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Project 4: BCR Phased PhosLock Project

Phoslock comes in a granular formation that easily goes into a slurry using application equipment with agitation moving high volumes of water. The Phoslock slurry is spread across the application area of a waterbody from a boat or barge by spraying the slurry across the surface or injecting into the water column. Following a likely slurry application of Phoslock to the surface waters of BCR, the lanthanum ions sorbed to the clay matrix will react preferentially with free phosphate compounds in water (removing free reactive phosphorus) and rapidly form a highly stable insoluble mineral on the reservoir bottom. The resulting min-eral complex becomes integrated as an inert component into the sediments of BCR and is not bio-available. Due to the specificity of Phoslock to phosphate, as long as binding sites are available, it will continually bind new incoming phosphorus from internal and external sources. A series of low-dose Phoslock applications can be made over the course of the summer (June-August) to help re-duce in-water phosphorus concentrations at the surface as well as hypolimnetic (deep water) phosphorus levels that are a major contributor to the annual phosphorus load. A phased low dose application process is recommended as part of an adaptive management program. The phase 1 will target the deeper areas of the reservoir (12 acres) around the BCWA buoy (Center of deep portion) with a heavy dose. A second phased low dose program will include a larger portion of the reservoir (80 acres). Ongoing water column monitoring will be used to adjust dosing and frequency (e.g., 2-years).

The Bear Creek Watershed Association (BCWA) has identified a problem of internal phosphorus loading in Bear Creek Reservoir. This internal loading contributes to eutrophication and excessive algal blooms. The reservoir standard for Chlorophyll a is 12.2 ug/l (chronic) = mean concentration measured through collection of samples that are representative of the mixed layer during summer months (July, August, September) and with an exceedance frequency of once in five years; and the standard for phosphorus is 22.2 ug/l (chronic) = mean concentration measured through collection of samples that are representative of the mixed layer during summer months (July, August, September) and with an exceedance frequency of once in five years. Neither of these standards can be consistently meet in the summer months. The reservoir is on the 303(d) list of impaired waters for chlorophyll and total phosphorus. Generally, the release of phosphorus from the bottom sediments is at a higher concentration compared with inflow water concentrations. This internal loading is major contributor to the phosphorus standard exceedance and a principle driver of phytoplankton growth, which causes the exceedance of the Chlorophyll standard. Reducing the internal loading of phosphorus is a critical management practice required for standards compliance.

Phoslock is a Phosphorus Locking Technology that has the potential to significantly reduce the reservoir internal phosphorus loading. Phoslock dispersed onto the bottom sediments can bind sediment phosphorus and reduce the internal loading by 30-80%, particularly in the growing season. A sediment sample (top 5-10 cm of bottom mud) was processes by SePro in 2012 (BCWA TM 2019.01 Sediment Survey BCR ). Additional sediment samples are needed for level 1-mobile vs. apatite & residual = $265/ sample; level 2-different phosphorus fractions=$500/sample (estimate need 6 level 2 samples=$3,000). The water quality analyses are completed on an ongoing basis by the BCWA. The BCWA will need to add a reactive or ortho-phosphorus analysis (= $800/year). The Phoslock is applied as slurry dose at the water surface to create an interaction with the water column or as granules for quicker layering on the bottom sediments. The application volume is based on the area of coverage. A full dose phase 1 application to the deeper portion of the reservoir (12 acres) =$62K for the media plus application cost. A light dose phase 2 to a larger area (80 acres)= $59K, but will require re-application every 2-years. A phase full dose application to the reservoir (110 acres) = $460K, but should last for 5-years. Although a major flooding event could require a re-application. The BCWA will continue normal water quality monitoring in the reservoir at 3 profile stations after applications. The BCWA will use an adaptive management approach to determine target standards compliance (Chlorophyll and phosphorus).

The BCWA will monitor for field parameters including specific conductance, water and air temperature, dis-solved oxygen, and pH in the water column. Laboratory samples will be collected for chlorophyll a (-1/2 m only), total phosphorus, orthophosphorus and total nitrogen at –1/2m and +1/2m in the water column. The BCWA will be able to determine internal loading reductions from the phased projects. Predictive tools will allow the BCWA to project future total phosphorus load reductions using PhosLock. Additionally, the BCWA and BCWF will determine the cost effectiveness of this nutrient management system.

This project will align multiple partners which include but not limited to Bear Creek Watershed Association, Bear Creek Watershed Foundation, City of Lakewood, U.S. Army Corps of Engineers and EutroPHIX (SePro).

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