Remediation of Metals
Duncklee & Dunham has undertaken an innovative remedial action project to address metals contamination in the shallow and intermediate groundwater at an industrial facility. Metals contamination in groundwater represents one of the more difficult remediation scenarios because metals do not degrade and have limited capacity to attenuate under normal aquifer conditions. Our staff has extensive experience in the assessment and remediation of metals and other inorganic soil and groundwater contamination resulting from agri-chemical, electronics, plating and coating, wood treatment and mining operations.
Although the existing groundwater plume is still confined to the client’s property, 3D groundwater fate and transport modeling verifies that groundwater metals contamination will ultimately exceed regulatory standards at the facility boundary if left unabated. These metals continue to be released to the groundwater from a centralized soil source area. Metals in the groundwater beneath these source area soil act as a source for the strengthening plume.
The objective of the program is a unified remedy for both the current groundwater plume and the future release of additional metals contamination from the source area. Duncklee & Dunham’s senior staff, working with nationally recognized geochemical and groundwater modelers and treatability experts developed a unified strategy to address the existing groundwater plume and the continuing source area. The treatability-study results and the data from a groundwater assessment using a hydraulic-profiling tool equipped with a groundwater sampling system, and an extensive monitoring-well network were used to refine the groundwater model. These data helped to overcome heterogeneity in the hydrostratigraphic units at the site and adjust the remedial approach based on site-specific attenuation-capacity properties of the saturated zone, which were then used to design and implement a groundwater-extraction system that targeted select zones of the groundwater plume that maximized its efficiency.
Duncklee & Dunham also designed a remedial approach to address the source-area soil contamination by assessing the natural attenuation capacity of the unsaturated zone to evaluate the ability of these soils to mitigate the migration of metals to the water table. We calculated site-specific remediation goals that represented a metal concentration that would exceed the attenuation capacity of underlying soil and eventually leach to groundwater. We evaluated various remedial options and ultimately selected a metals-stabilization method by way of in situ soil blending. This remedial method allowed for treatment of soil on-site and substantial savings related to disposal costs. The treatability-study results allowed Duncklee & Dunham to increase the remedial goals, reduce the amount of soil that required treatment by approximately 50% while being protective of human health and the environment. This remedial approach amounted to a cost savings of over $600,000 when compared to conventional dig-and-haul methods for soil remediation. This is another example of Duncklee & Dunham’s intent and ability to use innovation and creative thinking to find effective solutions to serious environmental challenges.
The project involved conducting a comprehensive, multi-media environmental audit of a major university in North Carolina following the guidelines of the US EPA’s self-audit policy as published in Incentives for Self-Policing: Discovery, Disclosure, Correction and Prevention of Violations, Volume 65, Number 70, Federal Register 19618, April 11, 2000, and using the concepts of an effective Environmental Management System (EMS).
The intent of the audit was to develop an assessment of the University’s performance respective to compliance with applicable environmental regulations and ordinances, as well as provide a foundation for development or modification of environmental strategies as they relate to future University activities and proposed environmental regulations. The results of the environmental audit were used to perform a gap analysis on areas deemed deficient or requiring additional attention. By conducting the audit under the EPA’s self-audit policy, the University was able to disclose and correct compliance violations through systematic discovery and thereby not be subjected to economic and gravity-based penalties from EPA.
Scope of Work
The Audit Team conducted the audit of the University’s academic and support facilities and operations in accordance with the guidelines of the EPA’s self-audit policy and any other applicable local, state, and federal standards. The scope of our audit focus ranged from undergraduate and graduate academic facilities and departments in the arts, sciences and medicine, to facility support areas including energy services, housing and grounds maintenance, athletic facilities, and a hazardous waste treatment, storage and disposal facility. Elements of the environmental audits included:
- Site visits to over 200 undergraduate and graduate laboratories and support shops within the University’s on and off-campus academic facilities for inspection of hazardous waste management;
- Site visits to facility maintenance shops, energy service facilities, athletic facilities, service stations, grounds maintenance facilities, and other facility support areas for evaluation of compliance with local, state, and federal regulations pertaining to air emissions, wastewater discharges, hazardous waste management, and toxic/hazardous substances management;
- Evaluation of campus-wide compliance with Clean Water Act regulations, including Oil Spill Prevention, Control and Countermeasure Plans and stormwater management
- Following the site visits, performance of a closing briefing with pertinent facility personnel to discuss the audit findings. During the briefing, observations made during the site visits were discussed, with obvious non-compliance issues identified and recommendations for corrective action presented. In addition to the non-compliance issues, areas of suspected non-compliance and other observations were discussed, with suggestions for further evaluation or modifications to existing practices made;
- Preparation of an audit report for the University that summarized the audit findings, classified the findings as principal concerns (obvious violations), secondary concerns (if continued, could increase the likelihood of a regulatory violation), or observations (noted for documentation purposes only), denoted the applicable regulatory citation (if any) for each finding, provided recommendations for corrective action, and outlined the schedule for corrective action or status of the corrective action (if already performed).
Stormwater BMP Design
The project involved design of a stormwater best management practice (BMP) for capture and treatment of post-construction stormwater runoff from a commercial development in Brunswick County, North Carolina. The stormwater BMP was designed pursuant to the requirements outlined in the North Carolina’s Coastal Stormwater Regulations and the Brunswick County Stormwater Regulations, and because post construction built-upon area exceeded 30% of the total developed area and post-development peak runoff exceeded pre-development peak runoff from a 1-year, 24-hour storm.
Stormwater runoff from the site’s impervious surfaces (roofs, parking lots, and vehicle and pedestrian travel areas) and a portion of the off-site drainage areas (existing roadways) was designed to be through surface and subsurface conveyance measures (curb-and gutter) and finished surface grade into two (2) subsurface infiltration trench systems installed on the northern and southern corners of the property. Each infiltration trench system was designed to capture and treat the first 1.5 inches of stormwater runoff from its respective drainage area, in accordance with State Coastal Stormwater Management requirements. Runoff in excess of the first 1.5 inches was designed to be routed via sheet surface flow into vegetated ditches constructed within the Right-of-Ways along the southern property line.
Each infiltration trench system consisted of ADS 30-inch diameter perforated piping. The piping was installed in a row-like fashion and manifolded into a header at the inlet end of each trench. The piping was installed on a bed of 10-inches of washed stone with a 2-inch thick stone covering. A 12-inch stone border was placed along the outer perimeter of the chamber matrix, and the chambers and stone will be installed within a filter fabric liner, and covered with a minimum 2-inch layer of compacted fill and 2 inches of asphalt pavement. The infiltration trenches were installed at a final depth of at least two feet above the seasonal high ground water table depth in accordance with State BMP requirements. The piping was designed with a traffic loading rating of ASHTO H-20 due to the thin layer of cover required to maintain final site grade and depth restrictions.
The stormwater management system was permitted through the North Carolina Division of Water Quality and Brunswick County, and was installed in the Fall of 2007.
The projects involved design and installation of chemical and ultraviolet light disinfection systems to treat effluent from Wastewater Treatment Plants at two North Carolina Department of Correction facilities. The disinfection systems were designed to improve effluent water quality through removal of Fecal Coliform from existing wastewater treatment processes. The systems employed ultraviolet light and chemical (chlorination and de-chlorination) disinfection processes, and were designed for peak flows of 0.5 MGD and 1.83 MGD, respectively. The ultraviolet light disinfection system employed a bank of lights installed within a stainless steel open channel, with outlet serpentine weir flow control and built-in automation. The chemical disinfection system employed tablet dissolution into a liquid feed injection system through a baffled open channel flow regime, with built-in automation (variable feed through ORP control). Both systems were permitted through the North Carolina Division of Water Quality’s Construction Grants and Loans Section. The ultraviolet light system was installed in late 2007, and is performing as designed. The chemical disinfection system began operation in Spring, 2009.
Duncklee & Dunham responded to releases of propylene glycol and water at a solar-panel field in Robeson County, North Carolina in 2012. A mixture of propylene glycol and water is used as a heat-transfer agent by the solar panels, which supply energy for use at an adjacent industrial plant. Duncklee & Dunham reported the release to the Fayetteville Regional Office of NCDENR, who told us they would not add the site to the Inactive Hazardous Sites Inventory if we completed the assessment remediation within three months. We calculated a proposed Interim Maximum Allowable Concentration in groundwater for propylene glycol and submitted it to NCDENR, which accepted this concentration one month later. We used this IMAC to calculate a protection-of-groundwater preliminary soil remediation goal. Within a month, NCDENR approved our calculations and established this PSRG. We completed our report and submitted it to the Fayetteville Regional Office within the timeframe allotted. NCDENR did not add this site to the IHSI.