Golder Associates Inc.

1951 Old Cuthbert Road, Suite 301 SDMS DocID 2010529Cherry Hill. NJ 08034Telephone (856) 616-8166Fax (856) 616-18 74

September 13, 2002 Project No.: 003-6000

USEPA Region III1850 Arch StreetPhiladelphia, PA 19103-2029

Attn: Mr. Charlie Root

RE: RESPONSE TO USEPA/PADEP COMMENTS DATED JULY 31, 2002 ON THEPRE-DESIGN INVESTIGATION AND FOCUSED FEASIBLITY STUDY REPORTSMALVERN TCE SUPERFUND SITEEAST WHITELAND TOWNSHIP, CHESTER COUNTY, PENNSYLVANIA

Dear Mr. Root:

On behalf of the Chemclene Site Defense Group (CSDG), Golder Associates Inc. is pleased toprovide USEPA with the enclosed responses to USEPA/PADEP comments on the Pre-DesignInvestigation (PDI) Report and Focused Feasibility Study (FFS) Report for the Malvern TCESuperfund Site. Both reports were submitted to USEPA/PADEP on May 17, 2002. Aspreviously requested, copies have also been sent to Ms. April Flipse of PADEP and Ms. Mary JoApakian of CDM Federal. This response to comments package includes the followinginformation:

• Attachment A - provides a written response to each USEPA/PADEP comment;• Attachment B - provides red-lined pages of revised text and modified figures for the PDI

Report in response to USEPA/PADEP comments. Notably, an updated Section 5.0 andFigure 32 that pertain to the project schedule are also included; and,

• Attachment C - provides red-lined pages of revised text and new Figure 8 for the FFSReport in response to USEPA/PADEP comments.

Should you or your colleagues have any questions or comments regarding the enclosed responseto comments package, please do not hesitate to call Mr. Chris Young at de maximis, inc. (610-435-1151) or me.

Very truly yours,

GOLDER ASSOCIATES INC.

S. White, P.E.Principal

RSW:lrl( i :PR()J i :CTS003-bO(K)MAI .VERN PDI REPORT-RESPONSE LETTER.KTC

cc: April Flipse, PADEPMary Jo Apakian, CDM FederalCSDG Technical CommitteeChris Young, de maximis, inc.Paul Boni, Esq.

OFFICES ACROSS ASIA. AUSTRALASIA, EUROPE, NORTH AMERICA, SOUTH AMERICA

ATTACHMENT A

RESPONSE TO COMMENTS DOCUMENT

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RESPONSE TO USEPA/PADEP COMMENTSDATED JULY 31, 2002 ON THE

PRE-DESIGN INVESTIGATION REPORT ANDFOCUSED FEASIBLITY STUDY

PRE-DESIGN INVESTIGATION REPORT

PADEP Comment 1:

The Department is concerned that the PDI study was conducted almost entirely undersevere drought conditions, and that there seems to be a tendency here to discount results ofprevious investigations.

Response:

The CSDG recognizes PADEP's concern relative to the drought conditions currentlyobserved in the Site area. The following response is provided, and will be referenced in theresponses to related comments (e.g., PADEP comments 2, 3, 4 and USEPA comment 7).

Water level measurements collected during the Pre-Design Investigation (PDI) are consistentwith those recorded during the Remedial Investigation (RI) and, in addition, are within theoverall range of historical groundwater levels recorded over the past 24 years. While the PDIgroundwater data indicates that there has been a drop in elevation of about 25 feet over theduration of the investigation (as shown on Figure 14 of the PDI Report), similar groundwaterelevations and variations were noted during the course of the RI.

Water levels collected from wells CC-5, CC-9, CC-10 and CC-14 during the RI are presentedon Figure 15 of the PDI Report. This graph shows that there was a fluctuation ingroundwater elevation ranging from approximately 297 feet above mean sea level (MSL) toabout 321 feet MSL (a 24-foot variation). Furthermore, water levels collected in a USGSwell located less than 1 mile from the site indicate that water levels ranged from about 314feet MSL to 330 feet MSL (a 16-foot variation) during the RI and from 317 feet MSL toabout 326 feet MSL (a 9-foot variation) during the PDI. Data collected from this USGS wellfrom 1978 to the end of 2001 are shown on Figure 16 of the PDI Report. In combination,these data indicate that the groundwater elevations observed during the PDI are consistentwith those observed during the RI, not only in range, but also in magnitude and that the dataalso fall within the historical range of groundwater elevations observed over the past 24years.

Much of the information and supporting data that was collected during previousinvestigations was reviewed and incorporated into the conceptual site model presented in thePDI. However one substantial difference between the PDI hydrogeologic model and previousmodels is the direction of groundwater flow in the Former Disposal Area/Mounded Area(FDA/MA). Based on the information collected during the PDI, there is a consistentnortheasterly groundwater flow direction from the FDA/MA toward the Main Plant Area(MPA). This flow direction is in contrast to previous investigations that indicatedintermittent flow from the FDA/MA toward the south-southwest. This change in flowdirection is primarily the result of the cessation of pumping from the Philadelphia SuburbanWater Company well located south of Hillbrook Circle, and cessation of pumping from theresidences in Hillbrook Circle. The recent drought conditions are not believed to beresponsible for this change.

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Notwithstanding the above, future monitoring programs will be implemented as part of thegroundwater remedies at the Site to provide an ongoing assessment and evaluation of thecurrent hydrogeologic flow model. These monitoring programs will include both retrofittedresidential wells in the Hillbrook Circle development and monitoring wells in the FDA/MAand MPA portions of the Site. While it is not anticipated, in the event that groundwater flowdirections are seen to differ substantially from those that are currently present, a contingencymonitoring plan will be implemented during the Remedial Action to assess the need andscope for supplemental monitoring. The contingency monitoring plan will be developed aspart of the design of the groundwater remedies.

Sections 4.3.7 and 4.4.7 of the PDI Report have been modified to reflect the inclusion oflong-term groundwater level monitoring during the implementation of the groundwaterremedies.

PADEP Comment 2:

§4.3.2 states that the overall drop in the groundwater levels is about 25 feet. The SVE wellswill be installed to 35 to 40 feet BGS, based on the results of the sampling in the FFS. Thereported water table level is 60 to 70 feet BGS. When the water level rises again how doesGolder intend to deal with the possibility of water entering the vapor extraction system?

Response:

As discussed in the PDI Report, the large majority of VOC mass occurs above 35 feet belowground surface (bgs) and, as such, the primary SVE system includes wells distributed acrossthe entire FDA/MA extending to a depth of about 35 feet bgs (see Section 4.2.2 of the FFSReport). For groundwater monitoring wells located in the immediate vicinity of the proposedSVE system, the shallowest water level observed during the PDI ranged from 45.6 ft bgs atCC-5 to 58.2 ft bgs at CC-9. As stated above in Response to Comment 1, these water levelsare consistent with those observed during the RI, and local historical ranges. Consequently, itis not anticipated that a rise in groundwater elevation will interfere with the operation of theSVE system over the relatively short duration of its operation (i.e., less than 5 years), and theoverall effectiveness of the SVE system to achieve the protection of groundwater will not becomprised. However, should the long-term groundwater level monitoring, as described in theResponse to Comment No. 1, indicate that water levels could impact the operation of the SVEsystem, then an assessment of potential operational changes and/or system enhancementswould be made at that time.

Section 3.2.3 of the PDI Report and Section 4.2.2 of the FFS Report have been modified toinclude provisions for a potential groundwater level increase.

PADEP Comment 3:

§4.3.5 states that the elevation of Valley Creek is substantially higher than the reportedgroundwater elevation (330 to 350 feet MSL to 295 to 320 feet MSL). Which is reportedduring a drought, which has lowered the water by approximately 25 feet. Again, as thewater elevations recover from the drought conditions, it is entirely possible that the Creekwill return to previously plotted status as a gaining stream

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Response:

As noted in Response to Comment 1, future long-term water level monitoring programs willbe implemented as part of the groundwater remedies at the Site to provide an ongoingassessment and evaluation of the current hydrogeologic flow model. While it is notanticipated, if in the unlikely event that the groundwater flow directions change resulting inthe Creek being downgradient of the Site, then a contingency monitoring plan will beimplemented during remedial action to evaluate the need for and scope of any additionalmonitoring including the need to monitor water quality in Valley Creek. The contingencymonitoring plan will be developed during design of the FDA/MA groundwater MNA remedy.

PADEP Comment 4:

The MNA Plan for the FDA/MA needs to include continued monitoring of (at least)groundwater elevations in the monitoring and converted residential wells in the HillbrookCircle area, with the understanding that should the flow directions change as groundwaterrises to historic levels, monitoring of Valley Creek must be instituted.

Response:

See Response to Comment 3 above.

CDM Federal Programs Comment 1:

Page 24, Section 3.2.2, Third Bullet, Last Sentence. According to Figure 4, the smallnorthern portion of the Mounded Area (MA) referred to in this sentence contains volatileorganic compound (VOC) concentrations far in excess of Record of Decision (ROD)Clean-up Standards. The text indicates that the lateral delineation of this contaminationwill be completed during remedy implementation. Please explain how an effective remedialdesign will be completed without a complete knowledge of the contamination present at thesite.

Response:

The response to this comment is also applicable to CDM Federal Programs Comment 13.

The CSDG acknowledge that some additional confirmation of the lateral extent of VOCimpacts will be required, specifically in the northern part of the MA and in the area of boringGB-34. However, as discussed in both the PDI and FFS Reports, the lateral and verticalextent of VOC impacts in the FDA/MA have been sufficiently defined to effectively moveforward with design. A new figure (Figure 8) has been prepared for inclusion in the FFSReport. This figure depicts a preliminary layout of the SVE system, in plan view, and showsthe anticipated radius of influence (ROI) of each of the perimeter SVE wells which extendswell beyond the currently delineated extent of VOCs. Confirmation of this delineation willbe carried out during installation of the SVE wells, and if necessary, additional SVE wellswill be added. The mechanical systems (i.e., piping, blowers, treatment components, etc.)will be designed with sufficient flexibility to accommodate installation of additional wells, ifnecessary. Sections 4.2.2 and 4.2.3 of the Focused Feasibility Study have been modified to

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include a discussion of the proposed construction sampling confirmation program andsystems flexibility which will be detailed during the design.

CDM Federal Programs Comment 2:

Page 26, Section 3.2.2, Paragraph 2, Line 4. The majority of contaminant mass occurringin the interbedded unit is not apparent in the report. For example, Figures 3 and 4 denotesignificant contamination in the upper clay, based on the reported depths. Thecalculations used to determine that the majority of the contaminant mass occurs in theinterbedded zone should be included.

Response:

As illustrated in Figures 6 and 7 of the FFS Report, it is clear that the majority of VOC massoccurs within the upper 30 feet of the soil column. In addition, with the exception of theresults collected at VP-5, VOC concentrations are typically higher in the Intermediate Zonethan in the Upper Clay Zone. The important consideration is that regardless of thisinterpretation, both the Upper Clay Zone and the Intermediate Zone will be addressed by theinstallation of SVE wells that are screened across both zones. As the results of the SVE PilotTest demonstrated, both zones respond in a similar and uniform manner, and thereforescreening across both zones will be effective at removing VOCs from both the IntermediateZone and the Upper Clay.

CDM Federal Programs Comment 3:

Page 35, Section 4.2, Paragraph 2, Lines 6 and 7. Higher hydraulic conductivities arereported to be the cause of the relatively flat hydraulic gradient near the Former DisposalArea (FDA)/MA. The data used to support the hydraulic conductivities should bereferenced.

Response:

The RI indicates that the hydraulic conductivity values measured at the FDA/MA wells are• one to two orders of magnitude higher than those measured at the MPA. Table 3-3 of the RI

presents the hydraulic conductivity data. Section 4.2 of the PDI Report has been modifiedaccordingly.

CDM Federal Programs Comment 4:

Page 36, Section 4.2, Paragraph 1 and Figure 14. The water level for well CC-11 isreported to be not included in the contouring scheme. However, the potentiometric valuereported for the well in Figure 14 fits with the contouring scheme. If the data point isincorrectly posted, the correct value should be added. If the value is correct, a discussionshould be included that explains the significance of the value fitting with thepotentiometric surface.

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Response:

It is assumed that this comment refers to Figures 12 and 13, which present interpretedgroundwater elevation contours on 2/19/01 and 10/16/01, respectively, not Figure 14. Thegroundwater elevation posted on both Figures is correct. As stated in Note 2 of Figure 13, theelevation recorded at CC-11 was not included in the contouring scheme, but was posted onthe Figure for completeness. While the elevation recorded at CC-11 shown on Figure 12 fitsthe contouring scheme, this fit is considered to be coincidental as the heads measured at thislocation are believed to be a localized phenomenon not representative of regional conditions.

As stated in the PDI Report, sounding of this well during the PDI indicated that the totaldepth is approximately 70 feet shallower than the depth indicated on the well log.Furthermore, as shown on Figure 17, well CC-11 behaves differently than the other wellsmonitored in the FDA/MA and Hillbrook Circle, again indicating that this well monitors alocalized phenomenon, such as surface water runoff or a perched water zone. An additionalnote has been added to Figure 12, and the text in Section 4.2 of the PDI Report has beenclarified to indicate that the fit of the value recorded at this location is considered to becoincidental. In addition, Section 4.3.7 of the PDI Report has been revised to state that thedesign will address the abandonment and possible replacement of well CC-11 given thesuspect conditions.

CDM Federal Programs Comment 5:

Pages 37 and 38, Section 4.3.3. Two data sets (continuous water level monitoring andwater levels compared to precipitation) are presented to suggest that the hydrogeologicsystem beneath the FDA/MA is indicative of an interconnected, diffuse, fracture-flowaquifer. This type of data, although applicable and useful in an investigation of thisnature, should not be used to define fracture interconnectedness. Rather monitoring ofthis nature combined with a discrete aquifer stress of which the location is known (e.g., awithdrawal or, as in the case of the Main Plant Area (MPA), well drilling is acceptable)should be performed. The discussion and conclusion of the interconnectedness should bequalified to note the limits of the data sets.

Response:

The conclusion that the hydrogeologic system at the FDA/MA is indicative of aninterconnected diffuse fracture-flow system is based on the fact that the FDA/MA wellsrespond to precipitation in a similar manner compared to the MPA wells. While precipitationevents do not provide substantial aquifer stresses, they do nonetheless, cause a minor stress tothe aquifer system. The response to this stress (i.e., timing or magnitude of the response) cantherefore provide very useful, if only qualitative, information related to theinterconnectedness of the fracture system, as well as the nature of the flow system (i.e.,Karstic conduit). Sloto provides a similar conclusion regarding the nature of the aquifersystem based on aquifer test data conducted at well CC-18 (Sloto, 1997, page 55). Therefore,the interpretation of precipitation responses in combination with conclusions reached by Slotoare believed sufficient to justify the conclusions made with respect to fractureinterconnectedness. Section 4.3.3 of the PDI Report has been modified accordingly.

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CDM Federal Programs Comment 6:

Page 41, Section 4.4.1, Paragraph 1, Line 6. The hydraulic conductivity used in thecalculation of the groundwater velocity should be added and referenced.

Response:

The hydraulic conductivities used in the calculation of the Darcy velocity were based on theaverage of the results obtained from the slug testing completed during the PDI and arepresented in Table 8 of the PDI Report. These results are comparable to the RJ results.Section 4.4.1 of the PDI Report has been clarified accordingly.

CDM Federal Programs Comment 7:

Page 42, Section 4.4.3, Paragraph 2, Lines 11 and 12. A significant point to explain theobserved shallow gradient at the FDA/MA is that higher hydraulic conductivities arepresented in this area as noted on page 35. If true, this point is not discussed in section4.4.3. The data used to make the explanation should be presented and discussed in section4.4.3.

Response:

The referenced text refers to the southern and eastern portions of the MPA, not the entire Site.The PDI Report text in Section 4.4.3 has been modified to clarify the limits of this discussion.

CDM Federal Programs Comment 8:

Page 42, Section 4.4.4, paragraph 1. A qualitative statement describing the effectiveness ofidentifying dense non-aqueous phase liquid (DNAPL) with a video camera should beadded. Presently, the effectiveness is uncertain since the DNAPL that may be expected withthe types of contaminants identified should be a colorless liquid. Thus, identifying theliquid by a visual means may be very difficult if at all possible.

Response:

In accordance with the approved PDI Work Plan, two methods were used to assess thepossible presence of DNAPL. Visual determination of the presence/absence of DNAPL wascompleted using a downhole video camera. This method is considered to be applicable at theSite given the fact that the materials historically handled were most likely to have been usedsolvents. In addition, an interface probe was used to identify the possible presence ofDNAPL at the base of well CC-6 and open borehole CC-13. The results of theseinvestigations did not indicate the presence of DNAPL, which is consistent with the findingsof the RI. While the groundwater VOC concentration data suggest that some residual impactsexist in the subsurface, the RI and PDI data do not indicate any accessible/recoverableamounts of DNAPL that could impact the remedy design.

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CDM Federal Programs Comment 9:

Page 43, Section 4.4.5.1, Paragraph 3, Lines 1, 2, and 3. Based on the available data, theextent of the groundwater contamination is unclear. The well with the second highestdetected trichloroethene (TCE) concentration is GW-1. This well, with the exception ofwell GW-5 (which is located 450 feet northeast of GW-1), is the northernmost well in thenetwork. A significant amount of inference/extrapolation was performed to placeisoconcentration contours in this area (see Figures 27 and 28). Additional monitoringpoints should be installed north of GW-1 to insure that contaminants have not migrated inthis direction.

Response:

It is anticipated that an additional monitoring well will be required in the area to the north ofGW-1 in order to provide adequate monitoring coverage for the MPA groundwater remedy.This additional monitoring point will provide both hydraulic and geochemical data in thisarea of the Site. Details regarding the exact location and depth will be established concurrentwith the design of the MPA groundwater remedy so that the most appropriate location can beselected. It should be noted that Golder Associates originally attempted to install well GW-1further to the north, however access was denied. To this extent, USEPA's assistance willlikely be required to gain the necessary access during construction. Section 4.4.7 of the PDIReport has been modified to include discussion of this potential monitoring well location.

CDM Federal Programs Comment 10:

Page 44, Section 4.4.5.1, Paragraph 2. The hydraulic data used to conclude that the plumeis bounded to the north since the fault contact acts as a hydraulic barrier should bepresented.

Response:

Quantitative hydraulic data confirming groundwater flow characteristics across the faultcontact between the Chickies Quartzites in the north, and the carbonate bedrock beneath thesite are not available. However, based on a review of the available published data (e.g., U.S.Geological Survey Reports) the Chickies Quartzite is typically a poor water-bearing unit,which would indicate lower hydraulic conductivity values. Observations made during thefield investigation in support of the PDI, and from a review of the RI/FS Report for the Site,indicate that the Chickies Quartzites can be considered generally more resistant to erosion,hence forming the ridges that comprise the North Valley Hills. Given this character,hydraulic gradients across the fault contact between the Chickies Quartzites and the carbonaterocks are likely quite steep and directed away from (i.e., southerly) the North Valley Hillsinto the carbonate lowland below. In addition, the field geologic mapping conducted duringthe PDI positioned the contact between the Chickies Quartzite and the Ledger further to thesouth than previous regional mapping completed by USGS. Given the lower hydraulicconductivity of the Chickies, the generally higher topographic relief, and the more southerlylocation of the contact, and in consideration of the PDI groundwater elevation and chemicaldata, the overall impact on groundwater can only be the diversion of flow from the MPA,towards the northeast-east, parallel to the fault contact between these formations. Section4.4.5.1 of the PDI Report has been modified accordingly.

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CDM Federal Programs Comment 11:

Page 44, Section 4.4.5.1, Paragraph 3, Lines 1 and 2. The "observed vertical VOCconcentration decrease" should be elaborated on in this section. If comparisons are beingmade between concentrations of well CC-6 to well CC-13, a discussion on the wells'open/screened intervals and their impact on concentration differences should also beincluded. Based on Table 3, the screened interval of CC-6 is 11 feet and the open intervalof CC-13 is 5 7 feet.

Response:

Sloto indicates that the boring log for well CC-13 includes a fracture at a depth of 135 feetbgs, which was flowing at an approximate rate of six gallons per minute (gpm). Below thisdepth, no other fractures or flowing features were noted. This condition is not uncommon asfracture intensity and aperture frequently decrease with depth. During sampling of CC-13,the pump was placed at 135 feet bgs to draw water specifically from this feature. While thelonger open interval in CC-13 may result in some limited dilution of VOC concentrations, theobjective of the low-flow purge sampling method is to collect representative groundwatersamples from the aquifer at a specific interval. Therefore, the comparison of the data fromeach well is reasonable and indicates that lower VOC concentrations are found at depth.Section 4.4.5.1 of the PDI Report has been modified accordingly.

CDM Federal Programs Comment 12:

Figure 3. The EPA split sample collected from location GB-11-18 contained severalorganic compounds on the target compound list (TCL) list that were either not detected ornot analyzed for in the corresponding sample collected by Golder. Compounds found inthe split but not in the Golder sample include, but are not limited to:

• vinyl chloride at 16 ppb;• l,l,2-trichloro-l,2,2-trifluoroethane at 47,000 ppb;• 1,1-dichloroethene at 49 ppb;• acetone at 2100 ppb;• 1,1-dichloroethane at 250 ppb;• chloroform at 17 ppb;• cyclohexane at 150 ppb;• isopropylbenzene at 77ppb;• 1,2-dichlorobenzene at 67ppb; and• several pesticides at trace concentrations.

In order to ensure that the design is as protective as necessary, it may be prudent toconsider including the results of EPA split samples in the Pre-Design Investigation dataset.

Response:

The sample CDM Federal Program's comment refers to is a shallow soil sample collected atthe base of the northern excavation in the FDA. This soil will be addressed as part of SitePreparation described in the FFS Report. More globally however, the drivers of the remedy

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are PCE, TCE, and 1,1,1-TCA. The successful remediation of these constituents shouldadequately address other VOCs that are present in subsurface soils in the FDA/MA at lowerconcentrations. However, for completeness, the results of the USEPA spilt sample analyseswill be considered during design. Prior to including this data, Golder Associates would like toreview the laboratory data packages and data validation reports.

CDM Federal Programs Comment 13:

Figure 4. Given that VOC concentrations in GB-34 are as much as ten times greater thanROD Clean-up Standards, it appears that VOC concentrations have not been completelydelineated in the area southeast of this boring. Please explain how this data gap will beaddressed.

Response:

See response to CDM Federal Programs Comment 1.

CDM Federal Programs Comment 14:

Figures 20 and 21. If the last data points (data collected during 2001 drought) presentedin the graphs are removed, a decrease in contamination is not apparent. The contaminantconcentrations of 2001 may be lower due to the drought conditions. In order to avoidmisinterpreting the results, additional samples should be collected to ensure theconcentrations are decreasing due to natural attenuation. If data are available to showthat drought conditions do not adversely effect the groundwater contaminantconcentrations, then that data could be presented instead of additional sample results.

Response:

The design of the MNA program will include the measurement of water levels and thecollection of groundwater samples at monitoring wells and retrofitted residential wells in theFDA/MA area of the Site. The implementation of this MNA program, which will becompleted as part of the remedy, should provide an adequate database upon which to assessdata trends and to provide an assessment of the degree to which natural attenuation isoccurring. The MNA monitoring program for the FDA/MA groundwater remedy will bedeveloped during remedial design for USEPA review and approval.

CDM Federal Programs Comment 15:

Figure 24. Please explain the meaning of the three asterisks on this figure.

Response:

The meaning of the asterisks is described in Note 2 on Figure 24.

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CDM Federal Programs Comment 16:

Attachment G. Summary of Air Sampling Results. The results for samples PR2-1030 andMR1-01/02-900 appear to be anomalous when compared to the results of both the EPAsplit samples collected from these locations and other samples collected by Golder fromcorresponding zones at different times. Please confirm the accuracy of these results.

Response:

It is agreed that these samples are anomalous when compared to the results of both theUSEPA split samples and other samples collected by Golder Associates. Upon reviewing thesample handling activities, it was determined that sample PR2-1030, a Summa canistersample, incurred a vacuum loss from 6" to 8" Hg during shipping, and was in transit for 5days, which is within acceptable parameters, but may have contributed to potential sampleloss. Sample handling activities for MR1-01/02-900 revealed no anomalies, and it isconcluded that the sample may be anomalously low due to random sampling variability.These samples were taken during the beginning of the MR1 rebound test, in whichconcentrations may have been variable, and thus the samples may reflect actual concentrationvariability.

FOCUSED FEASIBILITY STUDY

USEPA Comment 1:

With the SVE approach there will be residual contamination left in place. The FFS doesnot address this issue. A discussion of how the residual contamination will be measuredand what institutional controls would be appropriate to address these contaminants left inplace needs to be added. Institutional Controls need to be added as a component of theremedy.

Response:

USEPA Comments 1, 2, 3 and CDM Federal Programs Comment 1 on the FFS Reportaddress performance objectives/monitoring for the SVE system and the need for institutionalcontrols to address residual soil impacts following implementation of the SVE system.

CSDG is in agreement that the ultimate goal of the SVE remedy is to be protective of theFDA/MA groundwater remedy. The SVE system will be operated until the limitations of thetechnology are reached as determined by VOC recovery (i.e., recoverable VOCconcentrations become diffusion limited). It is anticipated that all of the SVE wells will becycled to some degree based on the VOC recovery data, to meet the overall SVE remedyobjectives. Specific SVE well end-points will be developed on a well to well basis, withUSEPA concurrence, during remedy implementation. Upon reaching the end-point criteria, itis recognized that some degree of post-operational monitoring will be required to demonstratethat the completion of the SVE remedy is protective of the groundwater remedy. Details ofthe post-operational monitoring program will be developed during design. Followingcompletion of the post-operational monitoring program, the need for Institutional Controlswill be evaluated and, if needed, institutional controls will be made part of the final remedy.Section 4.2.4 of the FFS Report has been revised accordingly.

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USEPA Comment 2:

It should be noted that the ultimate success of the SVE system will be whether it removesenough source contamination from the soils to allow natural attenuation to occur inMA/FDA ground water.

Response:

See Response to Comment 1 on the FFS Report above.

USEPA Comment 3:

The only thing that concerns me is defining the asymptotic endpoint and whether all of thewells will be cycled before a turn-off decision is made. On page 15, it is noted that thisdefining the endpoint will be developed during design; cycling strategies should also bediscussed.

Response:

See Response to Comment 1 on the FFS Report above.

USEPA Comment 4:

I could not locate wells CC-2, 3, and 4 on Figure 2.

Response:

Wells CC-1 and CC-3 were inadvertently left off the Figure. Well CC-2 is located in thewestern part of the MPA. Well CC-4, originally located in the FDA/MA, was abandonedduring the RI. A revised Figure 2 will be provided.

USEPA Comment 5:

p. 36, typo: I believe the water company is Philadelphia Suburban, not Philadelphia WaterCo.

Response:

As noted in the comment, the correct name for the water company is the PhiladelphiaSuburban Water Company. The PDI Report text has been revised accordingly.

USEPA Comment 6:

P. 36, number 3: A few sentences regarding the specifics of regional pumping would behelpful.

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Response:

The overall aim of the PDI was to collect sufficient data with which to design a groundwaterremedy for the FDA/MA and the MPA that would be protective of human health and theenvironment. The PDI did not collect specific information regarding regional pumpingactivities. However, the Sloto report identifies Catanach quarry as a regional groundwatersink, estimating that the quarry was pumping as much as 5 million gallons per day at the timeof that investigation. It is not known whether this is consistent with current pumping rates ornot.

USEPA Comment 7:

Under 4.3.5 Valley Creek Assessment, p. 39, 3rd bullet, it is noted that the stream channelwas dry and/or exhibited low flows. Is it known how the creek was affected by the drought?

Response:

See Response to PADEP Comment 1 on the PDI Report.

CDM Federal Programs Comment 1:

Section 4.2.4. Page 15. First Sentence. Please indicate how the asymptotic endpoint isexpected to correlate to the ROD Clean-up Standards. In addition, please provideinformation on the confirmatory sampling program that will be used to ensure thatremedial objectives have been achieved prior to site closure.

Response:

See response to USEPA Comment 1 on the FFS Report.

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ATTACHMENT B

REVISED PDI JREPORT PAGES AND FIGURES

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Results of the pilot study indicate that the pilot system has met or exceeded the performance

criteria defined in the USEPA approved SVE PSWP for an effective remedy in the FDA/MA as

evidenced by the following observations:

• Mass removal rates of approximately 18 pounds per day were attained (PSWP criteria - >1 Ib/day);

• Air permeability was estimated to be 3xlO"9 cm2 to lxlO" s cm2 (PSWP criteria - > IxlO"9

cm2);

• The ROI30 was estimated to be 25 feet (PSWP criteria - > 10 feet); and,

• Air flow rates for the three SVE test wells combined were over 20 scfm (PSWP criteria -> 20 scfm).

The pilot study also indicated that the zones of potentially higher permeable material (i.e., the

thin, discontinuous layers of sands and gravel within the interbedded zone) did not result in short-

circuiting the performance of the system. In fact, the results indicate that the interbedded unit

(which contains the majority of the VOC mass) responded uniformly as a sandy/silty material.

This homogeneous domain (as observed during the pilot study) is more favorable than a domain

having preferential flow paths within highly permeability areas. The uniform vertical and

horizontal performance results observed during the test will also reduce the need for the

installation and operation of a system with targeted intervals in a full-scale SVE system, i.e.,

fewer wells with longer screens can be used. In addition, the upper clay provides a natural low

permeability cap over the system, minimizing ambient air infiltration and maximizing vapor

extraction from the most impacted unit, the interbedded zone, that lies directly beneath the upper

clay.

3.2.3 Design Considerations - Conceptual Model of FDA/MA Soils

As previously discussed, the overburden soils within the FDA/MA can be categorized into three

general geologic horizons:

• Upper clay - consisting of a locally disturbed surficial silty clay unit with an averagethickness of about 5 feet extending to depths of about 10 feet in places;

• Interbedded zone - consisting of silty sands, silts and clays interbedded with thin,discontinuous layers of sands and gravels lying about 20 to 25 feet below the upper clay;and,

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Lower clay - consisting of stiffer and more homogeneous silty clays lying below theinterbedded zone and on top of the underlying carbonate bedrock that variably liesbetween about 45 to 60 feet bgs.

The lateral and vertical extent of VOCs has been well defined, providing the necessary

information to move forward with the design and implementation of an effective soil remedy.

The majority of the subsurface soil VOC impacts are contained within the lower portions of the

upper clay and throughout the interbedded zone. Smaller amounts were found in the upper

portions of the lower clay. The VOCs of interest are PCE, TCE, and 1,1,1-TCA and their natural

breakdown products. Concentrations of VOCs within the lower portion of the upper clay and the

interbedded zone are variable, with a small number of samples exceeding concentrations of 1,000

mg/kg total VOC at depths approaching 25 feet (e.g., GB-2-B2 in the MA and GB-39 in the

FDA). However, VOC concentrations in the lower portion of the interbedded zone and upper

portion of the lower clay occurred over a smaller aerial extent and at lower concentrations that

quickly dimmish with depth generally below about 30 feet in the upper portion of the lower clay

resulting in a relatively clean zone existing on top of the bedrock surface. As discussed in

-t-he depth to groundwalor measured during the Pre Design Investigation has ranged

y 60 to 70 feel bgs below the FDA/MA.

Within the FDA/MA portion of the Site, the shallowest water level observed during the PDI

ranged from 45.6 ft bgs at CC-5 to 58.2 ft bgs at CC-9. As further described in Section

4.3.2, these water levels are consistent with those observed during the RI, and local

historical ranges. Consequently, it is not anticipated that a rise in groundwater elevation

will interfere with the operation of a SVE system over the anticipated short duration of its

operation (i.e., less than 5 years). However, should the long-term groundwater level

monitoring implemented as part of the FDA/MA groundwater remedy, indicate that water

levels could impact the operation of a SVE system, an assessment of potential operational

changes and/or system enhancements would be made at that time.

Results of the SVE Pilot Study indicate that the pilot system has met or exceeded the performance

criteria defined in the USEPA approved SVE Pilot Study Work Plan for the FDA/MA. Mass

removal rates of approximately 18 pounds per day were attained as compared to the performance

goal of one pound per day. The Pilot Study also indicated that the interbedded unit, which

contains the large majority of the VOC mass, responded in a uniform manner, thus reducing the

need for installation and operation of targeted intervals in a full-scale SVE system. In addition,

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4.2 Hydrogeology

Groundwater flow at the Site is controlled by structural features as well as hydraulic stresses

induced by regional pumping. Groundwater beneath" the site generally flows from the southwest

to northeast, following the strike of the bedrock. Much of the groundwater flow occurs in the

Ledger Formation, which has generally flat hydraulic gradients. Generally higher hydraulic

heads are observed to the west and north of the Site, and lower hydraulic heads are present to the

northeast and east of the Site. Proximal to the Site, Site bedding features are believed to strike in

a northeasterly direction forming a pinnacled surface of ridges and lows due to folds and

differential weathering along bedding planes. Groundwater movement is believed to be

northeastward m response to local hydraulic stresses and controlled by the more permeable

bedding planes forming the bedrock troughs. Based on the well yield reported in the Remedial

Investigation and continuous water level responses noted during drilling, the local system

behaves more like diffuse fracture flow with low storage, particularly in the area of the MPA,

rather than conduit drastic flow. To the north, a geologic contact fault striking northeastward lies

between the crystalline, metamorphic quartzites of the Chickies Formation to the north and the

Ledger-Elbrook carbonate formations that underlie the Site. This contact fault is believed to

influence groundwater flow in the immediate vicinity of the Site and ultimately controls the

downgradient direction of flow.

One of the important findings of the Pre-Design Investigation of FDA/MA groundwater is the

recognition of a predominant groundwater flow direction from the Hillbrook Circle area

northeastward towards the FDA/MA, and then northeastward to and past the MPA. Synoptic

manual water level measurements collected throughout the Pre-Design Investigation confirm this

northeastward flow direction. Figures 12 and 13 show the interpreted groundwater contour maps

for February 19, 2001 and October 16, 2001, respectively. As a result of higher hydraulic

conductivities in the geologic units beneath the FDA/MA, as measured during the RI and

presented in Table 3-3 of that report, the horizontal hydraulic gradients in the immediate

vicinity of the FDA/MA are quite flat. As a result, groundwater flow directions can be locally

variable in the immediate vicinity of the FDA/MA. However, the overall site-wide flow direction

is clearly to the northeast.

The northeasterly change in the direction of groundwater flow presented in this PDI Report is

likely a result of influences from:

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1) The formerly operating Philadelphia Suburban Water Company production well locatedsoutheast of Hillbrook Circle was put out of service on November 4, 1992 (see USGSReports and the Remedial Investigation Report);

2) Residential pumping in Hillbrook Circle ended in 2000 when the alternate public watersupply line was installed; and,

3) Hydraulic stresses imposed by widespread regional pumping.

Previous studies had interpreted a transient groundwater divide between the MPA and FDA/MA,

predominantly as a result of the heads measured at monitoring well CC-11. The head elevation

measured at well CC-11 is interpreted to be a localized phenomenon not representative of

regional conditions, and has not been included in the contouring scheme. Sounding of this well

during the Pre-Design Investigation indicated that the depth is almost 70 feet shallower than

indicated on the well log, and that, based on the well log and measurements made during the Pre-

Design Investigation, there is only a 2.2-foot open interval remaining. It is likely that caved

material has effectively plugged the flowing features in this well such that there is a lag in the

response of the water level in the well to changes in head that occur in the aquifer and/or the well

disproportionately monitors surface water infiltration or perched groundwater influences.

While the water level for well CC-11 shown on Figure 12 appears to fit the contouring

scheme, for the reasons described above, the elevations measured are considered to be

localized phenomenon, and hence the apparent fit of the data is considered to be

coincidental. Therefore, this well is not used in the contouring scheme presented on Figures 12

and 13, and will not be included in further hydrogeologic interpretations.

4.3 FDA/MA Groundwater Investigation Results

4.3.1 Hydraulic Gradients

Figure 14 presents a plot of manual water level measurements collected in the FDA/MA wells

over time. This figure shows the extremely consistent trend of water level measurements made at

all the FDA/MA wells. In fact, the difference in hydraulic head between all the wells in the

FDA/MA is generally less than 0.2 feet, and thus the trend plots overlap. The historic data

collected during the Remedial Investigation indicate similar head differences (generally less than

0.3 feet) with a maximum of 0.67 feet and a minimum of 0.14 feet.

The average horizontal hydraulic gradient in the vicinity of the FDA/MA measured during the

Pre-Design Investigation was l . lx lO" 3 . This value is very similar to the Remedial Investigation

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data that indicate a horizontal hydraulic gradient on the order of IxlO"3 (Sloto, 1997, p. 19). Using

the average hydraulic conductivity value of 290 feet/day calculated from the pumping tests

completed during the Remedial Investigation, a Darcy velocity of 116 feet per year (ft/yr) can be

calculated. Assuming a porosity of 10%, this results in an advective groundwater velocity of

1165 ft/yr.

4.3.2 Historic Water Level Trends

The data collected during the Pre-Design Investigation shows a steady decline in piezometric

groundwater pressure, as shown on Figure 14, due to drought conditions eastern Pennsylvania

experienced during the Pre-Design Investigation. While there has been an overall drop of 25 feet

since April 2001, the hydraulic heads measured are within the historic range based on the

Remedial Investigation data, as shown on Figure 15. The USGS data from an observation well

located less than one mile to the east of the Site on Moore Road, shows a similar trend with

current groundwater elevations at that location being low, but within the range recorded over the

last 24 years, as shown on Figure 16. Therefore, while the recent 2001-2002 drought conditions

have substantially influenced the groundwater elevations at the Site, the groundwater elevations

are not atypical of conditions encountered in the past and are thus useful for evaluating

representative hydrogeologic conditions.

4.3.3 Fracture Interconnectedness

The data presented on Figure 17 indicate that in the FDA/MA, the overall hydraulic response is

more indicative of an interconnected, diffuse, fracture-flow aquifer system than a classic karst

conduit-flow system. Figure 17 presents a graph of continuous water level measurements

collected from wells CC-5, CC-10, CC-11, DW-33 and DW-41. This graph clearly shows that

wells CC-5, CC-10, DW-33 and DW-41 respond very similarly1.

While there appears to be more fluctuation in the data for well CC-10 that is possibly a result of

transducer noise (see Figure 17), this fluctuation does not appear to be cyclical (i.e., is not

separated by regular intervals), and the overall trend of the water level data from this well is

consistent with that of wells CC-5, DW-33 and DW-41. If karstic features, or conduit flow zones

1 Well CC-11 responds in an entirely different manner. It is important to note that CC-11 is plotted against a secondaryaxis (as a result of the unique hydraulic heads measured at this well), however the scales of the primary and secondaryaxes are the same. These groundwater plots support the previous conclusion that well C-l 1 responds differently thanother nearby monitoring wells to the same hydraulic stresses, indicative of a localized condition not representative ofsite-wide hydraulic conditions.

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that transmitted substantial volumes of groundwater at high rates were present, it would be

expected that there would be greater differences in the hydraulic responses between monitoring

wells.

Figure 18 shows the response of wells CC-5, CC-10, DW-33 and DW-41 to precipitation. This

graph shows, particularly at the higher groundwater elevations, that there are limited and varied

reactions to precipitation events. These data are indicative of a diffuse fracture-flow system

rather than a karst feature-dominated system, which is often characterized by rapid and dramatic

responses to precipitation events. Although there appears to be some response to precipitation at

lower head elevations, as stated above in Section 3.4.3, historic groundwater trends indicate that

the hydraulic heads are reaching the lower end of their range, and recovery to more typical

elevations is should be expected. When this recovery occurs, there will likely be less response to

precipitation, as evidenced in the earlier portion of the hydrograph shown on Figure 18. While

precipitation events do not provide substantial aquifer stresses, they do nonetheless, cause a

minor stress to the aquifer system. The response to this stress (i.e., timing or magnitude of

the response) can therefore provide very useful, if only qualitative, information related to

the interconnectedness of the fracture system as well as the nature of the flow system (i.e.,

karstic/conduit). In addition, Sloto provides a similar conclusion regarding the nature of

the aquifer system based on the aquifer test data conducted at well CC-18 (Sloto, 1997, page

55).

4.3.4 Geochemical Data

Wells CC-5, CC-9, CC-10, CC-15, CC-18, DW-41, DW-66 and DW-69 were sampled during the

Pre-Design Investigation using low-flow sampling techniques, and analyzed for VOCs. The

laboratory sample analyses results are presented in Appendix E-3. A summary of detections is

shown graphically on Figure 19.

Consistent with past trends, VOC concentrations in the FDA/MA groundwater are substantially

lower than those observed in the MPA. Well CC-5 exhibited the highest concentrations of VOCs

in the FDA/MA wells sampled. TCE and PCE were detected at well CC-5 at concentrations of

600 and 130 ug/L, respectively. Cis-l,2-DCE was detected at well CC-5 at a concentration of

3,800 ug/L) and 1,1,1-TCA was detected at a concentration of 140 ug/L. In general, these results

are not indicative of the presence of a substantial source in the vadose zone, and are more

indicative of impacts from a diffuse source within the overburden material.

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The Pre-Design Investigation results confirm that natural attenuation is occurring in groundwater

at the FDA/MA, and in addition, provide further evidence that there has been a change in the

overall groundwater flow direction since the completion of the Remedial Investigation. The Pre-

Design Investigation data were compared to data collected during the Remedial Investigation

(Remedial Investigation Report Table 4-18 and Figure 4-15) and indicate that, in general, the

wells sampled south of the FDA/MA exhibited stable or decreasing VOC concentrations in

comparison to the Remedial Investigation data. At CC-9, concentrations of all detected

compounds had increased in comparison to the Remedial Investigation. These results are likely

the result of the change in predominant groundwater flow direction from generally southward (as

shown on Figure 9 of the USGS Report) to the northeast, as described above.

Figure 20 shows the overall trend of TCE concentrations measured at well CC-5 during the Pre-

Design Investigation, the Remedial Investigation and the data collected prior to the Remedial

Investigation. This graphical display shows a steady decrease in concentration with time. As

TCE was the only compound detected in residential well samples collected during the Pre-Design

Investigation, this compound was selected to provide a temporal comparison. Figure 21 presents

a similar graph of TCE concentration with time for residential well DW-41. The decrease in

concentration is far more pronounced, providing further support to the observed change in

groundwater flow direction and possibly the effects of natural attenuation of remnant

groundwater constituents. Historic data for wells CC-5 and DW-41 were taken from Appendix B

of the Data Summary Report (CH2MHill, November 1994) and Appendices A2-3 and A4-2 of

the Remedial Investigation Report.

4.3.5 Valley Creek Assessment

Based on the more complete understanding of groundwater flow and the analytical data presented

above, the results of the Pre-Design Investigation indicate that the Site cannot impact water

quality in Valley Creek. Further, the current hydrogeologic conditions do not support the

monitoring of Valley Creek as part of the MNA program for FDA/MA groundwater. This section

summarizes the assessment of potential site groundwater impacts to Valley Creek as determined

during the Pre-Design Investigation. The Pre-Design Investigation results, the evaluation of

PADEP's previous surface water monitoring results, in conjunction with pertinent hydrogeologic

findings of the Pre-Design Investigation, are summarized below:

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• As discussed above, the predominant direction of groundwater flow is northeasterly inthe vicinity of the FDA/MA while Valley Creek is located southeast of the FDA/MA.

• The elevation of the creek as it passes to the south of Hillbrook Circle is between 330 and350 feet MSL. This is substantially higher than the groundwater elevation in the vicinityof the FDA/MA (which ranges from 295 to 320 feet MSL).

• Pertinent field observations of Valley Creek accessed from Conestoga Road are shown onFigure H-l in Appendix H. Notably, the stream channel was dry and/or exhibited onlylow flows at several locations in the vicinity of the Site.

• The results of the "Aquatic Biology Investigation" conducted from June 8, 1993 toJanuary 12, 1994 provided by PADEP show that VOCs were not detected in surfacewater in any of the six stations in the vicinity of the Site along Conestoga Road north ofRoute 202 (see Appendix H). Certain VOCs were detected in surface water south ofRoute 202 well beyond the Conestoga Road/Phoenixville Pike intersection anddownstream of the confluence with other streams with no hydraulic relationship to theSite and/or groundwater plume.

• Similarly, the results of the PADEP investigation conducted in August 2000 also did notshow VOCs (except for low sub ppb levels of MTBE and chloroform) in samplingstations nearest the site (Stations 1 through 6 on Figure H-2 in Appendix H). AlthoughVOCs were detected south of Route 202 in Station 7 downstream of the confluence witha tributary to Valley Creek and further downstream, these detections cannot be attributedto the Site.

4.3.6 FDA/MA Groundwater Summary

The Pre-Design Investigation data indicate that there has been a change in groundwater flow

direction from that measured during and prior to the Remedial Investigation. The current

northeasterly groundwater flow direction is supported by all the data collected during the Pre-

Design Investigation, indicating that the groundwater divide identified during previous

investigations is no longer present. One apparent reason for the change in groundwater flow

direction is considered to be the discontinuance of pumping from the former public supply and

residential wells south of the FDA/MA.

In the immediate vicinity of the FDA/MA, hydraulic gradients are low, resulting in advective

groundwater velocities on the order of 1165 ft/yr. Long-term continuous water level monitoring

data show all wells'respond in a very similar manner indicating the bedrock aquifer system is well

connected and can be generally characterized as a more diffuse, fracture-flow system, rather than

a karstic, conduit flow system.

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Groundwater sample analyses results for wells in the immediate vicinity of the FDA/MA are

generally consistent with those collected during the Remedial Investigation. However, to the

south of the FDA/MA, there is a trend of stable or decreasing VOC concentrations, while in one

well to the northeast (CC-9), concentrations of VOCs appear to be slightly increasing. In the

residential wells, a pronounced decreasing trend in the concentration of TCE is observed in DW-

41. The more pronounced VOC concentration trends observed in Hillbrook Circle are believed to

reflect the change in groundwater flow direction, as the system recovers from the previous public

supply and residential well pumping to the south of Hillbrook Circle, as well as the effect of

natural attenuation processes.

4.3.7 FDA/MA Groundwater Design Considerations

Sufficient hydrogeologic data have been obtained during the Pre-Design Investigation to

effectively move forward with the design of the MNA system. Continuous long-term

groundwater level monitoring data will continue to be collected throughout the spring and

summer months to provide a full year's database from which to confirm groundwater flow

directions and selection of monitoring wells for the detailed design of the selected USEPA ROD

MNA program for FDA/MA groundwater.

Furthermore, a groundwater level monitoring program will be conducted during the

implementation of the FDA/MA groundwater MNA remedy to provide an ongoing

assessment of groundwater flow direction. This monitoring program will include both

retrofitted residential wells in Hillbrook Circle, and monitoring wells in the FDA/MA. In

the unlikely event that groundwater flow directions change substantially from those

currently observed, a contingency monitoring plan will be implemented which, based on the

changed flow conditions, will identify the need for and scope of any additional monitoring

including the need to monitor water quality in Valley Creek. In light of the data collected

tkiring the Pre Design Investigation, it-appears that the MNA program wi l l incorporate

monitoring of wells in the FDA/MA nr; well as downgradient locations to the northeast. The data

-support inc luding Valley Crook in the MNA program ax it is hydraul ical ly upgradient from

The contingency monitoring plan will be developed as part of the design of the FDA/MA

MNA system. In addition, the design will address the abandonment and possible

replacement of well CC-11 given the suspect conditions in this well.

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4.4 MPA Groundwater Investigation Results

4.4.1 Hydraulic Gradients

Hydraulic gradients in the vicinity of the MPA are higher than measured in the FDA/MA, as seen

from Figures 12 and 13. Based on the Pre-Design Investigation water levels, the horizontal

gradients in the vicinity of the MPA average 8.5xlO"3, and are fairly consistent across the MPA

and downgradient areas. These hydraulic gradients result in average Darcy velocities of 20 ft/yr,

along the main axis of the plume (i.e., GW-1 to GW-4) and assuming a porosity of 10%, the

average advective groundwater velocity is approximately 202 ft/yr, as shown on Table 6. The

average hydraulic conductivity values used in these calculations are based on the results of

the slug tests, which are presented in Table 8.

Table 7 presents the vertical hydraulic gradient measured between wells CC-6 and CC-13, based

on the water levels measured dunng the Pre-Design Investigation, and shows the vertical

gradients to be upward and range from 1.7xlO"3 to 3.4xlO"2. This is consistent with the Remedial

Investigation data, which showed upward vertical gradients ranging from 7.0xlO"J to 9.8xlO"3.

The source of the upward gradients is likely the influence of the Chickies ridge to the north

and/or the contact fault between the Chickies and carbonates.

4.4.2 Fracture Interconnectedness

Figure 22 presents a graph of water levels with time recorded during the drilling of wells GW-1,

GW-2 and GW-3. As shown, all of the wells that were monitored respond in the same manner to

hydraulic pressures created during drilling, indicating that the groundwater flow system is

dominated by interconnected, diffuse fracture-flow.

Figure 23 presents a graph of water level and precipitation with time recorded at well CC-2, CC-

6, GW-2 and GW-3. As can be seen from this graph, there is little immediate response to

precipitation events, and the response of well CC-2, CC-6 and GW-2 are all very similar. Again,

these results are more consistent with interconnected fractured bedrock flow rather than discrete

conduit karstic flow. GW-3 responds somewhat differently as a result of a markedly lower

hydraulic conductivity.

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4.4.3 Aquifer Performance Testing

The hydraulic testing conducted as part of the Pre-Design Investigation included slug testing of

the new wells, and re-analysis of the pumping data from the Remedial Investigation pumping

tests. The slug testing results are shown in Table 8, and the analysis is presented in Appendix I.

The slug testing results indicate a wide range in hydraulic conductivity from 2.97x10"7 cm/sec at

well GW-3 to 4.05xlO~3 at well GW-5. Exceeding the low conductivity in the vicinity of well

GW-3, the hydraulic conductivities range from 5.1xlO"4 to 4.1xlO"3 cm/sec along the axis of the

plume.

Data collected during the Remedial Investigation pumping tests were reanalyzed using the

FlowDim software developed by Golder Associates. FlowDim utilizes different flow models to

assess aquifer properties at different zones around a monitoring well borehole. Utilizing this

approach, a good correlation between the hydraulic conductivities for the inner and outer zones of

wells CC-21 and CC-19 was observed (i.e., the outer zone of one well is comparable with the

inner zone of the other well). This correlation provides a higher degree of confidence in the

hydraulic conductivity values calculated for these two wells. The inner zone for well CC-21 and

the outer zone for well CC-19 have similar hydraulic conductivities of 1.34x10 3 and 2.68xlO"3

cm/sec, respectively. The outer zone for well CC-21 and the inner zone for well CC-19 had

similar hydraulic conductivity values of 4.82xlO"4 and 9.68xlO"4 cm/sec, respectively. These

results are consistent with the results of the slug testing that indicate higher conductivities toward

the northern part of the MPA and lower conductivities te-toward the southern and eastern

portions of the MPA.

4.4.4 DNAPL Investigation

The downhole video logging of wells CC-6 and CC-13 did not indicate the presence of DNAPL,

consistent with the earlier investigations completed at the Site. These results were confirmed by

an oil/water interface probe measurement, which also did not identify free phase liquid. Based on

these results, it is concluded that a free phase or a recoverable DNAPL source does not exist in

the area of CC-6 or CC-13. The data are potentially indicative of the presence of residual source

material confined within the overburden and/or discrete bedrock fractures.

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4.4.5 Geochemical Data

4.4.5.1 VOC Results

Figure 24 presents the VOC results of the initial phase of groundwater sample analyses (i.e.,

following the installation of GW-1, GW-2, and GW-3), and Figure 25 presents the corresponding

results of the natural attenuation parameter analyses. The laboratory sample analyses results are

presented in Appendix E-4. The results indicate that in the vicinity of wells CC-6, CC-7 and CC-

13 (i.e., the source area), VOC concentrations were elevated (e.g., TCE at 82,000 ug/L at CC-6)

relative to the further downgradient wells in the MPA. Historically, however, VOC

concentrations in wells CC-7 and CC-13 exhibit a decreasing trend. Toward the northeast (i.e.,

along the interpreted centerline of groundwater flow), the concentrations of TCE at GW-1 were

23,000 ug/L, which is approximately one-fourth the concentration observed at CC-6. A similar

drop in PCE concentration was also observed between the source area and GW-1. To the east and

south of the interpreted centerline of groundwater flow, the concentration of VOCs declines

rapidly, as evidenced by low to non-detect concentrations at wells GW-2 and GW-3, respectively.

The initial monitoring well installation and sample analyses resulted in the installation of two

additional wells further downgradient along the interpreted centerline of the plume. These two

wells, GW-4 and GW-5 were surveyed and sampled following their installation. Well GW-1 was

also sampled concurrently to verify the concentrations observed previously. The results of the

second round of sample analyses are presented on Figure 24 and in Appendix E-4. The results of

the second sampling event indicate substantially lower VOC concentrations at the downgradient

wells with TCE concentrations ranging from 170 ug/L (GW-4) to 390 ug/L (GW-5), and PCE

concentrations ranging from 23 ug/L (GW-4) to 54 ug/L (GW-5). During the second sampling

event, TCE was detected at a concentration of 32,000 ug/L in GW-1, which is comparable to the

concentration detected in the initial sampling event. Figures 26 through 28 show the interpreted

isoconcentration contour maps for PCE, TCE, and cis-1,2 DCE. These figures combine the data

collected from wells GW-4 and GW-5 with that collected during the initial sampling event for all

the other MPA wells.

Close examination of the groundwater chemistry and hydrogeologic data provide boundaries to

the lateral extent of the VOC plume to the north and to the south and east. These results indicate

a relatively narrow plume, probably controlled by local bedding features. The extent of VOC

impacts in groundwater is bounded to the south and east, as shown by analytical data collected

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from wells CC-23, GW-2 and GW-3. The concentrations of total VOCs decrease considerably in

both a southerly direction (42 ug/L at CC-22 to 12 ug/L at CC-20; and, 28 ug/L at GW-2 to 6

ug/L at GW-3) and in an easterly direction along the southern limit of the plume (55 ug/L at CC-

19 to 12 ug/L at CC-20 to 6 ug/L at GW-3). These results are also consistent with the lower

hydraulic conductivities observed in the southern wells.

To the north, the plume is bounded by the contact fault between the Chickies Formation and the

carbonate rocks of the Ledger/Elbrook Formation. This contact acts as both a physical and

hydraulic barrier preventing groundwater from flowing further to the north. While quantitative

hydraulic data confirming groundwater flow characteristics across the fault contact are not

available, based on a review of the available published data (e.g., U.S. Geological Survey

Reports) the Chickies Quartzite is typically a poor water-bearing unit, which would indicate

lower hydraulic conductivity values. Observations made during the Field investigation in

support of the PDI, and a review of the RI/FS Report for the Site, indicate that the Chickies

Quartzites can be considered generally more resistant to erosion, hence forming the ridges

that comprise the North Valley Hills. Given this character, hydraulic gradients across the

fault contact between the Chickies Quartzites and the carbonate rocks are likely quite steep

and directed away from (i.e., southerly) the North Valley Hills into the carbonate lowland

below. In addition, the Field geologic mapping conducted during the PDI (as discussed in

Section 4.2) positioned the contact between the Chickies Quartzite and the Ledger further

to the south than previous regional mapping completed by USGS. Given the lower

hydraulic conductivity of the Chickies, the generally higher topographic relief, and the

more southerly location of the contact, and in consideration of the PDI groundwater

elevation and chemical data, the overall impact on groundwater can only be diversion of the

flow from the MPA toward the northeast-east, parallel to the fault contact between these

formations.

Vertically, the analytical data indicate that concentrations decrease considerably with depth in the

vicinity of well CC-13. The boring log for well CC-13 indicates a fracture at a depth of 135

feet bgs, which was flowing at an approximate rate of six gpm. Below this depth, no other

fractures or flowing features were noted. This condition is not uncommon as fracture

intensity and aperture frequently decrease with depth. During sampling of CC-13, the

pump was placed at 135 feet bgs to draw water specifically from this feature. While the

longer open interval in CC-13 may result in some limited dilution of VOC concentrations,

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the objective of the low-flow purge sampling method is to collect representative

groundwater samples from the aquifer at a specific interval. Therefore, the results of the

sample analyses are considered to be representative of groundwater flowing within the

deeper portions of the bedrock beneath the MPA. Consequently, biased on the observed

vertical VOC concentration decrease, in conjunction with the observed upward gradients, it is

reasonable to conclude that the plume in the area of the Site is limited in the vertical direction.

4.4.5.2 Conventional Treatment Parameters

Conventional parameters were collected from a select subset of the monitoring wells in order to

provide design information for the groundwater treatment train. The parameters that the samples

were analyzed for include COD, calcium, hardness dissolved iron, ammonia, total suspended

solids, and methylene blue activated substances (MBAS). In general, the concentrations of these

parameters should not restrict the use of conventional groundwater treatment technologies,

however this will be further evaluated during the detailed design.

4.4.5.3 Natural Attenuation Parameters

Appendix J presents the results of the natural attenuation assessment of the source and

downgradient portion of the MPA groundwater plume. A brief discussion of this assessment is

provided below.

Figures 29 and 30 present the interpreted isoconcentration contours for select natural attenuation

parameters sulfate, and ethene. As seen on Figure 29, sulfate depletion is occurring within the

source area with the greatest depletion occurring at well CC-7. This sulfate depletion is

coincident with the maximum detected 1,2-DCE concentration (Figure 28), and is indicative of

natural biological degradation processes occurring in the source area. The results also show

substantial ethene production indicative of complete biological degradation endpoints. As shown

on Figure 30, elevated ethene is observed in the vicinity of wells CC-6 and GW-3. The higher

concentrations observed at well GW-3 may be the result of fluctuating levels of biological

activity, which produce a "slug" type release of biological end-product compounds and/or ethane,

becoming trapped within the low conductivity strata. Notably, GW-3 also exhibited the lowest

VOC concentrations and hydraulic conductivities of any of the downgradient MPA wells.

Evidence that effective natural attenuation is occurring is further supported by the observation

that concentrations within MPA wells have been declining since the mid-1990's. Figure 31

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presents a graph of total VOC concentration versus time for wells CC-3, CC-7, CC-19 and CC-

21. At well CC-7, concentrations have dropped to nearly 50% of their original concentrations

(60,000 ug/L to 30,000 ug/L), whereas at well CC-3, concentrations have dropped by almost 80%

(18,500 ug/L to 3,400 ug/L). In the wells further downgradient, similar percentage drops are

observed. Clearly, these decreases in concentration, in the absence of any remedial measures on-

site, are the result of natural attenuation.

An estimate of VOC decay rates along the plume axis measured from CC-6 to well GW-1 then to

well GW-5 on Aston Road was made using the USEPA's BIOCHLOR software. This analysis

yielded decay rates corresponding to half-life values of 150 days for PCE and TCE, and slightly

higher values for cis-l,2-DCE and vinyl chloride. The PCE and TCE half-life times are within

the range of published values indicative of reductive dechlorination. Some abiotic natural

attenuation may be contributing to the higher than normal decay rates for cis-l,2-DCE and vinyl

chloride.

Overall, given the sulfate depletion, ethene production, decreasing concentrations (both temporal

and spatial) and documented decay rates for PCE and TCE consistent with published literature,

biological natural attenuation is effectively reducing VOC concentrations within the source area

arid downgradient plume.

4.4.6 MPA Groundwater Summary

Continuous water level responses measured during the drilling and installation of the new MPA

monitoring wells along with the well yields reported in the Remedial Investigation indicate that

the local hydrogeologic system in the MPA can be characterized as a diffuse flow system that is

interconnected and exhibits slow responses to precipitation conditions. The groundwater flow

direction identified during the Pre-Design Investigation is from CC-6 toward GW-1 in a

northeasterly direction, then flowing toward GW-4 and GW-5. The direction of groundwater

flow is likely influenced by hydraulic stresses imposed by regional pumping on the fault contact

between the Chickies formation north of the Site and underlying carbonate bedrock. The

northeasterly strike of the bedrock is also expected to locally influence groundwater flow.

Horizontal hydraulic gradients are in the range of 7xlO"3 to IxlO"2 . Hydraulic testing, in the form

of slug testing and reanalysis of Remedial Investigation pumping data indicates that the hydraulic

conductivity in the vicinity of the MPA is generally in the range of 3xlO"7 cm/sec to 4x10°

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cm/sec, while along the mam plume axis the hydraulic conductivity ranges from SxlO"4 to 4xlO"3.

These results yielded an average advective groundwater velocity of 202 ft/yr. Lower hydraulic

conductivities were observed along the southern limit of the plume, particularly at well GW-3.

Vertical gradients measured during the Pre-Design Investigation are consistent with those

measured during the Remedial Investigation and were shown to be upward, believed influenced

by pressures generated from the Chickies ridge north of the Site.

Sample analyses results show VOC impacts in groundwater characterized by on-site source area

TCE concentrations of 82,000 ug/L, and PCE concentrations of 9,600 ug/L. Following the

hydraulic flow field and approximately 90 feet downgradient of the source, VOC impacts are

reduced by over three times and are characterized by TCE concentrations of 23,000 ug/L and

PCE concentrations of 3,600 ug/L observed at GW-1. These concentrations further attenuate by

the time groundwater reaches GW-4 and GW-5, which lie only about 450 feet from GW-1. At

these locations, TCE concentrations are in the range of 170 to 390 ug/L, and PCE concentrations

are in the range of 23 to 54 ug/L. Other monitoring wells outside of the source area, also exhibit

decreasing concentration trends. VOC concentrations have been decreasing both temporally and

spatially as exhibited in wells CC-3, CC-7, CC-19, and CC-21 where VOC concentrations have

decreased considerably since the Remedial Investigation. The following summarizes the

observed decrease in VOC concentrations along the plume axis.

PCETCE

SourceConcentration ug/L

82,0009,600

% Reduction from SourceGW-172%62%

GW-4/GW-5>99%>99%

The VOC plume configuration is narrow, bounded to the south and east by geologic and

hydrogeologic factors such as local bedding features (i.e., along strike in the weathered troughs)

and low conductivity to the southeast. This configuration is demonstrated by the analytical data

collected at monitoring wells CC-23, GW-2 and GW-3, which show decreasing concentrations to

6 ug/L total VOC at GW-3. To the north, the plume is physically and hydrauhcally bounded by

the fault contact with the Chickies Formation. Vertically, the plume is believed to be limited,

particularly in the area of the Site as evidenced by the observed decrease in concentration with

depth, and the upward hydraulic gradients observed between well CC-7 and CC-13.

Natural attenuation processes have been documented to be effective as evidenced by the

substantial decreases in VOC concentration noted above, combined with the production of

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compounds associated with reductive dechlonnation (i.e., ethene), and reduced sulfate

concentrations in the source area. Decay rates of PCE and TCE using USEPA1 s BIOCHLOR

model are consistent with effective natural biological dechlorination rates in published literature.

4.4.7 MPA Groundwater Design Considerations

The data collected during the Pre-Design Investigation is sufficient to move forward with the

detailed design of a groundwater source control system and a MNA program for the

downgradient portion of the plume. Currently, it is envisioned that the source control system will

involve hydraulic control of the plume in the vicinity of well GW-1. It is anticipated that an

additional monitoring well will be required in the area to the north of GW-1 in order to

provide adequate monitoring coverage for the MPA groundwater remedy. This additional

monitoring point will provide both hydraulic and geochemical data in this area of the Site.

Details regarding the exact location and depth will be established concurrent with the

design of the MPA groundwater remedy so that the most appropriate location can be

selected.

Given the observed natural attenuation rates and relatively limited plume configuration, in-situ

treatment options are being considered in addition to conventional methods. In particular, one in-

situ treatment alternative that is being considered is accelerated biological treatment with in-situ

biological treatment enhanced by an aboveground addition of bioamendments and reinjection

immediately upgradient and/or within the source area. This treatment process will take advantage

of the existing in-situ biological treatment processes that are already occurring. Furthermore,

enhanced in-situ biological treatment is potentially able to provide more effective and faster

remediation of source area impacts particularly if residual source materials are present in bedrock

fractures.

While these various treatment alternatives will not substantially impact the design of a hydraulic

control system, they do impact the design of the reinjection system, as the location of reinjection

would be different (an enhanced remediation remedy would inject groundwater in the immediate

vicinity of the source area, whereas groundwater would be reinjected downgradient or

sidegradient from the source area if conventional treatment were used). In order to verify the

effectiveness of m-situ enhanced biological treatment of the source, the CSDG is considering the

implementation of a pilot study as discussed with USEPA on March 5, 2002. Should the USEPA

concur with this approach, a pilot study workplan will be submitted to USEPA, which will outline

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field procedures and laboratory testing that will be undertaken to demonstrate the effectiveness of

enhanced in-situ biological treatment of the MPA groundwater source area.

With respect to the MNA program for the downgradient portion plume, given the documented

rapid VOC decay rates observed during the Pre-Design, VOC impacts greater than the MCLs are

not expected to extend greater than 600 feet downgradient of GW-4 and GW-5. The

downgradient area of impact is expected to be further minimized by flow from other portions of

the drainage basin along the contact being influenced by regional pumping. Therefore, wells

GW-1, GW-4, and GW-5, which all lie within the predominant groundwater flow path from the

MPA and which extend along the axis near the interpreted plume boundary, provide reasonable

monitoring locations from which to measure the effectiveness of the source control and MNA

remedial actions for MPA groundwater. Refinements to this monitoring system wi l l bo evaluated

and defined dur ing detail design.

Groundwater level monitoring will be conducted throughout the implementation of the

MPA groundwater remedy in order to provide an ongoing assessment of groundwater flow

directions. In the unlikely event that the groundwater flow directions change substantially

from those currently observed, a contingency monitoring plan will be implemented which,

based on the changed flow conditions, will identify the need for and scope of any additional

monitoring to further assess the changed flow conditions. The groundwater monitoring

plan for the MPA groundwater remedy, including the contingency monitoring plan will be

developed during design.

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5.0 SCHEDULE

Figure 32 provides a projected schedule for the upcoming remedial design activities. The

schedule incorporates specific project details presented in this PDI Report. The following

provides additional discussion of some of the more notable schedule items:

• Focused Feasibility Study - USEPA is expected to complete the final review of theFocused Feasibility Study Report in mid-October 2002. A public information session hasbeen tentatively scheduled for October 9, 2002 to convey USEPA's plans to implementan alternative SVE remedy for FDA/MA soils. The design of the SVE system willcommence following USEPA's approval of the alternative SVE remedy (estimatedNovember 1, 2002). It is intended that the design of the SVE system will be completedin spring 2003 to allow sufficient schedule for solicitation of bids, finalize contracts,complete the construction of the SVE system, and begin operation in late 2003.

• Preliminary Design of Remedy Components - As no refinements to the USEPA RODRemedy are proposed for MPA soils and FDA/MA groundwater, the design of theseremedy components can begin following USEPA's final comment on the PDI Report(projected mid-October 2002). This schedule will allow the design of these componentsto begin on or about November 1, 2002. In addition, should USEPA agree to thealternative FDA/MA soil SVE remedy as discussed above, then the design of the SVEsystem for FDA/MA soils can begin on or about November 1, 2002.

• In-Situ Enhanced Biological Treatment Pilot Study - The CSDG is considering analternative treatment technology for the MPA groundwater system. At this time it isexpected that the CSDG will provide the USEPA with a submittal conceptuallydescribing the enhanced biological treatment system and detailing a proposal for a pilotstudy to field test the effectiveness of in-situ enhanced biological treatment of the MPAgroundwater source. The schedule assumes that, if acceptable, USEPA would includelanguage allowing for the consideration of alternative treatment approach for MPAsource area groundwater in the anticipated ROD modification for the alternativeFDA/MA soil remedy. As such, the schedule depicts design of the MPA groundwaterremedy following completion of the pilot study (estimated 6 months), presentation of theresults, and approval from USEPA (estimated 2 months).

The specific schedules for completion of the Preliminary Design and the remaining design tasks,

i.e., the 60% (if needed), 90%, and 100% Designs, are dependent upon a number of factors

described above, and, therefore, are not shown on Figure 32. The schedule of these activities will

be more fully developed following USEPA's approval of the PDI Report when the details of the

various remedy components and design direction are better defined.

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FIGURE 32PROJECTED PROJECT SCHEDULEMALVERN TCE SUPERFUND SITE

May June July Aug. Sept

Respond to Comments

USEPA Approval (est.)

Focused Feasibility Study

Respond to Comments

USEPA Approval (est.)

MPA Soil-Cover Remedy

FDA/MA Alternative Soil Remedy

FDA/MA Groundwater MNA Remedy

MPA Enhanced Biological Treatment Pilot StudyPrepare / Submit Pilot Study Work Plan

USEPA Review / Address Comments

USEPA Approve Pilot Study Work Plan

Implement Study / Present Results to USEPA

USEPA Approves Pilot Study and

Alternative Groundwater Remedy

MPA Alternative Groundwater Remedy Dsgn

SVE System Bid. Contract*. Coratfuction

roCOCD4T-roCO

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ATTACHMENT C

REVISED FFS REPORT PAGES AND FIGURE

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TABLE OF CONTENTS

Cover Letter

Table of Contents i

SECTION PAGE

1.0 INTRODUCTION 11.1 General Site Description 11.2 Background 2

2.0 BASIS FOR CONSIDERATION OF AN ALTERNATIVE SOIL REMEDY 42.1 Remedial Design Contingency Plan (Appendix C to RDWP) 52.2 USEPA Remedy Update Directive 52.3 USEPA Superfund Reforms 62.4 Refined USEPA ROD Remedy Cost Estimate 6

3.0 CONCEPTUAL SITE MODEL - FDA/MA SOILS 73.1 Surrounding Area 73.2 Site Geology 73.3 Nature and Extent of Constituents in Subsurface Soil 73.4 Summary of FDA/MA Soil Exposure Risks 9

4.0 DESCRIPTION AND TECHNICAL EVALUATION OF THE ALTERNATIVESOIL REMEDY 114.1 Remedial Action Objectives 114.2 Description of Alternative Soil Remedy 11

4.2.1 Site Preparation 124.2.2 SVE Well Installation 134.2.3 Collection and Treatment Systems Installation 144.2.4 System Operation and Performance Evaluation 154.2.5 Closure Activities 164.2.6 Alternative Soil Remedy Summary 16

4.3 Alternative Soil Remedy Performance Assessment 164.3.1 Summary of On-Site SVE Pilot Study Results 174.3.2 SVE as a USEPA Presumptive Remedy 184.3.3 Previous Evaluation of SVE by USEPA 194.3.4 Summary of Performance Assessment 20

5.0 DETAILED ANALYSIS OF THE ALTERNATIVE SOIL REMEDY 215.1 Protection of Human Health and the Environment 215.2 Compliance with ARARs 215.3 Long-Term Effectiveness and Permanence 225.4 Reduction of Toxicity, Mobility, or Volume 235.5 Short-Term Effectiveness 235.6 Implementability 245.7 Cost 255.8 State and Community Acceptance 25

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6.0 DETAILED COMPARISON OF THE ALTERNATIVE SOIL REMEDY TO THEUSEPA ROD REMEDY 266.1 Comparison of Potential VOC Mass Removal 26

6.1.1 Alternative Soil Remedy 266.1.2 USEPA ROD Soil Remedy 27

6.2 Threshold Requirements 276.2.1 Overall Protection of Human Health and the Environment 276.2.2 Compliance with ARARs 28

6.3 Balancing Criteria 286.3.1 Long-Term Effectiveness and Permanence 286.3.2 Reduction of Toxicity, Mobility or Volume 296.3.3 Short-Term Effectiveness 306.3.4 Implementability 326.3.5 Cost 32

6.4 State and Community Acceptance 34

7.0 SUMMARY 35

8.0 REFERENCES 36

In OrderFollowing

Page 36LIST OF TABLES

Table 1 Alternative Soil Remedy Cost EstimateTable 2 Revised Cost Estimate for USEPA ROD FDA/MA Soil Remedy Expanded to

Address the Extent of VOCs Identified During the Pre-Design Investigation

LIST OF FIGURES

Figure 1 Site Location MapFigure 2 Site LayoutFigure 3 Generalized Fence DiagramFigure 4 FDA/MA Subsurface Soil Characterization (Phase I)Figure 5 FDA/MA Subsurface Soil Characterization (Phase II)Figure 6 Interpreted Zones of VOC Exceedances of ROD SCSFigure 7 Conceptual Layout of SVE for FDA/MA SoilsFigure 8 Preliminary SVE Well Location Plan

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4.0 DESCRIPTION AND TECHNICAL EVALUATION OF THE ALTERNATIVESOIL REMEDY

This section provides a description of the Alternative Soil Remedy, including a technical

evaluation of the effectiveness of the SVE technology applied to FDA/MA soils.

4.1 Remedial Action Objectives

Given the results of the Baseline Risk Assessment presented in Section 3.4 of this Focused

Feasibility Study, the principal objective for remediation of subsurface soil in the FDA/MA, as

stated in the USEPA ROD, is "to reduce the potential for continued migration of contaminants in

these soils to the groundwater." USEPA developed the ROD SCS for VOCs based on the

groundwater protection objective as presented in the USEPA Technical Memorandum dated

December 20, 1996. The SCS were presented in the USEPA ROD as conservative standards to

guide the excavation remedy toward achieving the overall groundwater protection objective.

Notably, the concern for PCBs raised in the USEPA ROD focused on potential ecological

impacts, not potential impacts to groundwater. Therefore, the remedial action objective for PCB

remediation is to minimize ecological receptor exposures to PCBs in soils.

4.2 Description of Alternative Soil Remedy

Based on the results of the Pre-Design Investigation, VOCs are the primary constituents of

concern in FDA/MA soils and extend at concentrations exceeding the ROD SCS across the

FDA/MA to depths of about 30 to 35 feet bgs. PCBs are not a remedial concern in the MA. In

the FDA, PCBs marginally exceeding the ROD SCS were sporadically detected, primarily at

shallow depths. The deepest detection of PCBs exceeding the ROD SCS was at boring location

GB-35 (4.6 mg/kg at 16 feet bgs).

An Alternative Soil Remedy has been developed to address the above soil impacts and to achieve

the remedial action objectives for FDA/MA soils in a reliable and cost-effect manner. An SVE

system will accomplish the primary remedial action objective, namely, protection of groundwater

from future VOC impacts. Excavation of the limited shallow PCB impacted soils and adequate

cover over the remaining few isolated areas of deeper PCB impacts will accomplish the

ecological receptor protection objective.

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The Alternative Soil Remedy involves five major stages of implementation: site preparation

(which will accomplish the required PCB remediation), SVE well installation, VOC collection

and treatment systems installation, SVE system operation and performance evaluation (which will

accomplish the required VOC remediation), and closure.

4.2.1 Site Preparation

During typical site preparation for SVE systems, grading operations are performed to create a

generally flat working surface. Limited excavation of shallow PCB impacted soils is also

necessary to minimize ecological exposures and thus will be accomplished as part of site

preparation. As discussed previously, PCB impacts to MA soils are not a remedial concern.

Soils in the FDA impacted with PCBs at concentrations above the SCS will be excavated to a

depth of 2 feet and re-filled and graded with clean soil (18 inches of general fill covered with 6

inches of topsoil) as determined during remedial design to maintain proper grades.

The soil piles in the FDA area will also be removed or regraded as necessary based on the overall

grading plan prepared during detailed design and the results of sample analyses to be conducted

during remedial action. Soil piles, surface soil, and the remnant roll-off contents with

constituents at levels that exceed the ROD SCS will be removed and disposed of off-site. Soil

piles having PCB (and VOC) concentrations below the SCS will be used as grading material to

help fill in the surficial PCB excavation areas and other low lying areas.

The two partially water-filled excavations in the FDA are intended to be used as SVE extraction

galleries. Initially, the accumulated water will be removed from the two excavations during the

site preparation stage. The water will be tested and disposed of accordingly. To improve

pneumatic connection between the extraction galleries and surrounding subsurface soils, 2 feet of

sidewall and base materials (which have likely clogged with fine particles and vegetative debris

over the years) will be removed from the excavations and disposed of along with other impacted

soils removed from the FDA. The excavations will then be filled with a material having a higher

pneumatic permeability than the surrounding soils and covered with a low permeability layer to

mimic the upper clay low permeability cover over the interbedded zone that lies across the

remainder of the FDA/MA. The removal of this 2-foot soil/sediment layer from the sides and

bottom of the excavations will result in the removal of additional PCBs.

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Completion of the Site preparation work will leave only two measured PCB exceedances of the

ROD SCS. These two exceedances occur at depths between 10 and 16 feet bgs, which are

inaccessible to ecological receptors.

Grading will also be performed in the MA. When completed, site preparation will provide a

relatively clear and flat working surface to build and operate the SVE system and will have

accomplished the USEPA ROD objective for PCBs by providing protection of ecological

receptors.

Preparation activities also include improving the access road along the railroad right-of-way;

building a road crossing of the pipeline right-of-way; removing the fence around the FDA (where

needed to implement the remedial action in the area); installing a temporary fence around the

working area; and removing an old roll-off container and other debris if encountered and

characterizing and disposing of such items as appropriate. A contingency plan will also be

developed for the handling and removal of drum carcasses, if any are uncovered during the Site

preparation work.

4.2.2 SVE Well Installation

As shown on Figure 7, the SVE wells designed to remove VOCs from the lower portion of the

upper clay and throughout the interbedded zone will be installed at a 35-foot lateral spacing with

screens extending from about 5 feet below ground surface (feet bgs) to approximately 25 to 35

feet bgs. The results from the SVE pilot study demonstrated a 25-foot radius of influence (ROI).

Therefore, the 35-foot spacing provides more than 30% overlap of influence from adjacent SVE

wells.

Figure 8 shows a preliminary layout of the SVE wells and the interpreted extent of the zone

of influence effected by the SVE wells based on a 25-foot ROI. As shown on this figure, the

influence of the perimeter wells extends beyond the currently delineated lateral extent of

VOCs. Confirmation of this delineation will be carried out during installation of the SVE

wells. Soil samples will be collected from perimeter SVE well borings adjacent to existing

delineation borings VP-5, GB-29V, and GB-29 in the northern portion of the MA and

adjacent to GB-34 in the southern portion of the FDA. The samples will be field screened

and if necessary analyzed in a laboratory to confirm the delineation. Additional SVE

well(s) may be constructed and sampled to confirm that the SVE system addresses the

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extent of VOC impacts. The SVE well layout, specific screen interval and depth at each well

will be based on the Pre-Design Investigation results (e.g., boring logs and subsurface soil sample

analyses results) and will be finalized during design. The design will also specify procedures

for the perimeter confirmation sampling described above. Additional SVH vvcll(s) may be

to confirm that the SVK system addresses the extent of VOC impact*.

The deep wells used to extract VOCs from the lower clay below the interbedded zone will also be

installed at a 35-foot lateral spacing, as shown on Figure 7. Fewer wells are installed in this zone

as the lateral distribution of VOC impacts at depth are substantially less. The length and depth of

screens will be based on the Pre-Design Investigation boring results, which provided an overall

vertical delineation of VOC impacts and top of bedrock. Refinements to the screen settings, if

necessary, will be accomplished using borings installed during SVE well installation.

Water levels measured during the PDI are consistent with those measured during the RI

and are within historical ranges. Consequently, it is not anticipated that a rise in

groundwater elevation will interfere with the operation of the SVE system over the

relatively short duration of its operation (i.e., less than 5 years). However, should the long-

term groundwater level monitoring implemented as part of the groundwater remedy

indicate that water levels could impact the operation of the SVE system, then an assessment

of potential operational changes and/or system enhancements would be made at that time.

4.2.3 Collection and Treatment Systems Installation

A series of wellhead assemblies, piping (underground and/or aboveground, heat-traced as

necessary), condensate collection traps (if needed); knock-out pot, blower system,

valves/controls; monitoring equipment; and other appurtenances will be installed. A temporary

fence will be installed around exposed equipment associated with the SVE system. Electrical

power will be brought to the FDA/MA. The SVE air emissions treatment system will likely

consist of vapor phase activated carbon units constructed in series2. The type, size, and details of

the SVE collection and treatment systems will be defined during detailed design. Sufficient

operational flexibility and capacity will be incorporated into the design to accommodate

modifications required by the installation of any necessary additional SVE wells.

For the purpose of this Focused Feasibility Study, the vapor phase treatment component of the Alternative SoilRemedy is assumed to be activated carbon. Other vapor phase treatment technologies may be considered duringdetailed design. Further, it may not be necessary to treat extracted VOC vapors during the entire period of operation,particularly in the later stages when potential VOC emissions will be substantially reduced. In any case, vapor phasetreatment will be provided to the extent necessary to comply with federal and state air emission regulations.

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4.2.4 System Operation and Performance Evaluation

During start-up operations, the SVE system will be balanced to optimize extraction flow rates,

VOC mass removal, and energy use. Long-term operation of the SVE system will be conducted

on a routine basis and will include monitoring of flow rate, VOC concentrations and system

vacuums. Ongoing adjustments of the system operation will be made as needed to optimize VOC

mass removal until the SVE system begins to reach the limits of the technology. This occurs

when the rate of mass removal begins to become diffusion limited and further continuous SVE

operation does not efficiently remove VOCs, i.e., the system begins to reach its asymptotic

endpoint.

It is anticipated that different portions of the system will begin to reach their asymptotic

endpoints at different times. To maximize the efficiency of SVE performance in these portions,

the operation of the effected wells will be switched to a cycling mode (singly or in clusters).

Cycled operation maximizes the rate of VOC mass removal by allowing sufficient time for

remaining low levels of VOCs to diffuse from the soil matrix to the vapor phase where they can

be extracted in a pulsed manner. Cycling operations will be adjusted as needed and continued

until the removal of the rebounding mass is negligible. Ultimately, the operational effectiveness

of the SVE system will reach the limits of the technology where, after cycling operation, the rate

of VOC mass removal asymptotically levels off to a point that is negligible as compared to the

energy expenditure needed to continue operation of the SVE system. This point is commonly

referred to as the asymptotic endpoint of an SVE system.

As discussed in Section 4.1, the principal objective of the SVE remedy is to provide

protection of groundwater and the FDA/MA groundwater remedy (monitored natural

attenuation). To accomplish this objective, the SVE system will be operated until the

limitations of the technology are reached as determined by VOC recovery (i.e., recoverable

VOC concentrations become diffusion limited). It is anticipated that all of the SVE wells

will be cycled to some degree, based on the recovery data, to meet the overall SVE remedy

objective. Specific SVE-well end-points will be developed on a well by well basis, with

USEPA concurrence, during remedy implementation. Upon reaching the end-points, post-

operational monitoring will be required to demonstrate that the completion of the SVE

remedy is protective of the groundwater remedy. Details of the post-operational monitoring

program will be developed during design. Following completion of the post-operational

monitoring program, the need for Institutional Controls, to address residual impacts

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following implementation of the SVE system, will be evaluated and, if needed, institutional

controls, will be made part of the final remedy. Specific criteria for defining the asymptotic

ettdpaint (i.e.. the SVK operation performance objectives) wi l l bo developed during detailed

design. — Once the VOC removal reaches asymptotic conditions, system operation wi l l be

4.2.5 Closure Activities

Once the SVE system reaches its performance objectives, and following USEPA's system shut-

down approval, the SVE system and wells will be decommissioned and removed from the Site.

Site restoration activities such as vegetating disturbed areas will be completed and the fence will

be removed. It is estimated that closure activities may commence within 2 to 5 years following

start-up of the SVE system.

4.2.6 Alternative Soil Remedy Summary

The Alternative Soil Remedy contains an excavation component similar to the USEPA ROD

Remedy for FDA/MA soils albeit at a much smaller scale. However, unlike the USEPA ROD

remedy, the Alternative Soil Remedy removes the majority of the VOCs from soil via SVE rather

than excavation, thus facilitating the removal of deeper VOC impacts identified in the Pre-Design

Investigation. The SVE system will not only effectively extract VOC from shallow subsurface

soil as contemplated by the USEPA ROD Remedy, it will also remove VOCs from deeper, less

accessible locations not considered in the USEPA Feasibility Study or ROD. Treatment of VOCs

will be accomplished off-site as part of the vapor phase carbon treatment/regeneration. Operation

and maintenance activities and performance monitoring will be conducted to ensure the long-term

effectiveness of the Alternative Soil Remedy for meeting the principle objective of the USEPA

ROD, namely groundwater protection.

4.3 Alternative Soil Remedy Performance Assessment

Since the signing of the USEPA ROD, significant new, site-specific technical information has been

developed that has allowed a more refined and conclusive evaluation of the performance of the SVE

technology applied to FDA/MA soils. In particular, an on-site SVE pilot study was performed. This

section discusses the evaluation of the performance of SVE in FDA/MA soils for meeting the overall

groundwater protection objective.

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4.3.1 Summary of On-Site SVE Pilot Study Results

Golder Associates conducted a program of full-scale field testing to assess the potential performance

of SVE and to satisfy the concern identified in the USEPA ROD, namely that there was insufficient

information to adequately evaluate the SVE technologies' effectiveness in site-specific conditions.

Notably, USEPA's Feasibility Study also identified the need to conduct a pilot study.

Success Criteria

The SVE pilot study was completed in the MA portion of the Site in accordance with the

USEPA-approved SVE Pilot Study Work Plan (PSWP; Golder, 2001b). In the PSWP, Golder

Associates specified the following operational criteria to be used to determine "success" of the

SVE system:

• Remove and sustain the removal of significant quantities of VOC mass with initialrecovery rates in excess of 1 pound per day;

• Achieve adequate air flow through the impacted soil zones, defined as an air flow rategreater than 20 standard cubic feet per minute (scfm) at vacuum levels less than 16 inchesof mercury (in Hg);

• Achieve a 30-day time interval radius of influence (ROI30) of 10 feet or greater;

• Soil air-phase permeabilities should be greater than lxlO"q cm2;

• Chemicals should be volatile and exhibit appropriate Henry's Law constants and vaporpressures for effective removal by SVE;

• Depth to water table should exceed 10 feet; and,

• Highly permeable fill or man-made passageways (i.e., sewers or pipe ways) should beabsent to minimize airflow short circuiting or preferential flow.

SVE Pilot Study Results

Results of the pilot study indicate that the SVE pilot system has met or exceeded the performance

criteria defined in the USEPA approved SVE PSWP for the FDA/MA as evidenced by the

following observations:

• Mass removal rates of approximately 18 pounds per day were attained (PSWP criteria - >1 Ib/day), indicating that SVE can remove substantial VOCs at a sustainable rate. Thepilot study results showed an increasing area of influence around the extraction well andhence, increasing concentrations extracted with time;

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• Air flow rates for the three SVE test cluster wells combined were over 20 scfm (PSWPcriteria - > 20 scfm);

• The ROI3o was estimated to be 25 feet (PSWP criteria - > 10 feet);

• Air permeability was estimated to be 3xlO"9 cm2 to IxlO"8 cm2 (PSWP criteria - > IxlO"9

cm2);

• The VOCs of interest all exhibit Henry's Law Constants amenable to effective removalby SVE; and,

• The depth to groundwater ranges between 60 to 70 feet bgs (PSWP criteria is 10 feet).

The Pilot Study also indicated that the zones of potentially higher permeable material (i.e., the

thin, discontinuous layers of sands and gravel within the interbedded zone) did not result in short-

circuiting the performance of the system. In fact, the results indicate that the interbedded unit

(which contains the majority of the VOC mass) responded uniformly as a sandy/silty material.

This homogeneous domain (as observed during the pilot study) is more favorable than a domain

having preferential flow paths within highly permeability areas. The uniform vertical and

horizontal performance results observed during the test will also reduce the need for the

installation and operation of a system with targeted intervals in a full-scale SVE system, i.e.,

fewer wells with longer screens can be used. In addition, the upper clay provides a natural low

permeability cover over the system, minimizing ambient air infiltration and maximizing vapor

extraction from the most impacted unit, the interbedded zone, that lies directly beneath the upper

clay.

In summary, the results of the SVE Pilot Study indicate that removing substantial quantities of

VOC mass from the impacted soil zones in the FDA/MA is achievable and that SVE is a viable

alternative technology to consider for remediating VOC impacted soils in the FDA/MA.

4.3.2 SVE as a USEPA Presumptive Remedy

The SVE technology has been identified by USEPA as a presumptive remedy for sites with soils

contaminated by VOCs in the technical guidance entitled: "Presumptive Remedies: Site

Characterization and Technology Selection for CERCLA Sites with Volatile Organic Compounds in

Soils" (USEPA 540-F-93-048, 1993). In 1997, USEPA published supplemental technical guidance

that addresses and recommends SVE for removal of VOCs in low to moderate permeability soils,

such as those at the FDA/MA. In particular, the conditions within the FDA/MA meet the

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requirements for successful remediation presented in the 1993 and 1997 USEPA technical guidance

and the U.S. Army Corps of Engineers Design Manual (USACOE, 1995) as follows:

• The vast majority of the constituents present in the soil are halogenated volatile organicsthat are listed by the USEPA as amenable to SVE removal. Removal of the PCBs, doesnot interfere with the effectiveness of SVE;

• The constituents of primary concern have Henry's Law Constants >0.00024 (atm-m'Vmol) @ 20°C and vapor pressures >1.0 mm Hg @ 20°C, as shown below:

ConstituentPCETCE

1,1,1-TCA1,1 -DCE1,1 -DCA

Methylene chloride

Henry's Law Constant(atm-m3/mol)

0.0230.01030.0130.023

0.00590.00131

Vapor Pressure(mm Hg)

18.560100500180349

• The moisture content of the soil above the water table is well below 50 percent (5 to 18percent); and,

• The soil was found to exhibit less heterogeneity than predicted by the original conceptualmodel of the FDA/MA, and no high permeability preferential pathways negatively effectingsystem performance were identified during the pilot study.

The USACOE recommends pilot testing to confirm the feasibility of SVE in low to moderate

permeability soils, such as at the FDA/MA. A pilot study was performed that confirms SVE as a

feasible remedial technology for VOC removal under site-specific conditions. Moreover, the new

USEPA presumptive remedy guidance identifies ten case studies where SVE has been successfully

employed in low permeability soils impacted with VOCs. The mass removal rates and vapor flow

rates observed during the on-site SVE pilot study are within the ranges observed in these case

studies. In fact, the pilot study data presented for the FDA/MA Site predicts performance well in

comparison to the case studies presented by USEPA as successful applications of the technology.

4.3.3 Previous Evaluation of SVE by USEPA

SVE was investigated as a possible remedy for the soils in the FDA/MA in the USEPA

Feasibility Study. It was favorably recognized in the USEPA Feasibility Study to protect human

health and the environment; provide long-term effectiveness and permanence; reduce toxicity,

mobility, and volume of contaminants; and be implementable. The USEPA ROD states that the

SVE alternative remedy "will greatly accelerate the rate at which the clean up levels can be

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attained. VOC contaminants will be removed from the subsurface soils." However, the USEPA

ROD states that the effectiveness of SVE needs to be demonstrated for site-specific conditions

through a treatability study, which, while not conducted as part of the USEPA Feasibility Study

or ROD remedy decision process, was conducted during the Pre-Design Investigation as

described above.

4.3.4 Summary of Performance Assessment

In addition to 1) its designation by the USEPA as a presumptive remedy for VOCs; 2) the

identified Site conditions being amenable to successful SVE remediation as shown by

USEPA/ACOE studies and documents; and 3) positive review of the application of SVE to

FDA/MA soils by the USEPA in the Feasibility Study and ROD, the performance of SVE for

effectively removing VOCs from FDA/MA soils was confirmed by the results of the SVE pilot

study conducted at the Site. The limited PCB impacts will be addressed by excavation and off-

site disposal of PCB impacted soil within the first 2 feet of ground surface soil piles and the

sidewalls and base of the excavations. For the minor PCB impacts at depth (only two remaining

locations), ecological receptors will be protected by limiting exposure through the remaining

cover material.

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AR301+25

GENERAL LEGEND

/ V CHAM-LMK FENCE SURROUNDNG FDA

UM[T OF RESURVEYED AREA OF FDAMA: TOPOGRAPHC SURVEY 2001

A / APPROXHATE LATERAL DELMEATION OF MPACTED FDAMA SOILS/ V (DASHED WHERE NFERRED)

[ | EXTENT OF HOUNDED AREA ESTMATED M RDWP

| | ESTIMATED AREA OF INFLUENCE FROM SVE WELL OPERATION WITH A 26 FOOT RADIUS

[ | FDA/MA PORTION OF SITE

-̂ - - _ APPROXIMATE DIRECTION OF HSA ANGLE BORNG

SYMBOL LEGEND

^ PRELMNARY SVE WELL LOCATION

. PHASE I GEOPROBE SOIL BORING N MOUNDED AREA

Q PHASE II FDAMA SUBSURFACE SOIL SAMPLNG LOCATIONS

5* REMEDIAL INVESTIGATION SOIL BORNG (LOCATIONS APPROXIMATE)

FDA EXCAVATION BASE SAMPLES PHASE I* COLLECTED WITH HAND DRIVE TUBE OR BUCKET AUGER (LOCATIONS APPROXMATE)

A FDA EXCAVATION SIDEWALL SAMPLES PHASE Iw COLLECTED WITH HAND DRIVE TUBE OR BUCKET AUGER (LOCATIONS APPROXMATE)

• FDA SOIL PILE SAMPLES PHASE I COLLECTED WITH BUCKET AUGER (LOCATIONS APPROXMATE)

COLOR CODE LEGEND& NO EXCEEDANCES OF ROD SO*. CLEANUP STANDARDS

• ONLY VOC EXCEEDANCES OF ROD SOIL CLEANUP STANDARDS

• ONLY PCB EXCEEDANCES OF ROD SOIL CLEANUP STANDARDS

, VDC AND PCB EXCEEDANCES OF ROD SOIL CLEANUP STANDARDS

NOTES1 ) SEE FIGURES 4 AND 5 FOR SOIL BORNG / SAMPLNG LOCATION POINT DESIGNATIONS ANDLABORATORY SAMPLE ANALYSIS RESULTS

2) THE FINAL LAYOUT OF SVE WELLS WILL BE DEVELOPED DURING DESIGN

REFERENCE1 ) TOPOGRAPHIC FEATURES TAKEN FROM CADD FILE "MALVERN DWO* DATED DC/MM SUPPLIED TOd» tiMMnto. m BY USEPA IN MARCH 2000. EXCEPT AS NOTED BELOW

2 ) TOPOGRAPHIC FEATURES NSIDE THE L1IIT OF PRE-DESIGN NVESTIGATION SURVEY AREA TAKENFROM CADD FILE 'SOI 01 (2OOOT DATED 1M1/01 SUPPLIED BY PENNON I ASSOCIATES. MODIFIED BYGOLDER ASSOCIATES ON 04/1 OO2

CHEMCLENE SITE DEFENSE GROUPM A L V E R N TCE SUPERFUND SITE

EAST WHITELAND TOWNSHIP P E N N S Y L V A N I A

PRELIMINARY SVE WELL LOCATION PLAN

. GolderAssociates FIGURE 8