Both reservoirs are overflowing

Wrangell's water situation seems stable heading into the summer, with both reservoirs "overflowing" according to the latest update from Public Works.

A combination of factors led to the enforcement of conservation measures through the month of March, including low precipitation, a lengthy winter and high demand. During the winter, demand by the first week of February had spiked to 1,151,000 gallons per day, which for the previous year was second only to a summertime high the first week of July, at 1,227,000 gallons daily. More recently, demand by the end of April ebbed to half what it had been in February, on average around 563,000 gallons per day.

While some level of the increased wintertime usage was ascribed to residents letting their taps flow to prevent pipes freezing, detected breaks in the water mains had also contributed to the draw. Two had been identified during pressure tests conducted in late March, with the breaks together estimated to be losing just over 50,000 gallons of water per day. Those were repaired by Public Works, and a third break later discovered on a residential line in April was found to be losing about 43,000 gallons per day. It was repaired after being identified.

Leaky pipes are not the only problem with the system, with the borough's water treatment plant itself an issue. The plant's operators are trying to find ways to reduce water waste, which the assembly learned last month accounted for around 40 percent of all production. This water gets lost during recurring maintenance of both the roughing and the sand filter systems, and also includes the amount of water needed to rebuild water pressure before the resumption of operations.

In her monthly city manager's report on Tuesday, Lisa Von Bargen said the plant manager last month started to track how much water was being produced during routine maintenance procedures. For most of April, the plant took in over 16 million gallons of raw water, distributing 9.7 million of that after the treatment process. That indicated some 6.3 million gallons of water was being lost during treatment.

Though the plant lacks all the gauges necessary to track water usage through each stage of production, one major area of waste is from cleaning its four slow sand filter bays. During the filtration process, a layer of grime builds up – called schmutzdecke – causing clogs. Eventually the freeboard depth of water increases above the filters to the point where they must be drained and the filter surface cleaned. During that operation the filter unit is offline, and 135,000 gallons of semi-treated water gets wasted during the process.

The city would like to avoid this by diverting that water into the clearwell, which staff thinks can be done with some simple piping revisions. Von Bargen reported the city has obtained permitting from the Alaska Department of Environmental Conservation to make the fix, and has already begun procuring materials.

Another source of water waste is with the plant's roughing filters, which are a preliminary stage that prepares water for the slow sand filters. The filter setup has never been able to flush itself when clogged, requiring manual clearing on the part of staff. This is an inefficient process in terms of time and of resources, losing tens of thousands of gallons each time.

To correct this, a pilot

study on a self-cleaning

mechanical filter setup has been ongoing for the last month and a half. As designed, the Forsta-model filter unit initiates a backwash sequence when its filtration screen gets plugged. The hope is that the pricey mechanism would save on labor time and lose considerably less water than the current filters, which in the long term would pay for itself in lowered operating costs.

However, the test results have so far been mixed. Water clarity samples have come back below expectation, and a finer filter is being experimented with to see if that helps. Recurring flushings would also on a large scale lose much more water than first thought, up to 118,000 gallons per day compared to the modest test pilot model.

A possible reconfiguring of the system to discharge backwash water back into the roughing filter bays could work by allowing more time for sediment to settle before filtration.

The biggest fix, however, would be a full upgrade to Wrangell's plant, changing over from sand-based filtration to dissolved air flotation. A miniature test plant tried out in 2016 showed promising results, and in March Wrangell's assembly approved moving ahead with the replacement project. In all, it would take around three years to build and would cost $9.1 million.

To pay for this, the city has approached the Department of Agriculture for $3.82 million in loans and $3.16 million in grant monies, with another $2.5 million grant to be applied for through the Alaska Economic Development Administration. Remaining funds would come through the borough's reserves and other, smaller grant sources.

Currently, Von Bargen reported the city is putting together its application packet to the EDA, for submission next week. If given its approval for grant funding, the project could finally move ahead.