DOE/ORO/2327 Oak Ridge Reservation Annual Site Environmental ...

Annual Site Environmental Report
Fig. 3.42. Percentage of derived concentration guides (DCGs) at surface
water surveillance locations, 2009.
Figures 3.43 and 3.44 illustrate the concentrations of TCE (trichloroethene, trichloroethylene) and
total 1,2-DCE (dichloroethene, cis-1,2-dichloroethylene, trans 1,2-dichloroethylene) from K-1700 (which
monitors Mitchell Branch), the only surface water monitoring location where VOCs are regularly
detected. Concentrations of TCE and total 1,2-DCE are below the Tennessee General Water Quality
Criteria (WQC) for Recreation, Organisms Only (300 µg/L for TCE and 10,000 µg/L for trans 1,2-DCE),
(Appendix D, Table D.2), which are appropriate standards for Mitchell Branch. Moreover, the standards
for 1,2-DCE apply only to the trans form of 1,2-DCE; almost all of the 1,2-DCE is in the cis-isomer. In
addition, vinyl chloride has sometimes been detected in Mitchell Branch water (Fig. 3.45). VOCs have
been detected in groundwater in the vicinity of Mitchell Branch and in building sumps discharging into
storm water outfalls that discharge into the stream; however, storm drain network monitoring generally
has not detected these compounds in the storm water discharges. When detected, the concentrations are
lower than in the stream. Therefore, it appears that the primary source of these compounds is
contaminated groundwater.
Surface water has been routinely sampled by DOE contractors and TDEC for several years as part of
environmental monitoring programs. The DOE contractor surface water sampling program is conducted
in accordance with DOE order surveillance program guidance. In data collected as part of the DOE
contractor’s sampling effort, dry weather levels of total chromium over the past 10 years (Fig. 3.46) have
been shown to be generally less than 0.01 mg/L, or in some instances, at nondetectable levels. Results
from routine surface water monitoring conducted in fall 2006 showed a significant increase in the total
chromium level in Mitchell Branch but still below the WQC for total chromium. Sampling performed in
the spring of 2007 by DOE contractors and TDEC indicated that chromium levels had increased above the
levels found in the fall 2006 sampling. The highest total chromium result was a value of 140 µg/L, which
exceeded the then-applicable WQC of 100 µg/L. Based on these sampling results, a joint effort among
DOE contractor, TDEC surface water, and Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA) program personnel was initiated in June 2007. Historical maps and photographs,
utility and waste process pipeline drawings, monitoring records for building sumps, and other sources of
information were reviewed to search for possible uses and sources of chromium in the Mitchell Branch
watershed. A chromium collection system employing two extraction wells and pumps was installed to
pump water from the vicinity of storm water outfall 170 for treatment at the CNF. Since this system was
installed, chromium levels in Mitchell Branch have dropped dramatically, with levels being routinely
measured at less than 3 µg/L.
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