Honeoye Lake Aeration Engineering Planning Project
Update on the Honeoye Lake Aeration Engineering Planning Project
By Betsy Landre, Ontario County Planning Department
& Terry Gronwall, Chairman, HLWTF
It has been nearly a year since a team of professional lake managers and engineers led by Princeton Hydro started work on the design of an aeration system for phosphorus control in Honeoye Lake, with the end goal of reducing the frequency and intensity of Harmful Algal Blooms (HABs). Aeration is one of the key strategies recommended by NYS Department of Environmental Conservation (DEC) to manage HABs in Honeoye Lake. For more information on aeration, phosphorus and HABs, see Linda Vanderbeck’s article on below.
The consultant team reviewed multiple years of data for Honeoye Lake to understand its characteristics (physical, chemical, and biological) and patterns in nutrient concentrations and HABs occurrences. With a detailed understanding of the lake, the team assessed various methods of aeration or oxygen injection to prevent anoxia (absence of oxygen) in the deepest part of the lake (25-30 feet). Keeping deep waters oxygenated at the sediment interface is key to preventing nutrient release from bottom sediments during warm months after the lake thermally stratifies. Deep and cooler bottom waters have more density than the warmer surface water above. The thermal stratification that sets up every summer prevents the deep waters from mixing with surface waters and being reoxygenated by interaction with the atmosphere. This deep-water zone – the hypolimnion – is where
artificial oxygenation is needed to interrupt the typical summer pattern: warm weather leading to thermal stratification of the lake, leading to deep water anoxia and phosphorus release, and fueling HABs, particularly upon a lake mixing event driven by weather.
The consultant team includes engineers who have designed and implemented various types of aeration systems in the United States. The team reviewed several approaches, including aeration destratification and a side stream super-saturation system (SSS). While either approach is suitable for Honeoye Lake, their analysis leads the consultants to recommend a side-stream super-saturation system as most appropriate among the current options for Honeoye Lake.
A side stream super-saturation system operates during the time that anoxia occurs in the bottom sediments. Deep water from the hypolimnion is withdrawn from the lake (at a rate of 500,000 gallons per day) to a shoreline pumphouse where it is injected with oxygen in a mixing chamber and returned to the hypolimnion via perforated tubing anchored above the lake bottom. The artificially oxygenated water diffuses along a cool water density gradient, blanketing the bottom sediments of the hypolimnion. Low velocity, screens, and the anchoring system help prevent sediment resuspension and entrainment (trapping) of fish larvae and zooplankton. Oxygen used in this system is produced on site via an O2 generator in the pumphouse.
Why this approach? According to the consultants’ side-by-side comparison of alternatives, a side-stream super-saturation system requires much less equipment and hardware anchored to the bottom, thereby reducing risk of snagging and damage. The compressed air and power requirements for the side-stream super-saturation system are less than those required for an aeration destratification system, reducing operating costs. A side-stream super-saturation system can be calibrated during the operating season to adjust oxygen concentrations in bottom waters. For example, fish habitat can be benefited by the maintenance of an oxygen concentration above 4-5 mg/l (O2 concentrations at the bottom typically go to <1 mg/l during prolonged thermal stratification).
Maintaining consistent oxygen concentrations at the bottom can increase the biological activity in the sediment, accelerating decomposition of organic matter and potentially, over time, reducing the amount of oxygen needed to be injected at the pump house to maintain an oxygenated hypolimnion. The side stream super-saturation system also has somewhat lower capital and annual operating costs compared to aeration destratification systems.
Project costs can be reduced by siting the pump house as close as possible to the intake and outlet, to be located in the deepest part of the lake. Ideally, the pump house would be located on public land and a reasonable distance from residences. Candidate sites were reviewed as part of this planning project, but before an agreement with a landowner (public or private) is completed, the community will need to decide if an aeration system is indeed desirable. This includes support for a future application for grant funding (which may cover up to 75% of eligible project expenses) and the required 25% local match (based on current grant programs available).
What does a side stream super-saturation system cost? Princeton Hydro has estimated that the total capital cost would be ~$1,200,000. Some efficiencies may be realized in categories like permitting and bidding with in-kind assistance from local agencies. Annual operating costs are estimated to be $35,000-50,000 for utilities, maintenance, and annual inspection.
Certainly, this is a big project for the communities of Richmond and Canadice. The public will be invited to learn about aeration and the recommendations in the final project document directly from the consultants via a webinar, to be announced early in 2022. Questions are welcome any time. Send them to HLWTF at email@example.com.
Terry Gronwall (HLWTF and Town of Canadice) and Betsy Landre (Ontario County Planning Department) would like to thank local project committee members who have provided data, reviewed draft documents, and raised important questions throughout this project:
David Baker, Town of Richmond
Bruce Gilman, Professor Emeritus, Finger Lakes Community College
Nelson Hairston, Professor Emeritus, Cornell University
Linda Vanderbeck, Honeoye Valley Association
Staff from DEC Region 8 in Avon and in Albany are appreciated for their guidance. This planning project is funded by a Planning Grant from the NYS DEC Water Quality Implementation Grant program.
How Does an Aeration System Reduce the Impact of HABs?
By Linda Vanderbeck, Honeoye Valley Association
Harmful Algal Blooms (HABs) are obnoxious, unwelcome events that occur every year during the late summer and early fall around the world. HABs are a part of nature’s life-cycle so unfortunately, we will never be fully rid of them. We can however fight back and win battles that limit their frequency, weaken their intensity, and shorten their duration. Fuel for HABs comes from both external sources like stormwater runoff and drainage, and from internal sources like legacy phosphorus found in the lake bottom. Based on New York State Department of Environmental Conservation (NYS DEC) recommendations, the Honeoye Lake Watershed Task Force (HLWTF) together with Ontario County Soil & Water Conservation District (OCSWCD) have implemented a number of projects over the years to curtail storm water runoff into the lake. A few of these projects include: the Honeoye Inlet Restoration Project (pictured above), Debris Guards in Cratsley Gully, Briggs Gully Streambank Erosion Project, and Road Drainage and Stream Crossing Improvement. (For a full project list and details see our Projects Page).
In Honeoye Lake, 93% of HAB fuel - phosphorus - comes from lake bottom sediments (source: NYS DEC Total Maximum Daily Load for Total Phosphorus, page 12 and Harmful Algal Bloom Action Plan Honeoye Lake, page 50) so HLWTF and Ontario County Planning Department (OCPD) are now looking at ways to best curtail these sources. Phosphorus is mostly stored in the “muck” at the bottom of the lake. As long as there is plenty of oxygen in the water, the phosphorus stays in the muck. As summer goes on, the oxygen gets used up and phosphorus leaves the muck but stays in the colder water near the bottom of the lake. Because Honeoye Lake is shallow, strong winds and storms can cause mixing, sometimes called “lake turnover.” When this happens, the phosphorus in the colder deep water at the bottom raises to the surface where blue-green algae live; the sun shines and now there’s a HAB. This HAB-causing process is well understood and accepted throughout the professional and scientific community. Many formal studies have been conducted and peer reviewed that document how phosphorus leaves the muck when oxygen is used up and how this causes HABs. Specifically, research has confirmed that this is the condition that causes Honeoye Lake’s seasonal HABs.
Keeping oxygen in the water and therefore keeping phosphorus in the muck is what aeration systems can do. Two NYS DEC reports, Total Maximum Daily Load for Total Phosphorus and Harmful Algal Bloom Action Plan Honeoye Lake, as well as the HLWTF Honeoye Lake Watershed Management Plan Executive Summary all recommend an aeration system as a way to manage internal phosphorus loading for fighting HABs in Honeoye Lake. Aeration systems add oxygen into the water via a variety of methods and have been successfully deployed for many years in lakes, farm and fish ponds, water supply, fishery reservoirs, and waste water treatment facilities. Lake scientists and engineers have developed mathematical formulas that are applied to quantitative lake data to calculate the amount of oxygen a lake requires to mitigate phosphorus loading. From such analysis, aeration system engineers are able to design aeration systems specific to any given body of water.
No decisions have been made to install an aeration system at Honeoye Lake yet. However, HLWTF and Ontario County Planning Department are currently working with a lake management consultant Princeton Hydro to look at the feasibility of an aeration system. The effort is a planning exercise at this point. There are many additional steps necessary for an aeration system to become a reality including: buy-in from Richmond and Canadice, funding, grant proposals, request for proposals (RFPs), engineering, logistics, training, budgets, and more. Still, an aeration system may never happen. Keep in mind, that not even an aeration system will prevent HABs. Some phosphorus will always find its way into the lake from runoff during heavy rainfalls.
In the coming months more information about the planning effort will become available as well as opportunities for public input. The war on HABs has been waging for many years and we have won a lot of the battles. Now we are strategizing an attack on the mother lode - internal legacy phosphorus. If we win this battle, it just might be our greatest victory yet!
To understand the strategy for fighting HABs in Honeoye Lake, see: