Weaverville – A group opposing the expansion of Weaverville’s water treatment plant is questioning the reliability study the town used to justify its vote to move forward with the development.
The town council recently voted 5-2 to begin the expansion of their 1.5 million gallons per day (MGD) to three MGD at a cost of about $13 million. However, James Heinl of Save Ivy River is questioning a CDM Smith reliable yield study that the council used to support expanding the plant.
“That CDM Smith reliable yield study is full of holes. After digesting the study, I had a lot of questions. I am having another engineering firm ‘audit’ their report and give me a quote to provide their own “reliable yield” study that is much more in-depth and predictive, rather than using monthly averages,” Heinl told the Tribune. “I probably won’t be able to afford it, but I will try. Most of the questions below are rhetorical, but what gives with the bad math?”
Heinl alleges, “Shockingly, these guys (CDM Smith) charged that much money to town and didn’t even get their feet wet! The expense of that ‘cover your ass’ report could have been used to get an actual flow study performed at the intake.
The CDM Smith study
The Tribune reported back in January that the council, during their January meeting, heard a presentation by John Boyer with CDM Smith. Boyer divided his presentation into four parts – the objective of the study, the approach, the results, and the summary.
Boyer said the study’s objective was to answer two questions: how much water could reliably be produced from the river, and based on current climate trends, what impact would climate have on the river for future water production for the town? Boyer defined reliability as the minimum water flow under extreme drought conditions.
He said there were about 67 years of data on the river flow, which gave a good base from which to form the study’s conclusions, with the river’s lowest flow coming in 2008 at 4.91 cubic feet per second. Along with other data, the study’s results showed that 100 percent of the time, there were 2.6 million gallons per day (MGD) available, with 8.7 MGD available 99 percent of the time and 12.8 MGD available 95 percent of the time. The town has a state permit to take up to four MGD out of the river.
Boyer said there was “very little, almost negligible impact” to water levels in the future predictions, according to the study. He also said there is a negligible impact when removing three MGD in a low flow check.
Heinl questions about the Reliable Yield Study
Question 1: Did you perform an in-person site visit at the intake location for this study?
Question 2: Did you perform any instream flow measurements at the intake site for this study?
Question 3: All of your estimates for availability are for 100% of the water in the river, correct?
Question 4: Did you evaluate what federal and/or state requirements for withdrawal allowances are? If yes, what are those allowances? (IE, I assume we are not allowed to take all of the flow of the river)
Question 5: Why is your number different than what USGS shows for Aug 2008? Does this have a material impact on your assessment?
You used 4.9 cfs (3.2 MGD) as the lowest USGS measurement on record in Aug 2008; however, the USGS site (linked below) shows the lowest flow at 3.46 cfs (2.23 MGD) on Aug 25th, 2008. That is a 31% difference in your reported low and the actual low.
Question 6: Did you use the 70% as the flow difference between the USGS site and the intake for all your calculations? (This is mentioned in Section 3.2 “This entire process is an approximation technique and resulted in flow estimates at the intake of roughly 70 percent of flows at the USGS gage further downstream.”)
Question 7: If you did use the 70% to calculate the difference in the two locations, where does the 2.6 MGD number come from? 70% of 3.2 MGD = 2.24 MGD not 2.6 MGD
Question 8: Would your summation of the river’s reliability change if you recalculated your numbers using the following information? USGS’s lowest flow = 3.46 cfs (2.23 MGD) at the USGS site Intake lowest flow = 70% of 3.46 cfs (2.23 MGD) = 2.42 cfs (1.56 MGD)
Question 9: Could you please explain the 41% difference in the math of what was reported as the 100% reliable flow at 2.6 MGD and the 1.56 MGD calculated using your 70% and the actual USGS low flow?
Question 10: Was evaluating a multi-day low flow scenario out of scope for your report? If so, why?
Question 11: Do you agree that the following comment is inaccurate? “The fully reliable yield of the river is 2.6 MGD, but over the historic period of record spanning approximately 67 years, this minimum flow is encountered on only one day. All other daily flows were higher.”
Based on the USGS data, the following statement is inaccurate, using your 4.9 cfs number. Between Aug 22nd and Aug 25th, 2008, all four of those days had a low flow of under 4.9 cfs. In addition, 7 consecutive days had less than 3.0 MGD total available flow at the intake.
Question 12: Using the dates between Aug 10th, 2008, and August 25th, 2008, where the Ivy River had an extended low flow event, could the Weaverville Water Treatment Facility reliably provide 3.0 MGD daily given its systems, storage capacity, and allowable regulated withdrawal limits?
Contributor’s Note: The Tribune has sent the questions to CDM Smith’s John Boyer for a response, but has not heard back as of press time.