SBCT Final EIS - Govsupport.us

Chapter 3 ⎯ Affected EnvironmentFloodingBased on the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRM),SBMR is located in Zone D, which refers to areas that have not been mapped. The area containing thereach of Waikele Stream adjacent to WAAF has not been mapped.Surface Water QualitySBMP, WAAF, and SRAA are located in the Kaukonahua and Waikele watersheds. The State of Hawaiiclassifies these watersheds as second tier Category I under the Hawaii Unified Watershed Assessment.Based on the Hawaii Unified Watershed Assessment there are four watershed categories.Category I watersheds are those in need of restoration because they do not meet, or are close to notmeeting, clean water and other natural resource goals. Category 1 watersheds are further divided totier 1 and 2 watersheds. Tier 2 watersheds include those containing or drained by 303(d) impaired waterbodies (HDOH 1998).The classification of the Kaukonahua watershed was based largely on the fact that the coastal receivingwater, Kaiaka Bay, is classified as an impaired water body based on pathogens, nutrients, ammonium,algal growth, and turbidity (HDOH 2004). Kaukonahua Stream is not identified as an impairedwater body. HDOH has been developing total maximum daily loads (TMDLs) for Kaiaka Bay Watershedwith completion expected in 2008 for North and South Fork Kaukonahua Stream, and with ongoingphased TMDL development in Kaukonahua receiving waters, including Wahiawa Reservoir,lower reaches of Kaukonahua Stream, Kiikii estuary, and Kaiaka Bay (Koch et al. 2007).Waikele Stream is listed as an impaired water body based on nutrients and turbidity. TMDL developmentis in progress (HDOH 2004). The Waikele watershed drains to Pearl Harbor, which is alsolisted as an impaired water body based on nutrients, turbidity, suspended solids, and polychlorinatedbiphenols (PCBs). HDOH is in the process of developing TMDLs for listed water bodies in PearlHarbor Watershed (HDOH 2007).Water quality in the Wahiawa Reservoir has been affected by nutrients in the past. As mentionedabove for SBMR, the State of Hawaii classifies the Kaukonahua and Waikele watersheds as secondtier Category I, under the Hawaii Unified Watershed Assessment (HDOH 1998).The Army has started an assessment of offsite potential for contaminants at SBMP under the OperationalRange Assessment Program (ORAP). While still in the early stages of the assessment, preliminaryresults show no contamination of surface water by explosive residues.Groundwater OccurrenceThe groundwater resources on Oahu are well developed, yielding more than 635 million gallons perday (mgd) from numerous hydrogeologic units and aquifer basins. Approximately 50 percent of thefresh water used in Hawaii, and about 99 percent of the drinking water, is from groundwater (Nicholset al. 1996).Groundwater on Oahu occurs in basal aquifers, perched aquifers, and dike-impounded zones. Thebasal aquifer is a freshwater lens occupying porous and permeable volcanic rocks beneath the island.The freshwater lens is thickest near the center of the island and tapers off toward the edges of the island.Fresh water also occurs at higher elevations in perched aquifers and in dike-impounded zones,both of which are classified as “high-level” groundwater. Dike-impounded water is groundwatertrapped behind vertical dikes. Perched aquifers are saturated permeable layers or fractured zones thatoccur above the basal lens and are separated from it by unsaturated deposits (USAG-HI 2004).February 2008 3–20 2/25th SBCT Final EIS