Site Characterization Technologies for DNAPL Investigations

Transcription

1 Site Characterization Technologies for DNAPL Investigations ACEC Meeting December 8, 2004 Linda Fiedler Environmental Engineer Technology Information and Field Services Division Office of Superfund Remediation and Technology Innovation US Environmental Protection Agency

2 Site Characterization Technologies for DNAPL Investigations Published Sept Summarizes challenge of finding/delineating DNAPL in subsurface Gives inventory of technology toolbox currently available to characterize DNAPL For each, Includes description, uses, drawbacks, and short case studies cluin.org 11/18/04 2

3 Geophysical Techniques Used to survey large areas or describe small-scale conditions, such as those in and around borehole walls Measure physical properties of subsurface materials Changes in measurements may indicate changes in subsurface matrix (e.g., stratigraphy that locates preferential pathways for DNAPL migration) Report categories include: Borehole methods Electrical methods Electromagnetic methods Ground penetrating radar, Magnetics Seismic 11/18/04 3

4 NonGeophysical Techniques Other techniques shown to have some success in characterizing DNAPL sources and gaining access to subsurface strata where DNAPLs may be found Report categories include: Diffusion sampling Direct push technology equipped with tools to take depth-discrete samples/measurements along vertical axis (e.g., conductivity probe, induced fluorescence, membrane interface probe) In situ groundwater sampling (depth-discrete) Hydrophobic dyes (e.g., Sudan IV dye) DNAPL partitioning tests (e.g, PITT) Soil gas profiling 11/18/04 4

5 Report Conclusions Growing range of field-based tools to locate and characterize DNAPLs in wide variety (but not all) settings Some methods take direct chemical measurements, others measure physical site characteristics In many cases DNAPLs can be found by using correct mix of tools for site-specific conditions (i.e., line-of- evidence approach) Effective application of field methods requires systematic planning and dynamic workplanning (i.e., the 3 legs of Triad approach) to allow infield refinement of site conceptual model 11/18/04 5

6 VINT HILL FARMS STATION, VIRGINIA DNAPL Site Characterization Utilizing Membrane Interface Probe (MIP) and Direct Sampling Ion Trap Mass Spectroscopy

7 Background Elevated PCE/TCE levels detected in latter stages of property transfer at closed Vint Hill Farms Army installation 7

8 Preliminary CSM From Systematic Planning Outline Volatile organic compound (VOC) contamination in saturated overburden acre area Overburden GW flows NW (<0.4 ft/year) VOC contamination is sporadic, apparently resulting from one or more small spills of solvent Fractured bedrock aquifer also contaminated with VOCs Production well located 400 ft downgradient of bedrock aquifer contamination has not been impacted 8

9 Tool Box Including Real-Time Measurement Systems Membrane Interface Probe Soil Sampling Electron Capture Detector (ECD) Photoionization Detector (PID) Trapping of gas stream for speciation Passive Diffusion Bags (PDBs) - GW Temporary wells (1-inch inner diameter) Soil samples from Geoprobe borings On-site field laboratory DSITMS (MIP gas stream, groundwater, soil) 9

10 Principles of MIP Operation Heated probe Semi-permeable membrane Contaminant vapors partition into a carrier gas Transported to FID, PID, & ECD detectors at the surface Results are displayed in real- time on a lap-top computer. 10

11 Advancement of MIP Using Geoprobe Rig 11

12 Passive Diffusion Bag Sample Collection Chemicals diffuse from high to low concentration until equilibrium is reached Multiple PDBs within well screen determine vertical stratification 12

13 Dynamic Work Plan Allowed project to adapt in real time (while crew still in the field) to new information as it became available Provided framework for preliminary Conceptual Site Model (CSM) to be tested and modified in the field 13

14 Data Management and Communication During Systematic Project Planning and Dynamic Work Plan Development: Frequent teleconferences On-site pre-mobilization meeting to finalize the Dynamic Work Plan During One-Week Dynamic Field Effort: Rapid dissemination of field data using project website (with 3-D data visualization) data posted nightly 14

15 Sampling Conducted During Triad Investigation (November 2003) 15

16 Sample MIP Log MW34-4(2)-MIP 16

17 AREE 34 MIP ECD Responses 17

18 DSITMS Temporary Well Analytical Results Triad Investigation (November 2003) 18

19 Depth ( fee t) Depth ( feet ) DSITMS Soil Results vs. MIP ECD Response at H14 DSITMS Soil Results Total VOCs (µ g/kg)* H14-MIP ECD Log Response (µv) *Assumes non-detected compounds at 0 µ g/kg 19

20 Selected Findings of Triad Investigation No source of greater VOC contamination upgradient of MW34-4 Extent of the highest VOC contamination appears to be very limited and occurs within the finer grained soils (7.5 to 13 ft bgs) MIP ECD sufficiently sensitive to identify contaminated and clean areas 20

21 Triad Investigation Objectives Achieved CSM confirmed with high degree of confidence - two or more small sources of contamination over a 0.5 acre area Triad approach allowed rapid completion of site characterization activities that had been ongoing for several years 21

22 IW RS A Site Characterization for Chlorinated NAPL Remediation East Gate Disposal Yard Fort Lewis Washington I would like to recognize the people who helped make this NAPL characterization effort successful. Public works at Fort Lewis Rich Wilson the installation Project Manager Corps Team (Kira Lynch, Bill Goss, and Jeff Powers). Contractors: URS, GSA, TEG, Cascade Drilling/Boart-Longyear.

23 Received Logistics Center wastes from s. Cleaning and degreasing solvents and POLs. Di sposed in trenches in drums, free liquid or burned. EGDY History 23 The Logistics Center began operations in 1941 as the Quartermaster Motor Base and was later renamed the Logistics Center. The primary mission of the Logistics Center has been vehicle maintenance throughout its operational history. TCE was used as the degreasing agent of choice up until the 1970 s. Mixed solvent/petroleum hydrocarbon, oil and lubricant waste were generated. These wastes were reportedly transferred to the EGDY in drums and buried in the trenches. Drums may have been crushed during the operations or left intact. It was also reported that liquid wastes were poured directly into trenches and used to burn woody debris. Liquids may also have been poured directly into open trenches and subsequently buried.

24 Conceptual Site Model Primary COC waste degreasing agent, mineral spirits, and waste oil TCE, Cis-1,2-DCE, TCA, PCE, TPH GW at approximately 10 feet bgs Complex hydrogeology NAPL varies in density and is found as LNAPL and DNAPL DNAPL confirmed to 55 feet bgs 24

25 Aerial Photo Analysis Results Feet An analysis of aerial photographs of the site from the early 1940 s through the 1980 s was performed to determine the locations of trenches and pits used for disposal. Both open trenches and linear scars were used to identify disposal locations. The red shapes in this figure represent the approximate extent of trenches or pits identified from aerial photos. The analysis of the aerial photos was used to defined boundaries of the investigation. Because it was difficult to distinguish some trench scars from vehicle tracks and because portions of the area were sometimes regraded between photo events, an area somewhat larger than the area containing only trenches was included within the investigation boundary. This boundary set the limits of the area requiring a geophysical survey.

26 EM-61 Survey Results Feet An electro-magnetic survey was performed within the investigation boundary to locate trenches with metallic debris. The EM-61 method generates rapid EM pulses into the subsurface to measure the prolonged response from metallic objects versus shorter natural response. A closely spaced 2.5 x 5 foot grid over a the 35 acre area produced excellent results that clearly revealed narrow linear features. The location of metallic debris matches closely with the locations of trenches identified from aerial photographs. However, the EM survey revealed metallic debris in some areas that were missed in the aerial photo analysis due to lack of aerial photos when these features were visible. The combined aerial photography and EM-61 survey results were used to guide the initial sampling locations of the soil gas, trenching and groundwater methods.

27 Soil Gas Sampling Feet Soil gas samples were collected to try to determine the approximate location of NAPL sources in the vadose zone. 45 locations were sampled from a depth of 5 feet. Results were mixed. Some high VOC results, but most were uniformly low. Method only seemed to work if sample collected right at an area later confirmed to have NAPL. Area was too large to cost effectively blanket all suspected trenches with soil gas sampling locations so this method was discontinued. Results of soil gas sampling were used to direct the locations of some of the exploratory trenches.

28 Exploratory Trenching Results Feet Trenching results were added to the growing CSM. Groundwater drive point locations based upon trench, aerial and geophysical results.

29 Drive Point Groundwater Results Feet Three major hotspots identified where TCE containing NAPL likely present based upon greater than 10,000 ug/l in groundwater detected. A fourth area of less contaminated groundwater, but above 1,000 ug/l also encountered where NAPL likely present in lesser amounts than the other three areas. The three major NAPL areas were selected as areas where NAPL remediation efforts should be focused. Mention groundwater flow direction.

30 Drum Removal Results Feet Superimpose drum locations on NAPL evidence map. Locations of drums containing NAPL were plotted. Circles represent locations where one or more NAPL containing drums were located. This combined lines of evidence map was used as the basis for the planning of the Phase II investigation. The Phase II investigation was designed to fill data gaps associated with the EE/CA proposed remedies for the source area. Detailed logging of vadose zone NAPL.

31 MIP Results Feet NAPL was identified at the locations with solid triangles. Open triangles indicate no NAPL present based upon MIP results. Sonic cores were required to fill in the horizontal and vertical data gaps left from the MIP. The locations of sonic borings were used to compliment, not replace the MIP data.

32 Sonic Drilling Results Feet Sonic boring quantity, locations and depths were determined in the field. Sonic gave excellent NAPL ID results.

33 Selection of Treatment Volumes Feet Combined lines of evidence used to select the NAPL thermal treatment volumes. Sonic and MIP used primarily to determine limits of three main NAPL areas for thermal treatment, but extent of trenches containing drums and evidence of possible liquid waste disposal in NAPL area 2 from historical aerial photographic analyses also considered.

34 EGDY NAPL TREATMENT AREAS 34

35 Lessons Learned Toolbox Approach needed at this stage of tool development Treatment area could potentially have been refined if flux assessment had been conducted prior to definition of treatment areas 35

36 Characterizing Down Volume to Be Treated Solvents Recovery Services of New England (SRSNE) NPL site - Large site w/ as much as 1M gallons of solvent/phc contamination Initial (early 90 s) situation - lack of effective remedies and estimates of 400,000 cubic yards led discussions in direction of Technical Impracticability (TI) waiver Recent Developments - Advent of effective source removal/reduction options (e.g., in situ thermal) led to further site characterization New borings combined w/ existing data resulted in downward volumetric revision to 42,000 cubic yards 36

37 Conceptual Site Model Evolves Through Remedy Implementation S California wood treater Alhambra, Ca Initial site characterization on 100 centers In Situ Thermal remedy heater wells installed on 5-7 centers i.e., x20> spatial resolution Wells installed 2 below estimated bottom of contamination found additional contamination Treatment volume adjusted to reflect new data 37