Laserfiche WebLink
5 The Thornton Municipal Supply Well No 2 is located 115 feet from the former tank pit <br /> and 85 feet from well MW4 The well is completed to a depth of 245 feet with 14-inch <br /> diameter steel casing which is perforated from 135 to 150 feet, 160 to 185 feet, and 225 to <br /> 235 feet The well sand pack extends from 0 to 245 feet bgs A sanitary surface seal was <br /> installed which includes a 30 inch conductor pipe cemented in place from 0 to 70 feet bgs <br /> The well log indicates the first significant impervious strata was encountered from <br /> approximately 60 to 94 feet bgs during drilling activities On May 17, 1982, a field <br /> inspection of the well indicated the static groundwater level at the time was 34 9 feet bgs <br /> and when pumping the water table dropped to 77 4 feet bgs, a draw down of <br /> approximately 42 5 feet <br />' 6 Contaminants remaining in the vadose zone appear to threaten mass reduction of dissolved <br /> petroleum hydrocarbons in the vicinity of MW4 <br /> 7 Although not presently impacted by petroleum hydrocarbons, the close proximity of the <br /> dissolved petroleum hydrocarbon plume provides a potential health threat to the nearby <br /> Thornton Municipal Supply Well No 2 located approximately 85 feet from monitoring <br /> well MW4 <br /> 10.0 REMEDIAL ALTERNATIVES <br /> Based on the results of previous investigations, Smith Technology has considered three remedial <br /> alternatives for soil and groundwater Soil and groundwater remedial alternatives include natural <br /> attenuation, excavation of remaining petroleum impacted soil, and in-situ vapor extraction with air <br /> sparging A summary of each alternative is presented below <br /> 10.1 Natural Attenuation <br />' Natural attenuation, also known as passive bioremediation or intrinsic bioremediation, is a passive <br /> remedial approach that depends upon natural processes to degrade and dissipate petroleum <br /> constituents in soil and in groundwater Through biodegradation the actual reduction of <br />' petroleum constituent mass is realized <br /> Several detailed field studies have been performed examining indicators of intrinsic bioremediation <br />' and identify factors which significantly effect the rate and extent of bioremediation (Buscheck and <br /> others, 1993, McAllister and Chiang, 1994, Borden and others, 1995, Buscheck and Alcantar, <br /> 1995) Through these studies and on-going research on the factors which control biodegradation, <br /> it is now understood that dissolved petroleum hydrocarbons in groundwater will biodegrade, <br /> without artificial enhancement, due to the presence of naturally occurring (indigenous) <br /> microorganisms Technical protocols for implementing and monitoring intrinsic bioremediation <br /> studies in groundwater have been developed by the US Air Force and Chevron Corporation <br />' Intrinsic bioremediation in brief, is the use of indigenous microorganisms to degrade contaminates <br /> which have been released into the subsurface The biodegradation of the contaminants is <br /> w 1943261reporU\sumrpt doe 7 <br /> SMTH <br /> 1 <br />