Butte, Montana has legacy of contamination from mining, milling, and smelting activities since the 1860s. Silverbow Creek was designated a superfund site in 1983, one of the largest in the United States of America. The Silver Bow Creek Conservation Area (SBCCA) remediation and end land use project is a component of remedial actions required by the Butte Priority Soils Operable Unit (BPSOU) Consent Decree (United States and State of Montana, 2020).

There is contamination of soil, surface water, groundwater, and stormwater in Butte, which is relatively stable, except during stormwater surges when it can be mobilised and carried downstream. Prior to Ramboll’s involvement, a remediation master plan was designed to capture and separate impacted stormwater from contaminated soil and groundwater prior to being treated and discharged into Silver Bow Creek. Developed with considerable community input, the plan prioritises community uses and incorporates sustainability in design choices.

Incorporating nature-based solutions

To achieve the project’s stormwater management goals, the client is integrating nature-based solutions (NBS) which will also create high-quality habitats and community open spaces. These include bio-sequestration, adding native plants, and creating stormwater treatment ponds and wetlands within a 160-acre urban greenway in the heart of the town.

Working with local landscapers, Ramboll ensured planting schedules will create and support a diverse habitat that allows wildlife to thrive and will beautify the community over time. These solutions are expected to provide the following ecosystem services:

Long-term ecosystem services monitoring

As a voluntary addition to the project, the client committed to a long-term ecosystem services monitoring programme designed and implemented by Ramboll. The programme goal is to quantify how the remediation project improves ecosystem services and biodiversity. The client will use this study to better understand and communicate how a remediation project can change ecosystem services to the benefit of the local community.

Ramboll’s initial surveys, conducted from 2022-2024, monitor baseline conditions prior to construction for remediation. The study will continue for 30 years post-construction to document changes in both environmental and social ecosystem services and their impact on the local community.

We paired traditional field monitoring with audio recording, temperature sensors, and environmental DNA (eDNA) collection to survey and quantify ecosystem services in the remediation sites and a reference site. Comparing data from the reference site to project sites can help quantify remediation project success in case of regional changes due to outside factors such as climate change or extinction.

Results

In 2024, Ramboll is working on a third year of baseline analyses as sites prepare for construction. Selected results include:

As expected, our results show the remediation sites have lower biodiversity and ecosystem services than the reference site. After remediation, we can document changes in our measured ecosystem services, provide advice for adaptive management, and report successes and lessons learned to make the next NBS remediation project even better.

¹Humans are less stressed by noises associated with nature, like the sound of leaves blowing, when compared to exposure to anthropogenic noises, such as traffic (Alvarsson et al. 2010)

²Hajat et al. 2014; Lan et al. 2022