The URL can be used to link to this page

Home My WebLink About10-21-2004 Council Work SessionCouncil Work Session 5:45 p.m., Thursday, October 21,2004 Orono City Council Chambers AGENDA 1. Review of the Stubbs Bay Water Quality Feasibility Study 2. Preparations for the Upcoming Council Goal-Setting Process 3. Wetland Regulations (Continuing Discussion) 4. Selection Criteria for the Appointment of a City Representative to the Lake Minnetonka Conservation District (LMCD) • Review the purpose and operation of the LMCD • Review Past, Present, and Future LMCD Issues 5. Other TO: FROM: DATE: Mayor Peterson ami Council Members Ron Moorse, City Administrator Octol)cr 20, 2001 h SUBJECT: Stubbs Bay Water Quality Feasibility Study 'Hie City has l)cen working with the Minnehiilia Creek Watershed District (MCWD) to identily mctliods ol improving the water (|ualily in Stubbs Bay. 'I'lie MCWD initially hckl a public inronnation meeting lor residents adjacent to Stubbs Bay, <»r in the subwatershed of Stubbs Bay, to protide background regarding the water (|u;iiily issues lacing Stubbs Bay, iuid to obtain feedback from tlic residents rejpuding their prerercnces in relation to improved water (pi.-tlity in Stubbs Bay. llte MCWD next completed a fe;tsibility stutly that analyzed a number ol wsUcr tpiality improvement options, and recommended the implementation ol three siwcilic options. 1. Artilicial water circulation with iron addition, using lloating, sokir ix)wercd pumps, to reduce :tlgae growth, 2. Encouniging llte public to create rain water gardens :ts part of their landst aping to slow down and lilter rainwater 3. Creating three wet detention ponds in existing wethuul areas. A second public information meeting was then held to review the water <iu;dity improvement options, iuid obtiiin feetlback icg;uding tlic recommended options. 'Htc feedback was supportive of the recommended options. Excerpts from the feasibility study arc attached. Executive Summary The Minnehaha Creek Wiatrihed District (MCWD) 2003 Hydrologic Data Report indicates that the current Stubbs Bay water qa-.Kty would only support restricted use, based on the average total phosphorus concentration. Based on the average chloroph> 11-a concentration, Stubbs Bay should be subject u» nuisance algal blooms 50 percent or more of the time. In 2002, MCWD Managers authorized an investigation of Stubbs Bay after the City of Orono expressed concerns about its water quality. A diagnostic report, intended to evaluate the total phosphorus loadings to Stubbs Bay, was completed in 2004. As a follow-up to the diagnostic study, this report has been prepared to discuss the feasibility analysis for controlling phosphorus loads and improving water quality in Stubbs Bay. fliis report is intended to: • Summarize conclusions from previous studies that discuss watershed and internal pho.sphorus loadings and the resultant water quality of Stubbs Bay • Update the water quality response modeling for the planned (2020), full development land uses and use it as a benchmark for evaluating expected water quality improvements • Preseivt the results of this feasibility analysis to consider and evaluate the expected cost, feasibility and benefits of several water quality improvement options • Provide recommendations for further evaluation and/or implementation of specific water quality improvement options Based on the projected 2020 land uses, conversion of undeveloped and agricultural property will increase the residential land use percentage to approximately 80 percent of the upland area. Roadways will represent another 7 percent of the projected land use. Comparing the two land use coverages rev eals that approximately 983 acres (56% of the watershed area) will be developed or redeveloped by 2020. Of this area, approximately 314 acres have soils that should be appropriate for infiltration practices. Fach of the in-lake improvement options- in-lake alum application, hvpolimnctic aeration, diffused aeration and artificial circulation are expected to improve the water quality in Stubbs Bay to approximately the sanv* level. However, the annualized cost per unit decrease in total phosphorus concentration is at least twice as high for hypolimnctic aeration, compared to the other optior^, while the cost of artificial circulation is approximately two-thirds of the cost for an in-lake alum P U3V27\f ImDiaU Stubbs Hiy Feasibility Study doc application or diffused aeration. In addition, artificial circulation is the only in-lake improvement option in which the units could initially be rented, to verify their performance, before purchase. The predicted total phosphorus concentration should he reduced from 62 • g/L to 43 • g/L following implementation of the combination of artificial circulation with iron addition, rain water gardens, and additional wet detention ponding in Subwatersheds CLC-3, CLC-4 and SB-2. The predicted chtorophyll-a concentration should be reduced from 41 • g/L to 28 • g/L. and the Secchi depth should incicose from 0.66 meters (2.2 feet) to 0 82 meters (2 7 feet) with this improvement option combination. This should increase the maximum depth of aquatic plant colonization from approximately 4.2 to 5.0 feet, according to Canfield ct al. (1985). The severe and very severe nuisance algal bloom frequencies, as a percentage of the summer, should be reduced from approximately 100 to 45 percent and from 44 to 18 percent, respectively. Tliis combination of improvement options would result in somewhat higher annualized costs, but would result in the best water quality for Stubbs Bay. In addition, this option combines the more feasible and constructibic options that would have lower land acquisition costs. A bathymetric survey of the pond in Subwatershed CLC-4 should be completed to verify that the existing treatment volume is significantly .ess than the volume assumed for improvement option #8. Other potential BMPs (nut modeled for this feasibility analysis) that should be considered fur implementation in the Stubbs Bay watershed include: Street/parking lot sweeping Permeable pavement for driveways Public education concerning waste disposal, litter control, pet waste and lawn care practices Bank stabilization and vegetative bulfcrs for watershed ponds, wetlands, lakes and streams Implementation of the recommended improvement options will ensure that the Stubbs Bay phosphorus concentr.ations will meet the goals in MCWD’s Water Resource Management Plan (1997) and the Hydrologic/Hydraulic, and Pollutant Loading Study (2003b). The predicted phosphorus concentration very nearly meets the full use support designation and would fall in the review category for listing eutrophication impairments, based on phosphorus concentrations for the North Central llardworxl forest Ecoregion (MPCA. 2004). The MPCA intends to further review P \23\37\FIO\Oi<ft Stubfc* tUy Fcaiibitily Study ii ^ ' ' r N chlorophyll-a and Secchi depth data, as well as trends and user perception information for lakes in the review category to determine the impairment status. P \2iU7\FtO\Dian Siubbs Day FeatibiUiy Study doc ^ f ^ ' I 'r 4.0 Conclusions and Recommendations 4.1 Conclusions The results of the diagnostic study and this feasibility analysis support the following conclusions: • Based on the average total phosphorus concentration, Stubbs Bay water quality would only support restricted use, while the average chlorophyll-a concentration indicates that Stubbs Bay should be subject to nuisance algal blooms SO percent or more of the time. Based on the projected 2020 land uses, conversion of undeveloped and agricultural property will increase the residential land use percentage to approximately 80 percent of the upland area. Roadways will represent another ^ percent of the projected land use. Comparing the two land use coverages reveals that approximately 983 acres (56% of the watershed area) will be developed or redeveloped by 2020. Of this area, approximately 314 acres have soils that should be appropriate for infiltration practices. The updated average annual phosphorus load to Stubbs Bay for full development land use is estimated to be: .Stubbs Bay Hio.sphonis Load-Full Development Land U.se Average Load |kg]Peueutage Internal 567 48*W Atmospheric 61 5*0 External 565 47*--* Total 1193 100% The updated water quality modeling indicates that the predicted average annual total phosphorus concentration in Stubbs Bay will increase from 57 • g/L, under existing conditions, to 62 • g/L with fully developed land use conditions. Tlie primary drawback to killing algae with copper sulfate is that it is a short-term fix and not •/ long-term, sustainable solution. Also, the dead algae can release toxins to the w ater, toxic levels of copper can be deposited in the sediments and the composition of algae species can shift towards those that are more copper-resistant, but equally undesirable. rU3V:7\FI0\Duft Stubbs Bsy FcMibilily Study doc "i > ■ t n Each of the in-lake improvement options—in-Iake alum application, hypolimnetic aeration, diffused aeration and artificial circulation are expected to improve the \satcr quality in Stubbs Bay to the same level. However, the annualized cost per decrease in total phosphorus concentration is at least twice as high for hypolimnetic aeration, compared to the other options, while the cost of artificial aeration is approximately two-thirds of the cost for an in lake alum application or diffused aeration. In addition, artificial circulation is the only in- lake improvement option that could realistically involve an option of renting the units, to verify their performance, before purchase. The predicted total phosphorus concentration should be reduced from 62 • g/L to 43 • g/L following implementation of the combination of artificial circulation w ith iron addition, rain water gardens, and additional wet detention ponding in Subwatersheds CLC-3, CLC-4 and SB-2. The predicted chlorophyll-a concentration should be reduced from 41 • g/L to 28 • g/L, and the Secchi depth should increase from 0.66 meters (2.2 feet) to 0.82 meters (2.7 feet) with this improvement option combination. This should increase the maximum depth of aquatic plant colonization from approximately 4.2 to 5.0 feet, according to Canfield et al. (1985). The severe and very severe nuisance algal bloom frequencies, as a percentage of the summer, should be reduced from approximately 100 to 44 percent and from 41 to 18 percent, respectively. The total annualized cost for this improvement option is $8,200 per • g/L reduction in the Stubbs Day total phosphorus concentration. Implementation of the recommended improvement options will ensure tliat the Stubbs Bay phosphorus concentrations will meet the goals in MCWD’s Water Resource Management Plan (1997) and the Hydrologic, Hydraulic, and Pollutant Loading Study (2003). The predicted phosphorus concentration very nearly meets the full use support designation ;ind would fall in the review category for listing eutrophication impairments, based on phosphorus concentrations for the North Central Hardwood Forest Ecoregion (MPCA, 2004). Tlie MPCA intends to further review chlorophyll-a and Secchi depth data, as well as trends and user perception information for lakes in the review category to determine the impairment status. 4.2 Recommendations for Implementation The conclusions of this feasibility analysis support our recommendation to implement the combination of artificial circulation with iron addition, rain water gardens, and additional v\et detention ponding in Subwatersheds CLC-3, CLC-4 and SB-2 (see Figure 6). This combination of improvement options would result in somewhat higher annualized costs, but would result in the best P \23V27\HO\I)raft Stubbs Bay Feasibility Study doc r >1 water quality for Stubbs Bay. In addition, this option combines the mo- •; feasible and constructiblc options that would have lower land acquisition coits. A bathymetric survey of the pond in Subwatershed CLC-4 should be completed to verify that the e.xisting treatment volume is significantly less than the volume assumed for improvement option #8. 4.3 Monitoring Program Recommendations Currently, the MCWD watershed monitoring program includes collection of water quality grab samples and flow measurements on a weekly basis from the Classen Lake and Stubbs Bay Inlet creek sites. The samples are analyzed for total phosphorus, soluble reactive phosphorus, total nitrogen, total suspended solids, chloride, fecal, coliform. temperature and dissolved oxygen. The current MCWD lake monitoring program includes collection of water quality samples and measurements on a bi-weekly basis from the deep-hole location of Stubbs Bay. The surface water samples are analyzed for total phosphorus, soluble reactive phosphorus, chlorophyll-a. total nitrogen, chloride. Thermocline and deep-water samples are analyzed for total and soluble reactive phosphorus. Also, temperature, dissolved oxygen, pH, and conductivity profile measurements (at one meter intervals) are taken throughout the water column, along with a Secchi disc measurement. As previously discussed, some macrophyte surveys have been completed on Stubbs Bay in the past, but there currently arc no plans for another detailed survey to determine plant densities along transects throughout the lake urea. Also, water quality samples from Stubbs Bay have not been analyzed for phytoplankton and zooplankton species. The Stubbs Bay diagnostic and feasibility sfadies have idenified the following water quality concerns and issues associated with implementing the potential improvement options: Both watershed and internal sources of phosphorus arc contributing, and w ill continue to contribute, to the impaired water quality of the lake. It is important to collect detailed water quality data to establish an accurate account of the internal and e.\tcrnal phosphorus loadings to Stubbs Bay before future development and implementation of watershed and in-lakc improvement options. A significant reduction in the in-lake phosphorus concentrations may significantly reduce algae growth, but in turn, may booat the growth of macrophytes. It Is impo*iant to collect detailed data and establish the baseline conditions for the presence of the predominant macrophyte species in Stubbs Bay. P V21\27\FI(M>iafl SUibbi Bay Feaiibitity Study do,! Several of the in-lake improvement options are intended to create an environment that will reduce algae growih by limiting the internal phosphorus load (c recycling), limiting light, and/or improving conditions for algal grazing. Since this may result in a redistributiou of algae and grazing species, as wJI as lower algal bloom frequencies, samples should be analyzed for phytoplankton and zooplankton species both before and after implementation. Tlie following specific changes to the Stubbs Bay watershed monitoring program are recommended: Continuous flow monitoring equipment should be installed at the Classen Lake and Stubbs Bay Inlet creek locations Continuous flow and weekly water quality sampling should be done for a year, both before and after implementation of the chosen watershed and in-lake improvement options Th» following specific changes to the Stubbs Bay lake monitoiing program arc recommended both bfjk'te and after implementation of the chosen watershed and in-lakc improvement options: Total and soluble phosphorus samples should be taken at one-meter intervals and analy zed, on a monthly (or bi-weekly, if possible) basis, as part of the rcp 'lar lake water quality monitoring visits • Regular lake water quality monitoring events should continue, on a monthly basis in the winter, between November and March A detailed survey to determine macrophyte densities and depth of colonization for observed plant species along transects throughout the lake area Samples should be taken biweekly from May through September and cnumera'ed for phytoplankton and zooplankton species. Phytoplankton samples should be taken from a surface to 2-meter composite sample, and zooplankton from a botlom-to-surface vcrtic.-!! tow with a Wisconsin-style plankton net The recommended changes to the watershed and lake monitoring programs arc estimated to cost ar. additional $30,000 and $45,000. respectively, compared to the c.\isting programs, on an annual basis. f \2JU7\rt(M>«*ft Stubti* Bi> FeiSibilitj' Study doc i