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  • SAVAGE WELLTREATABILITY STUDY

    . . .

    Savage Well SiteMilf ord, NH

    Phase I - Technology Assessment

    October, 1989

    Prepared by:

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    hmm H M M A S S O C I A T E S , I N C .

    ENGINEERS, ENVIRONMENTAL CONSULTANTS & PLANNERS

  • HMM Ref. No. 2176-120/HAZ/2946

    November 9, 1989

    Richard GoehlertU. S. Environmental Protection AgencyJFK Federal Building, HSN-CAN5Boston, MA 02203-2311

    Subject: Rationale for Removal of the Pilot Plant Program from the Savage WellRI/FS Process

    Dear Mr. Goehlert:

    The purpose of this letter is to provide all parties with both the general and technicalrationale as to why the pilot plant program included in the Administrative Order shouldbe modified. Also included in this letter is the chronology of the events which led to thecurrent decision to remove the air stripping pilot tower from the project.

    General

    The pilot program was included in the Administrative Order at the request of the PRPGroup. This program was to include the installation of an 8" production well,performance of a 5-day pumping study, and the installation and operation of a 100-gpmair stripping tower to remove volatile organics. The decision to include this program wasbased on 1986 data and knowledge of the site conditions at that time. The primary intentwas to provide early treatment of the groundwater and to limit off-site migration ofcontaminants. The primary change being requested as a part of this correspondence isthe removal of the pilot air stripping tower component of the treatability studies.

    Chronology

    The remedial investigation field program started on November 23, 1988 with the approvalof the Project Operations Plan which provided for the commencement of a 2-phasegroundwater study in accordance with the work plan. The first phase of this programresulted in the installation of 36 monitoring wells and the collection and analysis of 54groundwater samples for volatile organics. Results were presented to EPA in two reportsdated March 28, 1989. The purpose of these reports was to provide a clear understandingof the existing conditions of the site and to help scope the Phase II program. Based onthese new data, the treatability study tasks commenced concurrent with the Phase IIprogram. This work was based on the VOC analysis available to date which was used as

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    input data in conducting computer modeling efforts to assist in the design of the airstripping pilot tower (size, air to water ratios, packing materials, emission rates, andtreated effluent quality for discharge). Based on a high concentration of VOCs and thespecific compounds detected in the Phase I program, both the efficiency of the airstripping tower and the emission rate became issues of concern. Specifically, it becameapparent that a 100-gpm pilot plant would require a tower over 25' high which wouldachieve an average efficiency of 95%, insufficient to meet the current MCL dischargelimitations. Based on these findings, HMM included an assessment of granular activatedcarbon, assessing mass transfer zones, contact times, and multicomponent adsorption.Computer modeling for this effort was conducted for vapor phase carbon to assess airemission limits for the air stripper and liquid phase carbon for effluent polishing to ensureachievement of the MCLs.

    Concurrent with the treatability study efforts, the Phase II groundwater monitoringprogram started in May of 1989. This program resulted in installation of 29 monitoringwells. The data were presented to EPA in a report dated August 1, 1989. This wasfollowed up by a Phase II groundwater sampling program which consisted of sampling 65groundwater wells. These data were presented to EPA in a report dated September 29,1989.

    The Phase II program focused on the heart of the plume identified in the Phase I program,included the analysis of chemical constituents, specifically VOCs, ABNs and metals, andthe investigation of physical influences of localized production well pumping. Two keyfindings resulted from that effort. First, there is a very high concentration of naturallyoccurring iron in the groundwater. The iron would oxidize out on the air stripper packingmaterial leading to precipitate and biological fouling of the packing material, ultimatelyresulting in degradation of the efficiency of the air stripper and a reduction in effluentquality. The second finding is that the cone of influence inferred from a 320 gpmproduction well is limited to approximately 300'. This would indicate that a 100 gpmpilot study would only impact a very small percentage of the plume and would not provideany significant long-term treatment benefit.

    Technical Basis and Recommendation

    A meeting was held on September 29, 1989, attended by EPA, HMM, NHDES, and amember of the PRP Group. Key issues discussed during that meeting are as follows.First, based on the results of the Phase II sampling program, there are new data that werenot available to the PRP Group in 1986. This includes the data for the VOCs whichindicate overall higher concentrations of contaminants that increase in concentrationwith depth. Additionally, data show high levels of iron. Both of these findings have adirect impact on the viability and operational efficiencies of an air stripping tower.Furthermore, these data indicate that additional components of treatment would need tobe included as part of the pilot program. This resultant expansion of the pilot studywould include the addition of pretreatment for metal precipitation and filtration in frontof the air stripper and, most likely, the addition of vapor phase carbon for controlling airemissions and liquid phase carbon for polishing of the effluent to ensure compliance withcurrent MCLs. This expansion is well beyond the scope of the original pilot studyproposal. Additionally, data relative to the transmissivity of the aquifer indicates that a100 gpm pumping well would provide only a fraction of the recovery necessary to impedethe flow of contaminants. In other words, the pilot plant program would not achieve theoriginal objectives of providing significant early treatment of the groundwater nor wouldit limit the off-site migration of contamination.

    2176-120/HAZ/2946 - 11/9/89

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    Additionally, while pilot studies can assist in selecting components of design prior toimplementation of a remedial alternative, pilot testing of a single unit process is notwarranted during the feasibility study. The advent of new proven computer modelingprograms allows rapid and cost-effective evaluation of individual unit processes relativeto efficiency and size based on the chemical constituents in the influent water. Theseindividual treatment units are then combined into an overall process train during thefeasibility study. It is the resultant treatment process train that should be pilot testedduring the design phase. Any treatability/pilot programs conducted at Savage during orafter the feasibility study should also focus on site-specific data for groundwaterrecovery.

    Recommendations

    The purpose of the treatability study is to supplement a feasibility study process and toaid in the selection of the most implementable, cost-effective remedial alternative. Thedata collected to date and the engineering effort conducted during the initial portion ofthe treatability study will be used in development and selection of the alternatives in thefeasibility study. Based on our current understanding of site conditions and remedialobjectives, it is HMM's recommendation that the air stripping pilot tower be removedfrom the program as it will not substantially improve the selection of alternatives norwill it significantly remediate the groundwater during this interim period and would onlycause an unnecessary delay in the project.

    There are two related components of the treatability study that should be carried forwardto improve the database for the feasibility study. First, it is recommended that a 5-daypumping study be conducted to further characterize aquifer hydraulics and to aid in thedevelopment of groundwater recovery systems. This step includes field studies necessaryto assess the hydrodynamics of the aquifer which are important factors in remedialalternative development. Secondly, based on the varying chemical constituents of theplume, it is also recommended that desorption coefficients be developed at two separatelocations within the aquifer near the OK Tool and Hitchiner facilities so that the overalltime frame for remediation of the aquifer can be evaluated. Soil column leaching studiesshould be conducted for each area to determine site-specific desorption coefficients forspecific contaminants in order to assess the method and time frame required to flushcontaminants through the soil column.

    If you have any questions, please do not hesitate to call me at (508) 371-4111.

    Sincerely,

    Richard C. CoteProject Manager

    RCC/c

    2176-120/HAZ/2946- 11/9/89

  • TABLE OF CONTENTS

    Page

    1.0 INTRODUCTION 1-1

    1.1 Technology Evaluation 1-1

    1.2 Computer Simulation Modeling 1-1

    2.0 TREATABILITY STUDIES 2-1

    2.1 Influent Sources 2-1

    2.2 Air Stripper Evaluation 2-5

    2.2.1 Experimental Design 2-5

    2.2.2 Results 2-6

    2.2.3 Minimum Tower Requirements (MCL) 2-11

    2.2.4 Loss of Tower Treatment Efficiency 2-11

    2.3 Vapor Phase Activated Carbon Evaluation 2-12

    2.3.1 Experimental Design 2-13

    2.3.2 Results 2-14

    2.3.3 Vapor Phase Carbon Considerations 2-14

    2.4 Liquid Phase Activated Carbon Evaluation 2-18

    2.4.1 Experimental Design 2-19

    2.4.2 Results 2-19

    3.0 CONCLUSIONS 3-1

    4.0 REFERENCES 4-1

    2176-060/HAZ/2926 - 11/9/89 -i-

  • SAVAGE WELL SITE TREATABILITY STUDY

    1.0 INTRODUCTION

    Th