Laserfiche WebLink
SENT BY:EMCON 6-16-98 1:55PM EMCON SACRAMENTO :x 5; 6 <br /> Mr. Ronald Rowe <br /> June 12, 1998 Project 20C42-001.026 <br /> Page 3 <br /> I <br /> firmly lagged for the first batch. This overlap provided continuity in the <br /> grout seal. In addition, �e second batch of grout was placed within the <br /> 2-hour window for grout tetup. <br /> • The well casing should have been removed prior to tremie pipe removal. <br /> - The tremie pipe was remved first, followed by the removal of well casing. <br /> Approximately 44 feel if casing were pulled. When the wellhead was <br /> removed, an additional 3 feet of casing were removed, for a total of 47 feet. <br /> The casing between 45 and 55 feet bgs was extensively corroded with <br /> numerous holes present. Iliese holes acted as perforations to allow the grout <br /> to extend to the formationj walls. After the casing was removed, a firm tag at <br /> 10 feet bgs confirmed thQ grout level. The order of tremie pipe and casing <br /> removal did not adversely affect the integrity of the grout seal. <br /> • The well destruction fell into, the category of Section 13.17.6 of the PHS/EHD <br /> Well Standards, which requikes complete removal of the well casing, screen, <br /> and filter pack. <br /> - Removal of the well casin and absence of filter pack in the interval to <br /> 55 feet is consistent with t e intent of Section 13.17.6. <br /> - Review of subsurface data collected during previous CPT and drilling <br /> programs identified a low-permeability, silty clay unit located between <br /> approximately 37 and 47 tet bgs. This unit correlates with the B-C aquitard <br /> by Harding Lawson Assoi iates (MLA) during subsurface assessment at the <br /> ARCO Products Company Distribution Terminal. Correlation of subsurface <br /> data(CPT profiles and bor ng logs) at the Tesoro Terminal shows this unit is <br /> encountered at approxima ely 38 feet bgs and is approximately 10 feet in <br /> thickness HLA repo ed laboratory permeabilities for soil samples <br /> collected li um the B-C aqt itard ranging from 1.43F,-6 to 7.61E-8. The grout <br /> seal encompasses this intcryal. <br /> The presence of the low-I rnreability unit (B-C aquitard) and the grout seal <br /> acres-, this interval provid a barrier inhibiting future vertical migration of <br /> the dissolved petroleum hydrocarbons present in the first- and second- <br /> encountered water-bearing zones into deeper cones along the well bore. <br /> Thus, the source areas repr4sented by these shallow water-bearing zones and <br /> no longer in communicatio with deeper aquifer units. <br /> I <br /> I <br /> SAON T10A C'421OC42W12.6Ar-981cbd1:I I EMCOA <br /> Rm 0,June 12,1998 F <br />