Current City of Seattle BSM specifications consist of 60% mineral aggregate and 40% fine compost consisting of nutrient-rich organic matter. This compost contains nitrogen, phosphorus, and metals such as copper, resulting in the export of nutrients downstream to receiving waters when underdrains are present. Utilizing water treatment residuals (WTRs) in compost-based BSM has the potential to reduce the export of nutrients while further reducing costs for stormwater treatment

Herrera conducted a study of the trophic cascade effects of trout stocking on algae blooms and cyanobacteria (blue-green algae) toxins in Washington lakes. Long-term water quality, cyanobacteria toxin, and trout stocking data were compiled and relationships among key variables were evaluated on a seasonal and annual basis using principal component analysis and multiple regression for Liberty Lake in eastern Washington and for 96 lakes in western Washington

The Washington State Conservation Commission (WSCC) selected Herrera Environmental Consultants (Herrera) to design and execute a quantitative microbial source tracking (MST) study to improve water quality management decision-making in Washington State. The goal of this study is to demonstrate the ability and cost-effectiveness of quantitative DNA-based MST technology to characterize pollution sources in surface waters with elevated fecal coliform bacteria levels in Washington State

The goal of this study is to develop recommendations for a statewide, high-performance bioretention soil media (BSM) specification that: 1) reduces contaminant flushing; 2) meets Ecology treatment objectives for total suspended solids, dissolved copper and zinc, and phosphorus; 3) grows plants; 4) is affordable and available; and 5) minimizes toxicity to aquatic organisms. This study tests individual media components for potential contaminant export and sorption capability, and media blends for hydraulic conductivity and plant fecundity

The CHWQP is a regional biofilter located in Seattle, Washington that was designed to treat 153 Mgal of stormwater annually. One of the three monitored biofilter blocks was configured with a polishing layer to reduce phosphorus export from the compost-based filter media. The biofilter with polishing layer reduced influent TP concentrations by an average of 75.8 percent. TP reductions were -58.4 and 27.6 for the two biofilters without polishing layers. This is the first full-scale field test of a polishing layer to reduce TP export from a compost-based biofilter

Monitoring data from several studies conducted in western Washington have indicated that some pollutants are exported from bioretention systems using the default 60% sand – 40% compost bioretention soil media, most notably nitrogen, phosphorus, and copper. To address this concern, Herrera implemented a study in partnership with Kitsap County to improve BSM performance for the capture and retention of these pollutants. This study tested pollutant leachability and sorption for 26 media components and subsequently tested the best performers in column study.

This design guidance manual provides methods and criteria for assessing the retrofit potential of existing stormwater ponds, and selection and design guidance for stormwater pond retrofits that improve water quality treatment performance. The Kitsap County Public Works Department currently has responsibility for operation and maintenance of over 300 of the approximately 600 stormwater ponds in the County. Herrera worked with the County to conduct a study of these ponds to assess water quality retrofit potential and identify retrofit solutions, and ultimately developed

Herrera Environmental Consultants, Inc. and Pacific Groundwater Group conducted a watershed health assessment, using available data, to evaluate the ecological condition of Vancouver’s watersheds, to identify data gaps, and to help the City prioritize watershed management programs and activities. The analysis included a spatial (GIS-based) statistical analysis to determine whether landscape conditions (such as, land use, terrain, and septic system density) and watershed management (e.g., stormwater facilities and habitat restoration) showed statistically significant

This literature review was conducted for the City of Redmond to summarize the results from studies which have investigated the affect of stormwater control measures on receiving water conditions. The review yielded 123 study references which are presented as an annotated bibliography in Appendix A of the report. In general, the reviewed studies indicated that a large portion (e.g., >50 percent) of the basin must be treated in order to see a measurable difference in receiving water conditions. In addition, it is apparent that in order for channel restoration to manifest