Public Notice: Five-Year Review
Sierra Army Depot, Herlong, California
The U.S. Army Corps of Engineers, Los Angeles District, has completed
the Sixth Five-Year Review for the Sierra Army Depot located in
Herlong, California. This statutory Five-Year Review was conducted in
accordance with the Comprehensive Environmental Response, Compensation,
and Liability Act Section 121, consistent with the National
Contingency Plan. The purpose of a Five-Year Review is to evaluate the
implementation and performance of a remedy in order to determine if
the remedy is or will be protective of human health and the environment.
Five-Year Reviews also identify issues found during the review, if any,
and provide recommendations to address them. The Five-Year Review
has been prepared because hazardous substances, pollutants, or contaminants
remain at the site above levels that allow for unlimited use and
unrestricted exposure.
This Five-Year Review evaluated the following six Installation Restoration
Program sites:
SIAD-001 (Trinitrotoluene Leaching Beds Area & Paint Shop subsite):
The remedy at SIAD-001 currently protects human health and the
environment because source removal actions were completed and Institutional
Controls (soil/groundwater restrictions, dig permits, and development
restrictions) prevent inadvertent exposure to contamination in soil
and groundwater. However, for the remedy to be protective in the long
term, the following actions need to be taken to ensure protectiveness:
• Re-evaluate the progress of the remedy component of monitored
natural attenuation, enhanced with the implementation of the
n-Situ Reactive Zone Demonstration Program, for treatment of
volatile organic compound contaminants of concern.
• Add hexavalent chromium, cis-1,2-dichloroethene, vinyl chloride,
2-amino-4,6-dinitrotoluene, and 4-amino-2,6-dinitrotoluene to the
list of groundwater contaminants of concern, identify appropriate
Protective Water Quality Objectives, and evaluate if the current
remedial approach will address the impact from these contaminants
at SIAD-001.
• Evaluate nitrate as a potential contaminant of concern and determine
whether additional action is required at SIAD-001 or if the
current remedial approach will address nitrate impacts.
• Conduct additional investigations to delineate the volatile organic
compound plume boundaries west of SIAD-001, near the Paint
Shop Subsite.
SIAD-002 (Defense Reutilization & Marketing Office Trench Area):
The remedy at SIAD-002 currently protects human health and the environment
because source removal actions were completed, and Institutional
Controls (soil/groundwater restrictions, dig permits, and development
restrictions) prevent inadvertent exposure to contamination in soil
and groundwater. However, for the remedy to be protective in the long
term, the following actions need to be taken to ensure protectiveness:
• Add cis-1,2-dichloroethene, vinyl chloride, and perchlorate to the
list of groundwater contaminants of concern, identify appropriate
Protective Water Quality Objectives, and evaluate if the current
remedial approach will address cis-1,2- dichloroethene, vinyl
chloride, nitrate, and perchlorate impacts at SIAD-002.
• Evaluate nitrate as a potential contaminant of concern and determine
whether additional action is required at SIAD-002 or if the
current remedial approach will address nitrate impacts.
• Complete the Enhanced Reductive Dechlorination rebound
evaluation initiated in 2019 to determine if monitored natural
attenuation will achieve the Remedial Action Objective of limiting
contaminant migration and degradation rates to within acceptable
ranges to the State of California and the Army.
• Conduct additional investigations to delineate the trichloroethene
plume boundary south- and northwest of SIAD-002 where
boundary wells DMO-06-MWA and DMO-07-MWA exhibit TCE
exceedances and an increasing trend at DMO-07-MWA.
SIAD-003 (Abandoned Landfill/Southern Sites Area): The remedy at
SIAD-003 currently protects human health and the environment because
land use controls (soil/groundwater restrictions, dig permits, and development
restrictions) prevent inadvertent exposure to contamination in
soil and groundwater.
However, for the remedy to be protective in the long term, the following
actions need to be taken to ensure protectiveness:
• Add cis-1,2-dichloroethene and vinyl chloride to the list of
groundwater contaminants of concern, identify appropriate
cleanup levels, and evaluate if the current remedial approach
will address cis-1,2- dichloroethene and vinyl chloride impacts at
SIAD-003.
• Delineate the Southern Sites Area western plume boundary
near groundwater monitoring well MPA-03-MWA and implement
appropriate contingency measures per the 2018 Final Monitored
Natural Attenuation Letter Work Plan.
• Conduct additional investigations to delineate the Southern Sites
Area southern plume boundary near groundwater monitoring well
SSA-01-MWA and potable supply well PSW-08 and implement
appropriate contingency measures per the 2018 Final Monitored
Natural Attenuation Letter Work Plan.
• Conduct additional investigations to delineate the Abandoned
Landfill plume boundary near groundwater monitoring well CCB-
01-MWA and implement appropriate contingency measures per
the 2018 Final Monitored Natural Attenuation Letter Work Plan.
• Expand the SIAD-003 Land Use Control boundary to include
all wells with detected trichloroethene and prohibit use of and
exposure to contaminated groundwater.
• Evaluate nitrate as a potential contaminant of concern and determine
whether additional action is required at SIAD-003 or if the
SIAD-010 (Upper Burning Ground Area): The remedy at SIAD-010
is protective of human health and the environment. Surface ordnance
and explosives/unexploded ordnance and scrap metal clearance, soil
excavation, and placement of contaminated soil in the Corrective Action
Management Unit was completed in 2006. Post removal action soil
confirmation sampling indicated that cleanup levels were met. Groundwater
samples collected from Upper Burning Ground Corrective Action
Management Unit wells indicate that no metal contaminants are being
released from the Corrective Action Management Unit and all contaminant
of concern concentrations in groundwater remain below Maximum
Contaminant Levels. Quarterly Corrective Action Management Unit
inspections confirm the dense graded aggregate layer and drainage
controls are in good working condition with only minor maintenance
required. Land Use Controls, including fencing, signs, dig permits, and
annual inspections, continue to restrict site use/access and mitigate
the risks to human health resulting from potential direct contact with
contaminated soil.
SIAD-014 (Building 210 Area): The remedy at SIAD-014 currently
protects human health and the environment because land use controls
(soil/groundwater restrictions, dig permits, and development restrictions)
prevent inadvertent exposure to contamination in soil and groundwater.
However, for the remedy to be protective in the long term, the following
actions need to be taken to ensure protectiveness:
• Add cis-1,2-dichloroethene and vinyl chloride to the list of
groundwater contaminants of concern, identify appropriate
cleanup levels, and evaluate if the current remedial approach
will address cis-1,2-dichloroethene and vinyl chloride impacts at
SIAD-014.
• Conduct additional investigations to delineate the trichloroethene
plume boundary east of the Building 210 Area, near the
Doyle Wildlife Area.
• Evaluate the effectiveness of the on-site treatment of trichloroethene
impacted groundwater via Enhanced Reductive
Dechlorination injections at the Building 210 Area. Additional
site characterization may be necessary to determine if residual
sources are contributing to TCE concentrations, rebounds, and
migration.
• Evaluate nitrate as a potential contaminant of concern and
determine whether additional action is required at SIAD-014 or if
the current remedial approach will address nitrate impacts.
SIAD-022 (Old Popping Furnace Area): The remedy at SIAD-022 is
protective of human health and the environment. Surface ordnance and
explosives/unexploded ordnance clearance, excavation, and consolidation
of the contaminated soil with placement of an engineered Corrective
Action Management Unit cover continue to reduce the potential for
windborne movement of surface soil containing antimony, arsenic, or
lead above their respective cleanup levels. Corrective Action Management
Unit groundwater monitoring continues to satisfy the Applicable
or Relevant and Appropriate Requirements, including the requirements
of Title 22 CCR § 66264.97. Administrative and engineered land use
controls (fencing, signs, dig permits, annual inspections) continue to
mitigate the risks to human health and the environment from potential
direct contact with soil containing antimony, arsenic, or lead at concentrations
exceeding their respective cleanup levels. Routine inspection
and maintenance activities and groundwater monitoring ensure longterm
protection of groundwater resources
This Five-Year Review evaluated the following seven Military Munitions
Response Program sites:
SIAD-006-R-01 (.50 Caliber Firing Range), SIAD-007-R-01 (1960
Demolition Area), SIAD-009-R-01 (Hazard Classification Test Site),
SIAD-010-R-01 (Honey Lake Demolition Range), SIAD-012-R-01
(Lower Burning Ground), SIAD-014-R-01 (Upper Burning Ground),
SIAD-015-R-01 (Bureau of Land Management – Administered
Land): The remedy for the Military Munitions Response Program Seven
Sites is protective of human health and the environment. Land Use
Controls (fencing, dig permits, annual inspections) are in place to prohibit
use of and restrict exposure to potential explosive hazards at the
Military Munitions Response Program Seven Sites. Annual Land Use
Control inspections occurred between 2016 and 2020 without lapse. All
Land Use Control inspections concluded that fences and signage were
in good condition and signage was spaced at approximately 600-foot
intervals.
The Sixth Sierra Army Depot Five-Year Review Report was signed on
January 21, 2022 and is available at the following information repositories:
Herlong Library
California Street, Building 2067
Herlong, California 96113
Susanville Library
1618 Main Street
Susanville, California 96130
Sierra Army Depot
74 Currant St., Building 63
Herlong, California 96113
Should members of the community have questions or comments about
the Sierra Army Depot Five-Year Review or are interested in additional
site information, please contact Cortney Carrier at (530) 827- 4612 or
via email at cortney.a.carrier.civ@army.mil.
Pub Date: February 17, 2022
Ad #21467