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Mr. Riddle • - 4 - Claim 4 - Claim No. 13324 Based on my review, I noted that monitoring well MW-3 was installed through the center of the former UST excavation using the hollow stem auger drilling method. A soil boring (SB-3), previously performed at this location, identified very high concentrations of TPH-G, TPH-D and TRPH in a soil sample collected from six feet (ft) below land surface (bls). My review of the Well Completion Log for MW-3 noted that this well was completed with a well screen extending from 7 to 32 ft. bls with a sand pack extending from 5 to 32.5 ft. bls. I also noted that the subsurface lithology at the location consisted of a lean clay from approximately 5 to 13 ft. bgs, silt from 13 to 16 ft. bls and a silty clay from approximately 16 to 26 ft. bls. At approximately 26 ft. bls, groundwater is encountered within a well-graded sand layer. Based on this information and the persistent presence of free product in this well, I am concerned that the long well screen and associated sand pack may be providing a conduit for the migration of contamination through the low permeable sediments (clays) and down to groundwater. I recommend that this well be properly abandoned and replaced with an appropriately constructed monitoring well with a shorter well screen and sand pack. Issue #3 1 agree with your statement that groundwater samples from'MW-3 have never contained PCE and that the former waste oil is not the apparent source of the PCE. Issue#4 Regarding the ineligible PCE, I believe that it is highly unlikely that the PCE identified in the groundwater beneath the site is associated with the unauthorized release from the waste oil UST. I base this conclusion on the fact that laboratory analysis of soil samples collected from SB-3, installed through the center of the former waste oil UST excavation, did not identify detectable concentrations of PCE. In addition, laboratory analyses of groundwater samples collected from MW-3, also installed through the center of the former waste oil UST excavation, have never identified detectable concentrations of PCE. Finally, my review found that the highest concentration of PCE has consistently been identified in monitoring wells MW-6 and MW-7. Both of these wells are located approximately 100 feet upgradient from the former UST location. You also stated that that any concentration of PCE less than 1,000 parts per million (ppm) in waste oil should be considered a de minimus quantity in petroleum, I again must disagree. I do not believe that the reference you cite applies in this case. However, this is a moot point given that PCE is an ineligible substance and it is not likely that the PCE identified in the groundwater beneath the site is related to the waste oil UST. California f'riviranm eatalPrateclion Agency P„a Recyc%dPopei