ARCHIVED REPORTS XR0012495 - Laserfiche WebLink

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Ms Mary Meays P Imams January 12, 1995 (94-47-8620) Groundwater Monitoring Wells Fugro proposes to install four 4-inch-diameter, 25-foot-deep, groundwater monitoring wells as shown on Figure 1 There will be two wells installed crossgradient, one installed downgradient of the site, and one installed near the eastern service bay The latter well may also be used for vapor extraction The direction of groundwater flow was estimated during Phases 1 and 2 of the investigation by installing piezometers in three of the HydroPunch® (CPT-1, CPT-4, and CPT-6) locations and surveying their relative elevations The depth to groundwater was then measured (approximately 15-feet bg) The hydraulic gradient beneath the site is approximately 0 002 ft/ft to the north/northeast An upgradient monitoring well is not proposed at this time because its location would be disrupted during tank replacement activities scheduled in the near future Groundwater Monitonng Well Installation The wells will be installed using hollow-stem augers Soil samples will be collected at a minimum of five-foot intervals, unless significant changes in lithology, indications of petroleum hydrocarbons in the soil, or water-bearing soils warrant more frequent sampling The samples will be geologically logged and inspected for volatile hydrocarbons, in the field, with a photo- ionization detector Selected representative soil samples will be prepared for analysis at a state- certified analytical laboratory At a minimum, the sample collected from just above groundwater will be submitted for analysis Groundwater monitoring wells will be constructed of 4-inch-diameter Schedule 40 PVC The screened interval will consist of 20 feet of 0 020-inch machine-slotted PVC The filter pack will be #3 sand from the base of the well up to one-foot above the top of the screen A 2-foot bentonite plug will separate the filter pack from the cement/5% bentonite surface seal A traffic- rated road box will protect the well head and locking cap Because of the screened interval lengths, these wells may also be used for vapor extraction Well elevations will be surveyed relative to a site benchmark Water levels will be measured and the wells purged and sampled according to SJCPHS/EHD requirements The groundwater samples will be analyzed for total petroleum hydrocarbons (TPH), as gasoline and benzene, toluene, ethylbenzene, and total xylenes (BTEX) Laboratory Analyses and Practical Quantitation Limits (PQL) Soil samples selected for analysis will be analyzed for • TPH, as gasoline, by modified EPA Method 8015 (PQL = 10 part-per-million (ppm) • BTEX by EPA Method 8020 (PQL = 0 005 ppm) 94478620 ADD -2-