MEMORANDUM Project No.: 050067-005C January 28, 2011 To: Ed Jones, Department of Ecology/NWRO cc: Tong Li, Groundwater Solutions Mike Merryfield, Art Brass Plating William Joyce, Salter Joyce Ziker From: Doug Hillman, LHG Principal Hydrogeologist Clay Patmont Anchor QEA, LLC Re: Duwamish Waterway Sediment Porewater Sampling Work Plan Art Brass Plating (ABP), Agreed Order No. DE 5296 On behalf of Art Brass Plating, Aspect Consulting, LLC (Aspect) and Anchor QEA, LLC (Anchor QEA) have prepared this memorandum describing the technical rationale and procedures for collecting and analyzing sediment porewater samples from the Duwamish Waterway (Waterway) downgradient of the ABP facility. The sediment porewater sampling is being completed as part of the on-going Remedial Investigation (RI). Investigations to date have identified elevated concentrations of certain chlorinated ethenes in groundwater near the eastern bank of the Duwamish Waterway. We anticipate using these data as one line of evidence when assessing the potential need for interim action and evaluating final remedy selection within the MTCA decision-making framework. Groundwater monitoring data suggest the potential discharge of the chlorinated volatile organic compound (VOC) trichloroethene (TCE), and its degradation products cis-1, 2-dichloroethene (DCE) and vinyl chloride (VC) along the eastern side of the Duwamish Waterway. Although groundwater concentrations have been characterized (and are currently being monitored) along the Waterway shoreline, the concentrations of chlorinated ethenes in sediment porewater discharging into the biologically active zone of Waterway sediments has not yet been characterized. As discussed in more detail, these porewater characterization data are needed to complete the RI/FS and evaluate possible interim actions. Conceptual Site Model Groundwater from upland areas generally flows toward the Waterway. High tides result in localized groundwater flow gradient reversal, although the time-averaged net groundwater flow direction is still toward the Waterway (Booth and Herman, 1998). The occurrence of localized and transient flow reversals is consistent with site characterization data collected at other similar sites in the Waterway, and with RI data collected to date at the ABP site, as documented in the plume maps submitted in earth + water Aspect Consulting, LLC 23 S. Mission Street, Suite B Wenatchee, WA 98801 509.888.5766 www.aspectconsulting.com
Transcript
MEMORANDUM
Project No.: 050067-005C
January 28, 2011
To: Ed Jones, Department of Ecology/NWRO
cc: Tong Li, Groundwater Solutions Mike Merryfield, Art Brass Plating William Joyce, Salter Joyce Ziker
From: Doug Hillman, LHG Principal Hydrogeologist
Clay Patmont Anchor QEA, LLC
Re: Duwamish Waterway Sediment Porewater Sampling Work Plan Art Brass Plating (ABP), Agreed Order No. DE 5296
On behalf of Art Brass Plating, Aspect Consulting, LLC (Aspect) and Anchor QEA, LLC (Anchor QEA) have prepared this memorandum describing the technical rationale and procedures for collecting and analyzing sediment porewater samples from the Duwamish Waterway (Waterway) downgradient of the ABP facility. The sediment porewater sampling is being completed as part of the on-going Remedial Investigation (RI). Investigations to date have identified elevated concentrations of certain chlorinated ethenes in groundwater near the eastern bank of the Duwamish Waterway. We anticipate using these data as one line of evidence when assessing the potential need for interim action and evaluating final remedy selection within the MTCA decision-making framework.
Groundwater monitoring data suggest the potential discharge of the chlorinated volatile organic compound (VOC) trichloroethene (TCE), and its degradation products cis-1, 2-dichloroethene (DCE) and vinyl chloride (VC) along the eastern side of the Duwamish Waterway. Although groundwater concentrations have been characterized (and are currently being monitored) along the Waterway shoreline, the concentrations of chlorinated ethenes in sediment porewater discharging into the biologically active zone of Waterway sediments has not yet been characterized. As discussed in more detail, these porewater characterization data are needed to complete the RI/FS and evaluate possible interim actions.
Conceptual Site Model Groundwater from upland areas generally flows toward the Waterway. High tides result in localized groundwater flow gradient reversal, although the time-averaged net groundwater flow direction is still toward the Waterway (Booth and Herman, 1998). The occurrence of localized and transient flow reversals is consistent with site characterization data collected at other similar sites in the Waterway, and with RI data collected to date at the ABP site, as documented in the plume maps submitted in
e a r t h + w a t e r Aspect Consulting, LLC 23 S. Mission Street, Suite B Wenatchee, WA 98801 509.888.5766 www.aspectconsulting.com
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quarterly progress reports and with site-specific water level measurements collected during multi-day tidal studies.
Water levels in the Duwamish Waterway are influenced by river flow and tidal effects from Puget Sound. The typical tidal range in Seattle’s Elliott Bay is approximately 11 feet, based on the difference between mean higher high water (MHHW) and mean lower low water (MLLW) (http://tidesandcurrents.noaa.gov).
Groundwater Flow and Tidal Variability Aspect previously performed a groundwater tidal monitoring study focusing on the area between the Waterway and 1st Avenue South. Results of the study were reported to Ecology in the Results from Hydraulic Studies memorandum dated August 5, 2010. Consistent with the conceptual site model outlined above, the tidal monitoring study confirmed that the mean (tidally-averaged) groundwater flow direction in the shoreline area downgradient of the ABP site is toward the Waterway. The groundwater flow contours illustrated in blue and red on Figure 1 are based on tidally averaged groundwater elevations for the shallow interval. Also presented in light blue on Figure 1 is the shallow interval groundwater contours from the area-wide W4 water level round completed in August.
In the two nearshore well clusters (MW-22 and MW-23), the tidally-averaged vertical gradients were slightly upward: +0.004 at MW-22 and +0.008 at MW-23. This slightly upward gradient is consistent with the regional flow path of groundwater discharge from adjacent uplands into the Waterway. The relatively dense saline water wedge that occurs in the Waterway results in an upward gradient of groundwater discharge into the river. In the Waterway, fresh surface water moving downstream overlies this tidally oscillating saltwater wedge. These conditions result in the occurrence of saline water in the groundwater zone beneath the channel. Less dense, low salinity groundwater does not readily mix or migrate into these deeper saline zones. As a result, fresh groundwater migrating beneath upland areas discharges upward primarily into shallower areas of the Waterway when it meets the saline groundwater wedge located directly beneath the channel. The size and shape of the saltwater wedge within this section of the waterway is dependent upon local groundwater flux, aquifer permeability, and seasonal upstream river flows and stages.
Groundwater Plume Discharge Area The groundwater plume position, nearshore hydraulic gradients, and Duwamish Waterway bathymetry are all factors that determine the location and concentration of groundwater discharges from the ABP site into the Waterway. Based on regional flow patterns and detailed investigations performed at other nearby sites on the Waterway, the prospective discharge area of groundwater affected by releases from the ABP site is depicted in yellow on the site plans, which also show the spatial distributions of TCE, DCE, and VC concentrations in groundwater (Figures 1, 2, and 3, respectively). Figures 4 and 5 provide cross sectional views of the extent of VOCs within groundwater near the waterway.
Immediately upgradient from the Waterway, TCE, DCE, and VC concentrations exceeding Washington State Model Toxics Control Act (MTCA) groundwater cleanup levels (based on potential drinking water use) are located between approximately elevations 0 and -25 feet MLLW. Given the upward gradient near the Waterway, these chemicals of concern (COCs) would discharge into the Duwamish Waterway within or above this interval. The isoconcentration contours illustrated
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on Figure 4 assume a horizontal gradient to conservatively estimate the maximum westward extent of contaminated groundwater discharging to the Waterway. Based on the upward gradient and the saltwater wedge at the base of the channel, it is likely that most of shoreline groundwater discharges in the shallower areas of the Waterway closer to the shoreline. The lateral extent of groundwater discharge from the ABP facility into the Waterway also depends on the variability in aquifer permeability and sediment physical characteristics. The investigation program described below is designed to characterize the spatial distributions of COC concentrations potentially attributable to the ABP facility that are currently discharging into the biologically active (porewater) zone of Waterway sediments.
Data Quality Objectives Because the Duwamish Waterway is tidally influenced, porewater concentrations in groundwater discharging into the Waterway are expected to vary both temporally (i.e., over a tidal cycle) and spatially (i.e., due to variable horizontal and vertical gradients near the sediment/water interface over a tidal cycle). Site-specific characterization requirements in this situation are also dependent on the exposure pathway and toxicity criterion being evaluated. The Waterway at the study location is an estuarine environment with a variety of marine habitats. Because the brackish/saline water in this area is not a potential source of drinking water, MTCA groundwater cleanup levels based on drinking water use are not applicable to the discharge zone. However, groundwater cleanup levels do take into account the potential for surface water exposure (e.g., consumption of fish from the Duwamish Waterway).
Potential aquatic life exposure pathways that are potentially applicable to surface water in the Duwamish Waterway are also relevant and appropriate to sediment porewater exposures to protect benthic organisms that reside in surface sediments within the Waterway. Potential benthic risks associated with exposure of COCs to organisms are addressed under two exposure scenarios:
Acute exposure- concentrations at which toxic effects may be observed over relatively short durations (typically 1 to 24 hours for aquatic life criteria); and
Chronic exposure – concentrations at which toxic effects may be observed over long durations (typically several days for aquatic life criteria).
While aquatic life bioaccumulation and associated human health criteria (e.g., through ingestion of organisms that have bioaccumulated COCs in their tissue) are applicable to surface water in the Duwamish Waterway, these criteria are not relevant and appropriate to individual sediment porewater samples. Human health risks via this pathway are appropriately averaged over relatively long periods of time (years) and over areas (typically miles of river) that include sufficient populations of organisms to support sustainable consumption.
As an initial screening, the maximum concentrations of TCE, total-1,2-DCE (cis + trans isomers), and VC detected in groundwater within the shoreline area (630 µg/L, 183 µg/L, and 200 µg/L, respectively) were compared with the most conservative freshwater or marine EPA chronic exposure ecological screening benchmarks (21 µg/L, 590 µg/L, and 930 µg/L, respectively), http://www.epa.gov/reg3hwmd/risk/eco/btag/sbv/fw/screenbench.htm. Based on this screening-level comparison, only TCE has the potential to pose a potential chronic exposure risk to sensitive aquatic life in Waterway surface sediments, and potentially only at localized discharge locations. However, because of tidal flow reversals and other mixing processes, temporally averaged surface sediment
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porewater concentrations in the Waterway are likely to be considerably lower than the maximum shoreline groundwater concentrations.
As discussed above, bioaccumulation-based surface water quality criteria are not relevant and appropriate to individual sediment porewater samples, given the relatively large spatial and temporal averaging that is required for direct comparisons with these criteria. Nevertheless, as a further screening-level human health exposure assessment, the upper 95 percent upper confidence level (UCL) of the average surface sediment porewater concentration in the site groundwater discharge area will be compared with these human health criteria. If sediment porewater UCL concentrations are below these conservative criteria, protection of human health is indicated.
Based on the considerations outlined above, the proposed porewater investigation will include the following:
Time-averaged concentrations of COCs in porewater at specific discharge locations will be characterized throughout several daily tidal cycles for comparison with chronic aquatic life benchmarks.
Spatially-averaged concentrations of COCs in porewater will be characterized across the study area for comparison with bioaccumulation-based surface water quality criteria. For practical purposes, the study area has been conservatively constrained to include only the area in the immediate vicinity of projected groundwater discharge from the ABP plume. This area is shown in yellow on Figures 1, 2 and 3. The proposed investigation will provide a more accurate characterization of the lateral extent of COCs in porewater from the ABP plume.
Consistent with MTCA and Sediment Management Standards (SMS) point of compliance requirements for sediments, porewater concentrations will be characterized at a depth of approximately 10 centimeters (cm) below the sediment mudline. This depth is below the biologically active zone for most benthic organisms.
The distribution of COC concentrations in the study area is expected to vary substantially due to sediment heterogeneity and preferential areas of groundwater discharge. Sufficient samples will be collected to reliably estimate average porewater concentrations across the study area (minimum of 20 surface sediment porewater samples). The number of samples required will depend on the actual heterogeneity of the sediments. Therefore, this work includes an initial study to assess the degree of sediment heterogeneity and more accurately determine the number and distribution of porewater samples to meet these data quality objectives. The design of the propose investigation is described in the section below.
Study Design and Methods As discussed above, the objective of the proposed porewater study is to characterize COC concentrations in surface sediment porewater at locations where groundwater is expected to be discharging to the Waterway. Sediment porewater characterization will be completed in a two-phased field program. The initial sampling program will assess the spatial variability and heterogeneity of groundwater discharge into the Waterway. This initial sampling effort will guide the sediment porewater chemical testing to be completed in the second field program.
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Since this sampling program is being conducted as scientific research and under an Agreed Order with Ecology, work is exempt from Army Corps of Engineers permit requirements and other related approvals.
Phase One – Assess Spatial Variability in Groundwater Discharge Sediment samples will be characterized to determine the potential heterogeneity of groundwater discharge in and around the area where hydrogeologic information suggests discharge should occur. To account for the likely heterogeneity of groundwater discharge, the proposed sediment porewater sampling grid is broader than the projected area of groundwater discharge from the ABP facility. Sampling transects will be laid out parallel to shore at a spacing of approximately 50 feet, with the first transect starting halfway between the Mean Sea Level and MLLW elevations. Sediment samples will be collected along four transects at 50-foot intervals, resulting in 32 proposed “coarse-grid” sediment sampling locations. Figures 1 through 3 illustrates the transect lines and sampling grid relative to groundwater data for TCE, DCE, and VC, respectively.
To incorporate further evaluations of spatial scales of sediment heterogeneity and preferential areas of groundwater discharge, the Phase 1 sampling grid will also include collection of approximately 32 “fine-grid” sediment sampling locations. While our experience in the Duwamish Waterway and other similar estuaries suggests that reducing the sediment porewater sampling grid size from 50 feet to 15 feet is not likely to improve the resolution of preferential groundwater discharge locations, we will nevertheless perform an additional statistically-based assessment to verify this condition during Phase 1 to ensure this issue is appropriately addressed. The “fine-grid” locations will be located on 15-foot centers within several randomly-located areas positioned between the MLLW line and 100 feet offshore of the MLLW line. The 15-foot grid sampling locations will be positioned in areas where groundwater would be most likely to discharge, to minimize the potential for supplemental Phase 1 sampling.
Grid Sample Locations Proposed grid sample locations are illustrated in plan view on Figures 1, 2 and 3. Actual locations may be adjusted in field based on field measurement of MLLW and local bathymetry. Actual coordinates and elevations will be recorded in the field using GPS and tidal gage records. Sampling will be conducted within two hours prior to or following the predicted low-low tide elevation to target the time of maximum expected groundwater discharge. The initial (phase one) sampling will also be performed during a period of relatively low river stage (i.e., during a period of little precipitation or snow melt) and relatively small tidal exchange (neap tide sequence) to maximize the difference between groundwater and Waterway salinity to assess spatial variability in groundwater discharge.
One sediment sample composited across the full Van Veen sample thickness will be collected per location for future sediment grain size sieve analysis. To determine the percent fines, a wet sieve analysis of each sample will be completed by Aspect. Sediment samples will be collected using a Van Veen power grab sampler, which collects sediment from the upper foot (30 cm) of the channel sediments. Most sediment sampling in the Puget Sound region is performed using a modified 0.1-m2
Van Veen grab sampler, which achieves good penetration (generally 10-20 cm in soft sediments), with minimal disturbance of the sediment surface, and accordingly is the recommended sampling equipment for collection of surface sediments (Ecology, 2008). The sediment sample is enclosed within the sampler and brought to the surface intact. Any surface water overlying the sediment will
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be removed with a siphon. A salinity probe will be inserted into the sediment to an approximate depth of 10 cm. Salinity is often used as a tracer of groundwater discharge and mixing in estuaries (Robinson et al., 1998).The salinity measurement and a physical description of each sediment sample will be recorded. A sediment sample composited across the full Van Veen sample thickness will be collected and archived for future sediment grain size sieve analysis. To determine the percent fines, a wet sieve analysis for each sample will be completed by Aspect.
The surface water salinity just above the mudline will also be recorded at each transect. After all samples are collected, the locations of the first sample collected along each transect will be resampled to determine variability in porewater salinity from the beginning to end of the sampling event. Duplicate sediment samples will also be collected at 10 percent of the sampling locations to evaluate small-scale variability in sediment composition. Field duplicate samples will be collected from a different location within the same Van Veen grab sampler, which is typical field duplicate sampling (Ecology, 2008).
Spatial Variability Analysis and Reporting The salinity data will be used to evaluate the scale of spatial variability in groundwater discharge patterns. Lower salinity in sediment porewater is anticipated in areas of higher groundwater discharge. Calculating the ratio of salinity in surface water to sediment porewater will provide an indicator of spatial variability in groundwater discharge patterns. The salinity data will be analyzed in a graphical/tabular data presentation to determine if there are discernable spatial patterns to higher rates of groundwater flow in the study area. For example, higher salinity along the western transects could indicate that the salt water wedge is directing groundwater to discharge nearer to shore. Salinity data will also be compared to grain size characterization to evaluate potential variations in groundwater discharge due to sediment heterogeneity, as less groundwater discharge is expected to occur through lower permeability sediments.
Analysis of the salinity data will also include a comparison of the “coarse-grid” and “fine-grid” data. If the salinity variance is not statistically different between the 50- and 15-foot porewater sampling grid data sets, the 50-foot spacing will be confirmed as suitable for determining focused sampling locations for the Phase 2 site characterization. However, if there are statistically significant differences (P < 0.05) in salinity variance between the 50- and 15-foot porewater sampling grid data sets, the 15-foot spacing will be used to determine Phase 2 site characterization locations. Should this occur, the need for supplemental salinity data collected at the 15-foot spacing will be evaluated, and additional porewater salinity sampling performed as necessary to complete the Phase 1 evaluation.
A memorandum summarizing the results of sediment sampling, data evaluation, and recommended Phase 2 porewater sampling locations will be prepared prior to conducting porewater sampling for VOCs.
Phase Two – Porewater Chemical Sampling The locations of the sediment porewater samples will be determined based on the Phase 1 sediment sampling results. Seeps above the MLLW elevation will not be sampled, because these would be located above the elevation where the highest concentrations of contaminated groundwater are expected to discharge. Field procedures are outlined in Attachment A and an overview of the porewater sampling and analysis program is provided below. A task-specific Quality Assurance
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Project Plan (QAPP) and Health and Safety Plan (HASP) will be adapted from the existing Work Plan (Aspect, 2008) and prepared and submitted with the memorandum presenting the sediment porewater results and the recommendations for porewater chemical sampling locations.
Due to differences in equilibration across sampler membranes, porewater samples will be collected using two methods:
Water samples for VOC analysis will be collected using polyethylene diffusion bags (PDB) and passive sampling methods. The PDB samplers are low-density polyethylene bags (LDPE) filled with deionized water. VOCs in groundwater diffuse across the bag material until concentrations inside the bag sampler reach equilibrium with concentrations in the surrounding groundwater. While PDBs are most commonly used with groundwater sampling in monitoring wells, PDBs and other similar passive sampling methods have been successfully used to sample sediment porewater in lakes, rivers, and streams (ITRC, 2006).
Rigid porous polyethylene (RPP) samplers, another type of passive sampler, will be deployed at each location for measurement of field parameters, including dissolved oxygen and salinity. The RPPs are constructed of thin sheets of foam-like porous polyethylene with pore sizes of 6 to 20 microns. When completely filled with water the pores allow a water-water interface, facilitating the equilibrium of water-soluble analytes with the deionized water of the RPP.
PDB and RPP samplers will be deployed and retrieved by a subcontracted diver or by Aspect field personnel in waders, depending on water depth at each location. The samplers will be placed at an approximate depth of 10 cm below the mudline. Coordinates and elevations of each sampler will be recorded using GPS and tide gage records. The samplers will be retrieved approximately three weeks after deployment allowing sufficient time for the water in the samplers to equilibrate with the in-situ porewater. Once retrieved, the PDB bags are opened to fill three 40-milliliter VOA vials. Samples will be submitted to Analytical Resources Incorporated of Tukwila, Washington, for analysis of chlorinated solvents by EPA Method 8260. The samples collected using the RPPs will be used to measure field parameters including dissolved oxygen, pH, temperature, and salinity.
Reporting and Schedule Pending Ecology approval and weather permitting, the first phase of sediment sampling and analysis will be conducted in February 2011. Results of the sediment heterogeneity study and the proposed porewater sample locations will be provided within 2 weeks of conducting the sediment sampling. Pending Ecology approval, porewater samplers will be deployed in March or April 2011. Data will be reported in the first quarterly progress report following completion.
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Attachments Figure 1 – Site Plan - Trichloroethene (TCE) Figure 2 – Site Plan - cis-1,2-Dichloroethene (DCE) Figure 3 – Site Plan - Vinyl Chloride (VC) Figure 4 – Cross Section F-F’ Figure 5 – Cross Section E-E’ Attachment A – Porewater Sampling Field Procedures
References Aspect, 2008, Remedial Investigation Work Plan, Revised, Art Brass Plating, September 24, 2008,
Seattle, Washington, Unpublished Work.
Booth and Herman, 1998, Duwamish Basin Groundwater Pathways Conceptual Model Report, Duwamish Industrial Area Hydrogeologic Pathways Project. Prepared for City of Seattle Office of Economic Development and King County Office of Budget and Strategic Planning. University of Washington and Hart Crowser, Seattle, WA.
Department of Ecology, 2008, Sediment Sampling and Analysis Plan Appendix (SAPA), Guidance on the Development of Sediment Sampling and Analysis Plans Meeting the Requirements of the Sediment Management Standards (Chapter 173-204 WAC). Ecology Publication No. 03-09-043, Dated February 2008.
ITRC, 2006, Technology Overview of Passive Sampler Technologies. Prepared by The Interstate Technology & Regulatory Council - Diffusion Sampler Team. Dated March 2006.
Robinson, M., D. Gallagher, and R. William, 1998, Field Observations of Tidal Seasonal Variations in Ground Water Discharge to Tidal Estuarine Surface Water. Published in Ground Water Monitoring and Remediation, Winter 1998, pages 83-92.
Limitations Work for this project was performed and this memorandum prepared in accordance with generally accepted professional practices for the nature and conditions of work completed in the same or similar localities, at the time the work was performed. It is intended for the exclusive use of Art Brass Plating for specific application to the referenced property. This memorandum does not represent a legal opinion. No other warranty, expressed or implied, is made.
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Shallow GroundwaterInterval 3.51 µg/LTCE Isoconcentration Line
Intermediate GroundwaterInterval 3.51 µg/L
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Hypothesis-Areaof Potential Plume
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PorewaterSampling
Grid
Transect #1 will behalfway betweenmean lower lowwater and meansea level
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MW-17-40 (150J)
AB-CG-140-70 (0.2UJ)
PSC-CG-138-40 (0.2U)
PSC-CG-140-30 (0.2U)PSC-CG-140-40 (0.2U)
PSC-CG-141-50 (0.2U)
PSC-CG-142-40 (0.2U)AB-CG-142-70 (0.2U)
PSC-CG-151-25 (3J)
MW-21-75 (0.2UJ)
MW-23-30 (0.2UJ)MW-23-50 (0.2UJ)
MW-16-40 (160J)MW-16-75 (6.7J)
MW-17-60 (110J)
MW-18-50 (0.2U)MW-18-70 (0.2U)
MW-19-60 (0.2U)
MW-21-50 (1.4J)
MW-22-50 (0.2J)
MW-24-50 (0.8J)
MW-11-30 (32J)
MW-22-30 (67J)
MW-24-30 (86J)
MW-8-70 (0.2U)
SPO-42 (0.2U)
MW-19-40 (20)
SPO-11 (340)SPO-13 (130)
SPO-17 (180)
SPO-18 (580)
SPO-19 (110)
SPO-41 (180)
SPO-44 (0.6)
SPO-10 (1U)
SPO-14 (93)
SPO-15 (27)
SPO-16 (23)
SPO-20 (36)
SPO-3 (3.6)
SPO-39 (31)
SPO-40 (61)
SPO-45 (49)
SPO-12 (4)
SPO-2 (42)
W4-2 (390)
AS-1 (2.5)
W4-1 (1U)
AS-2 (15)PSC-CG-138-70 (0.2U)
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Site Map with cis-1,2-Dichloroethene (DCE)Occurrence in Groundwater
Art Brass PlatingSeattle, Washington
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Tidally-influenced Half-foot Shallow IntervalGroundwater Elevation Contours from72-hour study period 6/4 - 6/6/10(NAVD88 Vertical Datum)
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Tidally-influenced Half-foot Shallow IntervalGroundwater Elevation Contours from72-hour study period 5/27 - 5/29/10(NAVD88 Vertical Datum)
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*NOTE: site conversion MLLW to NAVD88 is MLLW elev. + 2.87 ft = NAVD88 elev.
DCE in Groundwater at Well andProbe Sample Locations:
SampleLocation ID
Last measured DCE concentration at well locationor max DCE concentration at probe location in theshallow or intermediate interval (in µg/L)
Vinyl Chloride in Groundwater at Well andProbe Sample Locations:
SampleLocation ID
Last measured vinyl chloride concentration at welllocation or max vinyl chloride concentration at probelocation in the shallow or intermediate interval (in µg/L)
Detected Above Cleanup Level!.Detected, No Exceedance!.Not Detected (Detection Limit > Cleanup Level)!.Not Detected, No Exceedance!.
1 Sediment and Porewater Sampling Methods The field methods for sampling sediment and sediment porewater are described in this attachment. Field activities will be performed under the direction of Aspect Consulting (Aspect). Scuba diving assistance for placement and retrieval of the samplers will be performed by Research Support Services, Inc.
1.1 Location Positioning Sampling locations will be field-located using a Global Positioning Unit (GPS) unit with a horizontal accuracy of within 1 meter. Washington State Plane Coordinate System North coordinates in North American Datum 1983 (NAD83) will be used for the horizontal datum.
1.2 Sediment Sample Collection Once the sample location and mudline elevation have been confirmed sediment samples will be collected using a Van Veen power grab sampler. The relative advantages and disadvantages of different sediment sampling equipment are discussed in Ecology’s Sediment Sampling and Analysis Plan Appendix (SAPA): Guidance on the Development of Sediment Sampling and Analysis Plans Meeting the Requirements of the Sediment Management Standards (Chapter 173-204 WAC), Ecology Publication No. 03-09-043. As discussed in the SAPA, most sediment sampling in the Puget Sound region is performed using a modified 0.1-m2 Van Veen grab sampler, which achieves good penetration (generally 10–20 cm in soft sediments), with minimal disturbance of the sediment surface, and accordingly is the recommended sampling equipment for collection of surface sediments. Subject to availability, the hydraulically operated “Power Van Veen” owned and operated by Marine Sampling Systems (MSS) will be used for this sediment sampling effort to further ensure good penetration, given successful performance of the MSS sampler in other areas of the Duwamish Waterway.
The Van Veen sampler collects sediment from the upper foot (30 cm) of the channel sediments. The sediment sample is enclosed within the sampler and brought intact to the surface. Surface water overlying the sediment in the sampler will be removed using a siphon. After opening the sampler, a salinity probe will be inserted into the sediment to an approximate depth of 10 cm. The salinity measurement and a physical description of each sediment sample will be recorded. The SAPA discusses that interstitial salinity measurements are commonly performed on sediment samples collected using a modified 0.1-m2 Van Veen grab sampler.
A sediment sample composited across the full sample thickness will be collected, placed in a 12-ounce plastic jar, and stored for future sediment grain size sieve analysis. Sediment samples will be brought back to Aspect’s office for detailed sediment description and wet sieve grain size analysis to determine the percent fines.
A-2 PROJECT NO. 050067-005C NOVEMEBER 24, 2010
The surface water salinity just above the mudline will also be recorded at each transect. After all samples are collected, the locations of the first sample collected along each transect will be resampled to determine variability in porewater salinity from the beginning to end of the sampling event. Duplicate sediment samples will also be collected at 10 percent of the sampling locations to evaluate small-scale variability in sediment composition. Field duplicate samples will be collected from a different location within the same Van Veen grab sampler, which is typical field duplicate sampling (Ecology, 2008).
1.3 Porewater Sample Collection Porewater samples for analysis of volatile organic compounds (VOCs) will be collected using polyethylene diffusion bags (PDB) and passive sampling methods. The PDB samplers are low-density polyethylene bags (LDPE) filled by the laboratory with deionized water. VOCs in groundwater or sediment porewater diffuse across the bag material until concentrations inside the bag sampler reach equilibrium with concentrations in the surrounding groundwater. This method of sampling for VOCs in groundwater was developed by Don Vroblesky with the US Geological Survey (USGS, 2001). The PDB samplers have been proven to be effective for sampling several volatile organic compounds including trichloroethene and its degradation products cis-1,2-dichloroethene and vinyl chloride (USGS, 2001). While PDBs are most commonly used with groundwater sampling in monitoring wells, PDBs and other similar passive sampling methods have been successfully used to sample sediment porewater in lakes, rivers, and streams (ITRC, 2006).
A rigid porous polyethylene (RPP) sampler, another type of passive sampler, will also be deployed at each location. Porewater collected from these samplers will be used for measurement of field parameters. The RPPs are constructed of thin sheets of foam-like porous polyethylene with pore sizes of 6-20 microns. When completely filled with water the pores allow a water-water interface, facilitating the equilibrium of water-soluble analytes with the deionized water of the RPP.
The PDB and RPP samplers will be prepared by CAS laboratory. CAS will pre-fill each sampler with deionized water. Both ends of the PDB samplers are heat sealed after filling. The PDBs samplers will consist of a one-foot-long bag with a volume of approximately 110 milliliters (mL). The bag will be placed in a protective mesh that will be provided by CAS. The RPPs are approximately 6" long and hold approximately 100 mL.
Once the sample location has been determined using GPS coordinates, the diver will deploy two PDB samplers (providing a total sample volume of about 220 mL) and 1 RPP sampler at each location. The diver will gently push a length of plexiglass into the sediment to create a wedge into the sediment into which the PDB sampler can be placed at a depth of 10 cm. The plexiglass will then be removed allowing the displaced sediment to cover the sampler. Three adjacent wedges will be created at each sample location, one for the RPP sampler and two for the PDB samplers. If the sediment is too coarse to push in the board, the sampler will be deployed by digging a small trench with a hand tool and then covering the sampler with sediment. The locations will be marked with flagging so that they can be located for retrieval. Samplers will be placed horizontally in the sediment
ASPECT CONSULTING
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with the two wedges placed side-by-side. The samplers will be aligned parallel to surface water flow direction. Depth of water and time will be noted on the sampling forms for each location. Then actual sample mudline elevations will be accurately determined using available tide gage data.
The samplers will be retrieved approximately 3 weeks after deployment. The diver will retrieve the samplers and bring them to the surface for Aspect field personnel to process. Once in the boat, Aspect personnel will examine the samplers for tears and coatings (e.g., algal or iron). If any tears are observed on the bag, the sample will be rejected and not submitted to the laboratory. Coatings will be noted on the field form for reference when results are obtained from the laboratory. A coating may inhibit equilibration with the surrounding porewater.
The PDBs are designed to transfer the sample water to VOAs with minimal disturbance. Samplers will be processed by two field personnel. A small corner of the sampler, approximately 1/8 of an inch, is cut at one end of the sampler with a pair of decontaminated scissors. Then the water will be slowly poured into three VOA vials provided by ARI laboratory. The vials will be held at an angle by one person while the second person slowly pours the sample into the vials to minimize aeration. Once filled and capped, the vials should have no headspace (i.e., no visible air bubbles).
Porewater from the RPPs will be transferred to a cup for analysis of field parameters, including dissolved oxygen, pH, temperature, and salinity. The transfer will be completed to minimize the introduction of oxygen to the sample.
1.4 Sample Identification Sample labels will be filled out using indelible ink to indicate the sample number, date, preservative added, if any, and any pertinent comments. Porewater and sediment sample naming convention will be the sample identification location followed by the sample collection date (i.e., MMDDYY). For example, a porewater sample collected on December 1, 2010 from sample location PW01 would have the following name: PW01-120110. The sediment sample prefix will be SD, such that sediment sample identifications will start at SD01.
2 Sample Handling and Custody
2.1 Sample Handling Upon collection, porewater samples will be placed upright in a cooler. Ice will be placed in each cooler to meet sample preservation requirements. Inert cushioning material will be placed in the remaining space of the cooler to limit movement of the sample containers. Samples will be delivered directly to the analytical laboratory.
Upon sample receipt, the laboratory will fill out a cooler receipt form to document sample delivery conditions. A designated sample custodian will accept custody of the
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shipped samples and will verify that the chain of custody form matches the samples received. The laboratory will notify as soon as possible the Aspect project manager of any issues noted with the sample shipment or custody.
2.2 Sample Custody After collection, samples will be maintained in the Aspect’s custody until formally transferred to the analytical laboratory. For purposes of this work, custody of the samples will be defined as follows:
In plain view of the field representatives;
Inside a cooler that is in plain view of the field representative; or
Inside any locked space such as a cooler, locker, car, or truck to which the field representative has the only immediately available key(s).
A chain of custody record provided by the laboratory will be initiated at the time of sampling for all samples collected. The record will be signed by the field representative and others who subsequently take custody of the sample. Couriers or other professional shipping representatives are not required to sign the chain of custody form; however, shipping receipts will be collected and maintained as a part of custody documentation in project files. A copy of the chain of custody form with appropriate signatures will be kept by Aspect’s project manager.
2.3 Decontamination and Investigative-Derived Waste All non-disposable sampling equipment will be decontaminated before collection of each sample. The decontamination sequence consists of a scrub with a detergent (Alconox) solution, followed by tap water (potable) rinse, and finished with thorough spraying with deionized or distilled water.
Decontamination water will be containerized and then secured at the Art Brass Plating facility for profiling and proper off-site disposition.
