4>EPA EPA Region 6 Announces
Record of Decision Amendment
Proposed Plan
United States
Environmental Protection
Agency
North Cavalcade Street Superfund Site
Houston, Harris County, Texas July 2009
The Purpose of this Proposed Plan is to:
• Identify EPA's proposed alternative remedy for the remaining contaminated soil and to address the ground
water contamination for an expanded area, the original shallow water aquifer and a deeper interbedded water-
bearing zone;
• Describe the remedial alternatives for both soils and ground water, considered in detail in the Focused
Feasibility Study report;
• Describe revisions to the Remedial Action Objectives (RAOs) for soil and ground water;
• Solicit public review and comment on the proposed remedy, as well as information contained in the amended
Administrative Record; and
• Provide information on how community members can be involved in the remedy selection and amendment
process for the Site.
In this Proposed Plan, the U.S. Environmental Protection Agency (EPA) presents a re-evaluation of the remedy
selected in the 1988 Record of Decision (ROD), identifies other remedial alternatives and considers information
derived through additional investigation and the performance of the previously selected remedy. Hazardous
substances remaining in both soils and ground water at the North Cavalcade Street Superfund Site, Houston, Texas,
are addressed in this Plan. "North Cavalcade Site," or "Site," is used interchangeably with the more formal "North
Cavalcade Street Superfund Site" in describing actions in this Plan.
To summarize, the 1988 ROD selected biological treatment for contaminated soils to 1 part per million (ppm)
levels for carcinogenic polycyclic aromatic hydrocarbons (cPAHs). The level for cPAHs was later revised in 1994,
to 30 ppm. Contaminated soils were excavated from the Site and consolidated for treatment. After two years, in
1996, treatment was discontinued for failure to reach the revised cleanup goal for the volumes and timeframes
established for the project. Much of the original 22,300 cubic yards of soil were consolidated into a containment
cell at the north end of the Site pending selection of another remedy through the CERCLA process. That area is
referred to as Operable Unit 2 (OU2).
The 1988 ROD also addressed contaminated ground water, specifying that the creosote-related contaminants would
be extracted from the ground water and treated onsite until all non-aqueous phase liquids (NAPLs) were removed
and benzene concentrations in ground water did not exceed the Safe Drinking Water Act (SDWA) Maximum
Contaminant Level (MCL) of 5 micrograms per liter (^ig/L or parts per billion [ppb]). The ground water treatment
system was designed primarily for ground water and assumed that very little NAPL remained. In 1995, two years
into operation, the pump and treat system was suspended due to limited capacity and problems in processing the
large volume of extracted creosote. During delineation of the creosote source, dense NAPL (or DNAPL) was
found in the deeper water-bearing unit (designated as OU3), and characterized for extent in a 2004 investigation.
The additional contamination was the result of the same DNAPL source that had migrated vertically from the
shallow sand to the next sequence of interbedded silts and silty sands. The DNAPL material in the interbedded
zone was also sourcing a dissolved phase plume that had migrated beyond the boundaries of the Site. The 1988
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remedy and pump and treat system addressed the DNAPL source and associated dissolved contaminant phase for
the first shallow sand aquifer (designated as OU1).
In this Proposed Plan, the EPA proposes a remedy to:
• Modify and cap the existing containment cell to further limit exposure to the contaminated soils and
maximize protection of the underlying ground water ;
• To address the DNAPL source by stabilizing the DNAPL (in both the shallow and interbedded aquifers) by
in-situ solidification and select monitored natural attenuation to address the dissolved phase plume.
Ground water stabilization by solidification will more effectively control the source, eliminate further
migration of the DNAPL, and minimize expansion of the contaminant plume. The original remedy selected
pump and treat to remove both the DNAPL source and dissolved phase contaminants, with limited results.
Extraction will not completely remove the DNAPL source, which will, in turn, continue to leach contaminants
to ground water. Stabilization, however, will effectively bind the creosote source areas, minimizing the
leaching of contaminants to the dissolved phase plumes in the two shallow aquifers. Without an active source,
natural attenuation processes are expected to degrade the dissolved phase contaminants over time.
The proposed remedy for both soils and ground water is compared to the original remedy and to other remedial
options. The proposal and selection of remedy as an amendment to the 1988 ROD is in accordance with the
National Oil and Hazardous Substance Contingency Plan (NCP) §300.435(c)(2)(ii)(A) through (H). The actions
proposed in this plan are a continuation of those previous actions taken for the Site in accordance with the
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA or Superfund), 42 U.S.C.
§9617(a) and 40 CFR Part 300. Issuance of the Plan will adhere to the public participation and documentation
procedures specified in NCP §300.825(a)(2); and CERCLA §117(a).
The EPA Region 6 office is the lead agency for the North Cavalcade Street Superfund Site, and is issuing the
Proposed Plan with support from the Texas Commission on Environmental Quality (TCEQ). TCEQ conducted the
ground water investigation in January 2004 to define the extent of deeper ground water contamination, as well as
provided technical support and review of the 2008 Focused Feasibility Study (FFS) Report (Feasibility Study)
through a cooperative agreement with the EPA. The EPA developed the remedial alternatives and proposed action
in consult with TCEQ and will request concurrence by the State of Texas upon completion of the public comment
period.
In summary, the Proposed Plan addresses those proposed changes to the original 1988 ROD; describes the remedial
alternatives analyzed; provides discussion on the preferred alternative; and solicits public involvement in the
selection of a new remedy. Following public review and consideration of public comments provided, EPA will
make a final remedy selection that will be documented as a ROD Amendment.
Highlights of EPA's Proposed Alternatives
Ground Water - Source stabilization (in-situ solidification) with Monitored Natural Attenuation (MNA)
for the dissolved plume for both the shallow sand unit (Operable Unit 1) and the interbedded silt/sand unit (Operable
Unit 3). Institutional controls will be required to prohibit use of contaminated ground water.
Soil - Modify the existing containment cell and cap soils in place to contain and control exposure to contaminated
soils. Institutional controls will be required to restrict the property to industrial use and to prohibit activities that
would impact the integrity of the cap.
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Community Participation
The Proposed Plan fact sheet highlights key information from the 2005 Supplemental Investigation for Remedy
Evaluation and the 2008 Focused Feasibility Study (FFS) for the North Cavalcade Site. Information about
remaining soil concentrations and specifics about the current containment cell can be found in the 2000 Remedial
Action Closure Report for Operable Unit 2 (OU-2) and analysis of cell soils in the FFS. The development and
evaluation of the remedial alternatives to address the contamination are presented in the FFS Report. The EPA
encourages the public to review these documents in order to gain a more comprehensive understanding of the North
Cavalcade Site and the evaluation of alternative remedial options. The EPA also encourages the public to
participate in the decision-making process for the North Cavalcade Site by making comments on all aspects of the
Administrative Record File including those documents which have been added to amend the record and support the
decisions proposed in this Plan (i.e. Supplemental Investigation Report, FFS Report, and this Proposed Plan). The
Administrative Record File is available at the following information repositories:
Houston Central Library
Government Documents Area
Texas Room
500 McKinney Street
Houston, Texas 77002
Texas Commission on Environmental Quality
Building E, Records Management, First Floor
12100 Park 35 Circle
Austin, Texas 78753
(512)239-2920
Monday - Friday - 8:00 am to 5:00 pm
A public meeting to receive comments will be held at the Carnegie Regional Library, located at 1050 Quitman
Street, Houston, Texas, on Thursday, July 23, 2009, from 6:00 PM to 7:30 PM. The public is invited to comment
on this Proposed Plan to amend the Record of Decision. Final decisions regarding the remediation of the North
Cavalcade Site will only be made after public comments are considered. The official public comment period
begins on July 16, 2009, and ends on August 14, 2009. During the public comment period, written comments may
be submitted to:
Camille Hueni
Remedial Project Manager
EPA, Region 6 (6SF-RA)
1445 Ross Ave.; Suite 1200
Dallas, Texas 75202-2733
(214) 665-2231 or toll free (800) 533-3508
The EPA, in consultation with the State of Texas, will select a final remedy for North Cavalcade Site after the
public comment has ended and information submitted during this time has been reviewed and considered. EPA
will respond to all comments received during the public comment period in the Responsiveness Summary, which
will be attached to the amended Record of Decision. Both the Responsiveness Summary and the ROD Amendment
will be available to the public at the two repository locations noted above. Note that the final site remedy may be
different from the proposed remedy identified in this Proposed Plan based on comments, new information, or issues
received during the public comment period. Such changes or alterations of this Proposed Plan will be explained
and described in the ROD Amendment. The ROD Amendment will be signed by the Region Administrator for the
EPA Region 6.
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Site Background
Site History
The North Cavalcade Site is located northeast of the intersection of Cavalcade Street and Maury Street, about one
mile southwest of the intersection of Loop 610 and U.S. Highway 59, in Houston, Harris County, Texas. The Site
boundaries are Interstate Loop 610 to the north, Cavalcade Street to the south, and active rails on both the east and
west boundaries. The Site is approximately 21 acres in size and has an elongated triangular shape. Residential
areas are northeast and west of the site (as close as 200 feet from the site). Other surroundings include commercial
and industrial properties. The South Cavalcade Superfund Site is located directly south of the North Cavalcade
Street Site. The South Cavalcade Site was also a wood-treatment facility, but was not associated with the North
Cavalcade Site.
The North Cavalcade Site was developed for wood treating operations in 1946, when a small creosote wood
preserving business named Houston Creosoting Company, Inc. (HCCI) was established. The wood preserving
operations encompassed approximately nine acres on the southern portion of the property, and included creosote
ponds, various tanks and storage units, lumber shed, treatment facility, and other buildings. Wood preserving
operations continued until 1961 when the property was foreclosed. In 1964, the East End Bank of Houston sold the
property to the Monroe Ferrell Concrete Pipe Company. Subsequent property owners further divided the property.
There has been no further industrial activity on the Site since 1964. Data developed during the initial site
investigation indicated that creosote stored in areas corresponding to the historical operation area and creosote
lagoons contributed to the contamination. The operation area and creosote lagoons covered an area of
approximately one acre. The Site is currently being used by two commercial businesses. The two businesses are
located along the southwestern boundary.
The southern half of the site encompasses the former operations and waste pit areas of the old wood preserving
facility. Data developed during the site investigation indicated that creosote stored in areas corresponding to the
historical operation area and a creosote lagoon contributed to the contamination. To address those areas of ground
water contamination, a treatment system, including a network of extraction and monitoring wells, was installed for
the pump and treat remedy for the shallow aquifer selected in the 1988 ROD. The ground water remediation is
limited to the southern portion of the site. An estimated 22,300 cubic yards of contaminated soils, remaining from
the treatment operation, are held in a containment cell on the northern portion of the site pending final action
proposed by this Plan.
Site Contamination
Contaminants of concern for ground water and soils media included polycyclic aromatic hydrocarbons (PAHs),
volatile organic compounds (benzene, ethylbenzene, toluene, and xylene), and limited metals with concentrations
above background, associated with creosote-based operations. Pentachlorophenol, another wood treatment
chemical constituent reportedly used at the site, has never been detected.
History of Federal and State Investigations
The EPA proposed the North Cavalcade Street Site to the National Priorities List (NPL) on October 5, 1984
(49 Federal Register [FR] 40320), and added the site to the final list on June 10, 1986 (51 FR 21054). EPA
conducted a Remedial Investigation (RI) at the site from September 1985 to November 1987. Samples of the air,
surface water, sediments, soil, and ground water were collected. Results confirmed contamination in the soil,
sediments, and the upper ground water (shallow sand) unit at the site. The data for air and the drainage ditch water
showed no measureable contamination. The Record of Decision (ROD) for the North Cavalcade Street Superfund
site was issued on June 28, 1988.
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The ROD divided the site into two Operable Units (OUs). OU1 addressed the shallow ground water contamination,
and OU2 addressed soil contamination. The selected remedy for OU1 specified that contaminated ground water
would be extracted and treated onsite using oil/water separation and carbon absorption until all non-aqueous phase
liquids (NAPLs) were removed and benzene concentrations in ground water no longer exceeded the Safe Drinking
Water Act (SDWA) Maximum Contaminant Level (MCL) of 5 micrograms per liter (^g/L) and cPAHs were not
detected. Recovered NAPLs were to be incinerated offsite. The selected remedy for OU2 was onsite biological
treatment to 1 part per million (ppm) of carcinogenic polycyclic aromatic hydrocarbons (cPAHs) and 0.04 ppm for
benzene. In 1994, EPA modified the cPAH soil cleanup level to 30 ppm in an Explanation of Significant
Differences (ESD) after a field pilot test failed to demonstrate that bioremediation would reduce concentrations of
cPAHs below 1 ppm.
Through an agreement between EPA and the state, the Texas Natural Resources Conservation Commission
(TNRCC, now the TCEQ) obtained contracts to implement the selected remedies.
Shallow Sand Ground Water COUP
Interbedded Unit Ground Water (OU3)
The ground water extraction and treatment system was primarily designed for ground water and assumed that little
DNAPL remained in the subsurface. Construction was completed in December 1993. The ground water pump and
treat system operated for approximately two years until operations were suspended in 1995, due in part to problems
in handling the large volume of DNAPL coming into the treatment system. During those two years of operation,
more than 11,500,000 gallons of ground water were treated and 8,000 gallons of creosote (DNAPL) were recovered.
A five-year review conducted by EPA in 1998 recommended additional characterization to locate the extent of
remaining DNAPL and to determine if the contaminated ground water plume would naturally attenuate or if
additional treatment would be necessary.
Additional investigations and studies in 1998 through 2000 clarified the geologic framework at the site, better
defined the extent of DNAPL contamination and remaining volumes to support modification of the treatment
system and further evaluation of the remedy. The study better defined the DNAPL in the shallow sand aquifer and
also confirmed additional DNAPL in the interbedded unit below interbedded sand found at a depth of
approximately 25 - 40 feet below ground surface [bgs]). The ground water treatment system was modified to
separate larger volumes of DNAPL in 2000. The modified system began operation in August 2001, but again,
addressed only ground water and product extracted from the shallow ground water. EPA and TCEQ began
discussions on how to address the deeper contamination, now defined as Operable Unit 3 (OU3). EPA completed
the second five-year review for the site in September 2003. EPA recommended continuing evaluation of natural
attenuation of the ground water plume and re-evaluation of the current pump and treating system.
The ground water treatment system was suspended in October 2003, to allow the ground water to equilibrate to
static conditions prior to the January 2004 field investigation. This investigation is summarized in the 2005
Supplemental Investigation Report. The investigation provided water levels and sample data for the shallow sand
(OU1), and provided delineation of the NAPL and dissolved contaminant plume in the underlying interbedded unit
(OU3), onsite and offsite. The ground water pump treatment system has not been operational since that time. The
ground water was constructed to address the shallow sand unit only, which, as confirmed by the investigation, was
already contained onsite. The offsite contaminant plume, in the underlying interbedded unit, was not reduced or
contained by the existing system. The pump and treatment system was suspended, pending further evaluation of
remedial options, including expansion of the current system to include the deeper interbedded unit. The treatment
system, including the current extraction well network and monitoring wells, is still in place.
To facilitate the evaluation of ground water alternatives, the Idaho National Laboratory (INL) prepared a ground
water fate and transport model for EPA (2006) to evaluate natural attenuation of the dissolved phase plume and
potential remedial alternatives. The model was used to conduct predictive transport simulations and estimate
contaminant concentrations under the following scenarios: 1) no further action, where no additional remedial
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actions are taken; and 2) source stabilization, or chemical fixation, where chemical additives and amendments are
added to reduce the leachability of the contaminants and/or reduce the permeability of the source area. The ground
water model addressed dissolved phase constituents benzene and naphthalene in the interbedded unit. The
modeling concluded the dissolved phase benzene plume in the interbedded unit is likely at equilibrium already (i.e.
not likely to expand further). The modeling also concluded that the dissolved phase naphthalene plume is expected
to continue to expand for 50 to 100 years or more before an equilibrium condition is achieved. These conclusions
did not include the simulation of any actions to remediate the dissolved phase plume. The transport model also did
not consider the decreasing hydraulic conductivity and thinning of the interbedded unit to the west, which would
limit the migration of contaminants further offsite.
In 2008, EPA completed the Focused Feasibility Study (FFS) that supports this Proposed Plan. The FFS for
OU1/OU3 is based largely on findings from the 2005 report and the results of the INL fate and transport ground
water model for the interbedded zone.
Soil (OU2)
Contaminated soils from the operation areas and ditches were excavated and staged for biotreatment at a facility
constructed on the northern portion of the Site. Construction of the treatment facility, including pads and a
treatment cell, was completed April 18, 1996. Biotreatment was performed for 808 days without achieving the
cleanup level for cPAHs established in the 1994 ESD. Treatment was discontinued in August 1998. The TNRCC
contract was amended to include a modified closure phase to place the contaminated soil in the treatment cell and
cover it with a liner pending final determination of disposition by EPA and TNRCC. The soil containment cell
includes a leachate collection system and vent stovepipes around the perimeter of the site. The soil stockpile has
remained on-site and relatively unchanged since 1999.
In May 2001, the soil contained in the temporary treatment cell was sampled by TCEQ to characterize contaminant
concentrations to support evaluation of remedial options. Soil samples were analyzed for semi-volatile organic
compounds (SVOCs), VOCs, Toxicity Characteristic Leaching Procedure (TCLP) arsenic and TCLP chromium.
The analytical results indicated the cPAH concentrations remained above the site cleanup goal of 30 ppm.
Composite soils samples were taken from the containment cell again in 2006 to better characterize the soils for
remedial alternatives being considered. Those results were consistent with the 2001 findings and also confirmed
that cleanup levels had been reached for benzene.
Site Characteristics
Physical Characteristics
The North Cavalcade Site is located in the Southeast Texas Coastal Plain. This region is underlain with Holocene
and Pleistocene deposits to a depth of approximately 2,400 feet. Ground water used to supply water for domestic,
industrial, and agricultural purposes is pumped from the Lower Chicot and Evangeline aquifers. Both of these are
confined aquifers and are isolated from surface recharge. Public water supply wells are screened in the Evangeline
aquifer at depths greater than 600 feet. Industrial water users in the general area have wells screened in both
aquifers at depths ranging from 50 to 576 feet.
Regionally, the topography slopes gently south toward the Gulf of Mexico. The site itself is generally flat. Site
drainage occurs through three storm water drainage ditches. Two of these flank the site on the east and west sides
and drain to the third ditch, which bisects the site into northern and southern sections. The third ditch drains into a
flood control ditch which discharges into Hunting Bayou.
The two water-bearing zones that are the focus of this Proposed Plan are not used as sources of drinking water
onsite or within a two-mile radius of the Site. Onsite and neighboring residents are served by the City of Houston
water supply which originates from a deeper aquifer 10 miles from the site, or a surface water reservoir located
over 20 miles from the site. The closest water well to the impacted portions of the site is located to the northwest
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approximately one-quarter mile. Water from this well is for industrial use and the well is screened from 200 to 210
feet in the upper Chicot aquifer. In addition, the Houston-Galveston Coastal Subsidence District requires
notification and permits for the drilling of new ground water wells, discouraging the use of private wells in those
areas adequately served by the City of Houston municipal water supply system.
Although the shallow sand and interbedded unit are not currently being used as a source of drinking water, the
potential exists that these water-bearing units could be utilized in the future. The viability of these water-bearing
units as potential future drinking water sources depend on aquifer yield and water quality. A 1999 evaluation of
existing well yield and water quality data for the shallow sand and the interbedded unit concluded that the shallow
sand aquifer and the underlying interbedded unit could sustain pumping rates of approximately 1.5 gallons/minute
(gpm) and approximately 1.25 gpm, respectively. Comparison of these well yields to the requirements for the
Class 2 Ground Water Resources Classification as defined under the Texas Risk Reduction Program (TRRP)
indicates that the shallow sand aquifer and interbedded unit would likely meet the Class 2 yield limits of greater
than 150 gallons/day (gpd) and less than 144,000 gpd. Limited water quality data for the Site suggests that the total
dissolved solids and other parameters are within an acceptable range to meet the State of Texas standards for a
domestic drinking water well.
5*077 Contamination
An estimated 22,300 cubic yards of contaminated soils were excavated from operation areas and ditches draining
the site and consolidated for biological treatment, as per the 1988 ROD. The treatment failed to meet performance
goals within the expected timeframe and was discontinued after two years. The soils were consolidated in a
containment cell on the northern portion of the site. Pending the proposed final action to cap the soils in place, no
further action for soils will be required.
The current containment cell is approximately 550 feet long by 130 feet wide by 4.5 feet high and is constructed
with two 60-mil high density polyethylene (HOPE) liners and a leachate collection system. A 30-mil HDPE cover
caps an estimated 22,300 cubic yards of soils. Access to the northern portion of the Site is limited by a perimeter
security fence with locked gates.
Site Hydrogeology
The shallow and interbedded sand aquifers discussed in this Proposed Plan refer to water-bearing sand and silty
sand units, interbedded with thin clay units, from surface to approximately 40 feet. The first shallow aquifer is in a
sand unit approximately 12 to 15 feet below ground surface; the interbedded sand aquifer is the interbedded silty
sand/clay unit from about 25 to 40 feet below ground surface. Both units are hydraulically connected; the
potentiometric surface data indicate ground water flow direction is to the west across the southern part of the site.
These two water-bearing units are underlain by a thick regional confining clay, approximately 100 feet thick, which
serves as a barrier to continued downward migration of contaminants. The Pecore Fault, a local shallow fault with
surface expression, runs along the southern boundary of the site and may control the southward migration of dense
non-aqueous phase liquid (DNAPL) or contaminated groundwater to the south.
Ground Water Contamination
This section provides a summary of the nature and extent of contamination as depicted in the 2005 Supplemental
Investigation for Remedy Evaluation Report and interpretations of the extent of NAPL performed by EPA during
the 2004 field investigation. Ground water contamination at the North Cavalcade Street site is present in the
dissolved phase and free-phase in both the shallow sand aquifer and the interbedded unit. The primary
contaminants of concern at the North Cavalcade Street site are VOCs (primarily benzene), and PAHs (primarily
cPAHs and naphthalene). Ground water sampling conducted by TCEQ and EPA in 2004 provides the most
comprehensive snapshot on the extent of contamination in the shallow sand aquifer and interbedded unit. Results
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of the investigation are included in the 2005 Supplemental Investigation for Remedy Evaluation report, included in
the amended Administrative Record.
The lateral extent of the shallow sand and interbedded unit dissolved phase plume has been sufficiently delineated
in all directions. The dissolved phase plume in the shallow sand aquifer extends from these source areas towards
the west. The majority of the dissolved plume residing in the shallow sand aquifer is located within the boundary
of the site. Benzene contamination in the shallow sand aquifer has not migrated offsite at concentrations greater
than the MCL of 5 ug/L. The dissolved phase plume in the interbedded unit is more extensive than in the shallow
sand and has migrated off the western boundary of the site. Concentrations of benzene in the interbedded unit have
migrated offsite at concentrations greater than the MCL (5 ug/1). The downgradient extent of benzene detections in
the interbedded zone above the MCL reside between Elysian Street and Maury Street.
Contamination is the shallow sand and interbedded unit centers on two NAPL source areas corresponding to the
location of the former creosote lagoons and operation area. The maximum NAPL thickness in the shallow sand and
interbedded unit were estimated at approximately 5 feet and 3 feet thick, respectively.
Ground Water Modeling Summary
In December 2006, a Subsurface Contaminant Transport Modeling report for the North Cavalcade Street site was
prepared by the Idaho National Laboratory (INL) for the EPA. The report presented a modeling study of
contaminant movement in ground water at the North Cavalcade Street Superfund Site to predict how various
components of creosote might be transported under different circumstances. The results of the study were used to
support the review of remedial alternatives for the Site.
The transport model was calibrated for naphthalene and benzene concentration data gathered in 2005 from the
interbedded zone. The transport model was able to reproduce the current naphthalene and benzene plumes with
reasonable parameters. Modeling results suggest that biodegradation is likely a significant control on the present
distribution of both contaminants. Predictive simulations suggest that while the naphthalene plume has not reached
an equilibrium condition with the release rate after 100 years, its increase is relatively minor compared to
simulations run without biodegradation. In contrast, the benzene plume appears to have already reached an
equilibrium condition. Simulations representing source treatment alternatives show that for naphthalene, as with
other site-related contaminants, stabilization of the source will dramatically decrease sourcing of the dissolved
plume, which in turn will allow the existing dissolved concentrations to degrade over time through dilution and
biodegradation. Although the model conservatively allowed continued movement of the existing concentration
down gradient, there was no consideration of decreasing aquifer hydraulic conductivity to the west, which will
significantly restrict down-gradient flow. Simulations suggest the benzene plume could be reduced to less than
5 ug/L within 20 years if the source is stabilized. The transport behavior of other creosote components under
various scenarios was not considered but may be estimated in some cases from comparison with the observed
naphthalene and benzene distributions. Naphthalene and benzene concentrations were selected as the primary
indicators of creosote impact on ground water quality at the Site because they are the most mobile transport
constituents of creosote. Both of these constituents are found at the outer boundary of the dissolved plume;
therefore, modeling of these constituents indicates that all other constituents would be found within that boundary.
Monitoring of naphthalene and benzene will also indicate, over time, if the plume was stable or expanding beyond
this outer boundary.
Note that the model did not differentiate between the different technologies evaluated to reduce the NAPL source
and minimize impact to the dissolved phase ground water. Rather, the model evaluated the effect of reducing the
source concentrations and source area conductivity through source "treatment". With a reduction is source
concentration and source conductivity (~ Alternatives G-4 and G-5), RAOs for naphthalene will be met in 50 to
100 years for offsite (490 ppb) and under 50 years for onsite (1500 ppb). Similarly, the RAO for benzene (5 ppb)
is expected to be met in less than 20 years.
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Summary of Site Risks
The original 1988 Record of Decision directed that response actions be taken at the Site to protect public health and
the environment from the release or threatened releases of hazardous substances from the site. The ROD specified
that there was no current exposure to local residents or onsite workers. Potential future exposure pathways were
evaluated for possible impacts to human health. The risk assessment concluded that adverse public health or
environmental hazards could result if no action was taken to prevent exposure to contaminants found at the site.
The principal exposure pathways leading to unacceptable risks were those involving surficial soils and ground
water.
The recently completed Focused Feasibility Study (June 2008) re-evaluated the exposure scenarios and potential
risks to human health from exposure to both the shallow and interbedded ground water contamination, included an
assessment for both onsite and offsite risk, and considered a vapor intrusion pathway. No current exposure to local
residents or onsite workers is indicated. Potential future exposure pathways were evaluated for possible impacts to
human health. The contamination in the shallow sand ground water and the interbedded unit ground water were
considered in the evaluation.
The following information considers the change in ground water assumptions and contaminated soil since the
original ROD:
Chemicals of Concern (COCs)
COCs are chemicals that pose a carcinogenic risk to human health greater than 1 in 1,000,000 (1 X 10"6), have a
non-carcinogenic hazard index (HI) greater than (>) 1, or are found in Site-related ground water at concentrations
exceeding drinking water standards, or MCLs.
The following constituents are considered to be COCs at the Site:
Ground Water COCs: Benzene, Benzo(a)pyrene, and Naphthalene
Soil COCs: PAHs (Note that Benzene is no longer detected in the containment cell soils and
will not be considered a COC.)
COCs at the site pose a carcinogenic risk to human health greater than 1 in 1,000,000 (1 X 10"6), have a
Non-carcinogenic hazard index (HI) greater than (>) 1, or are found in Site ground water at concentrations that
exceed MCLs. The Basic Human Health Assessment (BHHRA) conducted at the site focused on naphthalene's
non-cancer effects and calculated its contribution to human health risk using the hazard index.
Land and Groundwater Use Assumptions
Land Use
Land use in the area is divided among residential, commercial, and industrial properties. The population in the area
is approximately 50,000. The nearest residential area is to the west with the closest residence approximately 200
feet from the site.
Use of the property at the Site is expected to remain commercial into the foreseeable future. The Harris Country
Toll Road Authority (HCTRA) will be constructing an extension of the Hardy Toll Road in the near future, along
the existing rail right-of-way at the western boundary of the Site. The construction is expected to impact the
current footprint of the Site.
Ground Water Use
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As mentioned in the Summary of Site Characteristics, the shallow sand aquifer and the interbedded unit aquifer are
not being used for sources of drinking water onsite or within a one-mile radius of the site. Although a deep onsite
aquifer is potentially useable as a public water supply source, onsite and neighboring residents are served by the
City of Houston water supply which originates from a deeper aquifer 10 miles from the site, or a surface water
reservoir located over 20 miles from the site. Although the shallow water-bearing zones are not currently being
used as a source of drinking water, the potential exists that ground water from these zones could be utilized in the
future. Based on sustainable yields in the shallow sand aquifer and interbedded unit and limited water quality data,
it appears that both water bearing units could theoretically be used as a future drinking water source.
Potential Exposure Pathways
Ground Water - Public water supply wells are screened in the Evangeline Aquifer at depths greater than 600 feet.
All local residents are connected to the public water supply. Therefore, under current site use conditions, there is
no plausible potential for local residents to be exposed to ground water contaminated by the Site. However, based
on aquifer testing and current Site conditions, the shallow sand and interbedded unit likely meet the Class II criteria
in TCEQ's Ground Water Classification system; therefore, future use of the ground water at the Site must be
considered in the evaluation of remedial options.
Soil - Contaminated soil and sediments at the Site were excavated during the original remedial action for OU2 and
consolidated for biological treatment. When the biotreatment failed to meet the performance goal defined in the
1994 ESD, the soils were consolidated in a containment cell and covered with an HDPE liner, pending evaluation
and selection of a final remedy. Containment of the contaminated soil limits the exposure to a local population,
utility workers, and construction workers. The proposed remedy is to cap contaminated soils in place. An
impermeable cap will restrict direct exposure to soils, and also prevent migration of contaminants to underlying
ground water (if the cell was not lined). The proposed remedy will continue to be protective as long as the cap is
maintained.
Vapor Intrusion - Potential public exposure to soil vapor via vapor intrusion has recently received more attention
at sites with VOC contamination. At the North Cavalcade Site, the dissolved phase plume in the shallow sand
extends beneath and/or adjacent to the commercial buildings located on the Site. To evaluate soil vapor intrusion at
the Site, a screening evaluation was conducted using the Johnson and Ettinger Model. This evaluation was
conducted to determine whether vapor intrusion at the Site was a potential exposure pathway. The results of the
modeling indicated that highest concentrations in ground water close to building footprints do not exceed screening
levels. The modeling however did not take into account biodegradation of naphthalene, which will reduce the
vapor intrusion impact. As a result of not including degradation, the modeling results should be considered overly
conservative. The results of this evaluation conclude that vapor intrusion is unlikely to be a potential exposure
pathway at the Site.
Exposure Pathways Affecting Each Population Group
Current and future land use-based exposure pathways through the use of ground water were evaluated in the
exposure assessment for the 2007 Basic Human Health Risk Assessment (BHHRA) for the Site. The following
receptors were evaluated for onsite and offsite areas of the Site in the BHHRA:
Future Offsite Adult/Child Residents - offsite domestic ground water use for residential adult and child (drinking, skin
contact while showering, and breathing vapors in the shower).
Future Onsite Industrial/Commercial Worker - onsite industrial/commercial drinking use for adult worker (drinking,
skin contact while showering, and breathing vapors in the shower).
Future Onsite Construction Worker - onsite incidental exposures during construction activities for adult worker (skin
contact while excavation and breathing vapors while excavation).
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Since drinking water is provided by the municipality and shallow water is typically not used for drinking purpose,
evaluation of potential risks associated with domestic or drinking use of ground water represents a very
conservative exposure scenario. The Hardy Toll Road Authority has developed plans to extend the Hardy Toll
Road from Loop 610, along the Site's western boundary, into downtown Houston. Therefore, future onsite
construction activities assumed in this assessment could occur in the near future. However, the specific behavior of
construction worker for commercial construction is likely to result in lower levels of exposure than those assumed
in this risk assessment due to the use of construction equipment for such large scale commercial building activities.
Thus the construction worker direct contact with site ground water scenario evaluated represents the high-end of
likely exposure for the site.
Summary of Human Health Risk Characterization for Potential Exposure to Ground Water
Risk estimates were calculated for future land use scenarios for hypothetical human receptors at the Site. Cancer
risks were estimated as the probability of an individual developing cancer over a lifetime as a result of exposure to
the Site's carcinogenic contaminants. Toxicity risk estimates for non-carcinogenic toxic chemicals are presented for
COCs. The potential for non-carcinogenic hazards due to potential exposures to chemicals was evaluated by
calculating an HI for the COCs at North Cavalcade. The Baseline Risk Assessment shows the detailed calculation
of risk and organized the types of risk at the Site according to various exposure scenarios. Each exposure scenario
specifies the type of human receptor (e.g., child resident, adult industrial worker), the exposure pathway (e.g.,
inhalation, ingestion) and the COC. If a contaminant or exposure scenario is found to produce a risk which will
require a remedial action (based on either the carcinogenic risk or the HI) that contaminant or exposure scenario is
said to "drive the risk" or "drive" the need for action. A remediation goal is set for the site-related COCs that drive
risk. The following exposure scenarios are driving the need for action at the Site (all risks are expressed as
Reasonable Maximum Exposure or RME).
Future Offsite Adult/Child Resident - The offsite ground water COC for these receptors is present at a
concentration above the non-carcinogenic target level (HI < 1); therefore presenting an unacceptable risk to human
health and the environment.
Future Offsite Adult/Child Resident (lifetime exposure) - The carcinogenic estimated cumulative lifetime risk for
these two receptors for ground water COCs was within the acceptable risk range of 1 to 10,000 (ten thousand) in a
million. However, considering both the non-carcinogenic and carcinogenic evaluations, the offsite ground water
poses an unacceptable risk to offsite residents, if the ground water is used as a drinking water source.
Future Onsite Industrial/Commercial Worker - Overall, the site ground water presented unacceptable risks if used
for drinking purpose by a future industrial worker.
Future Onsite Construction Worker - A cumulative lifetime carcinogenic risk for this receptor is well within the
risk range, where as the estimated HI slightly exceeds the acceptable non-carcinogenic target of HI < than 1,
primarily from the potential exposure to naphthalene in ground water.
Based on the results of the BHHRA, current onsite and offsite ground water conditions exceed the risk range for the
evaluated potential future exposure scenarios.
Remedial Action Objectives and Goals
Remedial Action Objectives (RAOs) provide a general description of what a Superfund cleanup is designed to
accomplish. This section provides a discussion of the existing Remedial Action Objectives (RAOs) and
Preliminary Remedial Goals (PRGs) as defined in the 1988 ROD for the North Cavalcade Street Site, as well as a
discussion of the development of revised RAOs and PRGs for this Proposed Plan.
RAOs are developed to consider the contaminants of concern (COCs), exposure route(s), receptor(s), applicable
federal and state standards, and anticipated future land use for the Site. The RAOs developed in the 1988
Feasibility Study for soil and ground water at the site required that existing contamination be removed and/or
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treated to ensure that human health and the environment are protected. As a point of comparison, the following
RAOs for soils and ground water established in the original 1988 ROD as follows:
Soil RAO (1988 ROD)
Removal and/or treatment of contaminants in subsurface soil that are in determined to increase the risk of cancer by
1x10-4 to 1x10-7 excess cases (1 excess case on ten thousand to ten million individuals) or cause exposure greater
than the reference dose.
Ground Water RAO (1988 ROD)
Removal and/or treatment of ground water containing concentrations exceeding Maximum Contaminant Levels
(MCLs) established under the Federal Safe Drinking Water Act.
As part of the 2008 FFS, the original RAOs were reviewed for applicability with current conditions at the Site and
revised accordingly. The revised RAOs for the Site still meet the overall remedial goals of the original RAOs of
ensuring that human health and the environment are protected. The revised RAOs for the Site are described below.
Soil RAOs (Proposed Plan)
• Prevent human exposure to contaminated soil in excess of the current site PRGs (30 ppm for cPAHs).
• Minimize migration of soil contaminants currently residing in the temporary containment cell into the
ground water, surface water and other site soil.
• Return a majority of site surface area to beneficial use wherever practicable.
Ground Water RAOs (Proposed Plan)
• Prevent or minimize source area migration and contribution to the existing dissolved phase plume [source
control].
• Prevent or minimize the potential that ground water contaminants from the shallow sand and interbedded
unit could impact deeper aquifers [prevent or minimize further migration of the plume].
• Prevent current and future use of the shallow sand and interbedded unit ground water impacted by past
site operations with ground water contaminants in excess of the current site PRGs (0.005 ppm or 5 ppb for
benzene, 0.0002 ppm or 0.2 ppb for benzo(a)pyrene, 1.5 ppm or 1500 ppb for naphthalene onsite, and
0.490 ppm or 490 ppb for naphthalene offsite) [prevent human exposure to contaminated ground water
above acceptable risk levels].
• Return ground water to its expected beneficial use wherever practicable [restoration].
The ground water RAOs meet the expectations for contaminated ground water under the National Contingency
Plan (NCP) and consider the site-specific conditions. The revised RAOs are applicable to both the shallow sand
aquifer and interbedded unit aquifer; two NAPL source areas that impact the shallow sand aquifer, the interbedded
unit aquifer, and the dissolved phase contaminants associated with both source areas.
Preliminary Remediation Goals
Preliminary remediation goals (PRGs) provide numerical criteria that can be used to measure progress in meeting
the remedial action objectives for the cleanup. The original preliminary remediation goals (PRGs) for soil and
ground water at the site were established in the 1988 ROD, as follows:
Soil PRGs (1988 ROD)
Benzene - 0.04 ppm
cPAHs - 1 ppm (revised to 30 ppm in 1994 ESD)
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The soil PRGs were established to prevent against an additional risk of cancer greater than 1x10"5 from exposure to
contaminated soil and also to ensure against non-carcinogenic hazards.
Ground Water PRGs (1988 ROD)
Benzene - 0.005 ppm, or 5 ug/L
cPAHs - non-detect
The 1988 PRGs for ground water were selected based on a future drinking water use exposure scenario. For
benzene, the PRO was selected to comply with the federal drinking water standard of 5 ug/L. The PRO for cPAHs
was selected to ensure that, in conjunction with the level for volatiles, the overall risk to potential consumers would
be less than IxlO"5. Note that the ground water 1988 PRGs were for the shallow sand aquifer only.
The original PRGs for soil and ground water at the Site were reviewed for applicability based on current conditions
at the site. The November 2006 analytical results from soil samples taken from within the cell indicate that the
performance goal for benzene has been met. The analytical results also demonstrated that the total concentration of
cPAHs in the soil still exceeded the PRG performance goal, and therefore will be retained.
The shallow sand and interbedded unit aquifers were assessed as having potential future use as drinking water
sources. Therefore, the PRGs for ground water were also chosen to comply with the federal drinking water
standards or a State standard in the absence of a federal drinking water standard. The original 1988 ROD specified
remedial goals for benzene at the MCL (5 ug/L) and cPAHs as "non-detect" for the shallow aquifer COCs. The
2005 Supplemental Investigation for Remedy Evaluation confirmed NAPL down to the deeper interbedded unit
with an associated offsite dissolved phase plume, defined by the extent of naphthalene. A ground water PRG was
developed for naphthalene based on a State standard (Protective Concentration Level, PCL) for potential onsite
(industrial/commercial) and offsite (residential) exposure scenarios. The cPAH PRG in the original 1988 ROD was
refined in this Proposed Plan to a benzo(a)pyrene equivalent to meet the MCL drinking water standard. The
revised PRGs for ground water will apply to both the shallow sand aquifer and the interbedded unit aquifer.
The Proposed Plan recommends the following PRGs:
Soil PRGs
Benzene - deleted
cPAHs - 1 ppm (revised to 30 ppm in 1994 ESD)
Ground Water PRGs
Benzene - 5 ppb, or 5 ug/L (MCL)
Benzo(a)pyrene - 0.2 ppb or 0.2 (ig/L (MCL)
Naphthalene offsite - 490 ppb (residential drinking water standard under TCEQ)
Naphthalene onsite - 1500 ppb (commercial/industrial drinking water standard under TCEQ)
Summary of Remedial Alternatives
The EPA has developed alternatives based on media impacted. These alternatives are analyzed in more detail in
the FFS, which is part of the Amended Administrative Record File.
Ground Water Alternatives
- Altern ative G-1: No A ction
- Alternative G-2: No Action for Source Areas and Monitored Natural Attenuation (MNA)for the Dissolved
Plume
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- Alternative G-3: Modified Pump and Treat for Source Areas andMNAfor the Dissolved Plume
- Alternative G-4: Source Stabilization withMNAfor the Dissolved Plume
- Alternative G-5: Source Stabilization with In-situ Chemical Oxidation Scrub along the Western Boundary
andMNAfor the Remainder of the Dissolved Plume
- Alternative G-6: Source Control by Capping and Perimeter Slurry Walls andMNAfor the Dissolved
Plume
Common Remedial Alternative Components
Each of the ground water remedial alternatives, except the No Action alternative requires the following remedial
components. The common components include:
• Institutional Controls (ICs) - ICs are non-engineered instruments such as administrative and/or legal controls
that minimize the potential for human exposure to contamination by limiting land or resource use. ICs are
generally to be used in conjunction with, rather than in lieu of, engineering measures such as waste treatment or
containment; can be used during all stages of the cleanup process to accomplish various cleanup-related
objectives; and, should be "layered" (i.e., use multiple ICs) or implemented in a series to provide overlapping
assurances of protection from contamination.
• Ground Water Monitoring Program - a ground water monitoring program provides an on-going comparison to
historical ground water conditions and the necessary data to evaluate the performance of the selected remedy to
meet the RAOs for the Site. The monitoring program monitors conditions both onsite and offsite, and
documents changes through on-going processes, such as natural attenuation.
• Technical Support - this component includes the continual technical evaluation of the selected remedy,
including, but not limited to, system parameters, field and analytical data, and system optimization. This
support will provide real-time evaluation of the selected remedy with the purpose of optimizing the operation
and effectiveness of the selected remedy and monitoring program.
• Five-Year Review - five-year reviews are required whenever a remedial action results in hazardous substances,
pollutants, or contaminants remaining on site above levels that do not allow for unlimited use and unrestricted
exposure. In each of the ground water remedial alternatives, contaminants will remain in the ground water at
concentrations above the site PRGs. Five-year reviews were previously conducted for the Site in 1998, 2003,
and 2008, and will continue on a five-year cycle.
Alternative G-l - No Action
Estimated Capital Cost: $0
Estimated Present Worth Operations and Maintenance (O&M) Cost: $0
Estimated Total Present Worth Cost: $0
Alternative G-l assumes no remedial action for contaminated ground water beyond that already performed. Under
this alternative, no action would be conducted at the site to prevent COC migration, and no provisions would be
included for ICs to restrict ground water use. Although this alternative does not meet the ground water RAO, it is
considered in this evaluation as a baseline for comparison to other remedial alternatives as required by the NCP.
Alternative G-2 - No Action for Source Areas and MNA for the Dissolved Plume
Estimated Capital Cost: $800,000
Estimated Present Worth O&M Cost: $1,800,000
Estimated Total Present Worth Cost: $2,600,000
Under this alternative, no action would be performed on the source areas in the shallow sand and the interbedded
unit, and the dissolved plume would be allowed to attenuate naturally under the Monitored Natural Attenuation
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(MNA) approach. Long Term Monitoring (LTM) would be performed to evaluate the progress of MNA. Under
this alternative, the flow and transport modeling for the interbedded zone indicated that the naphthalene plume
would not reach equilibrium for 100 years or more. The model also indicated that the benzene plume was at
equilibrium and no longer expanding.
The existing pump and treat system would no longer be required and the southern portion of the site would be
available for restricted use. ICs would be required to restrict ground water use on and downgradient of the site and
also to restrict onsite excavation in the source areas. Installation of downgradient monitor wells in the shallow sand
and interbedded unit will be required under this alternative to evaluate the effectiveness of MNA, to quantify the
natural attenuation rate, and to verify that the contaminated ground water is managed within the 1C (restricted-use)
boundary.
The primary components of Alternative G-2 include the following:
• Demolition of Existing Ground Water Treatment System
• Installation of New Ground Water Monitor Wells
• Plug and Abandonment of Existing Temporary Wells
• Long-Term Ground Water Monitoring (MNA)
• Institutional Controls
• Five-Year Reviews
Alternative G-3 - Modified Pump and Treat for Source Areas and Monitored Natural Attenuation (MNA)
for the Dissolved Plume
Estimated Capital Cost: $2,769,000
Estimated Present Worth O&M Cost: $4,361,000
Estimated Total Present Worth Cost: $7,130,000
Under this alternative, the existing treatment system would be modified to enhance NAPL recovery through use of
water flooding. The dissolved phase plume would be allowed to migrate and naturally attenuate over time.
Through enhanced NAPL recovery, the potential for the source areas in the shallow and interbedded aquifers to
serve as an ongoing source of contamination for the dissolved plume would be reduced. The cost projections for
this alternative assumed that the NAPL source area would be treated for 10 years. Based on the flow and transport
modeling, it is assumed that complete cleanup of the ground water will take between 50 to 100 years.
Water flooding involves a series of extraction wells located in the source area and a series of injection points
located around the peripheral of the source area. Water and NAPL are extracted via the extraction wells. The
NAPL and water are then separated via a separator with the NAPL being stored in tanks prior to disposal. A portion
of the extracted water is re-injected into the formation which acts to displace the NAPL toward the extraction wells.
A portion of the water extracted is treated and discharged to the drainage ditches to further ensure hydraulic
containment of the NAPL impacted areas.
Portions of the existing pump and treat system would no longer be required with the exception of the NAPL storage
tanks and the carbon adsorption units. ICs would be required to restrict ground water use on and downgradient of
the site. Installation of downgradient monitor wells in the shallow sand and interbedded unit will be required under
this alternative evaluate the effectiveness of MNA, to quantify the natural attenuation rate, and to verify that the
contaminated ground water is managed within the 1C (restricted-use) boundary.
The main components of Alternative G-3 include:
• Installation of the Source Area NAPL Extraction System with Water Flooding Component and Integration
with the Existing Treatment System
• Demolition of the unused Components of the Existing Treatment System
• Treatment System O&M
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• Installation of New Monitor Wells
• Plug and Abandonment of Existing Extraction and Temporary Wells
• Long-Term Ground Water Monitoring
• Institutional Controls
• Five-Year Review
Alternative G-4 - Source Stabilization with Monitored Natural Attenuation (MNA) for the Dissolved Plume
Estimated Capital Cost: $4,708,000
Estimated Present Worth O&M Cost: $1,675,000
Estimated Total Present Worth Cost: $6,383,000
Alternative G-4 provides for stabilization through in-situ solidification (S/S) of the source areas in the shallow sand
and the interbedded unit. The dissolved contaminant plume in both zones would be allowed to attenuate naturally.
Long term monitoring (LTM) would be required to assess the effectiveness of the MNA remedy. Under this
alternative, based on the flow and transport modeling conducted, it will take between 50 to 100 years for ground
water to reach RAOs (1500 ppb) for naphthalene offsite. Onsite RAOs (490 ppb) for naphthalene will be reached
in less than 50 years. The RAO for benzene (0.005 ppm, or 5 ug/L) will be reached in less than 20 years.
Shallow soil mixing is an in-situ technology that uses a large auger system with the ability to deliver a cement and
powdered activated carbon (PAC) slurry in addition to other additives while mechanically breaking up and mixing
the soil. S/S via shallow soil mixing reduces the mobility of hazardous substances and contaminants in the
environment through both physical and chemical means. The permeability of the soil is also reduced which reduces
the flux of contaminants from the source zone.
Alternative G-4 would minimize the potential for the source zones in the shallow and intermediate aquifers to serve
as a continuous source of contamination for the dissolved phase plume. Contaminated soil would be mixed until
adequately homogenized as a cement grout is injected under pressure to solidify and immobilize the contaminated
soil in a concrete-like form, and the potential for NAPL migration would be significantly reduced in the treatment
area. The existing pump and treat system would no longer be required and the southern portion of the site would be
available for restricted use. ICs would be required to restrict ground water use on and downgradient of the site and
also to restrict excavating in the source stabilization areas. Installation of downgradient monitor wells in the
shallow sand and interbedded unit will be required under this alternative evaluate the effectiveness of MNA, to
quantify the natural attenuation rate, and to verify that the contaminated ground water is managed within the 1C
(restricted-use) boundary.
The primary components of Alternative G-4 include:
• In-Situ Source Stabilization (shallow soil mixing)
• Handling of swell materials generated during stabilization
• Site Restoration
• Demolition of Existing Ground Water Treatment System
• Installation of New Ground Water Monitor Wells
• Plug and Abandonment of Existing Temporary Wells
• Long-Term Ground Water Monitoring
• Institutional Controls
• Five-Year Review
Alternative G-5 - Source Stabilization with an In-situ Chemical Oxidation Scrub along the Western
Boundary and MNA for the Remainder of the Dissolved Plume
Estimated Capital Cost: $5,878,000
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Estimated Present Worth O&M Cost: $2,000,000
Estimated Total Present Worth Cost: $7,878,000
Alternative G-5 is similar to Alternative G-4, except that the dissolved phase plume, along the western boundary of
the site, will be treated via in-situ chemical oxidation. As in Alternative G-4, S/S of the source areas in the shallow
sand and the interbedded unit would be accomplished through shallow soil mixing, and the dissolved plume outside
the property boundary would be allowed to attenuate naturally through MNA. However, inside the western
property boundary, treatment via in-situ chemical oxidation (ISCO) will be performed as a scrub of the dissolve
phase ground water plume before it migrates off-site. LTM would be performed to evaluate the progress of the
chemical oxidation treatment and MNA. Because this alternative is the most aggressive of all the ground water
alternatives the remediation time frame would be less than that anticipated for Alternative G-4.
With ISCO, an oxidant is typically delivered via a large number of injection points or flushed through the
subsurface with injection and recovery wells. Because elevated levels of dissolved contamination including residual
NAPLs of creosote are expected to be encountered, a strong oxidant will be required. Oxidant demand is expected
to be fairly high and it is anticipated that multiple oxidant injections will be required.
The existing pump and treat system would no longer be required and the southern portion of the site would be
available for restricted use. ICs would be required to restrict ground water use on and downgradient of the site and
also to restrict excavating in the source stabilization areas.
The primary components under this alternative include:
• In-Situ Chemical Oxidation (ISCO) Pilot Test
• In-Situ Source Stabilization
• Handling, Transportation, and Disposal of Swell Materials Generated during Stabilization
• In-situ Chemical Oxidation through injection wells along the western boundary of the site
• Site Restoration
• Demolition of Existing Ground Water Treatment System
• Installation of New Ground Water Monitor Wells
• Plug and Abandonment of Existing Temporary Wells
• Long-Term Ground Water Monitoring
• Institutional Controls
• Five-Year Review
Alternative G-6 - Source Control by Capping and Perimeter Slurry Walls and MNA for the Dissolved
Plume
Estimated Capital Cost: $2,157,000
Estimated Present Worth O&M Cost: $2,409,000
Estimated Total Present Worth Cost: $4,566,000
Alternative G-6 includes containment of the source zone(s) by capping with a low permeable cover on the ground
surface and laterally containing the source zone(s) using perimeter cutoff slurry walls. Extraction inside of the
slurry wall would be required to assure an inward hydraulic gradient. Under this alternative, the capping and
perimeter cutoff wall could also be extended to include the transition zones. After the slurry walls and caps have
been constructed, the dissolved phase plume will be allowed to naturally attenuate via MNA. The timeframes for
reaching RAOs are similar to those for alternatives G-3 and G-4.
Alternative G-6 would minimize the potential for the source zones in the shallow and intermediate aquifers to serve
as a continuous source of contamination for the dissolved phase plume. This remedy would significantly reduce or
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eliminate the potential for NAPL migration in the treatment area. The existing pump and treat system would no
longer be required and the southern portion of the site would be available for restricted use. ICs would be required
to restrict ground water use on and downgradient of the site and also to restrict digging in the protective cap and
slurry wall. Installation of downgradient monitor wells in the shallow sand and interbedded unit will be required
under this alternative evaluate the effectiveness of MNA, to quantify the natural attenuation rate, and to verify that
the contaminated ground water is managed within the 1C (restricted-use) boundary.
The primary components under this alternative include:
• Site Preparation (Clearing and grubbing)
• Source Control by Capping and Construction of Perimeter Slurry Walls
• Stormwater Control Measures
• Site Restoration
• Demolition of Existing Ground Water Treatment System
• Installation of New Ground Water Monitor Wells
• Plug and Abandonment of Existing Temporary Wells
• Long-Term Ground Water Monitoring and O&M
• Institutional Controls
• Five-Year Review
Soil Alternatives
- Alternative S-l: No Action
- Alternative S-2: Onsite Thermal Desorption with Offsite Disposal
- Alternative S-3: Offsite Incineration with Offsite Disposal
- Alternative S-4: No Treatment with New Onsite Disposal Cell
- Alternative S-5: Modify the Existing Cell and Cap In-Place
- Alternative S-6: Solidification with New Onsite Disposal Cell
Alternative S-l - No Action
Estimated Capital Cost: $0
Estimated Present Worth O&M Cost: $0
Estimated Total Present Worth Cost: $0
The no-action alternative constitutes the absence of any remedial actions (including interim actions), beyond that
already performed. "No Action" is considered in this evaluation as a baseline for comparison to all other potential
remedial actions, as required by the NCP. The soil targeted for remediation by the ROD currently resides in a
temporary containment cell located on the northern portion of the property. Under this alternative, no further
remedial activities would be implemented beyond those remedial activities already completed. The soil stored in
the temporary containment cell serves to minimize long-term human health and environmental risks for the site as
long as the integrity of the containment cell is maintained.
Alternative S-2 - Onsite Thermal Desorption with Offsite Disposal
Estimated Capital Cost: $16,940,000
Estimated Present Worth O&M Cost: $0
Estimated Total Present Worth Cost: $16,940,000
Alternative S-2 includes excavation of material exceeding PRGs from the temporary containment cell, treatment of
the soil to meet the land disposal restrictions (LDRs) for F034 and K001 listed waste, and disposal of the soil
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offsite in a RCRA permitted and licensed landfill. Treatment would include onsite thermal desorption of soil
containing PAHs in exceedance of the LDRs prior to shipping the soil offsite for disposal.
Thermal desorption is an ex-situ separation process that utilizes heat exchange to vaporize VOCs and SVOCs from
the soil. The vaporized contaminants are then typically treated by being burned in an afterburner prior to discharge.
Thermal desorption is a well known treatment technology used at wood treating site for the treatment of
contaminated soil associated with past wood processing activities.
The soil RAOs would be met by Alternative S-2 through the prevention of direct contact with contaminated soil
and the prevention of contaminants contained the soil from migrating to the ground water and/or surface water.
Since the material would be removed from site, the northern portion of the site would be available for unrestricted
use. In addition, the treatment of contaminated material would satisfy EPA's preference for treatment that reduces
toxicity and mobility as a principal element of remedial actions.
The main components of Alternative S-2 include:
• Excavation of Soil from the Temporary Containment Cell
• Onsite Thermal Desorption of PAHs in the Soil
• Demolition of the Temporary Containment Cell
• Offsite Disposal of Soil and Debris
• Site Restoration
Alternative S-3 - Offsite Incineration with Offsite Disposal
Estimated Capital Cost: $36,018,000
Estimated Present Worth O&M Cost: $0
Estimated Total Present Worth Cost: $36,018,000
Alternative S-3 includes excavation of material exceeding PRGs from the temporary containment cell, treatment of
the soil to meet LDRs for F034 and K001 listed waste, and disposal of the soil offsite in a RCRA permitted and
licensed landfill. Treatment would include offsite incineration of soil containing PAHs in exceedance of the LDRs
prior to shipping the soil to a landfill for disposal. LDRs would apply if the soil was removed from the site for
disposal.
The soil RAOs would be met by Alternative S-3 through the prevention of direct contact with contaminated soil
and the prevention of contaminants contained the soil from migrating to the ground water and/or surface water.
Since the material would be removed from site, and the northern portion of the site would be available for
unrestricted use. In addition, the treatment and immobilization of contaminated material would satisfy EPA's
preference for treatment that reduces toxicity and mobility as a principal element of remedial actions.
The main components of Alternative S-3 include:
• Excavation of Soil from the Temporary Containment Cell
• Offsite Incineration of PAHs in the Soil
• Demolition of the Temporary Containment Cell
• Offsite Disposal of Soil and Debris
• Site Restoration
Alternative S-4 - No Treatment with New Onsite Disposal Cell
Estimated Capital Cost: $5,183,000
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Estimated Present Worth O&M Cost: $567,000
Estimated Total Present Worth Cost: $5,750,000
Alternative S-4 includes excavation of material exceeding PRGs from the temporary containment cell and disposal
of the soil onsite in a new containment cell. The new containment cell will need to be built to RCRA Subtitle C
requirements because select PAHs exceed the LDR alternative soil cleanup standards (40 CFR 268.49).
The soil remedial objectives would be met by Alternative S-4 through the prevention of direct contact with
contaminated soil and the prevention of contaminants contained the soil from migrating to the ground water and/or
surface water. Under this alternative most of the northern portion of the property could be available for limited
reuse. Since the material would remain onsite, ICs, maintenance, and monitoring of the site would be required. In
addition, the encapsulation of contaminated material would prevent mobile constituents (if present) from migrating
in the future, and limit the need for monitoring or imposing restrictions on the remainder of the site.
The main components of Alternative S-4 include:
• Excavation of soil from the temporary containment cell
• Demolition and disposal of the temporary containment cell
• Construction of a low permeability cover and liner to control infiltration and leakage
• Stormwater Control Measures
• Site restoration
• Institutional controls
Alternative S-5 - Modify the Existing Cell and Cap In-Place
Estimated Capital Cost: $1,611,000
Estimated Present Worth O&M Cost: $567,000
Estimated Total Present Worth Cost: $2,178,000
Alternative S-5 includes modifying the existing temporary containment cell by removing the HDPE cover and
constructing a new long-term low permeable cover over the existing containment cell. Two types of low permeable
covers (soil and asphalt) are evaluated under this alternative. The low permeability soil cover is preferred and is
retained as the proposed remedy. For a cost comparison, the capital cost for the asphalt cover is estimated at
$1,401,000; estimated present worth O&M costs at $331,000: and net present value cost at $1,840,000.
Because the soil would be left in place, LDRs are not applicable.
The soil RAOs would be met by Alternative S-5 through the prevention of direct contact with contaminated soil
and the prevention of contaminants contained the soil from migrating to the ground water and/or surface water.
The northern portion of the property would be available for limited reuse with this remedy. Since the material
would remain onsite, ICs, maintenance, and monitoring of the site would be required. In addition, the encapsulation
of contaminated material would prevent mobile constituents (if present) from migrating in the future, and limit the
need for monitoring or imposing restrictions on the remainder of the site.
The main components of Alternative S-5 include:
• Removal and disposal of the existing HDPE cover liner
• Construction of a low permeability cover to control infiltration and leakage
• Stormwater Control Measures
• Site restoration
• Operation and maintenance (including ground water monitoring and cap inspections)
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• Institutional controls.
Alternative S-6 - Solidification with a New Onsite Disposal Cell
Estimated Capital Cost: $7,461,000
Estimated Present Worth O&M Cost: $567,000
Estimated Total Present Worth Cost: $8,028,000
Alternative S-6 involves excavation of material exceeding PRGs from the temporary containment cell, ex-situ
solidification/stabilization (S/S) of material exceeding PRGs using a combination of binding agents such as
Portland cement and PAC or other additives to solidify and stabilize the materials. A vegetative soil cover,
consisting of one foot of compacted clay and six inches of topsoil, will be placed over this area when
immobilization is complete.
The soil RAOs will be met under Alternative S-6 by preventing direct contact with contaminated soil and sediment,
preventing future leaching of COCs to the ground water through use of an immobilizing agent, grading of the
surface to improve precipitation run-off, and minimization of continued erosion of contaminated soil and sediment.
Since the material would remain onsite, ICs, maintenance, and monitoring of the site would be required. An
approved ground water monitoring system will be installed as an active part of this alternative to verify that ground
water concentrations remain below MCLs.
The main components of Alternative S-6 include:
• Excavation of Soil from the Temporary Containment Cell
• Demolition and disposal of the Temporary Containment Cell
• Ex-Situ Solidification/Stabilization of material exceeding PRGs
• Construction of vegetative soil cover over treated areas
• Stormwater Control Measures
• Site restoration
• Operation and maintenance (including ground water monitoring and cap inspections)
• Institutional controls
Evaluation of Remedial Alternatives
The EPA uses nine criteria to evaluate remedial alternatives for the cleanup of a release. These nine criteria are
categorized into three groups: threshold, balancing, and modifying. The threshold criteria must be met in order for
an alternative to be eligible for selection. The threshold criteria are overall protection of human health and the
environment and compliance with Applicable, Relevant and Appropriate Requirements (ARARs). The balancing
criteria are used to weigh major tradeoffs among alternatives. The five balancing criteria are long-term
effectiveness and permanence; reduction of toxicity, mobility or volume through treatment; short-term
effectiveness, implementability; and cost. The modifying criteria are state acceptance and community acceptance,
which are evaluated once the Proposed Plan public comment period is complete.
Based on the information and the analysis presented in the FS, EPA has identified the following Preferred
Alternative:
Ground Water
Alternative G-4 - Source Stabilization with MNA for the Dissolved Plume (Treatment)
Soil
Alternative S-5 - Modify the Existing Cell and Cap In-Place (Containment)
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The EPA may modify its position regarding site remediation based on its assessment of community acceptance and
state acceptance, the final two criteria, which will be described in the ROD Amendment after comments are
received.
Comparative Analysis of Remedial Technologies Relative to Impacted Media, and the Original
Remedy (1988 ROD)
The following section provides a comparative analysis of the remedial technologies for soils and ground water,
relative to the nine evaluation criteria and the remedy selected in the 1988 Record of Decision. [In 1988, EPA
selected the Site remedy to extract and treat contaminated ground water with carbon adsorption and to biologically
treat contaminated surface soils. It was estimated that remediation of contaminated ground water would be
complete 2 years after construction. Soil remediation was expected to be complete in 3 years.]
1. Overall Protection of Human Health and the Environment
The different technologies, or technology combinations, considered in the FS for the different media of concern
provide slightly differing degrees of protection for human health and the environment. Basic comparative analyses
for the technologies, or technology combinations, for the different media of concern are presented below.
Ground Water
All alternatives, except Alternative G-l, provide protection of human health and the environment. During active
remediation, protection is provided through the use of LTM to confirm the ground water exposure pathway
remains incomplete, and through the use of ICs to restrict ground water use in the affected areas during active
remediation. Currently, although the aquifer is considered a potential drinking water source, there are no identified
users.
In all alternatives, contaminated ground water in the dissolved plume outside the source areas would be allowed to
attenuate naturally. Alternative G-5 includes not just natural attenuation of the dissolved plume but also includes
some limited in-situ chemical oxidation of the dissolved plume along the western site boundary. LTM would be
used to track remediation progress in all alternatives except Alternative G-l. In addition to MNA for the dissolved
plume, Alternatives G-3, G-4, G-5, and G-6 all involve various forms of source area control or reduction, ranging
from water flooding (G-3), in-situ solidification (G-4 and G-5), in-situ chemical oxidation for the western site
boundary (G-5) and physical source control using slurry walls and caps (G-6). With Alternative G-2, no action
would be performed in the source areas, allowing the NAPL/residual NAPL to continue to source the dissolved
plume, although LTM and ICs would control exposure while the plume naturally attenuates over time.
The ground water model estimates it will take between 50 to 100 years for ground water to reach RAOs (490 ppb)
for naphthalene offsite. This estimate is based on a scenario where the source is removed, conductivity through the
source is reduces, and biodegradation is ongoing. Based on the ground water model, onsite RAOs (1500 ppb) for
naphthalene will be reached in less than 50 years. The RAO for benzene (0.005 ppm, or 5 ug/L) will be reached in
less than 20 years. The remediation time frame is anticipated to be the shortest for Alternative G-5 (in-situ
solidification for source areas and additional in-situ chemical oxidation for the dissolved plume along the western
site boundary). A monitoring plan will be developed to verify the attenuation rates throughout the plume for those
alternatives with a MNA component.
Soil
All soil alternatives are considered protective of human health and the environment. Alternative S-l would be
protective of human health and the environment provided that the integrity of the existing containment cell is
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maintained. Alternatives S-2 and S-3 would be protective of human health and the environment by treating the
contaminated soil to meet the PRGs and then disposing of the soil offsite in a RCRA Subtitle C facility.
Alternative S-4 would be protective of human health and the environment by disposing of the soil in an onsite
containment cell meeting RCRA Subtitle C requirements. Under Alternative S-4, long-term O&M and ICs would
be required to ensure the long-term protectiveness of the containment cell. Alternative S-5 would provide
protection of human health and the environment; however, similar to Alternative S-4, long-term O&M and ICs
would be required to ensure long-term protectiveness. Alternative S-6 would be protective of human health and the
environment because mobility of the contaminants in the soil would minimized through solidification/stabilization
and construction of a low permeable cover over the soil. Under Alternative S-6, long-term O&M and ICs would
also be required to ensure long-term protectiveness.
Alternatives S-2 and S-3 are equally protective of human health and the environment in terms of meeting the RAOs
and PRGs for the site. As compared with the other four alternatives, Alternatives S-l and S-5 would be less
protective because soil containing COCs in excess of the PRGs would remain onsite. Of the two, S-5 is more
protective of human health and the environment through construction of a more permanent low permeability cover.
Materials are contained onsite in a manner that minimizes human exposure to soil and contaminant transport to
ground water. Alternative S-6 would be more protective that S-l and S-5 because the contaminants in the soil
would be immobilized to minimize leaching potential to ground water.
Original Remedy (1988)
The original remedy was selected to be protective of human health and the environment. The selected remedy was
expected to reduce soils and ground water contamination to an acceptable 1 x 10~5risk to human health, prevent any
non-carcinogenic hazards, and prevent continued leaching of creosote compounds from soils into ground water.
Treatment of contaminated soils was discontinued after two years for failure reach remedial goals. Although, the
ground water system did retrieve and treat contaminated ground water and NAPL, the system could not effectively
treat the volume of NAPL. Contamination was confirmed at a deeper interbedded zone, which was not considered
in the 1988 ROD.
2. Compliance with ARARs
Ground Water
All the proposed alternatives, with the exception of the No action alternative (G-l) are anticipated to comply with
ARARs, although achieving site cleanup goals and compliance with ARARs for drinking water protection (MCLs)
would likely require a significant amount of time. Alternative G-6 incorporates the use of engineering controls
(perimeter slurry wall and cap) to help meet RAOs in the source areas.
Soil
It is expected that compliance with ARARs would be achieved by all of the alternatives. Alternative S-l would be
in compliance with the ARARs as long as the integrity of the existing cover is maintained. A waiver would likely
be required for Alternative S-l to meet ARARs because the soil is considered a listed and hazardous waste and the
existing cell would have to meet Subtitle C requirements. Alternatives S-2 and S-3 have common ARARs
associated with the excavation, treatment and disposal portions of the remedy. Onsite air emissions from the
thermal desorption activities would require monitoring for Alternative S-2, while landfill construction requirements
would be applicable to Alternatives S-4, S-5 and S-6. Alternatives S-2 and S-3 would be required to meet LDRs
prior to offsite disposal. Meeting LDRs is not required for Alternatives S-4, S-5 and S-6 because remediation will
be conducted within the area of contamination; therefore, LDRs are not triggered. All of the alternatives except
Alternative S-l can be designed and implemented to achieve applicable ARARs.
Original Remedy (1988)
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The selected remedy was consistent with those laws applicable or relevant and appropriate to CERCLA activities.
3. Long-Term Effectiveness and Permanence
Ground Water
All the alternatives, with the exception of the no action alternative G-l provide long-term effectiveness and
permanence, although they vary greatly in the length of time required to meet RAOs. Alternatives G-3, G-4, G-5,
and G-6 include provisions to minimize plume expansion from the NAPL source areas, potentially reducing the
length of time to achieve RAOs. Alternatives G-3 through G-5 would provide a more permanent reduction of
source with minimal maintenance of the remedy. Alternative G-6 reduces the source by containment with a cap
and slurry wall, which will require maintenance over the life of the project. Alternative G-5, however, offers the
best likelihood of long-term effectiveness due to the use of two different treatment methods to achieve the site
cleanup goals. Source area stabilization and the addition of chemical oxidation for the dissolved phase plume along
the western would most likely enhance cleanup of portions of the dissolved phase plume, and achieve plume
stability, and reduce contaminant concentrations at a faster pace than in-situ solidification alone (in Alternative G-
4).
Soil
The long-term effectiveness of Alternative S-l depends on maintaining the integrity of the existing containment
cell. Alternatives S-2 through S-3 would achieve long-term effectiveness and permanence by eliminating potential
future exposure through treatment via either thermal desorption or incineration of the contaminated soil to below
the PRGs. Both treatment technologies have been proven effective in treating organic contaminants. For
Alternatives S-2 and S-3, the treated soil would be disposed in an offsite RCRA Subtitle C facility. Alternative S-4,
the soil would be disposed onsite in a containment cell meeting RCRA Subtitle C requirements. Alternative S-5
would achieve long-term effectiveness through construction of a more permanent low permeable cover over the
existing temporary containment cell. This alternative is adequate and reliable as long as the protective elements of
the cell are properly maintained, particularly the cap. Alternative S-6 would achieve long-term effectiveness and
permanence because the contaminants in the soil posing unacceptable human health and environment risk would be
bound to the soil matrix through stabilized/solidified and placed into a newly constructed onsite containment cell.
Alternatives S-2 and S-3 would provide the highest level of long-term effectiveness and permanence because the
soil is treated to below site PRGs and the treated soil is disposed offsite in a RCRA Subtitle C facility. Alternatives
S-4 through S-6 would provide less long-term effectiveness and permanence that Alternatives S-2 and S-3 because
soil exceeding the PRGs would remain onsite and effectiveness and permanence of the remedy would depend on
long-term O&M and ICs. Alternative S-l would provide the least long-term effectiveness and permanence
because the existing cover was intended to be temporary.
Original Remedy (1988)
The original remedy, as selected, met the criteria for long-term effectiveness and permanence through the reduction
of contaminant concentrations through treatment. Soil concentrations, however, were not effectively reduced by
treatment. The ground water pump and treat remedy was reducing contaminant concentrations, but with limited
efficiency.
4. Reduction of Toxicity, Mobility and Volume (TMV) of Contaminants through Treatment
Ground Water
Alternatives G-l (no action) and G-2 (no action for the source areas and MNA for the dissolved plume) do not
include active treatment to reduce the TMV of source material or the contaminated ground water. The COCs in the
plume would be left to attenuate naturally over time. The ground water modeling report predicts that, under a no-
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action scenario, the naphthalene plume is expected to continue to expand for 50 to 100 years or more before an
equilibrium condition is achieved. The report indicates that the benzene plume appears to have reached an
equilibrium condition.
Alternative G-3 (extraction and treatment using water flooding in source areas) includes NAPL removal and
treatment to reduce the TMV of NAPL in the shallow sand and interbedded unit, with treatment performed at an
offsite incinerator facility. Alternatives G-4 through G-6 incorporate active treatment in-situ to reduce the mobility
of the NAPL source material. However, of these, only Alternative G-5 provides an in-situ treatment to reduce the
toxicity and volume of contaminants in the dissolved phase plume (through in-situ chemical oxidation) through
active treatment, rather than an attenuation process.
Soil
Alternative S-l reduces the mobility of contaminants present in the soil through containment. However, this
alternative would not result in reduction of toxicity or volume because no treatment would be performed.
Alternatives S-2 and S-3 provide for reduction in TMV through treatment. Alternatives S-4 through S-5 are similar
to Alternative S-l in that containment would only reduce the mobility of contaminants present in the soil.
Alternative S-6 would provide for reduction in TMV through not only containment, but also through
solidification/stabilization (S/S) of the contaminants present in the soil. The S/S process does, however, expand the
volume of materials treated the addition of cement and other additives.
Alternative S-3 offers the best reduction in TMV since contaminants would be destroyed. Approximately 22,300
yd3 of soil exceeding the PRGs would be removed for offsite incineration and disposal in an offsite RCRA Subtitle
C landfill. Alternative S-2 offers the next best reduction in TMV by treating of soil above PRGs via onsite thermal
desorption and disposing of the treated soil in an offsite RCRA Subtitle C landfill. It is estimated that 22,300 yd3 of
soil will require treatment to meet LDRs prior to disposal. Alternative S-4 would provide reduction in mobility by
disposing of the soil in a containment cell meeting RCRA Subtitle C requirements. This alternative would not result
in reduction of toxicity or volume because no treatment would be performed prior to construction of the permeable
cover. Alternative S-5 would provide a reduction in mobility by utilizing the current containment cell and capping
the contaminated soil with a long-term low permeable cover. However, this alternative would not result in
reduction of toxicity or volume because no treatment would be performed prior to construction of the permeable
cover. Alternative S-6 would provide a reduction in mobility by binding contaminants in the soil; however, similar
to Alternatives S-4 and S-5, this alternative would not result in reduction of toxicity or volume. Alternative S-6
likely offers better reduction in mobility than Alternatives S-4 and S-5 because the soil will stabilized/solidified to
bind the contaminants to the soil matrix and then placed in a new low permeability cover containment cell.
Alternative S-l would is similar to Alternative S-5.
Original Remedy (1988)
The selected remedy selected the preference for treatment to completely remediate soils and ground water.
Remedial objectives for soils could not, however, be reached for contaminated soils. Treatment of ground water
did not differentiate between addressing the source and the dissolved phase plume.
5. Short-Term Effectiveness
Ground Water
In the short-term, risks to workers, the community, and the environment are anticipated to be minimal for all five
alternatives (excluding the no-action alternative). For the no action Alternative G-l, short-term risks are still
expected to be minimal; there are no current ground water users. However, construction of the Hardy Toll Road
expansion adjacent to the site may increase the likelihood of exposure in the short-term.
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Assuming the plume is not stable, Alternatives G-4 through G-6 would require the shortest time to achieve ground
water RAOs because these alternatives rely on source stabilization or control to prevent/minimize plume expansion
from the source area to the existing dissolved phase plume and to the deeper aquifers. Of Alternatives G-4 through
G-6, Alternative G-5 would likely require the shortest time to achieve ground water RAOs, because of the use of
in-situ chemical oxidation to treat a portion of the dissolved plume along the site boundary. Because NAPL
removal and ICs would not immediately eliminate the plume expansion, Alternative G-3 would likely require more
time than Alternatives G-4, G-5, and G-6 to achieve the RAO for preventing plume expansion and protecting the
downgradient ground water. It should be noted that in the short term, Alternatives G-4, G-5, and G-6 could result in
an increase in contaminant concentrations in the ground water in the immediate vicinity of the source area because
disturbing the source area could mobilize additional contamination.
Alternatives G-l and G-2 would have the lowest short-term effectiveness because they rely solely on natural
attenuation and thus require a longer period to achieve the RAO for preventing plume expansion and protecting the
downgradient ground water.
Soil
Short-term risks to residents, workers, and the environment primarily originate from the construction required to
implement each of the alternatives. Alternative S-l has no short-term risks because further remedial construction is
not involved. There would be potential risks to construction workers during excavation of contaminated soil from
the temporary containment cell in Alternatives S-2 through S-4 and S-6. These risks are primarily associated with
equipment movement and exposure to contaminated soil and dust. However, engineering controls would be
implemented to control the potential for exposure, and workers would be required to wear the appropriate level of
protection to avoid exposure during excavation and treatment activities.
Alternative S-5 would provide the lowest short-term risks compared with the other alternatives because this
alternative does not require excavation and management/treatment of contaminated soil. Alternatives S-2 through
S-4 and S-6 would present short-term risk to nearby residents and onsite workers with the additional activity
associated with demolition of the temporary containment cell, excavation of soil, staging of contaminated soil,
construction of the new RCRA Subtitle C containment cell (Alternative S-4), and solidification/stabilization and
construction of a low permeable cap (Alternative S-6). Alternative S-2 presents additional short-term risks to
nearby residents and onsite workers because of the increased handling required for waste material (feed)
preparation, and additional emissions from the onsite thermal desorption process. Performance testing would be
required for Alternative S-2 to ensure the LDRs or PRGs can be achieved via thermal desorption. Likewise,
Alternatives S-2 and S-3 would also present additional short-term risk to nearby residents because offsite transport
of soil would be required. All the short-term impacts can be managed with proper safety and engineering controls.
During the remedial action, short-term, health-related risks will be minimized through air monitoring and use of
emission control techniques. Short-term noise impacts and safety-related risks to residents can be lessened by
minimizing haul routes through residential areas.
The short-term effectiveness with respect to the time until the RAOs are achieved is shortest for S-5 because it does
not include excavation and disposal/treatment of contaminated soil in the existing containment cell. The next
shortest time is for S-4.
Original Remedy (1988)
The short-term risks of the original remedy were thought to be minimal as treatment for soils and ground water
were first proposed as in-situ processes. The soil and ground water remedy was expected reach remedial goals in
3 years, considered very effective for the short-term.
6. Implementability
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Ground Water
All alternatives are readily implemented. There are no technical issues associated with implementation of
Alternatives G-l and G-2. Alternatives G-3, G-4, G-5, and G-6 all involve technologies, services, and materials that
are readily available. Implementation of water flooding technology in the interbedded unit under Alternative G-3
may present a challenge. The general interbedded nature of this zone could adversely impact the efficiency of the
water flooding technology. Also, during slurry wall construction under Alternative G-6, it may be difficult to
achieve the design permeability and underflow restriction which could lead to loss of containment. An efficient
field Quality Assurance/Quality Control (QA/QC) program will be required during construction to ensure the
proper permeability and underflow restriction is achieved. Alternative G-5 would present the most challenges in
terms of implementability because of the uncertainty associated with an in-situ chemical oxidation process in a
lower permeability zone, such as the interbedded zone. Application parameters and expected performance would
have to be validated in the field before installation. The in-situ solidification or slurry wall construction for
Alternatives G-4 to G-6 will require additional safeguards to protect adjacent buildings and the pipeline/rail
systems along the east boundary of the Site.
ICs are required to maintain the permanence and effectiveness of Alternatives G-3 through G-6. Implementation of
the ICs for ground water use restrictions will enforced through registration with the Texas Department of Licensing
and Regulation (TDLR). The TDLR has previously delineated restricted drilling areas in response to individual
requests from the TCEQ for several Superfund sites. Drillers must first contact the TDLR's Water Well
Driller/Pump Installer Section prior to drilling any new water wells within the outlined restricted drilling area. In
addition, restrictive covenants would potentially be negotiated with and agreed to by all affected property owners.
Administrative problems affecting implementation of the ICs are not anticipated.
Soil
No administrative coordination labor, equipment, materials or outside services are required for Alternative S-l.
Aside from Alternative S-l, Alternative S-5 provides the most straightforward implementation action because
excavation and management of contaminated soil from the temporary containment cell are not required during the
remedy implementation and the personnel and equipment necessary to implement this remedy are readily available.
Implementation of Alternative S-5 would also require that the soil in and outside the containment cell have
sufficient strength to support a cover. An assessment of the existing cell and the closure criteria referenced in the
Remedial Action Closure Phase Report, Soils Operable Unit (2000) will be included as part of the Remedial
Design.
Under Alternative S-2, personnel and equipment required to implement the remedy are readily available.
Alternative S-2 would require significant efforts to mobilize and setup the thermal treatment unit. Available space
to setup the thermal treatment unit and stage soil is available at the site. A proof of performance test would be
required to verify treatment efficiency. Treatment residuals would require verification testing to ensure that
applicable LDR are met prior to disposal. No O&M would be required under this alternative because the
contaminated soil would be treated and removed from the site. For Alternative S-4, O&M will be required to
maintain the integrity of the onsite disposal cell; the availability of onsite space for construction of a RCRA cell is
limited; and the soil beneath the RCRA cell must have sufficient strength to support the RCRA cell. For Alternative
S-6, stabilization/solidification is more complex than leaving material in subsurface; however this is a standard
available technology and it can be implemented without many constraints. Construction and maintenance of the
cover would be relatively easy to maintain.
Alternative S-3 unlike the other alternatives is limited in the availability of equipment (incinerators) capable of
implementing this remedy. Incinerators tend to have limited throughput rates and storage thus requiring that this
alternative use multiple incinerators for treatment or that the treatment is staged in phases. The nearest commercial
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hazardous waste incinerator is located approximately 25 miles from the site. Like Alternative S-2, no O&M would
be required under this alternative because the contaminated soil would be treated and removed from the site.
Alternatives S-2 through S-4 and S-6 would be more difficult to implement than S-5 because of the uncertainties
associated with excavation, management, and treatment and disposal of the contaminated soil. It is likely that of
the four alternatives (S-2 through S-4, and S-6), that Alternative S-6 would be more difficult to implement because
of the limited space available onsite to perform solidification/stabilization and to construction a new containment
cell with a low permeable cap.
Original Remedy (1988)
The biological treatment of soils was considered as not easily implemented due to the significant amount of testing
and coordination with the State agency before start-up. The ground water pump and treat system was considered
implementable.
7. Cost
Ground Water
[Note that the periodic cost estimates includes the cost for five-year reviews conducted over a 30 year period.]
Alternative G-l, the no action alternative, will have no associated cost.
Alternative G-2 is estimated to be $2,600,000 (net present value) based on $800,000 total capital cost, $1,735,000
total O&M cost, and $65,000 total periodic cost. The capital cost includes installation of additional wells,
demolition of existing treatment system, establishment of ICs. Total O&M cost includes water quality and natural
attenuation monitoring for the restricted water use boundary for 30 years. This is the lowest cost alternative.
Alternative G-3 is estimated to be $7,130,000 (net present value) based on $2,769,000 total capital cost,
$4,296,000 total O&M cost, and $65,000 total periodic cost. The total O&M cost includes the assumption of
operating the NAPL recovery/ground water injection system for 10 years and includes water quality and natural
attenuation monitoring for the restricted water use boundary for 30 years. This is the second highest cost alternative.
Alternative G-4 is estimated to be $6,383,000 (net present value) based on $4,708,000 total capital cost,
$1,610,000 total O&M cost, and $65,000 total periodic cost. The total capital cost includes source area stabilization,
installation of additional wells, demolition of existing treatment system, and establishment of ICs. Total O&M cost
includes water quality and natural attenuation monitoring for the restricted water use boundary for 30 years. This is
the third lowest cost alternative.
Alternative G-5 is estimated to be $7,878,000 (net present value) based on $5,878,000 total capital cost,
$1,935,000 total O&M cost, and $65,000 total periodic cost. The total capital cost includes source area stabilization,
In-Situ Chemical Oxidation of the dissolved phase plume along the western site boundary, installation of additional
wells, demolition of existing treatment system, and establishment of ICs. Total O&M cost includes water quality
and natural attenuation monitoring for the restricted water use boundary for 30 years after completion of LTRA and
also includes an annual chemical oxidation injection along the western site boundary for a period of 4 years after
the initial three rounds on injections. This is the highest cost alternative.
Alternative G-6 is estimated to be $4,566,000 (net present value) based on $2,157,000 total capital cost,
$2,301,000 total O&M cost, and $108,000 total periodic cost. The total capital cost includes slurry wall and cap
construction, installation of additional wells, demolition of existing treatment system, and establishment of ICs.
Total O&M cost includes water quality and natural attenuation monitoring for the restricted water use boundary for
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30 years after completion of LTRA and costs for maintenance and repair of the low permeable cover. This is the
second lowest cost alternative.
The costs associated with Alternatives G-2 and G-6 are significantly lower than Alternatives G-3, G-4, and G-5.
The higher costs associated with Alternatives G-3 are due to the long-term operation of the ground water
containment and treatment system. The high cost of Alternative G-4 is due to the incorporation of the stabilization
component. The high cost of Alternative G-5 is due to the incorporation of the stabilization component and the in-
situ chemical oxidation component. Alternative G-l is the least expensive alternative.
The cost estimates presented above have been developed strictly for comparing the six remedial alternatives. The
final costs and the resulting feasibility will depend on actual labor and material costs, competitive market
conditions, actual site conditions, final project scope, the implementation schedule, final engineering design, and
other variables. The cost estimates have an intended accuracy range of+50 percent to -30 percent.
Soil
Alternative S-l is estimated to be $0 (net present value) based on zero total capital cost, zero total O&M cost, and
zero total periodic cost. The total periodic cost includes completion of five-year reviews for a period of 30 years.
This is the least expensive cost alternative.
Alternative S-2 is estimated to be $16,940,000 (net present value) based on $16,940, 000 total capital cost, zero
total O&M cost, and zero total periodic cost. The capital costs associated with this alternative include general site
work, excavation, on site thermal desorption, disposal of treated soil, demolition and disposal of temporary
containment cell. There will be no cost related to O&M because no contaminated soil will be left onsite. This is the
second highest cost alternative.
Alternative S-3 is estimated to be $36,018,000 (net present value) based on $36,018,000 total capital cost, zero total
O&M cost, and zero total periodic cost. The capital costs associated with this alternative include general site work,
excavation and load soil from the containment cell, offsite incineration of soils, demolition and disposal of
temporary containment cell. There will be no cost related to O&M because no contaminated soil will be left onsite.
This is highest cost alternative.
Alternative S-4 is estimated to be $5,750,000 (net present value) based on $5,183,000 total capital cost, $459,000
total O&M cost, and $108,000 total periodic cost. The capital costs associated with this alternative include general
site work, excavation and load soil from the containment cell, demolition and disposal of temporary containment
cell, construction of new RCRA Containment Cell, and construction of general site-related stormwater controls.
Total O&M cost includes cover inspection and maintenance, and long-term ground water monitoring. The total
periodic cost includes completion of five-year reviews for a period of 30 years. This is the fourth highest cost
alternative.
Alternative S-5 includes two cost options based on two types of low permeable covers (soil and asphalt) selected
for this alternative.
a) The soil cover cost option is estimated to be $2,178,000 (net present value) based on $1,611,000 total
capital cost, $459,000 total O&M cost, and $108,000 total periodic cost. The capital costs associated with
this alternative include general site work, cover construction and construction of general site-related
stormwater controls. Total O&M cost includes cover inspection and maintenance, and long-term ground
water monitoring. The total periodic cost includes completion of five-year reviews for a period of 30 years.
This is the second lowest cost alternative.
b) The asphalt cover cost option is estimated to be $1,840,000 (net present value) based on $1,401,000 total
capital cost, $331,000 total O&M cost, and $108,000 total periodic cost. The capital costs associated with
29
022957
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this alternative include general site work, cover construction, and construction of general site-related
stormwater controls. Total O&M cost includes cover inspection and maintenance, and long-term ground
water monitoring. The total periodic cost includes completion of five-year reviews for a period of 30 years.
This is the lowest cost alternative.
Alternative S-6 is estimated to be $8,028,000 (net present value) based on $7,461,000 total capital cost, $459,000
total O&M cost, and $108,000 total periodic cost. The capital costs associated with this alternative include general
site work, excavation and load soil from the containment cell, construction of new onsite containment cell,
solidification/stabilization of the excavated soil, transportation of treated soil to the new onsite containment cell,
demolition and disposal of existing containment cell, and construction of general site-related stormwater controls.
Total O&M cost includes cover inspection and maintenance, and long-term ground water monitoring. The total
periodic cost includes completion of five-year reviews for a period of 30 years. This is the fourth highest cost
alternative.
The cost of Alternative S-3 is significantly higher than the rest of the alternatives. The highest cost associated with
Alternative S-3 is driven by the use of offsite incineration. High costs for treatment transportation and disposal post
treatment further increase alternative life-cycle costs. Alternative S-2 is much less expensive than Alternative S-3;
however, the cost is based on the assumption that the contaminated soil can be treated to meet the PRGs.
Alternative S-5 has a lower cost than Alternatives S-2, S-3, and S-6 because treatment is not required for
modification of the existing containment cell. Both options under Alternative S-5 are less expensive than
Alternative S-4. Of the two options under Alternative S-5, Alternative S-5b is slightly less expensive than
Alternative S-5 a. Alternative S-l (no action) is the least expensive alternative.
The cost estimates presented above have been developed strictly for comparing the five remedial alternatives. The
final costs and resulting feasibility will depend on actual labor and material costs, market conditions, actual site
conditions, final project scope, implementation schedule, the firm selected for final engineering design, and other
variables. The cost estimates have an intended accuracy range of+50 percent to -30 percent.
Original Remedy (1988)
In 1988, the capital costs for the selected remedy were: $1,475,000 for biological treatment of soil; $971,000 for
ground water treatment.
8. State Acceptance
The EPA developed the remedial alternatives and proposed action in consult with TCEQ and will request
concurrence by the State of Texas upon completion of the public comment period.
9. Community Acceptance
Community acceptance of the Proposed Remedy will be evaluated after the public comment period ends and will
be described in the Record of Decision Amendment for the site.
Summary of the Proposed Amended Remedy
Ground Water
The proposed amended remedy for addressing the contaminants in ground water and meeting the primary remedial
objectives is Alternative G-4: Source Stabilization through In-Situ Solidification with Monitored Natural
Attenuation (MNA) for the Dissolved Plume. The source will be solidified in place, reducing mobility of the
NAPL material and minimizing the leaching of contaminants to the dissolved ground water. The proposed
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remedy will more efficiently reduce the source concentrations over time, compared to the original pump and treat
remedy. When the dissolved phase concentrations are no longer sustained by a continuing source of contaminants,
the contaminant concentrations will attenuate over time to reach the Remedial Action Objectives. Area residents
and commercial operations are provided potable water through the City of Houston public water supply system.
The contaminated ground water is not used as a drinking water source.
Ground water monitoring would be performed to verify that natural attenuation is successful in achieving the
reduction in contaminant concentrations in ground water, onsite and offsite, and that performance standards for the
system are being met. Institutional controls (i.e. deed notices) will be put in place to provide notice to property
owners and prospective purchasers that contaminated water from the shallow and interbedded water-bearing zones
should not be used for drinking water or non-drinking uses until remedial goals are met. Restrictions will be placed
to prohibit digging or placement of structures over the solidified source area. There will be approximately a 30%
increase in material with the in-situ solidification process, which may limit reuse of the areas near the two sources.
The treatment system and piping, however, will not be used with this remedy, and can be taken down.
Protective measures will have to be implemented to ensure that the building (to the west) or the pipeline/rail
easements (to the east) are not impacted by the in-situ application.
The in-situ solidification remedy limits extensive long-term maintenance as this is one-time application. The
integrity of the remedy will be contingent on regular maintenance for the system. The existing monitoring network
will be redesigned to measure performance of the remedy for both the shallow sand and interbedded zones.
Soil
The proposed amended remedy for soil will be Alternative S-5: Modify the Existing Cell/Cap Soils in Place.
The alternative can be easily implemented as the soil is already contained in an existing cell, constructed with
protective liners and a leachate collection system. The soils have been in place for ten years. The existing cover
would be removed and replaced with a more permanent low-permeability cover. The low-permeability cover
would maximize protectiveness by eliminating human exposure to soils exceeding risk-based levels and by
providing a barrier to surface water infiltration, through the soils, to underlying ground water. Restrictions would
be needed to prevent digging into the cap. Long-term effectiveness and continued protection to human health would
be contingent on proper maintenance. Scheduled inspections and maintenance will be required to protect the
remedy.
The proposed containment remedy is a replacement remedy for the original treatment remedy selected in the 1988
ROD. There will be limited reuse potential for the northern part of the Site, excluding the footprint of the cell.
Glossary
Administrative Record - The body of documents available to the public associated with characterization and
remedy selection at a site.
Applicable or Relevant and Appropriate Requirements (ARARs) - The Federal and State environmental laws
that a selected remedy will meet. These requirements may vary among sites and alternatives.
Human Health Baseline Risk Assessment - An evaluation of the potential threat to human health in the absence
of any remedial action.
Carcinogen - Capable of causing the cells of an organism to react in a manner to produce cancer.
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) - was enacted by
Congress on December 11, 1980. This law created a tax on the chemical and petroleum industries and provided
31
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broad Federal authority to respond directly to releases or threatened releases of hazardous substances that may
endanger public health or the environment.
Contaminant Plume- A column of contamination with measurable horizontal and vertical dimensions that is
suspended in and moves with ground water.
Dense Non-aqueous Phase Liquids (DNAPL) - A DNAPL is an organic substance that is relatively insoluble in
water and denser than water. DNAPLs tend to sink vertically through sand and gravel aquifers to the underlying
layer.
Excess Lifetime Cancer Risk - Cancer posed by a contaminated site in excess of the lifetime probability of
developing cancer from other causes.
Feasibility Study (FS) - Identifies and evaluates the appropriate technical approaches and treatment technologies
to address contamination at a site. The 2008 Focused Feasibility Study for the North Cavalcade Site evaluated the
proposed changes to the soil and ground water remedy selected in the 1998 Record of Decision.
Ground Water - Underground water that fills pores in soils or openings in rocks to the point of saturation.
Ground water is often used as a source of drinking water via municipal or domestic wells.
Ground Water Monitoring - Ongoing collection of ground water information about the environment that helps
gauge the effectiveness of a cleanup action.
Human Health Risk Assessment - A study that determines and evaluates risk that site contamination poses to
human health.
Institutional Controls - Actions, such as legal controls, that help minimize the potential for human exposure to
contamination by ensuring appropriate land use.
Microgram per Liter Oig/L) - A unit of measurement equivalent to one microgram of contaminant per liter of
water.
Milligram per Kilogram (mg/kg) - A unit of measurement equivalent to one milligram of contaminant per
kilogram of solid (typically soil).
Monitored Natural Attenuation (MNA) - refers to a ground water remedy that relies on natural processes to
cleanup or attenuate pollution and actively monitors these processes.
National Oil and Hazardous Substance Pollution Contingency Plan (NCP) - Regulations governing cleanups
under EPA's Superfund program.
Natural Attenuation - The processes in soil and ground water environments that act without human intervention
to reduce the mass, toxicity, mobility, volume, or concentrations of contaminants in those media. These in-situ
processes include biodegradation, dispersion, dilution, adsorption, volatilization, and chemical or biological
stabilization or destruction of contaminants.
Present Worth Cost - A method of evaluation of expenditures that occur over different time periods. By
discounting all costs to a common base year, the costs for different remedial action alternatives can be compared on
the basis of a single figure for each alternative. When calculating present worth cost for Superfund sites, total
operations & maintenance costs are to be included.
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Proposed Alternative - Final remedial alternative that meets NCP evaluation criteria and is supported by
regulatory agencies.
Remedial Action - Action(s) taken to correct or remediate contamination.
Remedial Action Objectives (RAOs) - Remediation objectives for protection of human health and the
environment.
Record of Decision (ROD) - A formal document that is a consolidated source of information about a Superfund
site, the remedy selection process, and the selected remedy.
Receptor - An organism that receives, may receive, or has received environmental exposure to a chemical.
Remedial Investigation (RI) - A study conducted to identify the types, amounts, and locations of contamination at
a site.
Resource Conservation and Recovery Act (RCRA) - The Federal act that established a regulatory system to
track hazardous wastes from the time they are generated to their final disposal. RCRA also provides for safe
hazardous waste management practices and imposes standards for transporting, treating, storing, and disposing of
hazardous waste.
Screening Level Concentration - an empirical or modeled concentration corresponding to a fixed level of risk
used for comparison against measured sampling data in order to provide an initial conservative risk evaluation.
For more information, please contact:
Camille Hueni, Remedial Project Manager
U.S. EPA, Region 6
1445 Ross Ave. (6SF-RA)
Dallas, TX 75202
214-665-2231
800-533-3508 (toll free)
Hueni.Camille@epa.gov
June Hoey, Community Involvement Coordinator
U.S. EPA, Region 6
1445 Ross Ave. (6SF-TS)
Dallas, TX 75202
214-665-8522
800-533-3508 (toll free)
Hoey.Phyllis(S)epa.gov
David Bary, EPA Region 6 Press Office
U.S. EPA, Region 6
1445 Ross Ave. (6XA-CE)
Dallas, TX 75202
214-665-2208
800-533-3508 (toll free)
Barv.David@epa.gov
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Marilyn Long, Project Manager
Texas Commission on Environmental Quality
MC-136
P.O. Box 13087
Austin, TX 78711
512-239-0761
MLong@tceq.state.tx.us
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Figure 1: Site Location Map. Note location of existing containment cell (OU-2) in the northern
section of the North Cavalcade Street Superfund Site and two commercial businesses in
the southern section. (FocusedFeasibility Study, 2008)
—
Cavalcade St?
LEGEND
Site Boundary
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022963
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Figure 2: Location of Geologic Cross-Sections (Focused Feasibility Study, 2008}. The southwest-
northeast cross-section, A-A1, is detailed in Figure 3.
i® S&^fej
mOK R
^8
LEGEND
Cross Sections
C-C'
D-D'
022964
36
-------
A
Southwest
Saturated interval uartBS
with water table jn this area.
Water level at OW-11 in Feb
2D04 was 41.77 ft MSL.
[nterbedded wet to saturate
silty lenses rtoted on Borinr
Logs beglnn ne at 24 to 24.!
rt at 122-112 rind H18-1/2,
Legend
Concrete Y//X Lean Clay (CL) [ ] Elastic Silt (MH)
No Recovery |-|-|-| Fat Clay (CH) | | Clayey Sand (SC)
Fill |~[~|~| Lean Silt (ML) | | Silty Sand
Poorly Graded Sand (SP)
Well Graded Sand (SW)
Shallow Sand Zone (contact dashed where infered)
Interbedded Zone (contact dashed where infered)
Figure 3: Southwest-Northeast Cross-Section. Note that the deeper interbedded zone is comprised
of clays and silts, and thinning to the southwest. (Focused Feasibility Study, 2008}
37
022965
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LEGEND
-^- Monitor Wells
•^ Recovery Wells
• Temporary Wells
.0.005^— ISO Concentration Contours for Benzene in Milligrams Per Liter (mg/L)
Benzene MCL = 0.005 mg/L
Figure 4: Extent of Benzene Contamination in the Shallow Sand. The outer concentration isopleths
corresponds to non-detect (ND). The next inward isopleths corresponds to 5 ppb, the MCL for benzene.
Yellow colored symbols indicates benzene was detected above the MCL.
Blue colored symbols indicates benzene was detected below the MCL.
Green colored symbols indicates benzene was not detected.
Contaminant concentrations and isopleths were obtained from the Supplemental Investigation for Remedy
Evaluation Report (Shaw, 2005).
38
022966
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LEGEND
•^ Monitor Wells
^- Recovery Wells
B Temporary Wells
ISO Concentration Contours for Naphthalene in Milligrams
Per Liter (mg/L)
Figure 5: Extent of Naphthalene Contamination in the Shallow Sand. The outer concentration isopleths
corresponds to non-detect (ND). The next inward isopleths corresponds to 1000 ppb to 5000 ppb to
10,000 ppb.
Contaminant concentrations and isopleths were obtained from the Supplemental Investigation for Remedy
Evaluation Report (Shaw, 2005).
39
022967
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Figure 6: Extent of Benzene Contamination in the Interbedded Zone. The outer concentration isopleths
corresponds to non-detect (ND). The next inward isopleths corresponds to 5 ppb, the MCL for benzene.
Yellow colored symbols indicates benzene was detected above the MCL.
Blue colored symbols indicates benzene was detected below the MCL.
Green colored symbols indicates benzene was not detected.
Contaminant concentrations and isopleths were obtained from the Supplemental Investigation for Remedy
Evaluation Report (Shaw, 2005).
Approximate Location 01
Pecore Fault Line
LEGEND
•£ Monitor Wells
& Recovery Wells
B Temporary Wells
•0.100^ ISO Concentration Contours for Benzene in Milligrams Per Liter (mg/L)
Benzene MCL = 0.005 mg/L
40
022968
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LEGEND
^ Monitor Wells
•flj Recovery Wells
• Temporary Wells
• 0.100 ^ ISO Concentration Contours for Naphthalene in Milligrams
Per Liter (mg/L)
Figure 7: Extent of Naphthalene Contamination in the Interbedded Zone. The outer concentration
isopleths corresponds to non-detect (ND). The next inward isopleths corresponds to 1000 ppb and then to
10,000 ppb.
Contaminant concentrations and isopleths were obtained from the Supplemental Investigation for Remedy
Evaluation Report (Shaw, 2005).
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022969
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Figure 8: Treatment Area for Proposed Alternative G-4 (Stabilization/In-Situ
Solidification. Extent of NAPL is shown for the shallow sand and the interbedded unit.
The dashed line near the eastern edge represents the approximate boundary of the railroad
and pipeline easement. (FocusedFeasibility Study, 2008}
Approximate Location of
Pecore Fault Line
LEGEND
Approximate Extent of MARL Product in the Shallow Sand
Approximate Extent of NAPL Product in the Interbedded Unit
Approximate Boundary of Railroad Easement
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022970
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6" Top Soil
24" Protective Surface Soil
6" Clean Sand Layer
Vegetative Layer
Geotextile Fabric
*
*\_ 60 mil HDPE Geomembrane
24" Compacted Clay
Contaminated Soil
6" Sacrificial Layer (Select Fill)
Leachate Col lection
(12" Sand)
Leak Detection Layer
(6"Sand)
\_ Grading Fill to provide
working surface for
cover construction
_ Geotextile Fabric
Leachate Collection Liner
(60 mil HDPE FML)
Leak Detection Liner
(60 mil HDPE FML)
b) Existing Contaminant Cell with
a Low Permeability Soil Cap
Contaminated Soil
6" Sacrificial Layer (Select Fill)
Leachate Collection
(12" Sand)
Leak Detection Layer
(6" Sand)
tT
*-—
Cell Liner
(30 mil HOPE)
Geotextile Fabric
Leachate Collection Liner
(60 mil HOPE FML)
Leak Detection Liner
160 mil HOPE FML)
a) Cross Section of Existing Containment Cell
4" Asphalt
8" Crushed Rock
Contaminated Soil
6" Sacrificial Layer (Select Fill)
Leachate Collection
(12" Sand)
Leak Detection Layer
(6" Sand)
Grading Fill to provide
working surface for
cover construction
Geotextile Fabric
Leachate Collection Liner
(60 mil HDPE FML)
Leak Detection Liner
(60 mil HDPE FML)
c) Existing Contaminant Cell with
a Low Permeability Asphalt Cap
Figure 9: Alternative S-5 Cross-Section of the Existing Containment Cell with Proposed
Modifications (Focused Feasibility Study, 2008}
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