The lake liner at Fountain Park is currently in good condition, but as the potential lifetime of the product is getting closer it is prudent to plan a strategy for replacement, according to representatives with Black & Veatch Engineering.

The firm had recently completed a year-long evaluation of the Fountain, lake and associated equipment. The Town Council met in a special work session on May 11 to discuss the study and potential issues with Fountain Lake and its operating equipment.

The evaluation generally concluded that some equipment exceeds typical useful life but remains in good condition. The life could be extended with additional specialized maintenance and testing.

The replacement of check valves on the main pumps is approved and the parts ordered. Delivery has been delayed but expected shortly.

Repair of the pumphouse intake screen is also approved and is in progress. Installation of arc flash labels on electrical equipment has been completed.

Additional upgrades to the operating controls are to be determined.

The discussion by the council last week focused on the lake liner, as it is the most expensive and complex project being considered.

Michael Caruso, P.E., with Black & Veatch said there appears to be no immediate concern regarding the integrity of the lake liner, however, their recommendation is to continue periodic evaluation with evaporation tests on a two-to-five-year basis.

Caruso also presented the “what if” scenario of future evaluation indicating concern, or an unforeseen event that damages the liner (i.e. vehicle crash or similar incident).

Caruso and John Corbin, P.E., outlined the various steps and options the town would have regarding overall liner replacement. They noted that repair of damage in the event of an accident might be relatively simple, isolating the area with a cofferdam, removing the water and making the repair.

Challenges

If the periodic evaluation shows signs of deterioration of the liner and total replacement is recommended, it is a complex, lengthy and expensive project. The major areas to consider include disposal of the water in the lake (100 million gallons), removal of aquatic life, disposal of lake sludge and maintenance of surrounding vegetation, as well as maintaining water delivery to customers (golf courses).

For disposal of lake water, Black & Veatch presented options that include multi-stage liner replacement, aquifer recharge of the water and direct use for irrigation.

The multi-stage approach uses cofferdams. The overall lake level would be reduced with a cofferdam installed to divide a section of the lake; the water and sludge are pumped out and aquatic life removed and relocated (all into the portion of the lake still intact).

Once the water and sludge are removed that section of the liner is replaced and the process moves on to another section. This is repeated until the entire lake is completed.

This is a time-consuming process, as the dams are moved numerous times to allow for seam connection of the various sections. The cofferdams are also expensive.

The advantages of this process are reduced volume of water to manage, minimal management of aquatic life and it is independent of other entities.

Current cost estimates for this option are $2.3 to $2.9 million. Projected to 2030, the costs are expected to be $3.4 to $4.4 million. This does not include the liner.

The second option of installing a recharge well includes locating and drilling the well site, leasing pumping and skid-mounted treatment equipment (pretreatment filtration, microfiltration membrane and UV disinfection). This would allow for the full drawdown of the lake and sludge removal and disposal.

This option minimizes the construction schedule and is also independent of other partners.

The well equipment comes with a high cost, it may impact other wells and there are technical and permitting challenges.

There are also challenges and disadvantages of asking the Fountain Hills Sanitary District to treat and recharge the water in its existing wells, including a lack of excess capacity.

This option also does not include the cost of the liner and installation.

The current cost estimate is $2.7 to $3.4 million, with 2030 estimates at $4 to $5 million.

Direct reuse of the lake water would require the leasing of pumping and treatment equipment. The water would then be delivered to the well recovery piping with blended water delivered to water users.

There are complexities to blending the water to keep the dissolved salt content acceptable for golf course and park irrigation uses. Black & Veatch also evaluated a two-month and three-month process for complete drawdown of the lake using this process.

The reuse option has a current cost estimate of $1.4 to $1.8 million and 2030 projection of $2.1 to $2.7 million. Again, this does not include the cost of the liner and installation.

Black & Veatch is estimating the liner cost to be $2.6 to $2.9 million and the 2030 estimate to be $4 to $4.4 million. This is based on the 2000 cost to replace the liner of $1.3 million and a 4-percent escalation rate.

Other steps

The management of the aquatic life in all scenarios would require the cooperation of Arizona Game and Fish. The fish could be relocated to other municipal or private lakes. Specialized species may be rescued. Euthanization would be used in cases of invasive species or non-native species.

Disposal of lake sludge is another challenge. The recommended approach is to pump the sludge in liquid form from the lake and run through leased dewatering equipment. The dewatered sludge would be removed for landfill disposal (this would require use of a landfill certified for this use).

This is a relatively rapid method of removing sludge and minimizes odors and insects (a significant issue during the project in 2000).

Vegetation maintenance is the fourth challenge needing to be addressed. Those options include maintaining an existing source using a cofferdam or install a new dedicated irrigation reservoir and pump station.

Black & Veatch suggested using a cofferdam to isolate the area around the current pumphouse.

The second proposal would entail the installation of a dedicated 500,000-gallon irrigation reservoir and new pumps. The source would no longer be connected to the lake. This disconnection to the lake could result in increasing dissolved solids and toxicity to aquatic life. This could be managed.

The new dedicated irrigation reservoir has some appeal to the council as it is an option that has been previously discussed as a method to improve the quality of irrigation water for both parks and secondary users (golf courses).

Councilman Mike Scharnow noted this has been discussed as part of irrigation system upgrades, and it could be done separately and ahead of any concerns related to lake liner replacement.

Town Manager Grady Miller agreed, saying he does not believe in an approach that would wait until the need for liner replacement reached a critical situation and he supports any effort to take interim steps or even plan for replacement ahead of 2030.

Caruso told the council the estimates for the dedication irrigation reservoir are currently between $1.2 and $1.4 million. That jumps to $1.6 and $2.1 million by 2030.

The council took no specific action at the conclusion of the presentation.