SITE INFORMATION AND CORRESPONDENCE

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Attachment - Memo to Greg V--In -3- 8 November 1989 Groundwater Assessment Repo Kearney-KPF, San Joaquin County Because ground water levels have declined in the past year, two of the four new shallow monitor wells (KS-1 and KS-5) have gone dry since installation. As of 'July 1989, the two functioning monitor wells (KS- 4 and KS-6) have only two to three feet of a 20-foot screen interval remaining below the water table. Historical ground water levels from wells within a three mile radius of the facility and with total depths and/or screen intervals between 140 and 265 feet below ground surface (BGS) , indicate that the ground water table has been deeper than current water levels. Refer to Table 1 (attached) . These wells show an historical decline in the water table to the lowest recorded elevation between -70 and -80 feet MSL in the mid to late 1970s. This elevation is approximately 20 to 30 feet lower than current ground water levels. If current drought conditions and dewatering of the aquifer continues, it is possible that the ground water levels could again decline to these elevations. 8. p. 37 The background concentration for all constituents listed in Table 8, except mercury, are within the ranges reported in Table 3.1 of The Soil Chemistry of Hazardous Materials by James Dragun. The background concentration for mercury slightly exceeds the maximum of the range listed in Table 3.1 . Concentrations of mercury were also found to exceed both the maximum and statistical background concentrations in soil boring samples at the site. Mercuric oxide has been a process chemical at this facility (Table 2). 9. p. 39 The concentration of VOCs listed in Table 10 are in general similar to those VOC concentrations detected in previous deep borings, T-6 and SB-6. However, concentrations of tetrachloroethylene (PCE) were higher in the samples from T-6. 10. p. 40 There is a discrepancy between the results of the sieve analyses and the descriptions of materials from KSH-1. The sample collected from KSH-1 at a depth of 204 to 214 feet BGS consisted of sand, gravel and cobbles. However, Table 12 gives the results of the sieve analysis from this interval and shows 100 percent of the sample passing the 1-1/2 inch screen. This size is within the coarse gravel range (3 to 3/4 inches) in the Unified Soil Classification System. Other lithologic descriptions from the KSH boreholes also describe this zone as consisting of cobbles. It is possible that the angular fragments may be portions of larger size rocks which are broken during drilling. 11 . pp. 40, The report states that a coarser sand and larger slot size could have 41 been used in the intermediate and deep wells but that No. 16 sand and 0.020 inch slot screen were used and would not affect well yield. However, the sieve analyses in Table 12, when compared to the specifications of the No. 16 sand (Monterey Sand Company) on a grain size distribution graph, show that this sand is generally finer grained than the formation material , and therefore is restrictive. A restrictive filter pack can increase well losses. But because well losses increase as the pumping rate increases, the yield of the well may be affected by well losses. Because these wells are monitor wells, the yield of the well would not necessarily be of primary importance (as compared to a supply well) . However, if a monitor well is used for