To: PRB Committee From: CDM Smith Date: April 4, 2013 Subject: Technical Memorandum No.1: Evaluation Criteria for the Permeable Reactive Barrier (PRB) Pilot Project - Final CDM Smith is pleased to present Technical Memorandum No. 1: Evaluation Criteria for the Permeable Reactive Barrier (PRB) Pilot Project. This is the first of six technical memorandums that will culminate with the recommendation of two PRB demonstration sites. Technical Memorandum No. 1 discusses the findings from Tasks 1.1.10, 1.1.11, and 1.1.12 of the contract scope of work and includes the following sections: Section 1 – Summary of Existing PRB Knowledge Base Section 2 – Environmental Permitting / Approval Requirements of PRBs Section 3 – Potential Down-Gradient Impacts of PRBs Section 4 – Summary Section 5 – Summary of Comments from March 13, 2013 Project Meeting Section 6 – Works Cited 1.0 Summary of Existing PRB Knowledge The following is a summary of existing PRB research that has been performed, specifically relating to the removal of nitrate in groundwater. The focus of this research includes the following aspects: Available and proven PRB technologies implemented for the removal of nitrate Performance metrics of operating PRBs Reliability of PRBs to remove nitrate with scientific and regulatory certainty Important design and siting considerations Applicability of PRBs for treatment of nitrate in groundwater in Falmouth, Massachusetts 1.1 Existing PRB Systems for Removal of Nitrate The following section provides an overview on the types of PRBs that are currently identified as successful technologies for the removal of nitrate in groundwater. Table 1-1 and Table 1-2 include a comprehensive list of PRB studies that were conducted specifically to evaluate the effectiveness of nitrate removal, along with other design factors such as system longevity, hydrogeological and PRB Committee April 4, 2013 Page 2 geologic impacts, environmental impacts, and multi-contaminant impacts on PRB performance. Table 1-1 includes full scale and pilot scale PRB installations and Table 1-2 provides a list of laboratory scale studies. In total, CDM Smith has identified 17 pilot scale PRB installations designed to study the efficacy of nitrate removal in groundwater, amongst other design consideration, and 10 full scale installations, not all of which were solely designed to remove nitrate but all evaluated nitrate removal to some extent. In most instances, when the PRBs identified in Table 1-1 were designed to treat additional contaminants, those contaminants included chlorinated solvents and inorganics and are identified by the multi-PRB designation. These pilot and full scale PRBs are discussed further in Section 1.2. 1.1.1 Configurations There are several types and configurations of PRBs that currently exist and that have been found to be successful in the removal of nitrate in groundwater. Configurations of PRB installations can include any one of the following (The Interstate Technology & Regulatory Council, 2011): Continuous PRB: Reactive media is spread across the width and vertical extent of the contaminant plume Funnel-and-gate: Uses low permeability media to direct the groundwater to the treatment zone In situ reactive vessels: Uses a funnel or trench to direct the groundwater flow into the reactive vessel In most instances, PRBs are constructed vertically to intercept horizontal groundwater flow but horizontal PRBs can also be constructed with high permeability media to capture groundwater flowing vertically. 1.1.2 Reactive Media The type of PRB most commonly investigated for the removal efficacy of nitrate is with wood-based organic carbon reactive media. Multiple bench, pilot and full-scale installations have used this type of media as the substrate for biological reduction of nitrate. This media offers a number of advantages, including low cost, being readily available, and sometimes allowing the reuse of waste materials (e.g., mulch, compost). In some instances, PRBs using organic carbon reactive media may need to be rejuvenated after a certain number of years of operation, as was the case for the mixture of mushroom compost, woodchips and soybean oil at a PRB installed in McGregor, TX. This installation was primarily designed for perchlorate reduction but also assessed effectiveness of nitrate removal. Although the PRB was still performing satisfactorily after four years of operation, metrics were developed to plan for rejuvenation with emulsified vegetable oil due to slowing removal rates. Conversely, several organic carbon based reactive media PRBs have been operating for over an extended period of time and have not needed rejuvenation ((Kaszuba, et al., 2004), (Roberston, Vogan, & Lombardo, 2008), (Roberston, Blowes, Ptacek, & Cherry, 2000), (Robertson, Ptacek, & Brown, 2009)). The need to rejuvenate will also depend greatly on the existing conditions of the chosen sites, and can be assessed during the pilot testing. PRB Committee April 4, 2013 Page 3 Table 1-1 Full Scale and Pilot Scale PRBs Year Study Dimensions of Scale of Lifetime of PRB at Authors Title of Study/Report Location Reactive Media Initiated PRB (HxLxW) Implementation time of Report Treatability Study of Reactive polyelectrolyte- Materials to Remediate Ground 3 months (column impregnated porous Water Contaminated with Los Alamos Batch scale, tests) Conca et al. 2002 gravel, Apatite II layer, 12.5”x24.5”2” Radionuclides, Metals and Nitrates National Lab bench and pilot 100 days (2-D Aquifer layer of pecan shells, in a Four-Component Permeable Box Test) limestone gravel layer Reactive Barrier Nitrate Removal in NITREXTM Permeable Reactive Barriers Waquoit Bay, NITREXTM (Woodchips Bizzari, Lauren 2007 6.5’x66’x10’ Pilot scale 2 years Investigating Denitrification Using a Falmouth, MA and lime) 15 NO3 Tracer Western Groundwater Nitrate Removal Using Pilot scale (and Fahrner, Sabrina 2002 Australia (by Sawdust 6.5’x558’x5’ Over a year a Bioremediation Trench column tests) the coast) Nitrate Removal for On-Lot Sewage Hagerty, Paul; Bench and pilot Treatment Systems: The POINTTM unknown Lab Sawdust Unknown Unknown Taylor, James scale System Design, Installation, and Los Alamos 10% cottonseed meal, 10’&20’ Approximately one Kaszuba, John P., Performance of a Multi-layered National Lab, 65% pecan shells, and 2004 (depending on Full scale year (10 year design et al. Permeable Reactive Barrier, Los Mortandad 25% pea gravel (by the cell)x23’x17’ life) Alamos National Laboratory Canyon volume) W.D. Robertson, J.L. Nitrate Removal Rates in a 15-Year- Southern sand and wood particle Vogan, and P.S. Old Permeable Reactive Barrier 2008 Ontario (Long 2.5’x4’x2’ Pilot scale 15 years (sawdust) mixture Lombardo Treating Septic System Nitrate Point site) Waquoit Bay Effectiveness of Reactive Barriers and Childs NITREXTM (Woodchips 5’x40’x6’ Pilot scale and Vallino et al. for Reducing N-Loading to the 2008 3 years River and lime) 2.5’x65’x12’ bench scale Coastal Zone Falmouth, MA PRB Committee April 4, 2013 Page 4 Table 1-1 (Cont’d) Full Scale and Pilot Scale PRBs Year Study Dimensions of Scale of Lifetime of PRB at Authors Title of Study/Report Location Reactive Media Initiated PRB (HxLxW) Implementation time of Report The Effects of Seawater Intrusion on Microbial Nitrate and Sulfate Reduction within a NITREXTM Waquoit Bay NITREXTM (Woodchips Vincent, Angela 2006 5’x40’x6’ Pilot scale 1 year Permeable Reactive Barrier Falmouth, MA and lime) Designed to Mitigate Groundwater N-Pollution Schmidt, Casey; Efficacy of a denitrification wall to Alachua, 2012 Sand and sawdust 6’x181’x5.5’ Pilot scale 1.5 years Clark, Mark treat continuously high nitrate loads Florida High-Permeability Layers for Southern Robertson et al. Remediation of Ground Water; Go 2005 Wood particles 6.5’x4’x6’ Pilot scale 3 months Ontario Wide, Not Deep Wood decomposition after five Waquoit Bay years in anaerobic nitrate rich and Childs NITREXTM (Woodchips 5’x40’x6’ Feinberg, Daniel groundwaters: Implications for 2010 Pilot scale 5 years River and lime) 2.5’x65’x12’ lifetime of Nitrex™ Permeable Falmouth, MA Reactive Barriers Influence of NIRTEX barrier on groundwater flow paths, dissolved Waquoit Bay NITREXTM (Woodchips Moreau, Sabrina 2005 5’x40’x6’ Pilot scale Less than a year organic carbon and nitrate Falmouth, MA and lime) concentrations Upflow Reactors for Riparian Zone Southwestern Fine and Coarse wood 20 months and 4 Van Driel et al. 2006 3.5’x3.5’x3.5’ Pilot scale Denitrification Ontario particles months Hydraulic constraints on the performance of a groundwater Farm in New Shipper et al. 2004 Sawdust 10’x131’x10’ Pilot Scale 141 days denitrification wall for nitrate Zealand removal from shallow groundwater Denitrification of Agricultural Southern Fine and Coarse wood 26 months and 20 Van Driel et al. Drainage Using Wood-Based 2006 10’x131’x10’ Pilot scale Ontario particles months Reactors Several Wood−Based Filter for Nitrate NITREXTM (Woodchips Robertson et al. 2005 locations, unknown Full scale 3 to 5 years Removal in Septic Systems and lime) Ontario PRB Committee April 4, 2013 Page 5 Table 1-1 (Cont’d) Full Scale and Pilot Scale PRBs Year Study Dimensions of Scale of Lifetime of PRB at Authors Title of Study/Report Location Reactive Media Initiated PRB (HxLxW) Implementation time of Report Long-Term Performance of In Situ Several Wood mulch, sawdust, Robertson et al. Reactive Barriers for Nitrate 2000 locations, unknown Full scale 6 to 7 years leaf compost Remediation Ontario Geochemical and Hydrogeological Impacts of a Wood Particle Barrier Southwestern 3’x26’x8’ Robertson et al. 2007 Coarse wood particles Pilot scale Unknown Treating Nitrate and Perchlorate in Ontario Ground Water In Situ Denitrification of Septic- Robertson, W.; Southwestern System Nitrate Using Reactive 1995 Sawdust 5’x26’x26’ Pilot scale 1 year Cherry, J. Ontario Porous Media Barriers: Field Trials Nitrogen Removal from Landfill Robertson, W.; Leachate Using an Infiltration Bed Toronto, 1999 Sawdust 3.5’x42.5’x14’ Pilot scale 3 years Anderson, M. Coupled with a Denitrification Ontario Barrier Robertson, W.; In-Stream Bioreactor for Southwestern 2009 Woodchips 3.5’x65’x8’ Pilot scale 1.5 years Merkley, L.