The AJ Mine-Related Water Study, which has been released in draft form, shows that Gold Creek is currently over-allocated.
City Engineering Department Director Rorie Watt gave a public presentation of the 80-page study on Wednesday night.
Watt started with a slideshow of historical photos showing what the mining areas of the Silverbow Basin and others in the area used to look like before going into the five sections of the report.
Part of the report looks at water supply needs. A graph shows water usage flow for Salmon Creek, Last Chance Basin and the total. The markings are spiky, with Salmon Creek ranging from no flow to 2 million gallons per day (MGD). Salmon Creek is currently unfiltered, and is taken offline when turbidity is too high. Last Chance Basin ranges from a low of 2 MGD to a high of 4 million. The total MGD fluctuates from 3 MGD to about 4 1/2 MGD.
The city uses about 4 1/2 MGD in summer months, with about 1 million used by cruise ships in those months. In winter months, the city uses 3 1/2 MGD.
“We are selling a lot of water to cruise ships in the summer,” Watt said. “This poses some water management issues for our utilities. Salmon Creek used to be somewhat more predictable than it is now. Gold Creek, as a ground water source, we do not have turbidity problems.”
The cruise ships are using about 20 percent of the city’s water use in the summer, Watt said.
Watt said when the water color is chocolate milk brown, the drinking water quality is still good.
Watt also said even though the water flow graphs show large spikes between flow amounts, there does seem to be an average trendline to lower usage.
One citizen asked if it was because of leaky pipes.
“We try to find leaks as best we can,” Watt said. “There are 100 miles or more of underground piping. When there’s a big leak it’s usually easy to find. Small leaks are not as easy to find. The statistician in me notices the downward trend. This could be increased metering. It could be with the avalanche problems with the Borough system and conservation, maybe that some of that behavior has stuck.”
He also said it could also be that the pipes the city built in the 1940s and ‘50s are being replaced, starting in the ‘90s.
“It could be all of those things combined,” he said.
Gold Creek’s water rights are split between the city and Alaska Electric Light & Power.
Watt referred to a chart that shows the average monthly water flow out of Gold Creek. One month shows a high of 326 cubic feet per second (CFS), which is about 4 1/2 million gallons per day. Another month shows an average of 2.32 CFS.
In terms of water rights, the city has rights to 10.8 CFS, while the power company has rights to 137 CFS — so, if both were to need their full allotment there would be some cases where there wouldn’t be enough.
That said, the water study has found AEL&P uses lower amounts than it’s certified for, with averages broken down per month. Its highest CFS was in Juneau at 97 CFS, and lowest in March at an average of 8.
“Seventy percent of the time the flow (of Gold Creek) is less than the combination, so it’s over allocated,” Watt said. “The power company does not run the flume all of the time, but there is a balance. If there is a diversion of the drain tunnel, where that water goes matters.”
Another issue that came up in the meeting, though not in the report, is the status of AEL&P’s Salmon Creek dam. Watt discussed one scenario for developing an additional water source or related improvements. He spoke of one option that would divert water from the well field at Gold Creek and beef up Salmon Creek’s services, but what’s changed since that idea (a mitigation proposed during Echo Bay’s proposal period), is that the condition of the dam due to age.
“As AEL&P watches the condition of the dam, they’ve had to reduce the water level in the dam down a little bit,” he said. “What we have been seeing is that we are getting turbidity (in Salmon Creek) at different times of the year when we have not gotten turbidity (before). The best explanation we have, is sediments that built up below the old level now get washed out at different times of the year.”
Watt said the reduction in water level is a huge loss of money and it’s in everyone’s best interest the company is able to find a way to fully restore the dam. He said it also has other implications with available pressure. Watt said there have been some other changes in routing around Salmon Creek since the initial look at the scenario.
Watt also talked about the condition of the drain tunnel. He said overall it’s in good shape, but there is one point of concern where it is partially collapsed.
“That is an area of concern,” he said. “The rock is less competent, it’s crumbly. If there was a mining operation that clearly could get fixed. I don’t know if we have the expertise to do that on our own. If the drain tunnel plugs, it will fill the deep north rather rapidly. Water would overflow and likely come out the Ebner Adit at the Perseverance Trail. That would probably be very exiting if it were a sudden event. There would be erosion of the trail and parking lot. I think its something we could manage.”
Watt said that the city had decided years ago that it would not work on the drain tunnels or mine, which hasn’t had any substantial work done with it since the 1940s.
One citizen said the drain tunnels were developed decades ago by miners, and there should be very careful and thoughtful planning with the remnants.
“There is a lot potentially at risk,” she said.
She added she was a little disappointed the report doesn’t make a move toward developing a secondary water system that could be used as a primary system. The report does explore four scenarios for options.
• Contact reporter Sarah Day at 523-2279 or at firstname.lastname@example.org.