2014-06-19_GENERAL DOCUMENTS - C1981041 (5)

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Roadside Mine a #00489 -0004 ` Huddleston -Bern• 06/19/14 ri <s T,. '$, HC Final Hazard Evaluation As indicated above, based upon our observations, HBET believes that the risk of a catastrophic failure of the earthen plug is low. In addition, based upon our estimates of water `ponded' behind the earthen plug, HBET believes that the risk of impacts to Interstate 70 from a catastrophic failure of the plug is low. Water and/or debris associated with a failure could impact the 1 -70 off ramp and/or could flow beneath the underpass. However, the energy loss at the base of the steep hills would likely reduce the velocity of flow significantly and as a result, HBET believes that there is a low risk to human health and safety for vehicles on I -70, the 1 -70 off ramp, and the I -70 underpass. Also, based upon the site topography, the majority of any water and /or debris associated with a failure would flow south of the existing fruit stand in the northern portion of the site. Water and/or debris could reach the fruit stand building; however, as indicated above, HBET anticipates that the velocity of flow would be fairly low and as a result, HBET believes that there is a low risk to human health and safety for workers and/or patrons of the fruit stand. Recommendations Although HBET believes that the risk of a catastrophic failure is low and that the consequences of a failure are minimal with regard to human health and safety, the stability of the earthen plug could change over time. Dewatering of water ponded behind the earthen plug will tend to result in a gradual decrease in the seepage flows and decrease in saturation in the surrounding soils. However, the conditions should be monitored at least daily and HBET should be immediately contacted to re- evaluate the hazards if any of the following conditions occur: • The seepage at the south end of the portal becomes cloudy (* *critically important * *) • The seepage at the south end of the portal suddenly (within —12 hours) increases dramatically or ceases completely • The seepage below the retaining wall at the north end of the portal suddenly increases dramatically • The zone of saturation at the south end of the portal doubles (it will likely increase some over time) • Saturated soils are observed elsewhere along the face of the fill slope • Slumping or other evidence of mass earth movement is observed • Any other dramatic change in the conditions at the site General The conclusions and recommendations above available information, and upon our experience. only for the subject project. are based upon our observations at the site, The conclusions and recommendations are valid X:12008 ALL PROJECTS100489 - JE Stover Associates Inc`.00489.0004 L061914.doc