Pollution model for Flathead Basin completed

A long awaited computer model for nutrient pollution in the Flathead Basin is completed. The U.S. Environmental Protection Agency contracted with TetraTech to support development of the model, and a draft report on the model was released Nov. 3.

Deficiencies in the model are described in the draft report. While the model reportedly did well in simulating point sources, nonpoint source modeling proved difficult, an issue with political ramifications for the Flathead’s cities and towns, where officials are concerned about spending millions of dollars on treatment plants that will provide small incremental benefits to the watershed.

“There is uncertainty associated with the simulated loading results from many of the nonpoint sources,” the report concludes. “Given the lack of source-specific monitoring data, quantifying the uncertainty is not possible.”

Many nonpoint sources are caused by natural changes in the watershed, and the report states that “additional work outside of this modeling framework would be necessary to quantify the split between natural and anthropogenic (manmade) nonpoint sources.”

In 2001, the Montana Department of Environmental Quality completed a total maximum daily load (TMDL) analysis for nutrients in Flathead Lake. Too much nutrient loading can cause algae growth, which can adversely impact water quality.

DEQ’s 2001 report called for a 15 percent reduction in nitrogen and phosphorus loading, but insufficient data existed to specifically link potential nutrient sources to observed water quality problems. One of the report’s recommendations was to create a basinwide model.

The Flathead watershed spans 7,093 square miles in the U.S. and Canada and includes 191-square-mile Flathead Lake, “an outstanding aquatic resource of international importance,” the modeling report states. A total of 14,055 miles of streams and 3,372 lakes covering 192,114 acres drain into the watershed.

The load simulation program was set up to model continuous hydrology, sediment contributions and nutrients — both manmade and natural. Field data was inputted to calibrate the model and to corroborate its findings. Hydrology data was collected from 2000 through 2012, and water quality data was collected from 2002 through 2012.

The watershed was divided into 392 subwatersheds for modeling. Because the South Fork of the Flathead River drainage passes through the Hungry Horse Dam, it was treated similarly to a point source.

Point sources in the watershed include 419 facilities with permits to discharge wastewater to surface or ground waters. Of those, 275 are stormwater discharges. Point sources include public and private sewage treatment plants, industrial sites, fish hatcheries and Glacier National Park’s treated sewage discharge into McDonald Creek.

Nonpoint sources account for the vast majority of nutrient loading in Flathead Lake. They include septic systems, stream bank erosion, stream bed degradation, atmospheric deposition, unpaved roads, forests burned by wildfires, timber harvesting, agricultural lands and golf courses.

More than 1.3 million acres of public forest land in the Flathead watershed burned between 1900 and 2008. About 52 percent of that was in Glacier Park.

About 3 percent of the Flathead watershed is agricultural land, with most intensive farming and ranching taking place between Flathead Lake and Columbia Falls. The model takes into account crops, livestock, irrigated land, fertilizers and overall trends.

There are 10 golf courses in the Flathead Valley. Turf is more intensively managed than agricultural land, with more chemicals used. Fertilizer application rates in the model were based on amounts used at Buffalo Hill Golf Course.

The draft report is available online at http://montanatmdlflathead.pbworks.com. Comments can be sent online to http://comment.cwaic.mt.gov. Deadline is Jan. 31. For more information, contact Christina Staten, the DEQ’s Flathead TMDL project coordinator, at 406-444-2836 or CStaten@mt.gov.