ARCHIVED REPORTS_XR0010585 - Laserfiche WebLink

Home Browse Search

f sohnst3 WWI CASE STUDY After site assessment with cone penetrometer testing(CFT°) Expedited Assessment of an equipment, the investigators identified two ages of alluvium beneath the site Because of the contrast in permeability MTBE Release between the two ages of alluvium, the site hydrogeoiogist h November 1999, low concentrations of MTBE were suspected that the MTBE plume may have been migrating detected in a private industrial well located downgradient Preferentially within the upper more permeable unit Little from a known leaking underground fuel storage tank was known about the off-site location of the MTBE plume (LUST} The site is located in a narrow valley underlain Because the impacted supply well is not directly by young alluvial seciments Groundwater occurs at a depth downgradient of the LUST site, the hydrogeologist of approximately 8 feet, and flows toward the southeast suspected that the dissolved plume may have dnfted at a velocity estimated to be about half a foot per day A southeast, away from the well(following the regional flow map depicting the LUST and vicinity is shown in Figure 1 gradient), in the two months since the impacted well was Pnor to beginning the field investigation, a conceptual shut down model of the site was developed that incorporated all The site owner authorized the consultant to install a relevant information about the tank construction, release transect of 13 CMT wells midway between the LUST and history, prior land use, operating records of nearby water the impacted well Because of the uncertainty in the wells, as well as published information regarding the location of the dissolved plume, the transect was installed geology,hydrogeology,and groundwater extraction in the man arc downgradient of the known release area(Figure 1) site vicinity was also reviewed The CMT wells were installed on 25-foot centers, and extended to an average depth of 50 feet The wells were installed in continuously-cored borings drilled with a sonic anil rig A 4-inch-diameter temporary steel casing was advanced, which was ideal for installing CMT wells Thirteen CMT wells were installed in just four days at the locatons shown in Figure 1 Groundwater elevations were measured In the CMT wells, confirming the downward hydraulic gradient A thin, narrow plume of MTBE was identified, flowing within the shallow alluvium(Figure 4) • .I Non-detect(ND)values for MTBE were recorded in sampling points on all sides of the plume, thus ensuring that no portion of the plume escaped the mcrutonng network Using the MTBE concentration data and the hydrawic Figure I Site layout A transecr of 23 CiTT wells was installed properties of the shallow alluvium, the flux of MTBE between the LUST and the mpacted water we1L The transect was emanating from the source area was estimated This oriented perpendicular to the groundwater flow direction but calculation proved to be a powerful tray of assessing the was extenaed in an arc to ensure that no portion of the suspected impact of the dissolved contaminant plume on the plume escaped derectio downgradient industrial well N4t0 LL47A M tO rw N" I I rW MI.-4 N" 11W Y41, Yl t3 16.13 UL-14 (CPT IO) /Cirri/ (CR-i K3"-2) ICAr-tit Wr-o (�-q 0 L i w 4n w no a y` tr 0. ul 7 1 SON!0 M a O FM Mi ' �[1lGLNYXOI�ipL� 1® Figure 4 Isoconcentratton contours of MTBE measured in groundwater samples collected friom the CWT wells A thin,narrow plume of dissolved . MTBE was identified within the shallow younger alluvium, In this figure, the MTBE plume ars flowing out of the page toward the reader Pn„>ea in tom= For further mformanon, please contact_SoliAst Canada Ltd- 09/00 35 Todd Raid Georgetown, ON, Crrnarda L7G 4R8 E-mail wisaianentsQsolanst com 1 TEL (905)873-2255 or(800)661-2023 FAX +l(905)873-1992 or(800)516-90$I FYe6 www so lrru2mm $r