# Presentation: 232716

## In Situ Biological Treatment of Hexavalent Chromium at the Selma Pressure Treating Superfund Site

**In Situ Biological Treatment of Hexavalent Chromium at the Selma Pressure Treating Superfund Site**

**Charnjit Bhullar, USEPA**
**Sam Martinez, CA-DTSC**
**Wally Shaheen, P.E., USACE**
**Larry Hudson, Daniel Leigh, David Cacciatore, Dr. Paul Lear,**
**Shaw Environmental, Inc.**

**CA-DTSC**

**Notes:**
Good Afternoon.
My name is David Cacciatore.  I am a senior engineer and project manager with Shaw Environmental, Inc. in Concord, California.  My presentation today is on the Design and Implementation of an Expanded In Situ Anaerobic Bioremediation System operated at Naval Station Treasure Island.  My co-authors on this presentation are Dan Leigh, Michael Yurovsky and John Baur, also from the Concord office of Shaw Environmental and Scott Anderson from the Naval Facilities Engineering Command, Southwest, in San Diego, California.

## Site Location Map

**Site Location Map**

**Selma, CA**

## Site History

**Wood pressure treating facility from 1930s**

**Discharges of Cr****6+**** occurred in several areas Primarily  “Retort Area”**

**Wood was pressure treated with chromate and allowed to dry in racks in retort area.**

**Remediation of soils included excavation and on site stabilization**

**Retort area was capped.**

**ROD signed in 1988**

## Site History

**Site History**

**Pump & Treat selected as remedial technology for groundwater**

**P&T Generally effective for controlling plume**

**Modeling indicated over 50 years to remediate plume using P&T**

**August 2003, Shaw proposed ISB as remedial enhancement**

**P&T system installed in 1998 – treats up to 200 gpm**

## Site Location 

**Site Location**

**Selma **
**Pressure **
**Treating **
**Superfund Site**

**Notes:**
This shows the location of the site relative to the city of Selma. The box on the left is the area covered by the picture on the right. The Selma Wood Treating superfund site is highlighted on the right picture.
Highway 99 is the major road on the map.
The plume migrated approximately 4000 feet downgradient.

**Cr****6+**** Concentration**

**> 50 ****μg/L**

**> 1,000 ****μg/L**

**> 10,000 ****μg/L**

**> 50,000 ****μg/L**

**March, 2004**

**Phase 1**

**Phase 2**

**Phase 3**

**Phase 4**

## Investigation Method

**Investigation Method**

**Bench Tests - October 2004 to March 2005**

**Phase 1 – Source Area Pilot Test - March 2005**

**Phase 2A – Area Treatment - October, 2005**

**Phase 1A – Source Area Treatment Test - January, 2006**

**Phase 2B – Downgradient Treatment - July, 2006 to present**

## Bench Test Methodology

**Bench Test Methodology**

- 3 triplicate samples

- Evaluated EHC, lactate, molasses

- Evaluated arsenic mobilization

- Evaluated potential High Cr6+ Toxicity effects

- Evaluated remobilization of Cr3+

- Evaluated Degradation of Cr6+ under aerobic conditions

**Notes:**
Explain EHC
Eh is the aquifers potential to transmit electrons. It is similar to pH.
EHC is a trademark that is used to describe a product that includes carbon and reduces the EH, hence EHC 

EHC is a mixture of zero valent iron and biodegradable carbon. You get both chemical and biological reduction of the Cr^.

We evaluated arsenic mobilization because, under reducing conditions arsenic is reduced from As5 to As3 just as Cr6 is reduced to Cr3. However Cr 3 is less mobile than Cr6 whereas As3 is more mobile than As 5. As was not mobilized in the bench tests.

We evaluated degradation rates of Cr6 at varying concentration of Cr6.  Very high concentrations of Cr6 are toxic to microorganisms. We did see some inhibition at 80,000 ug/L but not very much. Not much inhibition at 40,000 ug/L. The toxic level must be much higher than 100,000 ug/L.

## Eh Range for Various Electron Acceptors

**Eh Range for Various Electron Acceptors**

**Decreasing Amount of Energy Released During Electron Transfer**

**Redox Potential (Eh****0****)**
**in Millivolts @ pH = 7**
**and T = 25****0****C**

**500**

**Aerobic**

**Anaerobic**

**1000**

**0**

**-250**

**Notes:**
This figure shows the order in which chemicals are reduced. Notice that hexavalent chromium is the first chemical to be reduced followed by oxygen, nitrate, arsenic, manganese, iron, sulfate and carbon dioxide, in that order. 

This is significant because any molasses that is present after the reduction of hexavalent chromium is excess and will result in the reduction of these chemicals. That is why we see manganese, iron and methane go into solution. Because there is too much molasses.

## Summary of Bench Test Results

**50**

**45**

**35**

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**10**

**5**

**0**

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**0**

**30**

**60**

**90**

**120**

**150**

**Cr****6+**** Concentration (mg/l)**

**Days**

**Molasses Amended Tests**

**Lactate Amended Tests**

**EHC Amended Tests**

**Notes:**
This figure shows the bench test results, in triplicate.

## Nitrate / Cr6+ Molasses Bench Test Results

**Nitrate / Cr****6+**** Molasses Bench Test Results**

**Nitrate**

**Cr****6+**

**Days**

## Summary of Bench Test Results

- Cr6+ Reduction quicker with molasses than sodium lactate

- Biodegradation observed even at concentrations up to 80,000ppb

- Cr6+ reduction occurs prior to nitrate reduction and can occur with oxygen present

- Arsenic was not mobilized in bench tests

- Cr3+ was not converted to Cr6+ under aerobic conditions

## Phase 1 – 3-4/2005

**Phase 1 – 3-4/2005**

**Phase 1A – 1/2006**

**Phase 2A – 10/05 - 1/06**

**Notes:**
This figure shows the location of the injections during phase 1, 2A and 1A,

## Pilot Test Methodology

**Pilot Test Methodology**

**Use direct push technology to distribute substrate**

**Substrate (molasses) target concentration ~ 4,000 mg/L target**

**Phase 1, 1A and 2A**

**Monitor reduction of Cr****6+**

**Monitor geochemical changes**

**Notes:**
Dan Summarizes and hands off to Larry

## Selma Superfund Site – Source Area

**Selma Superfund Site – Source Area**

**Notes:**
This figure is a conceptual model of the injection process.

## Phase 1 Pilot Test Results

**-400**

**-300**

**-200**

**-100**

**0**

**100**

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**300**

**RA2**

**RA1**

**R23I**

**ORP (mv)**

**Days**

**Phase 1 Pilot Test Results**

## Cr6+

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- Concentration (ug/L)

- Days

**Cr****6+**

**Total Cr**

**Well RA-1**

**Phase 1 Pilot Test Results**

**Notes:**
This is the change in concentration of chromium both hex and total, during the phase 1 injection
Notice that the change in Cr 6 concentration is faster than in the lab tests. This is probably because of the following reasons
Bench tests are conducted in 100 ml Serum vials with about 90% water
The aquifer is 75% soil and about 25% water
The bacteria are mostly adsorbed on the aquifer matrix so there are a lot more in the aquifer already
The bacteria  in the aquifer are acclimated to the site conditions.

## Geochemical Changes During Pilot Test

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- Mn Concentration (mg/L)

- Fe2+, NO3-, SO4- Concentration (mg/L)

- Days

- RA-1

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- Nitrate

- Manganese

- Ferrous Iron

- Sulfate

**Notes:**
This figure shows the change in concentration in nitrate, manganese, ferrous iron, and sulfate during phase 1. As anticipated, after quick reduction of hexavalent chromium, nitrate decreased, manganese and iron increased and sulfate decreased, in the predicted order. This indicates that we have an excessive amount of molasses and that we are creating excessively reducing conditions.

## Phase 1 – 3-4/2005

**Phase 1 – 3-4/2005**

**Phase 1A – 1/2006**

**Phase 2A – 10/05 - 1/06**

**Notes:**
This figure shows the location of the injections during phase 1, 2A and 1A,

## Limitations of Direct Push Technology

**Limitations of Direct Push Technology**

- Direct push requires overdosing of site to assure sufficient substrate for Cr6+ degradation.

- Overdosing with substrate results in establishment of excessively reducing conditions which result in mobilization of some metals (i.e. iron, manganese).

- Limited to depths of less than 110 feet bgs at this site

## Phase 2B

**Phase 2B**

- Purpose: Biologically degrade Cr6+ in down-gradient plume

- Solution: Groundwater recirculation with metered substrate addition

- Challenge: Down-gradient plume deeper (120 feet)
-  - Direct push method not feasible.

- Challenge: Prevent excessively reducing conditions during  biodegradation process

## Phase 2B (cont.)

**Phase 2B (cont.)**

**Treatment Strategy**

**Groundwater Extraction**
**	****11 Extraction Wells**

**Amendment with substrate **

**Injection of Amended Groundwater**
**	****5 Injection Wells**

**Distribute Substrate**

**Monitor Degradation**

**In extraction wells**

**In 3 monitoring wells clusters**

**Low Concentration Molasses (500 to 15 mg/L)**

**Low Concentration Sodium Lactate (100 to 15 mg/L)**

**Notes:**
The phase 2b strategy involves recirculation rather than direct injection. This is because it is too deep for direct push injection. Also, we have better control of the injection process and will be able to prevent the establishment of excessively reducing conditions. 

We will have 4 nested monitoring well pairs to evaluate substrate distribution and biodegradation

## Phase 2B

**Notes:**
This figure shows the relationship between phases 1, 1A, 2A and 2b. The red dots are proposed injection wells. The blue dots are proposed extraction wells. The molasses will be distributed through 2b by recirculation of groundwater.

## Slide 24

## Phase 2B Area

**Phase 2B Area**

## Phase 2B Injection Skid System

**Phase 2B Injection Skid System**

## Phase 2B Injection Extraction and Monitoring Wells

**Phase 2B Injection Extraction and Monitoring Wells**

## Phase 2B Conceptual Design

**Phase 2B Conceptual Design**

## Phase 2B Substrate Injection

**Injected Molasses Concentration**

**Phase 2B Substrate Injection**

## Phase 2B Analytical Results

**Phase 2B Analytical Results**

## Phase 2B Analytical Results

**Phase 2B Analytical Results**

## Phase 2B Analytical Results

**Phase 2B Analytical Results**

## Phase 2B Analytical Results

**Phase 2B Analytical Results**

## Phase 2B Analytical Results

**Phase 2B Analytical Results**

## Phase 2B Analytical Results

## Cr6+ Concentration

**Cr****6+**** Concentration**

**> 50 ****μg/L**

**> 1,000 ****μg/L**

**> 10,000 ****μg/L**

**> 50,000 ****μg/L**

**March, 2004**

**March, 2007**

## Lessons Learned

**Lessons Learned**

**Molasses Rapidly Utilized**

**Causes biofouling in wells and distribution piping**

**Limited distribution in aquifer.**

**Low concentration of substrate sufficient for Cr****6+**** reduction**

**Contaminant treatment diffusion limited**

## Conclusions:

**Conclusions:**

**In Situ bioremediation is an effective technique for treatment of Cr****6+****.**

**Bench testing is valuable in defining treatment processes. **

**In situ delivery methods must be designed for a variety of site conditions.**

**Chemical and biological processes (i.e. aerobic/anaerobic) **
**should be optimized  for site conditions.**

**Field testing is necessary to confirm assumptions about system design. **

## Acknowledgments

**Charnjit Bhullar, Roberta Blank**
**	****	****Region 9**

**United States Army Corps of Engineers**
**	****Rapid Response Program**

**Larry Hudson, Dan Leigh, and many others**

**	****	****Sam Martinez**
**California Dept. of Toxic Substances Control**