Protecting Waterways with Stormwater Treatment and Long-Term Monitoring

Located 20 miles east of Seattle, WA, Redmond is home to 50,000 residents and many high-tech and biomedical companies, including Microsoft. Redmond’s downtown drainage area is dominated by commercial, industrial and roadway areas with typical surface pavement contaminants such as metals, nutrients and sediments.

Redmond’s stormwater flows into the Sammamish River and Lake Sammamish, important waterbodies for rearing and migrating salmon species. To help prevent stormwater runoff from harming these waterways, the City of Redmond developed stringent stormwater regulations and sought a stormwater treatment system that exceeded existing environmental guidelines.

Solution

The city selected Water Tectonics as the vendor to supply the permanent stormwater treatment system at the new McRedmond Regional Water Quality Facility, located on a 15.5-acre site in downtown Redmond. This system is a pilot study and part of a $40 million, multi-phased, citywide stormwater infrastructure improvement program.

FIgure 1: This large water quality treatment train was easily installed in less than one day.

Water Tectonics, in conjunction with Royal Environmental Systems, designed a system to remove total and dissolved metals, phosphorus, and suspended sediments. The end product is one of the first of its kind in the country and is currently being monitored as part of a long-term evaluation study.

The McRedmond Regional Water Quality Facility incorporates two different stormwater treatment technologies: ecoStorm, a gross particle separator; and ecoStorm Plus, a stormwater filtration system installed in series to form a treatment train.

Figure 2: Schematic of McRedmond monitoring and sampling system.

Stormwater initially flows into the ecoStorm, where greater than 80% of floating pollutants, settleable solids, and litter are removed. The effluent is then sent to a splitter manhole, where it is distributed into four pipes that lead to four ecoStorm Plus units.

Sediments are further removed from the stormwater by gravitation using a hydrodynamic separator before flowing upward through the ecoStorm Plus filter, where >80% of the remaining Total Suspended Solids (based on Sil-Co-Sil 106 particle size), metals and phosphorus are removed through chemical transformation, precipitation, and sorption. The treated stormwater effluent flows from the ecoStorm Plus units to the Sammamish River.

Figure 3: Porous concrete revolutionizes stormwater filtration.

At the city’s request, the system at the McRedmond Regional Water Quality Facility was oversized by a factor of two to study performance using a slower treatment rate to meet standards for infiltration to groundwater within a wellhead protection area. This system far exceeds the 1.3 cfs that the facility is required to treat. Typically, four ecoStorm plus units treat up to 3.2 cfs.

Measuring Effectiveness

During a two-year study, the treatment facility’s performance will be evaluated through online monitoring of rainfall, flow, and turbidity with real-time remote monitoring capability. Rainfall and flow will also trigger flow-weighted auto-sampling to capture representative composite samples from individual storm events. Three auto-samplers will collect samples upstream and downstream of the ecoStorm and upstream and downstream of the ecoStorm Plus units.

The auto-samplers are programmed to collect composite samples from events that meet the minimum requirements of a qualifying storm event. Sampling lines and cables are routed to a monitoring trailer through a permanent conduit. The monitoring trailer contains all of the auto-samplers and online monitoring equipment.

Monitored parameters include total and dissolved metals (e.g., zinc, copper, and lead), hydrocarbons, total phosphorus, orthophosphate, and particle size distribution. The sampling design also includes online monitoring of bypass flows and turbidity at the three sampling locations. This long-term monitoring is expected to provide a clear understanding of the effectiveness of the treatment systems, and will be a model for future water quality treatment facilities.

About the Companies

Royal Environmental Systems offers a complete line of Water Treatment and Utility Infrastructure products designed to increase the longevity of projects while reducing long-term costs.

WATERTECTONICS engineers scalable water treatment solutions, from single contaminant removal to treatment of complex process and stormwater streams.