Report of the
Bradfordville Citizen Storm Water Study Group
to the
Leon County Board of County Commissioners

October 14, 1997

Study Group Members:

Robert E. Deyle, chair
William T. Cooper
William S. Jordan
Charles L. Mesing
Rhett A. Miller
Joseph Travis
Timothy B. Waddle

Focus and Procedures

Interpretation of Charge from the Board (see "Final Report," pp. 1-2)

The Study Group took its direction principally from Section 4.b. of the Bradfordville Center Publix Site Mediation Agreement dated 8 April, 1994, and Objectives 8.1 and 8.2 and Policies 8.1.2 and 8.2.1 of the County Comprehensive Plan which we understand served in part as antecedents to the Publix Mediation Agreement. On this basis, the Study Group has interpreted its charge to be as follows:

(1)To recommend the geographic and substantive scope for a study to be conducted by a qualified consultant that will provide the Board of County Commissioners with (a) a factual base for understanding the probable impacts of future development on flooding and the environmental quality of the water bodies of the Bradfordville area and (b) recommendations for policy and regulatory initiatives that would serve to prevent unacceptable cumulative impacts from storm water discharges.

Procedures of the Study Group (p. 2)

The Study Group generally met at two week intervals. GEM staff provided administrative support for recording minutes and providing notice of meetings. Technical support was provided by GEM, the County Department of Public Works, and the Tallahassee-Leon County Planning Department. The Study Group reviewed the scope of the studies that already have been conducted of the environmental quality of lakes and the hydrology and conveyance systems for storm water in the study basins. We did not conduct a thorough review of the content of the available studies; that is a task to be included in the Scope of Work for the storm water study. We also reviewed the state and county regulations that govern storm water discharges to surface water bodies. Storm water experts were also consulted from various agencies and organizations including Florida State University, the University of Florida, Georgia Institute of Technology, Camp, Dresser, and McKee, the Florida Department of Environmental Protection, the U.S. Geological Survey, the Northwest, Southwest, and St. Johns Water Management Districts, and the Atlanta Regional Commission.

Recommended Substantive Focus of the Study (pp. 3-4)

The Study Group recommends that the focus of the Bradfordville storm water study be directed at two principal issues:

(1)the effects of storm water quality on the environmental quality of the lakes within the study basins, and

(2)the potential for future development to create or exacerbate flooding problems within the study basins.

During our conversations with representatives of the homeowner associations that were parties to the Publix Mediation Agreement and other residents of the Bradfordville area two other issues were raised: (1) the potential impacts of storm water discharges on ground water quality and (2) the effects of development on "environmentally sensitive areas." While these are issues that merit attention by the Board of County Commissioners, we believe that they are not as urgent as those concerning flooding or the environmental quality of lakes within the study basins.

Recommended Geographic Focus of the Study (pp. 4-5)

Figure 1 (see "Final Report") defines the recommended geographic boundaries of the area to be encompassed by the Bradfordville storm water study.

The Study Group recognizes that the impacts of storm water generated within the study basins may extend to water bodies beyond these boundaries. The analyses performed for the Bradfordville storm water study should include projections of storm water volumes, rates, stages, and quality that can be used as inputs to subsequent analyses that may be done for other portions of the drainage basins of which the study basins are a part.

Findings Concerning the Issues to be Addressed in the Study

The Study Group reviewed the scope of the studies that already have been conducted of the environmental quality of lakes and the hydrology and conveyance systems for storm water in the study basins. We did not conduct a thorough review of the content of the available studies; that is a task to be included in the Scope of Work for the storm water study. We also reviewed the state and county regulations that govern storm water discharges to surface water bodies. Here we summarize our findings.

Principles of How Lakes Work (pp. 6-7)

Lakes serve to varying degrees as "sinks" where suspended sediments, nutrients (nitrogen, phosphorus, and carbon), oxygen-demanding substances (biochemical oxygen demand or "BOD" and chemical oxygen demand or "COD"), and pollutants (metals and toxic organics) accumulate. Under natural conditions, a lake can assimilate a certain quantity of nutrient inputs on an annual basis without significant changes to its ecosystem. However, when this assimilative capacity is exceeded and nutrients accumulate, they eventually reach levels that cause changes in the plants and animals that live in a lake. This process is accelerated by human-caused increases in the loadings of nutrients that flow into a lake. When the levels of nutrients in a lake are already high, relatively small changes in nutrient loadings can cause the rapid expansion of populations of algae or aquatic plants. These can alter the habitat of a lake as well as produce significant declines in dissolved oxygen which can cause fish kills or other, more long-lasting changes in the lake's ecosystem. When metals or organic chemicals associated with storm water runoff from urbanized areas accumulate in aquatic ecosystems they can cause diseases among fish and other aquatic organisms and can eventually lead to the loss of some species. Elevated levels of such pollutants in fish may also make them unsafe for human consumption.

Findings Regarding the Environmental Quality of Lakes in the Study Basins (pp. 7 9)

The following summarizes what the Study Group has been able to conclude from the information currently available about the environmental quality of the lakes within the study basins.

1.The lakes within the study basins vary in their origins and uses.

2.The available data are insufficient for estimating the additional storm water loadings that the lakes in the study basins can assimilate without causing significant changes to their environmental quality.

3.Water quality degradation will eventually occur in most of the smaller lakes in the study basins.

4.Most of the small lakes in the study basins are likely to be highly sensitive to increased loadings of suspended sediments, nutrients, or oxygen-demanding substances from additional storm water discharges.

5.Available information for Lake McBride indicates that it also may be quite sensitive to increased storm water loadings.

6.No information is available on metals or organic pollutants, but caution is warranted.

Findings Regarding Potential Flooding Problems (pp. 9-10)

Based on our review of information provided to us by the County Department of Public Works about existing and proposed studies of storm water hydrology and conveyance systems within the study basins we conclude the following:

1.Considerable analysis of storm water discharge volumes and conveyance has been completed or is in progress for study basins 1, 2, 3, and 5 (see Figure 1).

2.Conveyance modeling has not been completed for Basin 4 (Lake McBride).

3.The focus of the previous studies was downstream of the Bradfordville area. Therefore this previous work may have to be analyzed, extended, and re-presented to address the more localized concerns with potential flooding within the study basins.

4.Some extension of previous conveyance modeling may be required to provide consistent analyses for comparable future development scenarios.

Findings Regarding Applicable Standards (pp. 10-11)

Our findings regarding current state and local standards that may be applied in determining how best to minimize the cumulative adverse impacts of storm water on private property and the environment include the following:

1.Adherence to state numerical standards for surface water quality does not guarantee protection of the environmental quality of lakes in the study basins.

2.It is not possible at this time to estimate how effective any specific "best management practices" (BMPs) for storm water are likely to be in preventing or delaying the degradation of the lakes in the study basins.

3.BMPs for protecting water quality during construction are the weakest link in the storm water management system.

Recommendations

Recommended Short-Term County Initiatives (pp. 12-13)

The Study Group recommends that the Board of County Commissioners take initiatives immediately that minimize the potential for significant water quality impacts during the construction of new development and from finished developments that may be initiated before completion of the storm water study. We believe these initiatives are consistent with the language of Section 4.b. of the Publix Mediation Agreement and the intent of policies 8.1.2 and 8.2.1 of the County Comprehensive Plan.

1.The Board of County Commissioners should adopt a policy of strict enforcement of county regulations governing control of erosion and sedimentation during construction and should provide adequate staff and supporting resources to the Department of Growth and Environmental Management to assure frequent inspection of construction sites that have significant potential for impacting vulnerable surface water bodies throughout the county.

The committee emphasizes that adequate control of storm water during construction is essential. Given the evident sensitivity of the lakes in the study basins to increases in sediment and nutrient loadings, the impacts of inadequately controlled construction runoff may be sufficient to seriously degrade a lake. The potential impact on Lake McBride of the proposed widening of Thomasville Road and related commercial development is a specific area of concern in this regard.

We recommend that the Commission require the use of best management practices (BMPs) and/or source controls that limit loadings per acre of suspended sediments, nutrients, and oxygen-demanding substances to levels that are equivalent to the loadings per acre that would occur if the storm water from residential development at a density of one unit per acre were subjected to wet detention treatment of the runoff from the first 3 inches of rainfall, with the detention treatment volume available again within 72 hours of the storm event, and no more than one-half of the treatment volume discharged within the first 60 hours.

The committee must stress, however, that without the knowledge to be gained from the proposed study, there is no guarantee that any particular BMP will provide adequate protection for any of the individual lakes in the study area.

1.The Board of County Commissioners should avoid making significant changes that intensify allowable land uses within the study basins during the course of the storm water study so as to avoid undermining the validity of the study before it is completed.

Recommended Objectives of the Study (pp. 13-15)

The Study Group recommends that the Bradfordville storm water study be conducted in two phases. The first phase would principally focus on water quality concerns because this is where there is the greatest need for new information. The first phase would also include a review and assessment of the existing information on storm water hydrology and conveyances. The second phase would involve filling in the gaps identified by that assessment.

Therefore, we recommend the following specific objectives for the two-phased storm water study. The more detailed Proposed Scope of Work lays out the specific tasks that we recommend be included in a request for proposals (RFP) for the study.

Phase One (estimated duration six to twelve months)

1.To classify the lakes in the study basins according to origin, principal uses, and important physical attributes likely to influence vulnerability to storm water discharges.

2.To characterize the current environmental quality and the trophic state of each of the lakes in the study basins based on existing data.

3.To collect additional data as necessary to characterize the trophic states of each of the lakes in the study basins under typical, seasonal, worst-case conditions.

4.To identify the one lake in each study basin that is most vulnerable to degradation of environmental quality as a result of urban storm water discharges. These "designated" lakes are to be the focus of the storm water quality impact analyses that follow. If two or more of these lakes are sufficiently similar, the sample of designated lakes may be reduced to no fewer than three.

5.To estimate the probable water quality treatment performance of storm water quality best management practices, designed to meet current county design and performance standards, when operated and maintained under typical (rather than ideal) practices.

6.To estimate current average annual loadings of suspended solids, nutrients, and oxygen demanding substances from point and non-point sources to each designated lake.

7.To estimate the annual loadings of suspended sediments, nutrients, and oxygen-demanding substances that each designated lake can assimilate without changes in water quality that exceed the mesotrophic ranges for Secchi disk transparency, total nitrogen, total phosphorus, and chlorophyll a.

8.To estimate future loadings to each designated lake for alternative future land use scenarios based on the probable water quality treatment performance of storm water management facilities designed to meet existing county design and performance standards.

9.To estimate the cumulative impact of projected loadings on the water quality of the designated lakes.

10.To assess the effectiveness of alternative changes to current county development standards and/or permissible land uses, including the interim standards recommended by the Study Group, that could be initiated by the county to reduce the cumulative water quality impacts of storm water discharges from future development to acceptable levels.

11.To review, summarize, and evaluate the existing analyses of storm water hydrology and conveyance for all study basins.

12.To describe and estimate the costs of any additional analyses that are needed to predict the potential for increases in the frequency, duration, stage, or extent of flooding within the study basins as a result of storm water discharges from new development.

Phase Two (estimated duration six months)

1.To conduct the supplemental analyses of storm water hydrology and/or conveyance identified under Phase One, Objective 12 as being needed to fully characterize the potential flooding impacts of new development within the study basins under alternative future land use scenarios.

2.To assess the effectiveness of alternative changes to current county development standards, permissible land uses, and/or storm water conveyance structures that could be initiated by the county to reduce the cumulative flooding impacts of storm water discharges from future development to acceptable levels.

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