Funnel and Gate System with Biotreatment
- System consists of six treatment gates, constructed in three rows of two gates each; Waterloo sheet piling located on both sides of gates to direct groundwater flow through gates
- Biotreatment includes injection of air and nutrients into the gates; air injection began in October 2000, with air injected into all six gates; nutrient injection was performed at Gate 1, using a solution that contained potassium nitrate and potassium phosphate from late June 2001 to October 2002
- As of June 2003, flow of groundwater was directly through treatment Gates 1 and 2, but at an obtuse angle through Gates 3-6
- Free product sumps are used to collect free product creosote prior to its entering the treatment gates
- Groundwater monitoring is performed using 7 shallow groundwater monitoring wells and 8 containment performance monitoring wells
- System expected to be in place approximately 20 years
- Results are available through June 2003
- As of June 2003, groundwater concentrations for the contaminants of concern had been reduced to below detection limits in several wells; however, concentrations of all five contaminants remained above the cleanup goals in one or more monitoring wells
- With the exception of naphthalene, detected concentrations ranged from about 1.4 to 7.9 µg/L; naphthalene concentrations were as high as 6,100 µg/L
- Naphthalene concentration data for September 2000 to June 2003 provided for one monitoring well show that concentrations of this contaminant have remained relatively constant over a three-year period (in the range of 5,000 to 7,000 µg/L, with a concentration of 6,100 µg/L as of June 2003)
- The concentration of microbial degraders has been decreasing in Gates 1 and 2 over a period of 2 1/3 years, indicating that the biodegradation may be decreasing
The Moss- American Site, located in Milwaukee, Wisconsin, is approximately 88 acres in size, and consists of a former wood preserving facility, portions of the Little Menomonee River, and adjacent flood plain soils. The discharge of wastes from wood preserving operations resulted in the contamination of groundwater at the site with PAHs, including creosote, and BTEX from No. 6 fuel oil. A mixture of creosote and fuel oil were present as free product in the subsurface at the site. The site was added to the National Priorities List in 1984, and a record of decision (ROD) was signed in 1990, with an Explanation of Significant Difference (ESD) signed in 1997 changing soil treatment to thermal desorption and groundwater treatment to a biotreatment funnel and gate system. Free product recovery was performed from 1996 to 1999, with about 12,500 gallons of liquid extracted. In addition, contaminated soil was excavated and treated using thermal desorption.
The biotreatment funnel and gate system consists of six treatment gates, with Waterloo sheet piling located on both sides of the gates to direct groundwater flow. Operation of the system began in October 2000, with the injection of air, followed by the addition of nutrients in Gate 1 in June 2001. In addition, sumps are being used to collect any free product prior to its entering the treatment gates. During the three years of operation for which data are available, the concentration of benzene, benzo(a)pyrene, benzo(b)fluoranthene, and chrysene have been reduced to near or below cleanup goals in most monitoring wells. As of June 2003, naphthalene concentrations were as high as 6,100 µg/L. The concentration of microbial degraders has been decreasing in Gates 1 and 2 over a period of 2 1/3 years, indicating that biodegradation may be decreasing. The PRP contractor suggested that the relatively fine-grained soil and low groundwater flow rates have lead to low oxygen conditions and inhibited the ability to introduce nutrients and other additives. To address the low levels of dissolved oxygen, well packers were installed in Treatment Gate 5 injection wells in June 2000. However, this did not lead to substantial increases in DO levels in those wells. The contractor is continuing to evaluate alternatives for air injection into the treatment gates.