7
Integrated Water Module

The Integrated Water Module (IWM) is one of the most substantial parts of the Draft CCAM. It consists of stormwater and wastewater components, which have been used to generate loadings of total phosphorus (TP), total nitrogen (TN), biochemical oxygen demand (BOD), and total suspended solids (TSS) to the near-coastal waters of the Florida Keys. The IWM thus generates “land-side” loads from “wastesheds” on the many islands of the Florida Keys. The integration of the IWM with the GIS and Scenario Generator (for land use and population projections) is very thorough and represents a significant and commendable effort on the part of the contractor.

Stormwater runoff is generated based on seasonal average rainfall, which is converted to runoff using coefficients that are a function of land use and thus subject to change in the model. Runoff volumes are, in turn, converted to loads using event mean concentrations (EMCs) for the four constituents as a function of land use, with the option for load reduction by best management practices (BMPs). EMCs and BMP efficiencies are extrapolated from studies elsewhere in Florida, and in some cases, from other states; there are no regional EMC or BMP data for the Florida Keys. A “spreadsheet approach” is used to generate the seasonal loadings from the wastesheds that is consistent with first-order estimates of stormwater routinely used in engineering practice. The stormwater loads are entirely uncalibrated, however. While the loads may be suitable for comparing one management option or land use to another, they should not be used to make inferences about receiving water quality in the absence of any local data for calibration and verification of the load estimates. Time averaging also makes



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A Review of the Florida Keys Carrying Capacity Study 7 Integrated Water Module The Integrated Water Module (IWM) is one of the most substantial parts of the Draft CCAM. It consists of stormwater and wastewater components, which have been used to generate loadings of total phosphorus (TP), total nitrogen (TN), biochemical oxygen demand (BOD), and total suspended solids (TSS) to the near-coastal waters of the Florida Keys. The IWM thus generates “land-side” loads from “wastesheds” on the many islands of the Florida Keys. The integration of the IWM with the GIS and Scenario Generator (for land use and population projections) is very thorough and represents a significant and commendable effort on the part of the contractor. Stormwater runoff is generated based on seasonal average rainfall, which is converted to runoff using coefficients that are a function of land use and thus subject to change in the model. Runoff volumes are, in turn, converted to loads using event mean concentrations (EMCs) for the four constituents as a function of land use, with the option for load reduction by best management practices (BMPs). EMCs and BMP efficiencies are extrapolated from studies elsewhere in Florida, and in some cases, from other states; there are no regional EMC or BMP data for the Florida Keys. A “spreadsheet approach” is used to generate the seasonal loadings from the wastesheds that is consistent with first-order estimates of stormwater routinely used in engineering practice. The stormwater loads are entirely uncalibrated, however. While the loads may be suitable for comparing one management option or land use to another, they should not be used to make inferences about receiving water quality in the absence of any local data for calibration and verification of the load estimates. Time averaging also makes

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A Review of the Florida Keys Carrying Capacity Study calculated loads inappropriate for making decisions about predicted water quality. Wastewater loads are generated based on relatively accurate water use data for the Florida Keys. Water demand reflects all users (permanent and transient); hence, wastewater loads as a function of land use also reflect all landside population factors at the time the water use data was collected. Use per equivalent dwelling unit will not necessarily remain constant, however, if the mix of land uses changes over time. This coefficient will need to be recalibrated at regular intervals to be reliable. Possibly significant loadings from small craft discharges directly into receiving waters are not included in the estimates, however, because the contractor had no basis for such estimates. The extent to which these direct discharges impact water quality is thus not included in the Draft CCAM. Wastewater loads are a function of type of treatment (e.g., septic systems, secondary treatment) and type of disposal into the ground. Only deep well injections (e.g., the 2000-ft injection well at Key West) are not expected to migrate quickly (hours to days) to the near-shore region. The limestone that underlies almost all of the Florida Keys is assumed to provide no reduction of any constituent except TP, for which a 50% reduction is assumed. Wastewater loading estimates also reflect general engineering practice for such an effort, but the estimates are similarly uncalibrated and reflect gross estimates for both the wasteshed and the season. Again, comparisons of management options (e.g., upgrading of treatment facilities) are likely to be useful, but the wastewater loadings should not be used to drive a receiving water model without calibration and verification. Moreover, without some verification of loading estimates, it would be dubious to even compare relative magnitudes of stormwater and wastewater loads, the comparison of which is implied in Tables 4.14 through 4.19 of the Draft CCAM report. MAJOR CONCERNS Water Quality In general, the Draft CCAM predicts improved water quality in the form of reduction in stormwater and wastewater loadings given the implementation of the Smart Growth scenario. It is important to emphasize that reduced loadings depend entirely upon the implementation of the Monroe County Stormwater Management Master Plan (Monroe County Growth Management Division, 2001a,b) and Sanitary Wastewater Master Plan (Monroe County Growth Management Division, 2000). Without the political will to implement and fund the improvements that these plans require (typically over a 20-yr period), the predicted reduced loadings and possible improved receiving water quality associated with the Smart Growth scenario will not occur.

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A Review of the Florida Keys Carrying Capacity Study The current version of CCAM does not include several important water quality considerations that impact receiving waters in the Florida Keys. In particular, the model is missing: consideration of pathogens, such as coliforms, that may cause beach closings, affect shellfish harvests, and impact human health; consideration of water quality in dead-end canals (“finger canals”) that are heavily impacted by local runoff from adjacent urbanization and which tend to be poorly flushed in the Florida Keys due to small tidal amplitude; and direct loadings to marine waters from illicit waste dumping from small craft, which may increase with population growth (both permanent and transient) in the Florida Keys. Possible limits to growth based on these factors therefore cannot be assessed by the current version of the CCAM. Loadings The seasonal average loadings generated by the IWM do not allow for event-based analysis or continuous simulation, which might provide extremes and a distribution of concentrations for receiving water analysis. For instance, beach closings due to bacterial contamination are short-lived events; the present version of CCAM could not be used to evaluate such events even if bacteria were included as a parameter. In principle, however, the model could be modified to use given hourly rainfall data with which to generate event-based loadings. Although no load reductions are assumed for any parameter except TP while traveling through groundwater on the Florida Keys (certainly conservative assumptions), even the assumed 50% TP reduction may be too high over the long term if sorption sites are filled through continuous discharge of septic systems and through shallow wells. More study is needed to determine the long-term phosphorus assimilative capacity of the underlying limestone. Coefficients The entire CCAM contains many sets of coefficients, not all of which may be adjusted by users; those that may be changed are generally identified in Appendix C of the Draft CCAM report. One example from the IWM is the BMP removal efficiencies given in Appendix C—Table 4.5 of the Draft CCAM. These efficiencies were selected based on expert judgment of the contractors and their stormwater experts. Future users of the model may be tempted to take BMP removal efficiencies at their face value and assume that a given BMP “device” may be employed and will provide the indicated reductions regardless of where it

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A Review of the Florida Keys Carrying Capacity Study is implemented and whether or not it is appropriate for that location. As the Draft CCAM mentions, however, the effectiveness of any stormwater BMP on the Florida Keys is suspect if BMP relies on data from areas with dissimilar geology. In the future then, the IWM should be applied by informed professionals not by those without knowledge of the particular component being examined. This need for good engineering and scientific judgment extends to information taken from other documents, such as the Monroe County Stormwater Management Master Plan, which similarly needs to be implemented with advice from appropriate professionals (Monroe County Growth Management Division, 2001a,b). MINOR POINTS Percentiles (10% and 90%) are provided for EMC values in Table 4.4 in Appendix C of the Draft CCAM report. Although these percentiles were apparently not used in the CCAM, there should be some discussion in the report about the significance of these values since they are provided. Most of the stormwater coefficients and numbers (e.g., EMC values, BMP effectiveness) are taken directly from the Monroe County Stormwater Management Master Plan (Monroe County Growth Management Division, 2001a,b). In principle, this document is accessible, but in practice it is not. It would be useful to identify the geographical locations (cities) used to derive EMC values and BMP effectiveness. Parking lots are a principal source of stormwater runoff and a dominant land use in some sections of the Florida Keys. The revised report should include Table 4.6, “Runoff Coefficients by Land Use category” (Draft CCAM Appendix C) in the main body of the text along with some comments on the significance of these coefficients. CONCLUSIONS In summary, the IWM may reasonably be used to compare seasonal stormwater load estimates for alternative land use and control options. Wastewater loadings can be compared on the same basis. In the absence of any monitoring to confirm the magnitude of these estimates, they should not be used to drive a receiving water module, such as the Marine Module, nor can the two loadings realistically be compared to each other. The remarkable load reduction predicted by the Smart Growth Scenario might well occur, but only if the Monroe County Stormwater Management Master Plan (Monroe County Growth Management Division, 2001b) and Monroe County Sanitary Wastewater Master Plan (Monroe County Growth Management Division, 2000) are implemented in their entirety and only if maintenance and oversight is provided to ensure that their provisions function properly over time. These caveats should be emphasized in any conclusions regarding water quality drawn from the application of the CCAM.