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• pms POTENTIAL MINE SUBSIDENCE: an area that may <br />be subject to ground-surface displacement <br />caused by collapse of the voids formed in <br />rock by underground mining. The shaded areas <br />have been undermined but the effects of <br />subsidence could extend outward from these <br />areas. Residential or commercial <br />construction in these areas should be <br />undertaken only after a geotechnical <br />investigation determines the maximum possible <br />extent of past and future mining. <br />ph POTENTIAL HYDROCOMPACTION: an area which may <br />be subject to the downward displacement of <br />the ground surface by collapse of certain <br />low-density, weak soils after wetting. <br />Excessive wetting from irrigation, broken <br />water lines, surface ponding, or drainage <br />diversions can cause hydrocompaction. A <br />soils foundation investigation should be made <br />to determine the severity of this hazard and <br />ascertain effective mitigation methods. <br />es EXPANSIVE (SWELLING) SOIL OR ROCK: soil or <br />rock that contains clays that expand <br />significantly upon wetting and shrink upon <br />• drying. In the study area, the Mancos Shale <br />and deposits derived from the Manchos Shale <br />are especially prone to such changes in <br />volume. Expansive soil or rock may cause <br />structural damage to buildings, roads, and <br />pipelines and should be evaluated by a soils <br />and foundation engineering investigation. <br />• <br />PanhZS APPLICI~tIOP EXH-12 - 4 - <br />