SITE INFORMATION AND CORRESPONDENCE

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s • 8) Total nitrogen is 33 ppm and phosphate is 11 ppm, as analyzed by AAS. Mass balance calculations for a [theoretical] plume 100 feet in length, 45 feet in width and 55 feet in depth, with an average hydrocarbon concentration of 1,000 ppm, and assuming a porosity of 19% (a very low estimate for medium- to fine-grained sand with silt), indicates that 41.7 pounds of nitrogen, 2.08 pounds of phosphate and less that 1 CFM of oxygen will be needed to convert 350 gallons of existing hydrocarbon into biomass. Currently at the site, there is 1,100 pounds of naturally occurring nitrogen (26 times more than required) and 367 pounds of naturally occurring phosphate (more than 176 times more than required). It should also be noted that both aerobic and anaerobic bacteria will be used in the inoculation(s), decreasing the importance of oxygen concentration in the soil. 9) The "radius of influence" of the bacteria is a function of soil type, hydrocarbon type and, most importantly, time. Theoretically, a single inoculation well within a plume would be sufficient for motile hydrocarbon-degrading bacteria to remediate the plume, given sufficient time. However, by increasing the inoculation-well density, larger numbers of bacteria are introduced and better dispersed within the plume, allowing for faster remediation. The"optimum"well spacing is thus dependant on the rate at which remediation is desired. Until such time as at least limited inoculation has been permitted, no site-specific data on the rate of bacterial migration and hydrocarbon mitigation can be obtained. The .hydrocarbons at this site are primarily gasoline and gasoline-breakdown products. The soil type is primarily medium- to fine-grained sand with some silt. Our review of existing literature and discussions with microbiologists lead us to conclude that motile bacteria, under optimal conditions, are able to migrate in excess of 15 feet within three to four weeks in medium- and fine-grained sands. Soils with a greater clay content and heavier hydrocarbons (diesel) would require a greater inoculation volume and well density. For example, in field tests conducted in 1989 and 1992 near Santa Barbara, California and Conway, Texas, bacteria migrated fifteen (15) feet through sand and five (5) feet through clay during the first three (3) months of remediation (James Hoeltgen,.Personal Communication; 1993). Inoculation wells at this site are located on approximately 15-foot centers. At the present time, we believe that this well density is appropriate for a one to two year remediation period. This estimate will be reviewed frequently during the early stages of remediation as monitoring data become available, and additional wells and/or monitoring points can be installed to accelerate the remediation as needed to maintain this schedule. 10) GeoAudit recommends the following additions to the existing monitoring program: A. Soil Borings (vicinity of inoculation wells; dates are approximate and based upon an inoculation date of February 1, 1994): 3 a..inxawn.n