SCHMELTZER, APTAKER & SHEPPARD, P.C.COUNSELORS AT LAW

ISOO MASSACHUSETTS AVENUE, NORTHWESTWASHINGTON, D.C. 2OO3G-I879

EDWfcHO SCHMELTZER CABLE-SHIP Ul TfeLEX 4-JO5I7 WM. ROGER TRU1TT

EDWARD J. SHEPPARD IV - (gOS} 823-OOO ROB£RT L. ZISKU. THOMAS ESSUNGER - PATRICK O. CAVANAUGHiflA MICHAEL SHEPAHO . ____ - , : .. ------ . - . - - - - '- - DEANA FRANCES DUDLEYGEORGE J.WEINCR .... ROBERT L. DU3TONMICHAEL A. BROWN COUNSEL KATHERrNE BREWERPAUL M. HEYLMAN EOWAflO APTAKER DONAVEE A, SERGESSTEPHEN HORN , MARGARET X FREESTON MARY ROSE KORNRE1CH. PM O.PAUL M, HONIGBCRG SUZANNE LANGFORD S*NFORD« - CHRISTINE R, PEMBROKE"CHRtSTOPHEfl HARRIS DEBORAH ANN KLINE*

•NOT ADMITTED IN O.C.

March 26, 1988

DNRECNew Castle OfficeCERCLA Management Branch715 Grantham LaneNew Castle, Delaware 19720-4801 . . .

Re: Delaware Sand & Gravel (*DS&G'M Site

Dear Sirs:

This letter and its attachments are submitted for therecord on behalf of New Castle County ( the County") with regardto the Remedial Investigation ("RI"), Feasibility Study ("FS")and Proposed Plan for the above-referenced site.

At the outset, it must be pointed out that the countywas provided a very short period of time to review, analyze andcomment upon the voluminous technical data presented in the DS&GRI/FS and its lengthy appendices. In fact, the County was notprovided with a copy of the FS until February 26, 1988, after thepublic comment period was opened, despite repeated earlierrequests by the County for drafts of both the RI and FS. Needlessto say, the County is very distressed that the coordinationcontemplated in Section 20 of the August 1, 1984 administrativeConsent Agreement between the County and EPA (Docket No. 111-84-12-DC) has not been honored*1 Accordingly, the County hereby

1 In particular, the Consent Agreement specifies that the Countywill be involved "in any meeting with the State the purpose ofwhich is to discuss the nature, scope and/or expense of anyremedial activities which would respond to both sites.* (Emphasisadded). The County has recently become aware of numerous ex partemeetings and discussions among EPA, DNREC and/or Dunn Geoscience,Inc. involving remedial activities related to the Army Creek(Footnote continued on next page)

SCHMELTZER, APTAKER & SHEPPARD, P.C.

DNRECMarch 26, 1988

(Red)Page 2 ORIGINAL

notes its objection to the foregoing process and expresslyreserves its right pursuant to the Consent Agreement toparticipate in all meetings and discussions concerning remedialactivities which relate to both the DS&G and Army Creek sites andto submit additional comments, within a more reasonable period oftime, as may be appropriate.

GROUNDWATER CONTAMINATION

As DNREC and EPA-Region III are already aware, theCounty is at a loss to understand the reasons for or technicalbasis of those portions of the DS&G RI/FS that appear to suggestthat "contaminants* presumed to be emanating from the Army CreekLandfill are impacting one of Artesian Water Company's LlangollenEstates wells. The County's groundwater experts at the Army Creeksite for the past 15 years, Roy F. Weston, Inc. ("Weston"), havereviewed and evaluated the various assumptions, findings andconclusions contained in the groundwater modeling performed byDunn Gebscience, Inc. ("Dunn") for the DS&G RI/FS and found Dunn'sconclusions in this regard to be entirely unsupportable. Weston'stechnical critique is appended hereto and made a part of theCounty's comments for the record.

From Weston's analysis, the following conclusions can bedrawn: - -

o There is no factual basis to conclude that wellAWC-7 is being impacted by the Army CreekLandfill;

o There is no factual basis to conclude that the ArmyCreek recovery well system is not functioning in aneffective manner;

o It is probable that the source of the levels of 1,2dichloroethane in AWC-7 either predates theinstallation of the recovery well system or is apresently unidentified source in the vicinity ofAWC-7; and

o The levels of contamination in AWC-7 arecontinually declining, thus negating Dunn's theoryof a continuing regional source.

(Footnote continued from previous page)Landfill that occurred during preparation of the DS&G RI/FS.

A

SCHMELTZER, APTAKER & SHEPPARD, P,C.DNRECMarch 26, 1988Page 3

Fortunately, your agency and EPA-Region III haveclarified the intent, scope and function of the groundwatermodeling performed in the DS&G RI/FS in a March 25 letter fromAndrew Palestini to David C. Clark and a March 25 letter fromJoseph Hardman to David C. Clark, which are appended hereto.Simply stated, these letters make clear that the groundwatermodeling performed by Dunn cannot be utilized to predict thesource of contamination of AWC-7 other than to conclude that theDS&G Site is not a present source. Moreover, these lettersindicate that the DS&G studies cannot be relied upon to drawconclusions concerning sources of contamination which existedprior to installation of the Army Creek recovery well system.

RECOMMENDED REMEDIAL ALTERNATIVE

The County notes that the DS&G site remedial alternativepreferred by DNREC and EPA includes managing the groundwater plumeemanating from DS&G through continued operation of five recoverywells (RW 13, RW 12, 31, 29 and 28) heretofore installed andmaintained by the County, with treatment at a wastewater treatmentfacility currently being designed by the County. While the Countyhas recognized for some time that this recovery well system hasbeen performing an invaluable service for the DS&G site, it isconcerned that the estimated cost for this portion of thepreferred alternative ($4.75 million) is not sufficient to reflectDS&G's e<juitable share of capital, operating and monitoring costsincurred by the County since 1973, as well as future expendituresto construct, rehabilitate and maintain the recovery well systemand treatment facility.2 Furthermore, it is not at all clearthat, but for the contaminants attributable to DS&G found in thesefive wells, the County would not be required by DNREC to constructan expensive wastewater treatment facility.3

The preferred alternative also includes the removal andon-site incineration of an unspecified volume of waste andcontaminated soil in the drum disposal and ridge areas of the DS&Gsite. The County cannot support this alternative at this time in

2 It is our understanding that the $4.75 million estimated cost(as presented in the Amended Proposed Plan distributed at theMarch 16, 1988 public meeting) does not include any allowance forprior expenditures and is based on a present worth analysis foronly ten years of operation.

3 For example, recent monitoring data indicates that total ironconcentrations in Recovery Wells 28 and 29 are among the highestlevels of any of the recovery wells.

SCHMELTZER, APTAKER & SHEPPARD, P.C.DNRECMarch 26, 1988Page 4

view of the lack of any assessment in the RI/FS of the impact ofthis activity upon the quality of groundwater in recovery wellsimpacted by DS&G contamination. The County is concerned that theopening and subsequent disturbance of these areas could result insignificantly greater concentrations of contaminants in therecovery wells which may negatively impact upon the design andoperation of the treatment system and ultimately precludedischarge permit compliance. This matter will need to be studiedin more detail and coordinated with the County during the remedialdesign phase.

The County appreciates this opportunity to comment uponthe DS&G studies and hopes that DNREC and EPA will involve theCounty in all future discussions concerning remedial actions atthe DS&G site.

Very truly yours,

Wm. Roger Truitt

Enclosures

cc: Donald E. Marston, EsquireDavid C. Clark, P.E.Mr. Phil RetailickKaren Kellen, Esquire

MEMORANDUM

TO: David C. Clark, P.E.New Castle County

FROM: W.M. Leis, P.G. u 1""R.F. Weston, Inc.

DATE: 28 March 1988

SUBJECT: Review DS&G RI/FS

The review of the DS&G RI/FS documents were conducted by ourstaff. Our comments regarding the conclusion of themodeling efforts by Dunn Geosciences are attached.

R-f\ f\ I **s f*$ f\304288

INTRODUCTION

The firm of Roy F. Weston, Inc. (WESTON) had been requestedto evaluate Remedial Investigation/Feasibility Study (RI/FS)documents which were prepared for the Delaware Sand andGravel site in New Castle County, Delaware. These RI/FSdocuments were prepared by Dunn Geosciences, Inc. (Dunn) andwere dated 29 December 1987 and 12 February 1988. WESTONwas asked specifically to evaluate the following areas ofthe RI/FS:

A. The ground-water flow paths passing through bothDelaware Sand and Gravel and the Army CreekLandfill.

B. The models utilized by Dunn to predict andevaluate contaminant flow from Delaware Sand andGravel.

C. The ultimate fates of contaminants in the areasdowngradient of Delaware Sand and Gravel and theArmy Creek Landfill.

METHODOLOGY

In order to complete the above evaluations WESTON reliedupon the following three principal sets of data:

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A. The field and laboratory data collected in supportof the Dunn RI/FS.

B. The ground-water modeling effort conducted by_Dunnand associated calibration data, as supplied toWESTON by Dunn. , ---

C. Past ground water quality and water-level dataavailable through the WESTON project files.

The analyses of these data and the resulting conclusionsregarding the RI/FS for Delaware Sand and Gravel arepresented below.

1* Pumping Patterns ;

Utilizing Figures 6.15-18 (attached) from the^Dunn RI/FS,the simulated pumping periods of Army Creek Recovery wells(1974 to 1981) indicate continued successful maintenance ofa ground water divide at, and downgradient from, the ArmyCreek Landfill. In contrast, flow lines originating atDelaware Sand and Gravel for that same time period indicateno ground water divide between DS&G and the Artesian WaterCompany's Llangollen Estates well field. Dunn's own dataillustrate ground water flow and contaminant migration fromDelaware Sand and Gravel landfill to the area of wellAWCG-3. Because any well extracts water from a 360° areaaround the well, with the shape of the drawdown area afunction of aquifer heterogeneity and anisotropy, it isprobable that ground water flow, originating at DelawareSand and Gravel landfill as depicted by Dunn, could enterth@ pumping areas of AWCG-3 and could be drawn into AWC-7,

Calibration of the model used in the RI may be responsiblefor the variations in later (post-1981) simulations. Thecalibration is discussed further below.

2. Contaminant Sources

The nature of contaminants from both the Army Creek landfilland the Delaware Sand and Gravel landfill are wellunderstood, and are generally distinguishable from eachother. The contaminants from the Army Creek landfill areprimarily inorganic compounds whereas the DS&G landfillcontributes typically organic contaminants. The mix ofcontaminants detected in the area south of the Army Creekground water divide is not representative of contaminantsseen in the Army Creek landfill recovery wells. Also Dunndocuments many organic contaminants including1,2-dichloroethane in DS&G wells at levels greater than2,000 ppb. These observations strongly indicate that theArmy Creek Landfill control program has been successful, anddoes not support the post-1981 distribution patternsproj ected from the Dunn model. The modeled flow patternswithin the Potomac aquifer strongly support the DS&Glandfill as a major source for organic contaminants.

Because modeled flow patterns do support a DS&G source, andbecause no pattern of Potomac aquifer contamination can bedemonstrated from the Army Creek Landfill, alternatehypotheses of organic contamination _ should have beenevaluated by Dunn to fully develop their conclusions. Dunnhas neglected to evaluate other potential contaminantsources that have been previously documented and discussedwith the DNREC. These potential sources, shown in Figure 1,

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include known repositories and trash dumps at the followinggeneral areas: :_;

1. On the west end of Grantham Lane south of the DS&GLandfill. f':~=":

2. The old Avisun and Amoco Chemical Companyi - ai-' - ;-_= disposal areas north of DS&G and along Route 9.

3. A large disposal area along Route 9, east ofAWCG-3. : _

4, Disposal areas along and north of Llangollen Lane.

5. Other disposal areas and waste piles adjacent toLlangollen Estates, i.e, Park Avenue, SaienniBoulevard, and Schaeffer Boulevard.

Many of these sites represent potential sources of organiccontaminants (including 1,2-dichloroethane) that are relatedneither to DS&G nor to Army Creek. It is important to notethat the clay layer which generally separates the ColumbiaFormation from the deeper Potomac sands is known to thinconsiderably over relatively short distances and is actuallynot present in one area near the DS&G landfill. Thissuggests th© possibility of other areas where a significantconnection between ground water in the Columbia Formationand tha Potomac sands may exist. Drawdown patterns at the

i - • ^'j •Artesian Langollen wellfield show a local dewatering of theColumbia Formation in an elliptical pattern ""around thewells. This dewatering indicates a high degree of localhydraulic interconnection between the Coluiobia"and Potomacaquifers, and supports the premise that water quality in the

Artesian Water Company well AWC-7 is likely affected byother sources downgradient of the Army Creek ground waterdivide.

In addition, sampling and analysis of Artesian WaterCompany's well AWC-7 for 1,2-Dichloroethane has shown, forthe period 1982 through 1986, a consistent downward trendfor this parameter. (Data are plotted on Figure 2.) As canbe seen, the downward trend is reflected in the mean valuesand standard deviation values recorded for each of the yearsplotted. This downward trend provides direct evidence thatthe contaminant source for 1,2-dichloroethane in AWC-7 isprobably a small source and one that is probably local tothe pumping cone of AWC-7 and does not support a moreregional source as offered by Dunn.

In WESTON's opinion, Dunn should have evaluated theadditional sources mentioned above, as well as past flowpaths from DS&G, prior to speculating on the sources ofcontaminants in ground water downgradient of the Army CreekLandfill.

3. Ground Water Modeling

It is important to understand that ground water modeling isa tool which is used to help understand complexhydrogeologic systems. Like any tool, modeling has limitswhich must be understood and respected. The data used toconstruct a model and how well the model matches theobserved behavior of the ground water system must agree withthe goals of the model. Key aspects in matching the realworld to the model must include careful consideration ofgrid spacing, calibration criteria and source representa-

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tion. For example, if grid spacing is larger in any area,the conclusions made from model simulations in that areamust be more generalized. Also, if calibration is approach-ed as a general match of real data, the correspondingconclusions based on simulations must, by necessity, begeneral. , '. :~^:- --'

In general, WESTON's comments on the Dunn ground water modelinclude the following: ;

1. The Dunn ground water model commences simulation ofcontaminant input from the Army Creek Landfill at atime earlier than from Delaware Sand & Gravel. It islikely, however, that initiation of pumping stress onthe Potomac aquifer was the principal cause of groundwater contamination in the Potomac as the water levelsdeclined. We believe, therefore, that the modelsimulation of "times of initiation" is incorrect, andthis error would cause changes in theinterrelationships of the predicted plumes in a waythat would probably be significant. "

2. The Delaware Sand and Gravel model simulation does notdiscontinue pumping at New Castle County Well RW-3 in1982, but allows the well to continue pumping beyondits actual period of operation. When RW-3 was turnedoff, recovery wells RW-10, RW-11, RW-12, RW-13 andRW-14 went on line. This means that the last six yearsof th© model simulation includes the effect of apumping well which was not operating. This, we feel,would significantly alter the simulated relationshipbetween the two plumes. It must be remembered that

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between 1974 and 1981 the simulated contours indicatecomplete control between the Army Creek Landfill andthe ground water divide.

Out of necessity, Dunn utilizes pumping rates for themodel which are average values over a pumping timeperiod. These averages are, of course, lower than thedesign pumping rate of any given well. The recoverywell field design recognizes and anticipates thevariation in pumping rates and relies upon maximumpumping rates to maintain positive control of theground water divide. When wells begin pumping belowthe optimal level, the New Castle County programinitiates a period of well rehabilitation to restoretheir efficiency. Thus the ground water flow controlmaintained by the county recovery wells is actuallymore efficient that an average pumping rate simulationwould conclude. Dunn's model cannot account for this,and therefore, the simulated contaminant distributioncannot be supported.

Dunn acknowledges in the RI Report, that this model wascalibrated for purposes of evaluating FS alternativesrelated to ground water conditions at the DS&G site.Therefore WESTON believes it should not be used formore extensive conclusions which would require a higherdegree of confidence in the model than is currentlysupportable. In Dunn's modeling effort, calibrationwas accomplished by matching contour maps of observeddata against simulated heads in the pumping wells.While this is an accepted method of attaining modelcalibration, it is not very rigorous. In a recentconversation with representatives from Dunn it was

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explained to WESTON that the intent of this method ofcalibration was to match the general shapes o f thepiezometric surfaces. Once that was achieved, themodel was considered to be calibrated and ready foruse* WESTON does not agree with that approach. Inorder to defend the conclusions that have been made inthe RI/FS based on this model, the palibration shouldhav© been done as rigorously as possible. A poorrepresentation of the real drawdown in the vicinity ofRW-3, for example, could significantly change theconclusions concerning the Delaware Sand & Gravel siteand the Army Creek Landfill plumes.

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STATE OF DELAWAREDEPARTMENT OF NATURAL RESOURCES

& ENVIRONMENTAL CONTROL .""DIVISION OF AIR & WASTE MANAGEMENT

89 KINGS HIGHWAY " . " -P.O. Box 14O1 _ .-: _- - .. - . . . . . . .

WASTE MANAGEMENT _ . ... _:. " DOVER. DELAWARE i 99Q3.. " - _ TELEPHONE; C3O2) 736 • 4.781SECTION

March 25, 1988

Mr. David C. Clark, P.E.New Castle County GovernmentDepartment of Public Works100 New Churchmans RoadNew Castle, DE 19720

Subject: Delaware Sand & Gravel (DS&G) Landfill RI/FS

Dear Mr. Clark:

In response to your verbal comments on the DS&G RI/FS, EPA has written aresponse addressed to you. The original letter was forwarded to your officeon March 25, 1988. A copy of this letter is attached.

The Department of Natural Resources and Environmental Control, CERCLAManagement Branch, has reviewed the letter and concurs with EPA's response.

We appreciate your interest in the site and hope through continuedcoordination between EPA, DNREC and New Castle County, we will successfullycomplete the remedial actions at both the Delaware Sand & Gravel and ArmyCreek Landfills.

Sincerely,

Joseph J. Hardman, P.E.Supervisor "

JJH:NC/mffNC2096.2

Attachment

cc: P. G. RetallickG. A. MolchanJ. Eberly, Legal