November 19, 2008

Stats Challenge Criticism of Lake Source Cooling

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Cornell recently released a report detailing the impact of the Lake Source Cooling project on Cayuga Lake. The report concluded that since its implementation in 1999, LSC has not had a detrimental effect on the lake, despite criticism that the project is a major source of pollution for the lake.
LSC works by bringing cold water from the depths of the Cayuga Lake up to the surface where it is used to cool water that runs through the air conditioning systems of Cornell and Ithaca High School. The water is then discharged back into the lake at its surface.
“The discharge contains soluble reactive phosphorus at two to five times the level that is in the shallow lake water,” said Walter Hang, owner of Toxics Targeting, Inc. “This promotes the growth of choking blooms of algae.”
The water at the bottom of the lake is much richer in phosphorus than the water at the surface, and when this water is brought to the surface it brings the phosphorus along with it. The report sought to determine if the changes in the levels of phosphorus were statistically significant.
“According to the analyses, the phosphorus does not negatively affect the lake,” said James Adams, director of utilities and energy.
Hang claimed that the raw data indicated that there was a statistical significance, especially at site seven, an area in the southeast corner of the lake, and site four, which is on the western side of the lake. According to Hang, Cornell’s initial report three years ago had not included sites seven and four. While the raw data shows a statistically significant amount of phosphorus at these sites, the methods of statistical analyses that were run on the raw data concluded that there was not a statistically significant amount of phosphorus.
Prof. Edwin Cowen, civil and environmental engineering, a member of the faculty oversight committee for the project, said that the reason Cornell had not initially included site seven is because they wanted to try to get the most accurate data possible, and adding more sites would introduce a multiple comparison effect that would skew the data. Cowen offered the analogy to tossing a coin eight times. If two people were to do this, then it is not very likely that a person would have just one “heads.” However, if 25 people were to do this, there is a much higher chance that there would be a person that got just one “heads,” but this would not be an accurate representation of the real probability.
“In trying to deal with the multiple sample comparison effect, Cornell and the Department of Environmental Conservation had decided to look at just four sites,” Cowen said of the initial report. “After three years the DEC came back and said they would like to look at the site four-seven comparison explicitly.”
According to Cowen adding the extra sites diluted the power of the statistics, which is why several different statistical analyses were run on the data to compensate. The analyses were run by people within Cornell in addition to those beyond the community, all of whom concluded that there was no statistical significance. [img_assist|nid=33725|title=Cold waters|desc=The Lake Source Cooling project, which pumps water from the bottom of Cayuga Lake to be used in air conditioning, has been criticized for causing increased levels of phosphorous in the lake.|link=node|align=left|width=|height=0]
Cowen also mentioned that site seven is right off of Stewart Park and is impacted by the Ithaca area wastewater treatment plant, the Cayuga Heights wastewater treatment plant, and runoff from Stewart Park, the East Shore Marina, and homeowners in addition to LSC. According to Cowen, the data shows that the water quality at site seven is actually very good.
On the other hand, Hang claimed that the water quality at site seven is so bad that swimming and boating are not possible there. He said that over the past 10 years, $80 million have been spent on cleaning up the lake, but the biggest and most severe problem is phosphorus concentration. The other discharges have been dramatically reduced, and the phosphorus has been cleaned up from the municipal wastewater treatment plants, which should have made the phosphorus in the lake go down as well. Hang claimed that LSC was the reason that the phosphorus levels were not going down.
“If you look over decades of data collected, phosphorus levels have cycled up and down and there are a lot of different reasons for this,” Cowen said. “The Clean Water Act in 1970 phased out phosphorus-based pollutants, but then the level bounced back up again as zebra mussels came into the lake, which was before LSC came in. There is nothing in the data set that says LSC is responsible.”
Cowen also added that along with the fact that there is no evidence of a water quality problem in Cayuga Lake due to LSC, there is significant evidence that LSC has had a huge impact on reducing Cornell’s carbon footprint. There has been an 85 to 90 percent reduction in carbon and sulfur pollutants in the air because of LSC, according to Cowen.
According to Adams, the DEC received the report two weeks ago, and is currently reviewing it. They will respond to Cornell sometime in the future.