SITE INFORMATION AND CORRESPONDENCE_FILE 1

Home Browse Search

09%04/97 15:39 GR%GSI—SRCTO 12094640136 p03 Response to SJCEHD tetter of August 26, 1997-Former Unocnt Station No. 0187 September 4, 1997 • A total of nine wells have been installed at this site. Wells U-1 and U-3 were installed with screen intervals of 25 feet (30 to 55 feet), and well U-2 was installed with a screen interval of 30 feet (30 to 60 feet). SJCEHD did not object to these well constructions. Wells U-4 through U-8 were installed with 20 fent of screen (35 to 55 feet). As constructed, well U-9 (30 feet of screen) is not inconsistent with other wells installed at the site. • At the time wells U-1 through U-3 were installed (August 1994), groundwater was measured at approximately 48 feet below ground surface(ogs). Groundwater in well U-9 is currently measured at approximately 32 to 33 feet bgs (August 31, 1997), a rise of 15 to 16 feet_ The screens in existing wells U-4 through U-8 (screened with 20 feet of screen, 35 to 55 feet)are submerged. • If well U-9 had been constructed with only 20 feet of screen as requested by SJCEHD, the well would have been semoed from 25 to 45 feet bgs. If groundwater levels return to historic lows (approximately 48 feet bgs), the well would be dry and could not be used to monitor groundwater quality. As installed (with 30 feet of screen), well U-9 is screened to allow collection of groundwater samples over the entire range of known groundwater fluctuation. • well U-9 is not constructed in such a way as to pass through an aquitard or to interconnect two hydrogeologic units. The boring log indicates the well is screened entirely within the uppermost water bearing zone. This well (U-9) was installed in an attempt to define the dissolved hydrocarbon plume downgradient of the onsite source area. Well U-9 and the other onsite and offsite wells may be monitored and sampled for sometime. If the well goes dry, it will no longer provide information on potential migration of the plume. Therefore, the construction of this downgradient well is critical, and we believe site conditions justified the lnstdllation of 30 feet of well screen. Should SJCEHD disagree with our rationale based on the site conditions,please provide a written explanation of your rationale and proposed course of action. a:li - URZAWpl 2 .