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r (3.81 cm) perforated injection body. The overlying interval was sealed off fi•om the injection zone by a 2-ft (0.6 un) by 2-inch (S.1 cut) sealing packer, and the section below the perforated target interval was scaled by a 6-inch (15.2 cm) by 1.75-inch(4.4 (,m) pre- probe. After pumping the proportionate amount of IIRC material [approximately 10 pounds (4.5 I<g) per vertical, saturated foot] into tlnc formation, the probe was driven another two feel (0.6 nn) and the process repeated. The injection was accomplished by use of a hydraulically-powered, progressive cavity,Moyno puunp Willi a tlowrate of 1 to 2 gallons per minute(3,8 to 7.8 liters per minute)at a pressure ranging from 200 to 300 Ibs. per square in. (14.1 to 21.2 Kg per square em). This method of injection, while a time consuming process, assures an even injection of the HRC material over the entire thickness of the target subsurface interval. We believe that this even H RC distribution is crucial to the success of the overall HRC injection project, particularly in low permeability aquifers. HRC material costs were approximately `(;31,200. Direct push boring costs, concrertc cutting and coring, site cleanup, field supervision, consulting oversight and design, and report writing costs were approximately $28,500. No future operating expenses, other than [lie expense of field collection and field and laboratory analysis of geucherr►ical parameters,were anticipated as a result Of tile HRC injection. PERFORMANCE MONITORING To document the effectiveness of HRC injection, quarterly sampling of the perched groundwater was continued as part of the response action. Prior to sample collcetion,the static perched groundwater elevation in all wells was measured and recorded. The monitoring wells to be sampled were purgcd utilizing TNRCC-approved low flow sampling techniques(Pols and Barcelona, 1996). subsequently, the monitoring wells to be sampled were purged by removing water using a peristaltic pump to ensure that representative perclied groundwater was collected. 'The wells were purged at low volumes until the parameters pH, conductivity, dissolved oxygen, temperature, turbidity, and oxidation reduction potential (as measured in the field during purging using a Horiba-22 water quality probe mounted in a now-through cell) were stabilised. Due to the low now purging, well drawdown was minimal [<0.3 ft ('0.1 m)l. All groundwater samples were obtained linin each well immediately upon the completion of purging of that well. C;roundwatcr elevation measurements taken during each sampling event document a consistent gradient direction toward tine southeast. Figure I provides it represcntativc illustration of groundwater gradient direction. Perched groundwater samples were collected from select monitoring wells and analyzed for each of the five COCs. During the most recent quarterly sampling events,monitoring Wells MW-3, MWA,MW-9,IvIW- 10, and MW-11 were sampled during each event. 'fhcse wells represent the wells nearest the source area and (lie most downgradient well. Figure 2 provides graphical presentatiun of the COC analytical results through time. In addition, geochemical analysis was performed on select samples to provide further evidence of biodegradation. Although dissolved-phase COCl will ultimately determine the effectiveness of the IIRC in program, analysis of geochemical properties was performed to provide additional evidence of HRC performance. Groundwater samples tiom monitoring wells MW-3, MW-11, MW-9, MW-10, and MW-