WORK PLANS - Laserfiche WebLink

Home Browse Search

Former Thrifty Co.Station No.172 Workplan for Additional Soil and Groundwater Assessment May 8,2017 be dependent on lithology observed during the drilling activities. Once the appropriate length of casing and well screen are installed, a filter pack consisting of #3 sand or equivalent will be emplaced in the annular space surrounding the well casing, extending approximately two feet above the top of the well screen, over which, a 3-foot thick layer of hydrated bentonite chips will be placed. The remainder of the annular space will be backfilled with cement grout to a depth of approximately one foot bgs. The well casing will be set within flush-mounted traffic-rated well vault. General field procedures are included in Appendix B. One monitoring well proposed to be screened in the shallow zone will be installed at the location shown on Figure 3. The borehole will be advanced using 8-inch diameter hollow stem auger drilling equipment and completed with 2-inch diameter schedule 40 PVC casing, with a well screen consisting of 0.010-inch slot screen. Based on previous site assessment activities, ATC's recommended monitoring well construction details are presented in Table 1; however, the precise depth and screened interval of the monitoring well will be dependent on lithology observed during the drilling activities. Once the appropriate length of casing and well screen are installed, a filter pack consisting of#3 sand or equivalent will be emplaced in the annular space surrounding the well casing, extending approximately two feet above the top of the well screen, over which, a 3-foot thick layer of hydrated bentonite chips will be placed. The remainder of the annular space will be backfilled with cement grout to a depth of approximately one foot bgs. The well casing will be set within a flush-mounted traffic- rated well vault. General field procedures are included in Appendix B. • Sample Selection and Analysis. Soil samples will be collected at 5-foot intervals, from the borings for logging purposes and samples will be sent under chain-of-custody procedures to a California State-certified laboratory. At least two samples from each boring will be analyzed for TPPH (a.k.a. TPHg), BTEX, MTBE, ETBE, TBA, TAME, DIPE, EDB, 1,2-DCA and ethanol by EPA Method 8260. At least one soil sample will be analyzed for Title 22 Metals to establish background metals concentrations. A composite soil sample will also be collected and analyzed for soil profiling and disposal purposes. • Well Development and Surveying. The monitoring well will be developed by rigorously surging the well over the length of the screen interval and by purging until the extracted groundwater is deemed clear (up to a maximum of 10 casing volumes of water from the well). Following installation activities, the newly installed monitoring well will be surveyed by a licensed surveyor to a local benchmark relative to mean sea level. Survey data including elevation, longitude, and latitude will be uploaded to the state GeoTracker database. • Soil Boring Advancement. ATC will contract with a C-57 licensed drilling company to advance one exploratory soil boring in the immediate vicinity of the former waste oil tank using direct push technology (Figure 2). Soil will be collected from the boring for lithologic logging and field screening using a 4-foot by 1.5-inch outside diameter core sampler equipped with an acetate liner. Soil samples will be screened using a photo- ionization detector (PID) and any noticeable staining will be noted. Soil samples for Iithological description will be collected at 4-foot intervals to the total depth explored, approximately 20 feet bgs. The soil boring will then be grouted to the surface by 8