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Mon, Dec. 09

Cleaning up Watson Lake
Prescott approaches final steps in plan for pollution reduction

Prescott’s Watson Lake — pictured Tuesday, April 17, 2018 with Canadian geese — has a low water level due to a lack of snowpack over the past winter. (Les Stukenberg/Courier)

Prescott’s Watson Lake — pictured Tuesday, April 17, 2018 with Canadian geese — has a low water level due to a lack of snowpack over the past winter. (Les Stukenberg/Courier)

Within a year, Prescott should have an answer to a longstanding question: What can be done about the polluted waters of Watson Lake?

Years of study, and hundreds of thousands of dollars of costs, are expected to culminate with a plan for reducing the pollutants that have long plagued the northeast-Prescott lake and the watershed that feeds it.

If the Prescott City Council approves spending $344,976 next week for the final steps of studying the levels and E. coli and other lake and creek pollutants, the final “deliverable” from consultant Amec Foster Wheeler Environment & Infrastructure, Inc. will be a recommendation on how best to clean up the lake and area creeks.

The report would be due in the next 12 months.


Based on a requirement by the Arizona Department of Environmental Quality, the city earlier approved an eight-step plan for evaluation of the problem.

The first five steps are now complete, and the City Council is expected to consider authorizing the final three steps at its April 24 voting meeting.

“The data has been collected, models have been developed, and now we are getting to the ultimate point of this project, which is to evaluate different alternatives … to achieve pollutant reductions,” consultant Rebecca Sydnor with Amec Foster Wheeler told the council during a study session this past week.

Ben Burns, the city’s senior utility infrastructure analyst, said the costs for the first five steps have totaled $496,282. The $344,976 for steps six through eight would be the final costs of the study.

Although a cost estimate for implementation of the recommended plan is not yet available, the needed improvements likely will come with a significant expense as well.



The map shows areas of Granite Creek being tested to determine the cause of pollution in Watson Lake and in the watershed that feeds the lake. (City of Prescott/Courtesy)

For more than a decade, Watson Lake has been listed as “impaired” for levels of phosphorous and nitrogen, as well as issues with pH and E. coli.

Matt Killeen, environmental coordinator for the city, told the council that four creeks – Granite, Miller, Butte, and Manzanita – were originally listed as impaired, along with Watson Lake.

“Subsequent to those listings, an additional eight creeks were listed as impaired,” Killeen said, adding, “The scale of it has essentially tripled just over the last couple of years.”

The study stems from Arizona Department of Environmental Quality’s reports on the Total Maximum Daily Loads (TMDL) for Watson Lake and the Upper Granite Creek Watershed, documenting the pollution for both.

(TMDL refers to the maximum amount of a pollutant that a water body can receive while still meeting a water-quality standard).

The pending action plan for dealing with the TMDL would address both of the study areas, Sydnor said. “There are a number of activities that feed into each other across both TMDL work efforts,” she said.

An earlier step in the process involved 12 months of data collections at five locations at two different lake depths, Sydnor said. The consultants also took street-dirt samples at various locations in the city to help identify the origins of the pollutants.


The next steps will include simulating different activities and actions that could be used to help reduce pollutants. The results of the simulations then would be used to come up with a lake management plan.

Consultants also plan to do “genetic-marker testing” on the E. coli to help determine whether it comes from humans or animals, Sydnor said.

The Virginia Street wash below Acker Park is “one of the hotspots for E. coli,” Killeen said – likely because of the large number of javelina and deer in the area, as well as dog-walking activities in the area.

Sydnor said the city has been working recently to line its sewer lines to help prevent leakage – a step that she said should help reduce the amount of human-caused E. coli.

Killeen said other recent city projects such as the detention basins and landscaped basins along city streets also help to filter pollutants out of runoff water before it reaches the creeks.

In response to questions from the council about possible solutions such as dredging the lake, Killeen said “Nothing has been removed from the table.”

But, he said, the recommendation would use a cost-benefit analysis to determine which solutions would be most effective for the money spent.

As a part of its efforts to reduce pollution, the city’s website now offers a “pollution reporting form,” which allows those who observe pollution, such as hazardous materials and sewage, to report it, at:

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