SDMSDocID 2004783

DRAFT WORKPLAN

forJOINT TIME-CRITICAL REMOVAL ACTION

MCCLEUR TAILINGS SITE

Prepared by:U.S. EPA Region 9

Emergency Response Section75 Hawthorne StreetSan Francisco, CA

andU.S. Forest ServiceSouthwest Region

2324E. McDowell RoadPhoenix, AZ

November 2003

Executive Summary: U.S. EPA and USFS will mitigate human and environmental healththreats posed by heavy metals and the McCleur Tailings Site by conducting a Joint Time-CriticalRemoval Action in early 2004. U.S. EPA and USFS will excavate tailings and waste rock from aheavily impacted stream channel on the Site, returning the channel to a near original form andcondition. Tailings and waste rock removed from the channel will be restaged above the channelbank. There, the materials will be treated using amended biosolids material to reduce thetoxicity, mobility and overall bioavailability of heavy metals that have been found in the tailingsand waste rock. The Site will be revegetated with native plants and grasses in order to controlerosion and return the area to a more natural state. This treatment will abate the human andenvironmental health threats posed by the heavy metals remaining at the Site that resulted fromhistorical mining operations in the area. Construction work is expected to take no greater than 14days. Secondary planting and monitoring will occur periodically in 2004.

1. Site Description

l.a. Physical Location

The Site is situated within un-incorporated areas of the Bradshaw Ranger District of the PrescottNational Forest (PNF). The physical location of the Site is approximately 8 miles south ofdowntown Prescott at the intersection of the Senator Highway (Forest Route 52) and the WalkerRoad (Forest Route 197). The geographic coordinates of the Site are 34° 25' 25" N latitude and112° 25' 34" W longitude, in Township 12 Vi N, Range 2W, Section 36 on the Groom Creek, AZ(7.5-minute) topographic quadrangle. See Figure 1 for a Site Location Map.

l.b. Site characteristics

The Site encompasses both privately owned land and United States Forest Service (USFS) land.Hazardous substances have been observed on both the private and USFS portions of the Site.The Site is situated alongside the Senator Highway, within and adjacent to the riparian corridorof a first-order, ephemeral stream. The stream is an unnamed tributary to the Hassayampa River;the Site is located approximately V4 mile upstream of the confluence of the unnamed tributary andthe river. Mine tailings and waste rock have been observed within and around the ripariancorridor of the stream. The unnamed tributary comes into confluence with a second unnamedtributary immediately downgradient of the Site forming the Maple Gulch tributary.

Tailings and waste rock have been observed within the stream channel, bank and flood plain. Theimpacted area includes approximately 600 feet of the length of the stream corridor at a widthranging from 30 feet to 90 feet. The total volume of tailings and waste rock has been estimatedto be approximately 1,600 cubic yards. Tailings and waste rock material as well as soils andsediments on the Site are heavily stained, varying in color between white and dark red or rust.Significant impacts resulting from acid-mine drainage (AMD) have also been observed; thestream channel itself is rust-stained and vegetation is absent within the impacted area. A largewaste rock pile is located on a slope adjacent to the impacted area on a bench above the tributarynear the southern site boundary.

Substantial mining activities occurred at many sites in the area between the 1860s and 1950s.Historical records and visual observation indicate that the Site was an unpatented claim and waslikely used for milling operations. The only physical structures on the Site are a small concretepad or former foundation and a rock-lined pit. Mine tailings and waste rock cover thepredominant portion of the Site surface. A recent investigation of the Site by the USFSpostulated that a flotation mill operated at the Site.

I.e. Removal site evaluation

In July of 1999, the U.S. EPA conducted a removal site evaluation of several sources or sites inthe Hassayampa River Watershed. During the investigation the Superfund Technical Assessmentand Response Team (START) observed tailings within the stream channel at the McCleurTailings Site. START collected samples from soils, sediments and surface waters at the Site.

Base map source: U.S. Department of Agriculture, Forest Service, Prescott National Forest

A R I Z O N A

Ecology and Environment, Inc.

Figure 1

SITE LOCATION MAPPrescott National Forest

Prescott, Arizona

Analytical results indicated the presence of hazardous substances at concentrations exceedingtheir respective health-based benchmarks. These included antimony, arsenic, cadmium, lead, andmercury.

On May 1, 2003, U.S. EPA and START conducted a walkthrough of the Site. Two USFS On-Scene Coordinators (OSCs) also participated and provided pertinent background informationregarding various sites within the Lynx Creek and Hassayampa watersheds. In addition, anattorney from the U.S. Department of Agriculture (USDA) Office of General Counsel and fromU.S. EPA Region 9 participated in the Site walk. Representatives from the U.S. Fish andWildlife Service (USFWS) and Arizona Department of Environmental Quality (ADEQ), WaterQuality Division, also accompanied U.S. EPA and the USFS.

l.d. Release or threatened release into the environment of a hazardous substance, orpollutant or contaminant

Releases of waste rock and tailings material from the Site have occurred. Tailings and wasterock containing high levels of heavy metals have been deposited into the stream channel of theunnamed tributary. The threat of future releases of finer-grained tailings and waste rock ladenwith heavy metals from the Site is on-going. Concentrations of arsenic and lead were detected insoil and sediments collected at the Site during investigations conducted in 1999, 2001 and 2003.

Analytical results from samples collected from tributary sediments and from tailings and wasterock piles indicated the presence of heavy metals. In soil samples, arsenic was detected at 52.4milligrams per kilogram (mg/kg), 35.5 mg/kg and 173 mg/kg. Lead was detected in soil at aconcentration of 1,180 mg/kg. In sediments, collected from the stream channel of the unnamedtributary, arsenic was detected 255 mg/kg and 24.4 mg/kg and lead was detected at 2,750 mg/kgand 435 mg/kg. In addition, a pH of 2.2 was measured in on-Site stained soils; a pH of 2.9 wasmeasured in on-Site stream channel sediments. Table 4.1 contains a summary of selected pastanalytical results. Other heavy metals identified in various sampling events include, antimony,cadmium, chromium, copper, iron, mercury, selenium, silver, and zinc.

Analytical results also indicate the likelihood of AMD discharges. Sulfates were measured intailings at much greater concentration than comparable background samples. Analysis of tailingssamples also revealed high acid-generating potential. Similarly, pH measurements in impactedsoil and sediments, as well as stream flows were significantly more acidic than comparablebackground measurements.

Table 1.1 - Summary of Selected Analytical Results

Contaminant

Lead

Arsenic

PH

Soil(mg/kg)

249 '

52.41

1192

3S.52

1,180'

1733

2.2'

Sediments(mg/kg)

2,750'

2551

4352

24.42

2.92

EPA PRO(mg/kg)

400

21

AZSRL(mg/kg)

400

10

Not applicable

1 - E&E sampling result July 1999.2 - Weston sampling result, May 2001.3- SAIC sampling result, June 2003.Note: bolded results indicate that measured concentrations exceed applicable health-based benchmarks.EPA PRO - U.S. EPA's Preliminary Remediation Goal; AZ SRL - ADEQ's Soil Remediation Level.

2. Proposed Actions

2.a. Proposed action overview

U.S. EPA and the USFS intend to carry-out a Time-Critical Removal Action at the McCleurTailings Site in order mitigate imminent and substantial threats to human health, welfare, or theenvironment. The Time-Critical Removal Action will involve measures aimed at preventing therelease of hazardous substances and AMD from mine tailings and waste rock to the surfacewaters of the unnamed tributary and to the surrounding environment where there is a highlikelihood of direct human contact. The removal action will include the following specificobjectives:

• Remove tailings and waste rock from the stream channel of the unnamed tributary withinthe Site boundary. Remove or stabilize all on-Site tailings and waste rock within theriparian corridor of the unnamed tributary as deemed necessary based on field screeningfor heavy metals.

• Mitigate the threat of future releases of hazardous substances within the tailings andwaste rock using a possible combination of three options: disposal off site; restaging andcapping on site; and capping in place. Site grading and bank stabilization techniques maybe used to abate the release of tailings deposits within or in close proximity to the streamchannel.

• Utilize amended biosolids material to cap mine tailings either in-place or in tailings andwaste rock restaging areas. Amended biosolids will reduce the toxicity of the tailings andwaste rock. Native plants will be planted in the cap to establish vegetative structure andcontrol sheet erosion.

2.b. Treatment approach

Research conducted by U.S. Department of Agriculture, U.S. EPA's Environmental ResponseTeam and the University of Washington has indicated that biosolids will complex heavy metalspresent in tailings and metals contaminated media, binding them in place and effectivelyreducing toxicity. The metal complexing ability of biosolids minimizes the toxicity ofcontaminated material by decreasing leaching and migration potential and also bioavailability.Research efforts have also shown that the metal complex formation phenomenon of biosolidsexhibits is an ostensibly irreversible process or hysteresis effect.

Treatment effectiveness will be enhanced at the Site by amending biosolids and mixing thematerial into the tailings in place. The organic matter content and soil structural properties of the

biosolids-amendments-tailings mixture should also increase water-holding capacity. Figure 2includes a rough sketch of the treatment process.

• Tailings, waste rock and contaminated soils and sediments will be removed from thestream channel. These sediments along with the tailings/waste rock promontory will be"peeled back" and re-graded in place above the stream bank. The new embankment grademust have a sufficient angle (approximately 2%) to prevent erosion of the re-stagedmaterial.

A buffer strip (i.e., an intermediate area between the stream channel and ultimate materialdeposition area) will provide the necessary distance margin to further reduce the potentialfor treated material to re-enter the stream channel during high-flow periods or floodconditions. In addition, more permanent bank stabilization measures may be employedto protect the restaged tailings from scour during flooding. These measures will likelyinclude the placement of rip-rap rock in areas where heavy scour and erosion areanticipated.

Biosolids will be composted and brought to the Site for application to the tailings andwaste rock material. Amendments such as wood ash, lime and/or an iron oxide sourcewill be blended or incorporated with the organic biosolids material. The biosolids-amendment mixture will be mixed into the tailings to achieve reduced mobility andbioavailability of arsenic, lead and other heavy metals. A backhoe will be used to blendthe biosolids and amendments before application.

• The biosolids-amendment mixture will be placed on the tailings, waste rock andcontaminated soils in place or in restaging areas. The biosolids mixture will bemechanically worked or tilled into the tailings. Mechanical tilling (e.g. roto-tilling ortractor work) will serve to increase contact area and enhance metal complex formationability of the applied biosolids-amendment mixture.

Reduction in arsenic mobility will be achieved by specific amendment recipe aimed atraising the iron-oxide content of the biosolids. In addition, pH adjustment may berequired to achieve a pH of approximately 6 (not higher). Oxidizing conditions must beestablished in-situ to ensure that the As5* species dominates because this is the least toxicspecies of arsenic.

The amended area will be graded and compacted. Where feasible, the surface of theamended area will be graded to a slope of approximately 2%. The treated area will besoaked and compacted using a water truck and a roller or vibratory plate. The materialwill be worked in place until 85-90% compaction is achieved and until sufficientmoisture content is established.

Once all of the material is in place and the proper grade achieved, some planting will berequired to stabilize the new ground surface. This is likely to be completed in twophases. Immediately following construction, native grass seed will be sowed in the

Figure 2McCleurTailings Site Map

Scale Approximate

treated area. More substantial vegetative cover, including native trees and shrubs, will beplanted at the Site in the early part of the growing season.

2.b.l Stream channel stabilization and restoration design

Efforts will be made to return the stream channel to its shape prior to impacts from area miningoperations. As described above, treated areas in the outer riparian area, above the streamchannel, and will be graded and compacted to prevent loss of amended materials and decreaserainwater runoff velocities.

The stream channel restoration design is in progress and includes technical support from U.S.EPA Region 9, ERT, USFS expertise and possibly other local expertise. Steep stream channelbanks will be regraded and rip-rap will be added to prevent cut bank slope failure. Restorationtechniques, such as installation of erosion control matts and/or biologs, will be implemented topromote grass establishment and minimize seed loss due to sheet erosion during planting periods.If necessary, culverts on the Site may require improvements as well to accommodate higherchannel flowrates.

3. Field and Performance Monitoring

3.a.l Site characterization

U.S. EPA's START contractor will conduct confirmation soil and sediment sampling during theexcavation activities. After tailings are excavated from within the stream channel sampling willtake place within the channel to determine if the area is below the cleanup goal.

A modified systematic grid sampling method has been selected as the best method for meetingSite stream channel cleanup goals. This sampling approach allows for the statistical evaluationof the cleanup levels in separate and manageable decision units or grid cells. The method allowsfor the sampling and analysis of soil from excavated grid cells while other cells are undergoingexcavation. Grid cells that have been determined to have contaminant levels below site actionlevels will undergo no further excavation, while grid cells that have been determined to havecontaminant levels that exceed site action levels will be excavated further.

The treated soil will be sampled and analyzed to assess the effectiveness of the treatment methodand the level of teachability of metals in the soil. Soil samples collected from the treated soilwill be compared to samples collected from tailings prior to treatment. Sampling in the treatedareas will also utilize the systematic grid sampling method. The Simulated PrecipitationLeaching Procedure (SPLP) will be used to analyze the soil samples. Treatment effectivenessmay be further evaluated using indices of bioavailability and ecotoxicity (see section 3.b).

3.a.2 Dust monitoring and ambient air analysis

START will conduct dust monitoring during soil excavation and treatment activities inaccordance with the site Health and Safety Plan. MIE Miniram monitors will be used todetermine fugitive dust emissions in the ambient air at the Site. START will measure total

particulate levels and not specific contaminant concentrations. Previous analytical results fromthe site indicate that the potential levels of lead and arsenic in dust generated from the minewaste at the Site will be below OSHA permissible exposure limits (PELs). The OSHA PEL forgeneral particulates (particulates not otherwise classified) has been calculated to be the mostconservative level to use for site health and safety concerns and will be used as the default dustlimit for the site, 15 milligrams/cubic meter (mg/m3) (See Attachments 2 & 3).

3.b. Ecological setting and monitoring for treatment effectiveness

Efforts will be made to attain optimal conditions for treatment effectiveness. Ecologicalmonitoring will be used to troubleshoot the treatment and identify necessary changes. In orderfor the technology to be effective, specific ecological conditions must be established in-situ.Experts from U.S. EPA and University of Washington will provide technical guidance indesigning and implementing the treatment methodology. Performance monitoring will assess theecological conditions .

Within the areas immediately adjacent to the potentially treated areas there may be severalconcerns for impact to the stream from the treatment action. Ephemeral Streams can have animportant stream benthic community, referred to as the hyporheic zone community. This is acommunity of insects and other invertebrates, which move into the spaces between the streambedmaterials as the surface flow of the stream decreases. In hyporheic zone systems there is a streambase flow, which is below ground surface often reaching substantial depths below grade.Hyporheic systems are flowing and aerobic.

Monitoring will be undertaken to ensure that dissolved oxygen (DO) does not dramaticallydecrease in the stream community and that arsenic does not convert to soluble forms due toanaerobic conditions. Groundwater monitoring points will be installed within the stream channelboth above and below the treatment areas. Piezometers or Geoprobe points will be employed tocollect basic water quality measurements such as DO, pH and perhaps total organic carbon(TOC). In addition, direct sampling of the hyporheic zone community may be deemed necessary.

The performance monitoring efforts described above will be tasked to START. Further short-term ecotoxicity assessment may also be performed under a monitoring scope of work, by eitherSTART. This may include plant tissue analysis or soil invertebrate analysis.

3.c. Inter-agency Monitoring Contributions

S.c.l. Biological monitoring

USFS and possibly USFWS personnel will provide guidance for mitigation of potential impactsto on-Site or nearby biological resources. Guidance will include identification of habitat forFederal threatened or endangered species so designated by the Endangered Species Act.

Consultation has been sought from a qualified biologist to ensure that habitat quality is notreduced by Site operations and to ensure that no take on a threatened or endangered species

occurs. A qualified biologist has provided information concerning necessary steps for protectionof critical habitat, appropriate operating "windows", noise levels, and other mitigationrequirements.

3.C.2. Archeological monitoring

USFS, PNF qualified archeologists have identified historic resources at the Site. The PNF'sAugust 2003, Inventory Standards and Accounting Report, McCleur Mine Hazardous MaterialsClean-up Addendum has provided several recommendations regarding means for mitigation ofpotential impacts to historic resources (See Attachment 4). These recommendations will befollowed. The OSC will seek informal consultation from the PNF archeologist regarding Siteoperations.

3.C.3. Watershed monitoring

The ADEQ has listed the headwaters of the Hassayampa River as water quality impacted basedon the findings of their Total Maximum Daily Load study. In the report, ADEQ specifies thataction should be taken at the McCleur Site to improve watershed conditions. ADEQ willconduct will conduct future watershed monitoring in the vicinity of the Site. These efforts mayindicate the long-term effectiveness of the removal action.

4. Attachments and Supporting Documentation;

1. To be provided. McCleur Tailings Site Work Plan, prepared by Project Resources, Inc.

2. To be provided. McCleur Tailings Site Sampling Plan, prepared by START.

3. To be provided. McCleur Tailings Site Health and Safety Plan, prepared by START.

4. August 2003. Inventory Standards and Accounting Report, McCleur Mine HazardousMaterials Clean-up Addendum.

5. Definitions and Acronyms

ADEQ Arizona Department of Environmental Quality

aerobic Relating to an oxygen rich environment or metabolic process requiringoxygen.

As Elemental symbol for arsenic, which comes in different electro-chemicalforms (species) based on charge. As5+ is less mobile and less toxic thanAs3+. As5* is the desired form of arsenic in the treated area.

Unavailability

Biolog

Cut bank

DO

Ecotoxicity

osc

EPA

Geoprobe

hysteresis

in-situ

mg/kg

MIE Miniram

OSHA

PELs

The degree to which humans, animals and plants metals may come intocontact with, or be exposed to, the hazardous properties of contaminants.High bioavailability results in higher risk of human and ecotoxicity.

A natural fiber "roll" that may be used to decrease erosion rates andfacilitate plant establishment.

The lateral side of a stream bank which is faced with the highest velocitystream water flows. The cut bank is the channel wall where scour is mostlikely to occur.

Dissolved Oxygen; an in-situ measurement of the amount of oxygendissolved in water used as a indicator of water quality.

Measure of the effects of a poison on an ecosystem. Contaminants thatdisrupt ecosystems functions are said to be ecotoxic. Ecosystem functionsinclude providing plants and animals with food, shelter, and reproductivehabitat.

On-Scene Coordinator; appointed representative of EPA or USFS taskedwith conducting the Time-Critical Removal Action

U.S. Environmental Protection Agency; Region 9, San Francisco, CA

Brand name; an instrument used to collect soil, water or air samples atdepth beneath the ground surface. A Geoprobe is used to advance belowground borings or piezometers.

The irreversibility of a reaction or process brought about by an externalagent. Research shows that once metals are bound by biosolids, they willnot become available again over time or due to other factors.

In place

milligrams/kilogram

A direct light scattering aerosol instrument used to measure dustconcentrations in ambient air.

Occupational Safety and Health Administration

Permissible Exposure Limits; time-weighted average concentration limitsbased upon exposure over a given time-period, that are established byOSHA.

PH

Piezometer

PNF

PRGs

Riparian corridor

Rip-rap

scour

SPLP

SRLs

START

Stream channel

Systematic grid

TOC

A measurement of the acidity of water, soil or sediment.

A boring advanced to a given depth below ground surface. Piezometersare used to measure hydraulic pressure or head in groundwater systems.They are also used to measure chemical conditions in waters beneath theground surface.

Prescott National Forest

Preliminary Remediation Goals; contaminant specific soil cleanup goals(concentrations) derived from an environmental risk-based exposuremodel. PRGs are developed by U.S. EPA.

The area in the vicinity of the stream bank; the riparian corridor consists ofstream dependent flora and fauna..

Medium sized stones (approx. 4"-8") in diameter which are placed on thestream bank as a foundation. Rip-rap prevents scour and erosion from thestream bank.

The flushing out of soils, sediments, stone and debris from a streamchannel as a result of water flow-through.

Simulated Precipitation Leaching Procedure; a chemical analysis done in alaboratory to measure the potential for dissolution or teachability of heavymetals in surface water. SPLP concentrations are indicative of metalsconcentration in the environment and the potential for those metals tomigrate away from their source.

Soil Remediation Levels; contaminant specific soil cleanup goals(concentrations) derived from an environmental risk-based exposuremodel. SRLs are developed by ADEQ.

Superfund Technical Assessment and Response Team; provides support toU.S. EPA On-Scene Coordinators.

The physical path of the stream or streambed during average water flows.

A statistical sampling methodology utilized to collect randomized samplesof material that can be considered to represent a larger area.

Total Organic Carbon; an in-situ analytical measurement of organic carbonin water used as an indicator water quality.

USDA U.S. Department of Agriculture

USFS U.S. Forest Service

USFWS U.S. Fish and Wildlife Service

MCCLEUR TAILINGS SITE WORKPLANPHOTOGRAPH LOG

Photograph 1. The confluence of two tributaries in the Maple Gulchdrainage occurs immediately downstream of the McCleur Tailings Site.

Photograph 2. Weathered tailings cover the stream bank and evidence ofacid mine drainage is observed in the streambed.

MCCLEUR TAILINGS SITE WORKPLANPHOTOGRAPH LOG

Photograph 1. Evidence of environmental impacts is observed due to thepresence of mine tailings and concomitant acid mine drainage.

Photograph 2. Visual observation suggests that mine tailings are enteringsurface waters during peak stream flows.