Evaluation of GW Quality and Interactions with Surface Water in the Port Riviera Area, Port Tobacco River Watershed Charles Co, MD

Objectives

The Port Tobacco Riviera was selected for a study of ground-water quality and interactions with surface water, as a representative residential area for defining the potential ground-water transport of contaminants from septic systems and to assist in evaluating the need to retrofit septic systems in the watershed. The objective of the proposed work is to use water-level data and distributions of analytes in the ground water to evaluate the potential transport and fate of contaminants from septic systems in the area to the Port Tobacco River. Major ground-water flowpaths to the Port Tobacco River in the Port Tobacco Riviera will be identified, and ground-water samples along selected flowpaths will be analyzed for major ions, nutrients, copper, dissolved organic carbon (DOC), bacteria, and redox indicators, including dissolved oxygen, ferrous iron, sulfide and methane. A preliminary evaluation will be made of the geochemical controls on fate of septic system contaminants during transport to the surface water.

Statement of Problem

High levels of bacteria and nutrients have been detected in surface water in the Port Tobacco River watershed in Charles County, Maryland, and septic system failure in seven major residential areas in the northern part of the watershed has been identified as one of the potential anthropogenic sources. All residences in Port Tobacco River have septic systems, and a high rate of system failure is known or suspected based on a study conducted by Port Tobacco River Conservancy (PTRC). These failing systmes could be a major source of nutrient, bacteria, and other contaminants to the surface water. Determining sources of surface water contaminants, however, has not been possible by surface water studies alone. Ground water studies are also needed to better define sources and factors controlling transport and fate of contaminants to the Port Tobacco River and watershed streams.

Strategy and Approach

Ground-water hydrology and water-quality data will be collected to obtain a preliminary evaluation of (1) ground-waterflow directions in the Port Riviera area and flowpaths to the Port Tobacco River, (2) contaminant transport from septic systems in the Port Riviera area to underlying aquifers and the Port Tobacco River, and (3) geochemical controls and fate of potential major septic system contaminants during transport to the Port Tobacco River. The general approach will include a reconnaissance phase to identify major ground-water discharge areas, and a Phase 1 sampling and waterlevel monitoring to evaluate different potential mechanisms of ground-water flow to the Port Tobacco River according to the conceptual model detailed above. After completion of Phase 1, the conceptual model for ground-water and contaminant transport in the area will be refined and Phase 2 sampling effort will be planned accordingly.