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WESTON WAYWEST CHESTER, PA 19380PHONE: 215-692-3030TELEX: 83-5348

lESlGNERS 'CONSULTANTS

13 March 1992

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

W.O. No. 1631-16-02

Dear Ms. Dehnhard:

This -letter presents Sussex County's responses to the agency review commentsspecifically concerning the performance of the drilling, well installation and wellinventory/redevelopment work presented in the Remedial Investigation / Feasibility Study(RI/FS) Sampling and Analysis Plan (SAP) dated 23 December 1991 for the SussexCounty Landfill No. 5 (Laurel Landfill). These agency comments on the SAP werereceived by Sussex County on 14 February 1992 and were comprised of comments fromDelaware Department of Natural Resources and Environmental Control (DNREC),Dynamac (the EPA oversight contractor), and EPA Region HI. The purpose of this letteris to focus directly on the comments pertaining to the performance of the proposedmonitoring well and piezometer installations and associated tasks, such as the wellinventory and redevelopment work. It is Sussex County's intent to reach an agreement onthis portion of the program and commence with implementation of the drilling programthe week of 23 March 1992. The reason for expediting the drilling program is tofacilitate access to several drilling locations situated adjacent to neighboring agriculturalfields, prior to the commencement of agricultural activities (tilling, application ofagricultural chemicals, etc) in early April 1992.

Sussex County's responses to comments provided by EPA and Dynamac, on the drilling,well installation and well inventory/redevelopment program at the Laurel Landfill arepresented below. The revisions to the SAP indicated by the following responses arepresented in Attachment 1, which include Pages 3-1 through 3-14 of the SAP. It shouldbe noted that other revisions to this portion of Section 3 of the SAP have been madebased on agreements reached during a 14 February 1992 site meeting attended by SussexCounty, WESTON, EPA, Dynamac and DNREC site representatives.

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Ms. Stephanie Dehnhard -2- 13 March 1992U.S. Environmental Protection Agency

RESPONSES TO EPA REGION III COMMENTS

Section 3.2 Groundwater Investigation

Response to Comment No. 1 - The appropriate portions of this section have been revisedto clearly state that approval of monitoring well permit applications by the DNREC WaterSupply Branch will be received prior to monitoring well installation and that wellconstruction and abandonment will be performed in accordance with applicable DNRECregulations, which includes submission of well completion and well abandonment reportsas required.

Section 3.2.2 Monitoring Well Abandonment

Response to Comment No. 1 - The narrative has been revised to indicate that a cementand bentonite grout seal will be tremied in place from the top of the sand toapproximately one foot below ground surface. The PVC casing will be cut offapproximately one foot below ground surface and the remaining borehole interval fromground surface to one foot below ground surface will be filled with a cement andbentonite grout mixture.

Section 3.2.3.2 Drilling Methods and Lithologic Sampling

Response to Comment No. 1 - Based on discussions between WESTON and EPArepresentatives, and agreed to in a telephone conversation on 28 February 1992, thedrilling method to be employed for the well installation program at the Laurel Landfillwill be hollow stem auger techniques, with contingencies to be incorporated as fieldconditions necessitate. This section of the SAP has been revised to present the proposeddrilling method and agreed upon contingencies to be employed to complete theinstallation of the seven monitoring wells and two piezometers at the Laurel Landfill site.

Response to Comment No. 2 - The text has been revised to indicate that the split spoonsampling will occur continuously during drilling and that lithologic descriptions will beprovided by the on-site geologist. Soil samples will also be screened for organic vapors.Split spoon sampling will not be necessary at proposed well locations LS-6R, LS-16, andLS-18 as these monitoring wells will be paired with adjacent deeper monitoring wells.

Response to Comment No. 3 - The text has been modified to provide additional detaildescribing the procedures for obtaining organic vapor readings on split spoon soil samplescollected during drilling activities.

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Ms. Stephanie Dehnhard -3- 13 March 1992U.S. Environmental Protection Agency

Section 3.2.3.3 Well Construction

Response to Comment No. 1 - The selection of the screen slot size and filter pack grainsize was accomplished by initially selecting a filter pack which would retain most of theformation and has a uniformity coefficient (Uc) of 1-3 (dimensionless). This will insuregood porosity and hydraulic conductivity. The well screen was then selected to retaingreater than 90% of the filter pack material. The geologic formation being screened isknown as the Beaverdam Formation and has been described in published literature as auniform, fairly well-sorted, medium sand (Delaware Geological Survey Report No. 8,1976). This is equivalent to a grain size of approximately 0.01 to 0.02 inches. FollowingDriscoll (1986), the filter pack is selected by multiplying the seventy-percent retained sizeof the formation by three or four. The seventy percent retained size or Morie No. 1 sandis approximately 0.04 inches, which is the appropriate size for the Beaverdam Formation,assuming the seventy percent retained size of the Beaverdam Formation is between 0.01and 0.015 inches. The Morie No. 1 sand also has a Uc of 1.3, which is obtained bydividing the forty percent retained size of the material by the ninety percent retained size.The 0.02-inch slot well screen will retain greater than 90% of the No. 1 Morie sand filterpack.

Response to Comment No. 2 - The length of bentonite seal to be placed above the sandpack in each of the newly constructed wells will be ten to twenty feet, as recommendedby EPA.

Response to Comment No. 3 - The text has been revised to indicate that the concretepad surrounding the surface protective casing will be constructed so that there is a slopeaway from the well's protective casing.

Response to Comment No. 4 - The placement of a bentonite seal during the constructionof the piezometers will occur in the vadoze zone. The text has been revised to indicatethat a bentonite slurry will be used as a seal.

Response to Comment No. 5 - Two figures have been prepared which show the proposedmonitoring well and piezometer construction designs and are included in the SAP.

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Ms. Stephanie Dehnhard -4- 13 March 1992U.S. Environmental Protection Agency

RESPONSE TO DYNAMAC COMMENTS

Section 3.2.1 Containment of Development Water

Response to Comment No. 2 - The text has been revised to indicate that developmentwater will be containerized and staged on site pending analytical results. Followinganalysis, arrangements will be made to properly dispose of the development water.

Response to Comment No. 5 - The determination of the depth of each well will be byusing. a properly decontaminated, weighted measuring tape. Measurements will berecorded in the field log book to the nearest .01-foot.

It is hoped that the above responses and associated revisions to the SAP will meet withyour approval so that the drilling program at the Laurel Landfill can begin during theweek of 23 March 1992. The remainder of Sussex County's responses to the agencycomments on the SAP will be prepared and submitted to the EPA by 5 April 1992.It should be noted that EPA's bioassessment work group comments on the SAP werereceived by Sussex County on 6 March 1992.

If you should have any questions concerning the above, please do not hesitate to contactus.

Very truly yours,

ROY F. WESTON, INC.

Thomas A. Drew, P.O.Project ManagerGeosciences Department

TAD/bac

cc: Michael A. Izzo - Sussex Co.Patrick Doran - WESTON

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ATTACHMENT 1

SECTION 3 (Revised, p 3-1 to 3-14) - FIELD SAMPLING PLAN

OF THE RI/FS SAMPLING AND ANALYSIS PLAN

13 March 1992

SECTION 3FIELD SAMPLING PLAN

This section describes the field activities for the RI and the procedures to be followed tocomplete these activities.

3.1 SURVEYING AND MAPPING

A new topographic map for the site and vicinity will be produced and will serve as a basemap for this RI. An overflight of the Laurel Landfill will be scheduled for early springof 1992 in order to provide the aerial photographs from which the topographic base mapscan be prepared. The aerial will be field checked by a ground survey crew who willestablish a localized baseline and benchmark. These references will be used to locate allnew and existing monitor well locations and elevations, as well as all future samplinggrids and sampling locations. All survey points will be tied into the established baselineso that they may be accurately located on the site base map. Survey accuracy will be ±1 foot for the horizontal plane for all sampling and monitoring points, and ± 0.01 foot forthe vertical plane for all new and existing monitoring well locations and the settlementpoints.

The topographic map covering the approximately 40 acre site and immediate surroundingarea will consist of contour lines on 1-foot intervals and use a scale of 1 inch = 200 feet

Vertical elevation surveying will be conducted on settlement points which will be

installed in the landfill cover material. The settlement points will be surveyed at leasttwice every month during the RI field activities (May through October, 1992). Allelevations for the settlement points will be referenced to the established site benchmark.

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3.2 GROUNDWATER INVESTIGATION

The activities which are planned as part of the groundwater investigation focus onsupplementing existing data for the site, and include the following:

• A site reconnaissance and well inventory

• Installation of additional monitoring wells and piezometers

• Collecting groundwater samples for chemical analysis from new and

existing site monitoring wells and selected nearby residential and irrigationwells

• Aquifer testing to determine hydraulic characteristics of the water table

aquifer

• An assessment of potential impacts from pumping of the nearby irrigation

wells.

3.2.1 Site Reconnaissance and Well Inventory

The purpose for the site reconnaissance and well inventory is to evaluate the physicalcondition of existing site monitoring wells, and to locate and review proposed locationsof the landfill borings and landfill cover settlement points.1

The initial review of existing well conditions will be performed by means of visualinspection of the monitoring wells. Observations will include an inspection of the surfaceprotective casing and security (lockable), the integrity of the surficial well seal and the

SUSSEX-5\SECTN-3.TXT 3-2 , _ - -QR301Q96

uppermost portion of the well (i.e., portion within the protective casing). Also,

measurements of depth to water, the total well depth, and well casing stick-up aboveground surface will be obtained at all existing site monitoring wells. The total well depth

will be determined using a properly decontaminated, weighted measuring tape.Measurements will be recorded in the field log book to the nearest 0.01 foot.

To further evaluate the condition of existing site monitoring wells, measurements of pH,specific conductance, turbidity and temperature will be obtained at each existing

monitoring well during the planned well redevelopment effort The redevelopment ofexisting wells will include alternating mechanical surging and pumping at each well withthe measurements of the above referenced parameters taken in the field during thepumping portion of redevelopment. The redevelopment at each well will be performedfor at least one hour, and until turbidity, temperature, specific conductance and pH of the

well discharge water have stabilized, or a maximum of three hours at each location. Thepurged water will be containerized and staged on-site. Following receipt of laboratory

analytical results, arrangements will be made to properly dispose of the developmentwater.

A sample of the discharge water from the developing well will be collected at regularintervals during the pumping periods in a clean glass container for the field measurementof turbidity, temperature, specific conductance, and pH. All readings from these field. measurements, along with the cumulative volume of discharge, color and any organicvapor readings will be recorded in the field log book. Redevelopment will occur at allexisting site monitoring wells except for monitoring wells LS-1, LS-2 and LS-3 which arescreened in or very close to the waste material and monitoring wells LS-6 and LS-7which are to be replaced. The results of the above-described redevelopment work, and

other well inventory observations and data will be reported to the EPA(within two weeksof the completion of the above-described work. Monitoring wells to be abandoned willbe abandoned according to the procedures discussed in Subsection 3.2.2.

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During the site reconnaissance, the proposed locations of the landfill borings andsettlement points will be established in the field for EPA's review and concurrence.

3.2.2 Monitoring Well Abandonment

Based on an assessment of monitoring well construction details, two existing site

monitoring wells will be replaced as part of the RI field activities. The replacement ofthese wells (LS-6 and LS-7) will include abandoning the existing wells and installationof replacement wells. Also, based on the results of the above described sitereconnaissance and well inventory work, additional existing monitoring wells may beconsidered for replacement The well abandonment will be conducted in accordance withthe State of Delaware Regulations (DNREC, 20 January 1987).

Monitoring well abandonment will include the following procedures:

• The total depth of the monitoring wells should be confirmed prior to

adding any fill or sealing materials.

• The screened intervals of the monitoring wells should be filled with a

clean silica sand (#1 Morie or equivalent) to 5 feet above the top ofscreen.

• A cement bentonite grout seal will be tremied in place from the top of the

sand to one foot below ground surface. A mix ratio of not more than 6gallons of water and 5 pounds of bentonite per 100-pound bag of cementwill be used.

• The protective surface casing will be removed and the PVC well casing

will be cut off approximately 1 foot below ground surface (BGS), and the

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remaining borehole interval (0-1 feet BGS) will be backfilled with acement and bentonite grout.

• At monitor well LS-6, hollow stem augers (4-1/4 inch ED) will be used tooverdrill the PVC casing to a depth of 15 feet BGS. The augers will befilled with cement bentonite grout and slowly removed, topping off theborehole with grout as needed.

• The appropriate DNREC well abandonment report will be completed

within thirty .days of the above described work and submitted to theDNREC, as required.

3.2.3 Monitoring Well and Piezometer Installations

To further characterize groundwater conditions (hydraulically and chemically) in the

vicinity of the Laurel Landfill, the existing monitoring well network will be supplementedwith the installation of additional groundwater monitoring wells and piezometers. Theresults of the monitoring well inventory will be used to evaluate the usability of theexisting monitoring wells. Any existing monitoring well determined to be unacceptablefor obtaining the required RI hydrogeologic and chemical data will be considered forreplacement No monitoring wells or piezometers will be installed prior to approval ofmonitoring well permit applications by the DNREC Water Supply Branch. Monitoringwell completion reports will also be submitted to DNREC in accordance with the Stateof Delaware regulations. \

-J . -

3.2.3.1 Monitoring Well Locations

The proposed locations for the new monitoring wells and piezometers are shown onFigure 3-1. The locations shown are different from the proposed locations presented in

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the RI/FS Work Plan. However, the indicated locations were identified and approved byEPA during a site visit on 14 February 1992. A total of five (5) new monitoring wells

(LS-15 through LS-19) and two (2) piezometers (PZ1 and PZ2) will be installed at thesite. In addition, two existing monitoring wells LS-6 and LS-7 will be replaced (thesereplacement wells are designated as LS-6R and LS-7R). The details regarding drillingmethods, monitoring well and piezometer construction and development are discussedbelow.

3.2.3.2 Drilling Methods and Lithologic Sampling

Prior to the start of drilling, the drilling and sampling equipment and well components

will be decontaminated according to procedures specified in Subsection 4.1. All newmonitoring wells (LS-15 through LS-19) and the replacement wells (LS-6R and LS-7R)will be drilled using 4-1/4 inch I.D. hollow-stem augers However, there is the potentialfor encountering "running sand," which would limit the depth capability for using hollowstem augers. Therefore, the following contingencies will be incorporated into the drillingprogram as field conditions necessitate.

1. If greater than six inches of "run-up" into the augers occurs, potable waterwill be used initially to flush the sand out of the hollow-stem augers. Ifthe use of water only is unsuccessful in removing sand from within theaugers, a pure bentonite drilling mud (Aquagel* Gold Seal* or equivalent)will be used to flush out the augers. Additionally potable water or a purebentonite drilling mud may be added to the hollow-stem auger to minimizesand "run-up" when advancing the augers.

2. The use of fluids to flush out the augers will increase the potential forbinding of the augers as the depth of the borehole increases. If the on-sitefield geologist and driller feel that continuing to flush out the augers will

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L.s-1 e /Laurel

Legend— — — Landfill Boundary

Proposed Monitor WellMonitor WellInstalled January, 1979Monitor WellInstalled January, 1986Monitor WellInstalled Nov.-Dec., 1988Monitor WellInstalled April, 1990

•©• Proposed PiezometerScale In Feet

401-6049d

FIGURE 3-1 PROPOSED AND EXISTING MONITOR WELL LOCATIONSLAUREL LANDFILL, SUSSEX COUNTY, DELAWARE

3-7 A R 3 0 I I O I

create an unacceptable risk of losing all or a portion of the augersdownhole, then the hollow-stem augers will be removed and the boreholecontinued using mud rotary drilling techniques.

3. With mud rotary drilling, pure bentonite (Aquagel* Gold Seal* orequivalent) will be used in the drilling fluid. The borehole will beadvanced, using an eight-inch (nominal) diameter drag bit, to a depthequivalent to ten feet above the top of the proposed well screen interval.

4. At this point, a six-inch diameter steel casing will be temporarily installed

to the base of the borehole, and the drilling mud will be flushed from theborehole. The borehole will then be advanced using a six-inch diameter(nominal) drag bit using only potable water as the drilling fluid. Thetemporary casing will be advanced as necessary to maintain boreholestability and to facilitate the lithologic sampling and proper wellconstruction.

5. If the use of potable water and temporary casing are unsuccessful inadvancing the borehole, a minimal amount of the pure bentonite necessaryto maintain an open borehole will be added to the drilling fluids.

During the drilling process, soil samples will be collected continuously from groundsurface to the final well borehole depth, using a split-spoon sampler. At the locations ofwell pairs, split-spoon soil sampling will only be conducted during the drilling of thedeeper well, which will be drilled first at each location.

A field geologist will be responsible for maintaining a log book of the drilling and wellinstallation operations, and lithologic descriptions of each split-spoon sample collected.Lithologic information including sample depth, blow counts, sample recovery, color,texture and moisture content will be recorded in the field log book. Upon opening the

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split-spoon sampler, a decontaminated stainless steel trowel will be used to transfer a

representative portion of the sample to a sample jar, filling the jar approximately half full.After placing a piece of aluminum foil and the lid on the jar and allowing one to twominutes for equilibration, head space readings will be obtained using direct readinginstruments (i.e., flame ionization detector (FID) and/or a photo-ionization detector (PID))by inserting the probe through the foil. The remaining portion of the soil sample will be

placed into an appropriate labeled sample container for archiving. All drilling mud andsoil cuttings will be containerized and staged on site pending disposal, as described inSubsection 4.4 of this SAP.

Two piezometers (PZ1 and PZ2) will be installed using hollow stem auger techniques.Split-spoon samples will also be collected as described above to obtain lithologicinformation at these locations. The borehole will be advanced to a depth of ten feetbelow the observed water table. Details pertaining to the construction of the piezometersand monitoring wells are discussed below.

3.2.3.3 Well Construction

All new and replacement monitoring wells will be constructed using two-inch innerdiameter (ID), threaded flush-joint, schedule 40 PVC well screen and casing. The wellscreen will be ten feet in length with 0.02-inch slots. The planned screened interval foreach new monitoring well is summarized on Table 3-1. However, the well screenintervals may be modified if unexpected lithologic conditions (i.e., confining layer) areencountered and/or direct reading instruments (DRIs) indicate possible contamination atdiscrete depth intervals other than those proposed for the well screen intervals. The EPAor its representative will be consulted prior to implementing any changes to the proposed

well screen intervals.

Once the desired well depth has been reached for the monitoring wells, the well screenwhich is attached to the necessary length of well casing, will be positioned at the bottom

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Table 3-1

Proposed Well Screen Intervals

LS-6R

LS-7R

LS-15

LS-16

LS-17

LS-18

LS-19

SUSSEX-5VTBL3-I.TBL

3-10

40-50

80-90

60-70

40-50

80-90

40-50

80-90

of the borehole. Two sets of well centralizers will be attached to the well casing. Aclean, well-sorted silica sand (#1 Morie or equivalent) will be emplaced around the wellscreen from the base of the borehole to approximately five feet above the top of the wellscreen. A ten to twenty foot thick bentonite slurry seal will be tremied in place above

the sand pack. The remaining annular space above the bentonite seal and to within twofeet of ground surface, will be backfilled using tremie-pipe methods with a Portland TypeI cement and pure bentonite grout mixture. A mix ratio for the grout of not more than6 gallons of water and 5 pounds of bentonite per 100-pound bag of cement will be used.The upper two feet of the annular space will be filled with concrete (Sakrete™ orequivalent), and a six-inch ID protective steel surface casing, equipped with a lockablecap will be installed over the well casing stick-up and into the concrete seal. The well

will be completed so that the top of the well casing is approximately 2-2.5 feet aboveground surface. A two foot by two foot by four inch thick concrete pad will also beinstalled around the base of the protective surface casing, and graded so that the concretepad slopes away from the well. Figure 3-2 shows the proposed monitoring wellconstruction design.

The protective casing and well cap will be clearly labeled with the corresponding wellnumber. Protective posts made out of 3-inch diameter steel filled with concrete will beinstalled around the new wells and piezometers.

The two piezometers will be constructed using 1-1/4 inch ID, schedule 40 PVC screenand well casing. The well screen will be 10 feet in length and 0.020-inch slotted. Thebottom of the piezometer will be positioned at a depth approximately ten feet below theobserved water table, or if a clay layer is encountered below the planned depth isachieved, the bottom of the piezometer may be placed at the top of the clay layer,assuming saturated conditions occur above this clay. The EPA or its representative willbe consulted should unexpected lithologic conditions be encountered, so that thepiezometer screen is placed at the optimal depth interval. The construction andcompletion of the piezometers will be similar to the monitoring well construction,

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KSJGNERS-CONaiJAHTS

Sussex County Landfill No. 5 - Laurel, DelawareWell Construction Diagram (Typical)

Locking Cap

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750)'c.

oBentonite faSeal

Interval(10-20FI.) >

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—— >- ik 5 Ft. ',

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Screened

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—— Protective Steel Casing

tTTTT*

< ————— Cement/BentoniteGrout

2" i.D. Sch. 40 PVC,Flush Joint Casing

« —————— Bentonite Seal

—————— No. 1 (Morie Sand)Filter Pack

2" I.D. Sfih. 40 PVH,0.020" Slot Well Scree

(Not to Scale)464-8021

FIGURE 3-2 WELL CONSTRUCTION DIAGRAM (TYPICAL)

3-12 AR30M06

although 1-1/4 inch well casing and 4-inch steel protective casing will be substituted and,depending on depth to water below ground surface encountered, the amount of filter sand

will be extended 1-2 feet above the top of the well screen to allow the placement of atleast two feet of a bentonite slurry seal. All other construction details will remain thesame. Figure 3-3 shows the proposed piezometer construction design.

3.2.3.4 Monitoring Well Development

All newly installed monitoring wells will be developed using alternating mechanical

surging and pumping techniques. Well development will be initiated no sooner than 24hours after completion of well installation. All equipment used for development of thewells will be decontaminated prior to use and between wells, according to detailsspecified in Subsection 4.1. The newly installed monitoring wells will be developed aminimum of one hour, and until field measurements (turbidity, temperature, pH, andspecific conductance) of the discharge water have stabilized, or a maximum of three hoursat each location. All well development information will be documented in the field logbook. All well development water will be containerized and staged on-site pendingproper disposal.

3.2.4 Groundwater Level Measurements and Sampling

3.2.4.1 Water Level Data Collection

Measurements of the depth to water will be taken from the surveyed referenced point onthe top of the PVC monitoring well and piezometer casing. Water levels will bemeasured to the nearest 0.01 foot. Measurements will be taken from all new and existingsite monitoring wells and piezometers at a frequency of approximately once per monthduring RI field activities (expected period from May through October 1992). The depthto water measurements will be recorded in field log books.

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Sussex County Landfill No. 5 - Laurel, DelawarePiezometer Construction Diagram (Typical)

Locking Cap

vConcrete Pad -~- ___

>

i.CDQ

'

103Sic~Q

Bentonite ^Seal

Interval

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I1rrt

CLfe

COCO

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- — — -_ _ __ — — . .•I-j-L-— — —

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dxX§XX

< —— Protective Steel CasingWTV™1VV

VVV

>"•0 .*>'• •<

^s^

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< —————— Cement/BentoniteGrout

—————— 1 1/4" I.D. Sch. 40 PVC,Flush Joint Casing

< —————— Bentonite SlurrySeal

—————— No. 1 (Morie Sand)Filter Pack

1 Mi." in fifih 4f> PVO0.020" Slot Well Screer

464-8020_____________;_____(Not to Scale)FIGURE 3-3 PIEZOMETER CONSTRUCTION DIAGRAM (TYPICAL)

3-w AR30II08