Monitored Natural Attenuation of Perchlorate in Groundwater, Maryland

Site Name:

First Demonstration: Building 1419 at Indian Head Naval Surface Warfare Center (NSWC) Second Demonstration: Solid Waste Management Unit (SWMU) at Manufacturing Site

Location:

PRB Demonstration: Indian Head, Maryland
Source Area Demonstration: Maryland

Period of
Operation:

PRB Demonstration: 38-month performance monitoring period
Source Area Demonstration: 23-month performance monitoring period

Cleanup
Type:

Field Demonstration

Technology:
Monitored Natural Attenuation (MNA)

This project evaluated the effectiveness of MNA at two field demonstration sites for the in situ remediation of perchlorate-contaminated groundwater. The demonstration sites were assessed using the following three-tiered approach:

  • Tier 1 — Plume stability and geometry
  • Tier 2 — Biogeochemical parameters and biological indicators
  • Tier 3 — Biodegradation rates


Contaminant concentrations, biogeochemical conditions, and molecular biological tool (MBT) enumerations were performed along the entire well network as part of the Tier 1 and Tier 2 evaluations. In Tier 3, specialized studies were designed and implemented to determine biodegradation rates.

Details about each demonstration are provided below:

Indian Head Demonstration
  • 35 monitor wells and 10 piezometers were installed across the site and into Mattawoman Creek to characterize the site and facilitate data collection.
  • Four geomorphological zones were identified for the land surface and land leading into the creek.
    • Zone 1: Land area south of Building 1419
    • Zone 2: The Littoral Zone located within Mattawoman Creek (region above the low-water mark and below the high-water mark)
    • Zone 3: The Subtidal Channel located within Mattawoman Creek (a relatively narrow channel-like depression along the creek bank at the edge of the Littoral Zone)
    • Zone 4: The Subtidal Shallows located within Mattawoman Creek (accreted sediment located south of Zone 3)
  • The monitoring well/ piezometer network was sampled up to five times during the 38-month performance monitoring period.


Manufacturing Site Demonstration
  • The monitoring well network consisted of existing wells and four additional monitoring well pairs that were constructed in December 2006.
  • The new and existing monitoring wells were sampled up to five times during the 23-month performance monitoring period from May 2006 and April 2008 to evaluate aquifer conditions and how those conditions might affect the potential for natural biodegradation of perchlorate.
  • The plume at the TCE/Perchlorate-impacted SWMU was divided into transects.
    • Transect 1 (mid-plume conditions): Located approximately 500 to 700 feet downgradient of the presumed source.
    • Transect 2 (mid-plume conditions): Includes three well pairs installed along Elkton Road to fill out the well network for this project.
    • Transect 3 (Presumed Discharge Zone): Includes well pairs situated near Little Elk Creek, which are located just before the wooded zone that forms a buffer between open playing fields and the creek.

Cleanup Authority:
Department of Defense (DoD)

Contacts:

Principal Investigator
Tony Lieberman
Solutions-IES, Inc.
1101 Nowell Road
Raleigh, NC 27607
Phone: 919-873-1060, Ext. 117
Email: tlieberman@solutions-ies.com

Co-Principal Investigator
Robert C. Borden
Solutions-IES, Inc.
1101 Nowell Road
Raleigh, NC 27607
Phone: 919-873-1060, Ext. 123
Email: rcborden@solutions-ies.com

Project Manager
Sheri L. Knox
Solutions-IES, Inc.
1101 Nowell Road
Raleigh, NC 27607
Phone: 919-873-1060, Ext. 174
Email: sknox@solutions-ies.com

Contracting Officer Representative
Bryan Hare
Naval Facilities Engineering Service Center
1100 23rd Avenue, Code 411
Port Hueneme, CA 93043
Phone: 805-982-1795
Email: bryan.harre@navy.mil

Environmental Restoration Program Manager
Andrea Leeson
ESTCP
901 Stuart Street, Suite 300
Arlington, VA 22203
Phone: 703-696-2118
Email: andrea.leeson@osd.mil

Contaminants:
Perchlorate

Waste Source:
Indian Head Demonstration: Activities associated with the former perchlorate clean-out facility (Building 1419) resulted in a perchlorate-contaminated plume that extends eastward about 300 to 400 feet toward Mattawoman Creek, a large tributary of the Potomac River.

Source Area Demonstration: Ammonium perchlorate continues to be used to manufacture and test rocket engines at this facility, which in combination with other historical industrial activities at the site and in the surrounding areas have resulted in a commingled TCE and perchlorate plume. The plume extends 3,400 feet east of the presumed source area.

Type/Quantity of Media Treated:
PRB Demonstration: Groundwater (quantity not documented)
Source Area Demonstration: Groundwater (quantity not documented)

Purpose/Significance of Application:
The primary purpose of the two field demonstrations was to evaluate the potential for MNA to remediate perchlorate-contaminated groundwater and identify the conditions for the use of MNA as a remedial technology.

Regulatory Requirements/Cleanup Goals:
Performance objectives for both demonstrations are detailed below:

  • Further develop and evaluate lines of evidence established during the site selection process for their applicability to MNA in the field
  • Evaluate the use of various biological indicators of perchlorate biodegradation
  • Compare biodegradation rates established in microcosm studies with biodegradation rates in the field
  • Evaluate the cost-effectiveness of MNA of perchlorate at the Indian Head site
  • Validate the approach identified in the Protocol

Results:
Indian Head Demonstration:
Results from the Tier 1, 2, and 3 evaluations are summarized below:

  • The Tier 1 and 2 evaluations showed that groundwater conditions are conducive to perchlorate biodegradation beginning in the nutrient-rich shallow groundwater beneath the Littoral Zone and continuing out into Mattawoman Creek. However, complex hydrogeology and the potential impact of the mixing and dilution activities made additional research (Tier3) necessary to evaluate site conditions and MNA.
  • The Tier 3 evaluation indicated that the first-order biodegradation rate constant ranged from 0.12 to 0.63 per day. The results support the information obtained in Tier 1 and 2 and provide additional evidence for the natural attenuation of perchlorate at the site.


Source Area Demonstration:
Results from the Tier 1, 2, and 3 evaluations are summarized below:
  • The Tier 1 and 2 evaluations showed that groundwater conditions are minimally conducive to biological degradation of perchlorate until closer to discharge into Little Elk Creek. Non-biological attenuation mechanisms have resulted in decreases in perchlorate concentrations over distance. Perchlorate mass flux in the intermediate zone declined significantly during groundwater flow from Transect 1 to 3. However, there is a substantial increase in the shallow zone mass flux in Transect 3 as groundwater migrates from the intermediate to the shallow zones near Little Elk Creek. Total mass flux declines from an average of 28 grams per day (g/d) to 18 g/d of perchlorate from Transect 1 to 3.
  • Tier 3 evaluation results indicated that the first-order biodegradation rate constant was 2.9 per year.

Cost Factors:
Indian Head Demonstration:
The total cost of the Indian Head test demonstration was approximately $509,100. Primary cost elements are described below:

  • Technical Demonstration Plan, White Papers/Design: ~$51,300 (10%)
  • Additional Characterization: ~$103,600 (20%)
  • Performance Monitoring & Data Acquisition for Tiers 1 & 2: ~$209,300 (41%)
  • Tier 1 and 2 Data Evaluation: ~$14,900 (3%)
  • Tier 3 Data Acquisition and Evaluation: ~$60,000 (12%)
  • Technical Reporting: ~$70,000 (14%)


Manufacturing Site Demonstration:
The total cost of the Manufacturing Site test demonstration was approximately $292,900.
Primary cost elements are described below:
  • Technical Demonstration Plan, white papers/design: ~$17,000 (6%)
  • Additional characterization: ~$45,000 (15%)
  • Performance monitoring and data acquisition for Tiers 1 & 2: ~$101,900 (35%)
  • Tier 1 and 2 evaluations: ~$21,000 (7%)
  • Tier 3 data acquisition and evaluation: ~$58,000 (20%)
  • Technical reporting: ~$50,000

Description:
Two field demonstrations were conducted to evaluate the effectiveness of MNA for the remediation of perchlorate-contaminated groundwater. The demonstrations were conducted near Building 1419 at Indian Head NSWC in Indian Head, MD (Indian Head Site), and at the TCE/Perchlorate SWMU field site at a manufacturing facility in Maryland. The purpose of the demonstration was to evaluate the tools needed to evaluate whether MNA can be an effective remedy for managing the environmental impacts of perchlorate contaminated groundwater at specific sites. Both demonstrations were implemented following a three- tiered approach to develop multiple lines of evidence related to perchlorate MNA.

Indian Head Demonstration

Based on site conditions, microcosm studies, site logistics, and cost considerations, the Indian Head site was selected for testing the potential for MNA of perchorate in groundwater. Perchlorate-contaminated groundwater was identified near Building 1419, the former perchlorate clean-out facility. Site investigation results indicated that plume was migrating about 300 to 400 feet toward Mattawoman Creek, a large tributary of the Potomac River. No perchlorate-contaminated wastewater has been discharged from the site since 1996; however, a study conducted in 2001, indicated the presence of a persistent source of perchlorate. Results from the 2001 study showed that the perchlorate flux at the site did not change over time and suggested the possibility of a vadose zone source that would continuously release perchlorate to the aquifer during periods of heavy rainfall. As a result, monitoring results indicated a high temporal variability of perchlorate concentrations in wells located 180 and 125 feet downgradient from the presumed source area. The plume is at least 400 feet wide along the creek bank, and dispersion of the plume has resulted in similar perchlorate concentrations being observed throughout the thickness of the surficial aquifer.

During this demonstration, the monitoring well/ piezometer network was sampled up to five times during the 38-month performance-monitoring period. Trends in groundwater flow, biogeochemical parameters, microbial populations, and perchlorate concentrations indicated that perchlorate attenuates mostly as a result of nonbiological mechanisms near the presumed source and areas downgradient from the source but prior to discharge to Mattawoman Creek. Biodegradation rates were calculated by several methods and were generally reproducible, providing supporting lines of evidence for natural bioattenuation.

Maryland Manufacturing Site

The second demonstration was conducted at a 600-acre manufacturing facility in Maryland. Since the 1930s, the facility has been used for various industrial purposes such as fireworks manufacturing, munitions production, pesticide production, and research and manufacturing of solid propellant rockets. Ammonium perchlorate continues to be used to manufacture and test rocket engines at the facility. The surrounding areas also have a diverse history of industrial activities. Recent site investigations have identified a commingled TCE and perchlorate plume on the east of the manufacturing facility that has attenuated over time. The plume migrates through an intermediate aquifer to Little Elk Creek, which lies almost 3,400 feet east of the presumed source area. From 1997 through 1998, a pump and treat system was used as an interim remedial measure to capture and treat contaminated groundwater from the intermediate aquifer in the vicinity of the source. The pump and treat system has removed over 800 pounds of volatile organic compounds (VOCs) since it was installed. Pre-demonstration groundwater and soil sampling results indicated perchlorate concentrations ranging from 1,200 micrograms per liter (µg/L) near the presumed source to an average of 215 µg/L at a downgradient monitoring well about 30 ft from the creek. TCE concentrations showed an increase from 1,300 µg/L near the source to an average of 2,015 µg/L at a downgradient monitoring well.

During the demonstration, new and existing monitoring wells were sampled up to five times during the 23-month performance monitoring period from May 2006 and April 2008 to evaluate aquifer conditions and how those conditions might affect the potential for natural biodegradation of perchlorate. Trends in groundwater flow, biogeochemical parameters, microbial populations and perchlorate concentrations suggest that perchlorate is attenuating and, in some locations, is biodegrading prior to groundwater discharging to Little Elk Creek. Perchlorate biodegradation rates were calculated, but bioattenuation time frames were measured in decades.

Overall, the field demonstrations indicated that MNA can be used to help address perchlorate-contaminated groundwater. The site conditions favorable to perchlorate biodegradation were defined and tested in the field to confirm their usefulness for future MNA evaluations. The key favorable factors include: (1) mildly to strongly reducing conditions (ORP<+100 mV), (2) the absence of strongly acidic groundwater (pH>5.5), (3) relatively low nitrate concentrations, and (4) the presence of TOC to supply electrons for perchlorate reduction (TOC greater than 4 to 6 mg/L).