A Cost-Effective and Practical Remedial Alternative Paul R. Lear, - PowerPoint PPT Presentation

In-situ Stabilization at MGP Sites – A Cost-Effective and Practical Remedial Alternative Paul R. Lear, Ph.D.

Manufactured Gas Plants • Starting in late 1900s, gas was “manufactured” by heating coal in specialized oven • Common in many urban areas of the US • Manufactured gas was used for residential and street lighting and cooking • An unintended consequence was the release of byproducts including coal tar November 14, 2012 2

Technology Description • “In situ Stabilization/Solidification (ISS) is the mixing of impacted soils with reagents (such as Portland cement and/or slag) to reduce the leachability of contaminants while decreasing the permeability of the stabilized materials. ” • ISS can be applied using “auger - based” and “excavator - based” approaches. • “Auger - based” ISS has been practiced for many years, primarily in the geotechnical and deep foundations arenas. • “Excavator - based” ISS has been practiced for many years, primarily at waste impoundments and sites with subsurface obstructions November 14, 2012 3 3

Technology Description • To date, approximately 75 MGP sites have been remediated via ISS • Some locally completed WRScompass ISS projects at former MGP sites include: • CHGE MGP Site (Auger-Based) – Poughkeepsie, NY • DelDOT/Jutison Landing Redevelopment (Excavator- based) – Wilmington, DE • NYSEG MGP Site (Auger-based) - Norwich, NY • Camden MGP Site (Excavator-based) – Camden, NJ November 14, 2012 4 4

Typical ISS Criteria for MGP Sites Parameter Value UCS > 50 psi < 10 -6 cm/sec Permeability UTS or Risk-based Leachability Leaching Criterion Free Liquids No free liquids November 14, 2012 5 5

Typical “ISS - Auger” Equipment Crane- Mounted Turn Table or Top Drive Reagent Drill Rig Batch Plant 4-foot to 12-foot Diameter Auger November 14, 2012 6 6

Completed ISS Columns Solidified Columns from Pilot Test November 14, 2012 7 7

Auger vs Excavator? • Auger-based ISS when: • Treatment depths below 20 feet (can go to 90 ft bgs) • Little to no subsurface obstructions • Lithologies with blow counts below 40 • Vapor capture and containment required • Slurry application of reagents required • Treatment volumes exceeding 15,000 cy November 14, 2012 8 8

Auger vs Excavator? • Excavator-based ISS when: • Treatment depths less than 25 feet • Subsurface obstructions • Lithologies with greater than 30 blow counts • Vapor suppression allowed • Dry addition of reagent required • Treatment volumes less than 10,000 cy (can do more) November 14, 2012 9 9

The “Ideal” ISS Site • No overhead restrictions • Pre-excavation of underground obstructions • Readily available water source (125 gpm) • Relatively flat ground surface • Sufficient lay down area for batch plant near work area (50’ x 50’) November 14, 2012 10 10

Leaching Criteria for ISS at MGP Sites • No regulatory criteria typically available contaminants – PAHs (especially naphthalene and methylnaphthalene) – BTEX • Default are typically Groundwater Quality Standards November 14, 2012 11

Leaching Criteria for ISS at MGP Sites – Alternative Approach • Utilize Existing Risk-based Approach to Site Remediation • Use Leachate Criterion instead of the GWQS as the leachate criteria for ISS below the Water Table – Still protection of human health or the environment – Will allow ISS to be considered for a wider range of sites November 14, 2012 12

Health-Based Leachate Criterion • Methodologies for risk-based cleanup standard development allow the use of a Health-Based Leachate Criterion when determining Impact to Groundwater Remediation Standards • Represents how much of a contaminant the soil can leach and still be protective of human health and the environment November 14, 2012 13

Leachate Criterion Calculation • Site – Specific Leachate Criterion – The higher of the health-based Groundwater Quality Criterion times site-specific dilution attenuation factor or the aqueous PQL • Default Leachate Criterion – Higher of the health-based Groundwater Quality Criterion times a default dilution attenuation factor of 13 or aqueous PQL November 14, 2012 14

ISS Leaching Criterion • Can be similar to health-based Leachate Criterion – Represent how much of a contaminant the ISS treated material can leach to groundwater and still be protective of human health and the environment – Recognize that the TCLP and SPLP leachates have higher TDS and ionic strength than groundwater typically does (higher PQLs) November 14, 2012 15

Suggested ISS Leaching Criterion • Example using default DAF for metals Contaminant Health Based Aqueous Suggested Contaminant Health Based Aqueous Suggested GW Quality PQL Leaching GW Quality PQL Leaching Criterion (µg/L) Criterion Criterion (µg/L) Criterion (µg/L) (µg/L) (µg/L) (µg/L) 43 A Aluminum 200 30 Lead 5 5 65 Antimony 6 3 78 Manganese 50 0.4 650 9 B Arsenic 0.02 3 Mercury 2 0.05 26 Barium 6,000 200 78,000 Molybdenum 40 2 520 Beryllium 1 1 13 Nickel 100 4 1,300 Cadmium 4 0.5 52 Selenium 40 4 520 Chromium 70 1 910 Silver 40 1 520 6 B Cobalt 100 0.5 1,300 Thallium 0.5 2 Copper 1,300 4 16,900 Vanadium 60 1 780 Iron 300 20 3,900 Zinc 2,00 10 2,600 A Adjusted so as to not exceed solubility B Adjusted to 3x Aqueous PQL November 14, 2012 16

ISS Leaching Criterion Rationale • Consistent with the existing use of Leaching Criterion for calculating site-specific Impact to Groundwater Remediation Standards • Recognizes that TCLP and SPLP leachates are chemically different than groundwater • Protective of human health and the environment November 14, 2012 17

ISS Leaching Criterion Rationale • Can be determined for most contaminants using a existing, well-developed regulatory framework • Can be easily implemented • Can be consistently applied from site to site November 14, 2012 18

Camden MGP Site • 1 st ISS at an MGP site in New Jersey • New electrical substation needed to support redevelopment of Camden’s waterfront – Site MGP impacts needed to be addressed first • Site contained last gasholder in New Jersey November 14, 2012 19 19

Camden MGP Site • Excavation and Off-Site T&D of material to 12 feet bgs – Depth necessary to accommodate new substation • ISS of material from 12 to 30 feet bgs (24,000 cy) – Leachability to Risk-Based Leaching Criterion – Permeability ≤ 1x10 -6 cm/sec (ASTM D5084) – Unconfined compressive strength (UCS) of 50 psi (ASTM D1633) • Backfill to grade November 14, 2012 20 20

Camden MGP Site • Excavator-based ISS selected – Treatment depth of 18 feet – Presence of cobble layers (>50 blow counts) • Batch plant to slurry reagents and pump slurry to ISS equipment • Operated 6 days per week, 10 hours per day for 2 months during winter • Average production rate of 800 cy/day November 14, 2012 21 21

Camden MGP Site • All samples passed for leachability, permeability, and UCS • Remedial work did not impact substation construction schedule November 14, 2012 22 22

Camden MGP Site • All samples passed for leachability, permeability, and UCS • Remedial work did not impact substation construction – Treatment took place during winter months • No lost-time safety incidents November 14, 2012 23 23

NYSEG Norwich MGP Site • MGP site adjacent to an active shopping center which remained open during remediation • ISS treatment necessary to redevelop the site – Treatment required to be done in the winter months • Extensive work prior to auger-based ISS treatment – Removal of asphalt, concrete obstructions – Location of existing gas mains November 14, 2012 24 24

NYSEG Norwich MGP Site • Auger-based ISS equipment included – 4000 series Manitowoc crane – Hain 450T drilling platform – 10 foot diameter auger tool – Batch plant November 14, 2012 25 25

NYSEG Norwich MGP Site • Auger-based ISS treatment – Treatment depth to underlying clay (32-46 feet bgs) – Treated 10 foot wide perimeter first, keyed 4 feet into underlying clay – Treated interior columns, keyed only 2 feet into underlying clay – Site was pre-excavated to accommodate swell November 14, 2012 26 26

NYSEG Norwich MGP Site • ISS Performance Criteria – UCS >50 psi – Permeability <1x10-6 cm/s • Mix Design – Initially 8% Portland cement + 1% bentonite – Reduced bentonite addition without adversely affecting UCS and permeability results November 14, 2012 27 27

NYSEG Norwich MGP Site • Treated 52,000 cy of MGP- impacted material – Conducted the treatment during winter months in Upstate NY – All QC samples met the performance criteria – Completed treatment on-time and on budget – Zero safety or environmental incidents November 14, 2012 28 28

Questions or Comments? plear@wrscompass.com 865-919-5205 November 14, 2012 29

Thank you for your time today. Visit us at www.WRScompass.com November 14, 2012 30 30