Helena, Montana — the state capital with about 33,000 residents — was founded as a gold mining camp in 1864 and grew into a city on the wealth of Last Chance Gulch. That mining heritage gave Helena its character. It also left behind contamination that persists more than 150 years later.
East Helena Superfund Site: ASARCO’s Legacy
The most significant contamination source in the Helena area is the former ASARCO lead smelter in East Helena, which operated from 1888 to 2001. The facility processed lead ore from mines across Montana and the region, and over its 113-year life, it released:
- Lead — Smelter emissions deposited lead in soils across a wide area. Residential yards in East Helena have been remediated, but contamination extends beyond the immediate smelter property.
- Arsenic — A byproduct of lead smelting, arsenic contamination is found in both soils and groundwater at the Superfund site
- Zinc and cadmium — Additional heavy metals from the smelting process
- Slag piles — Mountains of smelter waste containing heavy metals remain on the property
The EPA listed the East Helena site on the National Priorities List in 1984. Cleanup has been ongoing for four decades, and while significant progress has been made — including residential soil removal and groundwater treatment — the site is not yet fully remediated.
Groundwater contamination from the smelter site has affected wells in the East Helena area. The arsenic plume in particular has been documented migrating beyond the original site boundary.
Mining Legacy: More Than Just ASARCO
Helena’s broader mining legacy includes:
- Last Chance Gulch gold mining — The historic mining in Helena’s own gulch left behind mine waste, tailings, and mercury (used in gold processing) in the soils and waterways
- Prickly Pear Creek — This creek, which runs through the Helena Valley, has been affected by historic mining and receives runoff from disturbed mining lands
- Upper Tenmile Creek — Helena’s primary backup water source has a watershed affected by historic mining, with elevated metals in some tributary streams
- Abandoned mines — Lewis and Clark County has numerous abandoned mines that can produce acid mine drainage and metal-laden runoff
Helena’s Municipal Water Supply
The City of Helena draws drinking water from:
- Tenmile Creek watershed — the primary source, with treatment at the Tenmile Water Treatment Plant
- Missouri River — a secondary source via the Hauser Dam pipeline
- Supplemental groundwater wells
The Tenmile system has its own water quality complications — the upper watershed includes historic mining activity that has elevated metals in some source waters. Helena invested in a modern treatment plant to address these challenges.
Treatment includes:
- Conventional coagulation and filtration
- Chlorine disinfection
- Corrosion control for lead and copper management
- Arsenic treatment for source water with naturally elevated levels
Naturally Occurring Arsenic: Montana’s Challenge
Beyond industrial contamination, Montana’s geology produces naturally elevated arsenic in groundwater. The Helena Valley aquifer contains arsenic at levels that can exceed the EPA MCL of 10 µg/L in some areas, even away from known contamination sources.
This is a significant concern for private well owners:
- The EPA MCL for arsenic (10 µg/L) was lowered from 50 µg/L in 2006, and many private wells that were “compliant” under the old standard now exceed the current standard
- Helena-area wells in volcanic and metamorphic rock formations are most likely to have elevated arsenic
- Arsenic in water is tasteless, odorless, and colorless — testing is the only way to know
What the Data Shows
From Helena’s most recent Consumer Confidence Report:
- All regulated contaminants within EPA limits
- Arsenic in source water detected but treated below MCL in finished water
- Lead at 90th percentile below action level
- Disinfection byproducts within limits
- No SDWA violations
What Helena Residents Should Do
- Private well owners — Test for arsenic, lead, and other heavy metals annually. Helena’s geology and mining history make this essential, not optional.
- East Helena residents — If you live in or near East Helena, be aware of the ongoing Superfund cleanup. Check whether your property has been included in soil remediation programs.
- Gardening caution — In areas with historic smelter deposition, test soil before growing food gardens. Lead and arsenic in soil can be taken up by plants.
- Municipal customers — Helena’s treated water meets EPA standards, but review the CCR annually, especially for arsenic and lead results.
- Arsenic treatment — If your private well has arsenic above 10 µg/L, reverse osmosis at the point of use is the most effective and affordable treatment. Whole-house arsenic-specific media systems are also available.
Helena’s beauty is real — the mountains, the valley, the big Montana sky. But the ground beneath the capital carries the scars of 150 years of mining and smelting. Understanding what’s in your water is part of living responsibly in a landscape shaped by extraction.
If you’re concerned about your water quality, a certified water treatment professional can test your water and recommend treatment solutions appropriate for your situation.