 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
2009 E3 Small Projects Grand Prize
Groundwater Remediation Using Enhanced Anaerobic Bioremediation
ENTRANT: CDM
ENGINEER IN CHARGE: Leslie A. Turner, P.E., BCEE
 |
 |
 |
 |
 |
 |
Entrant Profile
In 1999, Rockwell Automation retained CDM to remediate groundwater contamination on a 9-acre site in Orlando, Florida, compromised by the release of various chlorinated solvents. Beginning in 2000, CDM conducted a supplementary groundwater site assessment, evaluated remediation options, constructed an onsite treatment plant, and conducted dual-phase extraction and enhanced anaerobic bioremediation (EAB) pilot studies. CDM developed all work plans and reports regarding these activities and submitted them to the Florida Department of Environmental Protection.
In 2007, CDM was awarded a design-build-operate (D-B-O) contract for full-scale implementation of the hydraulic control and EAB remediation systems to address the groundwater contaminants. The firm designed and built a complex hydraulic well system that controls the flow of groundwater, preventing the contaminated groundwater from flowing off site. CDM also designed and installed more than 50 vertical injection wells and three horizontal recovery wells that are used to circulate potassium lactate into extracted groundwater before it is re-injected into the aquifer system. By using a unique one-pass trenching technology, CDM was able to install the horizontal wells across multiple contaminated aquifer zones without having to dewater.
CDM has completed all design and construction activities and the plant is online. D-B-O project delivery allowed for the project to be completed in 8 months and under the initial estimated budget costs. Preliminary results show immediate and impressive reduction in groundwater contaminant levels.
CDM is a consulting, engineering, construction, and operations firm delivering exceptional service to public and private clients worldwide.
Project Description
When Rockwell Automation acquired the former PEC Industries property, shallow groundwater at the 9 acre parcel of land in Orlando, Florida was severely impacted. Chlorinated solvents, previously used in printed circuit board production, were released into the environment and leached into the groundwater. Methylene chloride; 1,1-dichloroethene; 1,1,1-trichloroethane; and vinyl chloride are the most prevalent volatile organic compound (VOC) contaminants onsite. Despite exhaustive efforts over several years, Rockwell was unable to find an appropriate remediation solution until partnering with CDM.
Integrated Approach
Identifying a solution - CDM's additional assessment revealed groundwater contamination well beyond previous findings-including methylene chloride at up to 2,000,000 parts per billion (ppb), far exceeding Florida guidelines of 5 ppb for groundwater.
Enhanced anaerobic bioremediation (EAB) and dual-phase extraction were selected for pilot testing after various cleanup options-monitoring, physical or hydraulic containment, in situ chemical oxidation, enhanced thermal processes, excavation and offsite disposal, and onsite treatment of excavated soils proved ineffective or cost prohibitive. CDM performed extensive aquifer testing and computer modeling to optimize the placement and pumping rates for the remediation wells.
Harnessing the power of nature - Leveraging the naturally occurring bacteria, Dehalococcoides spp., EAB was selected for its effectiveness remediating similarly contaminated sites. Injecting potassium lactate into groundwater through a series of wells gave the site a jump start-once added, the site underwent an unprecedented bacterial population boom, negating the need to introduce additional dechlorinating bacteria, often required with EAB.
Staying in place - As an in situ technology, EAB destroys the contamination in the ground, mitigating the risks typically associated with extraction technologies, such as accidental release or worker exposure.
Quality
Reducing combined contaminants - Because EAB was then an emerging technology, CDM pilot tested a 100-square-feet test plot to establish its effectiveness at such unprecedented concentrations of contaminants. Previously untested on a highly contaminated area with mixed chlorinated solvent plumes, EAB proved not only to be more cost-effective, but posed fewer health risks and a higher success rate than other technologies.
Accelerating decontamination - Three horizontal extraction wells transport groundwater to the onsite water treatment plant where lactate is added prior to reinjection into the aquifer. Lactate serves as an electron donor for the naturally occurring Dehalococcoides spp., speeding up the dechlorination process-breaking chlorinated solvents into harmless byproducts and effectively cleaning the groundwater. Within the first 6 months of full-scale operation, VOC mass was reduced by more than 90 percent. At startup, the highest concentration area had more than 2,000,000 ppb of methylene chloride. After 6 months, the methylene chloride in this target area had been completely remediated and has not been observed since.
Originality and Innovation
Complex wells achieve multiple goals - Groundwater extraction on the site boundaries using vertical well systems for hydraulic control prevent offsite migration of contaminants. This groundwater is discharged to a 425-gallon-per-minute onsite treatment plant, where it is treated with a high-efficiency air stripper. Designed specifically to treat contaminated groundwater, the plant cleans water to city standards, allowing discharge to the city sewer system for disposal.
Unique technology application - CDM's innovative well system-comprising horizontal recovery and vertical injection wells-effectively controls the groundwater flow and "floods" the contaminated zones with lactate to enhance the growth of dechlorinating bacteria. Continually recirculating the groundwater ensures that lactate, bacteria (Dehalococcoides spp.), and contaminants are in constant contact-creating an environment unmatched using typical injection techniques.
No dewatering necessary - To install horizontal wells, CDM used a unique one-pass trenching technology, which created the trench and installed the filter media in a single step, cutting through three zones of the surficial aquifer. Standard trenching methods requires dewatering and substantial benching or shoring of the trench, which increases the contaminated waste for disposal, as well as the associated costs.
Ensuring success - CDM continues to conduct extensive DNA testing at the site to verify the presence of the Dehalococcoides spp. bacteria and to ensure that bacteria possesses the specific gene required to break down the groundwater contaminants.
Complexity
Challenging geology, innovative solution - Contaminants were present in all three water-bearing surficial aquifer system zones, composed of sand, sandy clay, and clay to approximately 40 feet. Having distinct zones that required treatment, in an area with low transmissivity rates, additionally complicated the remediation challenge. CDM designed and built a groundwater circulation system, using horizontal wells that intersect the three zones and extracts groundwater from all water bearing units. The corresponding vertical wells re-inject lactate-enhanced groundwater back into individual target zones.
Reducing costs and energy - Through monitoring, CDM can determine which areas have established conditions optimal for reductive dechlorination and use the horizontal wells-which are on a separate control system-to redistribute the groundwater to spots where the conditions are not yet optimal. Areas where EAB conditions are appropriate can be shut off, saving energy and allowing the natural process to continue. This cycling system reduces energy use and costs by only operating select wells, based on field observations.
Social and Economic Advancement
Meeting state guidelines - In Florida, groundwater and drinking water standards are equivalent and any exceedance is considered a violation. The Floridan Aquifer-a major groundwater supply source of drinking water - lies beneath the surficial aquifer, making successful clean-up imperative. In order to protect this essential water source, the Florida Department of Environmental Protection issued a cleanup consent order for the site. Determined to get it clean, Rockwell turned to CDM for a solution and funded research, pilot studies, remedial action, and ongoing monitoring of the site.
Being a good neighbor - Located adjacent to State Road 435, the site is in a busy area of Orlando near popular tourist destinations. The added hydraulic control systems prevent groundwater from migrating offsite and eliminate the possibility of additional plume migration.
Proving potential - Currently a light industrial and commercial location, the site can reach full economic potential and accommodate a hotel or high-rise development following successful cleanup. The flexible groundwater treatment system can be expanded or modified so that remedial efforts can be tailored based on future use.
 |
 |
 |
 |
 |
 |
 |