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f - �s February 14, 1991 San Joaquin County Public Health Services Page 2 Exceltech Project No.3-49132-31 gasoline odor which was coming from this soil, the excavation was carefully continued. The clayey soil was removed in layers u and layer as encounund to tered.tered.The underlying sandnated with o gasoline1 did not the underlying sandy soli a glow appear to be contaminated with e. gasoline and later laboratory analyses showed tUhito�a the a sin With th e removal ra o al of the conducted l ated offal area, veral samples were btaineddoof the soils above and whit Qwere within this clayey oil for the increase nuring these Pmo suture wase of enot chin some ofthe sandy lsoils�closer to the examinations, a clayey soil; however, at no time was free water obs��served at the interfact between these two sol types. Borings logs and monitoring well construction details combined with field observationsrptypical of river the cross sections depicted in Figures Z, 3, and 4. The result is a stratigraphy y Ynstance P s. deposits consisting of be a continuouds s bed,bed,separates twos, and sandy soilIn this s beneath theasite.soil,As which may or may soil to the rainwaterinfiltrates waer could be slowed.t Some ohe f it may fl w laterally on soil, t,ie surface of this clayey movement As shown in the crass sections,the bongs soil and become localized depending on the geology- s layer at a shallower depth. No water was for NIW-2,MW-3,and MW-4 encountered this clayey y observed clayey the lower hat appears rid to be possibly a localized buried channils were encountered. in MW-1 the el where water ma�havie deeper clayey:.ell at upper auifer. collected creating an In addition to farming the base of this upper sandy unit,this clayey soil may also serve as an upper confining unit to the lower er sandy dwatEr levels located above the slottedior. screened sectio s of the explain the presence grow of the slotted sections of monitoring wells. As shown in the cross lsecctio 5,arhrning his clayey-sail-to-sandy-soil,interface 3, and MW-4 are located in this clayey Y Q allows samplingof petroleum hydrocarbons flowing along the top of this aquifer. In light of this information,it is our opinion that groundwater arenito ess wells MW-2, MW-3, at and MW-4 are properly installed and no ne couther ntered water above necessary and bye o! w the ce.Yey layer, Groundwater monitoring well MW-1,which was destroyed. MW-1 should be replaced with two groundwater monitoring wells,pperpe screened in the lower main aquifer and one screened in what is construed to be a localized upper p" aquifer. Amended Work Plan an,Phase 3 Work Plan for Exceltech, Inc., proposes to amend its pravictober submitted 30 1990P1as detailed below. Two Soil and Groundwater Investigation, dated usO groundwater monitoring wells to monitor thellocalizeed to pd perchelace d aquifer and a dendwater eper well to monitor shallow well will bedesignedUnder the direction of an Exceltech geologist,the deeper well will be the lower aquifer(Figure 5). upper 20 feet will be solid polyvinyl chloride drilled r a depth of approximately 30 feet. The layer. The shallow well (pVC)casing and the lower 10 feet will be slotted topping i inhthe clayey sil observed,in borings will be drilled to a depth of approximately t feet, bottoming Y Y drilled near this location. The anpr[oringf well designswill be lmay be modifiedid pVC casing bythe on-sitte Exceltethe lower 10 feet will ch slotted. Boring depths a les will be analyzed as geologist as site conditions indicate. Soil and groundwater same