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Chapter 4Nature and Extent of Contamination
4.1 Introduction
Chapter 4 presents a summary of the analytical data collected during the RI activities at theHalby Chemical site and an evaluation of the nature and extent of contamination at the site.Nature and extent are discussed according to contaminated media (soil, surface water,sediment, and groundwater).
The data are presented and discussed to illustrate the nature and extent of contamination.Discussions of the migration of chemicals, such as geochemical explanations of observeddistributions and descriptions of the relationships between chemical concentrations in adjacentmedia, are reserved for Chapter 5, "Contaminant Fate and Transport."
Analytical results obtained during earlier investigations are discussed because an objectiveof the current RI is to obtain information that complements the earlier data, providing acomprehensive view of the nature and extent of contamination at the site. The analytical datafrom earlier investigations, particularly the EBASCO RI (1990), are available in reports onthose activities. .For activities in which new data were collected at previously sampledlocations (e.g., monitoring wells), data from previous investigations are not included infigures in this report but the results are described, where appropriate, in the text. Alsoincluded in the discussion are data collected: to support bioassay studies (Knight andSprenger, 1992; Weston, 1992); during USEPA's expedited removal action in 1995; byWeston (1995); and during investigations performed by Witco in 1993, 1995, and 1996.
The presentation on the nature and extent of contamination begins with a discussion of thequality of the data (section 4.2), then proceeds through descriptions of contamination in thesoil, surface water, sediment, and groundwater (sections 4.3 through 4.5). Analytical resultsfrom biota sampling are discussed in Chapter 7, "Ecological Risk Assessment." Summarytables of selected statistics on contaminant concentrations are presented in this chapter. Thesummary tables use only detected chemicals in the statistics. The analytical data obtainedduring the RI activities are in Appendix D.
The primary chemicals selected for discussion in this chapter include those determined to bechemicals of potential concern (COPCs) for human health after screening for exposure torisk-based concentrations (RBCs) calculated in accordance with USEPA Region III guidance(USEPA, 1993). For each constituent that was detected in a medium, the maximum detectedconcentration was compared to the RBC. If the maximum detected concentration was higherthan the RBC, the constituent was considered a COPC. The RBCs were calculated by usingconservative exposure parameters determined from knowledge of the site and from USEPAguidance. The COPCs for human health are listed in Table 4-1. The details of how the
4-1
SR302275
Table 4-1Chemicals of Potential Concern for Human-Health Evaluation
Halby Chemical SiteSoil
Surface Soil*
Carbon disulfide AluminumVinyl Chloride Antimony
ArsenicAnthracene BerylliumBenzo[a]anthracene CadmiumBenzo[b]fluoranthene CopperBenzolklfluoranthene ManganeseBenzo[a]pyrene MercuryChrysene Thalliumlndeno[1,2,3-cd]pyrene Vanadium
Zinc
Residential Plot Soil
AluminumAntimonyArsenicCadmiumChromiumManganeseThallium
Surface WaterOnsite
Carbon disulfideAmmoniaArsenicThiocyanate
Subsurface Soil
Carbon Disulfide BerylliumCadmium
Anthracene ChromiumBenzolblfluoranthene CopperBenzo|k)fluoranthene ManganeseBenzolalpyrene MercuryChrysene Vanadiumlndeno|1,2,3-cdlpyrene Zinc
AluminumAmmoniaAntimonyArsenic
Offsite
AmmoniaArsenicCyanide
SedimentOnsite
ArsenicBerylliumCopper
Offsite
Benzo(a)pyreneArsenicBeryllium
Groundwater (onsite)Columbia
Acetone AmmoniaBenzene ArsenicCarbon disulfide BariumChlorobenzene Cadmium1 , 1 -Dichloroethane Cobalt2-Hexanone Manganese4-Methyl-2-pentanone NickelTetrachloroethene SilverToluene ThalliumTrichloroethene ThiocyanateVinyl chloride Vanadium
ZincAldrinHeptachlor
Upper Potomac
BenzeneCarbon disulfide1 , 1 -DichloroetheneTetrachloroetheneTrichloroethene
AluminumAmmoniaArsenicBerylliumCadmium
CobaltCyanideManganeseNickelSilverThalliumThiocyanateVanadiumZinc
Lower Potomac
AmmoniaManganeseThallium
Groundwater (offsite)Columbia
Benzene Arsenic2-Butanone BariumCarbon Disulfide Beryllium1,1 -Dichloroethane Cadmium1,1-Dichloroethene ChromiumTetrachloroethene CobaltToluene CyanideTrichloroethene ManganeseVinyl Chloride Nickel
SilverAldrin Thallium
ThiocyanateAmmonia ZincAntimony
Upper Potomac
Carbon disulfide
AmmoniaArsenicBerylliumCadmiumCobaltManganese
NickelSeleniumSilverThalliumThiocyanateVanadiumZinc
Lower Potomac
None
FishNo COPCs were identified for fish fillet samples.' Surface soil includes constituents detected in surface and subsurface soil, but does not include samples
from the residential plot.
AR302276
COPCs were determined are presented in Chapter 6, "Human Health Risk Assessment," andin Appendix E. Other chemicals are discussed that are not defined as COPCs but for reasonsof the frequency of detection, known use on the site, or high level of concentration, appearto be indicators of the nature and extent of contamination.
COPCs for ecological risk also have been defined and are listed in Table 4-2. The COPCswere selected by comparing maximum concentrations of detected chemicals to variousecological criteria for soil, surface water, and sediment. The criteria and the distribution andeffects of COPCs for ecological effects are discussed in detail in Chapter 7, "Ecological RiskAssessment."
The quantitative criteria for selecting chemicals as COPCs for both human and ecologicalhealth are included in the summary tables for soil, surface water, sediment, and groundwaterin this chapter. The criteria are only for screening purposes and do not necessarily representgoals for remediation.
4.2 Data Quality
Quality control (QC) reviews were performed on the analytical data collected in thisinvestigation, as required by the CLP and the CRL. Validated data packages were receivedby CH2M HILL from the validators and were reviewed for completeness and accuracy beforebeing used. Corrections to the data packages were provided by the validators and areavailable with the data packages. Complete data packages are not included in this reportbecause of their volume but are kept in the project files. All data obtained during this RI andused in the evaluation were validated properly according to USEPA guidelines andprocedures. Data from EBASCO (1990), USEPA's expedited response action, and Witco'sresponse action also were validated.
Field QC performed during the site investigation included collecting duplicate samples, tripblanks, equipment blanks, and field blanks. The analyses of the QC samples were evaluatedduring the data review at the laboratory before the data packages were completed. Field QCsample results are in Appendix D. In addition, samples were collected from the bentonite andsand used in drilling and constructing monitoring wells. The complete analytical results ofthe bentonite and sand samples are presented with the soil analytical data in Appendix D.
In some cases, sample detection limits differed from the contract-required detection limits.Correcting soil-sample results for moisture content and factoring for dilution of samplesaffected detection limits. Some detection limits for some compounds exceed concentrationsat which potential adverse health or ecological risks are predicted. In addition, raising thedetection limit of some samples may cause some compounds not to be detected. Theanalytical approach of the RI did not allow for the potential for false negatives to beevaluated. However, according to the QC review of the data, CH2M HILL feels that theanalytical results are representative of conditions existing at the site.
4-3
flR302277
Table 4-2Chemicals of Potential Concern for Ecological Evaluation
Halby Chemical SiteSoil
Carbon disulfide4-MethylphenolMethylene chloride
AluminumArsenicBariumBerylliumCadmiumChromiumCobaltCopper
CyanideIronLeadManganeseMercuryNickelSeleniumSilverThalliumVanadiumZinc
Surface Water
Carbon disulfide
4,4'-DDTEndosulfan IIEndrinMethoxychlor
AluminumAmmoniaAntimonyArsenicCadmiumChromiumCopper
CyanideIronLeadManganeseMercuryNickelThiocyanateZinc
Sediment
Acetone2-ButanoneCarbon'disulfideEthylbenzene4-Methyl-2-pentanoneMethylene chlorideTetrachloroetheneToluene1,1,1 -TrichloroethaneTrichloroetheneVinyl chlorideXylene
4,4'-DDT
AcenaphtheneAcenaphthyleneAnthraceneBenzole acidBenzo(a)anthraceneBenzo(a)pyreneBenzo(b)fluorantheneBenzo(k)fluorantheneBenzo(ghi)peryleneBis(2-ethylhexyl)phthalateButyl benzyl phthalateChryseneDiethylphthalateFluorantheneFluorenelndeno(1 ,2,3-cd)pyrene2-Methylnaphthalene4-MethylphenolNaphthalenePhenanthrenePyrene
AluminumAmmoniaArsenicBariumBerylliumCadmiumChromiumCobaltCopperCyanideIronLeadManganeseMercuryNickelSeleniumSilverThalliumThiocyanateVanadiumWeak-acid-dissociable cyanideZinc
AR302278
4.3 Soil
The discussion of the nature and extent of contamination in soil is presented in foursubsections. Background conditions and potentially site-related chemicals, including COPCsfor human health, are discussed first (4.3.1). Then, chemicals in onsite surface soil (4.3.2),onsite subsurface soil (4.3.3), and offsite soil (4.3.4) are discussed. Surface soil around theresidential trailers along Terminal Avenue is discussed in subsection 4.3.2.
As shown in tables 4-1 and 4-2, many COPCs are identified for surface and subsurface soil.Only arsenic and carbon disulfide in surface soil and arsenic, antimony, and carbon disulfidein subsurface soil are included in the figures because the preliminary risk-based screeningdescribed in section 4.1 indicated that these chemicals contribute most to human-health riskat the site. On most of the site, the industrial worker is the human most likely to be exposedto contaminated soil, so the industrial-worker RBCs are provided in all figures illustrating soilcontamination. In Figure 4-1, in which the residential-trailer area is shown, the residentialRBCs also are provided. The residential-trailer area is the only location where residentialRBCs are applied. Human-health risk is referenced when discussing soil contaminationbecause the determination was that ecological risk posed by soil is limited to a narrow bandbordering the onsite lagoon, the only place where significant ecological exposure to soilwould occur.
The statistical summaries include the maximum, minimum, and average detected value foreach analyte detected; the detected and total count for each chemical detected; concentrationsin the background samples; the industrial-screening RBCs described in Chapter 6; and theecological risk criteria described in Chapter 7. Data from EBASCO (1990), CH2M HILL'ssoil sampling in 1993, and USEPA's expedited removal action in 1995 are included in thesummary tables and discussion. The data from Witco's soil-grid sampling in 1993, Witco'sresponse action performed in 1995 and 1996, and residential soil sampling performed in 1996are included only in the discussion.
4.3.1 Background
For the purposes of this discussion, background soil concentrations are defined by dataprovided by DNREC (1996) that comprises background information collected at the sites of50 previous investigations in Delaware. These data were selected for background becausethe extensive filling near the site made properly defining background conditions difficult.Background data are available only for metals; organic compounds were not considered tobe present under background conditions.
Chemicals at onsite locations with concentrations lower than the background concentrationare considered not site-related. If the onsite samples had concentrations of a chemical thatwere higher than background levels (which typically was the case), then the chemical wasconsidered potentially site-related. Other factors, such as the proximity of other possible
4-5
AR302279
' TRAILER AREA X s'
LEGEND— - — - • ;. ~£ BOUNDARY . - NOTE:
ALL UNITS ARE IN MILLIGRAMS/KILOGRAMS©^v-C WCN.TOR.NS WEu. LOCATION N0 , NOT DETECTED
• SB-/3 SOIL BORING LOCATION WITH NA • NOT ANALYZEDSURF ACE-SOIL SAMPLE
• PA-19 RESIDENTIAL-PROPERTY SAMPLE
//
;v>-3 SO'_-BC!plNC ^.OCATiON \V;THc'- •• :;^yfw--ACt SOIL SAw a
k ;« j- "5* - T ,OCAtiOr4 "vViTnC\,-- <;_:J3^—ACL SO-L SAVfVC^
INDUSTRIAL WORKER RESIDENTIALRBC RBC
(mg/kg) (mgAg)AS • ARSENIC 3.8 0.43CS2 • CARBON DISULFIDE 310 NA
Figure 4-1ARSENIC AND CARBON DISULFIDE "
CONCENTRATIONS DETECTED IN SURFACE-SOILSAMPLES IN NORTHWEST PART OF THE SITE
________________________Halby Chemical Site09-JAN-1997 4979f007.dgn
sources and the history of use at the site, were considered in the subsequent evaluation and,in some cases, suggested that a chemical at a concentration above background was not site-related. The fact that the soil at the site to a depth of several feet consists largely of materialtransported to the site as fill contributes to most of the chemicals analyzed for appearing tobe site-related. Therefore, although the analytical results are compared with backgroundlevels in the following discussion, the primary focus is on the chemicals that exceed RBCsfor various exposure scenarios.
4.3.2 Onsite Surface Soil
Fifty surface-soil samples were collected on the site during all investigations, up to 20 ofwhich were evaluated in Table 4-3. Because of the large number of samples, the analyticalresults for arsenic and carbon disulfide are discussed in three separate subsections: thenorthwest part of the site (referred to in Chapter 2 as the "Former Lagoon Sampling Area"),the vicinity of the process plant drainage ditch, and the former process plant area.
Table 4-3 shows the summary statistics on all detected chemicals, background concentrations,RBCs, and ecological criteria. The analytes shaded in the table are those determined to beCOPCs on the basis of human-health and ecological risk-based screening. Most of theinorganic analytes were detected on the site at at least one location at concentrations thatexceeded the background concentrations, indicating that they may be site-related. Exceptionsare antimony (which was detected at a maximum of 5.9 mg/kg although the backgroundconcentration is less than 30 mg/kg) and thallium (which was detected at a maximum of0.93 mg/kg although the background concentration is less than 2.0 mg/kg). No backgrounddata were provided for organics but they are assumed to be zero.
4.3.2.1 Northwest Part of Site
Figure 4-1 shows the areal distribution of concentrations of arsenic and carbon disulfide insurface soil. Arsenic exceeded its RBCs at all locations sampled. Carbon disulfide was notdetected but is included in the figure because it exceeded its RBC elsewhere on the site. Ofthe COPCs not shown in Figure 4-1, aluminum, beryllium, manganese, nickel, and vanadiumalso were detected at concentrations exceeding their RBCs. The maximum concentration ofaluminum detected in surface soil on the site was found at SB-2.
The residential samples were only analyzed for metals, and sample PA-19 (and its duplicatesample PA-18, not shown in the figure) were analyzed only for antimony, arsenic, cadmium,cobalt, and lead. As shown in Figure 4-1, arsenic exceeded its RBC at all three locations.Aluminum, antimony, beryllium, cadmium, chromium, lead, manganese, and thallium alsoexceeded their RBCs on the residential property.
4-7
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AR302283
4.3.2.2 Former Process Plant Area
Figure 4-2 shows the areal distribution of concentrations of arsenic and carbon disulfide insurface soil in the former process plant area. Arsenic exceeded its RBC at all locations. Thehighest level of arsenic was found at SSS-09. Arsenic concentrations varied widelythroughout the area, suggesting that isolated spills may have caused the elevated levels.
Carbon disulfide was detected well below its RBC at all locations; concentrations of otherVOCs also were low to not detected. The highest concentrations of SVOCs were detectedat SSS-09, the location that also had the highest level of arsenic, and at SSS-17, near the reargate. The limited areal distribution of the SVOCs suggests that isolated spills were thesources of the contamination. The isolated distribution of detections was consistent with thatreported by Langan (1993).
4.3.2.3 Vicinity of Process Plant Drainage Ditch
Figure 4-3 shows the areal distribution of arsenic and carbon disulfide concentrations insurface soil in the vicinity of the process plant drainage ditch. Arsenic exceeded its RBC atall locations. The highest level of arsenic was found at SED-02A. Concentrations of arsenicvaried widely among the other sampling locations. Aluminum, beryllium, copper, mercury,and zinc also were detected at concentrations above their respective RBCs, although at veryfew sampling locations.
The highest concentrations of carbon disulfide were detected in samples from the northernend of the drainage ditch (locations HCS-3 and SED-03A). At station SED-02A, vinylchloride, toluene, xylenes, PCE, trans-1,2-dichloroethene, and TCE also were detected; thestation is in the drainage ditch. Location SB-18 had high levels of several SVOCs, includingthe highest onsite level of benzo(a)pyrene.
4.3.3 Onsite Subsurface Soil
Soil samples were collected on the site in two specific areas during the current RI: (1) thenorthern part of the site, to assess the potential levels of contamination in the onsite fill andin former lagoon sediment that is now under the fill; and (2) what was referred to as the"Focused Soil Sampling Area" in Chapter 2, located northwest and just outside the formerprocess plant area, to assess the presence of contamination at locations where past plantactivities were noted in aerial photographs. Analytical results reported by EBASCO (1990),by USEPA as part of their expedited response action, and by Witco as part of their responseaction are included in the discussion.
Table 4-4 shows the summary statistics on all detected chemicals, background concentrations,RBCs for human health, and ecological criteria. The analytes shaded in the table are thosedetermined to be COPCs on the basis of risk-based screening for human health and ecological
4-10
AR302281*
AR302285
/ SED-07 (SOUTHWEST CORNER OF PLANT),m AS 93.2,' • CS2 0.32
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(mg/kg)AS = ARSENIC 3.8CS2 = CARBON DISULFIDE 310
Figure 4-3ARSENIC AND CARBON DISULFIDE CONCENTRATIONS
IN SURFACE-SOIL SAMPLES IN THE VICINITYOF THE PROCESS PLANT DRAINAGE DITCH f?5T7CTTI
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AR302289
effects. Only the industrial RBCs are provided for reference for human-health risk becausethis is the most likely exposure scenario. All inorganic analytes were detected on the site atat least one location at concentrations that exceeded the background concentrations, indicatingthat all of the analytes may be site-related. No background data were provided for organicsbut they are assumed to be zero.
4.3.3.1 Northwest Part of Site
Subsurface samples were obtained from 15 soil borings drilled and sampled in the northwestpart of the site during the current RI. Samples from one well borehole (IMW-10) drilledduring the current RI, two samples from locations SSS-14 and SSS-15 reported in EBASCO(1990), and samples from Witco's test pits TP-28, TP-29, TP-37, and TP-39 also wereavailable for evaluation.
Inorganic Chemicals. Many of the detected inorganic chemicals were at concentrationsabove their background concentrations, and several inorganics exceeded their RBCs forhuman health (the COPCs in Table 4-1). Figure 4-4 contains the results for arsenic, antimony,and carbon disulfide.
Locations with the Highest Concentrations. Borings SB-8, SB-13, and SB-20 had thehighest concentrations of most inorganics and identify an area of likely contamination.Arsenic and beryllium concentrations were highest at SB-13 and SB-8, respectively. Thefollowing information supports the likelihood of an area of contamination around theseborings:
• The highest concentration of arsenic (2,350 mg/kg) was detected at 8 to10 feet bgs in SB-13. The next-highest value was 130 mg/kg, detected at adepth of 12 to 14 feet bgs at SB-10. Other arsenic concentrations in thevicinity of this sample were much lower than 130 mg/kg but still above theRBC.
• Antimony was detected above its RBC at two locations: 3,810 mg/kg at adepth of 4 to 6 feet bgs at SB-20 and 13.3 mg/kg at a depth of 3 to 3.5 feetbgs at TP-29. Antimony commonly was not detected elsewhere.
• Manganese was detected above its RBC at a depth of 4 to 6 feet bgs at SB-20;the next-highest concentration was detected at a depth of 8 to 10 feet bgs atSB-8.
• Beryllium was detected at its highest level (7.1 mg/kg) at a depth of 4 to6 feet bgs at SB-8, near SB-13.
4-17
4R302290
COO
. sa-s/ (6-3)
AS 6.9/SB 5.0/ CS2 ND
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LEGEND_ . _ . . SITE BOUNDARY
) MONITORING WELL LOCATION AgSB • ANTIMONY 8.5
APPROXIMATE SOIL-SAMPLING LOCATION CS2 ' CARBON DISULFIDE 310
• SSS-14 NOVEMBER 1988. SEPTEMBER 1989NOTE:
^.j nu. umio MRE IN MILLIGRAMS/KILOGRAMS
• SB-3 SPRING 1993B • INDICATES THAT COMPOUND WAS DETECTED
IN THE ASSOCIATED METHOD BANK.(4-6) DEPTH OF SAMPLE IN FEET
A TP-37
APPROXIMATE AREA WHERE „.,,. ,„,FORMER LAGOON SEDIMENTS 3C*" 'WERE ENCOUNTERED
4979t009.cJgn 10-JAN-1997
Figure 4-4ARSENIC, ANTIMONY AND CARBON DISULFIDE *
CONCENTRATIONS IN SUBSURFACE-SOIL SAMPLESIN NORTHWEST PART OF THE SITE
__________________________Halby Chemical Site
• SB-20, at a depth of 4 to 6 feet bgs, had the highest levels of total chromium,nickel, and vanadium, besides having the highest level of manganese. Thesecond-highest value of nickel was detected at sb-8, and the second-highestvalue of total chromium was detected at SB-13.
• The highest concentration of copper (24,300 mg/kg) and the only one thatexceeded the RBC was detected at a depth of 8 to 10 feet bgs at SB-13. Thenext-highest value, 576 mg/kg, was found at SB-10. The highest concentra-tions of cobalt, zinc, and mercury also were detected at a depth of 8 to10 feet bgs at SB-13.
• The highest concentration of vanadium was detected in SB-20 at a depth of4 to 6 feet bgs.
• The two highest levels of lead were detected in SB-8 and SB-13.
Most of the samples in the northwest part of the site were obtained at depths greater thanabout 4 feet bgs so that the former lagoon sediment could be adequately investigated.Therefore, there are few shallow samples for supporting trends in depth vs. concentration.Concentrations of arsenic were detected well above RBCs at all depths.
Thiocyanate was" detected at locations SB-6, SB-7, and IMW-10 at concentrations rangingfrom 82 to 264 mg/kg. These concentrations are below the RBC of 2,100 mg/kg but areunusually high in comparison to thiocyanate concentrations in the vicinity.
Chemicals in the Former Lagoon Sediment. The primary objective of collecting soilsamples in the northwest part of the site during the RI was to assess the level of potentialcontamination in the former lagoon sediment and the extent to which the potentialcontamination may serve as a source of future contamination of groundwater. In support ofthis objective, the analytical data from the samples of former lagoon sediment or of samplesof material at the expected depth of the sediment were reviewed. The approximate areaswhere materials were encountered that indicated the presence of former lagoon sediment areindicated in Figure 4-4. The former lagoon sediment may exist at other locations, but noevidence of them was observed.
Table 4-5 contains information on all samples taken of the former lagoon sediment or fromsediment either just above or just below the horizon of the sediment. The table shows thedepth, the lithologic character, and a summary of available analytical results. Whenencountered, the former lagoon sediment was characterized by:
• Wood fragments in a matrix of silt or sand
• A thick black liquid found on the soil sampler at many locations, either in theformer lagoon sediment or in adjacent samples
4-19
AR302292
Table 4-5OBSERVATIONS OF FORMER LAGOON SEDIMENT
Halby Chemical SitePage 1 of 2
BoringTest PitLocation
SB-1
SB-2
SB-3
SB-4
SB-5
SB-6
SB-7
SB-8
SB-9
SB-10
SB-11
SB-12
Sample Depth(ft bgs)
10-19
8-11
10-12
—
6-8
7-10
9-11
12-17
7-11
—
5-14
—
12-14
-
Lithologic Character
Organic wood fragments,peat, and organic silt in finesilty sand; oily shine onparticles
Organic soil with largewood fragments
No obvious organic material
No obvious organic material
Organic fragments in elasticsilt
Vegetative matter and rootsin black silt with sand
Black elastic silt
Organic soil, peat
Silt and wood chips mixedin silty sand
No obvious organic material
Scattered wood fragmentsand organic matter in siltand silt with sand
No obvious organic matter;black elastic silt at 9-10 ft.bgs
Silt with sand
No obvious organic material
OtherObservations
Black liquiddetected on
sampler at 12-14ft. bgs
Strongunidentified odorat 10-12 ft. bgs
Strong organicodor at 4-6 ft. bgs
—
--
—
Strongunidentified odorat 8-10 ft. bgs
Faint oily sheen at7 ft. bgs, blackoily liquid on
sampler at 10-14ft. bgs
—
Black oily liquidin sampler at10-14 ft. bgs
—
~
~
ChemicalsAbove RBCs*
Not sampled
Not sampled
As detected inblank
Not sampled
Not sampled
Not sampled
As, Al
As, Cd
As
Not sampled
As
~
None
Not sampled
AR302293
Table 4-5OBSERVATIONS OF FORMER LAGOON SEDIMENT
Halby Chemical SitePage 2 of 2
BoringTest PitLocation
SB- 13
SB-19
SB-20
IMW-10
TP-37
TP-39
Sample Depth(ft. bgs)
8-10
14-16
8-10
12-14
9-13
8-8.5
8-8.5
Lithologic Character
Organic soil with fine rootsand wood fragments
Silt with sand
No obvious organic material
Organic soil with woodfragments
Gravel fill with woodfragments, organic soil
Brown organic peaty silt
Clayey silt with mattedplant debris
OtherObservations
Thick black liquidon sampler at8-10 and 12-14
ft. bgs
—
Thick blacksubstance onsampler
Thick black liquidin sample
-
Strong odor noted
-
ChemicalsAbove RBCs*
As, Cu, Pb, Tl
As
As
As
As
CS2
Not sampled
*Chemicals with concentrations exceeding risk-based soil concentrations as defined in Chapter 6, "RiskAssessment."
WDCR1026/010. WPS
AR3Q2291*
• Arsenic concentrations exceeding their RBCs in all analyzed samples
• Cadmium, copper, lead, and thallium exceeding their RBCs in some of theanalyzed samples
Organic Compounds. VOC concentrations were elevated above background (assumed zero)for the few compounds shown in Table 4-4. Carbon disulfide was detected at about one-halfof the locations up to a maximum of 570 ug/kg in the sample from 8 to 10 feet bgs at SB-13.However, most other concentrations of carbon disulfide were less than 100 ug/kg. All VOCconcentrations with RBCs were well below their respective RBCs.
The sample from 4 to 6 feet bgs at SB-8 had the highest levels of the largest number ofSVOCs, and some were above RBCs. Location SB-20 also had a large number of maximumvalues, but most high SVOC concentrations were in the sample from 12 to 14 feet bgs,whereas most high metal concentrations were detected in the sample from 4 to 6 feet bgs.SVOCs at a few hundred mg/kg were detected widely in other soil samples.
PAHs were detected in some of the samples obtained from the former lagoon sediment,usually the sediment with the associated thick black liquid. However, none of the PAHs weredetected above their respective RBCs in samples from the former lagoon sediment.
As shown in Table 4-4, most pesticides and PCBs were detected infrequently. Most of thepesticides were detected in subsurface soil over the entire site in fewer than 10 of almost40 samples, and Aroclors were detected in 3 or fewer of 39 samples. All concentrations werewell below RBCs.
Summary of Results for the Northwest Part of the Site. All the locations shown inFigure 4-4 exhibited selected inorganic chemicals above their respective RBCs. LocationsSB-8, SB-13, and SB-20 had the highest concentrations of chemicals and the widest varietyof chemicals exceeding their RBCs. The only SVOC concentration that exceeded its RBCwas detected at SB-8.
4.3.3.2 Former Process Plant Area
Samples were obtained by EBASCO (1990) and Witco in 1995 on the nature and extent ofsubsurface contamination in the former process plant area. Samples were obtained from soilborings and from test pits.
Inorganic Chemicals. Figure 4-5 contains the results for arsenic and the few availableresults for antimony and carbon disulfide. Table 4-4 includes summary statistics on alldetected chemicals, background concentrations, RBCs, and ecological criteria for onsitesubsurface soil.
4-22
AR302295
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Arsenic was detected above its background concentration and above its RBC in about halfof the samples. Antimony was not detected in any of the samples but is included in thefigure because of its human-health significance elsewhere on the site. The highestconcentrations of arsenic generally were found in the northeast part of the area, near theformer sump and the rear gate. Samples from soil boring SSS-25 contained the highestconcentrations of arsenic and zinc. Boring SSS-25 was located in a topographic low thatlikely collected contaminated surface runoff. The concentrations of both inorganics typicallydeclined with depth. Outside of the vicinity of the sump and the rear gate, the higherconcentrations of arsenic were distributed erratically, suggesting isolated releases.
Organic Chemicals. The highest concentration of carbon disulfide (66.9 mg/kg) wasdetected at a depth of 4 feet in SSS-25, in the same sample that contained the highestconcentration of arsenic. Other VOCs, such as TCE, were detected at scattered locations butgenerally were limited to the locations exhibiting elevated levels of carbon disulfide. SVOCsalso were elevated at scattered locations. Location SSS-25 also had detections of benzene,ethylbenzene, toluene, and xylenes (BTEX compounds); detections of BTEX compounds areunusual at the site.
Summary of Results for Former Process Plant Area. The highest concentrations of arsenicand carbon disulfide were found in soil in the northeast part of the area, near the sump andthe rear gate. Scattered high concentrations of both inorganics and organics suggest isolatedreleases of contaminants.
4.3.3.3 Vicinity of the Process Plant Drainage Ditch
Soil samples were obtained from soil borings and test pits drilled and sampled in the processplant drainage ditch and its vicinity. Samples were obtained by EBASCO (1990), CH2MHILL during the current RI, USEPA during the expedited removal action, and Witco duringthe response action. The sampled locations were spaced along the ditch, starting from nearthe material-storage area and progressing downstream to the head of the lagoon. Locationsnorth of the former process plant area (SB-15 through SB-18 and SSS-06) are included in thisdiscussion because of their proximity to the drainage ditch. The samples were obtained atvarious depths within a few feet of the surface.
Figures 4-6 through 4-8 show the distributions of arsenic, antimony (when available), andcarbon disulfide obtained from the sampling locations. The data are presented on threefigures, for clarity, because of the large number of samples analyzed. Table 4-4 includes thesummary statistics for the onsite subsurface soil.
Not shown in the figures is a buried 16-inch cast-iron water main that serves the Port ofWilmington. The line is located between the Conrail tracks and the property boundary. Thewater main is close to the property line shown in the figures.
4-25
&R3Q2297
Inorganic Chemicals. Arsenic was detected at its highest levels in samples obtained alongor very near the drainage ditch. Significant concentrations of arsenic were found as deep as12 feet bgs. Antimony was detected infrequently and without an obvious pattern.
Locations with the Highest Concentrations. Among EBASCO's data, borings SSS-04, SSS-05, and SB-02 had the highest concentrations of most of the inorganic chemicals and identifyan area of likely contamination. The following information supports this observation:
• The highest concentrations of arsenic (4,430, 2,520, and 1,670 mg/kg) weredetected at 3 feet bgs at SSS-04, at 2 feet bgs at SED-02, and at 4 to 6 feetbgs at SB-02, respectively (Figure 4-6).
• The highest concentration of antimony, and one of only two concentrationsabove the RBC, was detected at a depth of 4 to 6 feet bgs at SB-02(Figure 4-6). The other exceedance of the RBC for antimony was detected ata depth of 2 to 3 feet bgs at TP-24, near the south end of the drainage ditch.
• The highest level of manganese (1,010 mg/kg) was detected at a depth of3 feet bgs at SSS-04, the next-highest level (765 mg/kg) at a depth of 3 to4 feet bgs at SSS-16.
• The highest concentration of beryllium (0.76 mg/kg) was detected in SSS-05at a depth of 3 feet bgs.
• The two highest concentrations of nickel and cobalt were detected at a depthof 3 feet bgs at SSS-04 and at 4 feet bgs at SB-02. The RBCs were notexceeded.
• The two highest concentrations of total chromium were detected at 3 feet bgsin SSS-04 and at 4 and 10 feet bgs in SB-02. The RBC was not exceeded.
• The two highest concentrations of lead were detected at a depth of 3 feet bgsin SSS-04 and SSS-05 (Figure 4-8). The RBC was not exceeded.
• The three highest concentrations of thiocyanate were detected at SB-14,SSS-04, and SB-02. The RBC was exceeded.
Figures 4-7 and 4-8 also show the distribution of arsenic and, in some cases, antimony, nearthe process plant drainage ditch. Elevated levels of both inorganics can be seen in thesamples.
Location SB-14 and several test pits excavated by Witco had thiocyanate concentrationsabove 1,000 mg/kg. The concentrations were below the RBC of 2,100 mg/kg.Concentrations above the RBC were unusual elsewhere on the site.
4-26
AR302298
AR302299
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Samples from several test pits were analyzed for reactive sulfide and reactive cyanide.Reactive sulfide was detected in almost every sample at concentrations ranging from a fewtens to a few hundreds of mg/kg. The highest concentrations typically were detected in thedeeper samples from the pits. Reactive cyanide was not detected.
Total versus Hexavalent Chromium. Several soil samples were analyzed for both total andhexavalent chromium. Most of the samples were collected from borings in this area, so thistopic is discussed here. The purpose of analyzing for both total and hexavalent chromiumwas to obtain the valence state of chromium so that its relative mobility could be assessed.The results are in Table 4-6.
Table 4-6COMPARISON OF TOTAL AND HEXAVALENT CHROMIUM CONCENTRATIONS
Halby Chemical Site
Boring
SB-6
SB-6
SB-13
SB- 14
SB-15
SB-16
SB-16
SB-17
SB-17
SB- 18
SB-24
SB-24
Sample Depth(ft. bgs)
0-1
0-1
0-1
10-12
2-4
0-1
10-12
2-4
10-12
12-14
6-10
6-10
Total Chromium(mg/kg)
266
110
4830
22.8
22.3
18.4
24.9
18.1
20.3
27.4
14.2
15.3
Hexavalent Chromium(mg/kg)
<0.010
<0.010
2.04
1.62.26
<0.010
1.58
1.46
1.44
1.49
1.53
2.00
The hexavalent-chromium concentration typically is less than about 10 percent of the total-chromium concentration. Langan (1993) obtained similar results from surface-soil samplesfrom the former process plant area. The low concentration of hexavalent chromium incomparison to total chromium suggests that most chromium at the site is in the lower,trivalent state. Chromium in this valence state has been observed to be less mobile thanwhen chromium is in the hexavalent state.
4-33
AR302302
Palmer and Puls (1994) report that hexavalent chromium as a strong oxidant is readilyreduced in the presence of several common materials in the environment, including organicmatter and ferrous iron in oxides and pyrite (iron sulfide). Iron concentrations in the site soilare high, perhaps because of the presence of pyrite in the fill, and organic matter is providedin the former lagoon sediment. Therefore, rapid reduction of hexavalent chromium to thetrivalent state would be expected in the environment at the site.
Organic Compounds. The distribution of carbon disulfide in the drainage ditch is illustratedin figures 4-6 through 4-8, not only by the concentrations at sample locations but also byshading over the approximate areas that contain carbon disulfide above its RBC. Althoughthe configuration of the shaded area varies between the figures, the general trend in eachfigure is that carbon disulfide is highest close to the ditch. Free-product carbon disulfide wasobserved in soil in the ditch by USEPA during the expedited removal action in 1995. PCEat levels as high as 21 mg/kg also was detected in samples from the drainage ditch. Thehighest concentrations of SVOCs were detected at SSS-05 and SED-03. Elsewhere, theSVOC concentrations ranged from undetected to a few hundreds of mg/kg. Although veryhigh concentrations of SVOCs were detected at the surface at SB-18, concentrations ofSVOCs in subsurface soil were low at this location.
Few pesticides were detected, and all were below RBCs. Aroclor 1254 was detected atconcentrations above its RBC of 120 ug/kg in several test pits. Although most of the test pitswith Aroclor 1254 are near the railroad tracks, a likely source, test pits TP-13 (with thehighest concentration) and TP-26 are further from the tracks, and Aroclor 1254 was notdetected in other test pits and soil borings near the tracks.
Many test pits encountered black-stained soil that emitted a strong organic odor. Soil samplesfor analysis generally were collected from this horizon if it was present. It is likely that thehorizon represents former lagoon sediment that were covered when the site was filled in thepast. Other explanations could be layers of contaminated backfill. Although high levels ofcarbon disulfide frequently were associated with this type of material, this was not alwaysthe case. In fact, some intervals with high concentrations of carbon disulfide exhibited noobvious lagoon sediment, whereas some organic, peaty material had little or no carbondisulfide.
In August and December 1995, Witco excavated several pits along the water main thatparallels the railroad tracks to evaluate the nature and extent of potential contamination,particularly from carbon disulfide, in soil along the main (Witco, 1996). The pits excavatedfor this purpose were TP-1 through TP-6 and TP-28 through TP-33. The locations of all butTP-28 and TP-29 are shown in Figure 4-8; the locations of TP-28 and TP-29 are shown inFigure 4-4. The water main is just to the east of most of the pits and is just west of TP-28and TP-29. Test pits TP-30 and TP-31 were excavated around the main itself.
During excavation, black groundwater reportedly entered most of the test pits, accompaniedby pungent odors. Globules of an oily black liquid were noted in some pits. Carbondisulfide was detected in a groundwater sample from TP-31 at 1,500 mg/1. Carbon disulfide
4-34
AR302303
was detected in most of the excavations using Draeger tubes; neither hydrogen sulfide norammonia was detected. Carbon disulfide was detected up to a concentration of 3,900 mg/kgin soil, with the highest concentrations from depths of 5 to 6 feet in pits TP-4, TP-5, andTP-31. Arsenic was detected at concentrations up to 1,560 mg/kg, with the highestconcentrations at depths of 3 to 6 feet bgs in pits TP-3, TP-4, and TP-31. The reported depthof the main is 2.5 to 3.5 feet bgs. Examination of the main revealed no structural orcorrosion problems.
Summary of Results for the Vicinity of the Process Plant Drainage Ditch. The highestconcentrations of arsenic and carbon disulfide were detected in soil obtained from thedrainage ditch. The data consistently define an area with high levels of carbon disulfidealigned with the drainage ditch.
4.3.4 Offsite Subsurface Soil
Soil samples were collected off the site in two areas: (1) near the site, including just west andsouth of the site and east of the site between the former process plant area and the location(Bio-7) in the tidal marsh where a sediment sample was determined to be acutely toxic duringtests in 1991 (USFWS and USEPA, 1991); and (2) other offsite locations to help evaluate thestudy-area soil-contamination levels. The areas are discussed separately.
4.3.4.1 Near-Site Sampling Locations
The near-site sampling locations are shown in Figure 4-9. Arsenic was detected above itsRBC in samples from SSS-13 and DMW-7. Antimony was not detected. The concentrationsof arsenic declined with depth. Carbon disulfide was detected in only one sample, fromDMW-7, and at only 1 mg/kg.
The objective for collecting soil samples between the former process plant area and the Bio-7location was to assess the potential that site-related contamination may have migrated throughthe soil or some other pathway and contributed to the acute toxicity detected at the BSA inthe tidal marsh. Five subsurface-soil samples were obtained from four soil borings (SB-21through SB-24) drilled and sampled in this area. Table 4-7 shows summary statistics on alldetected chemicals, background concentrations, and RBCs.
Cadmium was not detected in any of the samples. Most of the inorganic chemicals weredetected below background concentrations. Iron was detected above its RBC but it isconsidered a human nutrient. None of the low-RBC SVOCs detected on the site was detectedin this area.
Analyses of the sediment from the Bio-7 location (USFWS and USEPA, 1991) detected highconcentrations of arsenic, lead, acetone, carbon disulfide, 2-butanone, thiocyanate, ammonia,and several SVOCs. PCE, ethylbenzene, and several other VOCs were detected. However,
4-35
AR302301*
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in the soil samples both arsenic and lead were detected at only low concentrations.Thiocyanate was detected in only one soil sample. Among the SVOCs, only bis(2-ethylhexyl)phthalate and di-n-octyl phthalate were detected. Among VOCs, only acetone (one locationat 12 tig/kg) and 1,1,1-TCA (one location at 0.5 ug/kg) were detected.
The conclusion is that site-related contaminants have apparently not migrated through thesubsurface soil from the former process plant area to the Bio-7 location. This conclusiondoes not preclude migration of site-related contaminants through groundwater, a subject thatis discussed in subsection 4.5.2.2.
4.3.4.2 Other Offsite Sampling Locations
Subsurface samples were obtained from six monitoring-well boreholes. Six samples fromfour locations reported in EBASCO (1990) also were available for evaluation. Table 4-8provides summary statistics on all detected chemicals, background concentrations, and RBCsfor the subsurface-soil data in the offsite sampling locations. Analytical results for arsenic,antimony, and carbon disulfide are shown in Figure 4-10.
Inorganic Chemicals. Arsenic and most other inorganic chemicals were detected off the siteabove their background concentrations. Arsenic was detected above the RBC in about halfof the samples. The boreholes for IMW-11 and IMW-12 had the highest concentrations ofmost inorganic chemicals. The highest concentration of arsenic (132 mg/kg) was detectedat 3 to 5 feet bgs in IMW-12. Several other arsenic concentrations above 50 mg/kg weredetected. Only beryllium was higher at another location (at a depth of 10 feet bgs at SB-04,the borehole for well DMW-3B). These boreholes are widely separated in the study area.
Metals such as arsenic have been determined to be site-related. However, no mechanism isapparent for transporting the metals to these widely spaced locations and to depths of up to11 feet bgs. Some of the metals (e.g., lead) were detected at higher concentrations at theselocations than on the site. The conclusion is that other sources, such as the Christina River,fill materials, spills, or the petroleum coke piles, have contributed the chemicals at theselocations.
Duffield (1986) reported that the presence of elevated concentrations of cobalt, nickel, andsulfate in groundwater beneath the petroleum coke piles suggested an influence of the cokepiles on groundwater quality. The borehole for well IMW-2 (on the east side of the tidalmarsh) yielded samples with some of the highest arsenic, lead, copper, and cobaltconcentrations of any offsite location. These results were confirmed by the samples fromnearby SB-03, the borehole for well DMW-2. On the other hand, nickel concentrations werenot particularly high in comparison to the background concentration (Table 4-8). In addition,the surface-soil samples at nearby borings SSS-07 and SSS-08 had somewhat lowerconcentrations of these metals, and a sediment sample (not shown in the figures) obtained
4-38
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LEGEND— - — - - SITE BOUNDARY NOTE:APPROXIMATE SOIL-SAMPLING LOCATIONS *"- UNITS ASE IN MILLIGRAMS/KILOGRAMS
0/MW-6 MONITORRir^3)WELL LOCATION ' DETECTED IN THE ASSOCIATED METHOD BLANK.
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(3-5) DEPTH OF SAMPLE IN FEET _____SCALE IN FEET
INDUSTRIAL WORKERRBC
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Figure 4-10ARSENIC, ANTIMONY, AND CARBON DISULFIDE ®J
CONCENTRATIONS DETECTED IN SELECTED _____OFFSITE SUBSURFACE-SOIL SAMPLES KMBItti
Halby Chemical Site4979f015.dgn 09-JAN-1997 flR3023IO
from a low area bordering the tidal marsh and near IMW-2 contained very low concentrationsof metals, ammonia, and cyanide. Therefore, the influence of the petroleum coke piles onsoil cannot be clearly defined on the basis of these data.
Organic Compounds. Among the VOCs, carbon disulfide was detected only at IMW-6,west of the site, at a concentration of 2 ug/kg. All VOCs were detected well below theirrespective RBCs.
The highest concentrations of low-RBC SVOCs were detected in samples obtained within8 feet bgs at IMW-2 and SB-03, located near one another on the eastern edge of the tidalmarsh. The sample from 5 to 7 feet bgs at IMW-2 also had the only detections of fluorene,fluoranthene, naphthalene, and phenanthrene. Pyrene also was detected in that sample andat a depth of 9 to 11 feet bgs at IMW-11. A sediment sample (not shown in the figure)obtained from a low area bordering the tidal marsh and near IMW-2 contained concentrationsof SVOCs as high as those detected in the sample from 2 to 4 feet bgs at SB-03. On theother hand, SVOCs were not detected at concentrations significantly above background atnearby borings SSS-07 and SSS-08. Elevated concentrations of SVOCs would be an indica-tion of the influence of the coke piles on the soil. If such an influence on soil exists, itappears to be only localized.
4.3.4.3 Summary for Offsite Soil
The following generalizations can be made for offsite soil:
• In the area between the former process plant area and the Bio-7 location, nochemicals were detected above their respective RBCs. Chemicals do notappear to have migrated through the subsurface soil from the process plantarea to the Bio-7 location in the tidal marsh, where acute tpxicity to organismshas been identified. Toxicity of chemicals to organisms is addressed inChapter 7, "Ecological Risk Assessment."
• Chromium is largely in its less mobile, trivalent, state, presumably because ofthe reduction of hexavalent chromium in the presence of such materials asorganic matter and pyrite.
• Site-related chemicals were identified in offsite subsurface soil near theChristina River and Lobdell Canal, but transport mechanisms from the site tothese locations and depths are lacking. Therefore, the conclusion is that manyof the detections of site-related chemicals off the site have been derived fromother sources.
• Although elevated concentrations of cobalt and SVOCs have been detected insoil near the petroleum coke piles, the influence of these piles on soil cannotbe clearly established, and such influence, if it exists, may be only localized.
4-42
flR3023lI
4.4 Surface Water and Sediment
4.4.1 Surface Water
Surface-water samples were collected during the current RI at 3 locations (2 in the onsitelagoon and 1 in the tidal marsh); by EBASCO (1990) at 11 locations in the onsite lagoon,the tidal marsh, Lobdell Canal, the 1-495 drainage ditch, and the Christina River; and byWeston (1995) at 4 locations in the lagoon and the tidal marsh. This subsection describesthe analytical data obtained from these samples.
Tables 4-9 and 4-10 list all of the chemicals detected in the surface-water samples. Thesamples collected by Weston in 1995 are not considered in this total. The tables includemaximum, minimum, average, frequency of detection, industrial and recreational RBCs, andthe ecological criteria. The recreational RBCs assume exposure to a resident but in arecreational scenario. Of these chemicals, only arsenic, carbon disulfide, ammonia, andthiocyanate were detected in onsite surface water at concentrations exceeding their respectiveRBCs. Therefore, only those chemicals are designated as COPCs for human health for onsitesurface water. Ammonia, arsenic, and cyanide were detected in offsite surface water atconcentrations exceeding their respective RBCs and are designated as COPCs for humanhealth for offsite surface water. The range of concentrations of the human health COPCs aretabulated in Table 4-11 and plotted in Figure 4-11. All surface-water sampling locationsdiscussed in this subsection are shown in Figure 4-11.
The State of Delaware has classified the surface water in the Christina and Delaware riversfor use purposes (DNREC, 1993). The following designated protected uses apply to thesegment of the Christina River in the vicinity of the site:
• Industrial water supply
• Secondary-contact recreation (a water-based form of recreation, the practiceof which has a low probability of total-body immersion or ingestion of water)
• Fish, aquatic life, and wildlife (all animal and plant life found in Delaware,either indigenous or migratory, regardless of economic importance, includingshellfish propagation)
For the discussion in this chapter, industrial and recreational RBCs are used for comparison.The environmental effects of chemicals in the surface water are discussed in Chapter 7,"Ecological Risk Assessment."
4-43
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Table 4-11COMPARISON OF SELECTED SURFACE-WATER RESULTS AND RBCs
Halby Chemical SiteChemical
Arsenic
Cyanide
Carbon Disulfide
Ammonia
Thiocyanate
Lagoon RangeLow
ND
ND
2
310
ND
High(Station)597(C-01)69
(SW-03)4,000(C-01)20,000(SW-01)265,000(C-01)
Tidal Marsh RangeLow
ND
ND
ND
120
ND
High(Station)6.4
(HAL-5W)11,800(SW-08)3B
(SW-07)18,000(SW-08)9,600(SW-08)
RBC
2.8a
2,920a
2,336b
6,772a
15,000a
Units are in ug/l.ND = not detectedB = chemical also detected in a method blankalndustrial-worker scenariobResidential/recreational scenario
A sample (SW-11) collected slightly upstream of the confluence of the 1-495 drainage ditchand the Christina River was identified as representative of background by EBASCO (1990).Sample SW-12, collected slightly downstream of the confluence, had analytical results similarto those of SW-11. The only COPC detected in sample SW-11 was ammonia, at 300 ug/l.The sample also contained calcium, magnesium, potassium, and sodium at 28.1 mg/l, 21.5mg/1, 7.18 mg/l, and 116 mg/l, respectively. In most of the samples obtained from the onsitelagoon, the calcium, potassium, and sodium concentrations were somewhat higher thanbackground concentrations. Potassium and sodium compounds were used at the formerprocess plant area.
Weston (1995) obtained a background sample from the river upstream of the site, nearWilmington (location not shown in Figure 4-11). Arsenic, cyanide, ammonia, and thiocyanatewere not detected.
The sample from location C-01, in the process plant drainage ditch, exhibited the highestconcentrations of the COPCs. Carbon disulfide was at 4,000 ug/l in the first sampling roundand at 70,000 ug/l in the second sampling round in 1993; however, the value from the secondround was qualified with a "B" because carbon disulfide also was detected in an associatedblank sample. Ammonia was highest at location SW-01, near the head of the lagoon. All
4-49
AR3023I7
concentrations exceeded those in the background samples. These two locations also exhibitedthe highest concentrations of lead, chromium, manganese, nickel, and zinc. Highconcentrations of site-related contaminants at these locations are consistent with the proximityof the locations to the former process plant area. The arsenic RBC was exceeded at alllocations except SW-03, nearest the outlet for the lagoon; arsenic was below the detectionlimit at that location. Location SW-03 had the highest sulfide concentration of all surface-water samples.
Concentrations of all COPCs in the tidal marsh exceeded background concentrations. Thehighest concentrations of all COPCs were detected at locations HAL-5W and SW-08, whichare the locations sampled in the tidal marsh closest to the former process plant area.Concentrations of most metals in samples from the tidal marsh also exceeded those in thebackground sample.
Surface-water samples from the 1-495 drainage ditch and the canal were similar in quality tothose from the river. An exception is that cyanide was detected, at concentrations well belowthe RBC, in samples from the 1-495 drainage ditch. The presence of cyanide in thesesamples probably indicates an effect of the site.
A sample of water was obtained from a concrete box set below grade located just outside theperimeter fence of the former process plant area. The box was between the perimeter fenceand the railroad tracks on the northeast side of the former process plant area and apparentlyserves as a sewer junction. At the time of sampling, the box contained several inches ofsediment and was filled to about 3 feet below the surface with water. The water samplecontained several site-related chemicals, including arsenic at 51.8 ug/l and cyanide at19.5 ug/l.
In summary, the highest concentrations of COPCs for surface water were detected at thelocations in the process plant drainage ditch, onsite lagoon, and tidal marsh nearest the formerprocess plant area. Pipes that used to carry discharge from the lagoon into the tidal marshprobably were responsible for distributing site-related contaminants into the marsh. Flowthrough at least one of these pipes can still be observed. Because the marsh is flushed bythe tide twice daily, the presence of high levels of ammonia and arsenic at SW-08 suggestsa continuing source of contamination.
4.4.2 Sediment
Sediment samples were collected during the current RI at three locations (two in the onsitelagoon and one in the tidal marsh). Samples also were collected at 11 locations by EBASCO(1990); at 10 locations by EPA (Knight and Sprenger, 1991); at 4 locations by Weston (1992)in the onsite lagoon, the tidal marsh, Lobdell Canal, the 1-495 drainage ditch, and theChristina River; and at 7 locations in the lagoon and tidal marsh by Weston (1995). Allsediment-sampling locations discussed in this subsection are shown in Figure 4-12. Thissubsection describes the analytical data obtained from these samples.
4-50
AR3023I8
•*•- .
Tables 4-12 and 4-13 list all of the chemicals detected in sediment samples obtained from adepth of less than 3 feet, which is the maximum depth of sediment of concern in the humanhealth risk assessment. The tables contain the detected maximum, minimum, and average;frequency of detection; the industrial and recreational RBCs; and the ecological criteria. Thesamples obtained by Weston in 1995 are not considered in these tables. Of these chemicals,only arsenic, beryllium, and copper were detected in onsite sediment at concentrationsexceeding their respective RBCs, so only these chemicals are designated as COPCs for humanhealth for onsite sediment. Arsenic, beryllium, and benzo(a)pyrene were detected in offsitesediment at concentrations exceeding their respective RBCs and are designated as COPCs forhuman health for offsite sediment. The ranges of concentrations of the COPCs and additionalsite-related chemicals are tabulated in Table 4-14 and plotted in Figure 4-12. The additionalsite-related chemicals are ammonia and carbon disulfide because both appear to havesignificant ecological effects.
For the discussion in this chapter, industrial and residential/recreational RBCs are used forcomparison. The environmental effects of chemicals in the surface water are discussed inChapter 7, "Ecological Risk Assessment."
Two samples (SED-22 and EPA-1) collected slightly upstream of the confluence of the 1-495drainage ditch and the Christina River represent background conditions. Sample SED-23,collected slightly downstream of the confluence, had analytical results similar to those of thetwo background samples. Only the COPCs arsenic and benzo(a)pyrene were detected in thebackground samples above RBCs. Sample EPA-10 was collected from a small drainagewaythat discharges into the southern end of the tidal marsh; this location is not considered asuitable background location, because it is not subject to tides and brackish water, whichinfluence the chemical characteristics of sediment elsewhere on the site and in its vicinity.
Weston (1995) obtained a background sample from the river upstream of the site, nearWilmington (location not shown in Figure 4-12). Among the inorganics, only arsenic wasdetected above its RBC, but it also was detected in a blank sample. Benzo(a)anthracene,chrysene, bis(2-ethylhexyl)phthalate, fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, andindeno( 1,2,3)pyrene also were detected above their respective RBCs.
Unlike in surface water, the highest concentrations of COPCs in the onsite lagoon were notnecessarily detected at the head of the lagoon. Arsenic and copper were highest at SED-08,near the outlet of the lagoon, and both were well above background concentrations.Beryllium was highest at SED-05, not far from the head of the lagoon. Carbon disulfide washighest at the head of the lagoon but only slightly lower near the outlet. The concentrationsof VOCs generally declined with depth. Ammonia concentrations were fairly uniformthroughout the lagoon.
4-53
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Table 4-14COMPARISON OF SELECTED SEDIMENT RESULTS AND RBCs
Halby Chemical SiteChemical
Arsenic
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Copper8
Carbon Disulfideb
Ammoniab
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270
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328
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High(Station)3,110
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(SED-15)5,010
(SED-14)44
(SED-24)1,650
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283,240
1.1
Units are mg/kgND = Not detected"Only a COPC for the onsite lagoonbNot a COPC for either the lagoon or the marshcOnly a COPC for the tidal marshdlndustrial-worker scenario
The concentrations of arsenic and beryllium in the tidal marsh were distributed erratically,and benzo(a)pyrene was detected primarily in the northern part of the marsh. Arsenic andbenzo(a)pyrene were detected above background concentrations. The highest concentrationof arsenic (1,400 mg/kg, not shown in Figure 4-12 or the tables) was detected at a depth of6 feet at location SED-24; the location is opposite the onsite lagoon. The second-highestarsenic concentration was detected at the northern end of the marsh (SED-10), opposite theonsite lagoon. Location SED-14 had high concentrations of arsenic, cadmium, copper, zinc,and lead. The site-related chemical thiocyanate was detected in a few locations but washighest (3,260 mg/kg) at a depth of 3 feet at SED-27. This value is below the RBC, sothiocyanate is not a COPC. It is noteworthy that the highest thiocyanate concentrationdetected in the onsite lagoon was at SED-27, almost directly across the railroad tracks fromSED-24.
4-58
AR302325
Ammonia was detected primarily in the southern part of the marsh, although most samplescollected in the northern part were not analyzed for ammonia. The highest concentration ofammonia was detected at EPA-7, the sampling point in the marsh closest to the formerprocess plant area. That also is the location of the sample designated "Bio-7" collected forbioassay; the results of the bioassay are discussed in Chapter 7.
By far, the highest concentrations of carbon disulfide were detected in the lagoon at SED-04and in the tidal marsh at SED-24. The sample at SED-24 from less than 3 feet deepcontained 44 mg/kg, and the sample from a depth of 5 feet contained 222 mg/kg. LocationSED-24 is opposite the onsite lagoon. TCE and tetrachloroethene also were found at SED-04and SED-24. The next-highest concentration of carbon disulfide was detected nearby at SED-25, although it also was detected in an associated blank. The highest concentrations ofSVOCs were detected in the tidal marsh, suggesting an influence by the petroleum coke piles.
Sediment samples from the 1-495 drainage ditch and the canal typically contained higherlevels of arsenic, copper, and ammonia than did the samples from the river. The sample fromthe 1-495 ditch also had the highest concentration of sodium, suggesting the influence of thesalt piles on the other side of 1-495. Metal concentrations generally increased with depth inthe tidal marsh, suggesting that the contamination there is due to past deposition ofcontaminated sediment. Metals were not detected at elevated levels in sediment from nearthe petroleum coke piles.
The samples of sediment collected by Weston (1995) were analyzed for herbicides becauseSilvex was detected in a sample collected from a carbon disulfide tank on the site and Silvexand 2,4-D were detected in the onsite sump. Silvex-was detected in six of the seven sedimentsamples analyzed, including the background Christina River sample. However, the highestconcentrations were detected in the onsite lagoon, and the highest concentration was detectedat the head of the lagoon, where the process plant drainage ditch discharges. Other sedimentsamples from the general location of the Bio-7 sampling station contained high concentrationsof the compounds MCPA and MCPP. Low levels of a few pesticides also were reported byWeston (1995) but generally have not been detected in sediment samples at the site.
A sample of sediment was obtained from the sewer junction box at the edge of the formerprocess plant area. The sample contained a high level of arsenic (254 mg/kg) but no otherCOPCs above RBCs.
In summary, the highest concentrations of COPCs and such site-related chemicals as carbondisulfide and thiocyanate in sediment generally were detected erratically distributed in theonsite lagoon and in the tidal marsh near the lagoon and the former process plant area. Thepresence of high concentrations of COPCs in the marsh near the lagoon and the formerprocess plant area may be due to the pipes that used to, and apparently still, carry dischargefrom the lagoon into the tidal marsh.
4-59
AR302326
4.5 Groundwater
4.5.1 Introduction
The discussion of the nature and extent of contamination in the groundwater in the study areais organized by water-bearing unit, beginning with a description of background groundwater-quality conditions in each unit. Data for each well are shown in figures and are statisticallysummarized in tables. All data are in Appendix D.
The discussion in this chapter is based on two rounds of water-quality sampling, in Augustand December 1993. EBASCO (1990) reported the results of groundwater samplingperformed in 1989. Almost all the wells sampled at that time were resampled as part of thecurrent RI. The two exceptions are W-1A and W-1B near Insteel Products, northwest of thestudy area; they could not be located in 1993. Because the wells sampled in 1989 wereresampled, the data reported by EBASCO (1990) are not used extensively in this discussionof nature and extent. However, reference is made to the 1990 data when appropriate todescribe trends.
Data on metals for both filtered and unfiltered samples are included in Appendix D. Onlythe filtered data for metals are shown in figures and discussed in this chapter. This approachis consistent with USEPA Region III guidance on data where a disparity exists betweenfiltered and unfiltered monitoring-well data for aluminum, iron, and manganese (USEPA,1992). Filtered data better represent the actual concentration in a well that has beendeveloped completely by long-term pumping, such as a residential well. Filtered data alsobetter represent the concentrations of a chemical in groundwater as it migrates through theporous media.
The discussion in this chapter includes a determination of whether a chemical detected ingroundwater is potentially site-related. A site-related chemical is likely to have been derivedfrom a source on the site. The former process plant area of the site seems to be a likelysource for many of the organic chemicals, sulfur compounds, and cyanide and relatedchemicals. Other likely sources are discussed when appropriate.
Two background wells each were identified for the Columbia and upper Potomac water-bearing units, and one was identified for the lower Potomac water-bearing unit. Selection ofthe background wells is discussed below by water-bearing unit. Because of the small numberof background wells for each unit, statistical methods, such as calculating the 95th percentileupper-bound concentration, were not considered appropriate for estimating the backgroundconcentration. For this discussion, the background concentration is assumed to be the highestconcentration in the background wells. If an inorganic chemical was not detected in a back-ground well, the background concentration in the well was assumed to be half of the detec-tion limit. The background concentration for all organic compounds was assigned a valueof zero, whether or not the compound was detected in a background well. The exception wasfor acetone in well W-3B in the first round of sampling, when acetone was detected.
4-60RR302327
Soil is the primary source of groundwater contamination on the site. As discussed insection 4.3, all metals analyzed for plus various pesticides, SVOCs, and VOCs were detectedin onsite soil above background concentrations. Therefore, these chemicals are consideredsite-related. Many of these chemicals were detected in groundwater, but at or belowbackground concentrations. In this discussion, the term "site-related" is used in its originalsense: the chemical could have been derived from the site, even though it has not necessarilybeen determined to have affected groundwater quality. Antimony is an example. As withthe background-well data, the small number of data points does not warrant the use ofstatistical tests to determine the equality of variances and to compare the means. A singleconcentration of a site-related chemical above background conservatively qualified thatchemical as potentially attributable to the site.
Table 4-1 contains the list of COPCs for human health for each water-bearing unit. Thediscussion will stress these chemicals. Other chemicals are discussed when necessary so thatthe nature and extent of contamination can be defined adequately. The RBCs defined inChapter 6 for COPCs are included in the summary tables for comparison with the observedconcentrations.
The detection limits and background concentrations of the compounds listed above werecompared with the RBCs. In some cases, the detection limit of the COPC was higher thanthe RBC, particularly for COPCs, such as arsenic and beryllium, that have RBCs of less than1 ug/l.
Because of the wide range in concentrations of COPCs in groundwater, the concentrationsin the figures have not been contoured. Wells that exhibited chemical concentrations that areelevated in relation to background and to the concentrations in other wells have been flaggedin the figures.
The figures for each water-bearing unit are organized into four groups: (1) selected dissolvedmetals (one or two figures); (2) cyanide and cyanide compounds (one figure each for theColumbia and upper Potomac and no figure for the lower Potomac); (3) common ions (oneor two figures); and (4) VOCs (one figure each for the Columbia and upper Potomac and nofigure for the lower Potomac). The figures for dissolved metals, cyanide and cyanidecompounds, and VOCs show the distribution of COPCs. The figures for common ions showthe distribution of other chemicals that are not COPCs but that may indicate site effects ongroundwater quality. Not all COPCs are included in each figure, and some figures includechemicals that are not COPCs. The figures illustrate the areal extent of site-related chemicalsrather than merely showing the distribution of the major chemicals that contribute to human-health risk.
4.5.2 Backfill Groundwater
One well, BMW-10, was screened in the backfill in the north part of the site. The lower partof the screen is open to the underlying Columbia. The analytical data for this well are shown
4-61
AR3Q2328
in figures 4-13 through 4-17, which also show analytical data for the Columbia water-bearingunit.
There is no background well for the backfill with which the analytical results obtained fromBMW-10 can be compared. The results from BMW-10 are compared with the data from wellW-3A, the nearest background well for the Columbia, in this discussion.
The sample from BMW-10 contained concentrations of most chemicals above those measuredin the sample from W-3A. In particular, the concentrations of arsenic, manganese, calcium,iron, magnesium, potassium, sodium, thiocyanate (Round 1 only), chloride, sulfate, sulfide,and ammonia were elevated above background. The presence of thiocyanate suggests thatgroundwater contamination from the former process plant area at least periodically influencesBMW-10. No COPCs were defined for the backfill groundwater because no reasonablescenario included use of the groundwater from the unit.
Although well BMW-10 is screened partly in the Columbia, the concentrations of most metalsdiffer appreciably between backfill well BMW-10 and Columbia well SMW-10. As shownin Figure 4-13, concentrations of arsenic are appreciably higher and concentrations ofberyllium, nickel, manganese, cobalt, and zinc are appreciably lower in BMW-10 than inSWM-10. These data indicate that well BMW-10 is exhibiting water quality that can beassumed to be representative of the backfill rather than the Columbia in this part of the site.
A sample of the groundwater in a test pit near the process plant drainage ditch was found tocontain 1,500 mg/l of carbon disulfide. This value is about 65 percent of the solubility ofcarbon disulfide (about 2,300 mg/l) and strongly suggests the presence of free-product carbondisulfide in the soil and groundwater at this location. Free-product carbon disulfide in thesoil was observed by USEPA at this location during the expedited response action in 1995.Arsenic was detected at 3.84 mg/l in this sample.
4.5.3 Columbia Water-Bearing Unit
4.5.3.1 Background Groundwater Quality
As discussed in Chapter 3 on the physical characteristics of the study area, groundwater flowin the Columbia appears to be to the northeast beneath the site (subsection 3.5.3.3). The waterlevel in well SMW-12, located next to the Christina River (Figure 4-13), indicates acomponent of groundwater flow toward the south or southwest, but this is believed torepresent local conditions only near well SMW-12. The general flow direction to thenortheast is consistent with the topography and the likely groundwater recharge-dischargerelationships in the study area.
4-62
AR302329
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Under these groundwater-flow conditions, well SMW-6 should represent an upgradientbackground sampling location. Well W-3A also is a likely background well, even though itis sidegradient to the site. Although sidegradient to the Halby site as defined in this report,well W-3A is upgradient from the probable location of former lagoon sediment northwest of1-495 that was at one time contiguous with the sediment on the site. The former lagoonsediment northwest of 1-495 would have been affected by discharges of effluent from HalbyChemical. Therefore, well W-3A is a useful facility for monitoring groundwater qualityupgradient of the former lagoon sediment. Also, there is no reason to expect thatgroundwater flow from the site would ever have passed near well W-3A. Even if pastgroundwater pumping at Forbes Steel, northwest of the site, had affected groundwater beneaththe site, the direction of flow from the site would have carried contaminated groundwater eastof well W-3A and would not have affected groundwater quality at well W-3A. Because ofits location, definitely upgradient of the site, SMW-6 was considered the only backgroundwell for the Columbia in the risk assessment (Chapter 6), but, for the reasons provided, W3-Ais included as a background well in the following discussion.
The assumption was that the highest concentration of a chemical detected between the twowells and the two sampling rounds was the most appropriate concentration to use as abackground level. The background concentrations are listed in Table 4-15 (Round 1) andTable 4-16 (Round 2). When a chemical was not detected in either background well, thebackground concentration was assigned as half the detection limit if the chemical wasinorganic and zero if the chemical was organic.
The samples from well SMW-6 consistently exhibited higher concentrations of the commonions calcium, magnesium, sodium, and potassium than did W-3A. The Round 1 sample fromwell SMW-6 also contained cyanide at 27 fig/1 and thiocyanate at 4,950 ug/l, indicatingpossible site influence on well SMW-6, although a transport mechanism to this well isunknown. Cyanide was not detected in SMW-6 in Round 2 above the 10 ug/l detection limit,but thiocyanate was detected again, this time at 5,260 ug/l. Nevertheless, well SMW-6 wasconsidered an acceptable background well for other chemicals because concentrations of suchchemicals as arsenic and cadmium, which were determined to be COPCs for the Columbia(see subsection 4.5.2.2 below), were below the detection limit in well SMW-6. The likelyrelationship of the contamination in well SMW-6 and the site will be discussed in Chapter 5(subsection 5.3.3.1) on fate and transport.
Inorganic Chemicals. The filtered analytical results for inorganic chemicals for thebackground wells are presented in figures 4-13 through 4-16 and tables 4-15 (Round 1) and4-16 (Round 2). The COPCs for the Columbia, which are listed in Table 4-1, are noted inthe tables.
The samples from wells SMW-6 and W-3A in both rounds contained no detectable levels ofthe COPCs arsenic, cadmium, cobalt, nickel, silver, thallium, vanadium, or zinc. The onlyinorganic COPCs with detectable concentrations in any background wells were barium andammonia (both wells) and thiocyanate (SMW-6). Other inorganic chemicals that were belowdetection limits are indicated in tables 4-15 and 4-16.
4-68
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The common cations calcium, magnesium, iron, manganese, potassium, and sodium weredetected in the samples from the background wells at concentrations ranging from a fewhundred to several tens of thousands of ug/l (Figure 4-15). The common anions chloride,sulfate, and sulfide were detected in the samples from the background wells at concentrationsranging from single-digit values to 563 mg/l (Figure 4-16).
EBASCO (1990) used W-3A as the background well for the Columbia. Analytical resultsreported in EBASCO's document for inorganic chemicals are comparable to those obtainedfrom the recent RI sampling for well W-3A for all chemical groups.
Organic Compounds. The only organic compounds detected in samples from the back-ground wells were TCE (both rounds) and PCE (Round 2 only) in SMW-6 (Figure 4-17) andacetone (Round 1 only) in W-3A. Detections of TCE and PCE are consistent with theindustrial nature of the study area. The detection of acetone in W-3A cannot be attributedto laboratory contamination because acetone was not detected in associated blank samples.
EBASCO's (1990) results for organic compounds generally compared well with thoseobtained from the recent RI. One exception is acetone, which was detected in W-3A byEBASCO at 8 ug/l but also was detected in a blank sample, whereas the 18 ug/l detectedduring Round 1 of the current RI sampling in W-3 A was not associated with a blank-samplecontamination. Therefore, there is a possibility of background contamination by acetone.
4.5.3.2 Columbia Groundwater Quality
Onsite wells in the Columbia referenced in this discussion are SMW-1, SMW-8, andSMW-10. Offsite downgradient wells in the Columbia that are referenced are SMW-2,SMW-9, SMW-11, SMW-12, W-4C, and W-5B. SMW-9 is located just east of the site andwest of the tidal marsh; the other wells are located east of the tidal marsh. Offsite wellW-2A is sidegradient to the site.
Inorganic Chemicals. The analytical results for inorganic chemicals for samples from thewells are presented in figures 4-13 through 4-16. The mean and maximum of theconcentrations for each chemical are listed in tables 4-15 and 4-16. Data from well W-2Awere not included in the statistics.
Aluminum, antimony, beryllium, chromium, mercury, and weak-acid dissociable cyanide werenot detected above the background concentration in samples during either sampling roundfrom wells on the site. Copper, selenium, and nitrate/nitrite were detected above backgroundconcentration only in one sampling round. These chemicals will not be discussed further.
The remaining inorganic chemicals were reviewed to determine which are likely to beattributable to the site. A chemical is considered possibly attributable to the site when it isdetected in a sample from a single onsite well at a concentration higher than background
4-77
AR3023UI*
concentration. The following chemicals were detected at concentrations above backgroundon the site and may be derived from sources on the site:
Arsenic (COPC)• Barium (COPC)• Manganese (COPC)
Thiocyanate (COPC)Ammonia (COPC)
• Cyanide• Iron
SulfideSulfate
• Sodium• Potassium• Calcium• Magnesium
Chloride
In general, the highest concentrations of these chemicals were detected in samples from wellsSMW-8 and SMW-1, those nearest the former process plant area.
Arsenic, barium, manganese, iron, and sulfide would be expected from the disposal of pyrite(iron sulfide) wastes at the site. Sulfate would result from oxidation of sulfide. Arsenic isa component of arsenopyrite, a common contaminant in pyrite. Arsenic contamination alsoprobably is derived from use of the chemical at the former process plant area. Thiocyanateand cyanide would have been derived from site operations.
Figure 4-15 shows that the highest concentrations of sodium and potassium were detected inwells SMW-1 and SMW-8. This is consistent with the usage of compounds of thesechemicals at the former process plant area. Sodium concentrations in these wells were wellabove the background concentration. The derivations of elevated concentrations of calcium,magnesium, and chloride are unknown.
The following chemicals also had elevated concentrations on the site but generally werelimited to the samples obtained from well SMW-10:
Cadmium (COPC)Cobalt (COPC)Nickel (COPC)Silver (COPC)Thallium (COPC)
• Vanadium (COPC)Zinc (COPC)
• Lead
4-78
AR3023L,5
The elevated concentrations of these chemicals in comparison to background in SMW-10suggest an onsite source of these chemicals near well SMW-10. Because none was knownto be used extensively (if at all) in the former process plant area, the assumption is that theywere derived from the site backfill.
EBASCO (1990) had only well SMW-1 for obtaining data on onsite groundwater quality forthe Columbia. Generally, the analytical data from the EBASCO report compare well withthose of the current RI. Chemicals such as cyanide, ammonia, arsenic, and manganese weretwo to four times higher in the recent analyses than in the analyses from EBASCO's report.
Analytical results from offsite downgradient wells were compared with the results from onsitewells to evaluate whether site-related contaminants are migrating eastward from the site andwhether potential sources east of the site could have contributed site-related chemicals to thegroundwater. Off the site are several other potential sources of contaminants in thegroundwater as it moves downgradient from the site, including (but not necessarily limitedto) the petroleum coke piles east of the site; the salt piles north of the site; surface water inthe tidal marsh, the lagoon, Lobdell Canal, and the Christina River; and operations atindustrial facilities east and north of the site.
The offsite downgradient wells nearest to the site are SMW-9, just east of the site by the tidalmarsh, and SMW-2 and W4-C, both just east of the tidal marsh. Well SMW-9 exhibitedelevated concentrations of the site-related chemicals arsenic, sodium, thiocyanate, cyanide,sulfide, and ammonia. At least one of wells SMW-2 and W4-C exhibited elevatedconcentrations of such site-related chemicals as arsenic, manganese, iron, potassium, sodium,thiocyanate, cyanide, sulfide, and ammonia. Well SMW-2 typically exhibits somewhat higherchemical concentrations than does well W4-C. The very high concentrations of potassiumand sodium detected in W4-C, which is directly downgradient of the former process plantarea, strongly suggest that the plant area is the source of these chemicals.
The ammonia detected in SMW-2 and W4-C probably is coming from the site because of thehigh concentration of ammonia detected in onsite wells. According to reports on the qualityof the effluent discharged from Halby Chemical to the onsite lagoon during the late 1960sand early 1970s, the concentration of ammonia was elevated. This high-ammonia dischargewould have entered the tidal marsh adjacent to the locations of these wells. The same maybe true for the thiocyanate and cyanide detected in those wells. Arsenic, manganese, iron,thiocyanate, cyanide, and sulfide also may be coining from other sources east of the tidalmarsh. Other potential sources for groundwater contamination are discussed in Chapter 5(subsection 5.3.1).
Wells SMW-11, SMW-12, and W5-B are located along surface water bodies east of the site.All exhibit unique groundwater quality, including high levels of arsenic, cadmium, lead,manganese, cobalt, zinc, iron, and sulfate and occasional detections of thiocyanate. Ammoniawas detected in all three wells in both sampling rounds. Although all of the chemicals aresite-related, it is not likely that they were derived from the site. Many of the concentrationsdetected were much higher than any observed on the site. In addition, many of these
4-79
chemicals were not detected at significantly elevated concentrations in intervening wells, suchas W4-C.
EBASCO (1990) used wells SMW-2, W-1A, W-1B, W-2A, W-4C, and W5-B for offsitedowngradient data. Well W-1A could not be located for the recent RI, so recent results forthat well are not available. Generally, the data collected by EBASCO compare within afactor of two with those of the current RI, some results being higher and some lower.Table 4-17 presents the data for several site-related contaminants, showing the generalvariability in trends. Arsenic has varied in its trend, and thiocyanate concentrations havedecreased a great deal in each of the wells. Ammonia concentrations also have varied intrend between wells.
The concentrations of such chemicals as manganese, calcium, iron, magnesium, potassium,and sodium in the onsite lagoon are several times higher (e.g., by a factor of 2 to 10) thantheir concentrations in the Christina River as reported by EBASCO (1990). In addition, theconcentrations of these chemicals in the Columbia wells along the river (SMW-11, SMW-12,and W5-B) are many times higher than the concentrations in the river.
Organic Compounds. Several organic compounds were detected in onsite wells atconcentrations higher than in background wells (tables 4-15 and 4-16). Of these compounds,carbon disulfide is derived from the site. The following compounds also may be derivedfrom sources on the site:
• Naphthalene • Aldrin• Phenanthrene • Heptachlor• Acetone • 4-Methyl-2-pentanone• 1,1-Dichloroethane • Toluene• 1,2-Dichloroethene (total) • Benzene• Ethyl chloride • Trichloroethene• Ethylbenzene • Tetrachloroethene• Vinyl chloride . • 2-Butanone
The highest concentration detected for a VOC on the site was for carbon disulfide in wellSMW-1, at a concentration of 333,000 ug/l in Round 1. There was one other detection ofthis chemical in well SMW-8, at a concentration of 99 ug/l (Figure 4-17). Concentrationsin Round 2 were lower. The source of carbon disulfide is assumed to be the site becausecarbon disulfide has been stored on the site.
A detection of TCE in SMW-8 in Round 1 also may be attributable to the site, although italso was detected in the upgradient well SMW-6 in both sampling rounds (Figure 4-17). Awide range of volatile compounds was detected in both rounds in well SMW-8 and probablyis attributable to the site because such a wide range was not detected in upgradient wellSMW-6. Vinyl chloride, benzene, and 4-methyl-2-pentanone also were detected in at leastone round of sampling, all in well SMW-8.
4-80
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Carbon disulfide in the sample from SMW-1 was at a much higher concentration from therecent sampling (330,000 ug/l in Round 1) compared with EBASCO's results (130,000 ug/l).However, several other VOCs (including 1,1,1-trichloroethane, PCE, and TCE) detected byEBASCO in the sample from SMW-1 were not detected during the recent RI.
Carbon disulfide was detected in samples from offsite downgradient wells SMW-2 and W4-Cin both sampling rounds. A wide range of VOCs was detected in samples from SMW-9 andW4-C, but there is little similarity between the two sets of compounds and little similarityto the set of compounds detected in the sample from onsite well SMW-8. The predominantcompounds in the samples from SMW-8 were 4-methyl-2-pentanone, carbon disulfide, andethyl chloride. The only VOC in the samples from SMW-2 was carbon disulfide. Thepredominant compounds in the samples from W4-C were carbon disulfide and vinyl chloride,the latter at an estimated concentration of 230 ug/l in the first round and 79 ug/l in thesecond round. This lack of similarity among the three sets of compounds suggests separatesources of contamination and also degradation of parent compounds, such as TCE.
Organic results from offsite downgradient wells were generally comparable between theEBASCO data and the data from the current RI. Table 4-17 shows the significant declinein carbon disulfide between data sets in samples from well SMW-2. Well W4-C, however,exhibited an increase.
4.5.4 Upper Potomac Water-Bearing Unit
4.5.4.1 Background Groundwater Quality
Groundwater flow in the upper Potomac appears to be to the northeast beneath the site,generally coincident with that in the Columbia. As in the Columbia, the water level in wellIMW-12 indicates a component of groundwater flow toward the south or southwest, but thisis believed to represent local conditions only in the vicinity of the well. The general flowdirection to the northeast is consistent with the topography and likely groundwater recharge-discharge relationships in the vicinity of the site.
Under these groundwater-flow conditions, well IMW-6 should represent an upgradientbackground sampling location. Well W-3B also is a likely background well, even though itis sidegradient to the site. Because of its location definitely upgradient of the site, onlyIMW-6 was considered a background well in the risk assessment (Chapter 6). However,well W-3B is considered a background well for this discussion for the reasons described forwell W3A (subsection 4.5.3.1).
The analytical data for background wells IMW-6 and W-3B are listed in tables 4-18(Round 1) and 4-19 (Round 2). The sample from well IMW-6 consistently exhibited higherconcentrations of the common ions calcium, magnesium, sodium, and potassium than didW-3B.
4-82
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Table 4-19
UPPER POTOMAC WATER-BEARING UNIT
BACKGROUND, ONSITE, AND OFFSITE
GROUNDWATER QUALITY: ROUND 2 SAMPLING
Halby Chemical
Site
Page 4 of 4
Downgradient Wells
Onsite Wells
E
(ground Concentratio
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Inorganic Chemicals. The analytical results for inorganic chemicals in the filtered samplesfrom the background wells are presented in figures 4-18 through 4-22. The COPCs for theupper Potomac, which are listed in Table 4-1, are noted in the tables.
The samples from wells IMW-6 and W-3B from at least one round (and usually both rounds)contained detectable levels of all COPCs. Other inorganic chemicals that were belowdetection limits are indicated in tables 4-18 and 4-19.
The common cations calcium, magnesium, iron, manganese, potassium, and sodium were alldetected in the samples from the background wells at concentrations ranging from a fewhundred to several hundreds of thousands of ug/l (Figure 4-21). The common anionschloride, sulfate, and sulfide were detected in the samples from the background wells atconcentrations ranging from single-digit values to above 3,000 mg/l (Figure 4-22).
EBASCO (1990) used W-3B as the background well for the Columbia. Analytical resultsreported in EBASCO's document for inorganic chemicals compare closely with thoseobtained from the recent RI for well W-3B for all chemical groups.
Organic Compounds. No organic compounds were detected in samples from the back-ground wells in the current RI. Similar results were obtained by EBASCO (1990).
4.5.4.2 Upper Potomac Groundwater Quality
Onsite wells in the upper Potomac discussed in this section are IMW-1, IMW-8, andIMW-10. Offsite downgradient wells in the upper Potomac that are discussed are IMW-2,IMW-3, IMW-9, IMW-11, IMW-12, W-4B, and W-5A. IMW-9 is just east of the site andwest of the tidal marsh; the other wells are east of the tidal marsh. Well W-2B generally isnot included in this discussion because of the likelihood that the well is contaminated by thesalt piles, but the well is discussed in the context of some chemicals, particularly thoseassociated with cyanide. The data are shown in figures 4-18 through 4-23.
Inorganic Chemicals. The analytical results for inorganic chemicals in samples from thewells on and off the site are presented in figures 4-18 through 4-22. The mean and maximumof the concentrations for each chemical are listed in tables 4-18 (Round 1) and 4-19(Round 2). The data from well W-2B are not included in the statistics.
The following inorganic chemicals were not detected above the background concentration insamples during either sampling round from wells on the site and will not be discussed further:antimony, barium, chromium, copper, lead, selenium, and nitrate/nitrite.
4-90
flR302357
ND0.65JBNDND303
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K-INDICATES CONCENTRATION IS BIASED HIGH.L-INDICATES CONCENTRATION IS BIASED LOW.R-INDICATES DATA WERE REJECTED DURING VALIDATION.ND-INDICATES THAT THE CHEMICAL WAS NOT DETECTED.
TWO CONCENTRATION VALUES SEPARATED BY A " I "INDICATES A SAMPLE AND ITS DUPLICATE. ' FiQUfe 4~ 18
RBC « RISK-BASED CONCENTRATION DISSOLVED AS, BE, Nl, CD, AND MNIN GROUNDWATER
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K-INDICATES CONCENTRATION IS BIASED HIGH.L-INDICATES CONCENTRATION IS BIASED LOW.R-INDICATES DATA WERE REJECTED DURING VALIDATION.ND-INDICATES THAT THE CHEMICAL WAS NOT DETECTED.
TWO CONCENTRATION VALUES SEPARATED BYA " I " INDICATES A SAMPLE AND ITS DUPLICATE.
RBC - RISK-BASED CONCENTRATION Figure 4-19DISSOLVED TL. V, ZN, CO. AND PB IN GROUNDWATER
UPPER POTOMAC WATER-BEARING UNITHalby Chemical Site
4979f022.dgn n-JAN-1997
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THIOCYANATECYANIDEWEAK ACID DISSOCIABLE CYANIDE
SAMPLING(8-93)
NOTE: B-INDICATES THAT CHEMICAL WASDETECTED IN THE ASSOCIATED METHOD BLANK.
J-INDICATES THAT THE SAMPLE CONTAINSCHEMICAL AT AN ESTIMATED CONCENTRATION.
K-INDICATES CONCENTRATION IS BIASED HIGH.L-INDICATES CONCENTRATION IS BIASED LOW.R-INDICATES DATA WERE REJECTED DURING VALIDATION.ND-INDICATES THAT THE CHEMICAL WAS NOT DETECTED.
TWO CONCENTRATION VALUES SEPARATED BY A " | " INDICATESA SAMPLE AND ITS DUPLICATE. '
RBC ' RISK-BASED CONCENTRATION _Figure 4-20CYANIDE AND CYANIDE COMPOUNDS IN GROUNDWATER
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302360
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NOTE: B-INDICATES THAT CHEMICAL WASDETECTED IN THE ASSOCIATED METHOD BLANK.j-INDICATES THAT THE SAMPLE CONTAINSCHEMICAL AT AN ESTIMATED CONCENTRATION.
K-INDICATES CONCENTRATION IS BIASED HIGH.L-INDICATES CONCENTRATION IS BIASED LOW.R-INDICATES DATA WERE REJECTED DURING VALIDATION.ND-INDICATES THAT THE CHEMICAL WAS NOT DETECTED.
TWO CONCENTRATION VALUES SEPARATED BY A " I " INDICATESA SAMPLE AND ITS DUPLICATE. ' FlOUTC 4~21
DISSOLVED CA. FE. MG. K. AND NAIN GROUNDWATER
UPPER POTOMAC WATER-BEARING UNITHalby Chemical Site
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J-INDICATES THAT THE SAMPLE CONTAINSCHEMICAL AT AN ESTIMATED CONCENTRATION.
K-INDICATES CONCENTRATION IS BIASED HIGH.L-INDICATES CONCENTRATION IS BIASED LOW.R-INDICATES DATA WERE REJECTED DURING VALIDATION.ND-INDICATES THAT THE CHEMICAL WAS NOT DETECTED.
TWO CONCENTRATION VALUES SEPARATED BY A " I " INDICATESA SAMPLE AND ITS DUPLICATE. '
Figure 4-22CHLORIDE, SULFATE, SULFIDE, AND AMMONIA IN GROUNDWATER
UPPER POTOMAC WATER-BEARING UNITHalby Chemical Site
4979.026.0gn 06-MAY-«96 AR3Q236Z
VV-3BND || NDND NDND II ND I \
IMW-10140 || 26BND NDND II ND
IUW-1 r.___870 || 3.000B3J ND IND II ND
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LEGENDSITE BOUNDARY I «.„_, I DENOTES SIGNIFICANTLY
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ND | CARBON DISULFIDE (CS2)ND TRICHLOROETHENEND I TETRACHLOROETHENEROUND 2SAMPLING(12-93)
NOTE: B-INDICATES THAT CHEMICAL WASDETECTED IN THE ASSOCIATED METHOD BLANK.
J-INDICATES THAT THE SAMPLE CONTAINSCHEMICAL AT AN ESTIMATED CONCENTRATION.
K-INDICATES CONCENTRATION IS BIASED HIGH.L-INDICATES CONCENTRATION IS BIASED LOW.R-INDICATES DATA WERE REJECTED DURING VALIDATION.ND-INOICATES THAT THE CHEMICAL WAS NOT DETECTED.TWO CONCENTRATION VALUES SEPARATED BY A " I " INDICATESA SAMPLE AND ITS DUPLICATE. '
Figure 4-23VOLATILE ORGANIC COMPOUNDS IN GROUNDWATER _____
UPPER POTOMAC WATER-BEARING UNIT fr;ifir/i//|fHalby Chemical Site
4979.026.dgn 06-MAY-1996 AR302363
The remaining inorganic chemicals were reviewed to determine which are likely to beattributable to the site. A chemical is considered possibly attributable to the site when it isdetected in a sample from a single onsite well at a concentration above backgroundconcentration. The following chemicals were detected at concentrations above backgroundon the site and may be derived from sources on the site:
• Arsenic (COPC)Beryllium (COPC)
• Cyanide (COPC)• Thiocyanate (COPC)• Ammonia (COPC)• Weak-acid dissociable cyanide• Mercury• Potassium• Sodium• Chloride
Concentrations of potassium and sodium, both used in the former process plant area, wereparticularly elevated in well IMW-8 on the site.
The following chemicals also had elevated concentrations on the site but generally werelimited to or were highest in the sample obtained from well IMW-10:
Aluminum (COPC) • Vanadium (COPC)• Cadmium (COPC) • Zinc (COPC)
Cobalt (COPC) • Iron• Manganese (COPC) • Sulfate
Nickel (COPC) • SulfideSilver (COPC) • MagnesiumThallium (COPC) • Calcium
The elevated concentrations suggest an onsite source of these chemicals in the vicinity of wellIMW-10. High levels of cadmium, cobalt, nickel, silver, thallium, zinc, and lead also wereobserved in well SMW-10, in the overlying Columbia water-bearing unit. Sodium andpotassium were particularly elevated in onsite well IMW-8, within the former process plantarea.
EBASCO (1990) reported IMW-1 and IW-01 (an industrial well) as onsite wells for the upperPotomac. IW-01 was not sampled during the current RI. Generally, the analytical data forIMW-1 compare well between the two data sets, although concentrations of most chemicalsare lower in the recent data. An exception is ammonia, which increased from 26,500 ug/lin 1989 to 47,200 ug/l (Round 2 of the current RI). Thiocyanate, which was at aconcentration of 690,000 ug/l in EBASCO's report, was still at 835,000 ug/l during Round 2of sampling in the current RI.
4-97
AR302361*
With very few exceptions, the concentrations of chemicals, including site-related thiocyanate,ammonia, and cyanide, in onsite wells from both sampling rounds in the upper Potomac werehigher than the concentrations of the same chemicals in the overlying Columbia. Exceptionsare arsenic and potassium, both likely to be derived from the site.
The analytical results from offsite downgradient wells in the upper Potomac were comparedwith the results from onsite wells in the same unit to evaluate whether site-relatedcontaminants are migrating eastward from the site and whether potential sources east of thesite could have contributed site-related chemicals to the groundwater. Offsite potentialsources of contaminants in the groundwater in the upper Potomac are the same as for theColumbia.
The offsite downgradient wells nearest to the site in the upper Potomac are IMW-9, just eastof the site by the tidal marsh, and IMW-2 and W4-B, both just east of the tidal marsh. WellIMW-9 has exhibited high levels of thiocyanate, cyanide, and sulfide, all of which are site-related. In comparison to well W4-B, well IMW-2 has exhibited very high concentrationsof manganese, zinc, cobalt, calcium, iron, magnesium, potassium, sodium, chloride, sulfate,and ammonia. High concentrations of such site-related chemicals as thiocyanate, manganese,and sodium would be expected in downgradient well IMW-2, but similar high concentrationswere not detected in well W4-B, located directly across the tidal marsh from the formerprocess plant area. Most likely, the thiocyanate and cyanide in IMW-9 and the ammonia inIMW-2 came from the site. Alternatively, the high levels of metals detected in IMW-2 couldbe derived from petroleum coke piles.
Wells IMW-11, IMW-12, and W5-A are near surface-water bodies east of the site, and wellIMW-3 is near Christina Avenue and an active industrial area. These wells exhibit severalunique characteristics:
• The elevated arsenic concentration in well W5-A may not be attributable tothe site because only low levels of arsenic are detected in intervening wells.A high concentration of arsenic also was detected in well W5-B in theoverlying Columbia.
• Cobalt, iron, and zinc concentrations were very high in wells W5-A and IMW-11 and may not be attributable to the site because only low levels of thesecontaminants were detected in intervening wells.
• Ammonia detected in wells along the river may not be attributable to the sitebecause much lower concentrations were detected in intervening wells.
Calcium and magnesium concentrations in offsite downgradient wells were variable, thehighest concentrations being in W-2B (near the salt piles) and IMW-2. Potassium, sodium,and chloride also were highest in W-2B. High concentrations of these chemicals also werereported by EBASCO (1990) and by DNREC (1985) from a study of the salt piles. Both ofthese sources reported that much higher concentrations of these chemicals were detected in
4-98
AR302365
the upper Potomac unit than in the overlying Columbia. This can be explained by the sinkingof a high-density plume of water into the upper Potomac directly beneath the piles. The siltlayer underlying the Columbia over most of the study area is absent in the vicinity of the saltpiles, so there is an unrestricted hydraulic connection between the Columbia and theunderlying upper Potomac.
High concentrations of thiocyanate and cyanide were detected in well W-2B during bothsampling rounds of the RI and were reported by EBASCO (1990). Thiocyanate also wasdetected in overlying well W-2A in Round 1 and was reported in this well by EBASCO(1990). This location is sidegradient to the groundwater flow in these water-bearing units,so it is unlikely that thiocyanate is migrating in this direction. Other possible explanationsare that (1) the contamination is residual from the time when the well at the Forbes Steelplant was being pumped and presumably drew groundwater from the site in that direction,(2) there is another source of the chemicals not related to the site, and (3) contamination isbeing drawn from the former lagoon sediment that underlies the area of the salt piles.
EBASCO (1990) used wells IMW-3, W-2B, W-4B, and W-5A for offsite downgradient datain the upper Potomac. Generally, the two data sets compare within a factor of two.Table 4-20 contains data for selected chemicals, showing the general variability in trends.Arsenic appears typically to have declined, as has ammonia, but thiocyanate appears to haveincreased at some wells.
Unlike the onsite wells and with few exceptions, the concentrations of chemicals in offsitewells from both sampling rounds in the upper Potomac were lower than or comparable to theconcentrations of the same chemicals in the overlying Columbia. Possible reasons will bediscussed in Chapter 5, "Contaminant Fate and Transport."
Organic Compounds. Tables 4-18 and 4-19 show organic compounds detected in onsitewells at concentrations higher than in background wells. Of these compounds, carbondisulfide is known to be derived from the site. The following compounds also may bederived from the site:
• Acetone• Tetrachloroethene• Trichloroethene• Methylene chloride• Xylene
The highest onsite concentration detected for a VOC was for carbon disulfide in well IMW-1,at a concentration of 870 ug/l (Figure 4-23). It also was detected in the other onsite wellsat a concentration of 330,000 ug/l (Round 1) and 160,000 ug/l (Round 2) in SMW-1 in theoverlying Columbia. Carbon disulfide was detected only in the Round 1 sample from offsitedowngradient well IMW-2.
4-99
AR302366
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Carbon disulfide in the sample from IMW-1 dropped from the 5,700 ug/l reported byEBASCO (1990) to 870 ug/l (Round 1). The source of carbon disulfide is assumed to be thesite, considering past operations.
Acetone was detected in IMW-10 at a concentration (100 ug/l) that probably is not a resultof laboratory contamination, because it was not detected in associated laboratory blanks.Detections of TCE and PCE in IMW-8 (Figure 4-23) probably are attributable to the site.Acetone was reported by EBASCO (1990) for the sample from IMW-3 at 330 ug/l (140 ug/lin the duplicate). However, acetone was not detected in the sample from IMW-3 during therecent RI.
4.5.5 Lower Potomac Water-Bearing Unit
4.5.5.1 Background Groundwater Quality
The groundwater-flow direction in the lower Potomac appears to be to the south beneath thesite. Under these groundwater-flow conditions, wells DMW-2, DMW-3A, DMW-4, DMW-5,and W4-A may represent background sampling locations. Well DMW-5 was selected as themost representative background well because it is the most upgradient well in relation to thesite; all other wells are sidegradient to the site to some degree. In addition, well DMW-5 isless likely to have been affected by site-related contamination migrating downgradient in theoverlying upper Potomac water-bearing unit and leaking downward into the lower Potomac.The analytical data for background well DMW-5 are listed in tables 4-21 (Round 1) and 4-22(Round 2).
Inorganic Chemicals. The analytical results for inorganic chemicals in filtered samples fromthe background well are presented in figures 4-24 and 4-25. The COPCs for the lowerPotomac, which are listed in Table 4-1, are noted in the tables.
The samples from well DMW-5 from both rounds contained detectable concentrations of veryfew chemicals. Thiocyanate and cyanide were detected unexpectedly in the Round 1 samplefrom well DMW-3A, located sidegradient of the site. Neither cyanide nor thiocyanate wasreported by EBASCO (1990) in the sample from this well, nor were they detected in thesecond round. Therefore, the Round 1 detections of thiocyanate and cyanide are considereddue to sampling error.
The common cations calcium, magnesium, iron, manganese, potassium, and sodium weredetected in the sample from the background well at concentrations ranging from a fewhundred to a few tens of thousand of ug/l (Figure 4-25). The common anions chloride,sulfate, and sulfide were detected in the sample from the background well at concentrationsranging from less than 1 mg/l to about 9 mg/l (Figure 4-26). Ammonia was detected in thewell at a concentration of 0.12 mg/l in Round 1 and 0.49 mg/l in Round 2 (Figure 4-26).
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MO ELEVATED CONCENTRATION— nww-7 '————' OF INDICATED CHEMICAL• u MONITORING WELL LOCATION
APPROXIMATE DIRECTIONI IMITC A DC IM .«-./! I lln™™1 M|-|-n W AIMrt 1 C L/IHCO I IUINUNITS ARE IN ug/l ggg I ^ QF GROUNDWATER FLOW17529.862.6J132
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J-INDICATES THAT THE SAMPLE CONTAINSCHEMICAL AT AN ESTIMATED CONCENTRATION.
K-INDICATES CONCENTRATION IS BIASED HIGH.L-INDICATES CONCENTRATION IS BIASED LOW.R-INDICATES DATA WERE REJECTED DURING VALIDATION.ND-INDICATES THAT THE CHEMICAL WAS NOT DETECTED.
TWO CONCENTRATION VALUES SEPARATED BY A " I " INDICATESA SAMPLE AND ITS DUPLICATE
RBC • RISK-BASED CONCENTRATION _. . _ .Figure 4-24DISSOLVED MM, ZN, TL, AND THIOCYANATE IN GROUNDWATER
LOWER POTOMAC WATER-BEARING UNITHalby Chemical Site
49791027.Ogn 10- JAN-1997
LEGEND_. _ .. c-rnr nniiwriARY I -*S APPROXIMATE DIRECTION----- SITE BOUNDARY I——————^ Qf GROUNDWATER FLOW
A DMW-7 MONITORING WELL LOCATION
UNITS ARE IN ug/l9.8109,4503.470BJ1.820J7.930J
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J-INDICATES THAT THE SAMPLE CONTAINSCHEMICAL AT AN ESTIMATED CONCENTRATION.
K-INDICATES CONCENTRATION IS BIASED HIGH.L-INDICATES CONCENTRATION IS BIASED LOW.R-INDICATES DATA WERE REJECTED DURING VALIDATION.ND-INDICATES THAT THE CHEMICAL WAS NOT DETECTED.
TWO .CONCENTRATION VALUES SEPARATED BYA " I " INDICATES A SAMPLE AND ITS DUPLICATE.
Figure 4-25DISSOLVED CA, FE, MG, K, AND NA IN GROUNDWATER
LOWER POTOMAC WATER-BEARING UNIT_________________________ Halby Chemical Site
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LEGEND_. _.. qiTp HouisinARY l *S APPROXIMATE DIRECTION— - — SITE BOUNDARY I——————^ OF GROUNDWATER FLOW
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J-INDICATES THAT THE SAMPLE CONTAINSCHEMICAL AT AN ESTIMATED CONCENTRATION.
K-INDICATES CONCENTRATION IS BIASED HIGH.L-INDICATES CONCENTRATION IS BIASED LOW.R-INDICATES DATA WERE REJECTED DURING VALIDATION.ND-INDICATES THAT THE CHEMICAL WAS NOT DETECTED.
TWO CONCENTRATION VALUES SEPARATED BY A " I " INDICATESA SAMPLE AND ITS DUPLICATE. FiOUTe 4-P6
CHLORIDE, SULFATE, SULFIDE,AND AMMONIA IN GROUNDWATER _____
LOWER POTOMAC WATER-BEARING UNIT &MISIIHHalby Chemical Site
4979f029.dgn OS-MAY-1996
The inorganic-chemical data are almost identical between the EBASCO (1990) data and theresults of the current RI, although the current RI found iron was about one-third and ammoniawas about one-fourth of that reported by EBASCO.
Organic Compounds. No organic compounds were detected in the samples from thebackground well.
4.5.5.2 Lower Potomac Groundwater Quality
The onsite well in the lower Potomac included in this discussion is DMW-1. The only offsitedowngradient well in the lower Potomac is DMW-7.
Inorganic Chemicals. The analytical results for inorganic chemicals for the samples fromthe onsite and offsite wells are presented in figures 4-24 and 4-25. The concentrations foreach chemical are listed in tables 4-21 (Round 1) and 4-22 (Round 2). Statistics were notcalculated because only one well was available.
Only iron, manganese, selenium, thallium, thiocyanate, vanadium, and ammonia were detectedabove their background concentrations. Iron, manganese, and thallium probably would nothave been derived from the site. Although thiocyanate is a site-related chemical, it wasdetected only once in DMW-1 among the three sampling rounds in 1989 and 1993, and,therefore, is not attributed to the site. Although ammonia was detected at more than 1 ug/lin DMW-1 in 1989, it was detected in 1993 at concentrations similar to background and,therefore, is not attributed to the site. Selenium and vanadium were detected abovebackground concentrations only in one round and they are not COPCs, so they will not bediscussed further.
DMW-1 was the only onsite well in the lower Potomac available to EBASCO (1990). Theresults from the earlier sampling are almost identical to those obtained during the current RIexcept that thiocyanate was not detected previously and ammonia was almost four timeshigher.
The data from the offsite well was reviewed to determine which chemicals are likely to beattributable to the site. Of the chemicals detected in the offsite well, only manganese,potassium, sodium, and ammonia are likely to be attributable to the site. However, theirconcentrations are either below or are very similar to background, so the chemicals are notattributed to the site. No downgradient wells were available to EBASCO (1990).
Organic Compounds. No organic compounds were detected in the samples fromwell DMW-1. Carbon disulfide was reported by EBASCO (1990) in the sample fromDMW-1, but it was estimated below the detection limit.
4-111
Ethylbenzene, toluene, and xylene were detected at low levels in the samples for bothsampling rounds from offsite well DMW-7. These chemicals were not defined as attributableto the site, although both chemicals reportedly were used on the site. No downgradient wellswere available to EBASCO (1990).
4.6 Summary
The nature and extent of contamination were investigated, particularly in groundwater and insoil in three areas on and near the site. Surface water, sediment, and biota also weresampled. The information obtained during the RI then was combined with information fromseveral previous investigations to develop a complete and comprehensive picture ofcontamination at and in the vicinity of the site.
Contamination of both surface and subsurface soil was investigated. On the site, surface soilis contaminated above background concentrations and RBCs by site-related chemicals, suchas arsenic. In particular, surface soil within the former process plant area exhibits elevatedconcentrations of arsenic. Because the areas of high concentrations tend to be scattered,contamination can be attributed to individual releases of chemicals. VOCs and SVOCs rarelywere detected in surface soil.
Subsurface soil contains levels of arsenic and other inorganic chemicals in excess ofbackground concentrations and RBCs in the northern part of the site (between ChristianaMotor Freight and the onsite lagoon), in and around the former process plant area, and in theprocess plant drainage ditch. In the northern part of the site, sediment samples from theformer lagoon (since backfilled) contained arsenic and other inorganic chemicals and mayserve as a source of contamination of groundwater.
VOCs and SVOCs were detected in a few scattered subsurface samples across the site.However, in and around the process plant drainage ditch, concentrations of carbon disulfidewere as high as 110,000 ug/l. Contamination by carbon disulfide extends into thenortheastern corner of the former process plant area. Contamination at the observed highlevel indicates that carbon disulfide was release to the surface in a concentrated form,probably as a dense nonaqueous-phase liquid (DNAPL). Free-product carbon disulfide hasbeen observed in subsurface soil in the ditch. The subsurface contamination observed at thesite is a risk to human health and the environment because of the potential for ingestion,inhalation, dermal exposure, and, possibly, leaching to groundwater. Explosions observedduring test-pit excavation indicate that soil laden with carbon disulfide is also a safety risk.
Surface water and sediment contain contamination that is site-related. In particular, the headof the lagoon and the northern and central parts of the tidal marsh (across the railroad tracksfrom the onsite lagoon and the former process plant area) have high levels of arsenic,ammonia, and other site-related chemicals. The lagoon was and still is connectedhydraulically with the tidal marsh through pipes and culverts under the railroad tracks,
4-112
AR302379
allowing discharge of surface water with site-related contaminants into the tidal marsh.Currently, the onsite lagoon is isolated from the 1-495 drainage ditch, through which it usedto discharge to the Christina River.
Groundwater quality was investigated in three water-bearing units: the Columbia and theupper and lower Potomac. One groundwater sample also was obtained from the backfill inthe northern part of the site. The groundwater sample from the backfill containedconcentrations of several inorganic chemicals above background levels. The presence ofmany of these chemicals probably is attributable to the site. Little effect of surface water onwater quality in this well was observed.
In the Columbia unit, onsite wells contained concentrations well above background and RBCsof inorganic chemicals, such as arsenic, thiocyanate, ammonia, and manganese that are site-related. In particular, elevated levels of several metals in the northern part of the site suggesta specific source in that area. Carbon disulfide was detected at a concentration of 330 mg/lin well SMW-1, near the center of the site. A concentration this high suggests the presenceof a DNAPL of carbon disulfide contaminating the groundwater in this part of the site.
Downgradient of the site are wells (e.g., W4-C) along the east side of the tidal marsh thatcontain elevated concentrations of some chemicals that are site-related, such as carbondisulfide and thiocyanate. This contamination can be attributed to the site because of theproximity of former effluent discharge from the Halby Chemical facility. The chemicalsfound in these wells and other downgradient wells suggest that other sources also may becontaminating groundwater.
There is little geochemical evidence of interaction between the Columbia and the surfacewater in the lagoon and the tidal marsh. Although some chemical parameters have similarconcentrations, others differ sufficiently to suggest that, although there may be somehydraulic connection, the amount of interaction is limited, and there is effectively no evidenceof migration of surface water into the underlying Columbia. If anything, discharge from theColumbia to the surface water is likely to predominate.
Onsite contamination in the upper Potomac water-bearing unit is similar to that in theColumbia but typically at higher concentrations. Arsenic, carbon disulfide, and potassium (alllikely to be attributable to the site) were at higher concentrations in the Columbia, but othersite-related chemicals, such as thiocyanate, ammonia, and cyanide, were higher in the upperPotomac. High levels of certain metals were detected in a well in the northern part of thesite, similar to the high levels detected in this area in the overlying Columbia. Carbondisulfide was detected at a high concentration in well IMW-1, underlying the possiblelocation of a DNAPL mass of carbon disulfide in the overlying Columbia.
Off the site and downgradient, the concentrations of chemicals generally were lower in theupper Potomac than in the Columbia. Concentrations of several inorganic chemicals in wellsalong the river may be attributable to the site but also may be from other sources because theconcentrations of many of the chemicals in wells near the river typically are higher than in
4-113
AR302380
intervening wells. Some contamination by site-related chemicals is likely in wells along theeast side of the tidal marsh.
In the lower Potomac water-bearing unit, several chemicals were detected at above-background concentrations. Of those chemicals, ammonia and thiocyanate may be attributedto the site. No organic compounds were detected on the site that could not be attributed tolaboratory contamination. The only chemicals that were detected in the downgradient wellthat may be derived from the site are ammonia and, although less likely, sulfide, potassium,manganese, xylene, and toluene. However, because all of the chemicals detected in the lowerPotomac have concentrations similar to background, none is attributed to the site.
4.7 References
DNREC. Preliminary Hydrogeologic Investigation at the Salt Piles Along 1-495; Wilmington,Delaware. February 6, 1985.
____. Surface Quality Standards. Delaware Department of Natural Resources andEnvironmental Control. May 15, 1974. Amended February 26, 1993.
EBASCO. Final Remedial Investigation Report, Halby Chemical Site; New Castle County,Delaware. USEPA Work Assignment No. 119-3LL7. September 1990.
Knight, P.T., and M.D. Sprenger. Analytical Chemistry and Solid Phase Toxicity Bioassayon the Halby Chemical Company Superfund Site, New Castle County, Delaware. Preparedfor the Hazardous Waste Management Division, USEPA. April 1991.
Langan. Preliminary Remedial Design Report for Operable Unit 1 (OU-1), Halby ChemicalSite, Wilmington, New Castle County, Delaware. Prepared for Witco Corporation by LanganEngineering and Environmental Services, Inc. 1993.
Palmer, C.D., and R.W. Puls. Natural Attenuation of Hexavalent Chromium in Ground Waterand Soils. USEPA/540/S-94/505. October 1994.
USEPA. Selecting Exposure Routes and Contaminants of Concern by Risk-Based Screening.Technical Guidance Manual, Risk Assessment. Hazardous Waste Management Division,Office of Superfund Programs. January 1993.
USFWS and USEPA. Analytical Chemistry and Solid Phase Toxicity Bioassay on the HalbyChemical Superfund Site, New Castle County, Delaware. Prepared by the U.S. Fish andWildlife Service and USEPA, Environmental Response Team, for USEPA, Hazardous WasteManagement Division, under Interagency Agreement No. DW-14933552-01-2. April 1991.
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Weston. Analytical Report, Halby Chemical, Wilmington, New Castle County, Delaware.Prepared for USEPA by Roy F. Weston, Inc. August 1992.
____. Trip Report, Halby Chemical Site, Wilmington, New Castle County, Delaware.1995.
Witco Corporation. Response Action Report, Halby Chemical Site, Wilmington, New CastleCounty, Delaware. EPA docket No. 111-95-55-DC. Prepared by Langan Engineering andEnvironmental Services, June 1996.
WDCR1026/007.WP5
4-115
AR3Q2382
