Nitrate concentrations have risen over the past 40 years in nearly 60% of 146 water wells within the Northern Guam Lens Aquifer, and are continuing to rise in at least 44% of wells, according to a scientific advisory paper from the Water and Environmental Research Institute of the Western Pacific, or WERI, at the University of Guam.
The most likely sources of increasing nitrate concentrations in the groundwater are sewage percolating from leaking sewage lines and effluent discharging from conventional septic tanks.
The paper was provided to members of the Guam Legislature as well as the water utility and Guam Environmental Protection Agency last week, according to WERI Director John Jenson.
It was attached as an addendum to WERI's testimony on Bill 404-35, one of four measures introduced by Sen. Régine Biscoe Lee intended to protect the aquifer. Her office is aiming to place all four bills on the session agenda in December.
WERI states that the general observation from available data indicates that there are "widely – if complexly – distributed sources of nitrate that have and continue to contribute steady-to-increasing amounts of nitrate to the aquifer."
However, the correlations between the location of sewage lines, septic tanks and nitrate concentrations in surrounding wells are complex, "and it is not yet possible with the data at hand to precisely measure the absolute or relative contributions of sewage line leaks and septic tank discharge at any given location or to the total amount of nitrate entering the groundwater," WERI stated.
Therefore, according to WERI, long-term approaches to managing nitrate contamination should address both issues.
The advisory paper offered generalized nitrate management considerations, stating that both leaking sewage lines and active conventional septic tanks have been and continue to be sources of contamination in the aquifer.
It noted that the Guam Waterworks Authority has invested in eliminating or reducing sewer leaks and there is an ongoing systematic program for routine inspection, scheduled preventative maintenance and timely repair of sewage systems.
But there is still a "large, and probably growing, number of conventional individual disposal and household septic systems" above the aquifer, according to WERI.
Nitrate discharges from these systems can only be eliminated by replacing them – either by connecting to a sewer line or by replacing the conventional septic tanks with modern treatment systems that can reduce nitrate to nitrogen gas, WERI stated. But like sewer systems, these modern treatment systems need regular maintenance and repair.
To limit nitrate contamination from septic tanks, Bill 404 would bar new septic tank systems if the land is located in the Groundwater Protection Zone and if a public sewer is available, regardless of the size of the lot and whether the lot is part of a parental subdivision.
If there is no connection available, the bill prohibits new septic tanks if the lot is less than half an acre, and again ignores whether the land is part of a parental subdivision, which would otherwise allow a landowner's descendants to circumvent requirements normally applicable to improvements made on subdivided land.
The bill has garnered criticism from property owners, realtors and others, who argue the measure would make it more difficult for local families to own a home, especially on property from their parents under the parental subdivision law.
As one couple related to The Guam Daily Post, the bill would be fine if sewer connections were available everywhere on island.