Chesapeake Bay Monitoring
8. pollutant inputs
Nutrients, organic material, sediment and other pollutants are introduced to the Chesapeake Bay from a variety of sources. These are generally separated into two broad classes, point and nonpoint sources. Point sources, as the name implies, are inputs with a specific point of entry into the system. Municipal sewage and industrial discharges are examples of the major point sources of pollutants to the Bay. Nonpoint sources do not have a readily identifiable point of entry to the system or they may have many, diffuse points of entry to the system. Rain water runoff and ground water discharges are examples of the major nonpoint sources of pollutants to the Bay.
All of these inputs must be effectively monitored in order to document the
present pollutant loadings to the Bay and to track the progress of cleanup
efforts. In addition, the point of entry, chemical form, magnitude and
timing of the inputs are important information required to understand and
evaluate the impact of the pollutants on water quality.
Maryland has been monitoring the major point sources of pollutants to the waters of the state for many years. The severity of the water quality impacts of many point source discharges warranted immediate attention to regulate and control the discharges. Over the years these regulatory and monitoring efforts have been steadily upgraded. Under the recent Chesapeake Bay initiatives, point source monitoring efforts are being further improved.
Nonpoint sources present a different sort of regulatory and monitoring problem due to the diffuse and unpredictable nature of the inputs. The situation is further complicated by the critical role that largely uncontrollable natural weather patterns play in determining nonpoint source pollution. As many point sources have been brought under control, the importance of nonpoint sources has become more evident and efforts to control and monitor nonpoint sources have been significantly increased.
The pollutant input monitoring program described here is divided into three major components; 1) municipal point sources, primarily sewage treatment facilities; 2) industrial point source discharges, of a variety of types; and 3) river inputs, the combined result of many upstream, point and nonpoint source pollutant inputs.
Municipal Point Source Monitoring Program
Point source discharges are regulated in Maryland by the Office of Environmental Programs as part of the federally mandated National Pollutant Discharge Elimination System (NPDES) which is administered by the U.S. Environmental Protection Agency (EPA). The OEP monitoring program for point source discharges was developed to meet the specific requirements of NPDES and EPA. The entire program is based on establishing and enforcing specific discharge permits. As part of its regulatory responsibility, OEP issues discharge permits and reviews monitoring data to assure compliance with the permits.
Several types of monitoring approaches are taken for municipal sewage discharges. The most comprehensive monitoring is carried out by the dischargers themselves. Daily sampling and records of effluent parameters and operational indices are generally required. To verify this self monitoring, OEP personnel conduct periodic compliance monitoring at varying frequencies depending on permit conditions, discharge volume and type of treatment process used. Onsite reviews of plant operation are also conducted regularly by OEP engineers.
The new Maryland Chesapeake Bay initiatives affecting municipal point sources are directed toward improving the operation of municipal sewage treatment plants through improved financial management and operator training, improved regulation and monitoring of industrial discharges which go into the municipal waste stream to be treated at sewage treatment facilities, and enhanced compliance enforcement efforts. However, the major focus of the existing point source monitoring efforts, that is, to verify the individual discharger's compliance with permit conditions did not change.
In the evaluation of water quality impacts of point source pollution the compliance monitoring data dealing with effluent flows and concentrations of associated nutrients are of primary concern. The bulk of the effluent monitoring data is collected by the plant operators. These data are periodically verified by comparison with State monitoring data. In the past, the effluent data for groups of plants have been complied only periodically to provide Bay or watershed point source loading estimates for specific planning purposes. In conjunction with the enhanced water quality monitoring activities in the Bay and its tidal tributaries, the data are now being complied on an annual basis.
Industrial Point Source Monitoring Program
In contrast to municipal sewage discharges, the nature of industrial discharges is much more variable. As a result, a more individually tailored discharge monitoring program is required based on the permit requirements for the individual discharger. In general terms, however, the industrial point source monitoring takes the same combination of approaches as used for municipal monitoring. Compliance evaluation inspections are done by OEP engineers to review records and plant operating procedures. Performance audit inspections are conducted to provide quality assurance and to review the discharger's self monitoring activities. Compliance sampling inspections are done to independently analyze the effluent and verify the results of self monitoring data.
As in the case of the municipal point source monitoring, Chesapeake Bay initiatives for the industrial program are focused on improving discharge permit compliance. In addition, biological evaluation of toxic waste discharges using bioassay techniques is being tested as an added regulatory tool for managing industrial discharges into Maryland's streams. The emphasis is on permit compliance for the individual discharger. The data are generally sufficient for Bay-wide, water quality evaluation needs. However, efforts are currently underway to enhance the monitoring where necessary to provide additional information on discharges.
River Input Monitoring Program
As a result of Maryland's Chesapeake Bay initiatives, the river input monitoring program has been enhanced considerably to provide more accurate data for evaluating sediment and nutrient loading to the Bay from its surrounding watersheds. Prior to the start of the new monitoring program in July 1984, routine water quality monitoring of streams in Maryland by OEP was primarily limited to monthly grab samples. With the new monitoring program, regular storm runoff sampling efforts are now being conducted on four major rivers in Maryland.
River inputs present a difficult monitoring problem because of the number of streams and rivers discharging to the Bay and the unpredictable nature of storm events and associated river flows. There are too many streams and rivers discharging to the Bay for it to be practical to monitor them all. In addition, the characteristics of water flowing in a river are constantly changing in response to rainfall in the watershed. Just as it is not practical to monitor every river flowing into the Bay, it is not practical to continuously monitor all water quality characteristics over time.
River flows can generally be divided into two basic categories, base flow and storm events. Under base flow conditions the river is fed primarily from groundwater and the volume of water and its water quality characteristics are relatively stable. During a storm event, however, the volume of water flowing in a river increases tremendously as base flow is supplemented and overwhelmed by direct runoff of rainfall. As the river rises and falls the concentrations of pollutants in the water can change radically. Thus, it is necessary to take numerous samples during the course of the storm to get an accurate estimate of the pollutant load from a particular storm. Because the volume of water delivered to the estuary is much greater during storm events, the loads of associated pollutants are also much larger than loads carried by base flow.
With careful selection of sampling locations and time of sampling it is possible to characterize a number of rivers for a range of conditions and then extrapolate the data to fill in the gaps in sampling coverage. The rivers that are being monitored have been selected to capture runoff from as much of the Bay watershed as possible and to obtain the maximum coverage of the range of different sources of runoff to the Bay and its tributary estuaries. Sampling times are chosen to emphasize storm events, when the majority of the river input loads are delivered to the Bay. The percentage of the total nutrient and sediment loads associated with these river flows is not as easily determined.
Each watershed has unique characteristics that may significantly influence the loads delivered by each river. In order to accurately extrapolate the monitoring data to cover unmonitored tributaries to the Bay, various approaches can be taken. Approaches range from simple flow based extrapolation of loading data (e.g. 80% of the flow delivers 80% of the load) to sophisticated watershed computer models. All of these involve assumptions about the transferability of water quality data from one watershed to another and are thus subject to considerable interpretation and debate.
In order to facilitate a comparison of the Chesapeake Bay river input monitoring program with the point source monitoring program, the results are presented together. It must be clearly understood that the loading estimates discussed below are not to be taken as a complete inventory of the nutrient inputs to the Bay. What is represented are the river input loads (point and nonpoint sources) for four rivers, representing 80% of the fresh surface water flow into Maryland's portion of the Chesapeake Bay, and the point source loads discharging into the Bay drainage area that are not measured by the river input monitoring program. The nonpoint source nutrient loads from the unmonitored 20% of the flow, the atmosphere, ground water, sediments and other potentially significant sources of nutrients have not been presented here.
In addition, the results shown for both river inputs and point sources indicate the amounts discharge at the location, or in the region indicated. The loads do not necessarily reach the mainstem of the Bay itself. For example, the impact on the Chesapeake Bay of the nutrient loads at the head of the Potomac estuary are substantially moderated by the natural processing which occurs in the Potomac estuary before any of that load reaches the Bay. In order to assess the relative impact of these loads on various regions of the Chesapeake Bay, so many factors must be taken into account that the problem is best addressed using complex mathematical models. Modeling efforts are presently underway in the Bay and a number of its tributary estuaries in order to carefully address these problems.
Maps 13 and 14 show the major river and point source nitrogen and phosphorus inputs to the Chesapeake Bay in Maryland for the period 1978 through 1985. River inputs include both point and nonpoint source pollutants discharged upstream of the monitoring stations. Point source inputs shown include only those point sources not captured by the river input monitoring stations.
Point source nutrient load estimates have been compiled from a number of
sources including the EPA Chesapeake Bay Program, Metropolitan Washington
Council of Governments and OEP compliance monitoring data. Historical point
source load estimates were only available for certain years. However, since
point source loads are fairly stable for extended periods, the gaps in the
data presented here do not prevent a meaningful comparison with the river
During the course of a year the amount of water and the associated nutrient
loads discharged by a river can vary considerably. This is particularly
noticeable during the 1984-85 monitoring period when flows averaged 10 -
30% above average in 1984 and 10 - 50% below average in 1985. The
seasonality of the flow and associated nutrient loads can be clearly seen.
In general, the winter and spring flows and nutrient loads are very high
compared to summer and fall contributions. However, as noted earlier, from
one year to the next, considerable variation occurs. For example, summer
and fall of 1984 had relatively high flows and winter and spring of 1985
had relatively low flows. As a result the winter/spring peak in nutrient
loads is not nearly as dramatic as occurred in calendar year 1984.
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