# Risk Management Guidance for Evaluating Arsenic Concentrations
in Soil

Hazardous Materials and Waste Management Division (303) 692-3300

Second Edition

June 2011

### Regulatory Limitation

This guidance does not modify, replace, or pre-empt any ex isting statutory or regulatory requirements, enforcement actions, agreements, policies or other legal mechanisms that may govern actio ns within the Hazardous Materials and Waste Management Division’s (the “Division’s”) va rious remedial programs. In the event of a conflict between this guidance and existing risk assessment guida nce and other programmatic requirements, this guidance defers to the various legal and operating mechanisms of those remedial programs.

This guidance was developed with the Division’s remedial programs in mind. Other State and Federal agencies are not obligated to use the process outlined herein, although the same analysis could apply to other sites undergoing investigation and cleanup where testing for arsenic is re quired and it may be present in sampled environmental media. Parties wanting to use this guidance at their site must seek approval to do so from the regulatory agency responsible for overseeing their remedial activities.



### Purpose
The Division has prepared this guidance for the purpose of making preliminary determinations when screening data collected from sites that don’t necessarily have a reason to believe arsenic contamination may be present, such as a routine Phase II investigation conducted prior to a property transaction. This guidance is simply meant to inform the regulated community of their responsibilities in ma naging arsenic risks: it is not regulation, nor does it

constitute an enforceable standard that must be complied with.



### Background
Arsenic is naturally occurring in some geologic enviro nments in Colorado due to weathering and erosion of bedrock and soil, including highly mineralized areas that are mined for metal ores. It is present in more than 200 different minerals, the most common of which is called arsenopyrite . It may also be present in the environment due to a number of anthropogenic activities including: military operations and firing ranges; mining, especially sulfide ores; smelting copper, gold and lead ores; preservation of wood (CCA); chicken feed operations and associated manures (CAFO) due to arsenic-containing growth prom oters; tanning and taxiderm y operations; coal-burning emissions and ash-derived residues from power plants; and may be present in landfills and landfill-derived leachate. Arsenic may also be found due to the manufacture, use a nd disposal of: ammunition; fireworks; pigments (paint, paper, ceramics, etc.); older herbicides, insecticides, and pesticides (examples: monosodium methanearsonate (MSMA), disodium methanearsonate (DSMA) and lead -arsonate); electronics containing Gallium-ArsenideSelenium (GAS) semi-conductors; lead acid battery plates; glass; and some pharmaceuticals. Other anthropogenic arsenic sources may likely exist. Arsenic contamination in so il is of public health concern due to its toxic effects as a carcinogen and a non-carcinogen. Making risk management decisions about arsenic can be difficult because natural occurring concentrations in soil often exceed carcinogenic risk based exposure values.

This guidance was prepared by the Division using a data set of background arsenic concentrations developed by the U.S. EPA Region 8. The data set includes over 2,700 samples from 44 counties in Colorado. The areas sampled included: native grasslands; agricultural areas; urban mixed land use; and mining. A summary of the data set is presented in the table below. The complete data set may be found on the U.S. EPA Region 8’s website at http://www.epa.gov/region8/r8risk/hh_exposure.html

.

Region 8 U.S. EPA 95% UCLM Background Soil Arsenic Concentrations in Colorado Land Use Concentration (mg/kg) Native Grassland, Rangeland, or Agriculture 3-14

Urban Mixed Use 19 Mining 10 Average of all land uses 11



### Division Guidance Regarding Ba ckground Arsenic Concentration

The Division’s approach to evaluating arsenic in soil is depicted in the following flowchart. This guidance assumes that, based upon the size, history and environmental concerns associated with a particular site, an adequate amount

of arsenic data has been obtained to make a determination re garding arsenic concentrations in soil. It isn’t meant to be a guide on how to conduct a background study for risk assessment and/or site closure purposes. Guidance on thesubject of data collection and analysis needs for c onducting a background study should be sought from other published sources. Soil samples should be collected and anal yzed for arsenic if the site history suggests it may be present as a result of anthropogenic activities. However, sin ce arsenic is one of the chemicals included as part of a standard “metals” analysis package from a laboratory, you may already have obtained arsenic data for your site.

The current residential/unrestricted land use remedial objective for arsenic is 0.39 mg/kg (i.e., Colorado Soil Evaluation Value, which can be found at http://www.cdphe.state.co.us/hm/csev.pdf ). If arsenic concentrations at your site are lower than 0.39 mg/kg, the Division will requi re no further action to address arsenic in soil. If arsenic concentrations are lower than 11 mg/kg (the average of the 95% UCLM of background concentrations found by the U.S. EPA in Colorado), and releases of arsenic could not have occurred at the site, b ased on historical data or process knowledge, the Division will require no further action to address arsenic in soil. If arsenic concentrations are greater than 0.39 mg/kg, and the available information suggests that a release of arsenic could have occurred at the site, the Division will require additional evaluation of the data and possibly add itional sampling to determine whether corrective measures for arsenic are required. Th is evaluation may include a site specific background study with sampling from offsite locations, and/ or additional sampling in areas of the site where activities that could have
contributed to environmental contamin ation never occurred. Please consult with the Division prior to performing any background study. If it can be demonstrated that arsen ic concentrations in soil are unrelated to site activities, the Division will require no further action regarding arsenic . It should be noted that material such as arsenicbearing mine tailings or oil and gas drill cuttings, although derived from a na turally occurring source material, are not considered to be naturally occurring background once they have been generated through human activity. Therefore, mine tailings and drill cuttings may be s ubject to remediation if ecological or health-based

concentrations are exceeded.

For more information please contact:
Colorado Department of Public Health and Environment
Hazardous Materials and Wa ste Management Division 4300 Cherry Creek Drive South Denver, Colorado 80246-1530 Customer Technical Assistance Line: (303) 692-3320 (888) 569-1831 ext. 3320 toll-free
E-mail: comments.hmwmd@state.co.us Website: http://www.cdphe.state.co.us/hm/ START

Arsenic is not a chemical of concern. Is there any reason to suspect that arsenic or arsenic containing materials may have been

used onsite?

Do sampling results exceed 11 mg/kg? Arsenic may be a chemical of concern.
Contact the Division and coordinate with the appropriate remedial program

to further evaluate the site. Do sampling results exceed 0.39 mg/kg? Arsenic is not a chemical of concern because
concentrations are below Residential/Unrestricted

r e m ed ial v al ues No

Yes

Yes Yes

No

No