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|Site Type: Non-NPL
County: Jefferson County
Street Address: 5201 W. 56th Ave.
ZIP Code: 80002
EPA ID: CO0001101476
Site Aliases: Thoro Products
Congressional District: 7
The Twins Inn site is located in both the City of Arvada and unincorporated Jefferson County, about 10 miles northwest of downtown Denver, Colorado. The site area includes a few residences and commercial/industrial businesses that primarily use municipal water supplies. One of the businesses in the area is the Twins Inn Tavern, from which the site derives its name.
In 1995, EPA discovered that the well at the Twins Inn Tavern was contaminated with a chlorinated solvent called trichloroethene (TCE) as well as other organic chemicals in excess of drinking water standards. In response, EPA sampled domestic wells, monitoring wells, groundwater, surface water, and some soil in the vicinity near the well. EPA traced the source area to the Thoro Products Co. property at 6611 West 58th Place. Thoro Products Co. was a small family-owned business that manufactured laundry spot removal, janitorial supplies and cleaning products. The company also acted as a distributor of bulk chemicals for various companies, including Dow Chemical Co. and others, and conducted solvent recycling and drum washing operations for a few years.
Operations on this property resulted in the soil and groundwater in the area being contaminated with chlorinated solvents and other chemicals. The groundwater contaminant plume from this site originates near W. 58th Ave. and Nolan St. in the City of Arvada. It extends east-southeastward almost to Sheridan Blvd. The plume generally runs parallel to Ralston Creek.
Currently, there is little risk to individuals being exposed to the contaminated soils on-site because the contamination is mainly below the ground surface. Based on earlier indoor air sampling, breathing indoor air at area residences situated directly over the plume does not pose an unacceptable risk to human health. However, indoor air sampling has not yet been conducted in commercial buildings overlying the highest groundwater concentrations levels. EPA's proposed remedy anticipates future air monitoring and mitigation efforts where necessary.
Domestic use of untreated groundwater for drinking, cooking, and bathing would pose an unacceptable risk to human health. Within the area of the plume, there are only two residences and a local tavern that use a well as a source for drinking, cooking and bathing. That well has been fitted with special carbon filters to treat and remove the contamination before it is used/consumed by the residents and/or the customers of the local tavern. Therefore, there is no risk to the users of that well.
In 1995, EPA provided bottled water and then installed a water treatment system for the two impacted residences and the Twins Inn Tavern. Annual water sampling is performed to see that the water treatment system is working properly.
EPA conducted field investigations and numerous site sampling efforts to understand the source and extent of the groundwater contamination and the source of the contamination.
In the summer of 2008, EPA determined that it would be both more cost-effective and time-efficient to proceed at the site using its Removal Authority, rather than with its Remedial Authority. The Remedial Investigation/ Feasibility Study (RI/FS) was renamed an Engineering Evaluation/Cost Analysis (EE/CA) following public notice and a comment period, and written response was made to all comments received. The renaming of this document indicates EPA's intent to move forward at this site using a Removal Action rather than a Remedial Action.
The EE/CA for the site recommended source removal in combination with monitored natural attenuation (MNA). At the time of the publication of the EE/CA, known residential use of the groundwater from the Twins Inn well existed at the site. Accordingly, the alternatives evaluated in the EE/CA included this residential risk element. The site Remedial Action Plan presented at the public meeting involved: a) removal of the contaminated soil sources located on the Thoro property, and b) monitoring the natural attenuation of the contaminants in the site groundwater.
Community involvement efforts at this site include fact sheets, public notices and public meetings. Fact sheets are used to elaborate on Site Documents and to provide definitions and background information on technical terms. Public notices inform the public where records are kept in the different communities.
EPA and the Colorado Department of Public Health and Environment (CDPHE) held a public meeting on May 21, 2007 to discuss cleanup alternatives. The comment period for the proposed cleanup plan was extended 30 days to July 5th, 2007. In June 2008, following written responses to all comments received, the Remedial Investigation/Feasibility Study was renamed an EE/CA following a public notice and comment period. Written responses were made to all comments received.
Engineering Evaluation/Cost Analysis (EECA), revised and updated August 2010
Fact Sheet, May 2007
Feasibility Study, January 31, 2007
Remedial Project Manager
U.S. Environmental Protection Agency, Region 8
1595 Wynkoop Street (EPR-SR)
Denver, CO 80202-1129
800-227-8917 ext. 312-6762 (toll free Region 8 only)
State Project Manager
Colorado Department of Public Health and Environment
Hazardous Materials and Waste Management Division
4300 Cherry Creek Drive South
Denver, CO 80246-1530
888-569-1831 ext. 3366 (toll free)
Site Information Repositories:
7525 W. 57th Avenue
Arvada, CO 80002
EPA Superfund Records Center
1595 Wynkoop Street
Denver, CO 80202-1129
To request copies of administrative record documents call:
800-227-8917 ext. 312-7273 (toll free Region 8 only)