River Gauging Program

Datasets: River Gauging Program

Project Description

The goal of this project is to provide water quality data to the SMS4s (Horry County, Georgetown County and the city of Conway) that lie in HUC 03040206. These data are designed to support the NPDES Phase II Stormwater programs undertaken by these SMS4s as covered by SC DHEC Permit #SCR030000. The data will be used to assess: (1) site-specific "normal" conditions for the Waccamaw and Pee Dee Rivers, (2) long-term trends, and (3) the occurrence of illicit discharges.

The data are collected via biweekly sampling at the sites listed in Table 1. Measurements of temperature, conductivity, dissolved oxygen and pH are made in situ. Depth- integrated grab samples are returned to the lab for analysis of: (1) nutrients (filtered TN and TP), (2) chlorophyll (and phaeophytin), (3) bacteria (Fecal Coliform), (4) 5-Day Biochemical Oxygen Demand (BOD5), (5) turbidity, and (6) water toxicity. Validated results are provided to the SMS4s and the public at this site. Table 1 lists other data collected concurrently, including water quality, height, velocity and discharge by the USGS. The former are collected at 15-min intervals. SC DHEC samples are collected monthly as noted in Table 1, with some sites being active only during basin study years, the last of which was 2008. Grab sampling is staggered with the SC DHEC schedule such that the pooled data represent three samplings per month.

Other project deliverables include: (1) an annual report containing a data summary, statistical analyses of temporal trends, exceedances of known water quality standards, a narrative interpretation and (2) emergency notification if sample results exceed SC DHEC's water quality standards or the US EPA's recommended water quality criteria.

Table 1. Sampling Sites showing data collected by USGS and SC DHEC plus 303(d) and TMDL

The 303(d) listing and TMDL status of the sampling sites are also shown in Table 1. Sites are listed for dissolved oxygen, fecal coliform and metals. Most of these listings have been continuous since the 1990s suggesting chronic issues with eutrophication, hypoxia, bacterial contamination and toxics. These problems are somewhat interlinked with conditions of low dissolved oxygen (hypoxia) arising from the introduction of sewage and septage that also carry bacteria into natural waters. Introduction of nutrients from runoff of fertilizers and the breakdown of organics, such as sewage and septage, stimulate plant growth. Overgrowth of algae produces organic matter which eventually decays, thereby reducing dissolved oxygen levels and leads to hypoxia.

The relationship between the parameters measured and existing water quality standards is presented in Table 2. The frequency which sites contravene the water quality standards is used to identify hot spots. This provides guidance for illicit discharge inspections and restoration activities. In some cases, site-specific standards need to be developed. This is another planned use of the data once a significant time period has been sampled.

Table 2. Status of Water Quality Standards for the Waccamaw River and Coastal Waters‌‌

Due to the high cost of measuring individual toxic compounds, a broad screen of water toxicity is being performed. Samples that have high toxicity should be further analyzed to identify the specific toxics. High levels of toxicity are indicative of the presence of toxics, such as heavy metals, pesticides, herbicides, etc. The IQ Toxicity Test™ by Kingwood Diagnostics is being used to perform this screen as it has been verified by the USEPA under their Environmental Technology Verification Program. The verification report for this test is located at: http://www.battelle.org/environment/pdfs/verifications/water/verifications/01_vr_aqua_survey.pdf. The IQ Toxicity Test™ characterizes the toxicity of a water sample by measuring short-term stressor-related suppression of enzyme activity in Daphnia magna, a freshwater aquatic invertebrate that reacts rapidly when exposed to toxins.

Data Decision Points

Two types of decision points are required by this project: (1) Detection of significant temporal and spatial trends for the seven sampling sites and (2) identification of single samples that contravene numeric water quality standards. The former will be detected with a seasonal Mann-Kendall trend analysis test after collection of three years of data (Gilbert 1987; Gibbons and Colman 2001) and the later with the protocols laid out in Gibbons and Colman (2001) for comparison of a single measurement to a regulatory standard. Development of site specific standards will follow the protocols laid out in US EPA (2000). Confirmations of 303(d) listing status and standards attainment will also be made using SC DHEC parameter thresholds (SC DHEC 2008).

Because this is an open-ended monitoring program, statistical analysis will be conducted on an ongoing basis.


Gilbert, R.O., 1987. Statistical Methods for Environmental Pollution Monitoring. John Wiley & Sons, 320 pp.

Gibbons, R.D. and D.E. Coleman, 2001. Statistical Methods for Detection and Quantification of Environmental Contamination. John Wiley & Sons, 384 pp. 


Quality Assurance Project Plan (PDF)