Publications

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 conceptual designs to retrofit the highest-ranking ponds. The methods used to evaluate the County-owned ponds and identify preferred water quality retrofit solutions for those high-priority ponds are summarized in this manual and can be used as templates for other retrofit evaluations across the region.

This study was implemented to assess the potential for groundwater contamination from infiltrating stormwater through a bioretention system constructed with a bioretention soil mix (BSM) composed on 60 percent sand and 40 percent compost (60/40 Mix). A new lined bioretention system installed at the southeast corner of 185th Avenue NE and NE Union Hill Road was studied from February 2012 through September 2013. Influent and effluent chemistry was assessed using automated samplers and continuous flow gauges. The study system was effective at treating influent concentrations of total zinc, dissolved zinc, TPH-Oil, and fecal coliform. During the second year of study system operation, the average percent reductions for these parameters were 89, 43, 88, and 77, respectively. Despite these reductions, the study system exported many other constituents. For example, during the first year of study, significant pollutant export was observed for all measured nutrients, chloride, hardness, total copper, dissolved copper, and total lead. During the second year of study, there continued to be significant export of total phosphorus, orthophosphate, and nitrate+nitrite. The results from this study indicate that bioretention systems which use a 60/40 BSM can potentially act as pollutant generating sources of nutrients and metals.

This study presents results from monitoring the performance of six full scale bioretention systems in Redmond, Washington from 2013 to 2015. The results from this study corroborate other recent studies in the region indicating that bioretention systems which utilize a BSM which meets the Ecology 60/40 specification will act as a pollutant generating source of nutrients and copper. These findings indicate that the previous assumptions regarding metals and nutrient reductions in bioretention, as summarized in two recent local literature reviews (Geosyntec 2013; Taylor Aquatic Science and Policy and Cardno TEC 2013), are not accurate for the 60/40 mix installed to the 2012 Stormwater Management Manual for Western Washington specifications. For systems installed with underdrains which discharge to sensitive receiving waters there is a potential for increasing downstream nutrient and copper loading. For such applications, bioretention projects should use sand with low metal and nutrient concentrations and find organic alternatives to compost, such as coconut coir. Follow up studies at both the bench scale and field scale are currently being conducted with the goal of formulating a BSM that does not export pollutants, while still reducing influent pollutant concentrations.

Burnt Bridge Creek is a highly modified, urban stream that flows westward 12.6 miles from its agricultural origins, through the heart of Vancouver, Washington, to its terminus at Vancouver Lake. This study analyzed water quality data collected in 2011-2017 for parameters such as temperature, dissolved oxygen, fecal coliform, TSS and nutrients along 11 stations in Burnt Bridge Creek. Statistical analyses included Kendall’s tau correlation analysis to evaluate significant increasing or decreasing trends, Mann-Whitney test to detect significant differences between recent and historical data, and Friedman Test with pairwise comparison to identify significant differences in water quality among stations. Water quality index scores were also computed. Water quality monitoring of Burnt Bridge Creek is ongoing, and results are reported annually.

The overall goal of this project was to develop new recommendations for a bioretention soil media (BSM) that protects beneficial uses of receiving waters and does not export nutrients and dissolved copper as is the case with the current BSM specification of 60 percent sand/ 40 percent compost (60/40). The project entailed selecting and testing media components, combining components in various ratios and placing the BSMs in columns for water quality testing, flushing and dosing the columns with stormwater to assess performance, conducting toxicological testing of influent and effluent stormwater, and finally recommending the best performing BSM. The best performing BSM consisted of a 2-inch compost blanket, underlain by 18 inches of a sand/ coconut coir/high carbon wood ash blend, underlain by 12 inches of a sand/ activated alumina/ iron filings blend. The BSMs were similarly able to prevent expected toxic impacts including acute lethality and reproductive impairment in C. dubia, and reduced growth and pericardial edema in D. rerio. However, collectively, the bioassays showed a reduced ability of all of the tested BSMs to prevent toxicity during the final dosing event (Event 5).

This report summarizes the data from five studies in the Puget Sound region that evaluated the hydraulic and water quality treatment performance of various bioretention soil mixes (BSMs). This study was conducted to help ascertain the duration and magnitude of metals and nutrient flushing from bioretention systems using the 60 percent sand, 40 percent compost (60/40) mix, to determine which media components contributed to pollutant export, and to establish whether other media compositions would perform better than the 60/40 Mix in bioretention systems. Of the 19 BSMs reviewed the 60/40 Mix was the best performer for total suspended solids removal, but the worst for total phosphorus, nitrate+nitrite, and dissolved copper (which were exported in all cases). The compost component within the 60/40 Mix appeared to be the source of the export. Of the 19 BSMs reviewed mixes which contained sand, coconut coir, and some combination of biochar, activated alumina, or iron filings, tended to perform the best for all pollutants of concern. The study concludes with a set of recommendations for further study.

From 2008 to 2011 Herrera assessed the hydrologic and water quality performance of a vegetated roof versus a metals roof and a pervious asphalt versus conventional asphalt basketball court in Redmond Washington’s Grass Lawn Park. The results from this monitoring indicated that the vegetated roof was effective at reducing peak flow rates and flow volumes; however, the vegetated roof was also a source of nutrients and copper relative to the adjacent metal roof. The results of the hydrologic monitoring of the basketball courts were confounded by the fact that the underdrain system beneath the pervious pavement basketball court was conveying shallow groundwater in addition to stormwater runoff. This resulted in an increased export of stormwater volume during the wet season relative to the conventional basketball court. Despite the groundwater exfiltration issue, the pervious pavement court reduced peak discharge rates by approximately 68.2 percent in the 2009, 2010, and 2011 wet seasons, and 93.4 percent in the 2009, 2010, and 2011 dry seasons.

The primary goal of the Green Duwamish Water Quality Assessment (GDWQA) was to provide analytical tools to evaluate water quality issues in the Green-Duwamish River watershed from 2002 to 2003. Commercial/Industrial land use exhibited significant positive correlations with ammonia nitrogen, total zinc, and dissolved iron. High-density residential land use exhibited significant positive correlations with fecal coliform bacteria and dissolved zinc. Agriculture was most strongly correlated with orthophosphate, total phosphorus, and dissolved copper. Finally, effective impervious area showed significant positive correlations with E. Coli, ammonia nitrogen, total copper, total mercury, and total and dissolved zinc. Additional analyses included principal component analysis, correlations between water quality and hydrologic parameters, hysteresis analysis, storm versus baseflow loading comparison, and a comparison among the various sampling strategies employed.

In 2001, King County initiated a comprehensive study of the Green-Duwamish watershed, called the Green-Duwamish Watershed Water Quality Assessment (GDWQA) Comprehensive Monitoring Program. The primary purpose of the program was to collect and analyze water quality data within the Green-Duwamish watershed. As part of the GDWQA, King County implemented the microbial source tracking (MST) study described herein to address bacterial contamination in the watershed and to better understand the relationship between land use and bacterial loadings. Human sources were most prevalent in areas of low-density development (i.e., septic systems), canine/feline sources were most prevalent in areas of high density development, and livestock sources were most prevalent in agriculture areas. Bacteria sources among stations generally did not vary consistently with hydrologic condition (base flow versus storm flow) or season (winter versus summer). Avian bacteria sources represented the largest percentage (26.1 percent) of all ribotypes, and were the predominant source at eight of the nine monitoring stations.

Herrera Environmental Consultants, Inc. (Herrera) was requested by Skagit County Public Works to assist County personnel in evaluating the current landfill gas (LFG) management system and determine if the aging system should be repaired, modified, replaced, or abandoned based on the current and projected landfill gas generation while protecting human health and the environment.

Herrera worked with City staff and FCS group to evaluate the City’s Stormwater Management Program (SWMP), which included interviews with City staff, a staffing needs evaluation, field review of problem sites, hydrologic modeling, development of construction projects to solve stormwater programs, and calculation of funding needs to implement the SWMP for the 6-year planning horizon (2020 through 2025). This document represents the result of those efforts and is the first major revision of the City’s Stormwater Comprehensive Plan since the original 2013 plan. In addition to detailing SWMP activities and projects for the next six years, this plan describes SWMP goals and accomplishments; the development and organization of this plan; background information including descriptions of water bodies, stormwater infrastructure, climate change considerations, and regulatory environment; and proposed programs, policies, and activities to meet the SWMP goals.

The Washington State Department of Ecology identified surface runoff as the most significant contributor of toxic chemicals to Puget Sound during earlier phases of the Puget Sound Toxics Loading Analysis. The objectives of the current study were to refine previous estimates of contaminant load contributions to Puget Sound via surface runoff by monitoring contaminant concentrations and discharge from four land uses: commercial/industrial, residential, agricultural, and forest/field/other. From 2009 to 2010, samples were collected from 16 streams in the Puyallup and Snohomish watersheds during two baseflow events and six storm events. Each stream received surface runoff primarily originating from one of the four land uses. Samples were analyzed for an extensive list of organic compounds, heavy metals, and conventional water quality parameters. The majority of the chemicals analyzed were detected more frequently and at higher concentrations during storm events than baseflow conditions among all land uses. Contaminant concentrations and area-normalized loading rates were generally higher in the commercial/industrial basins and lower in the forested basins than the other land-use categories for both flow conditions. The fall storm had the highest incidence of oil and grease, TPH lube oil, triclopyr, and other parameters.

The goal of this study was to determine how effective are watershed rehabilitation efforts at improving receiving water conditions at the watershed scale? The study was designed with a 10-year timeframe, this report summarizes the data collected in year 3 of the study. Seven streams within the City of Redmond were monitored for flow, water quality, sediment quality, habitat, and B-IBI. Two of the streams are in a forested preserve and functioned as Reference watersheds, two streams are in highly impacted basins and served as Control basins, the remaining three streams are also in impacted basins, but intensive watershed management actions are planned for these Application basins in an effort to restore stream function and habitat quality. In year 3 of this study many of these watershed management actions have not yet been initiated, so this report serves to present baseline data for the 10-year study.

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 sustainable environmental benefits, basin-wide issues (e.g., impervious surfaces, anthropogenic accelerated erosion) must be addressed.

The SR 167 Completion Project is one of two large projects comprising WSDOT’s Puget Sound Gateway Program. The purpose of the Phase 1 Improvements is to improve regional mobility of the transportation system to serve multimodal local and port freight movement between the Puyallup termini of SR 167, SR 410, and SR 512, as well as the I-5 corridor, the SR 509 freeway, and the Port of Tacoma. The purpose of this report is to identify and describe wetlands and streams in the study area within Pierce County, Fife, and Milton. Wetland biologists evaluated field conditions by traversing the study area and noting wetlands, streams, and other aquatic features. Twenty-three (23) wetlands covering 98.44 acres were identified within the study area. Wetlands in the study area typically provide a moderate level of hydrologic and water quality functionality, and a low level of habitat for wildlife.

A Stormwater Park in downtown Seattle, the Swale on Yale Project treats 190 million gallons of stormwater annually within the streetscape while also providing a gathering place and backdrop for life in a revitalized neighborhood in downtown Seattle. From 2015 to 2016 Herrera and Seattle Public Utilities (SPU) implemented an intensive water quality and quantity monitoring effort to assess the performance of one block of the four block swale project. The monitoring entailed continuous flow measurement of influent stormwater and treated effluent from the underdrain outlet and the surface flow outlet. Automated samplers were used to collect water samples from these same monitoring locations. The project was able to remove suspended solids for $20 – 28 per pound, compared with a more typical $60 – 64 per pound. The performance was better than the majority of the BMPs employed by SPU, including bioretention. Despite this, the nutrient removal performance was insufficient, and in the case of ortho-phosphate, the system exported.

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 correlations with water quality in the Burnt Bridge Creek watershed.