribution of the contaminants, and identification of possible source areas as shown on the figure immediately below (Note: monitoring wells MW-09 and MW-23 were not installed during this field event). In addition, soil vapour monitoring wells and air sparging test wells were installed at the TexCap property. The new monitoring wells and selected private supply wells were sampled the week of July 25, 2011. A second round of vapor intrusion sampling was collected the week of July 11, 2011, to assess differences in VOC concentrations between the summer and winter months.

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