Low impact development (LID) best management practices (BMPs) may aim to treat roadway runoff near its source through dispersion and infiltration. These BMPs are crucial for reducing chemicals such as 6PPD and 6PPD-q, which derive from tire preservatives and have been linked to high mortality rates in coho salmon. Unfortunately, WSDOT’s current methods for estimating runoff infiltration rates is believed to be overly conservative, rendering the LID BMPs infeasible and substantially increasing runoff mitigation costs. Runoff infiltration rate is the product of saturated hydraulic conductivity and the hydraulic gradient. The goal of this research is to refine the method WSDOT uses to estimate hydraulic gradients, enabling it to produce more accurate and less conservative estimates of infiltration rates. These refinements should help improve the feasibility, cost-efficiency, and environmental effectiveness of LID BMPs used in WSDOT stormwater designs. This in turn should encourage broader adoption of LID BMPs and help reduce 6PPD-related environmental impacts, particularly in fish-sensitive areas.

Principal Investigators:
Brett Mauer
Mike Gomez
Pedro Arduino
Civil and Environmental Engineering, UW

Sponsor: WSDOT
WSDOT Technical Monitor: Rani Jaafar
WSDOT Project Coordinator: Mustafa Mohamedali
Scheduled completion: May 2027

This study is evaluating the ecological impacts of culvert replacements on Padden Creek near Bellingham, Washington. Padden Creek supports runs of coho and chum salmon and migrating Chinook salmon and steelhead trout. WSDOT began construction in April 2021 to replace two culverts that have slopes that prevent fish passage to improve habitat for migratory species and other wildlife along the 2.7 miles of Padden Creek between Padden Lake and Bellingham Bay. A contractor is replacing the existing concrete box culvert at I-5 with two fish passable bridges and the double concrete box culvert at SR 11 with a 20-foot single span concrete box culvert. To evaluate the impacts of those replacements, UW researchers are sampling the water for DNA at Padden Creek and two control creeks monthly through September 2022. They will develop molecular assays for three to five species that are a priority for WSDOT, such as salmonids, lamprey, and freshwater mussels, by using CRISPR-Cas12a technology. The goal is to hand off these assays to WSDOT and other state agencies so that they may autonomously use these techniques in the future for evaluating these and other waterways.

Principal Investigator: Ryan Kelly, School of Marine & Environmental Affairs, UW
Sponsor: WSDOT

WSDOT Technical Monitors:
Tammy Schmidt  
Susan Kanzler 

WSDOT Project Manager: Jon Peterson  
Scheduled completion: March 2023