Changes in UV 254 and stage during a storm-flow period

Project Title Effects of Hydrology and Season on Concentration and Speciation of Organic Carbon in Raw Water Supplies for the City of Newport News 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 (THM's), haloacetic acids (HAA's), and total halogenated organic compounds (TOX's) when the waters are disinfected with chlorine or other oxidants for public supplies.  Organic compounds that form these disinfection by products (DBP's) must be removed when concentrations exceed certain levels because the DBP's are suspected carcinogenic compounds for which the U.S. Environmental Protection Agency has established maximum contaminant levels (MCL's) 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 DBP's.  DBP precursors (organic materials that can form DBP's) are abundant in wetlands environments and the water that discharges from these environments.  Therefore, DBP's 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 is primarily provided by the Chickahominy River and Diascund Creek Watersheds.  The city is evaluating the Mattaponi and Pamunkey Rivers as possible additional sources of water.  These watersheds drain extensive wetlands that 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 the City of Newport News 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 other 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 the Chickahominy River and Diascund Creek Reservoir Watersheds that were derived from different wetland environments.

Relevance and Benefits
Results of this study improve the understanding of the transport of DOC and DBP precursors through the Chickahominy River and similar watersheds.  This understanding helps the City of Newport News manage the withdrawal of water from the Chickahominy River in a manner to provide a public water supply that meets the drinking-water standards for DBPs at a minimum of cost.  Results will also help evaluate other watersheds as potential water sources.

Approach
This investigation related the formation potential for THM's, HAA's, and TOX's (indicators of DBP precursors), the absorbance of UV light at 254 (an indicator of concentrations of aromatic compounds that commonly form THM's), and DOC concentrations to wetlands
environments, seasons, and hydrology during baseflow and stormwater flows at selected sites in the Chickahominy River, Diascund Creek Reservoir, Mattaponi River, and Pamunkey River 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 were also evaluated.