Virginia Capes Range Complex Final Environmental Impact Statement

VACAPES Range Complex FEIS/OEISChapter 3 Affected Environment andEnvironmental Consequences3.1 – Bathymetry and Sediments3.1.3 Environmental ConsequencesThe primary effect of the Navy’s training activities in the VACAPES Study Area would be explosions inthe water and the deposition of expended training materials on the ocean bottom and their accumulationover time. The numbers and sizes of explosions that are summarized in Table 2.2-7 were used to evaluateeffects from explosions. Data from Tables 2.2-4, 2.2-5, 2.2-6, and 3.1-2 were used to determine the totalamount training materials deposited annually per square nautical mile of each training area and the entirestudy area.This section considers only the physical effects of these materials on bathymetry and sediments. Theeffects associated with the chemical properties of expended training materials are discussed in Section3.2.2. Effects of explosions and debris deposition on benthic organisms are addressed in Section 3.6,Marine Communities.3.1.3.1 No Action AlternativeExplosions in the WaterAs shown in Figures 2.2-1 and 2.2-5 through 2.2-10 and listed in Table 2.2-7, the No Action Alternativewould result in 1,411 explosions in the water each year from training in the VACAPES study area.Explosives would range from the 8-lb net explosive weight (NEW) charges in Hellfire missiles to the944.7-lb NEW charges in the nine MK-84 bombs that would be dropped annually in bombing exercises.All of the high-explosive MK-20, MK-82, MK-83, and MK-84 bombs that would be dropped at seawould be used in areas of deep waters and would explode before reaching a depth that could damage theocean floor or disturb deep sediments. Therefore, explosions in deep marine waters of the VACAPESStudy Area would not affect the bathymetry or sediments of the study area.Each year, 12 explosions of charges up to 20 lbs NEW would be conducted on the ocean bottom inshallow waters as part of mine neutralizations training exercises. Each charge would create a shallowdepression in bottom sediments, and would suspend a substantial volume of sediment in the watercolumn, causing a localized increase in turbidity. The turbidity increase would be short-lived, becauselarger particles would rapidly drop to the bottom and smaller particles would be dispersed by currents.Although the depressions would last longer, they would act as sediment traps, would soon be filled in,and would not have a lasting effect on bathymetry or sediments.Deposition of Expended Training MaterialsTables 2.2-4, 2.2-5, and 2.2-6 provide details on the numbers and sizes of the training materials expendedin each training area. The effects of expended materials from training activities on ocean bottomsediments were assessed as the number of items deposited per unit area of bottom surface. About1,816,383 training items would be expended annually under the No Action Alternative (see Table 3.1-2).Based on the VACAPES Range Complex sea space area of 27,661 nm 2 , this would be about 65.7 itemsper nm 2 . The density would range from less than one item annually per nm 2 in several of the trainingareas to 16,629 items annually per nm 2 in W-50C.Of the 1,816,383 training items, approximately 1,773,019 or 98 percent would be cannon shells (20, 25,30 or 40-mm) or small-arms munitions (.50-caliber or 7.62-mm bullets). These munitions (including thecase) are small, ranging from 2.75 to 5.5 inches long. Because of the small size and low density ofmilitary expended materials, sediment stability on the ocean bottom would not be affected by small-armsmunitions.Other military expended materials may be larger. However, two or more larger pieces would not likelysettle in the same vicinity, because training activities would seldom occur in the exact location, and oceancurrents would move the materials from where they entered the water to where they settled on the bottom.3-7 March 2009