Geology of the Hawaiian Islands

Transcription

1 Geology of the Hawaiian Islands Class April 2004 Any Questions? Local Environmental Issues Topics relevant to our study of the Geology of the Hawaiian Islands Deal with areas that we covered in this class, such as ground water, reefs and shallow marine environments These issues often in the local press What is Environmental Geology? Geology of today s Earth Tries to understand human interaction with the Earth s processes What is environmental Geology? Geology applied to solving environmental issues Human impacts on the environment Groundwater Waste disposal Local Environmental Issues Degradation of the Environment Sewage Discharge into Coastal Areas Runoff into the Coastal Areas Degradation of the Earth's environment Pervasive around the world Nearshore zone of the ocean is particularly at risk 1

2 competing purposes: Commercial Activity competing purposes: Transportation of goods and people Discharge of unwanted waste (domestic or industrial sewage) Bays, estuaries and nearshore environments among the most heavily polluted waters on Earth For reasons of convenience, entertainment and economics, people flock to the seashore and choose to live or vacation there, so degradation of this area is of great concern Our tourist-based economy is so dependent on having a nice near shore environment Many of the uses of the coastal zone would seem to be incompatible For example, should we fish or swim in waters used for waste discharge? In order to make decisions that affect the coastal zone, we need careful technical assessment and informed management actions Human impacts on the coastal zone are proportional to the nearby human population This suggests that we might have particular problems with the Hawaiian nearshore zone We have a state population of 1.2 million people That population has doubled in about the last 35 years All of our state's population lives within a few miles of the coast Most of the population makes use of the ocean for recreation Most of our waste products (sewage) ends up in the ocean Various of our land uses-- --housing development, agriculture, and so forth -- impact the nearshore environment 2

3 Sewage Discharge into Coastal Areas Prior to 1977, sewage was discharged into restricted area of Kaneohe Bay Severely damaged the reefs Sewage Discharge into Coastal Areas Also raw sewage discharged of into 40 feet of water off Sand Island Caused severe damage to reefs City of Honolulu corrected these problems in the late 1970's Solution takes into account the unique geologic environment of our islands Sewage Discharge into Coastal Areas Both of these sewage discharges have been diverted to deep ocean outfalls at water depths of 100 feet or more The slopes of the islands are very steep below 100 feet Local currents carry away sewage Sewage Discharge into Coastal Areas Impacts to the reefs from sewage discharges have ceased Formerly damaged areas are recovering Sewage Bypasses Sewage bypasses occur during or after heavy rains Result of water getting into the sanitary sewer lines Flow of water to the treatment plants increases so much that some water must be bypassed around the treatment facilities Sewage Bypasses A bypass under such conditions is the only alternative to flooding the plant or allowing the sanitary sewer lines to back up The bypassed sewage receives little or no treatment before it enters the ocean Sewage Bypasses As the sewer system ages, leaks will develop City of Honolulu has been lax in maintaining its sanitary sewers Result has been numerous bypasses 3

4 Sewage Treatment By law, raw sewage must be treated before it is discharged into the ocean Sewage Treatment Sewage Treatment Primary treatment is when sewage is screened to remove large objects and allowed to stand in a settling basin to allow smaller particles to settle out Primary Treatment -- Settling Primary Treatment At least 30% of the solids and organic matter are removed in this way The water that rises to the top of the primary treatment system still contains a large amount of organic matter So we may want to give it secondary treatment Secondary Treatment 4

5 Secondary Treatment During secondary treatment, water goes through additional filters -- bacteria and other organisms remove more organic matter Water coming out of secondary treatment has 85% of its solids and organic matter removed This water still has lots of inorganic nutrients, such as nitrogen and phosphorous, so it is not fit to drink Local environmental groups are pressing the City of Honolulu to convert all of their facilities to secondary treatment levels Do we need to subject sewage to secondary treatment before dumping it in the ocean? Decomposition of organic matter in raw or primary sewage consumes most of the oxygen in waters receiving sewage effluent Result is a foul-smelling environment in which few fish or other organisms can survive If we dump this material into an enclosed bay (like Kaneohe), there will be many problems Depletion of oxygen not a problem in the turbulent, open coastal waters of Hawai`i, because the water is continuously mixed The absence of oxygen depletion problem in Hawaiian coastal waters is main reason that the EPA has allowed the City of Honolulu to operate its two largest plants as primary, rather than secondary, treatment facilities The incompletely-treated treated sewage contains lots of organic matter, which can be thought of as fertilizer for the marine plants Their potential negative environmental impact arises only when these nutrients are abundant in comparison with naturally available nutrient supplies No need to run secondary treatment if sewage discharged into such vigorously mixed regions as we have in Hawaii Environmental groups not helping by making us spend our tax dollars to upgrade to secondary treatment plants 5

6 Nutrients from sewage are very small when compared to the natural nutrients brought up to the surface from waters deeper than 300 feet by natural mixing Sewage diluted with such a large volume of seawater does not significantly stimulate plant growth Secondary Treatment Necceary? Hawai`i is unlike many parts of the mainland, because there is not a broad, shallow continental shelf Because of the steep marine slopes off the islands, sewage dumped at 100 ft depth moves offshore and is diluted in the channels between the islands There are about 70 golf courses in Hawai`i with several more under construction About a dozen golf courses have been studied in many different environments in Hawai`i The marine environment adjacent to these golf courses has been monitored over several years These studies, however, all have a common conclusion: Existing golf courses are not presently causing environmental impacts in the ocean Small amounts of fertilizer carried into the water from the golf courses has been detected, but not enough to cause environmental problems No sediment or water samples in areas where there are only golf courses have shown evidence of pesticide contamination In comparison with agricultural land use, golf courses generally cause less fertilizer input to the ocean than sugar or pineapple agriculture No detectable pesticides have been found in the offshore regions that can be attributed to golf courses Positive aspects of Golf Courses On the Ewa Plain, golf courses serve as flood control areas Without the turf to absorb flood water, concrete culverts would have to be built to channel storm water directly into the ocean Positive aspects of Golf Courses Some of the golf courses also have on- site secondary sewage treatment plants and use the treated water for fertilizer and irrigation, lightening the loads on the City's plants Questions? 6

7 Thursday Continue with Local Environmental Issues 7