VOLUSIA_BLUE_WETLAND_RECHARGE_PROJECT.pdf

VOLUSIA BLUE WETLAND RECHARGE PROJECT

PRELIMINARY DESIGN STUDY UPDATE

LOAD TEST ANALYSIS

St. Johns River Water Management District | May 2021

VOLUSIA BLUE WETLAND RECHARGE PROJECT

PRELIMINARY DESIGN STUDY UPDATE

LOAD TEST ANALYSIS

Prepared for:

Volusia County

Water Resources and Utilities

3151 E. New York Avenue, 2nd Floor

Deland, Florida 32724

Prepared by:

Jones Edmunds & Associates, Inc.

730 NE Waldo Road

Gainesville, Florida 32641

Certificate of Engineering Authorization #1841

Geological Authorization #133

Jones Edmunds Project No.: 22015-022-01

May 2021

22015-022-01 i May 2021 Table of Contents

TABLE OF CONTENTS

1 INTRODUCTION

1.1 Purpose

2 SITE LOCATION

3 PROJECT EVALUATION

3.1 Groundwater Flow Model

3.1.1 Description of the SJRWMD Volusia Model

3.1.2 Local-Scale Model Development

3.1.3 Assumptions

3.1.4 Model Loading Analysis

3.1.5 Sensitivity Analysis

3.1.6 Load Testing

3.2 Site Layout

3.2.1 Infiltrating Wetland

4 PERMITTING AND COMPLIANCE

4.1 Wetland Mitigation Credits

5 WATER SUPPLY TO THE AREA

6 SUMMARY

7 REFERENCES

LIST OF TABLES

Table 1 Model Parameters

Table 2 Cell No. 1 Infiltration Calculations

Table 3 Cell No. 2 Infiltration Calculations

Table 4 Cell No. 3 Infiltration Calculations

Table 5 Cell No. 3 Recharge Period Infiltration Calculations

Table 6 Expanded Cell No. 3 Infiltration Calculations

Table 7 Site Summary Infiltration Calculations

Table 8 Summary of Potential Regulatory Agencies and Permitting List

LIST OF FIGURES

Figure 1 Site Location Map

Figure 2 Model Grid

Figure 3 Model Surficial Aquifer (Layer 1) Top Elevations

Figure 4 Model UFA (Layer 2) Top Elevations

Figure 5 Model Leakance

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Figure 6 Model Water Elevations vs. Surface Water Elevations

Figure 7 Model Results

Figure 8 Sensitivity Analysis Results

Figure 9 Load Test Cells

Figure 10 Load Test Water Levels

Figure 11 Cell No. 1 Load Test Data

Figure 12 Cell No. 2 Load Test Data

Figure 13 Cell No. 3 Load Test Data

Figure 14 Cell No. 3 Expanded Load Test Data

Figure 15 Cell No. 3 Expanded Load Test Data

Figure 16 Conceptual Site Plan to Recharge between 0.5 and 0.6 MGD

APPENDICES

Appendix A Load Test Plan

Appendix B Load Test Flow and Rainfall Data

22015-022-01 iii May 2021 Executive Summary

EXECUTIVE SUMMARY

The B&H Excavation Site, approximately 0.5 mile northeast of Blue Spring, was identified as a potential recharge site by the West Volusia Water Suppliers (WVWS) and the St. Johns

River Water Management District (SJRWMD). The site is an active mine covering approximately 60 acres that was excavated to approximately 40 to 50 feet below natural grade. The west side of the property borders a 10-inch force main owned by the Florida

Department of Transportation that conveys stormwater discharge from Mill Lake to the St.

Johns River.

Initial investigations at the site along with aquifer modeling was conducted and submitted in the Volusia Blue Wetland Recharge Project Preliminary Design Study (December 2018). The conclusions identified in the Preliminary Design Study show that the analysis and modeling was heavily dependent on the leakance variable, showing that onsite testing was required to further advance the analysis.

Subsequently, WVWS and SJRWMD proceeded with large-scale testing at the site that included the construction of large rapid infiltration basins (RIBs) filled with stormwater

(from a 10-inch stormwater force main discharging from Mill Lake) to measure the actual infiltration rates. Although the original plan for the site required a recharge rate of 2 to 5 million gallons per day (MGD) to be beneficial to all parties, the testing showed that the site is only able to handle approximately 0.5 to 0.6 MGD, well under the original design estimates.

This report updates the information presented in the Preliminary Design Study with the data from the onsite load testing of the RIBs and presents a design option involving treatment wetlands and wet-weather storage that may make this a viable project for some of the

WVWS members.

22015-022-01 1 May 2021 Preliminary Design Study

1 INTRODUCTION

Paragraph 373.042(2) of the Florida Statutes (FS) mandates the St. Johns River Water

Management District (SJRWMD) to adopt minimum flows and levels (MFLs) for all first-magnitude springs (springs with long-term average flows of at least 65 million gallons per day [MGD]).

SJRWMD approved a Minimum Flow Regime (MFR) for Blue Spring and Blue Spring Run in

December 2006. Adopting an MFR for Blue Spring protects the spring from a reduction in flows that could threaten its water resource values and functions including its use as a reliable winter warm-water refuge by manatees.

The Volusia MFLs prevention and recovery strategy requires groundwater withdrawals to be maintained at or below sustainable limits or for impacts from groundwater withdrawals to be offset through reclaimed water use, aquifer recharge and water supply projects, and conservation and regulatory measures. Projects and measures proposed in the strategy are designed to ensure MFLs in Blue Spring and the affected lakes (other than Indian Lake) continue to be achieved and to meet future water demands for public water supply utilities and other water users throughout Volusia County.

The B&H Excavation Site, approximately 0.5 mile northeast of Blue Spring, was identified as a potential recharge site by the West Volusia Water Suppliers (WVWS) and SJRWMD. The site is an active mine covering approximately 60 acres that has been excavated to approximately 40 to 50 feet below natural grade. The west side of the property borders a

10-inch force main owned by the Florida Department of Transportation (FDOT) that conveys stormwater discharge from Mill Lake to the St. Johns River.

1.1 PURPOSE

This report updates the Preliminary Design Study by presenting the data collected from load tests conducted at the site and updating the conceptual site plan for a beneficial use recharge/wet weather storage area. The background information used for preparing the groundwater capacity analysis model was presented in the Preliminary Design Study, and other than the exact initial model parameters and justification for needing the load tests, that information is not repeated here.

2 SITE LOCATION

Figure 1 shows the project area is in west Volusia County in Section 4 of Township 18 South and Range 30 East. The Site is approximately 0.5 mile northeast of Blue Spring on the south side of West French Avenue, approximately 1.8 miles west of the intersection of French

Avenue and US Highway 17-92 in Orange City, Volusia County, Florida.

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Figure 1 Site Location Map

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The property is currently an active excavation site. Land use near the project area includes residential and upland forest to the north, residential areas to the east and southeast, and upland forest to the south and west.

3 PROJECT EVALUATION

3.1 GROUNDWATER FLOW MODEL

Jones Edmunds performed a groundwater capacity analysis using the SJRWMD’s Volusia

Steady-State model to evaluate the potential recharge benefit to Blue Spring. Jones

Edmunds refined the model grid around the site and used the geotechnical data collected to modify the surficial aquifer hydraulic properties and develop an uncalibrated steady-state model of the site. The model was used in the Preliminary Design Study to assess the feasibility of the site to accept a recharge rate of between 2 to 5 MGD.

The conclusion of that report was that a load test at the site needed to be conducted to accurately determine the leakance at the site. The following sections describe the model with the details of the load test starting in Section 3.1.6.

3.1.1 DESCRIPTION OF THE SJRWMD VOLUSIA MODEL

SJRWMD developed the Volusia County groundwater flow model to simulate the surficial aquifer system (SAS) and the Floridan aquifer system (FAS) and to facilitate the evaluation of water resources in east-central Florida. The model was constructed using the

US Geological Survey (USGS) MODFLOW code (McDonald and Harbaugh, 1988), a three-dimensional finite-difference simulation tool. The model was calibrated to predevelopment hydrologic conditions and to average 1995 conditions. The Volusia model covers almost all of Volusia County, parts of south Flagler, east Lake, and north

Seminole Counties, and small portions of Putnam, Orange, and Brevard Counties. The coordinate system used for the Volusia model is the HARN UTM Zone 17N projection, North

American Datum of 1983 (NAD83).

The Volusia model was developed as a three-layer model with a constant grid spacing of

2,500 feet. Layer 1 corresponds to the SAS. Layer 2 represents the Upper Floridan Aquifer

(UFA) system. Layer 3 represents the Lower Floridan Aquifer (LFA) system. The three aquifer layers are simulated explicitly based on elevation data, and confining units representing the intermediate confining unit and the middle semi-confining zone are simulated as non-uniform areal distributions of leakance terms. Springs are modeled as drain cells, and surface water bodies greater than 500 acres in areal extent are modeled as river cells. A steady-state calibration was performed based on the average 1995 conditions.

3.1.2 LOCAL-SCALE MODEL DEVELOPMENT

3.1.2.1 Model Grid and Boundaries

Due to the large grid spacing of 2,500 feet in the Volusia model, the grid spacing in the local-scale model needed to be adjusted to accurately simulate the proposed recharge and mounding. Accordingly, the local-scale model was set up by defining a buffer zone of

10,000 feet around the site with a constant grid spacing of 100 feet. The grid spacing was

22015-022-01 4 then increased gradually outside the buffer zone by 50 percent until the maximum spacing reached 2,500 feet. As a result, the model area was discretized into 156 columns and

180 rows, and the model space area is 250,000 feet by 250,000 feet. Figure 2 shows the model grid.

Vertically, the hydrogeologic system in the model area was considered to consist of three layers representing the unconfined SAS shallow zone, the confined UFA, and the confined

LFA. The model was developed as a quasi-three-dimensional model in which the semi-confining layer between the SAS and UFA is simulated using a leakance term.

The refinement of the grid near the drain cell for Blue Spring required that the drain cell be adjusted to more accurately locate it spatially in the refined model grid. The drain representing Blue Spring is simulated in Layer 2 with a stage elevation of 1.5 feet, which was imported from the Volusia model.

3.1.2.2 Aquifer Parameters

Initial aquifer properties, SAS hydraulic conductivity, UFA transmissivity, and the leakance across the confining unit were imported from the Volusia model. The aquifer properties were revised using the site-specific survey and geotechnical data to account for changes in site conditions due to previous mining of site soils, which have removed a large portion of the surficial aquifer and potentially the underlying confining unit (Table 1).

Table 1 Model Parameters

Parameter Layer Volusia Model Revised Model

Hydraulic Conductivity SAS 20 feet/day 15 feet/day

Transmissivity UFA 6,400 ft2/day 6,400 ft2/day

Thickness SAS 51.6 – 58.2 feet 10.7 – 64.8 feet

UFA 326 – 340 feet 274 – 332 feet

Leakance SAS 0.00012 day-1 0.00012 – 0.0347 day-1

Note: ft2/day = square feet per day.

A survey of the site was used to revise the Layer 1 elevations. The model cells are 100 feet by 100 feet. The average cell top elevation was determined from the survey data and imported into the model. Figure 3 shows the Layer 1 top elevations used in the model. The top-of-limestone elevations from the boring logs were used to estimate the bottom of

Layer 1/top of Layer 2. Figure 4 shows the estimated top-of-limestone elevations used in the model.

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Figure 2 Model Grid

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Figure 3 Model Surficial Aquifer (Layer 1) Top Elevations

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Figure 4 Model UFA (Layer 2) Top Elevations

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The Layer 1 hydraulic conductivity and leakance parameters were then modified based on the extents and thicknesses of clayey materials identified in the boring logs and electrical resistivity imaging (ERI) profiles. The leakance parameters and surficial aquifer hydraulic conductivity were adjusted until the steady-state surficial aquifer water levels were approximately equal to the observed elevations in B-1 and the surface waters. Figure 5 shows the adjusted leakance used in the model. Figure 6 compares the modeled heads to the surface-water elevations obtained at the site.

Other than refinement of the drain location, the model boundary conditions and the properties of the LFA were not revised. A net recharge of approximately 24.4 inches per year (in/yr) (imported from the Volusia model) was used in the model.

3.1.3 ASSUMPTIONS

The following assumptions were included in the development of the hydraulic model:

Each layer is isotropic and homogeneous.

Net recharge is constant throughout the modeled area.

The loading rate is constant throughout each application area.

Leakage occurs from the surficial aquifer through the semi-confining unit.

The capacity analysis is steady-state.

Storage in the surface-water ponds is ignored.

Saturated conditions were assumed in which unsaturated vertical infiltration is neglected.

3.1.4 MODEL LOADING ANALYSIS

Once the groundwater model parameters were adjusted, a capacity analysis of the site was initiated. Since the site is an excavated mine, approximately 30 to 40 feet of elevation difference exists between the bottom of the pit and the top-of-bank. Accordingly, the assumption was that water levels in the pit could rise above ground surface. The lowest top-of-bank elevations are on the northeast side of the site at approximately 45 feet North

American Vertical Datum of 1988 (NAVD88). A berm approximately 5 feet high borders the property in this area, and the east toe of the berm is approximately 40 feet. Model simulations were run up to 38 feet to allow a buffer between the water surface and the lower elevations in the northeast corner of the site.

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Figure 5 Model Leakance

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Figure 6 Model Water Elevations vs. Surface Water Elevations

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The model was set to run in steady-state mode, and Specified Heads were added to the model cells within the proposed recharge area to simulate potential post-loading water elevations at the site. Multiple Specified Head scenarios were run to simulate water elevations between 18 to 38 feet NAVD88. The cells’ Constant Head mass balance was calculated for each simulation to determine the flux of water (i.e., site recharge capacity) needed to maintain the Specified Head elevation. Figure 7 shows the results of the model simulations.

Figure 7 Model Results

Since the goal of the project is to benefit flows from Blue Spring, we also used the model to estimate the potential benefit to the Spring. Blue Spring is simulated in the model as a drain cell in Layer 2. We used the pre- and post-loading mass balance of this drain cell to calculate the additional groundwater flow to the spring for each Specified Head simulation.

The red line in Figure 7 shows the estimated additional spring flow for each scenario as estimated in the modeling.

3.1.5 SENSITIVITY ANALYSIS

A sensitivity analysis was performed to evaluate the model’s response to changes in the leakance parameter. For the analysis, simulations were run where the leakance was reduced by half and where the leakance was doubled. The sensitivity analysis results show that reducing the leakance by half reduces the site capacity by half, whereas doubling the leakance approximately doubles the site capacity. Figure 8 summarizes the results of sensitivity analysis.

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Figure 8 Sensitivity Analysis Results

3.1.6 LOAD TESTING

The model was found to be very sensitive to the leakance parameter, resulting in large changes in water level for a target recharge rate. A design using wetland treatment requires a reasonably accurate estimate of water elevation; therefore, we recommended that the site be further evaluated through load testing. A test plan was developed to route water from

Mill Lake to load test three cells of approximately 3 to 4 acres each. Appendix A presents the load test plan and details additional monitoring wells installed for testing. Figure 9 shows the load cells and monitoring wells. The goal was to load each cell at approximately 1 foot per day – requiring a flow of approximately 1 to 1.3 MGD. During loading, water levels in the cells and monitoring wells were measured using staff gauges and/or pressure transducers. Rainfall was measured daily from a rain gauge installed at the site. SJRWMD provided potential evaporation data from the National Land Data Assimilation System

(NLDAS) tensioned to USGS potential evaporation using the factors documented in the

North Florida Southeast Georgia Groundwater Model (Durden, et. al. 2019). The County collected daily flow from a flow meter installed at the site. Appendix B presents the flow and rainfall data collected by the County during testing. Figure 10 shows the water elevations collected during testing. The data collected were used to estimate infiltration rates and refine the site capacity estimate.

3.1.6.1 Cell 1 Load Test

The County constructed Cell No. 1 on the west site of the site to evaluate an anomaly identified in the ERI survey that potentially represents a paleosink. The cell was constructed by leveling the cell bottom and moving materials at the site to create a berm approximately

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Figure 9 Load Test Cells

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Figure 10 Load Test Water Levels

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3 feet high around the perimeter. Staff Gauge SG-1 was placed inside the load cell. Surficial monitoring wells SMW-1 and PZ-9S are around the perimeter of the cell and were used to monitor aquifer levels during testing. PZ-9D was damaged and could not be used for monitoring.

Loading of Cell No. 1 began on June 2, 2020, and ended on June 3, 2020, when water levels reached the top of the berm. The flow meter stopped working during loading; however, the flow rate into the Cell was estimated to be 1 MGD. The County diverted flow to Cell No. 3 on the east side of the site while recovery in Cell No. 1 was observed. Several days of rainfall followed loading of Cell No. 1. Due to potential inaccuracies in the rainfall readings, we waited for water levels in Cell No. 1 to begin declining before using the recovery data to calculate infiltration rates. Water levels declined 6.36 inches (0.53 foot) from June 9, 2020, through June 24, 2020, and the cell received 4.75 inches of rainfall. The potential evapotranspiration (ET) during the recovery period was 3.41 inches. Figure 11 shows rainfall and the water levels measured in Cell No. 1 and the surficial monitoring wells during the load test and recovery period. Table 2 shows the measurements used to calculate infiltration. Assuming an evaporation equal to potential ET, the infiltration rate at Cell No. 1 over this period was 0.528 inch per day (Infiltration Rate = Water Level Decline + Rainfall –

ET). The pond elevation was approximately 23 feet NAVD88 during loading and surficial aquifer levels were approximately 10 feet NAVD88. Accordingly, the infiltration rates calculated are expected to be representative when 10 feet of hydraulic head can be maintained between the load cell and surficial aquifer.

Figure 11 Cell No. 1 Load Test Data

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Table 2 Cell No. 1 Infiltration Calculations

Measurement Location

Date/Time Measurement

Type Result Change

SG-1

SG-1

6/9/2020 22:00 Water Level

22.72 feet

0.425 inch/day

6/24/2020 23:00 22.19 feet

SMW-1

SMW-1

6/9/20 22:00 Water Level

10.89 feet

0.774 inch/day

6/24/20 23:00 9.92 feet

Rainfall Gauge

6/9/20

Rainfall

1.00 inch

0.317 inch/day

6/11/20 1.25 inches

6/12/20 0.25 inch

6/15/20 0.50 inch

6/19/20 0.50 inch

6/20/20 1.25 inches

Deland 6/9/20 to 6/24/20

Potential Evaporation

0.018 foot 0.213 inch/day

County staff observed significant amounts of clay at ground surface during construction of

Cell No. 1. After the initial load test showed slow recovery, the County dug clays out of the perimeter of the cell. A thick dark gray/brown clay several feet thick was observed. The

County again diverted water to Cell No. 1 from July 21, 2020 through July 24, 2020.

Approximately 1.9 million gallons (MG) were added over the 4-day period before a berm broke allowing water to flow out of the west side of the cell. Recovery data could not be used because of the breach in the berm; however, County staff observed no appreciative decline in standing water remaining in this cell and noted that the clay beneath the cell was dry when excavated. This indicates that some of the water-level decline observed at Cell No.

1 may have been from seepage along the berm and the calculated infiltration may be overestimated.

3.1.6.2 Cell 2 Load Test

The County constructed Cell No. 2 in the center of the site to estimate recharge rates outside the anomalous areas identified in the ERI survey. The cell was constructed with berms approximately 3 feet above existing ground surface. A staff gauge and shallow monitoring well SMW-2 were placed inside the test cell. Surficial well SMW-1 is on the west side of the cell and a deep well DWM-2 was near the northeast corner of the cell to monitor water levels in the Floridan aquifer. Loading of Cell No. 2 began on June 15, 2020, and ended on June 18, 2020, when water levels reached the top of the berm. Approximately

2 MG were added to Cell No. 2 during the 4 days of loading. Recovery in Cell No. 2 was monitored until June 26, 2020. Over this time, water levels dropped approximately 0.1 foot,

1.75 inches of rainfall was received, and potential evaporation was 1.83 inches. The potential ET was greater than the rainfall and water-level decline observed; therefore, Cell

No. 2 was assumed to have no measurable infiltration. Figure 12 shows rainfall and the water levels measured in Cell No. 2 and the surficial monitoring wells during the load test and recovery period. Table 3 shows the measurements recorded during the recovery period.

Although a rise in SAS levels is evident at the start of the test, the increase began before

22015-022-01 17 loading started and appears to be a respond to rainfall. No visible response is evident to Cell

No. 2 loading in SMW-2 indicating little connection to the SAS in this area.

Figure 12 Cell No. 2 Load Test Data

Table 3 Cell No. 2 Infiltration Calculations

Measurement Location

Date/Time Measurement

Type Result Change

SG-2

SG-2

6/19/2020 0:00 Water Level

2.20 feet

0.171 inch/day

6/26/2020 0:00 2.10 feet

SMW-2

SMW-2

6/19/2020 8:00 Water Level

9.17 feet

0.606 inch/day

6/26/2020 8:00 8.82 feet

Rainfall Gauge 6/19/20

Rainfall

0.50 inch

0.250 inch/day 6/20/20 1.25 inches

Deland 6/19/20 to 6/26/20

Potential Evaporation

0.076 foot 0.916 inch/day

3.1.6.3 Cell 3 Load Test

The County extended a berm approximately 3 feet high around the perimeter of the pond on the east side of the site to construct Cell No. 3. The pond has been excavated deeper than other areas of the site and an ERI anomaly and deeper surficial sands indicate the presence of a possible paleosink in the area. Cell 3 was located to assess whether the

22015-022-01 18 removal of more surficial materials and the ERI anomaly correlate with higher infiltration. A staff gauge was placed inside the test cell, and shallow monitoring well SMW-3 was placed outside the cell to monitor surficial aquifer levels. Loading of Cell No. 3 began on

June 4, 2020, and ended on June 7, 2020, when water levels reached the top of the berm.

Approximately 4.3 MG were added to Cell No. 3 during the 5 days of loading. Several rainfall events occurred at the start of the recovery period; therefore, recovery data from

June 11, 2020, through June 18, 2020, were used to estimate infiltration. Over this time, water levels dropped approximately 0.35 foot, 2 inches of rainfall was received, and potential evaporation was 1.69 inches. Figure 13 shows rainfall and the water levels measured in Cell No. 3 and the surficial monitoring well during the load test and recovery period. Table 4 shows the measurements used to calculate infiltration. Assuming an evaporation equal to potential ET, the infiltration rate at Cell No. 3 over this period was

0.585 inch per day (Infiltration Rate = Water Level Decline + Rainfall – ET). The pond elevation was approximately 13 feet NAVD88 during loading and surficial aquifer levels were approximately 10 feet NAVD88. Therefore, the infiltration rates calculated are expected to be representative when 3 feet of hydraulic head can be maintained between the load cell and surficial aquifer.

Figure 13 Cell No. 3 Load Test Data

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Table 4 Cell No. 3 Infiltration Calculations

Measurement Location

Date/Time Measurement

Type Result Change

SG-3

SG-3

6/11/2020 3:00 Water Level

12.95 feet

0.541 inch/day

6/18/2020 23:00 12.60 feet

SMW-3

SMW-3

6/11/2020 3:00 Water Level

10.06 feet

0.598 inch/day

6/18/2020 23:00 9.67 feet

Rainfall Gauge 6/11/20

Rainfall

1.25 inches

0.255 inch/day 6/12/20 0.25 inch

6/15/20 0.50 inch

Deland 6/11/20 to 6/18/20

Potential

0.076 foot 0.211 inch/day

The measured infiltration rates are on the low end of the sensitivity analysis, and the potential errors in rainfall and ET represent a large portion of the water budget. Therefore, the County expanded the berm around Cell No. 3 to allow a larger load test. Expanding the cell footprint and raising the berm elevation allowed a longer recharge period, which allowed infiltration measurements during the recharge and recovery. The higher berm allowed a higher pond elevation or hydraulic head, which increases the infiltration rate and helps minimize the potential errors associated with rainfall and ET measurements.

For the expanded Cell No. 3 load test, the County expanded the cell area to approximately

10 acres and raised the berm elevation to 21.5 feet NAVD 88. The expanded Cell No. 3 was loaded from December 21, 2020, to January 22, 2020. Table 5 shows the flow to Cell No. 3 and the calculated infiltration during the recharge period, using the following equation:

Infiltration = Q + (R x A)– (ET x A) – (∆h x A), where:

Q = Measured Flow Volume

R = Rainfall Volume

ET = Potential Evapotranspiration

∆h = Change in Pond Elevation

A = Cell Area, 10 acres

Table 6 shows the infiltration rate calculated during the recovery period. Figure 14 shows rainfall and the water levels measured in the expanded Cell No. 3 and the surficial monitoring wells during the load test and recovery period.

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Table 5 Cell No. 3 Recharge Period Infiltration Calculations

Start Date Duration (days)

Q

(MG)

Q (cfd) R (in) R x A (cfd)

ET

(inch)

ET x A (cfd)

∆h (feet)

∆h x A (cfd)

Infiltration (gpd)

Infiltration Rate

(inch/day)

Dec. 24, 2020 7 2.72 51,948 0.40 2,074 0.40 2,086 0.48 29,870 165,055 0.61

Dec. 31, 2020 6 2.68 51,146 0.02 104 0.34 1,748 0.40 24,943 214,319 0.79

Notes: cfd = cubic feet per day; gpd = gallons per day.

Table 6 Expanded Cell No. 3 Infiltration Calculations

Measurement Location

Date/Time Measurement

Type Result Change

SG-5

2/5/2021 15:00

Water Level

15.57 feet

0.674 inch/day 2/25/2021 8:00 14.48 feet

SMW-2

2/5/2021 15:00

Water Level

8.02 feet 0.131 inch/day

2/25/2021 0:00 7.81 feet

Rainfall Gauge 2/16/2021

Rainfall

2.80 inches

0.152 inch/day 2/19/2021 0.15 inch

Deland 2/5/2021 to 2/25/2021

Potential Evaporation

1.83 inch 0.075 inch/day

SG-5

2/5/2021 15:00

Water Level

15.57 feet

0.652 inch/day 3/12/2021 8:00 13.68 feet

SMW-2

2/5/2021 15:00

Water Level

8.02 feet

0.129 inch/day 3/12/2021 7:00 7.65 feet

Rainfall Gauge 2/16/2021

Rainfall

2.80 inches

0.099 inch/day 2/19/2021 0.15 inch

Deland 2/5/2021 to 3/12/2021

Potential

2.94 inches 0.085 inch/day

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Figure 14 Cell No. 3 Expanded Load Test Data

3.1.6.4 Site Capacity Summary

Table 7 summarizes the measured infiltration rates during load testing. The highest infiltration rates occurred at Cell No. 3 on the east side of the site. This area corresponds to an ERI anomaly, and boring logs show a thicker layer of sand in this area. Additionally, more surficial materials have been excavated from this site. The infiltration observed at Cell

No. 3 likely occurs over a localized area where the confining layer has been breached and/or more porous limestone occurs. Expanding the cell or digging out additional materials would not guarantee a proportional increase in infiltration capacity because of the potential variability in the clay content of the upper limestone in this area. Therefore, for analysis of the full site capacity, we assumed that the infiltration rates observed at the expanded Cell

No. 3 are limited to the 10-acre footprint. An infiltration rate of zero was assumed for Cell

No. 2, and the remaining area (approximately 16 acres) was assumed to have an infiltration rate equal to 0.27 inch/day (half the rate observed at Cell No. 1). Based on these assumptions, the site would have a capacity of 0.303 MGD under similar hydraulic conditions. However, if hydraulic heads are increased, the infiltration capacity will increase in accordance with Darcy’s equation.

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Table 7 Site Summary Infiltration Calculations

Cell No.

Measured

Infiltration Range (inch/day)

Average Infiltration Rate

(inch/day)

Cell Size (acres)

Average Infiltration

(MGD)

1 0.53 0.53 3.7 0.053

2 0 0 3.9 0

3 0.58 – 0.79 0.685 10 0.186

We used Darcy’s equation to calculate the average vertical hydraulic conductivity under the expanded Cell No. 3 to determine the potential capacity at a higher hydraulic head as followings:

Where, Q = flow =0.186 MGD

K = hydraulic conductivity i – hydraulic gradient = (pond elevation – SMW-2 water level) ÷ SMW-2 screen depth

A – area = 10 acres

Using the above information, we calculated a hydraulic conductivity of 0.102 ft2/day for the materials under Cell No. 3. Figure 15 shows the projected increase in capacity under Cell

No. 3 with increasing hydraulic head, assuming a hydraulic conductivity of 0.102 ft2/day. If water levels were increased to the current berm elevation around Cell No. 3, the capacity is approximately 0.54 MGD. With a little additional capacity from Cell No. 1 and the surrounding areas, the total site capacity is approximately 0.65 MGD if the site were flooded to 21.5 feet NAVD88.

kiAQ =

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Figure 15 Cell No. 3 Expanded Load Test Data

3.2 SITE LAYOUT

Jones Edmunds and Wetland Solutions Inc. prepared a conceptual site layout based on the necessity of the site to recharge at least 0.5 MGD, provide additional wetland treatment, and provide wet-weather storage. Figure 16 shows a conceptual model for the site that would use the minimal recharge area observed in Load Cell No. 1 for the treatment wetlands with overflow ponds that terminate in the primary recharge area (Load Cell No. 3). The site is laid out so that all incoming recharge water goes through the treatment wetlands thereby keeping them hydrated until excess flow fills up the area and overflowing through the overflow wetlands areas into the primary recharge area during wet-weather events. The model for this site is to use infiltrating treatment wetlands instead of BAM filters for the final water polishing before flowing to the recharge area.

This site layout requires the inundation level to be around 21.5 feet NAVD to achieve a minimum of 0.5 to 0.6 MGD of recharge. This site would be designed so that as the water level builds up to this level it will be flowing into the main recharge area.

22015-022-01 24

Figure 16 Conceptual Site Plan to Recharge between 0.5 and 0.6 MGD

3.2.1 INFILTRATING WETLAND

Based on the very low recharge capacity as measured during the load test, the infiltrating wetland with flow through overflow wetlands to the main recharge area is the best option for this site. The main advantages of the infiltrating wetland system are that:

The treatment is passive – once the water is distributed to the cells, no pumps or valves are needed for the treatment and eventual distribution to the recharge area. However, and small pump station and piping may be needed to recirculate the water from the recharge area back to the treatment wetlands during the dry season when there is minimal reclaimed or stormwater being sent to the site.

The infiltrating wetland provides valuable wetland habitat. Using the infiltrating wetland to provide passive recreational trails to the public may be possible. Using the wetland creation area to provide offsite wetland mitigation credits may also be possible.

The main disadvantage of the infiltrating wetland system is that the success of the plant community depends on the water level. Since the water level depends on the recharge rate, the success of the wetland design will highly depend on data from a load test.

Jones Edmunds and Wetland Solutions used the following conceptual design criteria.

Flow rate: 0.5 MGD.

22015-022-01 25

Water source: Reclaimed water with average Total Nitrogen (TN) at 3 milligrams per liter

(mg/L), assumed to be nitrate.

Safety Factor: 1.

Bottom area: 32 acres.

Total treatment area (area of wetlands needed to treat reclaimed water to a nitrate concentration of 0.35 mg/L): 10 acres.

3.2.1.1 Probable Construction Cost Opinion

The cost for a 10-acre infiltrating wetland and flow through, wet-weather storage system is approximately $4.5 million. The largest contributor to this cost is the earthwork and stabilization of the side slopes including installing sheet piling around the slopes along the recharge area.

Earthwork: $1,200,000

Structural Fill: $200,000

Wetlands (10 acres): $250,000

Concrete Structures: $100,000

Slope Stabilization: $500,000

Sheet Piling around Recharge Area: $300,000

Recycle Pump Station and Piping: $250,000

Distribution Piping to the Site: $675,000

The total estimated cost for the items listed above is $3,475,000 with a 10-percent mobilization/permitting/environmental protection line item ($347,500) and a 20-percent contingency ($764,500) the estimate comes to $4,587,000.

This site model also allows areas for park amenities including trails and a parking site. The park amenity costs are not included in the $4.5 million estimate to develop the site.

3.2.1.2 Probable Operation and Maintenance Cost Opinion

Wetland operation and maintenance costs are highly variable depending on the vegetation management plan and the degree to which controlling invasive exotic species is necessary.

The South Florida Water Management District (SFWMD) reports that the annual maintenance cost for the stormwater treatment area wetlands is approximately $600 per acre per year, which is on the low end and may be driven by economies of scale. Some wastewater utilities spend up to $3,000 per acre per year to manage wetlands in a park setting.

Our opinion of the operation and maintenance cost for an overflow wetland system ranges between $20,000 to $96,000 per year, largely depend on the diversity of the planting plan, the control of exotic plants, and side slope maintenance.

4 PERMITTING AND COMPLIANCE

Table 8 summarizes the permitting needs associated with the proposed project.

22015-022-01 26

Table 8 Summary of Potential Regulatory Agencies and Permitting List

Agency Jurisdiction Permit Comments

US Army Corps of Engineers (USACE)

Federal Clean Water Act, Section 404

No permits required as the project is isolated from Water of the US.

SJRWMD

Northeast/ North

Central Florida

Standard General Environmental Resource Permit

(ERP) and Dewatering Permit

ERP and Dewatering Permit applications should be submitted to the Florida Department of Environmental Protection (FDEP) for review since SJRWMD is the Owner.

FDEP State National Pollutant Discharge Elimination System (NPDES)

The project requires that the Contractor has an NPDES Master General Permit (NGP) for Construction Activities and for Dewatering Discharge.

FDEP State

Stormwater Pollution Prevention Plan

(SWPPP)

Prepared by the Contractor before construction.

FDEP State Beneficial Reuse Added to the wastewater treatment plant reuse plan.

FDEP State Mine Reclamation Requirements 62C-39

Vegetation and grading plan.

US Fish and Wildlife Service

(FWS)

Federal None Expected

No known or observed threatened or endangered species. The mining operation already disturbed most of the site.

Florida Fish & Wildlife Conservation Commission (FWC)

State None Expected

No known or observed threatened or endangered species. The mining operation already disturbed most of the site.

Florida Department of State, Historic Preservation Office

(SHPO)

State None Expected

No known or observed artifacts. The mining operation already disturbed most of the site.

Volusia County County None

Setbacks.

Perimeter berm or fencing.

Additional requirements if the site becomes a public park.

Landscaped perimeter

4.1 WETLAND MITIGATION CREDITS

Since this proposed site design uses infiltrating wetlands and open-water features, wetlands created at the site could potentially be permitted as a Regional Offsite Mitigation Area

(ROMA). If approved, wetland credits in ROMAs can be used to offset wetland impacts that

22015-022-01 27 occur elsewhere due to construction projects where on-site mitigation may not be feasible

(e.g., transportation or linear utility projects).

The following steps will be required during design to determine the potential for wetland mitigation credits:

1. Meet with the permitting agencies. This system will depend on a supply of pumped water to maintain the vegetative community. Previously, SJRWMD has permitted mitigation areas that depend on a pumped water supply. Jones Edmunds is not aware of a regulatory restriction preventing a mitigation area from using a pumped water supply.

2. Complete a Uniform Mitigation Assessment Method (UMAM) assessment. The site is currently a mining site that is very disturbed with some open-water features.

Based on our preliminary observation, Jones Edmunds would expect a high lift in the

UMAM score and therefore the number of wetland credits. Generally, we would expect the number of wetland mitigation credits to be equal to the wetland acreage created.

3. Determine the success criteria and monitoring requirements. Mitigation sites must be monitored to document the success and health of the vegetative community.

Generally, the monitoring is more robust following construction of the project to ensure the health of newly planted vegetative material. After the first year, monitoring is more limited and focuses on managing and controlling undesirable plant species such as cattail and invasive exotic plants.

5 WATER SUPPLY TO THE AREA

Jones Edmunds also prepared a rough order of magnitude (ROM) cost estimate to connect all of the properties within 1,000 feet of the site to the County water supply, including the entrance building at Blue Spring Park. Using aerial mapping and information from the

County, 13,150 feet of 6-inch polyvinyl chloride (PVC) and 15,840 feet of 12-inch PVC will be needed to connect these properties. Assuming current costs of $75 per foot for 6-inch

PVC installed and $120 per foot for 12-inch PVC installed, the cost computes to $2,887,050 just for the piping. This assumes that no roadway restoration/paving is needed and that no booster pump station is required. For budgeting purposes, we propose adding a 25-percent contingency to this estimate totaling a ROM cost of approximately $3,600,000.

6 SUMMARY

The load testing conducted shows that the site infiltration rates range from 0.53 to

0.69 inch per day, which is lower than previously estimated from preliminary groundwater capacity analysis modeling. We believe that most of the recharge occurs over a small area of Cell No. 3 where more materials have been excavated and borings show a deep layer of sand, which potentially represent a paleosink. Other areas of the site showed extremely low infiltration rates, resulting in an estimated site capacity of approximately 0.5 MGD. The

County attempted to excavate the upper clay layer at Cell No. 1; however, this did not result in a significant increase in recharge capacity. The clay found at the site forms an effective confining layer. Reworking of the clays at the site and a clayey upper limestone surface are the likely causes of the low infiltration rates observed. Excavating the upper clay

22015-022-01 28 at the site to increase capacity would be costly and potentially ineffective due to the clay content in the upper limestone surface.

Although the load testing showed that the site will not recharge the originally planned 2 to 5

MGD, the site can still be useful for a recharge wetland and wet-weather storage area but with a much lower infiltration rate. Jones Edmunds and Wetland Solutions developed a conceptual site plan with treatment wetlands and overflow areas for periods of extremely wet conditions. This site plan would provide some recharge capacity while providing additional treatment to reclaimed water before entering the aquifer.

7 REFERENCES

Durden, D. et. al., 2019. North Florida Southeast Georgia Groundwater Model (NFSEG v1.), St. Johns River Water Management District Technical Publication SJ2019-01.

McDonald, MG, and Harbaugh, AW. 1988. A modular three-dimensional finite-difference ground-water flow model: Techniques of Water-Resources Investigations of the United

States Geological Survey, Book 6, Chapter A1, 586 p.

Appendix A

Load Test Plan

26110-032-01 1 February 2020 Existing User Impact Analysis

TECHNICAL MEMORANDUM

Load Test Plan

TO: Scott Mays, PE (Volusia County)

FROM: John Horvath, PE, Michelle Hays, PG, Troy Hays, PG (Jones Edmunds)

DATE: February 3, 2020

SUBJECT: Volusia Blue B&H Excavation Site Load Test Plan

Jones Edmunds Project No. 22015-022-01

1 INTRODUCTION

The B&H Excavation Site, about 0.5-mile northeast of Blue Spring, was identified as a potential recharge site by the West Volusia Water Suppliers (WVWS) and the St. Johns River Water

Management District (SJRWMD). The site is a mine covering about 60 acres that was excavated to approximately 40 to 50 feet below natural grade. The west side of the property borders an existing 10-inch force main owned by Florida Department of Transportation that conveys stormwater discharge from Mill Lake to the St. Johns River.

Jones Edmunds conducted a preliminary geotechnical investigation of the site to assess the site’s suitability for recharge of between 2 to 5 MGD of reclaimed water to benefit flows from Blue Spring. The preliminary investigation included electrical resistivity imaging (ERI), fourteen standard penetration test borings to obtain site-specific soil information, and three shallow piezometers and three deep piezometers to monitor site water levels. Additionally, grain-size analysis was performed on 15 soil samples taken from the borings and permeability testing was completed on two samples of clayey materials. The water level data collected from the piezometers was used to estimate the leakance of the surficial aquifer at the site. Jones Edmunds performed a groundwater capacity analysis using the

SJRWMD’s Volusia Steady-State model to evaluate the potential recharge benefit to Blue

Spring. Jones Edmunds refined the model grid around the site and used the geotechnical data collected to modify the surficial aquifer hydraulic properties and develop an uncalibrated steady-state model of the site and assess whether the site can accept recharge in the range of 2 to 5 MGD. Our analysis indicated that the site could be engineered to meet the design goals specified by SJRWMD and WVWS – recharge of between 2 to 5 MGD of reclaimed water to benefit flows from Blue Spring while not adversely impacting water quality at the spring. However, Jones Edmunds recommended conducting a load test at the site to more directly determine the site infiltration capacity and better define design parameters. This technical memorandum details the Test Plan for the proposed load test.

22015-022-01 2 February 2020 Load Test Plan

2 SITE DESCRIPTION

Figure 1 is a site map that shows the site location. The property was an active excavation site during the preliminary geotechnical investigation, so some reworking and removal of soils has occurred since the preliminary investigation. A survey was completed by Pickett and Associates, Inc. on July 28, 2018. The survey was completed using Light Detection and

Ranging (LiDAR) to capture topography with simultaneous capture of high-resolution digital imagery. At that time, most of the site had been excavated to approximately 40 to 50 feet below natural grade. Land use near the project area includes residential and upland forest to the north, residential areas to the east and southeast, and upland forest to the south and west. The site is internally drained with no outlets. Portions of the Site have standing water that ranged in elevations from approximately 8 to 23 feet NAVD88 at the time of the preliminary investigation. The range in elevations indicates that localized perched aquifers occur on site. This observation is consistent with the partial removal of the confining unit separating the surficial aquifer from the UFA by removal of materials during the mining process.

3 LOAD CELL CONSTRUCTION

Figure 2 shows locations for three load cells, each approximately 4 acres, proposed for testing. Load Cell No. 1, on the west side of the Site, was located to evaluate an anomaly identified in the ERI survey that potentially represents a paleosink. Load Cell No. 2, located near the center of the site, was located where lower leakance was estimated by preliminary model simulations. Cell No. 2 was shaped to maintain a relatively flat bottom surface while minimizing earth work. Load Cell No. 3 was located to evaluate several ERI anomalies in the northeast corner of the site. The County has constructed a berm around the open water area to create Load Cell No. 3.

The County has constructed berms around the areas shown in Figure 2 to contain water within the load cells during the test. Where necessary excess materials were removed and used to create a relatively flat bottom surface at an approximate elevation of 23 feet NAVD.

Excess materials were used to create berms approximately 3 feet high around the cells. The

County also added berms to the north and south ends of the open water area west of Cell 1.

If water levels in Cell 1 reach the top of the berm during testing, the test in this cell will be stopped and water will be diverted to the open water area to the west for further testing.

22015-022-01 3

Figure 1 Site Location Map

26110-032-01 4

Figure 2 Site Plan

26110-032-01 5

4 TEST PLAN AND MONITORING

An existing 10-inch pipeline owned by Florida Department of Transportation that conveys stormwater discharge from Mill Lake to the St. Johns River borders the site on the west and travels along Blue Springs Avenue south of the site. Volusia County is in the process of constructing a new segment of 12-inch pipeline to bring water from the existing 10-inch PVC stormwater pipeline to the project site. The County will connect to the stormwater main south of the site along Blue Springs Avenue and run the new pipe north to the pit in the right-of-way of Cedar Avenue. Twelve-inch flexible hosing will be attached to the stormwater pipe that enters the site. The flexible hosing will be moved around the site to transmit water to each of the load test cells.

For the load test, we anticipate that each cell will be loaded at about 1-foot per day – requiring a flow of about 1 to 1.3 MGD – for a period of approximately two weeks per cell. The loading period will be followed by a week of no loading to assess the test cell recovery. The three cells will be loaded and rested in series.

County staff will perform the load test and will have staff on-site to monitor water levels during the day. The load test will run continuously during the two weeks. Flow rate will be controlled at the Mill Lake pump station. County staff will manage adjustments in the flow rate through coordination with Orange City. The flow rate will be established to maintain a constant rate during testing. At start-up of testing, the County staff will monitor water level rise in the load cell and, if necessary, will reduce the flow rate to maintain water levels below the top of the berm. If the water level rises to the top of the berm and the infiltration rate is too low to continue loading, the test will be terminated and recovery will be monitored. The flow rate and quantity of water discharged into the pit will be monitored by the County using a flow meter installed on the discharge line.

Each proposed load cell will be equipped with a staff gauge inside the test cell. Additionally, shallow monitor wells (approximately 15 to 20 feet deep) will be installed either inside or next to the load cell to monitor changes in aquifer levels and one deep monitor well installed within the upper limestone surface will be used to monitor water levels in the Upper Floridan aquifer at the site. Figure 2 shows the locations of the proposed monitor wells and staff gauges. Both the staff gauges and monitor wells will be equipped with pressure transducers with data loggers to record water levels every hour. The monitor wells will be constructed of 2-inch PVC and 10-foot PVC 0.01-inch slotted screens. The wells will include 20/30 silica sand packs in the annulus around the screen with a fine sand or bentonite seal above. The remaining anulus will be grouted to the surface to prevent infiltration of water through the annulus. Water levels will be continuously monitored during background, loading, and recovery phases of the test.

On January 24, 2020 pressure transducers were added to three of the existing piezometers remaining from the preliminary geotechnical investigation to begin background water level monitoring. PZ-9S and PZ-9D were selected because of their location near Load Cells 1 and

2. PZ-1S was not found. PZ-5D was selected to monitor background Upper Florida aquifer levels; however, significant silting was noted when the pressure transducer was installed indicating that this well may no longer be functional. Once the new monitor wells are installed pressure transducers will be installed to begin background water level collection. Monitoring

22015-022-01 6 will continue a minimum of 1-week following completion of the test.