Changes in streamflow in cubic feet per second (Flow) and light absorbance at 253.7 nanometers (UV254) during a storm-flow period on the Chickahominy River.

Project Title Effects of Hydrology and Season on Concentration and Speciation of Organic Carbon in Raw Water for Local Supplies Number VA104 Location Chickahominy River Watershed Cooperating Agencies City of Newport News Project Chief Gary Speiran Period of Project April 1995 through September 1999

Problem  
Certain organic compounds in natural waters form trihalomethanes (THMs), haloacetic acids (HAAs), and total halogenated organic compounds (TOXs) when the waters are disinfected with chlorine or other oxidants for public supplies.  Organic compounds that form these disinfection by products (DBPs) must be removed when concentrations exceed certain levels because the DBPs are suspected carcinogenic compounds for which the U.S. Environmental Protection Agency has established maximum contaminant levels (MCLs) for drinking water.  Humic and fulvic acids (high molecular weight, aromatic, organic compounds) have been identified as THM precursors and other compounds can contribute to the formations of other DBPs.  DBP precursors (organic materials that can form DBPs) are abundant in wetlands environments and the water that discharges from these environments.  Therefore, DBPs are a concern for public water supplies that use water that has flowed through wetlands.

Raw water for public supply for the City of Newport News and other localities in Virginia is provided by watersheds having extensive wetlands.  The city is evaluating additional watersheds having wetlands as possible new sources of water.  These extensive wetlands have a variety of vegetation and water regimes.  Knowledge of the effects that wetland environments, seasons, and hydrology have on concentrations of dissolved organic carbon (DOC) and DBP precursors in these watersheds can be used by localities to select times for withdrawing and storing raw water having low concentrations of DOC and DBP precursors.  Selective withdrawal can help reduce the cost of treatment to remove DBP precursors.  This knowlege can also help in evaluating watersheds as potential future water sources.

Objective
The objective of this project was to identify relations of hydrology and seasons to concentrations of DOC and DBP precursors in waters of watersheds in the Coastal Plain of Virginia having extensive wetlands, using the Chickahominy River and Diascund Creek Reservoir Watersheds as examples.

Relevance and Benefits
Results of this study improve the understanding of the transport of DOC and DBP precursors through watersheds having extensive wetlands.  This understanding helps localities manage the withdrawal of water from such rivers in a manner to provide a public water supply that meets the drinking-water standards for DBPs at a minimum cost.  Results will also help evaluate watersheds as potential water sources.

Approach
This investigation related the formation potential for THMs, HAAs, and TOXs (indicators of DBP precursors), the absorbance of UV light at 254 (an indicator of concentrations of aromatic compounds that commonly form THMs), and DOC concentrations to wetlands environments, seasons, and hydrology during baseflow and stormwater flows at selected sites in the Chickahominy River and Diascund Creek Reservoir Watersheds.  The amount of DOC and DBP precursors produced by organic detritus in the streams was evaluated.  The contribution of DOC and BDP precursors to stormwater flow and baseflow through different hydrologic pathways was also evaluated.