3

NOV 17 '94 04:40PM RETEC

p.2/1

Domormill Square 9 Pond Lane

Concord, MA 017^2-2851 (508) 371-U22

FAX (508) 369-9279 November 17, 1994

458987 SDMS Doc ID

SUPERFUND H E C O R D S C T R Mr. Ross Gilleland - Remedial Project Manager S!e P^A<> S T . C o r v g l

Waste Management Division HPS-1 Break j i Q U. S, Environmental Protection Agency

JFK Building Boston, MA 02203-2211

i-i«i4.200 Resoonse to Comments on the "Draft TreatabiUty Work Han for ' " ' ^ " ' ' N a S w ^ t i o n Evaluation for the Pine Street Banre Canal Site"

Dear Mr. Gilleland:

Please feel free to call if any additional infonnation is needed.

Best regards,

REMEDIATION TECHNOLOGffiS, INC.,

/

' Benjamin R, Genes Principal

BRGMcmb

cc (w/enc): Sheti Larsen - Vermont Gas Joe Kwasnik - New England Electric System Chris CrandeU - The Johnson Co. Laura Kelmar - RETEC

RIe 3.1i85-200\BRO\Gaiatf.041

REMEDIATION TECHNOLOGIES INCORPORATED

. B gs,MT . ChopelHill,NC • St. P..I, MN • Seo^a,WA • Mond^v.ikv lA • Tucson, AZ • l.hoc, NY { y g , r „n«rd,MA . F'iHsburgh, PA • Fort Collins, CO • Austin, TX • Billings,

NOV 17 '94 04:40PM RETEC P.3/13

RESPONSE TO EPA COMMENTS OF OCTOBER 3,1994

Responses to the comments are provided in bold and italics.

General Comments

1. There is no discusston on how the infonnaticHi to be gathered in this study will supplement the data collected during the EPA biorranediation treatability study. WiJl the data be compazabie? Will s a n locations complement previous sample locations? What are the differ^ces between the two studies?

y Re^mnse: The second paragraph qfpage 2 (Section 1.0) addresses the t^erenees f.V/ between ^ e 1991 study and the proposed natural degradation treatability Oudy.

t­ ^pecyUudly, micntldal eitumerations were nat conducted on the earlier treatabSity study sanqiks and differentiation between biodegradation losses and abiotic losses was not a focus tif this prenous study.

Will this data give us an indication of matdbc toxicity and what concentration of contaminants would be limiting to biodegradation?

Response: I f inst^j^fteient microbial populations to indiccOe potential for biodegradation are found daring either the screening activities or the initial characterization phase of the study, an evaluation qf the matrix toxicity wHl be conducted using the Mcroto:^ assay.

The sample collection methodologies are not provided in the Work Plan. If the Johnson Company SOPs are to be used for soil and groundwater sample collecti(»i, they should be referenced. If differrat san^)le collection methods are to be used, SOPs must be provided.

Re^fonset The Johnson Company ce^cted the samples for the screening study and their SOP is now rtferenced on page 1 (Section 2.0). RETEC wUl coUeet the samples for the treatability study and the expropriate SOPs are now included in Appendix A.

4. If would be helpful if the work plan defined more clearly what is meant by "natural biodegradation," since the stated purpose of the work is to determine if natural biodegradation of BTEX and PAHs is occurring in site media. RETEC plans to do this in four phases:

Phase.1 - Review available site data to identify data gaps and select appropriate locations for collection of treatability study samples.

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Biase-TT

a) Perform initial diaracterizations of three samples (unsaturated soil, saturated soil, and shallow groundwater) tD detennine v/btdaer the componoats needed for natural buTde^radatiai to occur aiepresent [Le., substrates (COD, BTEX, PAHs); BTEX and PAH-dograding microbes; and mineral nutrients],

b) Spike the samples with ^*C-labelled benzene and phoiantfarene and measure the production of carbon dioxide containing "C to determine if benzene and ph^ianthrene are degraded.

PhawTiT - Peifonn re^pdrom^ry testing to quantify rates of biodegradation and oxygen consumption (to be performed on unspiked san^les).

PhnmTV - Report and evaluate the data.

Response: Natural biodegradation is the reduction in constituent concentrations in in ^tu soib and sediments wUhota Ae modification of site conditions. The purpose of this study isto dOennine whether biodegradation nupf be one mechanism at work at Ae soUsfordie long-tenn reduction of constituent concentrations site, ffthe results of this preliminary study do not rule out biodegradation as a posable mechanisms, then additional studies wHl be designed and implemented^ both on ihe laboratoiy scale and pilot-sctde, tofurAer evaluate the viability of natural biodegradation as one long-term remedy at the tate.

Figure 1-1 has been included to i/^niify, stt^-ty-sUp, tite procedures to address Ae sequencing of the preliminaiy events to be conducted in this study.

5. To some reviewers not involved in previous discussions, the Work Plan, the ultimate objective is not dear. Is it to evaluate intrinsic biodegradation of PAHs on the Site, or biological attenuation of contaminant migration offtfie site? The objectives will determine sample location and type of media to be analyzed.

Response: Ihe purpose of die udy, as indicated on pages 1 and 2 (Section 1.0), is to determine whether natural degradation should be ej^lored as one mechanism that nwy be occurring to reduce Ae concentration ofAe constituents of interest in soUs and sedimeras at the site. An evaluation i^fAe potential reduaion in off'-site mijpation is not a primary goal of Ais study. IffurAer studies are warranted by Ae residts of this work, natural biodegradation at Ae edges ofAe contaminated areas wiU be evabttUed for its potential to i4fect off-site migration of constituents.

6. The Work Plan does not indicate the limitations of this study. The study should only be regarded as a screening study that assesses the maidmum potential fbr biodegradation. It does not provide adfifpiatfi data to assess the actual behavior of biological processes at the

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site. Factors that may produce much lower biodegradation rates under field conditions include:

a) Weathered organic constiturats are more refractory than the spiked organic constituents due to adsorption, absorption and other phenomena.

b) Phenanthrene is known to be readily degradable compared to the more complex carcinogenic PAHs su(^ as benzo(a)pyrene.

c) O j^en transfer to the area of biological activity is likdy to be limited. There is a significant probability that mudi of the site is under anaerobic conditions. Anaracibic processes are slowo^ fiian aerobic processes and follow diffiaait mechanisms.

Due to these factocs, next-level (e.g., pilot-scale) treatability tests should be conducted if tiie saeening tests show the biological remediation has promise. It is dear that the work in Phase n wiU contribute to an understanding of the potential fbr natural biodegradation (primarily by determining whether indigenous microoiganisms are present which can biodegrade site contaminants). However, the work plan is not clear in rdating how the Phase i n tests will provide infarmaiicHi on natural biod^radation, if one defines "natural" as not aihanced in any way (such as, by addition of non-indigenous microorganisms, addition of si qpplanenlal oxygen and nutrients, or providing mixing). The Phase IU woric wodd be useful in evaluating the feasibility of an engineered treatment system {in situ or ex situ) for the site, but it is not clear how the biodegradation rates determined in these tests could be used for predicting how rapidly the contaminants of concem could be expected to biodegrade under a "no action" or "natural attenuation" scenario. It needs to be clearly stated that the demonstration of successful ^ .e . , measurable) biodegradation in respirom^zy tests does not demonstrate that natural atiemiation is occurring at a reasonable rate. This would avoid the possibility that people reading the work plan will have unrealistic expectations of what the work will demonstrate.

s, '^sponse: We concur with Ae assessment that Acre are limitations to Ais study. X \'\'' m e work described in the Work Plan is intended to provide information regarding Ae ^ : viability of mound Inodegradadon at das site and wheAer additional studies (potentiaUy

j_ ^ including pilot'Scale studies) are wamuOed, The use of Ae oj^gen and nutrient ^l^ '}i enriched reactors in addition to Ae "active " test conditions should yield information ^^ < regarding whatfaOors may require a^ustment at Ae site to provide optimum conations

> for degradation at the various locations artd site conditions.

Lt situ stupes may be conduOed as additioruU s^ps in Ae overall evaluation of natural biodegradation as a potential site remedy mecharusm.

7. Objectives of the laboratory tests are stated; howev^, criteria for establishing success or fefluie of the treatability tests are not given. These criteria need to be devdoped to avoid

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unnecessary testing during subsequent treatability phases. The criteria should uidude specification of the ibllowing fiictars:

nunimum nutcieKit levels minimum number of microorganisms necessary fbr adequate biod^radation. minimum extent of target compound biodegradation within ten day period.

Criteria should be given to determine adequacy of BTEX and PAH removal.

Hie Work Plan should tabulate the test matrix. The test conditions should be limited induding soil matrix, test duration, number of sanqdes tested for each condition. The workplan gives an impression that only a single set of samples will be used for each matrix and each test condition. Duplicate testing is recommended.

Response: The minimum nutrient levels are now indicated to be a ratio of carbon:nitnfgen.'pho9>horus (C:N:P) of approjomatidy 100:5:1 (page 6, Section 2). Ihe nunimum number qf Coloity Forming Units (CPUs) deemed adequate for Imdegradation is 1& per gram of soU (page 4 , Section 1.0). A minimum exunt qf compound

~y degradation is not necessaiy for continued study. A^ty^tisticdl degradadon qfthe BTEX or PAH constituents wia constitute removed. , ^z . , c.,*. vvXi^ >^n^

Composite s a n ^ s wiU be collected and tested under eontrot(sterile}, active (ao amendments added) and amended conditions. D i ^ e a t e sampling ofAe reactors wiU be conducted at start-up to establish baseline conditions, Dt^UcaU sampKng wUl not be conducted subsequentiy.

g. It may also be hdpful to consider adding some tests to deteroiine the partitioning of BTEX and PAHs from tbe soil to the aqueous phase. Research performed by RETEC for tbe Gas Research Institute on Manufactured Gas Plant soils (e.g., see Rqiort No. eRI-92/0499, December 1992, The ( Accelerated Biotreatability Protocol Jbr Assessing Conventional Biological Treatment of Sails: Development and Evaluation Using Sails from Mamfactured Gas Plant Sites) has shown that mass transffex of contammants fiom die soil to the aqueous i^ase, wheare microorganisms can metabolise tiiem, may be the limiting factor in remediation by biodegradation (as opposed to availability of nutrients and presence of contamlnant-d^rading microorganisms). Mass transfer could be the limiting tictoratPineStreet, where there is a NAPL phase, a fair percentage of silt and day, and a fairly high organic content (all conditions which the rqwrt concluded wodd contiibute to mass transfer limitations and increase the treatment endpoints (i.e., cleanup goals attainable by biodegradation). Anotiier recent paper (Rogers, J. A. et al., "A Screening Protocol for Bioremediation of Contanunated Soil", Environmental Prvgress.Wol. 12, No. 2,1993) recommertds tiiat soil desoiption testing be performed akmg witii slurry bioreactor tests (which are analogous to tiie respirometry tests proposed in tile work plan). A copy of the paper is attached.

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Response: Dissolution qf the constituents of interest, particular^ the higher-ringed PAH cortstituents, nury well be Ae Umiting factor in biodegradation at Ais site, but a ladt qf dissolution can be inUrpr&ed as an attenuation mechanism. As Ae purpose of 0US s tas i s to determine wheAer natund deffodation may be one loss mechanism at the site and ntan^pulation qfthe dissolution potentiod itfAese compounds is not a feasible in situ mo^ication, limitations due to dissolution will not be direct evaluated during titis phase ofAe study. However, boA the disseivedfhase and soU-bound phases qfAe BTEK and PAH constituents wHl be evcduated during Ae respiromeOry testing phase of the udy and Uodeffadation tdnetics wUl be calcttiatedfor each of the water-phase test samples. This data can be used to evaluate Untitations in dissolution qfthe constituents. Dissolution rruty be rate Umiting, but in the context of long-tenn remediation and containment at the s&e, biodegradation may stiU contribute to Ae overall remedy.

Sperififi n n m f n m t s

9 . Section 7 1 pTinring -Hata ttftvifw an<1 P-valiiarinn (Pagp- 1)

This section states that "areas where conditions are amenable to natural biodqpadation could be IdentifiBd and evaluated as potential sampling locations". Please stale the conditionsfliat would be needed for an area to be considered amenable. Please also state the criteria that will be used to select appropriate sampling locations. For example, will consideration be givui to contaminant concentraticns and soil type (silty/clayey, high or low organic content, etc.)?

Response: Ihe sample locations witt be sheeted based on Ae results of the screerdng sampling cortdueted by The Johnson Co. Sample locations will be based on a combination of viable microbial populations and the presence of sUe-npreseniative concentratums of PAHs, as daermined by the field tmmurwassay testing conduced on multiple locations at Ae sUe (see Kgure 2-1). Criteria for location selection would include mictvbial populations and PAH concentrations of dmHar magnitude. Consideration will be given to saturated and utaaturated soil conS^orts only, and not soU type. However, toted organie concentrations (TOCs) will be avaUabUfor OH Ae soU screening sanqdes collected by The Johnson Ca, to cdlowfor a potential evaluation qf Ae relationship between constituent concentrations, microbial populations, and organic matter contettt.

10. SanHnn 7 7 Pi>M .<!amplif>£ P m g r a m (Pa£<» 1)

Please describe how the sample will be composite before it is placed into tiie tsxo­headspace cantainers (or will this be done at RETEC's treatability laboratory?). It may be worthwhile to coUect a sample for analysis of BTEX and PAHs at the same time tiie treatability composite is collected. This wodd give an indication of losses of BTEX and PAHs which codd occur during shipment and storage at KETEC before the studies begin.

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The Woric Plan slates that sample locations will be determined fiom existing data and tiie screening results of tiie Phase I ARI program. However, tfiere is no iscuit-rinn of tiie criteria which will be used to select sample locations. There are several statemoits tha indicate tiie samples should be "representative" of tiie site. It is doubtfd tttat two soil samples can be representative of tiie site due to tiie large range of contaminant concentrations. Criteria for sample locations must be stated and tied to data objectives.

Response: Ihe treatability samples witt be field composited prior to placement in a uro-headspace container for shipment. Volatile losses may occur during dnpment, however, samples for constitiient analyses wUl be collected at time a m (at Ote beginning OfAe treatability testing) to be representative of initial stitdy conditions.

Sanple locations wlB be selected based on average nticrabial counts and BIEX and PAH concentrations for die types ofsoU (i.«,» saturated or unsaturated^ evaluated during the screening study.

1 1 . .^wrinn 7 7 Pit»1H .Sampling Prngi-am (Pagi* 7)

Please describe more deady how the groundwaler sartqde will be collected. For example, will all 60 liters of samples be collected fiom one well or several? What equipment will be used to collect the sample? RETEC may want to consider using a submersible pump operated at kiw flow (using EPA's low flow samplmg metiiod) to minimize volatihzation losses and entrainment of particulates in tlie sample,

Response: Water s a n ^ s for titis study witi be from Ae near-surface saturated soils and not from groundwater monitoring wells. Ihe text in Section 2 has beeit modified to r ^ c t Ais intention more cleariy. SampHes will be cottected by excavating an area to ( fpraxinuaefy two-to-titrtefeet below ground surface and submerging sample botties in the water which witt accumulate in the excavation. Suffident water wttl be placed into arch suable conudner to ensure zero^ead^aee to minimize volatile losses during shqnnent and storage.

12. .Section ? T 1 Approach and Ohjerrives /Pag^ 7 hnn^tc)

Please also consider adding as an objective, determining soil/water partitioning of BTEX and PAHs to hdp evaluate potential mass transfer limitations to biodegradation rates (see Comment No. 8).

Response: The evabtation of Ote dissolved-phase and soO-bound BTEX and PAH concentrations wttt be conducted as detailed in tite response to Comment No. B, Additional partitioning studies may be conducted in future stupes if warranted by Ae results of titis study.

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13. Renrinn 7.'^ 1 A p p m a r h anri nhjfyriviiii (Page ^^ is t fiilT paragraph)

Please explain how oxygen-limited and oxygen-amended conditions will be simulated in an electrolytic respirometer. It is this reviewer's understanding that an electrolytic respirometer works by generatilng oxygra through the dectrdysis of water. The dectrdysis is initiated as microorganisms in the respirometer (a dosed system) consume oxygen and give off carbon dioxide. The carbon dioxide is removed fiom the air by a scrubber, which causes a reduction in tiie pressure within tiie syst^n. The reduction in pressure causestiie electrdysis to start, wiacii produces oxygea. Oxygen is produced until tiie pressure returns to its previous state. The amount of current required to generate the OJ gen is reoarded and converted to an oxygoi uptake rate by the respirometer software. If this understanding is correct, it seems that some reconflguration of the respirometer would be needed to simulate varying oxygen contents. Otherwise, oxygoi would be supplied as &stastiie microorganisms could use it and would not be a limiting fiactor. If the respirometer is simply being used as a reaction vessd during the "oxygoi-limited" tests, and the dectrolytic cell will somdiow be tumed off, then this should be explained in the work plan or m the sop fbr respirometry testing (Appendix A).

Response: lb stimulate oxygen-limited conditions, Ae ceU witt be tumed oft, TJiis is itow described on page 5 of Section 2,

14. .SftT-tifin I.T^ 7 T j h m a t n r y FvalTiari<>n Wnrlr Plan, .Sample rharar.TmTarinn anri MinPFjiliratiom Tpjiring (Page A)

It is suggested that duplicate sainples of the initial (before testing) soils be analyzed for BTEX and PAHs. This will allow some evaluation of variability in contaminant concentrations due to sample heterogendty. Also, please state when/from where the samples wiH be submitted (from the site or from RETEC's Seattie laboratory).

Page 4, paragraph 3 states "Further inorganic analysis, specifically heavy metals, may be initiaiEd if it is bdieved that metals inherent in the site media are inhibiting bioactivi^". What infonnation win be used to determine that this is the case and when will the dedsion be made to conduct further analyses? A^^ sample size be suffident for these furtiier analyses?

Response: Di^Hcate san^Sng wUl be conduct^ for Ae time^ero samples during the respirometry testing phase ofAe study (Section 2, page 10) to evaluate contaminant variability. Att samples for laboratory analyses witt be submitted from RETEC's Seattie laboratory.

Inorganic anatyses witt be conducted tfAe mineralization t e indicate an absence of microbial aetirity. Metal concentrations in Ae sonnies witt be compared to l&eraturt values that have established toxidty to microorganisms or ate-^eafic flora. Metal toxidty witt be difficult to prove condusivety, but metals anafysis couM be valuable in explaining poential microbial inhibitions. Suffident sott samples wUl be available for Aese analyses, tf necessary.

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15. Tablt* ?.-?., Page fi

Include unitsfoor soU PQLs also.

Response: Unite off^gfLfor sott PQjLs have been added to Table 2-2.

16. BespiromRtry Testing, Page 7

Please explain how the electrolytic respirometer would be modified so that it wodd not automatioilly provide oxygen (see Comment No. 13 also).

Page 7, paragraph 3 stales, "If tiie sanqtles evaluated in tiie mineralization testing reveal sufficient BTEX- and PAH- biodegrading microorganisms, then tiie rates of constituent biodegradation in Oie subsurface samples . . . will be evaluated in respirometiy testing." What number or range is considered to be "sufficient"?

Respirometry data on samples of peat would be of littie use since the BOD of tiie peat wodd overwhehn tiiat of PAH cmtaminants. The presence of peat may dramatically alter the rate of intrinsic bioremediation. Beddes high oxygen demand of peat, water sduhility of PAHs is so low tiiat tiiey will undoubtedly partition heavily into the peat and remain unavailable to rmcnooiganisms for metabolism. On the otiier hand, strong partitioning into peat may prevent migration of PAH contaminants off the site.

Respirometer tests do not measure PAH and BTEX. What are the critical variables for the respirometer tests? The work plan should list both critical and non-critical variables.

Response: Ihe electrolytic cell witt be turned off in Ae mcy^n-Hmited test condition.

As now stated on page 4 qf Section 1, mkrobial populations of Iff CPUs per gram of soU witt be considered adequate for contirtued evaluation.

Ihe c r i t i c variables of Ae respirometry tost are oxygen consumption and constituent ranovaL Iflti^i BOD due to peat is competing for ihe oxygen in Ae Oudy, constituent removal witt be reduced.

17. T t e S p ' " " " * ^ Teicring, P a g e «

Please state the quantities of soil and water antidpated to be added to the respirometer flasks. Also describe any soil pr^iaration which may be needed (such as screening to remove pebbles).

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Response: The re^dronutry flasks witt have a 20 percent solids buiding (300 grams of soa wiA 1.5 liters of water). SoU witt be screened so Aat particles greater Aon 4.5 mm witt be eliminated (page 10, Section 2).

18. .Serrinn 7 A Rvalnatinn of Tjhnrafnry liata (Page 0)

Ihe first sentence states that, "If BTEX and PAH r^noval rates are rapid in the presence of excess oxygen, then tbe rate of oxygen transport achievable in the substn&ce may limit tiie extent of natural biodegradation achievable at tiie site." This statement is too strong, because it is possible thattiie rate of transport of contaminants from tiie soil to the aqueous phase (in addition to or instead of the rate of oxygen transport) may be the rat&-limiting factor. The mass transfer of contaminants would be enhanced during the respirometry study (since the reactors are being shaken); such oihancement would not occur under natural conditions. Also see Ckmiment No. 8.

Page 9, paragraph 1, last sent^ce: This soitence is unclear to me - it refers to a "respirometry computer modd" which does not seem to be mentioned anywhere else in the Work Plan. If a computer modd wiU be used to evaluate data, the modd and parameters to be used should be deariy stated. Also, it is unclear how this laboratory data wUl be used to compensate the model o u ^ t .

Response: RETEC concurs that dissolution may wett be the limiting factor. However, oxygen transfer may also be a factor. See response to comment 8,

Rtferences to the respirometry computer model have att been deleted Jrom the Work Plan.

19. .^erfiftn X ± rftinptetenew^' Page. ^^ fitvimA Patngraph

The first sentence refers to "column flow rate", but no column tests are proposed earlier in tiie work plan.

Response: References to column Indies have been deleted from Ae Work Plan,

20 . .<;ft>rion 4 7 MinpraliTarinn Tejgring n^fp

This paragraph refers to soil columns fbr mineralization testing, but tiie SOP (Appendix A) says that incubation vessels wiU be \ised. Please darify.

Response: Liadtation vessels witt be used in Ae study* InadverterU rtferences to soU eobanns have been remove from the Work Man.

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2 1 . Rfrtinn 4 ^ Pegpitnmeh-y nata^ Page 2 , Firs t Paragraph

Please state for which constituents or groups of constituents a mass balance will be performed (e,g., total BTEX, total PAH, total carcinogenic PAH, or each contaminant of concem individually.

Re^Hfnse: Mass balanees witt be cortdueted on the indiridudl PAH and BTEX constituents.

22 . fl^^tirtn ± 1 Tgp^immet ty riata^ Page 7^ Tast : Paragraphs

Table 2-3 showstiiattiie soil in die re^nromettyflasks will be analyzed twice, at time zero and at the end of tiie tests (Day 21). If this is the case, then it will not be possible to do the analysis described here to distinguish betweoi zero-order and first-order kinetics fbr soil because there will only be two soil data points to work with for each set of test conditions. (It could be done for tiie aqueous phase since Table 2-3 indicates it will be analyzed at four intermediate time intervals as wdl as the beginning and end of the tests). Please clarify howtiie kinetic analy^ will be done and fbr what constituents (total BTEX, total PAH, total cardnogenic PAH, COD, etc.)

Response: ISnaic anatyses witt be conducted on Ote wtoer-phase data onfy. Ihe text has been revised to rifled titis. Calculations witt be conducted on the individtuU BlEX and PAH constituent onfy.

EPA Comments of October 21,1994

General Comments

1. We suggest that an additional sample be takea in the inland area at the edge of the wetiands/fiee-phase area near the former coal-gasification plant, since the "edge" areas are tiie focus of the natural biodegradation study. We don't see the need for two samples in tiie Ttirmng Baan and would find it acceptable if one of those samples were moved to the uplands area.

Response: An additiorud sample in tiie arat tf dte former coed-ga^ication plant was included in Ae screening sample locations (see Ftfftre 2-1), Ihe two samples in the Tuming Basin were Itfi to provide information regarding constituent and microbial hderogendty.

We siiggest thattiie sample positioned just NW ofttie edge of Maltex Pond (but sqiparentiy not intiie canal) be moved North to the "Palustrine Scrub/Shrub" wetlands area (see Fig 3-22 of the RO located due Nortii of tiie Maltex Pond-capped area.

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Response: Ihis sanple location was a^usted as suggested.

3. We suggest that at least cue and pos^bly two, screening san4>ks be located to the west of the canal. It would be preferable to have one per wetiand type (emergent and wooded wedands). We realize that tius may involve additional sample coUection in this area, but fed the extra time for sample collection will be minimal compared to the value of having data points here.

Response: Two sanple locations were added west ofAe canal as tmggested.

4. We question viAietiier or not tfaeie should be some kind of quality dieck on the samples sent to tiie laboratory for microbial evaluation (blank, spiked, and/or duplicate sanopLes). We are working whh our laboratory to identity whattibie appropriate sqiproach might be and would like to discuss this with you next week.

Response: A blind duplicate was cottected during sampling and a ^ rWxtd sand sample was prepared by tiu RETEC Seattie laboratory and s u b m i t ^ to the lab fbr rnicrobial anafysis. ^piking a sam/defor microbial anafysis was not deemed t^propriate.

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