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HDD "Fact Sheet" <br />Risk of Inadvertent Release (IR) or `Frac-Out' <br />• Depends on geology and geotechnical characteristics and drilling methods and procedures <br />• Sandysoils are usually better due to greater strength, measured by friction angle <br />• Mitigating Strategies <br />• Design considers geology and geotechnical characteristics <br />• Estimate formation limit pressure <br />• Estimate drilling pressure <br />• Drill with pressure instrument — real-time downhole measurement <br />• •bmpare real-time with estimated pressure — allows adjustment before IR occurs <br />Casing pipe at each end to protect near -surface soils and features <br />Intersect Pilot Hole — Drill from both sides to reduce drilling pressure <br />• Divers to monitor within river <br />Risk of Leak or Damage to Pipe and Ability to Repair <br />Damage is very unlikely — almost always during construction or testing before being placed into operation <br />Pipe can be monitored for Teaks or damage <br />Pressure Testing (305 psi/ 150/ 80) <br />Repairs can be achieved by: <br />• Sliplining — Pull a smaller pipe through damaged pipe <br />• Excavation - If depth is shallow and on land <br />