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Environmental Cleanup Site Information (ECSI) Database Site Summary Report - Details for Site ID 2461, Horse Heaven Mine

This report shows data entered as of April 21, 2019 at 9:25:24 AM

This report contains site details, organized into the following sections: 1) Site Photos (appears only if the site has photos); 2) General Site Information; 3) Site Characteristics; 4) Substance Contamination Information; 5) Investigative, Remedial and Administrative Actions; and 6) Site Environmental Controls (i.e., institutional or engineering controls; appears only if DEQ has applied one or more such controls to the site).  A key to certain acronyms and terms used in the report appears at the bottom of the page.

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Environmental Cleanup Site Information (ECSI) Database Site Summary Report - Details for Site ID 2461, Horse Heaven Mine

Site Photos
Click to View Photo Picture Date Caption Size
View Photo 08/09/2001 2461 8-9-2001 66 Kb
View Photo 08/09/2001 2461 8-9-2001 69 Kb
View Photo 08/09/2001 2461 8-9-2001 56 Kb
View Photo 08/09/2001 2461 8-9-2001 76 Kb
View Photo 08/09/2001 2461 8-9-2001 58 Kb
View Photo 09/11/2001 2461 9-11-2001 stope 489 Kb
View Photo 09/11/2001 2461 9-11-2001 retort and dump 552 Kb
View Photo 09/11/2001 2461 9-11-2001 waste dumps 608 Kb
View Photo 09/11/2001 2461 9-11-2001 waste dumps 563 Kb
View Photo 09/11/2001 2461 9-11-2001 calcine dumps 551 Kb
View Photo 09/11/2001 2461 9-11-2001 calcine dumps 524 Kb
View Photo 09/11/2001 2461 9-11-2001 retort 529 Kb
View Photo 09/11/2001 Retort Oven above tailings piles. 2461 9-11-2001 77 Kb
View Photo 09/11/2001 Tailings looking north. 2461 9-11-2001 65 Kb

General Site Information

Site ID: 2461 Site Name: Horse Heaven Mine CERCLIS No:
Address: 10S/18E/S12 TL 1000  
  County: Jefferson Region: Eastern
Other location information:
Investigation Status: Listed on CRL or Inventory
Brownfield Site: No NPL Site: No Orphan Site: No Study Area: No
Property: Twnshp/Range/Sect: 10S , 18E , 12 Tax Lots: 100
  Latitude: 44.7156 deg. Longitude: -120.5053 deg.  Site Size: 37.8 acres
Other Site Names:
  Sun Oil Co.
  Washington Industries (Montana)

Site Characteristics

General Site Description: (12/21/99 MMR/SAS) The mine is located in a steep area where contamination is moving onto adjacent BLM land through "Mass Wasting."

(1/14/10 wcw/vcp) Horse Heaven Mine is an inactive mercury mine that historically was the third largest Hg producer in Oregon history. Prior to implementation of remedial actions, the site included several open stopes, shafts, and adits that potentially access underground workings of the mine. Because the site is believed to be an important matrnity and hibernation resource for the Townsend's big-eared bat (corynorhinus townsendii) and because these mine portals represented physical hazards, the remedial actions included installation of bat gates and bat grates and/or fencing to eliminate access to human while preserving bat habitat.
Site History: Characteristic mercury contamination from Hg mining operations, which included retort (D-furnance) of mine ore. Mine produced 17,216 Flasks (Hg=76lbs/flask) from 1934 - 1958.
Contamination Information: (9/11/2001 JPD/SAS) Site visit conducted with representatives of SUNOCO. There are large quantities of tailings at the site. Retort oven still in place, and several adits are still open. Evidence of erosion into adjacent creek was observed and a sediment sample was taken approximately 0.25 miles downstream of the site. Laboratory results showed elevated mercury levels in stream sediments.

(11/15/2002 WCW/VCP) Expanded Preliminary Assessment (XPA) report: Mercury levels and volume analysis were performed as part of the XPA. Mercury levels were evaluated in several locations. Ranges for specific areas were as follows: Calcine: 5.54 - 120 mg/kg; Upper Tailings: 602 - 1140 mg/kg; Southern Tailings: 482 - 612 mg/kg; Leachate from tailings: 0.0011 mg/L. Volumetric analysis on all tailings piles indicate a total tailings volume of approximately 80045 cubic yards weighing an estimated 124270 tons. pH readings of sediment samples from the east drainage ranged from 3.85-3.98. Sediments in a seep at the toe of the calcine pile had a pH of 6.54 and total mercury of 6.36 mg/kg. Maximum detections for arsenic, beryllium and mercury were above DEQ maximum allowable soil concentrations.

Phase 2 XPA field investigations and risk assessments (human and eco risk) are considered draft (July 2004). DEQ requested supplemental information concerning finalizing the XPA and RA report based upon review of draft documents (7-6-04 wcw).

CRL/I: Based upon preliminary information concerning site conditions and site-specific sampling, DEQ concludes that it is appropriate to recommend that Horse Heaven Mine be listed on both the Confirmed Release List (CRL) and also the Inventory (I). This recommendation is based upon known physical hazards and suspected exceedances of screening based standards for residual mercury. Although the final risk analysis is not completed, specific site conditions and baseline risk evaluation merit proceeding with notifications to add this site to both the CRL and I databases. (wcw 7-6-04)

Manner and Time of Release: Past business practices, since 1934.
Hazardous Substances/Waste Types: Mercury, heavy metals.
Pathways: The site is located in or near sensitive salmon habitat as identified by DEQ GIS data.
Environmental/Health Threats: Mercury contamination documented at the site poses potential threats to aquatic receptors downstream of the site, although preliminary ecologic risk evaluation suggests that this potential is remote.
Status of Investigative or Remedial Action: (12/21/99 MMR/SAS) Initial site visit 11/3/99. It's rumored that mine tailings are being sold for use as construction material. (3/16/01 JPD/SAS) Info request sent to SUNOCO, Inc. - a past operator at the mine. (8/27/01 JPD/SAS) Further-action notification letter sent to Thomas Haines, SUNOCO, 8/3/01. Response letter received 8/20/01. Site visit scheduled for 9/11/01.

(3/14/03 JPD/SAS) Preliminary Assessment performed in Summer 2002. Report being reviewed by ER Cleanup staff.

(wcw/vcp 1-14-04) XPA report (Source Group, November 2002); Phase 2 PA field work (October 2003).

(wcw/vcp 3-27-07) Final Ecological and Human Health Risk (8/20/04). Feasibility Study and Remedial Action Plan (3/11/05). Addendum to FS and RAP (7/11/05). DEQ Record of Decision (December, 2005). Implementation of Remedial Design/Remedial Action (Phase 1)(1/15/07).
Data Sources: Quicksilver Deposits in Oregon, Howard C. Brooks, misc. paper 15; Jefferson County Assessment Office. MAP tech 7.5 minute quad. Expanded Preliminary Assessment (XPA) report, November 2002.

Substance Contamination Information

Substance Media Contaminated Concentration Level Date Recorded
No information is available

Investigative, Remedial and Administrative Actions

Action Start Date Compl. Date Resp. Staff Lead Pgm
OPERATION & MAINTENANCE  (Primary Action) 01/15/2008   David Anderson SRS
View Full Report Showing Action History

Site Environmental Controls

Control Description Begin Date End Date Last Reviewed By Last Review Date
Easement Equitable Servitude 03/13/2008   Cliff Walkey, DEQ
  Comments: Implements specific land-use, site-access, groundwater-use restrictions and site runoff controls.
Use Restriction Land 03/13/2008   Cliff Walkey, DEQ
  Comments: No permament or seasonal residential use of any part of the property except for the residence in place as of March 2008 and areas north of NE Gosner Rd.
Fencing or other access barriers 03/13/2008   Cliff Walkey, DEQ
  Comments: Maintenance of fencing and signs to prohibit entry and warn of potential site hazards (described in the 1/24/08 Site Maintenance and Monitoring Plan).
Use Restriction Groundwater 03/13/2008   C. Walkey, DEQ
  Comments: No use of groundwater at the property for consumption or other beneficial use.
Berms or impoundments 03/15/2008   C. Walkey, DEQ
  Comments: Maintain functional integrity of the Surface Water Runoff Control Berm and Retention Basins, according to the 1/24/08 Site Maintenance and Monitoring Plan.

Key to Certain Acronyms and Terms in this Report:

You may be able to obtain more information about this site by contacting David Anderson at the Eastern regional office or via email at If this does not work, you may contact Mitchell Frister at (503) 229-6783, or via email at or contact the Eastern regional office.