Project 8: Wilmont Drainage EutroSORB

The BCWA and Evergreen Metro District will conduct a pilot study in the in-flow water from Wilmont drainage to reduce phosphorus loading into Evergreen Lake. The BCWA will use EutroSORB (a phosphorus filtration system) to reduce phosphorus loading. EutroSORB filters are an efficient and economical solution designed for intercepting free reactive phosphorus (SRP) from moving water. The EutroSORB reactive filter media is contained in mesh bags that is secured within the flow channel and left for a specified period of time. The filter media is safe to aquatic life, does not dissolve, and is removed from the environment when the filter has met capacity. The BCWA will use a single application approach to reduce phosphorus loading. The pilot project will secure 88 twenty–five pound mesh bags (total of 2,200 pounds of EutroSORB filter media) in the Wilmot drainage channel adjacent to the City and County of Denver golf course. The placement of the 25-pound filter media bags will minimize any erosion potential. Water quality data collection will be done over 5+ months using a two point monitoring site process in the channel (above and below the project). The pilot project will run from July through December 2021. Most of the bags will be removed in 2021, several bags maybe left in the field to test how they endure winter conditions.

The Bear Creek Watershed Association (BCWA) has identified a suspected nutrient load source into Evergreen Lake. Evergreen Lake (Segment 1d) is a small reservoir constructed in 1927 and serves as the only direct use water supply for the Ever-green community. The lake is an important year-round recreation-al facility with fishing and winter ice activities. In recent years, Evergreen Lake is shifting toward a more eutrophic system with increased summer time phytoplankton blooms, including high concentrations of bluegreen algae. BCWA monitors in Evergreen Lake and has documented increased nutrient (total phosphorus and total nitrogen) loading in recent years. While most nutrient loads come from Bear Creek inflow, there are additional nutrients introduced into the lake from Wilmot drainage. There is also internal loading from bottom sediments contributing to the algal blooms. The BCWA has increased monitoring efforts to better characterize the reservoir and improve the water quality. The BCWA has established preferred management strategies for Evergreen Lake (BCWA Policy 20), which include nutrient management and reduction.

The BCWF/BCWA will collect total phosphorus and total nitrogen data from the two selected monitoring sites on the Wilmot drainage before the project to establish base-line water quality. The BCWA and Evergreen Metro District (EMD) staff will need to clean up excess vegetation in the channel (minimal) and establish sites for securing the filter media mesh bags. The BCWA and EMD staff will work with EutroPHIX staff in site selection and installation. The BCWA will conduct monthly monitoring (minimum) for total phosphorus, total nitrogen and soluble reactive phosphorus (orthophosphorus) above and below the project (Wilmot 101a and Wilmot 101b). The target for the demonstration project is to remove 30% of the phosphorus load from Wilmot Creek before it enters Evergreen Lake. After the demonstration period, the nutrient rich filter mesh bags will be removed for green-disposal (e.g., local land application as a soil amenity). The BCWA may also evaluate nutrient loading near the up-stream high school (upper Wilmot drainage). The BCWF will develop signage for the project. Site tours will be conducted for the pilot project.

The EMD will cover cost of the EutroSORB media and mesh bags for the pilot project (88 bags, $5,522). Since the BCWF will order 4 pallets of filter media for two projects, there is no shipping cost. The labor will be provided by the BCWA, City and County of Denver and EMD staff. The monitoring cost (field collection and laboratory) for the demonstration period are covered by the BCWA (assuming 8 sample sets) the orthophosphorus laboratory cost = $432, total phosphorus =$528, and total nitrogen = $528 for a laboratory monitoring cost value of $1,488 (including field collection the in-kind worth is $2,400). The estimated total project cost is about $7,010. The value-added in-kind services (labor and signage) will increase the project value to about $10,000.

The BCWA will monitor for field parameters including specific conductance, water and air temperature, dis-solved oxygen, pH and water flow. Laboratory samples will be collected for total phosphorus, orthophosphorus and total nitrogen. The BCWA will be able to determine load reductions from the pilot project and project future load reductions using a EutroSORB filtration system. Additionally, BCWA will determine the cost effectiveness of this nutrient reduction system. The BCWA will continue with the routine monitoring in Evergreen Lake. The BCWA will produce a Technical Memorandum for the project.

This project will align multiple partners which include but not limited to Bear Creek Watershed Association, Evergreen Metro District, City and County of Denver, Bear Creek Watershed Foundation and EutroPHIX. The BCWA is looking to involve Evergreen High School in the project.