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</div> </td><td valign="top" width="24"></td><td valign="top"> <div align="left"> <table border="0" cellpadding="2" cellspacing="4" width="400" align="left"> <tr> <td width="336"></td> </tr> <tr> <td width="336"> <b><font color="#000000" size="6" face="Arial">Most Asked Questions About TMDLs.</font></b> <p><font face="Times New Roman" size="3">The TMDL program was initiated to restore surface water sources like streams and lakes to their greatest potential beneficial use. These uses, defined for each water body by the state in which it lies, may include drinking water, fishing, swimming and other recreational activities, irrigation, and aesthetics. TMDLs are also designed to protect further degradation of surface water sources.</font></p> <p><font face="Times New Roman" size="3">TMDLs are particularly important for controlling nonpoint sources, because past regulations focused on point sources only.</font></p> <b> <p><font face="Arial" size="3">2. In setting TMDLs, how does one perform a watershed TMDL analysis that integrates</font></b><font face="Arial" size="3"> </font><b><font face="Arial" size="3">both point and nonpoint source loads?</font></p> </b> <p><font face="Times New Roman" size="3">Past pollution controls have emphasized point sources. However, there is now increased recognition of the impacts of nonpoint sources as human activities intensify on the landscape. The quality of water in a stream, lake, or estuary is the result of all the pollutants entering the system.</font></p> <p><font face="Times New Roman" size="3">So both types of sources have to be integrated in evaluating the impacts on water quality. That integration becomes very complex because of the need to reconcile measurements of load and concentration (Load = Concentration x Flow).</font></p> <p><font face="Times New Roman" size="3">In many ways it makes sense to treat the point sources as part of a constant baseline, like back-ground, natural inputs. The objective with management of point sources, of course, is to lower that baseline value.</font></p> <p><font face="Times New Roman" size="3">Nonpoint sources should be considered both in terms of loads and in terms of flow. Flow is valuable in streams, as long as it isn’t excessive. Aquatic life depends on the flow inputs. (It’s been said, half jokingly in some cases, that one effective way to lower loads is to eliminate flow.</font></p> <p><font face="Times New Roman" size="3">This is true. It also eliminates the potential for aquatic life in that part of the system.)</font></p> <p><font face="Times New Roman" size="3">The flow associated with high runoff periods, then, needs to be integrated into the baseline (groundwater plus point sources) flow in some rational way to produce a desired condition.</font></p> <p><font face="Times New Roman" size="3">It is important to remind yourself when working on TMDLs that the essential key to success is improved water quality and beneficial uses, not strictly meeting load allocations, which may be difficult to manage and predict. This information can be summarized as follows:</font></p> <p><font face="Times New Roman" size="3">- For <b>high concentration, low flow point sources</b>, focus on methods that lower both concentration and volume of flow. Lowering either will improve water quality. For example, in industry with high-biochemical oxygen demand (BOD) effluent, irrigating with wastewater during the summer may be good use, eliminating both concentration and flow altogether.</font></p> <p><font face="Times New Roman" size="3">- For <b>high concentration, high flow point sources </b>such as a wastewater treatment plant emptying into small stream, focus on lowering concentration while maintaining flow.</font></p> <p><font face="Times New Roman" size="3">- For typically <b>low concentration, nonpoint sources</b>: focus on lowering concentrations and possibly evening out flow, which creates less runoff and greater groundwater recharge for later slow release to the stream. An example: increasing infiltration into urban stormwater treatment systems that also filter out pollutants.</font></p> <p><font face="Times New Roman" size="3">When BMPs are implemented that address these targets in each source type, the overall health of the receiving water will improve.</font></p> <b> <p><font face="Arial" size="3">3. How does one calculate the watershed TMDL for a stream in which flow varies</font></b><font face="Arial" size="3"> </font><b><font face="Arial" size="3">significantly?</font></p> </b> <p><font face="Times New Roman" size="3">Stream flow rates can vary tremendously based on seasonal rainfall, snowmelt, stored water releases, and removal from the stream by irrigators and other users. A TMDL established for a pollutant at the 95 th percentile flow could be unrealistically large. Instead, consider the season of concern – is the pollutant a problem in high-flow, high-runoff periods, or during low-flow seasons – and base your TMDL on an average flow rate for that season. In some cases, seasonal minimum or maximum flow rates have been used. (For more detail on flow, see "Flow Measurements to Determine Loads")</font></p> <b> <p><font face="Arial" size="3">4. How does one calculate a TMDL for a lake?</font></p> </b> <p><font face="Times New Roman" size="3">Set loads for the lake, then assign portions of that load to the point sources, tributaries, groundwater, and sediments, based on what you think can be their minimal contributions. Remember that in some cases, groundwater and sediments may provide more than enough nutrient to keep the lake eutrophic (nutrient-rich).</font></p> <b> <p><font FACE="Times-Bold" size="3">5. How do we know if the TMDL program has succeeded?</font></p> </b> <p><font face="Times New Roman" size="3">Careful, frequent, and accurate monitoring and data analysis tell us when the TMDLs are working.</font></p> <p><font face="Times New Roman" size="3">Tracking trends over time – while taking into account weather differences and other year-to-year variables – provides the information necessary to determine whether or not the ecosystem is actually improving in quality.</font></p> <p><font face="Times New Roman" size="3">Effects of the cleanup of large point sources can be rapidly detected in the receiving waters.</font></p> <p><font size="3" face="Times New Roman">When the wastewater treatment plants along the Tualatin River enhanced their tertiary treatment and began releasing water containing 50 ppb total P instead of 7,000 ppb water during the summer, average river total P concentrations decreased from nearly 1,000 ppb to about 150 ppb within weeks.</font></p> <p><font size="3" face="Times New Roman">In contrast, nonpoint source cleanup, achieved for the most part by BMPs, can be much harder to detect. Watersheds are large and respond slowly to management changes, so changes in water quality can take a long time. US EPA is encouraging an emphasis on small watersheds and projects in watershed headwaters, where the impacts of BMPs can be more significant and measurable. EPA and NRCS are preparing a document that discusses the relative sensitivity of water bodies to changes in the inputs of P and N (NRCS/USEPA, in press: "A Procedure To Estimate The Response Of Aquatic Systems To Changes In Phosphorus And Nitrogen Inputs").</font></p> <p><font size="3" face="Times New Roman">The more careful the monitoring, the greater the likelihood of detecting changes early. Weather at the time of sampling must be taken into account; continuous monitoring data are most helpful here, since big events are not missed. Poor data collection, management, and interpretation can almost eliminate the potential for detecting improvements except in highly polluted, highly responsive systems.</font></p> <p><font size="3" face="Times New Roman">The ultimate test of success is not simply improvements in water quality parameters, but in the uses that can be made of the water body. At various times, biological surveys should be taken to determine whether or not desirable biological activity is being enhanced. The ability of the aquatic ecosystem to support swimming, fishing, boating, drinking water and irrigation water uses should be evaluated by direct measurements as often as is possible through the course of the TMDL program.</font></p> <p><font size="1" face="Arial">© 1999, YSI Incorporated </font></p> </td> </tr> </table> </div> </td></tr></table></body> </html>