2000-05-22_PERMIT FILE - M2000002 (17)

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Holt Belbnund • • Pttge 4 Mobile Po'emLr Concrete, /rrc Mnt~ 22. 2000 According to both TCHD and CDPHE, future sampling of gravel pit discharge will most likely occur in conjunction with the ongoing ground watet' quality testing. O/lter Anulytes. TCHD tested well 485A on the Tanabe property in October 1991 for a suite of 37 analytes both associated and not associated with RMA source contamination. These included volatile halogenated compounds, volatile hydrocarbons, volatile aromatic organics compounds, organophosphorus compounds (DIMP), organosulfur- herbicide related compounds, triazines, organochlorine pesticides, metal ions and cations. Table 2 lists the analytes that were not detected above their respective detection limits in October 1991. The results show only calcium, chloride, copper, DIMP, Fluoride, potassium, magnesium, sodium, sulfate, and nitrate as exceeding detection limits (Table 3). Only Fluoride was detected in 1991 above CGWS. Fluoride exceedance maps from 1997 show an isolated area of exceedance located south and hydrologically cross gradient from the Tanabe property. TCHD was not aware of any subsequent testing that includes this full suite of analytes due to the great number of non-detections encountered. The analytical data reviewed specifically addresses comments submitted to the DMG on the MPC mine permit application b}' Dorsey and Whitney, LLP and shows that various pesticides and other analytes either are not present in ground water or are present at concentrations below CGWS. Action Levels Dri/:king Water. In 1989, the EPA established a Lifetime Health Advisory of 600 Ng/L with a chronic Reference Dose of 0.08 mg/kg/day fot' DIMP in drinking water, the only currently known significant pathway for DIMP. In 1994, the Colorado Water Quality Control Commission (WQCC) adopted 8 Ng/L as the interim standard for drinking water. Despite some scientific disagreement over the validity of [he reports, both Colorado and [he EPA are currently using the 8 pg/L drinking water standard for the basis of plume delineation, cleanup, and assessment of health risks. According to the CDPHE and TCHD, drinking water is the main pathway for DIMP human exposure in the Offpos[ Study Area. Consequently, private domestic alluvial wells within the Offpost Study Area have been connected to South Adams County Water and Sanitation District water supply or provided bottled water since 1990. In doing so, CDPHE eliminated [he human exposure pathways because none of the ground water within the DIMP fringe area is used for drinking water. Sarface Water. Surface water on the South Platter River located proximate to [he Tanabe Property is classified as part of Segment IS on the river. A designated use in Segment IS is "water storage." Classifications and Numeric Standards, South Platte River Basin, 5 CCR 1001-38. The WQCC has promulgated a surface water standard of 8 Ng/L for such use in Segment I5. Basic Standards for Organic Chemicals, 5 CCR 1001-31. This is identical to the CGWS. Another pathway ideptified recently is the consumption of vegetables grown and watered with ground water containine DIMP concentrations above the CGWS. Known as the "veggie uptake" pathway, CDPHE found this pathway for DIMP exposure to be insignificant in a study released in mid-April 2000. ERO Resources Corporation