Designing an ISCO Remedy for a Wood Treating Site Using Hydrogeologic Testing, High-Resolution Site Characterization, and 3D Modeling

Transcription

1 Designing an ISCO Remedy for a Wood Treating Site Using Hydrogeologic Testing, High-Resolution Site Characterization, and 3D Modeling Joseph Ivanowski, P.G. Shanna Thompson, P.E.

2 Presentation Outline Site Background Treatability Testing High-Resolution Site Characterization Aquifer Testing 3-D Visualization Remedial Design (ISCO) Results and Path Forward 2

3 Site Background 3 Former creosote and PCP use for wood treating Primary COCs in groundwater are PCP and naphthalene Operations from Creosote Pentachlorophenol (PCP) City drinking water supply well located 1,000 ft away Remedial Design Barrier wall installation was performed by others Geosyntec performed groundwater treatment outside barrier wall

4 Site Background: 1970s Operations Black & Veatch 2010 Basis of Design Report 4

5 Site Background: Geology Dissolution features Sinkholes 5

6 Treatability Testing ISCO and ISEB treatability testing completed in May 2012 ISCO evaluate permanganate and persulfate (matrix, alkaline, and iron activation) ISEB evaluate aerobic and anaerobic (nitrate and lactate amended) conditions Permanganate PCP Reduction = 96% Naphthalene = 85% Reduction Persulfate PCP Reduction = 99% Naphthalene = 97% Reduction 6

7 Treatability Testing: ISCO Oxidant demand for permanganate was ~ 2 g/kg Recommended potassium permanganate: Longer persistence in subsurface Easier to measure in the field (look for purple color) No activation chemistry required 7

8 8 Treatability Testing: ISEB

9 Treatability Testing ISEB PCP No degradation after 83 days ~65% reduction after bioaugmentation with KB-1 Plus Naphthalene Aerobic degradation was most rapid and greatest reduction (280 ug/l to < 12 ug/l) Nitrate-amended showed some degradation (285 ug/l to 57 ug/l) Lactate-amended showed limited degradation (355 ug/l to 330 ug/l) Conclusion: ISCO performed better than ISEB (particularly with PCP) 9

10 High-Resolution Site Characterization Iso-Flow drilling and sampling performed to collect depth discrete bedrock groundwater data On-site mobile lab for quick TAT and data evaluation Data used to generate cross-sections and 3D model

11 11 High-Resolution Site Characterization

12 Aquifer Testing: Objectives 1. Estimate the hydraulic conductivity (K), storage (S) of the bedrock aquifer and evaluate potential anisotropy; 2. Evaluate preferential groundwater flowpaths; 3. Evaluate ROI to support injection/extraction well spacing; 4. Aid in well design; and 5. Evaluate injectate travel time to support ISCO remedy. 12

13 Aquifer Testing: Approach Pneumatic slug testing Preliminary testing of extraction well and pumping system Step drawdown test Evaluate drawdown and yield Tested four discharge rates (10, 15, 20, 25 gpm) for selecting rate for long-term test Constant rate/dye tracer test Evaluate T, S, hydraulic ROI, tracer travel time, porosity Potentially gain insight on mass recovery 13

14 Aquifer Testing: Layout One extraction well (80-95 ft bgs) 13 observation wells Two injection wells 15 ft and 25 ft distance ft bgs 14

15 Aquifer Testing: Layout Extraction and sampling system layout Sample Port Totalizer Carbon Filter Extraction Well Digital Flowmeter 15

16 Slug Test Results Bouwer-Rice Butler (1998) method for high k aquifers Well Screen Interval K (ft/day) (ft bgs) EW EW MW-30D MW-35D MW-36D 01 MW-26A MW-30D MW-31I MW-35D MW-36D Mean 100 Geometric Mean 52 16

17 Step Drawdown Results 0 Step 1 = 10 gpm 5 Step 2 = 15 gpm 10 Step 3 = 20 gpm Drawdown (ft) Step 4 = 25 gpm Step Drawdown Data Pump Intake Elapsed Time (min) Pumping conducted in 90 minute steps Evidence for well inefficiency Selected 20 gpm for constant rate pumping for 72 hrs

18 Constant Rate Test Results Time Elapsed (min) MW36D (80 95 ft bgs) MW30D ( ft bgs) MW26A (64 69 ft bgs) MW35D (80 95 ft bgs) 47.5 CMW01I ( ft bgs) Depth to Water (ft) Well MW31I (87 97 ft bgs) Pump Off Distance to EW01 (ft) MW36D 25 MW30D 40 MW26A 45 MW35D 15 CMW01I 47 MW31I 43 18

19 Constant Rate Test: Analytical Methods Time-drawdown plots per MW (Leaky solution, Hantush-Jacob) Best curve matches among solutions evaluated Ks are higher to account for leakage from overlying residuum Drawdown (in) r 0 = 595 ds = Distance (in) Distance drawdown (Jacob) Match drawdown with straight line at selected elapsed time Meets steady-state time requirements Areal averages K, S

20 Aquifer Testing: Results Hydraulic Conductivity (ft/d) by Well and Method Well Pumping Test Drawdown (ft) Slug Tests -- Confined Aquifer (Bouwer-Rice/Butler Methods) Constant Rate -- Leaky Confined Aquifer (Hantush-Jacob Method) EW * MW35D * Constant Rate -- Confined Aquifer (Distance Drawdown Method All locations) A 23* MW36D * Average Hydraulic Conductivity Constant Rate Values* (ft/d) Geometric Mean 50 * Used to calculate geometric mean since slug test stress is limited to radius of well. A average of analyses using pumping data and recovery data 20

21 Dye Tracer Test Can we achieve a measurable ROI? What is the actual travel time of the tracer (oxidant)? Would the tracer be recoverable? Lost? Turner Designs AquaFluor field fluorometer

22 Dye Tracer Test Injected two dye tracers Fluorescein MW-35D Rhodamine MW-36D Rhodamine injection at MW-36D Fluorescein injection at MW-35D

23 Dye Tracer Test Results Fluorescein (ppb) Rhodamine (ppb) Fluorescein (ppb = ug/l) Rhodamine (ppb = ug/l) Time (min) Dye Distance Time to Break Through Break Through Velocity Time to Peak Dye Peak Velocity Fluorescein 15 ft hrs ft/day hrs 7.90 ft/day Rhodamine 25 ft hrs ft/day hrs ft/day 23

24 Aquifer Testing: Objectives Met 1. Aquifer Parameters a. Range of K = 32 to 350 ft/d b. Mean K = 117 ft/d; Geometric Mean K = 79 ft/d 2. Preferential Flow Paths Identified a. MW36D high K = 350 ft/d, and low concentration of Rhodamine dye 3. Travel Time a. Break Through Velocity of 34 to 36 ft/d b. Peak velocity of 8 to 14 ft/d 4. Radius of Influence (ROI) a. Maximum = 50 ft (20 gpm); <1 inch drawdown at distance b. Effectively 25 ft

25 ISCO Design: 3D Model Environmental Visualization System (EVS Pro) used to generate plume model and geometry PCP > 100 ug/l PCP > 500 ug/l PCP > 1,000 ug/l 25

26 ISCO Design: 3D Model Well depth targeted using 3D model to guide placement Min. inj. depth 65 bgs Max. inj. depth 110 bgs Max. treatment thickness 55 ft. Clustered Wells Maximum 15 ft screen interval Possible vertical separation of 5 to 10 feet 26

27 ISCO Design: Well Network Clustered wells on 17 nodes that fall on 40-foot grid spacing One 4 diameter well in the apparent source zone to use as extraction well Two additional 2 diameter injection wells along building edge Proposed Injection Well Cluster Proposed 4 Well, use TBD after initial 9-mths of operation Additional Injection Well for better distribution under building 27

28 ISCO Injection Initial injection completed in Fall week field event 188,363 gallons of 4% KMnO 4 solution mixed onsite and injected Geosyntec self-performed the entire injection event 28

29 ISCO Injection Injection pressures generally less than 10 psi Flow rates generally 6 to 8 gpm Target volumes were delivered successfully to each interval 29

30 ISCO Performance Plume footprint reduced Plume volume significantly reduced Pre-Injection Baseline Three Months After Injection Estimated Plume Reduction Volume 29,000 CY 17,000 CY 42 % plume volume reduction in three months Mass 28.1 lb PCP 11.8 lb PCP 58% PCP mass reduction in three months 30

31 ISCO Path Forward Path Forward Additional injection event planned for Fall 2015 Event 2 will include extraction and re-injection to enhance oxidant distribution (existing KMnO 4 in aquifer) Additional oxidant will be injected into target areas with persistent PCP concentrations 31

32 ISCO Path Forward Targeted injection where PCP exceeds 500 ug/l Use extraction from EWs and IWs and reinjection to enhance distribution 32

33 Lessons Learned Take home message? Large-scale remedies are expensive Better conceptual site model allows for more focused and targeted remediation with less uncertainty Spend a little more up front, save a lot of your client s money! 33

34 34 Questions?