Impact of ph on Soil and Groundwater Remediation RE3 Conference November 14, 2012 Brad Elkins Technical Sales Representative

Transcription

1 Impact of ph on Soil and Groundwater Remediation RE3 Conference November 14, 2012 Brad Elkins Technical Sales Representative

2 Importance of ph Impacts conditions of silts and clays Controls dissolution of natural & contaminating metals Acid ph mobilizes metals (e.g., Fe, As, Pb) Neutral ph stabilizes metals (e.g., Pb, Zn, Cd, Cr +6, As) Alkaline ph precipitates metals Can promote chemical oxidation High ph can degrade RDX, TNT Controls microbial activity Acid ph supports fungal growth Too acid (ph <5.5) inhibits Dehalococcoides sp. Too alkaline can be toxic

3 Soil ph From USGS

4 Common Bases for Adjusting ph Brad Elkins Base Formula MW EOS Remediation OH- per Mole OH- per Kg Technical Sales Representative Milk of Magnesia Mg(OH) ph Solubility (g/l) Caustic Soda NaOH ,100 Baking Soda NaHCO 3 84 α Limestone CaCO

5 Case History Ex Situ Lead Stabilization at Big South Fork National River & Recreation Area - East Rim Firing Range Technical Sales Representative belkins@eosremediation.com Problem Years of small-arms fire resulting in elevated lead concentrations above the USEPA residential soil screening level CANNOT remove the soil from the berm because then the client becomes TS&D facility

6 Assessment Berm dimensions: 20 ft. x 200 ft. x 70 ft. (H x W x D) On the berm: 400 to 13,600 mg/kg Around the perimeter: ND to 400 mg/kg Total 250 tons of Pb contaminated soil Assessment Layout Bullet & lead fragments on surface Groundwater (>10 ft. bgs) and stormwater not impacted

7 Solution Lab Study Collect composite soils from different areas of the berm Mix composite soils with increasing amounts of EnviroBlend - Treatments: (1) = control; (2) = 2% EB; (3) = 4% EB; (4)= 6% EB; (5) = 6% + 2% Portland Cement Send to analytical lab for TCLP Pb - Recommended 5% EnviroBlend based on testing Field Application Tilled in EnviroBlend at 5% by weight into the top 12 inches of top soil. Perform confirmatory sampling of 2 composites from treated soil: TCLP = <0.025 to mg/l Perform confirmatory sampling of 6 composites from berm: Pb (total) = 10 to 25 mg/kg

8 Results Stabilized the Pb in 150 tons of hazardous soil 253 tons disposed of as non-hazardous waste Firing berm restored for future use 25% cost savings compared to T&D as hazardous waste

9 Groundwater Contamination

10 Magnesium Hydroxide for Aquifer ph Adjustment Mg(OH) 2(s) Mg 2+ (aq) + 2OH - (aq) Ksp = Magnesium Hydroxide is a sparingly soluble base and occurs in nature as the mineral brucite. Its solubility is controlled by the ph of the system. ph = How to make this transport in an aquifer? Faure; 1998, Principles and Applications of Geochemistry, Figure 9.2, pg123

11 CoBupHMg a Colloidal Suspension of Mg(OH) 2 a slow-release alkaline buffer an equilibrium ph of 9-10, a negative particle surface charge

12 Column Experiments Column Design Diameter: 2.58 cm Material: clear PVC pipe Length: 28 cm Packed with field sand Column Operation Up-flow direction Pore volume: 50 ml Effluent was collected to measure alkalinity and ph Pressure was monitored during injection

13 Pure Mg(OH) 2 in water vs. CoBupHMg

14 Effects on Permeability

15 Lab Titration Experiment to evaluate ph Adjustment Data provided by Shaw E&I 2012

16 Conclusions Understanding ph in soil and groundwater is a critical piece of any assessment Technologies and products are commercially available to favorably modify ph and soil conditions for remediation. EnviroBlend works well in soil to stabilize lead and other metals, allowing handling as non-hazardous waste CoBupHMg suspension can be effectively transported through aquifer material to adjust ph into range favorable for microbial activity.

17 Questions? If you are considering aquifer ph adjustment collect/understand: Soil Acidity Groundwater Acidity CVOC Concentrations Substrate selection Brad Elkins Technical Sales Representative ext 173