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.

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:

• Climate regulation
• Carbon sequestration
• Habitat development
• Pollination of flowering plants
• Soundscape improvement
• Viewshed improvement
• Pest and invasive species control
• Flood regulation
• Nature viewing
• Recreation and physical activity
• Support and increase biodiversity

Nature-based solutions harness the power of functioning ecosystems to help solve problems humans face. Ecosystem services are the benefits humans get from functioning ecosystems.

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.

Environmental DNA (eDNA) is an innovative new technology that allows biodiversity monitoring of an area by analysing soil, water, and genetic material samples to create a list of species that are present. eDNA does not reveal an exhaustive species list but complements other monitoring efforts. For example, eDNA identifies low population size species that are difficult to identify using traditional field methods—like amphibians in this case.

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

• The remediation sites had more anthropogenic noise and less natural noise than the reference site. Reducing stress by reducing exposure to anthropogenic noise is important for community health¹. After remediation, natural sounds increase for a healthier soundscape.
• The remediation sites’ temperatures were higher than the reference site, likely due to having less vegetation. Cooler temperatures are shown to be good for human health². Once the remediation sites gain more vegetation, they can become a cool oasis for the community.
• A bird biodiversity study found higher diversity at the reference site, as expected, although the marshy Grove Gulch remediation site has many bird species.
• Our eDNA biodiversity study found the species of native frog we were looking for as well as a suite of other species, including many mammals.

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