SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Mr. Joe Aldridge - 3 - 22 April 2009 NuStar Terminals Stockton Facility f • The source of TPHg, benzene, and MTBE detected in boring NIS-14 and NS-21 is on the KMEP facility. NuStar recommends installing B and C zone wells collocated with four borings downgradient of the Site and obtaining D-zone grab groundwater samples from three of the locations. The grab groundwater samples will be prepared for laboratory analysis using a glass filter and silica gel cleanup to remove non petroleum organics that may have been the cause of elevated TPHd concentrations in grab groundwater samples obtained from the borings. Our comments are presented below. 1. After two mobilizations and a proposed third, the vertical extent of pollution at this Site still has not been delineated. The collection of D-zone grab groundwater samples at the previous locations of NS-18, NS-15, and NS-21, and south of PS/MW-17 will not accomplish vertical delineation since NuStar is proposing to sample no deeper than the depths from which samples have already been collected from these borings. As stated in our 12 June 2008 letter, delineation means identifying the point of non-detect (ND) and would have been most efficiently achieved using the U.S. Environmental Protection Agency (EPA's) triad method. This method allows for immediate assessment of laboratory analytical results and advancement of deeper borings, if necessary. 2. We do not concur that another monitoring well is needed upgradient from PS/MW-17. Groundwater COC concentrations in PS/MW-17 are mostly below method detection limits. A D-zone or deeper well, however, is needed at boring NS-11 where elevated concentrations of TPH have been identified in the C-zone and likely extend to the D-zone. 3. The Investigation Report offers conclusions which appear to contradict or be unsupported by the earlier statements in the text. Page 14 states that there are no clear pathways to the D-zone from the MacSteel aboveground storage tank, but Page 15 attributes contamination observed in D-zone boring NS-21 to a source at the MacSteel facility. Page 14 attributes the elevated concentrations of TPHd in NS-21 to steep vertical migration from monitoring well SP/M-9 on the KMEP site, which is located just upgradient from NuStar. On Page 15, however, NuStar states that a pathway does not exist from the KMEP facility to NS-21, although cross-section B-B' identifies laterally continuous gravel and a water- bearing unit that extend from upgradient of KMEP directly to NS-21. A deeper laterally continuous sand unit is truncated from the western end of the cross-section where it is extrapolated to exist in other cross sections. NuStar explains that the variable thicknesses and depths observed in units that were previously thought to be laterally continuous show a lack of continuity. Page 12 states that the reclassified D-zone is a less significant pathway consisting of thinner and less continuous sand layers. While it is obvious that the flood plain sediments that underlie the Site vicinity are not arranged in a "layer cake" formation, the data do not show that this configuration makes them any less conductive than previously thought. The steep vertical migration from the A/B to the C- and D-zones described by NuStar communicates that pollution migrated through multiple fine-grained units to travel from the shallow source to