A Novel Method to Attain Groundwater Compliance at a Former Pesticide Formulating Facility
K.A. Hoenke, Chevron Environmental Management Company, San Ramon, CA 
Andy Davis, Geomega, Boulder, CO     

Pesticide and VOC Attenuation at Marzone Superfund Site

Ellen M. Haggerty, Blasland, Bouck & Lee, Inc., 8 South River Road, Cranbury, NJ 08512, Tel: 609-860-0590 x240, Fax: 609-860-8007, Email: emh@bbl-inc.com
Allen C. Just, P.E., Blasland, Bouck & Lee, Inc., 2600 Michelson Drive, Suite 830, Irvine, CA  92612, Tel: 949-474-9052, Fax: 949-474-9345, Email: acj@bbl-inc.com
Karl Hoenke, Chevron Environmental Management Company, 6001 Bollinger Canyon Road, K-2080, San Ramon, CA  94583, Tel: 925-842-9259, Fax: 925-842-0213, Email:  karlhoenke@chevrontexaco.com

The selected groundwater remedy for the Marzone Superfund Site was an in-situ, funnel-and-gate system.  The system was installed in 1998 and is currently operating to remove the constituents of concern (COCs) from groundwater.  Groundwater COCs include α-BHC, β-BHC, γ-BHC, DDD, DDT, methyl parathion, ethylbenzene, and xylenes.  Impacted groundwater is collected in the collection channel, conveyed via underground piping to two of the three activated carbon adsorption reactors operated in series.   The treated groundwater is then conveyed via underground piping through the soil-bentonite slurry wall and to the distribution channel.  Prior to start-up, the projected life of the primary carbon reactor was approximately six months.  The system has operated for more than 64 months without a carbon change-out.  In July 2003, a dedicated, discrete sampling device was installed within the activated carbon bed of the primary reactor to collect depth-specific groundwater samples and vertically profile the dissolved-phase constituents within the primary reactor. Samples collected from the discrete sampling device indicated nondetectable pesticide concentrations and only nominal and/or nondetectable VOC concentrations.  The analytical results suggest that contaminants were being removed from groundwater within the initial two foot of the carbon bed.  Preliminary depth-specific microbial studies within the carbon bed have provided results that do not correlate with contaminant distribution.  A more detailed investigation is being conducted to evaluate the potential mechanisms for pesticide and VOC attenuation within the primary reactor.  The primary reactor provides a unique opportunity to study the natural attenuation processes that are likely contributing to the decreasing dissolved-phase contaminant concentrations observed across the Site.

A Novel Method to Attain Groundwater Compliance at a Former Pesticide Formulating Facility

K.A. Hoenke, Chevron Environmental Management Company, 6001 Bollinger Canyon Road, San Ramon, CA  94583, Tel: 925-842-9259, Email: khoe@chevrontexaco.com
Andy Davis, Geomega, 2995 Baseline Road, Suite 202, Boulder, CO  80303

Natural attenuation (NA) has become an integral element of site closure in the U.S. While NA of many compounds can be demonstrated unambiguously, it is more complex for purportedly recalcitrant compounds with multiple isomers and low remedial criteria. Such was the situation at a site in Orlando, Florida, where technical grade lindane had been formulated for ~20 years. This product often contains a-BHC (60-70%), b-BHC (5-12%), g-BHC (10-15%), d-BHC (6-10%) each of which is regulated at very low (ng/l) concentrations. At the site it was necessary to evaluate natural attenuation for each isomer following a removal action to meet regulatory standards in groundwater. This analysis was complicated by the rapid groundwater velocities (1 foot/day) and water table oscillations (± 1.5m), that were inversely correlated with groundwater BHC concentrations (i.e., higher water table = lower BHC concentrations). However, when BHCs were evaluated on a total mass basis, a clear decline (10% per year) over seven years was apparent (r² = 0.84) following first-order kinetics. Over this period, the plume center of mass did not migrate in the direction of groundwater flow, remaining within 30 m of its centroid, compared to contemporaneous rapid transit across the site of an MTBE plume originating upgradient. The plume stability in conjunction with the decreasing BHC mass allowed the U.S. EPA and Florida DEP to accept that no further action was necessary to protect potential downgradient receptors. This site represents a novel approach to attaining compliance that would be appropriate for others with similar quasi-recalcitrant compounds.

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