# Estimation of River Flow Rate for Lower Three Runs Creek at MarTin, South Carolina

## Background

As part of CDC's SRS Dose Reconstruction Project, ATL has included
exposure pathways to surface water contaminated with water discharges
from SRS. One of the CDC-specified exposure locations occurs on Lower
Three Runs Creek at the town of Martin, South Carolina (LTRC-Martin). To
calculate exposure, data are needed in two areas: (1) the flowrate of
the creek at LTRC-Martin and (2) the quantities of radionuclides
discharged. This analysis addresses the approach for determining
flowrates at LTRC-Martin and presents the methodology, assumptions, and
analytical results (1).[^1]

The modeling approach for this project requires the use of constant
annual creek flowrates and constant annual releases. Therefore, an
average annual creek flowrate value is needed for each year of modeled
releases, from 1954 to 1992. Because direct measured flowrate data for
LTRC-Martin do not appear to be available, ATL estimated flowrates based
on other available flowrate measurements (2) (3).[^2]

## Analysis

ATL identified two sets of data usable in estimating 1954-1992
LTRC-Martin average flowrate values:

-   LTRC-Snelling monthly flowrate data for 1974 -- 2001 (4).

-   LTRC-Martin monthly flowrate data for 1998 -- 2001 (2).

USGS flowrate monitoring station at LTRC-Snelling is located
approximately 6 miles downstream of the Par Pond dam and 8 miles
upstream of the LTRC-Martin flowrate monitoring station (See Figures 1
and 2).

When comparing the monthly flowrate data from LTRC-Martin to
LTRC-Snelling for 1998 to 2001, it was observed that the flowrate at
Martin was generally twice the flowrate at Snelling. This ratio can be
used to estimate the flowrate of LTRC-Martin based upon the data
obtained for the LTRC-Snelling using the following basic formula:

\[LTRC-Martin Flowrate\] = \[LTRC-Snelling Flowrate\] x
\[Martin-to-Snelling Ratio\]

The ratios calculated by comparing the monthly flowrate at LTRC-Martin
and LTRC-Snelling are shown in Attachment 2. In calculating the
Martin-to-Snelling ratio, only data from 1998 to 2000 is considered
since no data is available at Martin for October, November, and
December, 2001, omitting an entire season of data. However, a review of
the 2001 LTRC-Martin monthly flowrates shows them to be comparable to
those for 1998 to 2000. The calculated ratios are summarized in Table
S-1.

The standard deviation and corresponding percent error show that the
average ratio is relatively consistent over the 1998 -- 2000 period,
taking into account possible seasonal and annual fluctuations for this
time period.

![](media/image1.png){width="5.73125in" height="6.554166666666666in"}

Figure S‑1 LRTC-Snelling Monitoring Station Location

![](media/image2.png){width="5.151388888888889in"
height="5.895833333333333in"}

Figure S‑2 LRTC-Martin Monitoring Station Location

Table S‑1 Average Ratio of Monthly Flowrate Data

  ----------------------- ----------------------- -----------------------
  Martin:Snelling from    Standard Deviation      Percent Error
  1998 to 2000                                    

  2.2                     0.3                     16.0%
  ----------------------- ----------------------- -----------------------

**1974 -- 1992 Flowrates.** For the purposes of dose reconstruction, it
is assumed that the average Martin-to-Snelling ratio is applicable for
the entire project study period. Attachment 3 shows the calculated
monthly and annual flowrates at LTRC-Martin for the 1974 -- 1992 period,
based on the measured monthly flowrates at LTRC-Snelling during the 1974
-- 1992 period and the average Martin-to-Snelling ratio. The calculated
annual flowrate value is used as the LTRC-Martin flowrate in the dose
reconstruction modeling calculations.

**1954 -- 1973 Flowrates.** The approach described above was suitable
for the 1974 -- 1992 period because flowrate measurements for
LTRC-Snelling were available for this period. To estimate flowrates for
the first part of the modeled period (no flowrate measurement data for
the 1954 -- 1973 period are available), this approach had to be
adjusted.

For this calculation, , it was assumed that the monthly flowrate at
LTRC-Snelling during the 1954 -- 1973 period was equal to the average
monthly flowrate during the 1974 -- 1992 period (calculated in
Attachment 1). LTRC-Martin flowrates for this period were then
calculated using the 1974 -- 1992 average monthly flowrate and the
previously calculated Martin-to-Snelling ratio. The resulting
LTRC-Martin monthly and annual flowrates for the 1954 -- 1973 period are
shown in Attachment 3.

**Data Gaps.** In applying the approaches described above, two minor
data gaps had to be addressed. Flowrate measurements for LTRC-Snelling
were not available for January, February, and March of 1974, and October
of 1984, as shown by shaded cells in Attachment 1. For the 1974 data
gap, it was assumed that the average monthly flowrates for the
corresponding months for the period 1975 to 1992 could be applied to
1974. For the 1984 data gap, it was assumed that the October 1984
flowrate is the average of the flowrate of September and November for
that year. Data gaps for January through May of 1997, and October
through December of 2001 are not addressed because flowrates are not
required for these time periods to determine flowrates at LTRC-Martin
from 1954 through 1992.

## References

1.  RAC, 2001. Risk Assessment Corporation. Final Report, Savannah River
    Site Environmental Dose Reconstruction Project, Phase II: Source
    Term Calculation and Ingestion Pathway Data Retrieval, Evaluation of
    Materials Released from Savannah River Site. U.S. Centers for
    Disease Control and Prevention. April 30, 2001.

2.  USGS, 2003a. Monthly Streamflow Statistics for South Carolina, USGS
    02197415 Lower Three Runs at Martin, SC \[online\]. 2003a. \[cited
    2003 March 28\]. Available from URL:
    *<http://waterdata.usgs.gov/sc/nwis/monthly/?site_no=02197415>.*

3.  Heffner J. Re: LTRC Flow Rate \[unpublished email\]. Savannah River
    Site. March 24, 2003.

4.  USGS, 2003b. Monthly Streamflow Statistics for South Carolina, USGS
    02197400 Lower Three Runs near Snelling, SC \[online\]. 2003b.
    \[cited 2003 March 28\]. Available from URL:
    [*http://waterdata.usgs.gov/sc/nwis/monthly/?site_no=02197400*](http://waterdata.usgs.gov/sc/nwis/monthly/?site_no=02197400)

[^1]: Data on the quantities of discharged radionuclides used in this
    analysis are based on Risk Assessment Corporation 2001 and
    supporting references.

[^2]: USGS monitoring data for LTRC-Martin for 1954-1992 are not
    available (2). SRS also does not have LTRC-Martin flowrate data (3).