89-1554 - Laserfiche WebLink

Home Browse Search

6w k Chevron U.S.A. - Page 4 We propose to install a total of 3 exploratory soil borings at the subject property at -� the locations shown on the site plan which is included as Plate 2 of this proposal. The purpose of those soil borings would be to provide data regarding the presence and vertical + extent of contamination in subsoils if encountered, and installation of ground water monitoring wells. Field screening of the subsoils samples will help to describe contamination persistence In a vertical relationship to ground water. A cursory review of published ground water data suggests ground water occurs beneath the subject property at depths ranging from approximately 70 to 80 feet belgw the existing grade. Each exploratory soil boring would be completed as a ground water monitoring well, which will allow sampling of the ground water, and to identify ground water depths, gradient, direction of flow, ground water quality, and long term monitoring. Please refer to the map at the end of the text for proposed well locations. Drilling will be performed utilizing a truck mounted drill rig equipped with flight hollow-stem auger. A Dames & Moore geologist or engineer will be present during drilling to assist in obtaining relatively undisturbed samples of the subsurface materials, to maintain a log of borings, to field screen samples with a device capable of detecting volatile 1 organic hydrocarbons as a trace gas, and to make observations of the site conditions. Subsoils will be sampled at approximate 5 foot Intervals commencing at an approximate }, {✓7 } ' ` depth of p esM: oboa Modified s was lined with bleves or rings. The sampler will ,,�;:�. be advanced by blows from a 140 pound hammer falling 30 inches. Upon retrieval, samples will be retained for chemical analysis, and will be capped with a plastic cap over a teflon seal, and taped at each end. The samples will be placed into a cooler chest under proper chain of custody protocol for shipment to the analytical laboratory. - Between sampling attempts, the sampler will be dissassembled and washed in a trisodium phosphate (TSP) solution, rinsed twice with purified water, and reassembled with brass rings to minimize the potential of spreading contaminants among samples, if any were present. Soils will be classified according to the Unified Soil Classification System. A health and safety plan will be prepared for the work to be accomplished at the subject property prior to commencement of the field portion of the investigation. The ground water monitoring wells would be installed by means of a the truck mounted drilling rig utilizing hollow-stem auger. Each monitoring well would be constructed using -- 4 inch flush-thread pvc schedule 40 well pipe. Screened intervals would be constructed utilizing schedule 40 pvc flush-thread 0.020 inch well screen. It is anticipated that the screened interval would consist of sufficient screening to accommodate a ten foot screened intern a ove an ow Die encoun I ere oun wa er wel. The screen length in any well inst on-site wo a a- um of 20 feet in en"flig . A No. 3_,graded sand would be J use „filter media�ro a screened in and comp eted to an gguivalent de t of Z feet above the_te1L4geen. A seal composed of bentonite pellets would be p aced to an , -- approximate thickness of 3 feet atop the filter media. Thc_=maining would be r JZackfilled with a sanaLs�ment_slurry with 3(Ye bentonite added from the seal to, the urface� ; vault. A locking well head would be Installed, and a secure surface vault would be placed _ at grade for well security. The design of the proposed ground water monitoring wells is in general compliance with the State of California Department of Water Resources Bulletin 74- 88 (Draft) Monitoring Well Standards (DWR 163907). Please refer to Plate 3 at the end of the text which illustrates typical monitoring well construction. I i