Sample Sites

Sample Sites

Point Sources

Point source monitoring sites are relatively straightforward. They are often established above the

outfall and then just below the mixing zone. The mixing zone is the area of a lake or wetland, or

length of stream, below the outfall in which the effluent is not uniformly mixed with the surface

water. The difference in water quality at these two points should be an initial indication, at least,

of the impact of the point source discharge on water quality.

Nonpoint Sources

Monitoring points for nonpoint source determinations are less clear in some systems, although

along other streams the optimal sample sites are quite obvious.

Typically, land use types such as forestry, agriculture, and urban are identified as they relate to

the water body in question. Sample locations are sited to represent transitional zones between a

contributing area (an area of the watershed that contributes runoff and/or groundwater to the

water body) dominated by one land use, and a contributing area dominated by another land use

(see schematic in Fig. 2). For practical reasons, most sampling sites are located at road or

highway bridges.

Figure 2. Schematic of sampling program for tributary stream. Site 1 is located at the transition from

forestry to agricultural land uses; Site 2, where agriculture meets urban land use; and Site 3, at a

confluence with a larger stream. Arrows indicate point sources (waste load allocations). In the Tualatin

watershed, maximum total P concentration at Site 1 was equivalent to 20 ppb total P; Site 2, 50 ppb;and Site

3, 70 ppb.

In Figure 2, the rectangles labeled Forestry Load Allocation, Agricultural Load Allocation, and

Urban Load Allocation represent areas of the watershed landscape that are dominated by the

respective land use. The large, expanding arrow represents a stream flowing through these

portions of the landscape. The arrows represent point sources injecting pollutant into the stream

at fixed points. Sites 1, 2, and 3 represent transition points between these areas of dominant land

uses, sites that are appropriate for assessing the land use impacts upstream. Site 1 will provide

Flow

Forestry

load

allocation

Agricultural

load

allocation

Urban

load

allocation

Site 1 Site 2 Site 3

information on forestry sites, the difference between Sites 1 and 2 represents agriculture’s

contribution in terms of flow and quality, and the difference between monitoring results at

Sites 2 and 3 represents urban land use contributions. Site 3 is the point at which the stream

leaves its watershed and may be entering a larger stream, a lake, or an estuary.

Expected Problems from Major Land Use Types

Urban

The major pollution inputs from urban systems relate to runoff from stormwater, although

groundwater may be contaminated as well before it seeps into streams or lakes. Land disturbance

during development, especially on hilly sites, frequently leads to large inputs of TSS, which

contain nutrients, organic carbon, and increase water turbidity. Runoff from roads, parking lots,

lawns, parks, golf courses and other urban areas may be highly enriched in dissolved nutrients

even though it contains no visible sediment. Urban pollution from runoff can include sediments,

pesticides, metals, de-icing agents and chemicals from automobile emissions that attach to road

surfaces. Urban runoff can also contain nutrients, organic matter, and bacteria associated with

pet wastes.

Temperature can be a problem because of poorly maintained riparian zones, including open

ditches, and because runoff flowing across hot pavement and rooftops picks up heat from the

surface, especially in the summer.

Agricultural

Topsoil and streambank erosion result in increased inputs of TSS into streams and lakes. Nutri-ents

and organic carbon are associated with these sediment particles. Animal manures are rich in

phosphorus, nitrogen, and organic carbon, as well as bacteria when fresh; without careful man-agement

manures can enter streams either from confinement sites (barns and barnyards) or from

animals directly entering the streams.

Excessive quantities and careless application of commercial fertilizers may result in increased

nutrient inputs into water bodies. If riparian zones are not well developed, bank erosion can

cause significant problems with sediment inputs, and the lack of shade can cause significant

heating of the water. Finally, irrigation on agricultural land acts no differently than normal

rainfall, and can cause runoff. Irrigation water can also contain pollutants such as salts, nutrients

or pesticides. For example, irrigation water may percolate out dissolved salts which then enter

into the return flow systems to our water courses as a pollutant – a common problem in some of

the western United States.

Rangeland

Poorly maintained riparian zones result in heating of waters and streambank erosion. Livestock

often graze on riparian plants, especially during the dry season or in drought years. Animals

entering the streams or using high runoff areas near the streams directly add manure and all of its

problems to the system (see the section on Agriculture above).

Forestry

Soil disturbance and loss of riparian zones are major adverse impacts of forest harvest operations.

Increased TSS and temperature are the primary results. In some cases forests are fertilized,

primarily with nitrogen, and poor application techniques can lead to N enrichment in the streams.

Overgrazing and burning can also result in overenrichment of streams (primarily with N & P),

erosion and more rapid runoff.

Groundwater: Mysterious Source and Sink

Groundwater can be a steady, constant source of flow – and potentially a source of pollutants. In

many cases, water quality mysteries have been solved by close examination of groundwater.

The flow of groundwater into streams and lakes represents a somewhat steady input of flow and

of pollutants where they are present. It is also cooler than most surface waters in the summer, so

it lowers the temperature as well when it enters streams (Herman and Judy Li of Oregon State

University found this on the John Day River in eastern Oregon; trout gather around the cool

groundwater seeps during the hot summer).

Nitrate in particular is associated with groundwater that comes to the surface and empties into

surface water (as in the case of the Chesapeake Bay, for example). In the Tualatin, deep ground-water

was found to be an important source of geologically derived phosphorus in the lower

portions of the valley, but was even important in the mountains in some geological forms.

Groundwater gives – but it can also take away. Research on the South Platte River between

Brighton and Ft. Lupton, Colorado showed that dissolved oxygen (DO) concentrations in the

groundwater immediately underlying the river were less than 0.2 mg/L, the result of stream

bottom sediments acting as a DO sink. In the same reach of river, groundwater discharge contrib-utes

15 cfs per mile. That much anaerobic groundwater has a significant effect on instream DO,

pulling DO levels below the regulatory limit of 5.0 mg/L during low-flow periods (McMahon et

al, 1992).

The hyporheic zone – saturated sediments surrounding a stream’s open channel that link the

stream to groundwater – can also contribute pollutants or alter water chemistry. Not many data

are yet available because so little is known about the hydrology, chemistry and microbiology of the

hyporheic zone, but it is clear that biological and chemical processes in the sediments can be

substantially different than those in the open channel (Findlay, S., 1995).

Air Deposition

This section contributed by Richard Artz, Deputy Director, Air Resources Lab, NOAA. 1999.

Personal Communication.

A significant source of water pollution typically goes unconsidered during the TMDL process:

the atmosphere. Though the severity of this problem differs by region, scientists estimate that as

much as one-third of the nitrogen and toxic chemicals entering the water come from pollutants

precipitating out of the air. Currently, the Chesapeake Bay Program Office estimates that 21% of

the nitrate entering the bay is from air sources. About 46% of the cadmium in Tampa Bay

reportedly falls from the sky. In the Great Lakes, air-related water quality concerns revolve

primarily around toxic air pollutants, not nutrient (nitrogen) deposition.

An official quoted in an article titled "Pilot Projects Unite Air and Water Regulations," in the

July 1, 1998 issue of Environmental Science and Technology said, "If you’ve got one-third

of your pollutants coming from the air, and you’re not working with the air program, then

you’ve got a problem." Concerns about air deposition to water bodies were first raised in

1988. In 1991 an article on the topic was published by D.C. Fisher and M. Oppenheimer in

Ambio 20 (3-4) 102-108 titled "Atmospheric Nitrogen Deposition And The Chesapeake Bay

Estuary."

According to the Environmental Science and Technology article the deposition of nitrogen and

mercury aerosols in the nation’s waters points up a serious gap in scientists’ understanding of

water pollution. Several agencies are now exploring nitrogen and mercury air deposition under

the Clean Water Action Plan. EPA is conducting two pilot projects to estimate how much mer-cury

is entering water bodies through atmospheric deposition. The pilot projects will be con-ducted

on a small lake in Wisconsin called Devils Lake and a portion of the Florida Everglades

30 miles west of Miami, Florida. Both of these water bodies are on US EPA’s 303(d) list, and

have fish consumption advisories due to high levels of mercury in fish.

The EPA pilot projects will test whether the Clean Air Act and Clean Water Act can be used in

tandem to control air sources of water pollution. According to an official in the EPA Office of

Water, the projects could lead to air permits that protect water quality. According to the above

mentioned article, John Seitz, Director of the Office of Air Quality Planning and Standards, said

EPA officials hope the pilot projects will provide states with a tool for developing TMDLs with

an atmospheric deposition component.

Airsheds Can Be Huge

"Airsheds" do not have boundaries like watersheds – they are not readily definable. In fact,

depending on the atmospheric lifetime of the pollutant in question, an airshed could include a

region, a hemisphere, or even the entire globe.

Dr. Robin Dennis, also with NOAA’s Air Resources Laboratory, uses an air deposition model to

provide an estimate of the emission region accounting for about three-fourths of the airshed

impacting the Chesapeake Bay Watershed (see Appendix III).

According to Dennis, atmospheric loading accounts for roughly 25% of the total nitrogen loading

deposited in the Chesapeake Bay watershed. About half of the atmospheric deposition is directly

to the water surface. The watershed for the Bay is huge – about 165,886 square kilometers. The

surface area of the tidal waters is 11,400 square kilometers – essentially the mainstem of the bay

and the tributaries affected by the tides.

The airshed dwarfs the watershed. About 75% of the atmospheric loadings impacting the Bay

come from an area roughly four times the size of the watershed, an airshed that stretches north up

to Montreal, south to about the North/South Carolina border, west to about Indianapolis and east

nearly to the coast. The rest of the nitrogen contamination to the Bay comes from the usual

sources – runoff, point source discharges, septic systems, groundwater inputs, etc.

Large, Erratic Nonpoint Source

In order to incorporate atmospheric deposition properly into a comprehensive program to calcu-

late TMDLs, it is important to recognize that atmospheric deposition – whether through

precipitation or from processes associated with the dry deposition of particles and gases – is

highly episodic. For most regions of the country, especially during the warm half of the

year, a few large events inevitably account for a major fraction of the total atmospheric

loading. Attempts to parse annual or seasonal atmospheric deposition estimates into daily

loads will usually lead to inadequate control strategies, though calculations of daily loads

based on seasonal data may be valid in coastal areas of Washington.

In short, atmospheric loadings must be treated as a very large, episodic nonpoint source.

To explore the complexities of addressing air deposition in water quality models and TMDLs, it

is interesting to consider ammonia. Ammonia’s volatility and mobility make it a very likely

contaminant of both air and water: in fact, more than half of the ammonia contained in chicken

manure left unattended may be emitted into the atmosphere.

However, agricultural sources of ammonia and ammonium (inorganic fertilizers and animal

wastes) to the atmosphere are currently very poorly accounted for in emission inventories.

However, mass balance modelers who wish to figure atmospheric ammonia into their models

need to be aware that if they are including agricultural inputs from runoff on the water side of the

equation (ammonia typically deposits close to source) they may already be accounting for some

atmospheric deposits of ammonia.