August 29, 1991Dear Mrs. Dehnhard: Pursuant to Section VIII. E. of the Administrative Order on Consent ( AOC ) , Sussex County is submitting the revised Work Plan. ... the ARARs identified

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August 29, 1991

Mrs. Stephanie DehnhardEnvironmental ScientistU. S. Environmental Protection AgencyDE/MD Remedial Section ( 3HW25 )Region III841 Chestnut BuildingPhiladelphia, PA 19107

RE: SUSSEX COUNTY LANDFILL NO. 5 (LAUREL, DE)WORK PLANDRAFT NO. 2LANDFILL FILE NO. 5.05-B.2

Dear Mrs. Dehnhard:

Pursuant to Section VIII. E. of the Administrative Order onConsent ( AOC ) , Sussex County is submitting the revised Work Plan.Also, a set of responses which reference the comments containedin your correspondence of July 26, 1991 are attached for yourbenefit. Sussex County is hopeful that we have sufficientlyaddressed the deficiencies of the original submittal, andrespectfully request approval of the revised Work Plan.

*»

This submittal is scheduled to be delivered to your officeon September 3, 1991. The extension to this date was mutuallyagreed upon, and was documented by my correspondence of August23, 1991. Thank you again for your cooperation in this matter.

If you should have any questions or comments, please do not.hesitate to contact me.

Sincerely,

Michael A. IzzoAssistant County Engineer

MAI/ccr

Attachment

cc: Mr. Robert W. Wood, P.E.Mr. Thomas A. Drew, P.G.Mr. Patrick H. Doran, P.G.George J. Weiner, EsquireMr. Jamie Hackney flR300095

Response to EPA Review Comments on the RI/FS Work PlanSussex County Landfill No. 5, Laurel, Delaware

This document presents Sussex County's responses to the Environmental ProtectionAgency's (EPA's) review of the RI/FS Work Plan (dated 3 June 1991) for the SussexCounty Landfill No. 5. The EPA review comments were attached to the June 26, 1991correspondence from Ms. Stephanie Dehnhard, the EPA Project Manager, to Mr. MichaelIzzo of Sussex County. A technical meeting was held on 15 August 1991 at the EPARegion EQ office in Philadelphia, Pennsylvania, to discuss and clarify the commentsprovided by EPA and to develop an agreed upon approach to address specific items ofconcern. Sussex County's responses to the EPA comments attached to theaforementioned correspondence are provided below.

. Introduction

Response to Comment No. 1.

The corrected reference to DNREC has been made on page 1-1 of the Work Plan.


Modifications have been made to the Work Plan stating that Sussex County hasimplemented remedial actions at this landfill to address the potential exposure tocontaminated groundwater.

Section 3 Previous Site Investigations


The extensive database from previous site investigative activities was used to formulatethe current understanding of site conditions, including identifying potential contaminantsources and migration pathways, and potential receptors in the site vicinity. Future datacollection activities, as defined in the RI/FS Work Plan, are intended to supplement theexisting database while fulfilling the data requirements identified for the site (see Section4.4, Identification of Data Requirements in the Work Plan). As we agreed upon in ourmeeting on the 15 August 1991, additional information on past activities has beenprovided in the RI/FS Work Plan. A summary table of the historical sampling events,including the wells sampled and associated analytical program, has been provided in theWork Plan. Analytical results from these past sampling events have been provided in anappendix to the Work Plan. Additional information provided in the Work Planappendices includes site monitor well drilling logs and well construction summaries, andavailable information on the residential supply wells identified in the "no-well zone" atthe Laurel Landfill.

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Section 3.3.2 Site Hydrogeology


The discussion on the derivation of the groundwater flow rate has been included in thissection of the Work Plan.


As previously mentioned, available information on the residential wells identified in the"no-well zone" has been included in an appendix to the Work Plan.


Figure 3.2 of the Work Plan has been revised to show the depth to water measurementat each monitor well. The water table contour map (Figure 3.2) was developed usingwater level data from the site monitor wells, including those positioned north of theLaurel Landfill. The water table contour lines extending past the area bounded by the sitemonitor wells have been deleted from Figure 3.2. Dashed lines are presented wherecontour lines are inferred.

Section 3.3.3 Groundwater Quality


In Section 3.3.3, the first bulleted item has been modified to state that the primary organiccontaminants of concern in groundwater are volatile organics (VOCs).


The discussion in this section has been clarified to indicate reference to all historicalgroundwater investigations versus the most recent sampling data.


The evaluation of the historical groundwater quality monitoring data from the monitorwells located downgradient of the landfill and the Joseph well suggests that other non-siterelated contaminant sources (i.e., on-site septic system located upgradient of the Josephwell, possible spillage of materials in the storage shed positioned over the well head, etc.)may be the source of the observed VOCs in this residential well. The RJ7FS Work Planwill include a full organic and inorganic analysis of groundwater samples collected fromall site monitor wells and selected residential wells downgradient of the landfill, including

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the Joseph residential well. That groundwater quality monitoring data will be evaluatedduring the RI process to assess whether the contaminants observed at the Joseph well aresite-related.

Section 3.3.6 Wetlands


The discussion in this section has been expanded to include more details on the soil andsurface water analytical data obtained during the Site Inspection (SI) investigativeactivities. It is important to note that the National Oceanic and AtmosphericAdministration (NOAA) report attached to the EPA comments, is based to a large extenton questionable data obtained during the SI activities (see Table 1 of the NOAA report).It is expected that the planned sampling activities for the RI at the Laurel Landfill willproduce more reliable data to adequately assess site media quality conditions.

Section 4.1.1 Potential Contaminant Sources


The Work Plan has been modified to read "closing" instead of "closure". The closing ofthe landfill is defined simply as the discontinuing of the placement of solid waste at thelandfill. During the operation and following the closing of the landfill, Sussex Countyhas continued to work with the DNREC in establishing programs that would adequatelymonitor groundwater quality and assess potential impacts from the Laurel Landfill.Physical actions taken to close the landfill are described in the Work Plan.


The discussions in paragraph 3 of page 4-1 have been clarified to reflect that, based onhistorical groundwater quality data, the primary organic contaminants of concern in sitegroundwater are volatile organics. Additional modifications have been made to the WorkPlan to distinguish between groundwater quality impacts observed at LD-1 (the monitorwell located immediately downgradient of the landfill) and the groundwater qualityconditions at the monitor wells located several hundred feet downgradient of the landfill.

Section 4.1.2 Potential Migration Pathwaysi


The Work Plan has been revised to delete the first two sentences under Section 4.1.2.

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Surface water is not expected to runoff of the landfill and discharge into the smalldrainage ditch adjacent to the landfill entrance road, or to the Collins and Culver ditch.The RI program has been revised to include a site reconnaissance that will identify, withthe assistance of the site topographic map, any surface runoff patterns at the landfill. Adiscussion in this regard has been included under Section 5.3, Soil and Surface WaterInvestigations of the Work Plan.


The RI air investigation has been modified to include evaluation of potential airborneasbestos migration.

Section 4.1.3 Potential Contaminant Receptors


If surface runoff occurs from the landfill, and surface soil and/or surface watercontamination exists on the landfill, potential receptors may also be located offsite. Thisstatement has been included in Section 4.1.3 of the Work Plan.


Sensitive environments have been included as potential receptors for the air migrationpathway.

Section 4.2.1.2 Location Specific ARARs


The Work Plan will note that the RI report will include correspondence documentationon all agency contacts.

Section 4.2.1.3 Action Specific ARARs

Response to Comment No. 1.i

Table 4-2 has been modified to include ARARs indicated in the comment As discussedin Section 4.2.1 of the Work Plan, the ARARs identified are a preliminary list and willbe revised as part of the RI/FS process.


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Section 4.4.1 Groundwater Data Requirements


The use of existing wells for groundwater sampling is addressed in the response tocomments for Section 5.


Site monitor well abandonment will be conducted in accordance with DNREC'sregulations governing the construction of water wells. The Work Plan has been modifiedto reflect this.


Depth to water measurements will be taken from all site monitor wells at a frequency ofonce per month during the RI field activities. This water level monitoring informationwill supplement the water level data collected on a continuous basis during the irrigationwell assessment program. Section 5 of the Work Plan has been modified accordingly toincorporate these supplemental water level monitoring activities.

Section 4.4.2 Surface Water and Soils Data Requirements


Section 4.4.2 has been modified to include, as a contingency, surface water and sedimentsampling in drainageways should the RI analytical data indicate the potential for surfacewater/sediment quality impacts resulting from the landfill.

Section 5.1 Site Survey and Topographic Maps


The site survey activities will include a determination of the approximate boundaries ofthe landfill in addition to the property boundaries. This work scope activity has beenincluded in Section 5.1 of the Work Plan.


The horizontal and vertical survey accuracies have been noted in Section 5.1 of the WorkPlan.


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The installation of settlement points in the landfill cover has been incorporated into theRI scope of work and is discussed in Section 5.1 of the Work Plan.

Section 5.2 Groundwater Investigation


Slug tests will be conducted on several existing monitor wells to assess the hydrauliccharacteristics of the aquifer underlying the Laurel Landfill. The methods of analysis arediscussed in the Work Plan. Specific methodologies for the performance of the slug testswill be provided in the Sampling and Analysis Plan (SAP).

Section 5.2.1 Monitor Well Installation


A site reconnaissance task has been added to the RI activities. During the sitereconnaissance, a visual inspection of the existing monitor wells will be conducted andmeasurements will be taken of the total depth of the monitor wells as well as depth towater in each monitor well. These well inventory results will be provided to EPA priorto the initiation of any monitor well installation activities.


Due to the questions raised concerning the reliability of data obtained from well LS-7, theWork Plan has been modified to include the abandonment and replacement of well LS-7.


Based on the agreements reached in the 15 August meeting and a subsequent follow-upletter from Ms. Dehnhard dated 23 August 1991, the following new monitor wells willbe installed to supplement the existing monitoring well network:

• Monitor well LS-15 will be installed upgradient of the landfill at thelocation shown on Figure 5.1 of the Work Plan. This well will bescreened at a depth of 60 to 70 feet below ground surface.

• In addition to the proposed installation of monitor well LS-16 west of thelandfill, another new well (designated LS-17) will be installed at the LS-16location shown on Figure 5.1 of the Work Plan. These monitor wells(LS-16 and LS-17) will be screened at separate depth intervals within the

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water table aquifer. LS-16 will be screened at 40 to 50 feet below groundsurface, and LS-17 will be screened at 80 to 90 feet below ground surface.These monitor wells will assess groundwater quality conditions west of theLaurel Landfill.

• In order to assess groundwater quality and potential influences fromirrigation well pumping on the eastern side of the landfill, a temporarywell cluster (designated LS-18 and LS-19) will be installed between thelandfill and the Collins irrigation well. Screened intervals will be identicalto the new monitor wells proposed for the west side of the landfill.

The above indicated screened intervals have been selected based on our currentunderstanding of the lithologic conditions underlying the landfill. However, the screenedinterval depths may be modified should unexpected lithologic conditions be encountered(i.e., presence of a fine grained confining layer) or the indication of discrete zones ofcontamination detected during the drilling activities.

The details of the aforementioned monitoring well installation program are described inSection 5.2.2 of the Work Plan.


See response to comment No. 3 above.

Section 5.2.2 Groundwater Sampling


Section 5.2.2 of the Work Plan has been modified to include the following:

• Groundwater samples will be obtained from three residential wells locatedimmediately downgradient of the Laurel Landfill. The residential wellsdesignated as well numbers 1 (Smith), 2 (Joseph), and 9 (Gullette) onFigure 5.2 of the Work Plan, would be included in the residential wellsampling program. Groundwater samples obtained from these residentialwells will be analyzed for TCL/TAL (Target Compound List/TargetAnalyte List) parameters and asbestos.

• The RI groundwater sampling effort will include the collection of samplesfrom all existing site monitor wells, newly installed monitor wells and theHastings irrigation well for analysis of TCL/TAL parameters and asbestos.


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It is envisioned that one round of sampling will sufficiently characterize the groundwaterquality conditions at the landfill and in the site vicinity. However, based on evaluationof the RI groundwater analytical data, additional sampling efforts may be required toverify analytical anomalies in the database.

The aforementioned groundwater sampling program has been incorporated into thediscussion under Section 5.2.3 of the Work Plan.


This comment is addressed in the above response statement


The analytical methods employed in the RI program will be detailed in the SAP. Thisplan will incorporate the use of EPA Methods 500 Series for analysis of groundwatersamples.


The groundwater sampling program will include the collection of filtered and unfilteredgroundwater samples from all sampling points for the metals analyses.


As previously mentioned, one set of groundwater analytical data should be sufficient tocharacterize groundwater quality conditions at the Laurel Landfill. Additional samplingevents may be scheduled to verify analytical results from the initial RI sampling effort


The outline of the requirements and format in which the analytical data validationpackages should be prepared has been noted and will be further detailed in the SAP.

Section 5.2.3 Impacts to Irrigation Well Pumping


The list of wells to be monitored during the irrigation well assessment activities has beenmodified to include monitor wells LS-2 and LS-3.

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Section 5.3 Soil and Surface Water Investigation


A sampling grid will be established at the site to direct the collection of soil and surfacewater samples on the landfill. Representative samples will be collected from designatedlocations within alternating grid areas on the landfill. Further details of the soil andsurface water sampling at the landfill is presented in Section 5.3.


Surface water samples will be collected from the depressional areas on the landfill foranalysis. WESTON has scheduled this activity to be performed in spring. However, theactual performance of this sampling activity will be dependent on the date of receipt ofEPA's approval of the Work Plan and supporting project documents (i.e., Sampling andAnalysis Plan and the Health and Safety Plan).


A contingency to sample surface water and sediment from drainageways adjacent to thelandfill if surface contaminant runoff or groundwater contaminant discharge shouldindicate that it is necessary, has been provided in the Work Plan. Also included as acontingency, should the air investigation indicate the detection of airborne asbestos, off-site soil samples will be collected and analyzed for asbestos.


A contingency for the sampling of Broad- Creek has been included in the Work Plan.Sampling of Broad Creek will be contingent upon review of groundwater analytical datafrom wells located between the landfill and Broad Creek.


The recommended chemical and physical parameters for surface water and sedimentsamples provided by the EPA in conjunction with this comment, has been noted and willbe incorporated into the SAP.

Section 5.4 Air Investigation


The discussion regarding the air investigation has been expanded to include informationon sampling locations and procedures. Also, a contingency has been provided for the


sampling of soil gas, on site and off site if warranted, in areas where the initial screeningindicates elevated levels of VOCs in landfill gas emissions.


As discussed previously, the list of analytical parameters for the air sampling program hasbeen expanded to include asbestos.

Section 5.5 Biota/Wetland Investigation


The discussion pertaining to the biota/wetland investigation has been expanded to includea more thorough discussion on the planned activities. The investigation will include abaseline environmental receptor survey, and consideration of exposure routes andassessment of possible impacts. Specific methodologies to be employed during thebiota/wetland investigation will be included in the SAP.


The Work Plan has been modified to indicate that sensitive environments will beconsidered when assessing potential contaminant migration via the air pathway.

Section 5.6 Solid Waste Thickness Evaluation


The Work Plan has been modified to provide a contingency for investigation, ifwarranted, of any identified hot spots located during the initial screening conducted forthe air investigation. Test pitting may be performed at the indicated hot spots to furthercharacterize these areas.


Since several of the landfill wells (i.e., LS-2, LS-3) are screened in and below the wastematerial of the landfill, samples collected from these monitor wells are considered to becharacteristic of leachate being produced at the landfill. Samples obtained from thesewells will be analyzed for TCL/TAL parameters and asbestos.

Section 5.7.1 Review of Existing Data


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Additional historical data has been compiled and included in the Appendices to the WorkPlan as indicated in previous responses to comments.

Section 6.6 Summary of Alternatives


It is our understanding that a comparative analysis in which the identified remedialalternatives are evaluated against one another to evaluate the advantages anddisadvantages of each is to be performed during the FS process. The results of thecomparative analysis will be included in the RI/FS report.

Section 7.0 Scheduling and Reporting


The actual timeline for the conductance and completion of the RI/FS according to thepreliminary schedule is less than 2-1/2 years. The schedule has been reviewed, and wherepossible, performance of some RI/FS activities has been shortened. Also, in order toexpedite the RI/FS process, the submission of a revised FS technical memorandum willbe incorporated into the remedial alternatives evaluation and FS report or, if necessary,a technical review meeting can be held to discuss the comments.


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Documents

August 29, 1991Dear Mrs. Dehnhard: Pursuant to Section VIII. E. of the Administrative Order on Consent ( AOC ) , Sussex County is submitting the revised Work Plan. ... the ARARs identified