Demonstration of Subaqueous Disposal of Mill Waste Dave Hinrichs, NewFields Mark Doolan, U.S. EPA Chris Wienecke, ATT Sunoco and Jasper County Group R.

Demonstration of Subaqueous Disposal of Mill Waste

Dave Hinrichs, NewFieldsMark Doolan, U.S. EPAChris Wienecke, ATT

Sunoco and Jasper County GroupR. Fischer and K. Tegtmeyer, NewFields

Mill Waste Characteristics

• Chat – from Barnsdall No. 3 mine, Kansas • Tailings – from Barnsdall No. 2 mine, Missouri• Tailings - net-alkaline, permeability 2 x 10-7

minimal ARD• Tailings – lab 0.03 ft/ft vertical settlement• Concentrations in tailings backfill

– Zinc = 18,730 mg/kg

– Lead = 570 mg/kg

– Cadmium = 130 mg/kg

Subsidence pit at Remedial Soil Repository West of Prosperity

Jasper Co. Site Subsidence Pit at North Edge of Remedial repository

Jasper Co. Site Subsidence Pits Subsidence Pit South of Carterville off of Lewis St.

Jasper Co. Site Subsidence PitWest of Carterville Off of Wilson St.

Existing Site Conditions

Subaqueous Disposal Theory

• Place waste in the saturated zone, cap and reduce oxygen by 10,000x

• Establish reducing/anaerobic conditions to reduce or eliminate ARD and metals release

• Lower disposal and O & M costs

• Eliminate pit as trash dumping site

• Eliminate as storm runoff metal load source

Expected Results of Subaqueous Disposal

• Short-term zinc loading to aquifer

• Shift from strongly oxidizing to reducing conditions, i.e., lower eH

• Increase in pH to mildly alkaline

• Greatly reduced rate of sulfide oxidation, ARD, and metals release compared to above-ground repository

Subaqueous Disposal Setting

Mechanisms for Metals Release in Subaqueous Setting

• Short term

– Dissolution of reactive secondary minerals

• Long term

– Stable sulfide minerals, dependent on final eH and pH conditions

Galena Leach Study

Subaqueous Field Demonstration Jasper County, Missouri

• Selected P4 Pond at Freehold mine in Kansas• Installed two monitoring wells in Boone aquifer• MDNR conducted dye tracing study• Collected 2 rounds of baseline samples, pre-backfill• Backfilled 200 ft x 200 ft x 35 ft pit• Installed Well P4 Central in July 2002• Collected 4 rounds of post-backfill samples• NewFields prepared summary report, Dec. 2003

Demonstration Site Map

Pond P-4

Site Conditions

• Shallow aquifer confined; gradient est. = 0.0008

• Local shale hydraulic gradient est. = 0.01

• Pit depth 35 feet; Penn shale 75 feet thick

• Freehold mine depth of 120 - 180 ft in Miss. limestone

• Pond water level 2 – 13 feet higher than shallow aquifer, poor hydraulic inter-connection

• Water levels in pits showed dramatic rise and fall with storm events

Pit Filling

• Filled pit with 58,500 yds3 of chat and tailings March - July 2002

• Surcharged to plus 4 feet

• Capped with 1.5 ft of topsoil

• Volunteer revegetation

Pond 4 - filling

Pond 4 - Post Filling

Filled Pit

Filled Pit Monitoring

• Installed wells P4NW and P15E Dec 2001

• Collected 2 rounds of baseline samples, pre-backfill

• Installed Well P4 Central in July 2002

• Collected 4 rounds of post-fill samples

Dissolved Zinc Concentrations

Date Sampled P4 Pond P4-NW P15-E Pond 16 Pond 10 Shaft 3 Pond

July 18, 2001 0.04 0.05 0.16 0.37

Feb. 20, 2002 0.08 1.1 0.038 0.06

P4 Pond filled with tailings 3/02 – 7/02

Sept. 4, 2002 5.8* 0.5 0.11 0.01

Nov. 26, 2002 3.5* 0.73 0.14 0.02

April 14, 2003 1.2* 0.3 0.084 0.01 0.01 0.91

August 25, 2003 0.44 0.68 0.097 0.014 0.033

* Sample results from P4-Central well

0

1

2

3

4

5

6

7

Dis

solv

ed Z

inc

Con

cent

ratio

n, m

g/l

P4 Pond/P4Central

Pond No. 16

Well P15-E

Well P4-NW

Pond

Fill

ing

Mar

ch to

Jul

y 20

02

P4 Pond Redox

P4 Pond

-60

-50

-40

-30

-20

-10

0

1 2 3 4

Re

do

x P

ote

nti

al

(mv

olt

s)

ZINC LOAD ESTIMATES

0

5

10

15

20

P4 Pond Demo OD-98 Chat Excavation Site

Zinc

, lbs

per

yea

r

1,129

Conclusions

• Subaqueous disposal did not increase metal loading to shallow aquifer due to low permeability/poor connection

• Subaqueous disposal should substantially reduce metals loading to surface streams

• Post-remedy footprint reduced = lower O & M cost• Jasper County FS includes subaqueous disposal as a

permanent, moderate cost alternative to conventional cap and cover

• Placement of wastes in mine pits reduces pit associated hazards and illegal dumping

Pit Selection• Prioritize pits that are or can be hydraulically

isolated from shallow aquifer. Indicators:low or negative eH,

low O2, poor vegetation and aquatic community

Rapid increase in water level if recharged

Slow to recover when test-pumped

• Prioritize pits that pose physical hazards, are used as trash dumps, or offer marginal aquatic habitat.

Engineering Aspects

• With scrapers and dozers, cost $4.50/cy• Tailings can be used in low-permeability

caps and liners. • Using chat only = higher predicted zinc

loads; mix tails with chat or fly ash• Predict consolidation before backfill• Surcharge pits and/or allow time for

settlement before placing the soil cap.