NCD095458527_19980701_FCX Inc. (Statesville)_FRBCERCLA RD_Remedial Design Work Plan OU-3-OCR

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REMEDIAL DESIGN WORK PLAN
FOR OPERABLE UNIT THREE (OU3)
FCX-STATESVILLE SUPERFUND SITE
STATESVILLE, NORTH CAROLINA
Prepared for:
EL PASO ENERGY CORPORATION
1001 Lonisim1a Street
Houston; Te,."as 77002
\ \ Tr-.'\SYS\D AT A \P l{OJ\0313. 02 \C\'Jt DOC
Prepared by:
ECKENFELDER INC.®
227 French Landing Drive
Nashville, Tennessee 37228
[phone]
July 1998
0313.02
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Letter of Transmittal
Table of Contents
List of Tables
List of Figures
1.0 INTRODUCTION
TABLE OF CONTENTS
1.1 Site Condition and Remedial Design Objectives
1. 1. 1 Soil Design Objectives
1.1.2 Groundwater Design Objectives
1.2 Background
1.2. l Site Description
1.2.2 Site History
1.2.3 Overview of Existing Data
1.3 Description of OU3 Remediation Technologies
1.3.1 Air Sparging
1.3.2 Soil Vapor Extraction
1.3.3 Monitored Natural Attenuation Overview
1.4 Organization of Remedial Design Work Plan
2.0 PRE-DESIGN INVESTIGATION
2.1 Evaluation of Existing Data
2.2 Installation of Monitoring Wells
2.3 Groundwater Sampling and Analysis
2.3.1 Monitoring Well Sampling and Analysis
2.3.2 Residential Well Sampling and Analysis
2.4 Evaluation Process for Natural Attenuation
2.5 Implications for the Remedy and AS/SVE Pilot Test
2.6 AS/SVE Pilot Test
3.0 REMEDIAL DESIGN
3.1 Preliminary Design
3.1.1 Data Summary
3.1.2 Design Criteria Report
3.1.3 Outline of Draft Plans and Technical Specifications
I-':'\DATA \l'HO,J\0313.02\ TOC.DOC
Page No.
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TABLE OF CONTENTS (Continued)
3.1.4 Plan for Satisfying Permitting Requirements
3.1.5 Preliminary Schedule and Project Delivery Strategy
3.2 Intermecliate Design
3. 3 Pre-Final Design
3.3.1 Design Analysis
3.3.2 Plans and Specifications
3.3.3 Construction Schedule
3.3.4 Cost Estimate
3.4 Final Design
3.5 Remeclial Action Work Plan
3.5.1 Construction Management Plan
3.5.2 Construction Quality Assurance Project Plan
3.5.3 Field Sampling Plan
3.5.4 Contingency Plan
3.5.5 Project Delivery Strategy
3.5.6 Groundwater and Surface Water Monitoring Plan
3.5. 7 Operation and Maintenance Plan
4.0 PROJECT MANAGEMENT PLAN
4.1 Team Organization
4.1.1 ECKENFELDER INC. Project Team
4.1.2 Chemical Analysis Laboratory
4.1.3 Subcontractors
4.2 Data Management
4.2.1 Field Data
4.2.2 Laboratory Data
4.3 Document Control
4. 4 Monthly Reporting
4.5 Project Meetings with USEPA
4.6 Community Relations
5.0 PROJECT SCHEDULE
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TABLE OF CONTENTS (Continued)
APPENDICES
Appendix A -Potential Source Areas Identified During RI
Appendix B -Supplemental Information on Natural Attenuation
ATTACHMENTS
Attachment 1 -Pilot Test Work Plan
Attachment 2 -Addendum to the Field Sampling Plan
Attachment 3 -Addendum to the Quality Assurance Project Plan
Attachment 4 -Health and Safety Plan
Attachment 5 -Response to Comments on the Remedial Design Work Plan
F: \DAT A \PROJ'\0313 .02\ TOG.DOC Ill
Page No.
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Task Name Start
Meet with USEPA & NCDEHNR at the Site Mar/03/98
Authorization to Proceed Mar/09/98
Remedial Design Work Plan rvlar/09/98
Prepare RD Work Plan Mar/09/98
Submit RD Work Plan to USEPA & NCDEHNR Mav/11/98
USEPA & NCDEHNR Review of RD Work Plan Mav/12/98
USEPA & NCDEHNR Annroval of RD Work Plan Jul/01/98
Pre-Desie:n lnvestie:ation Jul/01/98
InstaJJ and Samo le \V ells Jul/06/98
Perform Pilot Test Jul/01/98
Preoare Prelim. RD Reoort Section Seo/11/98
Preliminary Design Seo/11/98
Preoare Prehm. RD Reooli Sen/11/98
Submit Prelim. RD Reoori to USEPA & NCDEHNR Nov/10/98
USEPA & NCDEHNR Review of Prelim. RD Reoort Nov/12/98
USEPA & NCDEHNR Annroval of Prelim. RD Renart Dec/14/98
Intermediate Design Nov/12/98
Prepare Intermediate RD Nov/12/98
Meet with USEPA & NCDEHNH to Review Inter. RD ,Jan/14/99
Pre-Final/Final Desi"n Jan/15/99
Prepare Pre-Final RD Renort ,fon/15/99
Submit. Pre-Final HD Renart to USEPA & NCDEHNR Mar/22/99
USEPA & NCDEHNR Review of Pre-Final RD Renort l\far/23/99
Preoare Final RD Renort Anr/23/99
Submit. Final RD Renart rviav/24i99
USEPA & NCDEHNR Review of Final RD Reoort l\Iav/25/99
USEPA & NCDEHNR Annroval of Final RD Repon Jun/24/99
Remedial Action Work Plan Mav/25/99
Prepare HA Work Plan Mav/25/H9
Submit RA Work Plan to USEPA & NCDEHNH ,rul/27/99
USEPA & NCDEHNR Heview of HA Work Plan Jul/28/99
USEPA & NCDEHNH Annroval of RA Work Plan Au.,/27/99
Monthh· Progress Reports Anr/10/98
Q:iPROJ/0313.02/ELPASOA.TLP
FIGURE 5-1
SCHEDULE FOR REMEDIAL DESIGN OF OU3
FCX-STATESVILLE SUPERFUND SITE
End 1998
Feb l\Jar Apr May Jun Jul Aug Sep Oct Nov
i\far/0:1/88
1:, Mar/09/98
Jul/0I/98 I"/ / / / / / / / /,, rJ l\favlllfa8 ,
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dul/01/98 I ' 0
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Oct/27/98 I ,_ -
Nov/10/98 '· I
Dec
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Nov/10/98 c' I
Nov/10/98 ~ Ll ~
Dec/14/98 I
Dec/14/98 i '6
Jan/14/99 / / / //_. /
Jan/13/99 ~
Jan/14/99
Jun/24/H9
Mar/22/9!J
Mar/22/99
Aor/22/99
Mav/24/99
]\fay/24/99
Jun/24/99
Jun/24/99
Au,,/27/99
Jul/271[)9
Jul/27/99
Au,,-/27/99
Au.,/27/!39
Sen/10/99 --
Note: The schedule is dependent on the actual duration ofUSEPA and NCDEHNR reviews: and acmal approval dates.
1999
Jan Feb Mar Apr l\lay Jun Jul Aug Sep
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l\Jilestone /\,_ Summary t2Z2ZJ
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PILOT TEST WORK PLAN
FOR OPERABLE UNIT THREE (OU3)
FCX-STATESVILLE SUPERFUND SITE,
STATESVILLE, NORTH CAROLINA
Prepared for:
EL PASO ENERGY CORPORATION
1001 Louisiana Street
Houston, TX 77002
Prepared by:
ECKENFELDER INC.®
227 French Landing Drive
Nashville, Tennessee 37228
[phone]
July 1998
0313.02
\ \ TN\SYS\DATA \PROJ\0313.02\ptWll•COYCr.doc
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Task Name
Approval of RD Work Plan
Install and Sample Wells
Pilot Test Well lnstallation
Pre-Test Groundwater Samnlin"
Post-Test ({roundwater Samplinf!'
Pilot Test
Procure Materials
Install SVE Unit
Connect Air S upplv
Perform Svstem Check
Conduct Pilot Test
Perform Laboratorv Analvsis
Perform Data Validation
Prepare Prelim, RD Renart Section
Submit Prelim, RD Report
Q:/PROJ/0313.02/ELPASOPA,TLP
FIGURE 6-1
SCHEDULE FOR OU3 PILOT TEST
FCX-STATESVILLE SUPERFUND SITE
Start End 1998
Jun Jul Aug
Jul/01/98 Jul/01/98 i
>, i ~~
Jul/06/98 Sep/04/98 r" ,'/ ,77.7//// , ,
,Jul/06/98 Jul/24/98 I s 4¥ ; 5141;
i Aul!/10/98 Aug/14/98 "Gl7
Aue:/81/98 Sep/04/98 I I rl mt; I I
Jul/01/98 Oct/27/98 I /, ////~ L:,.::,(<,. '////// '/////// ,,
,Jul/01/98 Aug/07/98 '
Jul/20/98 Jul/81/98 I
Au.,/10/98 Aug/14/98 ~ ' '
Auf!'/17/98 Aug/18/98 '~ !
Aug/19/98 Aug/28/98 I~ i I -
Aurdl7/98 Oct/13/98 I,
Oct/14/98 Oct/27/98
Sep/11/98 Nov/10/98
Nov/10/98 Nov/10/98
~ate: The schedule is dependent on the actual date of USEPA approval of the RDWP.
Sep OcL Nov
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Milestone 6 Summary CZ¼:J
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ADDENDUM TO THE
FIELD SAMPLING PLAN (FSP)
FOR OPERABLE UNIT THREE (OU3)
FCX-STATESVILLE SUPERFUND SITE,
STATESVILLE, NORTH CAROLINA
Prepared for:
EL PASO ENERGY CORPORATION
1001 Louisiana Street
Houston, TX 77002
\ \ TN'\SYS\DAT A \.PRO.T\0313.02\fB11-co\·er.doc
Prepared by:
ECKENFELDER INC.®
227 French Landing Drive
Nashville, Tennessee 37228
[phone]
July 1998
0313.02
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ADDENDUM TO THE
QUALITY ASSURANCE PROJECT PLAN (QAPP)
FOR OPERABLE UNIT THREE (OU3)
FCX-STATESVILLE SUPERFUND SITE,
STATESVILLE, NORTH CAROLINA
Prepared for:
EL PASO ENERGY CORPORATION
1001 Louisiana Street
Houston, TX 77002
Prepared by:
ECKENFELDER INC.®
227 French Landing Drive
Nashville, Tennessee 37228
[phone]
July 1998
0313.02
\ \ TN\SYS\DATA \PROJ\0313.02\QAPP-cover.<loc
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ATTACHMENT 5
RESPONSE TO COMMENTS ON THE
REMEDIAL DESIGN WORK PLAi~
F:\DAT A \PROJ\0313.02\appendix covers.doc
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June 26, 1998
Mr. McKenzie Mallary
North Site Management Branch
EPA Region 4
Atlanta Federal Center
61 Forsyth Street
Atlanta, GA 30303
ECKENFELDER INC:
0313.02
RE: Remedial Design Work Plan Addendum -Response to Comments on the
"Remedial Design Work Plan for Operable Unit Three (OU3),
FCX-Statesville Superfund Site, Statesville, North Carolina"
dated May 1998
Dear Ken:
ECKENFELDER INC. is pleased to provide the attached response to the comments
on the subject Remedial Design (RD) Work Plan that were provided by the United
States Environmental Protection Agency (USEPA); the North Carolina Department
of Environment, Health, and Natural Resources (NCDEHNR); and Roy F. Weston,
Inc. (Weston). This letter and the response to comments are provided for
incorporation into the May 1998 RD Work Plan as Attachment 5.
The comments were provided in the letter to Ms. Nancy Prince, El Paso Energy
Corporation (El Paso), from McKenzie Mallary, USEPA Region 4, dated June 10,
1998. The main issues raised in the comments were related to the need for
additional weJls for plume definition and the need for clarification as to how the
selected remedial technologies will be evaluated and incorporated into the RD.
In addition to the response to comments, change-out pages for the May 1998 RD
Work Plan are also attached. The change-out pages include revised cover pages that
are dated July 1998 for RD Work Plan and Attachments 1 and 2; a revised table of
contents; a revised schedule for the RD (Figure 5-1); and a revised schedule for the
pilot test (Attachment 1, Figure 6-1). The revised schedules incorporate the time
required for installation and sampling of an additional monitoring well. This letter,
the response to comments, and a No. 5 divider page (attached) are to be inserted as
Attachment 5 to the RD Work Plan.
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Mr. McKenzie Mallary
Page 2
June 26, 1998
Please call Nancy Prince of El Paso at [phone] or me at [phone] if you have any questions or comments regarding the project status.
Sincerely,
ECKENFELDER INC.®
'~~ ~-c;;~
Kenton H. Oma, P.E.
Assistant Technical Director
Waste Management
cc:
N. Testerman, NCDEHNR
N. Prince, El Paso
S. Miller, El Paso
J. Porter, Andrews & Kurth
Q:\!'l{OJ\0313.02\L0GJ I.doc
H. Mitchell, Jr., Beaunit
J. Wright, Burlington
B. Wicker, Burlington
G. House, BPMH&L
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RESPONSE TO COMMENTS ON THE
REMEDIAL DESIGN WORK PLAN FOR OPERABLE UNIT THREE (OU3), FCX-STATESVILLE SUPERFUND SITE, STATESVILLE, NORTH CAROLINA
Dated May 1998
Following are the comments by the USEPA, NCDEHNR, and Weston reproduced in Italics without modification. Each comment is followed by a response.
Comments by the USEPA
1. As a general rule, EPA-Region IV requires that all activities conducted at its Superfund sites be consistent with EPA-Region IV Standard Operating Procedures (May 1996). Please state in the Remedial Design (RD) Worh Plan that all RD activities will be consistent with the EPA-Region ]\I Standard Operating Procedures.
Response:
The pre-design investigation activities will be conducted in accordance with the "Environmental Investigations Standard Operating Procedures and Quality Assurance Manual", May 1996, USEPA Region IV. ·
2. All data that is collected and submitted as part of the Remedial Design must be in the CLP format.
Response:
The groundwater quality data will be collected and submitted in the CLP format. This includes the TAL metals, TCL VOCs, total iron, and total manganese analysis. The CLP does not cover the other chemical tests that will be conducted; therefore, these data will not be submitted in the CLP format.
Comments by the NCDEHNR
3. Section 2.1: The location of the proposed monitoring wells (W-31s, 3Ji, and 20d) loolls good. Our office also proposes that additional nwniton:ng wells be established east of Phoenix Street and south of the site. J.1onitoring well W-18s contains PCE and TCE levels above the cleanup goals. The nearest wells, W-J0s and W-2Js (TCE at 4.0 and 7 ppb, respectively) and W-Js and W-13s (I JO ppb PCE and dry, resp.), indicate contamination levels above the cleanup goals. In addition, south of the site, monitoring well W-29i contained 23 ppb PCE.
. Response:
ECKENFELDER INC. agrees that an additional well down-gradient of W-29i would provide an additional level of protection to potential down-gradient receptors associated with the southern intermediate groundwater plume. One additional intermediate zone well, W-32i, is proposed to be installed down-gradient of W-29i. The location of this well will be determined in the field and
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Attachment 5
Response to Comments
Page 2 of 11
4.
5.
will take into account the direction of groundwater flow, the distance to potential down-gradient receptors, suspected surface water discharges, and available access. The location of this well will be presented to the USEPA and NCDEHNR for approval prior to installation.
Monitoring well W-32i will be installed within the underlying bedrock unit to evaluate the possible down-gradient extent of the groundwater plume. The boring will be advanced into the bedrock to a maximum depth of approximately 50 feet. As the boring is advanced, packer tests will be conducted on five-foot intervals to evaluate bedrock permeability. The screening interval will target higher permeable zones. If the selected screening interval is selected above the target depth of the boring, the boring will be back-filled with bentonite to the desired screening depth. The procedure for interval packer testing is included in Attachment 2, the Addendum to the FSP of the RD Work Plan.
Though levels of PCE and TCE have been detected in W-18s at or just above clean-up goals, ECKENFELDER INC. believes that the data does not support the need for additional monitoring wells east of Phoenix Street. A review of the groundwater elevations within the saprolite (Figure 15 of the RI) indicates that groundwater flow in this area of the plume is primarily to the north, parallel to Phoenix Street. Therefore, contamination in W-18s is probably a result of lateral dispersion of the groundwater plume. Preliminary data from the recent baseline sampling conducted in April 1998 indicate that detected VOC concentrations in W-18s have decreased toward the cleanup goals. Historical data from downgraclient well W-2ls indicate the presence of VOC concentrations at or just above the cleanup goals. The results from W-2ls suggest that the northern extent of the eastern portion of the groundwater plume has been generally defined. No potential receptors have been identified north of the site. 'I'herefore, the currently existing and proposed monitoring wells are considered to be protective.
Section 2.3.1: enclosed is the latest rnemo from EPA on low flow sampling. ECKENFELDER INC. 's protocol appears to follow EPA's guidance.
Response:
ECKENFELDER INC. did not receive the copy of the EPA's guidance on low flow sampling. Based on your comment, it appears. that ECKENFELDER INC.'s low flow sampling techniques are consistent with this document. Upon receipt and review of the document, ECKENFELDER INC. will confirm this.
Table 2-1: The proposed baseline sampling plan lists well W-7s and does not list W-J9s. Is W-19s replacing well W-7s? Either well is fine for inclu.ding i.n the sampling plan.
Response:
The baseline sampling was completed in April 1998 as approved by the USEPA and NCDEHNR. Monitoring well W-7s was replaced with W-19s in response to field conditions during the baseline sampling. The baseline sampling plan indicated that W-7s would be sampled for natural attenuation parameters and
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Attachment ."
Response to Comments
Page 3 of 11
6.
7.
8.
9.
TAL metals. During the baseline sampling, it was discovered that W-7s had only approximately 1 foot of water column within the well. The lack of appreciable water column would not allow for the employment of the slow purge sampling methods. If sampled, the TAL metals results and a number of the natural attenuation parameter results would have been impacted by suspended solids within the sample. Well W-19s was then selected as an alternative for the collection of natural attenuation parameters.
Table 2-1: Why is well W-20d not chosen for natural attenuation parameters?
Response:
Well W-20d was not chosen for natural attenuation parameters because the well installation protocols (sampling at depths until clean water is found in order to determine the vertical extent of impact) are intended to result in a clean groundwater sample that is not within the migration pathway. Clean samples are only of use for evaluation of natural attenuation if they are within both the same formation and the same flow path as the groundwater that has been impacted. Thus the data from well W-20d would have little value for evaluating natural attenuation.
Section 2.4: Bioremediation under aerobic conditions, cometabolism, can occur for the chlorinated parameters except PCE. If aerobic conditions exist, will cometabolism processes be evaluated?
Response:
TCE, DCE, and vinyl chloride, but not PCE, can undergo aerobic biodegradation as a result of cometabolism. However, the process requires the presence of a primary metabolite such as toluene, phenol, methane, propane, etc. It does not appear that any of these compounds are present in significant quantities within OU3. It is unlikely that cometabolism processes will play a significant or even detectable role during air sparging. Vinyl chloride and, possibly cis-1,2-DCE, can degrade aerobically while serving as the primary substrate precluding the need for cometabolism.
Section 2.4: Our office would lihe a copy of the article discussing ECKENFELDER INC. 's published in-house model performing the sensitivity analysis.
Response:
There is an editorial error in the text. The sensitivity analysis will be performed using the BIOSCREEN model.
Section 4. 5: The State needs to be included in review meetings.
Response:
The NCDEHNR will be included in the meeting with the USEPA to review the intermediate design and in any other agency review meetings associated with OU3.
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Attachment 5
Response to Comments
Page 4 of 11
Comments by Weston
Section 1.0 Introduction
JO. Page 1-4. paragraph 3. Please summarize the results of the Explanation of
Significant Difference (ESD) for OU3 in terms of its effect on this Worh Plan
and provide its date.
Response:
The ESD. which is in draft form. is dated April 1998. In the draft ESD, the
USEPA decided to use restrictive covenants as the institutional control in the
OU3 remedy in lieu of using deed restrictions. The draft ESD includes a
contingency measure consisting of supplying an alternate water supply to a
property owner(s) living down gradient whose groundwater is their sole source
of drinking water and whose groundwater is contaminated as a result of OU3.
The draft ESD also removes arsenic, barium, and bis (2-ethylhexyl) phthalate
from the ROD as Chemicals of Concern. Any other issues raised in the final
ESD will be addressed with the approval of the USEPA and NCDEHNR.
11. Page 1-6, paragraph 3, and page 2-3, paragraph 3. Please note the basis for i,.se
of twice bachground as a screening criterion for inorganic constituents in soils.
Response:
Section 1.2.3 is a brief summary of the Final Remedial Investigation Report
(July 23, 1996). The twice background screening criterion for inorganic
constituents in soil was presented in the RI and was subsequently approved by
the USEPA and NCDEHNR.
12. Page 1-8, paragraph 3. Please clarify the concept of airflow in discrete
channels; is this a desired result of air sparging or is diffuse flow through the
groundwater zone preferred? Is the formation of discrete channels unavoidable
or is it dependent on site specific conditions?
Response:
The current understanding of air sparging is that the injected air will move
through cliscrete channels except under rare conclitions. Diffuse flow would be
preferred but is not obtainable under nearly all field conclitions.
13. Page 1-10, paragraph 1. Please clarify that the form of "SVE" which worl,s for
biodegradable SVOCs and non-VOCs is Bioventing which differs a bit from
conventional SVE.
Response:
The intention here is to physically remove the constituents of interest from the
formation. Biodegradation will not be an important mechanism although vinyl
chloride and possibly cis-1,2-DCE may undergo biodegradation. Bioventing is
not an appropriate term for the proposed remedy.
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Attachment 5
Response to Comments
Page 5 of 11
14. Page 1-10, paragraph 5. The text states that natural processes seem to be operative at OU3. Please summarize the evidence of this and what mechanisms are thought to be involved. Is the aquifer naturally anaerobic such that reductive dechlorination may be occurring? This discussion may be relevant in considering where and how to apply AS/ SVE at the site.
Response:
The evidence of natural attenuation that is currently available is the presence of reductive dechlorination byproducts which are not believed to have been directly introduced at this site. For instance, cis-1,2-dichloroethene (cis-1.2-DCE) is not a product of commerce. In order for this to occur, at least some portions of the aquifer must be anaerobic. There is insufficient evidence at this time to speculate why anaerobic conclitions exist. We anticipate that the natural attenuation sampling and analysis task will increase our understanding of the aquifer conditions.
15. Page 1-11, paragraph 4. Please cite the AFCEE protocol fully here the fi.rst time it is re/erred to rather than on the next page.
Response:
We recognize that it would have been better to fully cite the AFCEE protocol at its first use. However, the protocol is cited on the next page, page 1-12, paragraph 1. This protocol was first made available to the public in the document, "Proceedings of the Symposium on Natural Attenuation of Chlorinated Organics in Groundwater," EPA/540/R-97/504, May 1997.
SECTION 2.0-PRE-DESIGN INVESTIGATION
16. Page 2-1, Paragraph 3. The text· discusses the need to determine whether conditions are appropriate for reductive dechlorination. This discussion should also address the question of whether, if reductive dechlorination is occurring, the proposed treatment systems will conflict with that process by increasing the oxygen tension and redox potential of the contaminated areas. Overall, the Work Plan should address the relationship among the various contaminated areas, the remedial technologies to be evaluated for each and the potential conflict between aerobic technologies and the anaerobic conditions required for PCE biodegradation.
Response:
Evidence from other sites, as discussed in a paper that ECKENFELDER INC. presented at a recent conference, indicates that air sparging can be detrimental to reductive dechlorination even after air sparging has been terminated. The impact appears to be limited to the radius of influence of the air sparging system.
As indicated in the Remedial Design Work Plan, air sparging with soil vapor extraction is being evahi"ated for use in the source area. Soil vapor extraction is expected to remove VOCs from the unsaturated soils. Air sparging is being
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Attachment 5
Response to Comments
Page 6 of 11
evaluated for remediation of the unconsolidated interval of the aquifer. Natural attenuation is being evaluated for the shallow unconsolidated and deeper bedrock portions of the aquifer both south and north of the source area.
The potential conflict arises from increases in oxidation potential and dissolved oxygen concentrations as well as changes in the naturally occurring organic matter within the area directly affected by the air sparging system. The anticipated removal of a significant portion of mass from the source area will greatly reduce the mass of constituents, thus reducing the demands on natural attenuation mechanisms. It is intended that the pilot test will identify conditions under which the net effect of the air sparging and soil vapor extraction processes will be substantially beneficial.
17. Figure 2-1. It would be helpful if these maps showed the CW plume to be addressed.
Response:
ECKENFELDER INC. agrees that depicting the groundwater plume would be helpful. These maps are presented in the RI and FS. The FS Figures 1-13 through 1-18 are attached to this addendum and provide isoconcentration information.
18. Page 2-2. paragraph 2. Please identify the nature of the force which would result in dissolved contamination progressing downward in the aquifer.
Response:
The addition of areal recharge into a water table aquifer often results in a downward migration of the down-gradient portions of a contaminant plume. Un-contaminated groundwater from areal recharge is introduced into the aquifer at the water table surface and therefore displaces the dissolved contamination downward with the water table aquifer.
19. Page 2-4. paragraph 4. Please summarize the natu.re of the OUl groundwater extraction system as it. may relate to remedial activities at OU3.
Response:
In general the OUl groundwater extraction system will remove some of the mass of constituents present south of the railroad tracks and will create gradients that will reduce the rate of migration within a portion of the aquifer. Both effects will reduce the burden on natural attenuation, possibly reducing the extent of migration and/or shortening the time until cleanup goals are met within the southern extent of the plume. The potential impacts of the OUl operation will be considered during the design of OU3. Following RA construction and startup of the OU3 system, operation of OU3 will be modjfied as appropriate (to the extent practicable) based upon significant impacts of OUl operations on the OU3 operations.
20. Page 2-5, paragraph. 4. Please define the fou.r plumes as they relate to the OU3 activities. What activities will address each of the four plumes? Where are the
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Response to Comments
Page 7 of 11
four plumes located? Pilot Test figure 4-1 is the only one which appears to show the plume and only one is evident. The appropriateness of the natural attenuation evaluation discussed in this section cannot be assessed without a definition of the four plumes to be addressed.
Response:
There is essentially only one plume within OU3. We have divided the plume into four sections to facilitate evaluation of natural attenuation. Because of a groundwater divide, migration occurs both to the south and to the north. Additionally while there is no aquitard between the shallow unconsolidated zone and the intermediate bedrock zone, groundwater movement and geochemistry are likely to be different in the shallow and intermediate zones, thus it is appropriate to attempt to determine fate and transport along four different flow paths.
21. Page 2-8, paragraph 1. Please discuss why Bi.oscreen is not considered appropriate for the sensitivity analysis and either discuss the ECKENFELDER INC. model or provide references where it is discussed and can be reviewed.
Response:
There is an editorial error in the text. The sensitivity analysis will be performed using the BIOSCREEN model.
SECTION 3.0-REMEDIAL DESIGN
22. Page 3-3. paragraph 1. Please discuss how the helium tracer test will be nscd to evaluate SVE.
Response:
Helium will be injected with air primarily to evaluate air sparging. Its presence will be screened for by sampling probes located within the saturated zone at different locations and depths to provide information regarding the flow path of the injected air within the saturated zone. Additional information will be derived from samples taken from probes located within the unsaturated zone. The recovered air from the SVE system will also be analyzed for helium to evaluate the effectiveness of the SVE system in capturing injected air.
23. Page 3-3. paragraph 3. The text refers to injection and extraction wells; should this refer instead to spa,ging wells, and SVE vents?
Response:
The terminology air sparging well and SVE vent could be utilized. However, they merely represent the specific use of an air injection well or a vapor extraction well. Additionally, the term vent typically refers to a passive well rather than an active extraction well with an applied vacuum.
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Response to Comments
Page 8 of 11
SECTION 4.0-PROJECT MANAGEMENT PLAN
24. Page 4-8. paragraph 1. The text refers to prouid,:ng s1tpport to the "Group".
Please identify this "Group" and all other pertinent organizations involved with
activity under this Work Plan.
Response:
The "Group" should be replaced with El Paso.
25. Page B-4. paragraph 3. Please provide documentation of the
ECKENFELDER INC. model, its application and previous experience it its use.
Response:
The ECKENFELDER INC. model is relatively new and has had limited use.
Where we have applied it. it is consistent with the results of BIOSCREEN. It
is based on the same equations used by BIOSCREEN, but also includes
provisions to terminate contributions from the source area at any time during
simulations. We have not as yet published any articles discussing the model.
To date we have used it to estimate future constituent concentrations down
gradient of remedial systems. One of these systems has been in operation for a
few months and the other has not been constructed as yet.
ATTACHMENT 1-PILOT TEST WORK PLAN
26. Page 4-3, paragraph 2. Referring to this table and to Figure 4-4, is an air
sample point needed after the air filter? How will removal of VOCs by the
liquid separator/air filter be assessed (and are t.hese data needed for the
design)? -.]f the sample point at the well head includes entrained moisture (since
it is before the moisture lmoclwu.t) will this affect interpretation of the VOC
removal by SVE in the gas phase?
Response:
The liquid separator and air filter serve to prevent entrained water and
particulates from entering the blower and possibly causing damage. They are
neither intended nor expected to remove VOCs. Entrained moisture is not
expected at the well head.
27. Page 4-4. paragraph 4. Please discuss how Qmax will be determined, and
whether the system settings will be s1tfficient.ly sensitive to allow for three
different settings of Q if Qmax is as low as 20 cfm (requ.iring according to I.he
plan, ?Q values of about 7 and 14 cf111).
Response:
We estimated a range for Qmax. We are anticipating a Qmax significantly greater
than 20 cfm. However. if Qmax is near the low end of the estimated range we
will change out the magnehelix gauge on the pitot tube to achieve the
appropriate sensitivity.
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Response to Comments
Page 9 of 11
28. Page 4-.5. paragraph 2. Please discuss how the hehwn tracer will show such
information as degree of homogeneity and ROI. What will helium data show
that won't be shown by the distribution of pressure and flow reading at the
various monitoring points?
Response:
Helium tracer tests are used primarily for evaluating the ROI (radius of
influence) and flow paths of air within the saturated zone. By screening
for/measuring helium in probes located within the saturated zone at different
distances from the injection well it will be possible to determine that the radius
of influence is less than the distance between the closest probe not containing
helium but greater than the distance to the farthest probe in which helium is
detected. Placing the probes at multiple depths provides an indication of the
shape of the airflow path. Placing probes in different directions from the
injection well will provide an indication of the symmetry of the flow path using
the specific injection well being tested. The use of pressure measurements for
air sparging frequently leads to over estimates of the ROI.
29. Page 4-8. paragraph 2. The compliance of the p.:Zot test with NC air permit
requirements has not been verified by this review. Although it seems highly
unlikely that this test would generate s11.fficient emissions to require I.he penn,:t.
noted here, are there any requirements in NC for a pilot lest perm.it or approval
for su.ch operations?
Response:
According to a conversation (April 22, 1998) with Tammie Watkins of the NC
Division of Air Quality, Mooresville Regional Office, they do not require a
permit or other written information as long as the emission threshold of five
tons VOCs per year is not exceeded.
30. Page .5-1. paragraph 1. Is it possible at this point to cilc the models which may
be used for design and if not when will these be provided?
Response:
The following publications describe the models used for evaluating the air
sparging and SVE data.
Rodriguez-Maroto, C. Gomez-Lahoz, and D. J. Wilson, 1994 "Soil Cleanup by
In-Situ Aeration. XVIII. Field-Scale Models with Diffusion from Clay
Structures", Separation Science and Technology, 29(11), pp. 1367-1399, 1994.
Wilson, D. J., A. N. Clarke, K. M. Kaminski, and E. Y. Chang, 1997
"Groundwater cleanup by In-situ sparging. XIII. Random Air Channels for
Sparging of dissolved and Nonaqueous Phase Volatiles", Separation Science
and Technology, 32(18), pp. 2969-2992, 1997.
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Response to Comments
Page 10 of 11
ATTACHMENT 2-ADDENDUM TO THE FIELD SAMPLING PLAN
31. Appendix B-1. page 1. paragraph 5. Is it possible to cite references for I.he
assertion that the selection of pressures will provide representative data?
Response:
The selected pressures cover the range of pressures used at a large number of
sites. In addition to our experience. the following references can be consulted.
Marley, M.C .• C.J. Bruell. and R.H. Hopkins. 1995. "Air Sparging Technology:
A Practice Update." In-Situ Aeration: Air Sparging, Bioventing, and Related
Remediation Processes. Eels. Hinchee. R.E .• R.N. Miller, and P.C. Johnson.
Battelle Press, Columbus, Ohio. 31-37.
Bass, D.R. and R.A. Brown, 1998. "Air Sparging Case Study Database
Update," presented at "the First International Conference on Remediation of
Chlorinated and Recalcitrant Compounds," Monterey, California, May 18-21,
1998.
32. Appendix B-2. page 2. top b11,llets. The issues discussed here appear to be
related to testing of water for bacteriologic qu.ality.as is often done for public
water supplies. Are they really a concern for the data in this program?
Response:
Bacteriologic quality is not a concern for this program. The potable water
sampling method presented in Appendix B is consistent with the EPA Region
IV Standard Operating Procedures (May 1996).
33. Appendix B-2. What will the effect of the sampling methods be on potential
detection of VOes in private wells? Won't the tap flushing procedures tend to
aerate the samples and possibly strip out VOes from the water? Won't
entrained or dissolved 02 in the water separate 011,t in the voe vial and be lost
at the point of analysis?
Response:
The potable water sampling meth.od presented in Appendix B is consistent with
the EPA Region IV Standard Operating Procedures (May 1996). As indicated
in the procedure, the selected sampling tap will be the first available tap off the
water supply or well. Preferably, this tap would be at the well or prior to the
water line entering the residence. Each tap will be inspected to ensure that no
aerator is present. The procedure requires a minimum of 15 minutes of purges
prior to sampling. During purging, water flow will be adjusted so that a
continuous stream of water is flowing from the tap, therefore minimizing the
potential aeration to the sample.
APPENDIX B-5
34. Page 1. paragraph 2. This Warning ca/I.lions against the 11,se of excessive
press/I.re which may cal/.se fracturing and decrease performance. Please
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Response to Comments
Page 11 of 11
distinguish between this event and the formation of "discrete channels"
discussed in section I, where it appeared to be a normal and desirable event.
Response:
The equations are based on the weight (mass times gravity) of the soils and the
groundwater above the top of the screen. The pressure that is required to
cause fracturing is approximately equal to that required to displace the soil
and groundwater located above the screened interval. The following text can
be consulted: Vapor Extraction & Air Sparging 1998, American Academy of
Environmental Engineers, Annapolis, M. D., Chapter 5. They do apply
universally.
Fracturing occurs by actually lifting the formation and requires the pressures
as determined by the cited equations. Channels occur as a result of particles of
soils moving aside to allow the air to flow through. As previously mentioned,
although the formation of discrete channels is difficult to avoid, it is not
desirable.
35. Page I, paragraph 3. Please prouide references for the calculation methods used
in this procedure. How was the equation for the pressure at which fractu.ring
may occur determined? Whal. is the basis for the various constants used in these
equations and do they apply universally?
Response:
See response to item 3,1_
36. Page 3, i:t.e,n 5. How is the m,.nunwn entry pressure detected (i.e., what
measurement of system operation show that this pressure has been reached?
Response:
The minimum entry pressure is determined by first applying a pressure equal
to that required to displace the water column in the well. The pressure is
gradually increased until flow occurs. The lowest pressure under which flow
occurs (as measured by the flow meter) is the minim um entry pressure.
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