Island waters run deep: Groundwater model reveals surprises in Bainbridge aquifers
March 6, 2009 · Updated 11:01 AM
One thing is assured: groundwater is a renewable resource that deserves careful monitoring.
But just how renewable it is and what levels of pumping island aquifers can sustain are still being analyzed.
“It’s a tough question to answer, how it looks 1,000 feet down there,” said Scott Shelton of the Island Utility Co. “If anyone could give you a 100 percent answer we’d be famous, rich and retired.”
This week, scientists from the United State Geological Survey presented initial research on a groundwater model that will help islanders and the city answer those million-dollar questions.
The USGS island-wide groundwater model will be the primary tool the city uses in making water-resource management decisions as it develops.
“This is exactly the direction we need to take,” said Jalyn Cummings, the city’s water resources program manager. “We need unbiased science for our council and city to make tough decisions about island management.”
The model is a complex mathematical computational tool that can assess how a multitude of factors will affect the future island water supply. It includes the impacts of more water usage, growth of impervious surfaces on groundwater recharge and stream vitality, and even hypothetical scenarios relating to dramatic changes in our weather patterns.
“This groundwater model doesn’t pass judgment,” said Matt Bachmann of USGS. “What we are talking about are scenarios. How things might be different in five, 10 or 20 years.”
But so far, the model raises more questions about island aquifers, and shows just how little we know about these complex underground systems.
The way the model is currently built, the Fletcher Bay aquifer, one of the deepest and biggest water producers for island residents, actually connects to the Kitsap Peninsula and could receive most of its recharge from the mainland.
“What it means in a very broad sense is that maybe we’re all connected,” said Martin Sebren, a hydrogeologist with Kitsap Public Utility District. “But what it means to water resources and how much I can pump or the city can pump, I’m not sure.”
Sebren has been involved in monitoring Kitsap wells since 1982; he’s worked with KPUD since 1994. He says, overall, Bainbridge has a fairly sustainable water supply.
“There aren’t any failures, and there is a positive message here,” he said. “We’re looking at our groundwater levels and we’re being responsible. More people are doing it now than ever before.”
However, there are some trouble spots on the island that have been documented in the past, Sebren notes.
Seabold water has experienced contamination relating to large amount of natural metals. The bedrock aquifer on the south end also recharges and produces at a much lower rate than other aquifers underneath the island’s surface.
Doug Elliott, a shoreline resident in the Seabold area, is one islander dealing with heavy amounts of iron and manganese in his well. His water supply began to go bad in the early 2000s.
“What I do know, in the Seabold neighborhood, we’ve had some problems,” Elliott said. “All the wells that went to the sea level aquifer are being replaced.”
A report issued by the Seattle engineering firm Kato and Warren in 2000, came to similar conclusions, showing that water problems on the island tend to be localized due to wells drilled in the wrong places or faulty distribution systems.
In general, those problems stem from excessive reliance on shallow sources of water, such as those in the Seabold area.
“It’s economics. You drill as shallow as you can get away with because every foot costs another 30 bucks, that makes for a lot of shallower wells,” Sebren said. “The broader issue here is what are the aquifers doing in response to all our miscellaneous pumping.”
Answers are hard to come by and current data is far from conclusive.
All data collected by the city and independent investigators to date do not indicate there is any saltwater intrusion on the island, nor any long-term declines in any of the island aquifers. In the past, there have been one-time hits for chloride (an indication of saltwater intrusion), which could not be replicated in subsequent testing. Information from near-shore private wells may prove otherwise, but that information has not been offered for inclusion in the city’s island-wide ground monitoring network.
“Trend analysis is great, but the hell is in the details,” said Ron Wiley, co-owner of Nicholson Drilling. “You can’t say the sky is falling because you see one drop or one reading. You need to tighten up the data stream, then you can see if there is saltwater intrusion or falling water levels before going into the movie theater and shouting fire.”
Media reports that wells have shown steep declines were actually referring to short-term occurrences that have since rebounded. Reports that Island Utilities Well 1 was overdrawn were also incorrect; the well has been out of service since 1999 and is acting only as a monitoring well.
The monitoring well has seen a decline, but that raises more questions because it is easy to attribute drops in aquifer levels to pumping. But a host of other factors also play into the equation.
“There is no such thing as a static aquifer; they are dynamic and they are always moving,” Sebren said.
By in large, a 2008 report by Aspect Consulting indicated island aquifers do fluctuate widely, closely tracking rainfall levels and showing direct correlations between recharge and rainfall rates.
According to USGS scientists, the island receives an average annual rainfall of about 37 inches. They estimate about 40 percent of that rain finds its way back into island aquifers.
But the abundance of rain doesn’t mean the area is immune from water shortages and problems.
In rare occasions, sea level aquifers have been taxed too far in Kitsap County, although a smorgasbord of varying geological and surface conditions play into the equation.
The Island Lake aquifer in central Kitsap was heavily drained for the Silverdale population in the 1980s and ’90s. That led to strict management of draft rates and a since-expired moratorium on new wells in the area.
The fragility of near-surface aquifers such as Island Lake have led many to go deeper in the search for water.
For Elliott, the spiraling cost of filtering his water has led him and a neighbor to go in on a well that will go over 1,000 feet deep in search of the Fletcher Bay aquifer.
“There is no guarantee we will hit the Fletcher Bay aquifer,” Elliott said. “If we don’t then I’ll be $100,000 out of luck and back with my old water system. I suppose my bigger concern is that if everyone is going deeper and tapping the Fletcher Bay aquifer, how do we know how well that will hold up?”
And that is exactly what the USGS is looking to find out – the state of island aquifers and how they are reacting to current and future changes in the island environment.
The USGS study has gathered data from some 70 wells on Bainbridge, information that is supplied from the groundwater monitoring network managed by Cummings at the city. They also take into account surface-water levels and discharge measurements from 19 streams.
Because there is a high likelihood that the Fletcher Bay aquifer reaches to mainland Kitsap, USGS scientists are also gathering data from across Port Orchard Bay to try and determine the relationship between draw and recharge on both sides of the water. Thus far, no direct relation has been established.
The model will not be completed until 2010, and will likely have to be recalibrated every 10 years to account for new data, data that Cummings is still eager to get her hands on.
“We always need more data and representative wells to be part of our monitoring network,” she said. “We need it for future planning... so we know where our water is and where it is going.”
View data samples that are providing the framework for the USGS study.
To participate in the city well monitoring network contact email@example.com