Summary of the Denver Radium Superfund Site

During the early 1900s, Denver was home to a radium ore processing industry.  Radium was used for
making self-luminous paints, such as for instrument dials and watch faces, in addition to cancer therapy

and research.  Through the 1920s, the City of Denver used these mill tailings to pave certain streets in
the Capitol Hill and Ruby Hill neighborhoods.  Various heavy metals plus radioactive elements such as
radium continued to contaminate the shallow soils and groundwater at the industrial mill properties.

Beginning in the 1980s, the Environmental
Protection Agency (EPA), Colorado Department of Public Health and Environment (CDPHE),and Denver Department of Environmental Health (DEH) performed assessments and determinations for clean-up by removal and permanent disposal of radioactive material.The Denver Radium Superfund Site consists
of over 65 properties, which were divided
into 11 Operable Units (OUs) located in the
City and County of Denver.Clean-up of the
Denver Streets OU began in 2002 and was
completed in 2007 at areas indicated in red
on the satellite image.  The material was
excavated using a method similar to the one
shown and transported to a licensed landfill
located in Utah.

Two of the major OUs exist near the intersection of Santa Fe Drive and I-25, and have since been
cleaned up and redeveloped. One example is the Shattuck Chemical Company site, OU 8, and the
former Robinson Brick Company, OU 4/5, which have been redeveloped into the Home Depot
retail site.

Since some low-level radioactive material was
left in place at several former radium processing
locations, environmental engineering controls
such as radon gas ventilation systems were
installed.  Radon gas, a radioactive decay
by-product of radium, can accumulate in
occupied areas with poor ventilation and
potentially cause health risks to humans.
Although the remedial actions by excavation
are now complete, these ventilation systems
will need to be operated for decades into the

The OUs that have been completely cleaned up have been petitioned for removal from the EPA National Priority List (NPL).  Monitoring of the other OUs will be ongoing, as will five-year reviews completed by CDPHE, to ensure the remedies remain effective until all of the OUs can be closed.

The current status of the Denver Radium Site can be important to the clients of Sundance Environmental Consultants in two ways:

1) Because the radium-laced mill tailings do or did exist on so many industrial properties and right-of-ways, there are a great many adjoining properties to this Superfund site. When we perform Phase I environmental site assessments, we evaluate whether a subject property could potentially be affected into the future by the Superfund site.

2) If a client were to consider purchasing a property that is actually part of the Superfund site, we would review the available documentation of what remedial action was undertaken at the specific property, inform the client on what the long-term monitoring and maintenance requirements are, and advise on whether there could be any restrictions on future land use or redevelopment options of a specific property.


Phase II of Historic Iron Foundry

Historic research as part of a Phase I performed by others included a review of Sanborn Fire Insurance Maps shown here from 1951 and 1974.

A former iron foundry with “earth” floors, a “cupola” furnace, and “iron” storage areas were mapped at what is today a light manufacturing facility. 

The Phase I determined that this former usage as a foundry constituted a “recognized environmental condition” and recommended that a Phase II be performed.    

A Phase II was performed by Sundance to evaluate the risk of residual heavy metals concentrations at the property.

image 1

A drilling program was established to test for heavy metals in soils and groundwater around the former foundry shop area and its cupola furnace.  Most of the test locations were now indoors and beneath thick concrete floor slabs.


The limited access to the interior of the facility  and low overheard clearance in the shop areas made the use of this portable hydraulic hammer direct-push drill rig ideal for collecting shallow soil samples and installing temporary groundwater wells.

image 2
image 3 Soil core samples were retrieved in clear acetate sleeves in 4 feet lengths allowed for visual inspection of the sub-soils.
Debris such as brick and wire helped to establish the working ground surface of the former foundry and its yard.

Groundwater samples were collected from the temporary wells.  Soil and groundwater samples were laboratory-analyzed for 8 RCRA heavy metals plus Iron, petroleum hydrocarbons such as oil and grease, and volatile organic compounds (VOCs).  

Only limited concentrations of heavy metals were detected in shallow soils at the former iron foundry property.  The Colorado Department of Public Health and Environment (CDPHE) reviewed the results, and concurred that in-place management of low concentrations of Arsenic in soil was appropriate, as they were under concrete slabs and within the range of natural background levels.  Based on these results, the State required “No Further Action” by the property owner and the pending property transaction was completed. 

Phase II Site Assessment


The refinancing of an auto transmission repair shop in Boulder required Phase I and II environmental due diligence site assessments. The property reportedly operated as a service station for less than one year in the 1950s and two underground storage tanks (USTs) were reportedly closed in-place with inert material in the 1970s. Soil testing was performed by others in 2001 to investigate the USTs and a No Further Action (NFA) determination was obtained from the Colorado Department of Labor and Employment Division of Oil and Public Safety (OPS) based on the evidence of no release(s) from the USTs. However, the long-time historic


usage of petroleum products including fuel, automotive oils/lubricants, a parts washer with acidic fluids, and possible chlorinated solvents use, were cause for environmental concern to the property and a Phase II was performed to confirm or deny the presence of recognized environmental conditions.

A portable hydraulic hammer direct-push unit was used to access tight spaces inside the shop area and drill soil borings to obtain soil and groundwater samples. Clear acetate sleeves in 4 feet lengths allowed for visual inspection of the soil core. Our field geologist performed field screening and head-space analysis. Small samples of soil were placed in resealable plastic baggies and the head-space was measured for volatile organic compounds (VOCs), using a photoionization gas detector (PID).
Groundwater samples were collected using polyethylene tubing and temporary PVC wells placed down the holes. Soil and groundwater samples were laboratory analyzed for oil and grease, target hydrocarbons, and VOCs. The results from the laboratory testing were compared to standards established by the Colorado Department of Public Health and Environment (CDPHE). The laboratory analysis of soil and groundwater on the property indicated compliance with the applicable State standards and confirmed no recognized environmental conditions were present.
During our inspection, 9 inch x 9 inch “checker-board” floor tiles were observed in the office area as suspect asbestos containing materials. Although out-of-scope for Phase I Environmental Site Assessments, property owners should be aware that suspected asbestos containing materials should be tested and abated/removed properly before
renovation and/or demolition. The CDPHE requires this work be done by licensed individuals and contractors. We work with several well established asbestos abatement contractors on projects as needed.

Natural Gas Condensate Spill Characterization and Remediation:

A tanker carrying an estimated 8,000 gallons of natural gas condensate oil crashed and spilled the contents onto a Colorado Department of Transportation R.O.W., vacant lot, and municipal stormwater conduits. Multiple berms and containment dikes were placed to prevent the release from reaching local waterways, specifically Rifle Creek. Sundance personnel and emergency response crews utilized vacuum trucks, power-washing units and heavy equipment to collect standing product throughout the various spill pathways. The spill pathways included streets, gutters, storm sewers, parking lots and private property. After ensuring that Rifle Creek was properly protected, crews flushed the impacted storm sewer and collected the rinsate for disposal. All impacted streets, parking lots and gutters were power-washed and all rinsate collected for disposal as well. All liquid wastes generated by the initial release and subsequent remediation efforts were transported to a frac tank off site for storage until disposal could be arranged. Heavy equipment was used to remove the berms and containments placed by initial responders and the impacted material was moved to the crash site for staging until disposal could be arranged.

Once the initial emergency clean-up was accomplished, Sundance conducted an investigation at the crash site. The private property adjacent to the crash site was visibly impacted due to the release, with the spilled condensate oil contained within a berm. Sundance and crews performed an exploratory excavation in the release area to determine initial extent of ground penetration and potential risk to ground water. After determining that there was no immediate threat to ground water, Sundance began working with the client, and regulatory agencies to develop an appropriate remediation plan in accordance with regulatory guidelines. Soil impacts beneath the roadway and sidewalk and around utilities were not feasibly removable and CDOT allowed levels of contamination to remain in place with the provision of a treatment plan. A 6% solution of Microblaze was applied to soil beneath the roadway with an infiltration gallery of 9 horizontal infiltration points advanced to 4 to 8 feet and placed 10 feet on center.

The solution was applied directly after installation of the infiltration gallery and again one week later. Microblaze solutions were also applied to the walls of the excavation, stormwater conduits, and impacted asphalt and landscaped areas. With the application of the Microblaze solution, this area of residual impacts will biodegrade over time.

An impermeable vapor barrier was installed between the utility R.O.W. and the clean backfill placed in the excavation on the privately owned vacant lot to prevent potential contaminant migration and vapor intrusion.

Remediation Pilot Testing with Injection of BOS-200®

Sundance Environmental Consultants performed a pilot test to verify a proposed technology for the clean up of a former gas station site. The test was designed for the injection of BOS-200®, which is an activated carbon/sulfate bioremediation compound. The activated carbon draws in the volatile contamination, and the sulfate salts create a sulfate-reducing environment to biodegrade the petroleum hydrocarbons, particularly benzene. We proposed this approach because of its potential for rapid remediation with limited surface disturbance. Additionally, the technology takes advantage of the generally anaerobic environment near a petroleum hydrocarbon plume, as an alternative to fighting the geochemistry by adding oxygen.


Detail – A total of 700 pounds of BOS-200® along with a microbe inoculant were injected at 9 locations within the pilot test area around well MW-12 in June 2007. An EPA Underground Injection Control Rule Authorization was required for these injections. Borings/temporary wells DP-19 and DP-20 were installed prior to the injections to define the lithology and baseline hydrocarbon concentrations. Following the injections, borings DP-23, DP-24, and DP-25 were installed, and wells DP-24, DP-25 and MW-12 have been sampled regularly.
The pilot test design loading rate was calculated to reduce the benzene concentration by 93 percent from 0.75 milligrams per liter (mg/l) to 0.05 mg/l. The reason the loading rate was not designed to effect 100% cleanup was so that the “partial” cleanup results could be used to validate the BOS-200® vendor’s loading rate estimation calculations.


Photo 1 – Direct-push drill rig drives injection pipe string to target depth of 12 ft, for the injection of the BOS-200® activated carbon/sulfate compound. The purpose is to enhance the bio-degradation of petroleum hydrocarbons.


Photo 2 – This equipment mixes the BOS-200® materials into an aqueous solution, for pumping into the subsurface under high pressure. Alpine Remediation, Inc. is an approved installer of BOS-200®, per the product distributor Remediation Products, Inc. of Golden, Colorado.BOS-200-pilot-test-graph

Graph – This graph presents the benzene-in-groundwater concentrations in the BOS-200® pilot test area. Benzene is no longer detected at well MW-12, which is partially due to short-circuiting of injectant to this well. Wells DP-24 and DP-25 show a reduction of benzene concentrations of up to 99% and 81%, respectively. The results generally validate the loading rate estimation calculations, and reductions in benzene concentration persist two years later. As with any injection program, there can be variations in how the injectant is distributed in the subsurface, which is observed as the difference in the results between these test wells.

Based on the success of this pilot test, Sundance has proposed the use of this technology to remediate portions of the source area, especially where surface disruption must be limited. Greater quantities of the BOS-200® compound will be injected in each shot hole, following the vendor’s loading rate calculations, in order to achieve a remediation that meets State cleanup standards.

Moisture Intrusion and Mold Abatement:

Sundance Environmental Consultants performed a water damage assessment/mold inspection and remediation at a music store where moisture intrusion occurred. The photographs below demonstrate where the water damage and mold existed in the southeast corner of the back store room.
Visible mold growth was initially cleaned with bleach by maintenance personnel. The white substance is salt from water evaporating on interior wall. During abatement, black mold was found to cover the back of the communications board, and back of drywall.


Primary cause of mold growth was incorrectly adjusted landscaping sprinklers causing water intrusion to tenant space.

Most of the water damage was due to the landscaping sprinklers which sprayed water directly on the exterior corner of the building. A lesser leak from the roof was addressed during a previous inspection and repair by a roofing contractor. The interior air sampling and bulk media sampling from the wall confirmed that active mold growths were present.

The landscaping sprinklers were adjusted so that they no longer sprayed on any portion of the building. After the water source was eliminated, the affected drywall and the plywood removed for thorough drying and mold abatement by a qualified contractor. Water dry-out and mold remediation activities were performed by the contractor during abatement based on visual observations and additional moisture meter readings. Gaps in the block wall were sealed and a liquid sealer was sprayed on the interior walls in the affected area. Postabatement clearance testing was performed to verify that the abatement was complete, before opening the area back up to the public.