Proposed Scope of Work
Bradfordville Storm Water Study

prepared by the
Bradfordville Citizen Storm Water Study Group

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
Proposed Scope of Work
Bradfordville Storm Water Study

Phase One

1.Classify each of the lakes within the study basins by origin, principal uses, and physical attributes likely to influence vulnerability to storm water discharges:

a.Origin/Use categories such as

-Type A - Natural water body

-Type B - Natural or pre-existing, artificial water body, with or without modifications, to which storm water has intentionally been directed from existing development

-Type C - Artificial water body designed at least in part for storm water rate control and/or water quality treatment

b.Physical attributes such as

-Ratio of lake volume to watershed area-

Residence time of the lake based on average annual runoff-

Ability to be drawn down

a.Include the following lakes: -

Study Basin 1: Arrow Head Lake and the Horseshoe Plantation lake (if access can be obtained)-

Study Basin 2: Lake Anna, Lake Carolyn, Lake Warner, and Gilbert Pond-

Study Basin 3: Lake Jeff, Rabbit Pond (Lake Jamie), Lake Mary Ann, Lake Charles, Lake Bess, Lake Faye, and Lake Tom John-

Study Basin 4: Lake McBride-

Study Basin 5: Pine Hill Lake, Lake Petty Gulf, Lake Diane, Blue Heron Lake, and Lake Monkey Business

temperature, pH, conductivity, alkalinity, color, depth, Secchi depth-

dissolved oxygen, dissolved oxygen saturation-

total dissolved solids, total suspended solids, turbidity-

biochemical oxygen demand (BOD)-

nitrate-nitrite, total Kjeldahl nitrogen (TKN), ammonia-

total phosphorus, ortho-phosphate-

total organic carbon-

chlorophyll a-

fecal coliform, fecal streptococci-

numbers of benthic macro invertebrates, numbers of taxa, measure of biodiversity, and description of macrophyte communities

3.Collect additional data as necessary to characterize the trophic states of each of the lakes listed in Phase One, Task 2.a. under typical, seasonal, worst-case conditions, based on the TSI parameters listed in Phase One, Task 2.c.

a.Design and implement a data collection and analysis program to supplement the existing data for Secchi depth, TKN, total phosphorus, and chlorophyll a.

b.For each lake, report the trophic state ranges within which the observed values fall for Secchi disk transparency, TKN, total phosphorus, and chlorophyll a, as described in Phase One, Task 2.c.

c.Indicate for each TSI parameter whether the levels recorded under typical, seasonal, worst case conditions exceed the mesotrophic range for the TSI parameters used by the Florida Lake Watch Program as described in Phase One, Task 2.c.

d.Identify potential emergent problems based on existing trend data and the supplemental data collected in Task 3.a., i.e. likely changes in water quality that would exceed the mesotrophic ranges for the TSI parameters used by the Florida Lake Watch Program.

4.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 based on the following characteristics. 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, further reduce the sample of designated lakes to no fewer than three.

a.Physical attributes - see Phase One, Task 1.b.

b.Available environmental quality data - see Phase One, Tasks 2 and 3

c.Existing and allowed land uses within the watershed of each lake

5.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.

a.Review applicable studies of the actual water quality treatment performance of storm water management facilities operated and maintained under typical practices; see for example Kehoe (1993), Kehoe et al. (1994), Harper (1995), and Nepshinsky et al. (1995).

b.Supplement the information reviewed in Task 5.a. with the collection and analysis of samples from the two storm water management facilities located in the Publix shopping center in Bradfordville.

Samples should be collected and analyzed for inflow to the facility and effluent from rate control and infiltration for three storm events each of which is at least one month apart. Parameters to be analyzed include total suspended solids, TKN, nitrate-nitrite, ammonia, total phosphorus, ortho phosphate, BOD5, and COD. Sampling and analysis procedures should generally follow those for NPDES MS4 permit applications as set forth in 40 CFR 122.21(g)(7) and 40 CFR 136.

6.Using an appropriate storm water quality model, calibrated through representative sampling of storm events within the time and resource constraints of this study, plus the results of the analyses conducted in Phase One, Task 5, estimate current average annual loadings of suspended solids, nutrients, BOD, and COD from point and non-point sources to each lake designated in Phase One, Task 4. These loading estimates should account for removals that occur upstream from each designated lake through deposition and assimilation in other water bodies.

a.Develop and calibrate one or more models of the physical, chemical, and biological functions and dynamics of aquatic ecosystems that can be applied to the different classes of water bodies included in the study basins (see Phase One, Task 1) to predict the effects of changes in storm water loadings on the water quality of the designated lakes as measured by the Lake Watch TSI parameters.

In response to the RFP describe and document the model(s) and/or modeling technique(s) that are to be used to accomplish this task and how the models would be calibrated to the conditions of the water bodies in the study basins.

8.Estimate future loadings to each of the designated lakes 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.

a.Determine the allowable land uses for each study basin under the current land use plan and zoning ordinance.

b.Define two future land use scenarios for each study basin:-

Build-out at the maximum intensities and densities allowed under the current county standards for maximum impervious area, natural areas, and landscaping requirements (Sections 10-257 and 10-258 of the Leon County Land Development Regulations).-

Build-out at the maximum intensities and densities allowed under the current county "site design alternative" to minimize natural areas, increase landscaping, and impervious areas (Section 10-259 of the Leon County Land Development Regulations).

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

a.Apply the model(s) developed in Phase One, Task 7.a. to estimate the water quality conditions in each of the designated lakes that are likely to result from the cumulative effect of the future loadings projected in Phase One, Task 8.

b.Determine the extent to which the projected cumulative impacts may result in exceeding the mesotrophic ranges for the TSI parameters used by the Florida Lake Watch Program as described in Phase One, Task 2.c.

10.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.

a.For lakes similar to those identified in Phase One, Task 9 as likely to experience unacceptable cumulative impacts on their environmental quality from development that is currently permitted under the county's land use plan and zoning ordinance, apply the methods employed in Phase One, Task 9.a. to evaluate the following alternative policy changes:-

changes in storm water source control requirements-

changes in storm water treatment facility design or performance standards-

changes in allowable land use types or intensities, percent of impervious area, or other relevant modifications of the county zoning ordinance or environmental management act.

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

a.Characterize the sources of current storm water inputs to each water body including-

Acreages of land in each major land use category - apply categories for which there are significant differences in storm water loadings of suspended sediments, nutrients, and/or oxygen-demanding substances (BOD and COD)-

Percentage of impervious surface area in the drainage basin -

Nature of storm water inputs - diffuse flow, discharges from conveyances or storm water management facilities-

Identification of specific storm water discharges from culverts or other storm water conveyances or management facilities and the areas they drain

c.Identify individual conveyances that are not adequately modeled in the existing studies, including new conveyances that have been constructed since those studies were conducted.

d.Determine whether the scale, precision, and assumptions of existing analyses are appropriate for predicting the potential for increases in the frequency, duration, stage, or extent of flooding as a result of storm water discharges from new development within the study basins.

e.Based on available data, make a preliminary determination of whether storm water discharge volumes or rates from proposed development in the Bradfordville area may have unacceptable impacts on the water level of Lake McBride or the adequacy of the outlet structure.

12.Based on Phase One, Task 11, 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

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

a.Identify areas within the study basins that are likely to experience new flooding problems or where existing problems may be exacerbated as a result of future land use as defined by the scenarios specified in Phase One, Task 8.b.

b.Characterize new conveyances that were not analyzed in previous studies.

c.Identify any storm water conveyances within the study basins that may not have sufficient capacity to accommodate the storm water runoff volumes and rates projected to result from the future land use scenarios.

d.Refine as necessary projected storm water discharge volumes, rates, and stages from each of the study basins under the alternative land use scenarios.

e.Detail all assumptions upon which projections are made including-

Applicable design and performance standards governing storm water generation (e.g. allowable impervious surface area) and management (e.g. storm water detention, retention, filtration)-

Assumed runoff rates for each land use type, intensity, and density-

Assumptions of model(s) used to predict flooding impacts of storm water inflows and discharges

2.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.

a.For study basins identified in Phase Two, Task 1.a. as having the potential to experience changes in existing conditions as a result of projected future development, identify and evaluate alternative structural and non-structural initiatives the county could take to prevent such flooding.

b.Identify and evaluate alternative strategies for remedying potential problems that may result from inadequate storm water conveyances identified in Phase Two, Task 1.c.

References Cited

Forsberg, Curt and Sven Olof Ryding. 1980. "Eutrophication Parameters and Trophic State Indices in 30 Swedish Waste-Receiving Lakes." Arch. Hydrobiol. 89: 189-207.

Harper, Harvey. 1995. "Pollutant Removal Efficiencies for Typical Stormwater Management Systems in Florida." In Proceedings of the 4th Biennial Stormwater Research Conference. October 18-20. pp. 6-19. Brooksville, FL: Southwest Florida Water Management District.

Kehoe, Mark J. 1993. Water-Quality Survey of Twenty-Four Stormwater Wet-Detention Ponds (Final Report). Brooksville, FL: Southwest Florida Water Management District.

Kehoe, Mark J., Craig W. Dye, and Betty T. Rushton. 1994. A Survey of the Water-Quality of Wetlands-Treatment Stormwater Ponds (Final Report). Brooksville, FL: Southwest Florida Water Management District

Kratzer, C. R., and Brezonik, P. L. 1981. "A Carlson-Type Trophic State Index for Nitrogen in Florida Lakes." Water Resources Bulletin 17: 713-715.

Nepshinsky, Janis, C. Dewey, P. Victor, and R. Brown. 1995. "Water Quality Assessment of Permitted Stormwater Management Systems." Paper presented at the 4th Biennial Stormwater Research Conference, October 18-20, Clearwater, FL. Palatka, FL: St. Johns Water Management District.