Project 7: Horseshoe Pond Lakewood EutroSORB

The BCWF and Lakewood will conduct a pilot study in the stormwater inflow water to Horseshoe Pond to reduce phosphorus loading and potentially reduce summer bluegreen blooms. The BCWF and Lakewood will use EutroSORB (a phosphorus fil-tration 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 BCWF and Lakewood will use a single application ap-proach to reduce phosphorus loading. The pilot project will secure 72 twenty–five pound mesh bags (total of 1,800 pounds of EutroSORB filer media in the inlet chan-nel). The channel width of 3-4 feet will require two bags at each P1 site. The placement of the 25-pound filter media bags will minimize any erosion potential. Data collection will be done over 6+ months using a two point monitoring site process in the channel (HSP 100a and HSP 100b), with an additional sampling location within Horseshoe Pond. The pilot project will run from July through January). Most of the bags will be removed in January 2022, several bags maybe left in the field to test how they endure winter conditions.

The Bear Creek Watershed Association (BCWA) and Lakewood have identified a suspected nutrient load problem leading to significant bluegreen algae blooms in Horseshoe Pond, Lakewood. The pond is in Bear Creek Greenbelt just east of the Stonehouse. Previous monitoring and BCWA field investigations has found toxic levels of cyanobacteria in this pond during late summer months, particularly near the stormwater source water inflow. The algal blooms are triggered by excess nutrient loading (total phosphorus and total nitrogen) coming from nearby neighborhoods through the stormwater drainage system. This is a popular recreational area with the potential for both human and pet water contact. An established nutrient management strategy will minimize nutrient loading to reduce potential bluegreen blooms.

The BCWF/BCWA will collect total phosphorus and total nitrogen data from the two selected monitoring sites at HSP before the project to establish base-line water quality. The BCWF and Lakewood staff will need to clean up excess vegetation in the channel (minimal) and establish P1 sites for securing the filter media mesh bags. The BCWF and Lakewood staff will work with EutroPHIX staff in site selection and installation. The BCWF will conduct monthly monitoring for total phosphorus, total nitrogen and soluble reactive phosphorus (orthophosphorus) above and below the project (HSP 100a and HSP 100b) and in eastern end of Horseshoe Pond. The target for the demonstration project is to remove 30% of the phosphorus load entering Horseshoe Pond. 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 BCWF will develop signage for the project. Site tours will be conducted for the pilot project.

The City of Lakewood will cover the cost of the EutroSORB media and mesh bags for the pilot project (72 bags, $4,518). 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 BCWF and Lakewood staff. The BCWA will cover the monitoring cost for the pilot project (assuming 10 sample sets) the laboratory cost for orthophosphorus = $810, total phosphorus =$990, and total nitrogen = $990 for a monitoring cost total of $2,790. There will also be a need to collect several phytoplankton samples in Horseshoe pond for species counts ($310/ sample, minimum 3 samples). The In-kind worth from the BCWF staff assistance for monitoring and field work is about $2,500. The estimated project cost is about $7,308. The value-added in-kind services (labor and signage) will increase the project value to about $9,500.

The BCWF 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 BCWF and Lakewood will be able to determine load reductions from the pilot project and project future load reductions using a EutroSORB filtration system. Additionally, Lakewood and BCWF will determine the cost effectiveness of this nutrient reduction system for use at other Lakewood sites. The BCWF will produce a Technical Memorandum for the project.

This project will align multiple partners which include but are not limited to Bear Creek Watershed Association, Bear Creek Watershed Foundation, City of Lakewood, and EutroPHIX.