The staff report prepared for the Water Commission’s August 13 meeting contains a good, readable synopsis of the problems facing ‘Iao aquifer. Here we reprint several key sections of that report:
Duty to Protect
On May 13, 1997, the commission met in executive session to confer with its deputy attorney general regarding the commission’s legal duties on ‘Iao aquifer on Maui. The intent of the state Water Code was for the commission to protect the resource before it was threatened, and that protection was intended to be the regulatory regime imposed through designation. HRS 174C-44 established seven criteria which must be evaluated in determining whether to designate a groundwater management area. Even if one or more of the criteria are met, the commission was advised that it is still discretionary whether to designate an area. However, the discretion disappears in the situation where actual pumpage is greater than 100 percent of the sustainable yield and the resource is clearly threatened. The pumpage from ‘Iao aquifer has exceeded sustainable yield for the last two years.
Rise in Transition Zone
The estimated sustainable yield is based upon an optimal spacing of wells. If the full sustainable yield were withdrawn from too few sources, localized effects would reduce the length of time those sources can be used. This is what is being observed with the current infrastructure.
Withdrawing any water reduces the height of water levels above sea level. Overpumpage causes water levels to continue declining without stabilizing. A reduction in water levels corresponds with a rise in the transition zone [i.e., the transition between fresh water and salt water]. Once the transition zone approaches the bottom of an existing well, the long-term prospect is to pump ever-saltier water. If pumpage levels out, the water levels and transition zone will stabilize. If pumpage is reduced below the safe capacity for that well, water levels will accordingly begin to move back toward their higher level, and the transition zone will move deeper with time.
The speed of movement of the transition zone affects the time left before the wells start to draw higher chloride water. The midpoint of the transition zone (9,500 ppm chlorides) rose more rapidly in the last year than in all previous years. The previous rate was about 7 to 8 feet per year, but over the last year the midpoint rose 10 feet. At the previous rate, it would have taken 50 years for the wells to salt up. The increased rate has reduced that to 35 years.
Below Allowable Levels
The water level data indicate that certain wells will not be able to continue pumping at current rates. The problem of concentrated pumping and pumping more than the aquifer can sustain in the long term exists throughout the ‘Iao aquifer. At Waiehu Heights well field, the minimum long-term water level is 9 feet and the water levels are already at 9 feet. The aquifer is not at equilibrium, so water levels will decline further. This suggests that 9 feet is already below ‘safe’ conditions.
The water levels at the North Waihe’e well field in the Waihe’e aquifer system reflect a similar situation. ‘Iao aquifer pumpage is also affecting water levels in this adjacent aquifer. These wells are not even pumping in regular service yet. The October 1996 water levels were at 7 feet above mean sea level, a decrease from the 12 feet above msl measured in 1989. It is unlikely that 1.5 mgd can be sustained in the long term from the North Waihe’e wells 1 and 2, and in fact, the long-term allowable pumpage will probably be 0 mgd unless the wells are modified. This is unfortunate news as the North Waihe’e [aquifer] was a prime source to relieve ‘Iao aquifer pumpage. Staff has been directed to re-evaluate the sustainable yield for North Waihe’e.
Current Pumpage Unsustainable
The current water levels indicate that current pumpage rates in current locations cannot be sustained in the long term. As stated by Bill Meyer of the USGS to the Maui Board of Water Supply, “you are borrowing on the time lag that it takes for salt to come up. Given this, the question becomes, “how long do we have?” Although it may take decades for the top of the transition zone to reach all wells from an aquifer standpoint, there will be localized chloride problems long before that due to upconing.
Pumpage should be limited to levels that maintain the minimum long-term water levels at each well. Twenty mgd clearly cannot be sustained based on the current infrastructure. If additional wells are drilled at some distance from the existing pumping center, and pumpages are readjusted, ‘Iao aquifer may sustain 20 mgd.
New Sources Delayed
There has been consistent slippage in schedules for each of the source alternatives. The ‘Iao Ditch Facility is behind schedule; the Department of Health denied the permit. In response, the Maui BWS hopes to accelerate the schedule for the North Waihe’e 1 and 2 wells by using a generator. Increased pumpage from Wailuku Shaft is no longer an option because of the declining water levels.
The North Waihe’e wells 3 and 4 are not likely to be an option because of the declining water levels.
The proposed Waikapu Well is still within ‘Iao Aquifer but will spread the pumpage and is needed just to maintain 20 mgd from the ‘Iao aquifer. If the yields are not as high as needed, more wells will have to be drilled to maintain the 20 mgd pumpage.
Longer Range Problems
In addition to bringing the 1997 new sources on line, Maui BWS must bring on line about 1 mgd a year from 1999 just to keep up with increasing demand. The track record of delays does not support this kind of program. The North Waihe’e wells are not likely to be a viable alternative for the long term. Wells 1 and 2 may be used in the short term, but cannot be sustained. Wells 3 and 4 are not likely to be an option at all.
The only likely long-range source area is East Maui, and the thinness of the lens indicates that each well will yield just 0.5 mgd each. Thus, at least two wells a year will be needed just to keep up with growth. East of the existing three East Maui wells, the USGS predicts that pumping groundwater will affect stream flows. The commission must recognize that if wells in East Maui are the only remaining alternative petitions to amend the Interim Instream Flow Standards are likely, and objections to the amendments are also likely.
Volume 8, Number 3 September 1997
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