Laserfiche WebLink
Attachment - Memo to GregV hn -4- 8 November 1989 <br /> Groundwater Assessment Rpo <br /> Kearney-KPF, San Joaquin County <br /> an aquifer test, then head losses may be of concern in determining <br /> representative aquifer parameters. If possible, monitor wells to be <br /> installed in the coarse-grained zones and to be used for aquifer testing <br /> should not be constructed with restrictive filter packs. <br /> 12. pp. 40, The sieve analyses in Table 12 indicate that the deep gravel zone is <br /> 41 relatively clean (containing less than five percent fines) and is fairly <br /> well graded. Because of these conditions, future wells installed in <br /> this interval could be naturally developed. <br /> 13. p. 46 Four shallow monitor wells (KS-1, KS-4, KS-5 and KS-6) were installed <br /> by Hargis in April 1989. These wells had 20 feet of screen across the <br /> interval from about 50 to 70 feet BGS. These wells were not installed <br /> at a lower horizon than previously installed walls (i .e. , wells TP-IA, <br /> TP-2A and TP-3A were installed in 1988 to a depth of about 70 feet BGS) . <br /> The ground water level in April 1989 was approximately 60 feet BGS where <br /> only ten feet of the screen interval was saturated. Two of the four <br /> KS-series monitor wells were dry by August 1989. This indicates that <br /> although a 20-foot screen interval was allowed, the screen length and <br /> screened horizon were inappropriate, particularly in view of the fact <br /> that there had been a documented and dramatic lowering of the ground <br /> water table at the site for the previous two years and that drought <br /> conditions were still prevailing in 1989. <br /> Because the historical record indicates that the ground water table has <br /> been at least twenty feet lower than current levels and because drought <br /> conditions and dewatering on the upper aquifer may continue in the <br /> future, screen lengths twenty feet or longer and at horizons below about <br /> 70 feet in depth are warranted for future shallow monitor wells. In <br /> addition, long screen lengths for these monitor wells are justifiable <br /> because a downward vertical gradient has been established and reported <br /> (pp 19-22) , and cross-contamination of lower water bearing zones is not <br /> of concern as the intermediate zone contains VOCs in concentrations <br /> similar to the shallow zone. Because this site is regulated by the <br /> Resource Conservation and Recovery Act (RCRA) , post-closure monitoring <br /> is estimated to be 30 years for closure in-place. By installing future <br /> monitor wells with long screen lengths, the facility should be able to <br /> use these wells for longer periods, in spite of a regionally dewatering <br /> aquifer. <br /> The facility should also consider an alternate well design which is <br /> blank casing between shorter screen length intervals. The annular <br /> space opposite the blank casing would be sealed. A packer would be <br /> placed in the blank casing interval to allow isolation of a selected <br /> screened interval . The lithology of the shallow portion of the upper <br /> aquifer consists of silty clay to clayey silt interbedded layers and <br /> does not contain distinct thick coarse grained layers. This well design <br /> would allow a single well to be used in fluctuating ground water <br /> conditions. <br /> 14. p. 46 Because only two out of 16 shallow monitor wells/piezometers have not <br /> gone dry, the facility may need to install additional shallow wells in <br /> areas previously monitored, so that the VOC plume can continue to be <br />