SBCT Final EIS - Govsupport.us

Chapter 3 ⎯ Affected EnvironmentLake Waiau, near the summit of Mauna Kea, located approximately 8 miles from PTA, is the nearestknown surface water body. There are also three freshwater springs in Pohakuloa Gulch on the slopeof Mauna Kea known as Hokupani Spring, Waihu Spring, and Liloe Spring (USARHAW and 25th ID[L] 2001b, 1996).One perennial stream occurs downstream of the PTA. This is Waikoloa Stream, which heads in theKohala Mountains, runs north parallel to State Highway 19, and discharges into Kawaihae Baythrough the Waiulaula Gulch (State of Hawaii 2002b). The proposed PTA Trail route crosses WaikoloaStream near the rock wall south of Highway 19, in the upper reach of Waiulaula Gulch.FloodingThe cantonment and airfield areas of PTA, north of Saddle Road, are on land that slopes gently to thewest. Under some circumstances, the runoff from the south slope of Mauna Kea could exceed thedrainage capacity of the area and result in temporary flooding or localized ponding. However, thesoils in the area are permeable, and the underlying lava flows contain sufficient secondary permeabilitythat infiltration to the subsurface is rapid.The civil defense tsunami evacuation map in the area of Kawaihae Harbor shows the evacuation areaas extending inland beyond the Kawaihae-Mahukona Road (Highway 270) to an elevation of about50 feet amsl (PDC 2001). The area west of the highway and north of the road to Spencer Beach Park,including the harbor, lies within the evacuation zone (USAG-HI 2004).Surface Water QualityAccording to Hawaii’s 1998 305(b) report, most of the state’s water bodies have variable water qualitythat declines when stormwater runoff carries pollutants into surface waters. The most significantsurface water pollution problems in Hawaii are siltation, turbidity, nutrients, organic enrichment, toxins,pathogens, and pH from nonpoint sources, including agriculture and urban runoff (USEPA 1998).Few data on surface water quality are available for the PTA watersheds. As stated above, there are noperennial streams within PTA. According to the 303(d) List of Impaired Waters in Hawaii preparedunder the Clean Water Act, none of the streams in the PTA are listed as impaired (HDOH 2004).Marine waters north of Waiulaula Point are considered to be Class A waters rather than Class AA.The objective of Class A marine waters is to protect recreational and aesthetic uses. Pelekane Bay/Kawaihae Harbor are identified on the 303(d) list as impaired water bodies due to turbidity and wereassigned low priority for development of TMDLs (HDOH 2004). Construction of the Kawaihae Harborin 1995 had adverse effects on coral growth and water quality due to changes in sediment inputsin Pelekane Bay (Tissot 1998).Groundwater OccurrenceGroundwater occurrence on the Island of Hawaii is not well studied due to the younger age of the island,continuing volcanic activity, and the greater thickness of the volcanic deposits. Rainfall is theprimary source of groundwater recharge on the Island of Hawaii. The geology of the island is characterizedby highly permeable lavas from which little or no runoff occurs. Most of the precipitation percolatesrelatively quickly to the underlying groundwater body and then moves seaward, discharginginto the coastal waters (Stearns and MacDonald 1946). The Island of Hawaii has the highest rechargerate among the Hawaiian Islands, with a rate of 188.4 cubic meters per second (Lau 1983). Sustainableyields for each of the island’s aquifers are considerably less and are described below for each aquifersystem underlying PTA (USAG-HI 2004).February 2008 3–27 2/25th SBCT Final EIS