The Oak Grove Village Well Site addresses concerns for human health from concentrations of TCE and several other VOCs which have been detected in samples from La Jolla Spring since the early 1990s. Concentrations in spring water samples have ranged from less than 1.0 to 12.0 µg/L in samples collected by the USGS, MDNR, and a PRP consultant. Other VOCs detected have included cis-1,2-dichloroethene, Freon 11, Freon 12, and Freon 21.
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Air sampling conducted within the Cave Complex from March 2013 until November 2015 continued to show the presence of the same contaminants that were detected from 2002-2005. TCE was detected as high as 660 µg/m3 in cavern air in October 2015.
Meramec Caverns voluntarily ceased cave tours in March 2016 until TCE concentrations could be decreased to below levels of health concern. In order for the tours to resume, the potentially responsible party (PRP) took further actions to lower TCE levels. The PRP has installed a permanent airlock; improved the air-sealing and ventilation control at the main entrance; installed water treatment system to remove TCE from water used to wash cave floors; installed a vent well in the roof of the cave to remove TCE vapors; installed sub-slab depressurization systems in the ball room, vault and gift shop area. The cave tour area was approved to reopened on August 5, 2016.
The PRP entered into an Administrative Settlement Agreement and Order on Consent (ASAOC) with EPA in July 2016. All work required under the July 2016 ASAOC has been completed, other than the continuing operations specified in the Post-Removal Site Control Work Plan (PRSCWP). The PRP has met the requirements of the July 2016 ASAOC by installing a combination of active and passive air controls to alter air flow patterns within the cavern, thereby reducing concentrations of TCE in cave air. Operation of these controls has succeeded at maintaining TCE concentrations below 6.0 μg/m3 averaged over an 8.5-hour workday period. Compliance is verified by routine PAM sampling. Operation of the air controls will continue as described in the USEPA-approved PRSCWP. Continuing operations include O&M of existing systems and routine monitoring to verify performance and evaluate potential secondary effects. The PRSCWP also specifies contingency actions if future conditions cause TCE concentrations to exceed the level of concern.
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