SBCT Final EIS - Govsupport.us

Chapter 3 ⎯ Affected Environment11. Military training activities are the most likely source of the elevated concentrations, based on thetraining land use in these areas. Few of the concentrations exceeded industrial soil PRGs. The combinednon-cancer occupational health risk associated with exposure to the observed metals concentrationsfrom the soil investigation is just below the threshold of no further action. Excluding the calculatedvalues for iron, aluminum, and manganese (known naturally occurring metals), the combinedrisk is above the one in one million cancer risk threshold (which mainly results from lead), but iswithin the range of what is considered acceptable under some circumstances (USAG-HI 2004).The Army has been working with and continues to work closely with the NRC and HDOH to determinethe facts. The Army verified the presence of DU fragments on PTA during a scoping survey.The Army will continue this collaborative effort as it evaluates the results of these surveys and determinesthe response required to ensure the protection of human health and the environment from thepotential effects of DU.Geologic Hazards and SeismicityAreas with slopes greater than 30 percent are primarily limited to the slopes of Mauna Kea, north ofSaddle Road, and to the southern portion of PTA on the north-facing slope of Mauna Loa. The potentialfor slope failure and landslides would be greatest in these areas.The USGS has divided the island of Hawaii into Lava Hazard Zones based on the probability of coverageby lava flows. Other hazards from volcanic eruptions are not classified in this system. Zone 1has the highest risk and Zone 9 has the lowest. PTA overlies areas categorized as Zones 2, 3, and 8(County of Hawaii 2002). The eastern margin and northeastern corner of PTA are in Zone 2, which isclassified as having 15 to 25 percent of the land covered by flows since 1800. Most of the PTA is inZone 3, which has had 1 to 15 percent coverage by lava flows since 1800. Zone 8 has had no lavacoverage over the past 750 years, and only a low percentage of the area was covered in the past10,000 years. Zone 8 represents areas near or north of Saddle Road that are underlain by lava eruptedfrom Mauna Kea. PTA Trail is entirely within Zone 8. Infrequently, Hawaiian volcanoes erupt explosively.Kilauea erupted explosively in 1790, creating a surge of hot gases and fine dust that killed agroup of Hawaiian warriors and their families near the summit.Most of the earthquake activity that occurs in the Hawaiian Islands is centered on the island of Hawaii.A magnitude 7.2 earthquake in 1975 that originated beneath Kilauea was the largest earthquaketo originate in Hawaii during the past century. Hazards associated with earthquakes include groundshaking, liquefaction, landslides, and tsunamis. The 1975 earthquake generated a tsunami that killedtwo people and damaged property along the coast (USGS 1997).PTA is in an area in which there is a 10 percent probability that an earthquake will cause a ground accelerationof more than 40 to 60 percent of gravity in the next 50 years, with the likely size of theearthquake increasing to the south, in the direction of Kilauea and the southern coast. Ground accelerationof more than 40 to 60 percent of gravity roughly corresponds to earthquakes of magnitude 6.9on the Richter Scale and intensity IX to X on the Modified Mercalli Scale, which can cause considerabledamage in specially designed structures, and subsequently greater damage in regular and poorlydesigned structures, respectively. Most of PTA is underlain by hard rock with thin or no soils, soseismic waves would not be amplified. A severe earthquake occurred on August 21, 1951, and had amaximum intensity of IX and a magnitude of 6.9. Scores of homes were wrecked or damaged on theKona Coast on the west side of Hawaii. Rocks fell from cliffs, causing a 12-foot wave (USGS 2001).More recently, a magnitude 6.7 earthquake occurred on October 15, 2006 (USGS 2008). Numerousaftershocks occurred, power outages were widespread, and a disaster declaration was issued by GovernorLingle (CNN 2008).February 2008 3–17 2/25th SBCT Final EIS