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04/25/2001 17:19 19493668090 REGENESIS PAGE 02/13 <br /> REGENESIS <br /> April 25, 2001 <br /> Yemia Hashimoto <br /> GeoSyntec Consultants <br /> 2500 Newell Avenue, Suite 840 <br /> Walnut Creek, CA 94596 <br /> Fax: 925-943-2366, Phone: 925-943-3034 <br /> Subject: Acceleration of De-Nitrification and Natural Attenuation of Pesticides at a Western <br /> Farms Facility - Vernalis, CA Site <br /> Dear Ms. Hashimoto: <br /> We have reviewed the information that you provided for the above-referenced site. In the following <br /> sections, we provide design and cost information for a pilot scale test approach. This information <br /> should be considered preluninary since a number of assumptions have been trade concerning site <br /> conditions and the extent of the contaminant plume requiring remediation. We look forward to <br /> working with you to develop a specific strategy that meets your objectives_ <br /> Use of HRC to Accelerate Bioremediation <br /> Hydrogen Release Compound (HRC is used to enhance in situ biodeg adation rates for chlorinated <br /> hydrocarbons (CHs) by supporting anaerobic reductive dechlorination processes. As part of the <br /> aquifer acclimation process into conditions favorable for reductive dechlorination, nitrates (NO3) are <br /> used as an electron acceptor and a nutrient. In an aquifer being geochetnically reduced by the <br /> introduction of HRC, reduction of nitrate proceeds via the following pathway NO3 (nitrate)-+ N07 <br /> (nitrite)—> NO (nitric oxide)-+ N20 (nitrous oxide) Nz (nitrogen gas). The nitrogen gas is then <br /> lost to the environment. The nitrate metabolism can proceed by both assimilative and dissimilative <br /> pathways_ The assimilative pathway reduces only enough of the nitrate to satisfy the cells need of <br /> the nutrient for growth. The dissimilative pathway uses a comparatively large amount of electron <br /> acceptor, typically nitrate, sslfate or carbon dioxide. Microbes that use the dissimilative pathway <br /> either excrete ammonia or reduce the nitrate to nitrogen gas. The excreted ammonia is typically <br /> used by assimilative microbes as a nutrient and results in the ammonia becoming part of the cell. <br /> HRC is a proprietary polylactate ester that, upon being deposited into the subsurface, slowly <br /> releases lactate. Lactate is metabolized by naturally occurring microorgani=, resulting in the <br /> creation of anaerobic aquifer conditions and the production of hydrogen. Naturally occurring <br /> microorganisms capable of reductive dechlorination then use the hydrogen to progressively remove <br /> chlorine atoms from chlorinated hydrocarbon contaminants (i.e. convert tetrachloroethene [PCE] to <br /> trichloroethene [TCE] to dichloroethere [DCE] to vinyl chloride [VC] to e-thene). It is our opinion <br /> 1011 Calle Sombra • San Clemente, CA 92673-6244 ■ TOU 949.366.8000 • fax: 949.366.8090 <br /> arc@regenesis.com • www.regenesis.com <br />