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

Transcription

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

2 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,

3 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,

4 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 (Excavatorbased) Wilmington, DE NYSEG MGP Site (Auger-based) - Norwich, NY Camden MGP Site (Excavator-based) Camden, NJ November 14,

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

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

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

8 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,

9 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,

10 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,

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

12 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,

13 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,

14 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,

15 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,

16 Suggested ISS Leaching Criterion Example using default DAF for metals Contaminant Health Based GW Quality Criterion (µg/l) Aqueous PQL (µg/l) Suggested Leaching Criterion (µg/l) Contaminant Health Based GW Quality Criterion (µg/l) Aqueous PQL (µg/l) Suggested Leaching Criterion (µg/l) Aluminum A Lead Antimony Manganese Arsenic B Mercury Barium 6, ,000 Molybdenum Beryllium Nickel ,300 Cadmium Selenium Chromium Silver Cobalt ,300 Thallium B Copper 1, ,900 Vanadium Iron ,900 Zinc 2, ,600 A Adjusted so as to not exceed solubility B Adjusted to 3x Aqueous PQL November 14,

17 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,

18 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,

19 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,

20 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,

21 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,

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

23 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,

24 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,

25 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,

26 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,

27 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,

28 NYSEG Norwich MGP Site Treated 52,000 cy of MGPimpacted 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,

29 Questions or Comments? November 14,

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