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these experiments, Shell obtained permission to install awaste-injection well <br />(Well D-1) near the mouth of Horse Draw to dispose of the waste water. <br />Disposal well D-1 was drilled, cemented through the Mahogany Zone and <br />completed with 7-inch pipe to the base of the leached zone of the Lower Aquifer. <br />The lower 50 feet of the pipe was slot-perforated for waste injection just above <br />the dissolution surface. Incomplete data obtained from the Colorado Department <br />of Health indicate that over 3-million gallons of sodium-bicarbonate waste water <br />with a specific conductivity of _75,000 uS/cm was injected into the Lower Aquifer <br />from January through July 1971. Summary data on Well D-1 from EPA (1974) <br />show that the well permit would have allowed over 10-million gallons of waste to <br />be injected into D-1. The large volume of injected wastewater would have <br />resulted in an original plume with an estimated diameter of +/- 500 ft using <br />porosity data in Robson and Saulnier (1981). Using data for hydraulic <br />conductivity and head potential in the Horse Draw area for the Lower Aquifer <br />from Robson and Saulnier (1981), the estimated travel distance for the leading <br />edge of the saline plume in the 28 years since active operations at D-1 could be <br />as much as 5000 ft. Well D-1 is located about 3600 ft up or side gradient from <br />American Soda well 21-3. Therefore, it is possible that saline water from D-1 <br />was encountered and sampled from the Lower Aquifer completion at well 21-3. <br />Further, the USBM coreholes in Horse Draw (Snyder and Terry, 1977) and data <br />from the drilling of well 21-3 indicate that fractures may be present in this area. <br />Such fractures could have allowed Lower Aquifer water to move upward from the <br />Lower Aquifer to the Upper Aquifer under the local upward gradient near <br />Piceance Creek. Saline water is observed in the Upper Aquifer in Well 21-3 <br />(Table 1) and this salinity may be a result of migration of the plume from disposal <br />well D-1. <br />Another example of Lower Aquifer contamination from extraneous processes <br />may be found in Horse Draw. American Soda Well 29-4 is located in Horse Draw <br />approximately 2700 feet downgradient from the USBM Horse Draw experimental <br />shaft that was constructed in 1977. The shaft was intended to provide access for <br />resource-recovery experiments in the oil shale and saline-mineral section of the <br />Lower Parachute Creek Member. The USBM shaft was bored with a 10-foot <br />diameter cutting head to a depth of 2137 feet bgs, penetrating both the Upper <br />and Lower Aquifers and the saline zone. Boring operations lasted 237 days <br />(Utter and Hawkins, 1978). Boring operations were suspended several times <br />during the drilling operations. The drilling fluid was aloes-filter-cake polymer <br />"mud" mixed with saline water designed to reduce dissolution of soluble minerals. <br />However, Cox (1979) reports that the salinity of the mud was not great enough to <br />stop in-hole dissolution of nacholite and halite. During several down-time periods <br />amounting to 59 days during drilling, the Lower and Upper Aquifers would have <br />been exposed to this saline mud. <br />After the boring was completed, a steel shaft liner was installed to seal off the <br />shaft from local groundwater. The steel shaft liner was floated into place in the <br />Senfember 7. 1999 8 <br />