Laserfiche WebLink
Stockton Charter Way Commingled Plume - 2 - 6 March 2025 <br /> Table 1: S mmary of Proposed ART Wells <br /> Casing Screen Interval Current Sand Bentonite Cement <br /> Well Location Diameter ft bgs) DTW (ft bgs) (ft bgs) (ft bgs) <br /> (in) Vadose GW (ft bgs) <br /> Near Min <br /> ART-9 SMW-10-81 & 12.94 <br /> SMW-10-117 <br /> adjacent prop Max 4-10 & 3-4 & 1-3 & <br /> Near 6 5-10 70-90 17.96 68-90 10-12 & 12-66 <br /> SMW-19-81 & 66-68 <br /> ART-10 SMW-19-120Avq <br /> Texacoprop) 14.48 <br /> GW= groundwater; DTW= depth to groundwater; in= inches; ft bgs= feet below ground surface; <br /> Min= minimum; Max= maximum; Avg= average <br /> Table 2: Ma and October 2024 Groundwater Data for MW-10 and MW-19 Well Groups <br /> DTW Last Benzene (ug/L) MTBE u /L TBA u /L <br /> Well Hist. Hist. Hist. <br /> (ft bTOC) Sampled Max Current Max Current Max Current <br /> SMW-10-81 14.56 4Q24 17,000 <5 295 195 117 115 <br /> (2Q10) (2Q24 (2Q24) <br /> 330 115 <br /> SMW-10-117 14.71 2Q24 25 <br /> 15 2.55 Q24 2024 <br /> 10,000 2 190 391 307 <br /> SMW-19-81 14.30 4Q24 4Q02 26.5 2Q23 4Q23 <br /> SMW-19-120 15.00 2Q24 (3Q02 <1 Q24) 30.2 (2Q 1 21.1 <br /> LTCP Thresholds Class 2 3,000 1,000 -- <br /> f4 <br /> Class 4 1,000 1,000 -- <br /> DTW= depth to groundwater; TPHg= total petroleum hydrocarbons as gasoline; MTBE= <br /> methyl tert butyl ether; TBA= tert butyl alcohol; Hist. Max= historical maximum; LTCP = Low <br /> Threat UST Case Closure Policy; 2Q24= second quarter 2024; ft= feet; bTOC= below top of <br /> casing; ug/L= micrograms per liter; bold= current value is above the laboratory reporting limit; <br /> MM= current value is above LTCP Thresholds; •- 40= current value is historical <br /> maximum <br /> While Staff did not request that you address MTBE in the MW-10 well group in our <br /> November 2024 directive letter, MTBE concentrations in these wells warrant <br /> augmenting the proposed scope of work. While MTBE concentrations in monitoring <br /> wells SMW-10-81 and SMW-10-117 are both below Low-Threat Closure Policy (LTCP) <br /> Groundwater Criteria Class 2 and 4 thresholds, concentrations in both wells are <br /> generally increasing, as shown in the Graphs 1 and 2 below. Both wells contained <br /> historical maximum MTBE concentrations of 295 micrograms per liter (ug/L) and 330 <br /> ug/L, respectively in May 2024. At that time, these wells both contained 115 ug/L tert <br /> butyl alcohol (TBA), which is a historical maximum for well SMW-10-117. In order to <br />