In 1994 a sampling of a drinking water well by the Colorado Department of Health (CDH), in accordance with Colorado drinking water regulations for "non-transient non-community" systems, showed the well containing CCl4 in concentrations (9 parts per billion [ppb]) above the Maximum Contaminant Level (MCL) [5 ppb]. Four other drinking water wells within a 1/2 mile radius also were tested with no detections of CCl4.On October 25, 1994, EPA initiated the Removal Action and began supplying bottled water to 33 residents. A Treatability Study was conducted by EPA’s Emergency Response Team (ERT) to determine the best method of removing the CCl4, which ranged from 6 to 99,000 ppb. Four air strippers and 29 carbon filters were installed on 33 homes. A thorough investigation was conducted by EPA Contractors (TAT and REAC) in 1995 and 1996. A source removal system was installed in March of 1997; it consisted of 4 pumping wells, 6 reinfiltration wells, a shallow tray air stripper system, and carbon polishing tanks.
The source area around Cornelius and Vosler Streets, where we are pumping and treating groundwater, continues to clean up slowly. We have pumped, treated and reinjected over 22.2 million gallons of contaminated water as of July 18, 2012.
The carbon absorption systems continue to work well. We found only three systems this year experiencing breakthrough of contaminant between the primary system and secondary carbon tank.
Compared to data from 2012, the average carbon tet concentration of all residential well samples decreased to 13.4 ug/L from 16.3 ug/L. After 18 years of treatment by individual home systems and 16 years of pumping and treating in the source area, the residential sampling results for carbon tet can be summarized as follows:
4 homes at non-detect
11 homes between 0 and 5 ug/L;
7 homes between 5 and 11 ug/L;
2 homes between 11 and 20 ug/L;
3 homes between 21 and 49 ug/L;
0 homes between 51 and 100 ug/L; and
1 home greater than 100 ug/L, with the highest at 315 ug/L.
