Publications

Kitsap County Stormwater Pond Retrofit Design Guidance Manual

Reference: Herrera. 2012. Kitsap County Stormwater Pond Retrofit Design Guidance Manual. Prepared for Kitsap County Department of Public Works, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Final Report: 185th Avenue NE Bioretention Stormwater Treatment System Performance Monitoring

Reference: Herrera. 2014. Final Report: 185th Avenue NE Bioretention Stormwater Treatment System Performance Monitoring. Prepared for City of Redmond Department of Public Works, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Final Report: City of Redmond Six Swales Bioretention Monitoring

Reference: Herrera. 2015. Final Report: City of Redmond Six Swales Bioretention Monitoring. Prepared for City of Redmond Department of Public Works, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

2017 Trend Analysis Report. Burnt Bridge Creek Ambient Water Quality Monitoring Program

Reference: Herrera. 2018. 2017 Trend Analysis Report. Burnt Bridge Creek Ambient Water Quality Monitoring Program. Prepared for the City of Vancouver, Washington, by Herrera Environmental Consultants, Inc., Portland, Oregon.

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...

Bioretention Media Blends to Improve Stormwater Treatment: Final Phase of Study to Develop New Specifications Final Report

Reference: Herrera. 2020. Bioretention Media Blends to Improve Stormwater Treatment: Final Phase of Study to Develop New Specifications Final Report. Prepared for King County Department of Natural Resources and Parks, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Pacific Northwest Bioretention Performance Study Synthesis Report

Reference: Herrera. 2016. Pacific Northwest Bioretention Performance Study Synthesis Report. Prepared for City of Redmond Department of Public Works, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Final Data Report: Grass Lawn Park LID Monitoring (October 2008 to September 2011)

Reference: Herrera. 2011. Final Data Report: Grass Lawn Park LID Monitoring (October 2008 to September 2011). Prepared for The City of Redmond, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Water Quality Statistical and Pollutant Loading Analysis: Green-Duwamish Watershed Water Quality Assessment

Reference: Herrera. 2007. Water Quality Statistical and Pollutant Loading Analysis: Green-Duwamish Watershed Water Quality Assessment. Prepared for King County Department of Natural Resources and Parks, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Green – Duwamish Watershed Water Quality Assessment: Microbial Source Tracking Study Report

Reference: Herrera. 2006. Green - Duwamish Watershed Water Quality Assessment: Microbial Source Tracking Study Report. Prepared for King County Department of Natural Resources and Parks, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Inman Landfill Post-Closure Care Landfill Gas

Reference: Herrera. 2018. Inman Landfill Post-Closure Care Landfill Gas. Prepared for Skagit County Public Works, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Public Review Draft: City of Lacey Stormwater Comprehensive Plan 2020

Reference: Herrera. 2020. Public Review Draft: City of Lacey Stormwater Comprehensive Plan 2020. Prepared for City of Lacey by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Toxics in Surface Runoff to Puget Sound: Phase 3 Data and Load Estimates

Reference: Herrera. 2011. Toxics in Surface Runoff to Puget Sound: Phase 3 Data and Load Estimates. Prepared for Washington State Department of Ecology, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Redmond Paired Watershed Study: Water Year 2018 Data Summary Report

Reference: Herrera. 2019. Redmond Paired Watershed Study: Water Year 2018 Data Summary Report. Prepared for City of Redmond Department of Public Works, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Redmond Paired Watershed Study: Monitoring Literature Review Summary Report

Reference: Herrera. 2015. Redmond Paired Watershed Study: Monitoring Literature Review Summary Report. Prepared for City of Redmond Department of Public Works, by Herrera Environmental Consultants, Inc., Seattle, Washington.

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...

Wetland and Stream Assessment Report

Reference: Herrera. 2019. Wetland and Stream Assessment Report. SR 167 Completion Project, Stage 1A SR 167/70th Avenue East Vicinity Bridge Replacement Project. Prepared for Washington State Department of Transportation, by Herrera Environmental Consultants, Inc. Seattle, Washington.

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...

Swale on Yale: Innovative Regional Green Stormwater Infrastructure in an Urban Neighborhood

Reference: Herrera and SPU. 2017. Swale on Yale: Innovative Regional Green Stormwater Infrastructure in an Urban Neighborhood. Presented at StormCon, Bellevue, Washington, August 27 – 31, 2017.

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...

Vancouver Watershed Health Assessment

Reference: Herrera and PGG. 2019. Integrated Scientific Assessment Report. Vancouver Watershed Health Assessment. Prepared for Prepared for the City of Vancouver, Washington, by Herrera Environmental Consultants, Inc., Portland, Oregon and Pacific Groundwater Group, Seattle Washington.

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...