This feature class depicts Comstock-era mill locations within the Carson River Mercury Site (CRMS). These locations were obtained in order to define the investigation area boundaries of Operable Unit 1 (OU1) within CRMS. Completion of this dataset took place over several years and phases, as described below.
EPA survey
The first mill survey took place in 1993 by EPA, contracted by Piedmont Engineering.113 mills were identified in this survey. Later, Nevada Division of Environmental Protection (NDEP) conducted historic research on Comstock-era mills to expand upon this dataset, identifying an additional 87 mill sites, bringing the total number of mills in the dataset to 200. This process is described below.
NDEP Historical Research
Mill site locations were determined based on georeferenced maps procured from the EPA, NDEP, Storey County and the UNR digital map library. All maps were georeferenced based on available landmarks by heads-up digitizing techniques. The maps utilized had varying degrees of accuracy based on their date of production. Some maps utilized dated back to the 1860's.
Once all historic maps were scanned, imported and georeferenced, all map sources were evaluated and mill site locations were digitized based on the preponderance of evidence (by comparing mill locations as shown on the various source maps) to determine each mill's location.
A vector layer of mill sites was thus constructed using georeferenced raster layer resources. This layer of mill sites contains the locations of 188 historic Comstock Era mills as well as 12 additional tailings locations that are not directly associated with a mill site. 33 additional sites were identified; these consisted of sites that were known to exist but not located on historic maps, as well as cyanide mills.
Broadbent and Associates, Inc. field surveys
In 2012 NDEP contracted Broadbent and Associates, Inc. to survey all mill sites defined in this dataset. The contractor successfully verified the remains and evidence of 73 mills. Inconclusive mill evidence was found for 98 of the sites in the dataset. For 65 mill sites, the contractor was not given permission by the landowner to access the property and therefore the mill site location was not surveyed. Survey status is unknown for 1 mill.
The contractor provided a feature class of all 236 mills accompanied by a detailed report on their survey efforts, listed below:
Broadbent and Associates, Inc., Eric M. Seitz, Project Manager. January 31, 2013, Final Report – Comstock Archaeological Mill Site Inventory, Unpublished.
NDEP reviewed this report and the associated feature class to confirm each mill point location and provide attribute information on the survey status of each mill site. NDEP added the attrtibute field \"Field Verified\" to provide information on the field verification status of each site. A value of \"No\" indicates the site was not surveyed in the field. This was due to to access limitations and denials for sites located on private property. A value of \"Yes\" indicates the site was surveyed and evidence of the mill was found. A value of \"Surveyed\" indicates the site was surveyed but inconclusive or little evidence of a mill was found.
Sample points are derived from either digitizing on scanned maps or converting from coordinates collected in fields. The attribute information is filled with the unique Sample ID renamed by adding neighborhood name and the original sample ID. The unique sample ID is also used to relate with parcels and sample results table.
This feature class depicts residential and non-residential parcels within the Carson River Mercury Superfund Site (CRMS) and whether or not the parcel has an institutional control associated with the property. Institutional controls include both Environmental Covenants and Covenants, Conditions, and Restrictions (CC&R's), and are part of the Nevada Division of Environmental Protection's long term management of the Carson River Mercury Superfund Site.
In 2005 environmental covenants were created with the passage of Senate Bill No. 263 by the Nevada Legislature. An environmental covenant is an instrument used to define the appropriate activities and/or uses on real property that has been subject to contamination. It is a recordable instrument that is attached to the deed and runs with the property. Prior to 2005, Covenants, Conditions, and Restrictions were used as a type of Durable Notification Mechanism on properties within the Carson River Mercury Superfund Site.
This feature class contains Comstock-era tailings locations throughout Operable Unit 1 (OU1) of the Carson River Mercury Site (CRMS) within Lyon and Storey Counties, Nevada. Piedmont Engineering was contracted by NDEP to conduct an archeological survey of Comstock-era mining and milling features. These locations were obtained in order to define the investigation area boundaries of the Carson River Mercury Site. The field survey took place in 1993; NDEP later created the geospatial data representing the surveyed features. Additional features were added by NDEP using historical documents and aerial imagery.
The hardcopy Piedmont Engineering maps of Comstock-era mills and tailings sites were georeferenced by NDEP. Tailings polygons were digitized in ArcGIS Desktop. The original hardcopy maps were drawn at a scale of 1:2400 (written as 1\" = 200' in the maps).
EPA has compiled a significant volume of soil, sediment, surface water and biota geodata, collected either directly, by contractors and in many cases by our Federal, State and Tribal agency partners (grantees) to complete the remedial investigation (RI) and Feasibility Study at the Operable Unit (OU) 2 (i.e., the river, the floodplain and biota). EPA’s goal for the OU2 area is to select a remedy in 2020 that reduces, or controls risks to human health and the environment. Specifically, this RI involves the investigation and evaluation of the heavy metals (mercury, arsenic and lead) contamination and associated drainages in the Carson River Basin which has resulted from contaminant migration from the Carson River Mercury Mines Site. The Human Health and Ecological Risk Assessments, contained within the RI, evaluated past and current releases and their impact to human health and the environment. The primary concern is the effect of mercury contamination from the mining operations on the residences near the former stamp mills, the fisheries, waterfowl, water plants and recreational users of the Carson River (“River”) Basin. The OU1 area Superfund Site consists of mining wastes and releases from approximately 236 abandoned gold and silver mines from three basic source areas: the main stem of the River starting at New Empire (Morgan Mill) to Dayton, the Comstock Lode in Gold, Six and Sevenmile Canyons and several mills around Washoe Lake. Mercury from the former mill sites, has contaminated soils at and near the former mill sites, sediments in the drainages and the floodplain, the river banks, the fish and wildlife over more than a 130-mile length of the River extending downstream to the Lahontan Valley and ultimately at its terminus at the USFWS Stillwater and Fallons National Wildlife Refuges.
Contamination from the Site is a legacy of the Comstock mining era of the late 1860s, when mercury was imported to the area for processing of gold and silver ore. Ore mined from the Comstock Lode was transported to the individual mill sites, where it was crushed and mixed with mercury to amalgamate the precious metals before refining. The mills were located in the drainages in and around Virginia City, Silver City, Gold Hill, Dayton, Six Mile Canyon, Gold Canyon, and along main stem of the Carson River between New Empire and Dayton. An estimated 7,500 tons of mercury were discharged into the tributaries and River, primarily in the form of mercury-contaminated tailings.
Data was collected from the early 1990s through December 2016 for the OU2 Remedial Investigation.
This feature class depicts the boundaries of Operable Unit 1 (OU1) within the Carson River Mercury Site (CRMS), including the four Area of Investigation boundaries.
NDEP lead an initiative to refine the boundaries shown on maps identifying the Carson River Mercury Superfund Site (CRMS) from the initial site identification and description as the Carson River hydrographic basin beginning in Carson City, NV to its terminal points in Churchill County, NV. This description of the CRMS was used in many of the early site investigation studies and reports and continued to be used in all public education and long-term site management controls until approximately 2012. Using site contaminant fate and transport determinations from the CRMS OU1 Remedial Investigation (RI) and Conceptual Site Model (CSM), it seemed inappropriate to include the much larger area of the hydrographic basin as being potentially impacted by site contaminants of concern (CoC). NDEP created protocols to estimate areas that are likely to have been impacted by CoCs and created maps using these protocols to redraw the CRMS boundary limits.
In the development of these protocols, NDEP used:
Historic records and documentation of probable source areas;
The 2012 archaeological mill site research and field study conducted by Broadbent & Associates to locate the historic source areas;
Soil and sediment transport mechanisms identified in the CSM and general soil transport and sedimentology principals to predict areas where CoCs have likely been located at and downstream of the historic sources.
The overall area of transport was estimated to be reasonably large to include possible anthropogenic activity as well as historic and future natural events such as flooding and channel migration. Additionally, NDEP added a “buffer” to extend the potential areas beyond the conservatively defined primary areas of potential contamination to further address unknown and future effects. These buffers have been identified separately from the primary areas of concern and labeled as such on maps using these protocols. These revisions were formalized in the 2013 Explanation of Significant Differences to the OU-1 Record of Decision (RoD) to adopt the new site definition and boundaries identified by NDEP as new estimates of the CRMS extents.
NDEP identified four geographic areas of prime importance to the CRMS. Originally labeled by NDEP as “Risk Areas”, the intent of this terminology was to indicate these were the areas understood to have the most likely “risk” of contamination. Under consultation with EPA R9 risk assessment staff, the term has been changed to “Area of Investigation” to avoid confusion that any actual quantitative level of human or ecological risk has been determined for these areas. They are only estimates of potential contamination and new or additional information that contradicts these boundaries as being insufficient will be used to adopt new boundaries as appropriate. The four Areas of Investigation have become the foundation for the residential soil sampling program mandated by the OU-1 RoD. Summarized briefly;
Investigation Area 1 (IA 1)- This includes all areas in the Carson River drainage basin from about the area of the historic settlement of Empire in Carson City, NV downstream to the existing or historic terminal points of the river at Carson Lake, Carson Sink, Indian Lakes and the Stillwater National Wildlife Refuge that lie outside the buffer zones of the other three Investigation Areas. It is least probable that CRMS CoCs will be located in these areas. It is unlikely that any sampling will be requested on areas developed within IA 1, but it might be requested in special circumstances, especially near and around the source areas of the contamination where historic activities could potentially have caused contamination beyond the typical boundaries as identified by the CSM.
Investigation Area 2 (IA 2)- This area is defined as a buffer that lies 100 feet along a normal horizontal to the Investigation Area 3 boundary. For Comstock-era mill sites and isolated tailings piles, this translates to the area between 350 feet and 450 feet from the center point of the historic feature. For the 100-year FEMA floodplain and areas of irrigation, this is the area beginning at the limit of the flood plain boundary or irrigated land along a normal to 100 feet.
Investigation Area 3 (IA 3)- This area is defined as a buffer that lies 100 feet along a normal horizontal to the Investigation Area 4 boundary for Comstock-era mills or isolated tailings piles. For Comstock-era mill sites and isolated tailings piles, this translates to the area between 250 feet and 350 feet from the center point of the historic feature. It is also defined as the limits of the FEMA 100-year floodplain or past or current flood irrigation practices. A tributary of the Carson River must have a Comstock-era mill site or tailings pile located along it to be mapped in IA3 and only the portion of the tributary downstream of the historic feature is included, not including the IA3 area and buffer drawn around the historic feature itself. If a tributary does not have FEMA 100-year flood plain defined, then IA3 has been defined as the area 100 feet along a normal to Investigation Area 4 boundary of that tributary.
Investigation Area 4 (IA 4)- This area represents the highest likelihood of mercury contamination. Multiple steps were used to define the extent of this area, described below:
The area within a 250 foot radius from the center point of a Comstock-era mill
Comstock-era tailings pile polygon with a 250 foot buffer
A 100 foot buffer around the centerline of the current channel of the Carson River (50 feet either side). The river channel itself is not part of OU1, however this area immediately adjacent to the river is within the FEMA 25-year floodplain and has a higher probability of contamination than the 100-year floodplain.
Tributaries to the Carson River, where Comstock-era mills and tailings piles were located are enclosed in a polygon 50-feet wide (25 feet either side) from the approximate center of the tributary channel.
Irrigation canals are enclosed in a polygon 20 feet wide (10 feet either side) from the approximate center of the ditch.
This feature class shows the boundaries of the Washoe Lake Future Study Area/Operable Unit of the Carson River Mercury Site.
Last updated in 2020.
This data set contains polygons of Nevada Counties with boundaries tied to the best available 1:24,000 or larger-scale control data and legal descriptions as of June 30, 2013.