DESIGN OF A UV OXIDATION SYSTEM FOR TREATMENT OF TCE-CONTAMINATED GROUNDWATER

Several design issues were encountered by EPA and Metcalf & Eddy durin g the design of a UV oxidation system for treatment of TCE-contaminate d groundwater at the Groveland Wells Superfund Site. The issues includ ed: 1) the need to execute treatability studies of the UV oxidation te chnology as required by the Record of Decision, to provide data needed to develop a more accurate design and cost estimate; 2) the need to e valuate pretreatment options for removal of inorganics prior to UV oxi dation, both to minimize maintenance problems and to ensure that appli cable discharge limits for metals would be met; 3) the need to evaluat e measures for ensuring that residual oxidant(s) in the effluent from the UV oxidation system would not cause the effluent to exceed toxicit y limits for discharge to surface water, and 4) the need to develop a performance specification for the UV oxidation system which would ensu re fair competition among vendors of UV oxidation systems, while also ensuring that EPA would receive a system which was cost-efficient and able to meet discharge limits. Metcalf & Eddy competitively procured a UV oxidation vendor to perform bench-scale treatability studies on si te groundwater and designed a pretreatment system consisting of an equ alization tank inclined plate clarifier, and dual media filters. The s pecification for the UV oxidation system was written to allow the UV o xidation vendor maximum flexibility while still ensuring that discharg e limits for VOCs of concern and toxicity are met. The specification a llows for the use of hydrogen peroxide, ozone, or a combination ofthe two as the oxidant and requires that the effluent not exceed toxicity limits. The vendor is allowed to meet toxicity limits either by using oxidant concentrations that result in a non-toxic residual or by insta lling a module to reduce residual oxidant concentration(s) to non-toxi c levels before discharge. This approach allows the vendor to use proc ess alternatives that result in an overall system which minimizes cost s.