FIELD DOCUMENTS_CASE 1 - Laserfiche WebLink

Home Browse Search

Monitoring Well Destruction and Soil and Groundwater Investigation Report US Can—Welty Road December 28,2010 Based on information obtained from the Water Well Drillers reports, four of the wells identified are presumed to be located either on site or down-gradient of the site: • A `domestic' well identified as being located"South of Vernalis Store" (Map ID 2), which is estimated to be approximately 50 feet from affected groundwater at soil boring SB-19 and screened from 190 to 210 feet bgs. This well was installed in 1977. • A `domestic' well(Map ID 3) listed on the Well Drillers reports as located at 35401 S. Welty Road. Based on the location sketch from the Water Well Drillers report, this well likely corresponds to the water supply well identified on Figure 2 as W-1. A sample was collected from this well in 1995 and the COPCs were not detected at or above the laboratory reporting limits. • Two `public' wells (Map IDs 5 and 6) located at 35275 S. Welty Road have screened intervals from 288 to 328 feet bgs and 320 to 340 feet bgs, respectively. Of the nine wells identified,three wells are located up-gradient or cross-gradient, and are not of concern. The up-gradient wells(Map IDs 1 and 4)are located at least 1,500 feet from the site (note that well identified as Map ID 4 may be beyond the 2000 foot search radius based on available information). The cross-gradient well (Map ID 7) is not a concern because it is screened interval from 225 to 245 feet bgs and has a 100-foot sanitary seal. Of the water supply wells identified in the search, the location of two of the wells could not be accurately located so these wells are listed only in the table. An `industrial' well located in Vernalis, California(no address)was identified during the search but a more exact location cannot be determined from the Well Drillers report. This well was installed in 1968 and oil was noted in the well log between 72 and 76 feet bgs. The DWR search identified a `domestic' well installed in 1975 and located at 3725 Welty Road,but this does not correspond to an existing address. 6. CONCLUSIONS AND RECOMMENDATIONS SAIC-Benham evaluated the results of this investigation and concludes the following regarding the nature and extent of affected soil and groundwater at the site: • All site monitoring wells have been properly destroyed. • The lateral extent of affected soil and groundwater west of affected Areas 1 and 2 has been delineated by borings SB-44 and SB-45,respectively. • With the exception of two detections that slightly exceed the very conservative naphthalene RSL (0.00055 mg/kg), the lateral extent of affected soil exceeding RSLs and ESLs east of Area 3 has been delineated by borings SB-46 and SB-47. • The lateral extent of affected groundwater north-northeast of Area 3 has been investigated to the extent practicable. The lateral extent of affected groundwater can be inferred based on down-gradient borings from prior investigations. Due to the age of HPP-BTR releases,the extent of affected groundwater is stable or decreasing and concentrations of dissolved constituents will gradually decrease as the petroleum hydrocarbon mass is depleted by natural attenuation. 6TheBenham Companies,LLC 541 wr, L a on ...,,od s.n� ry dca From SaonCo ro Sa!urnms