STORMWATER ASSESSMENT 6-22

Stormwater Assessment City of Tucker

June, 2022

June 2022 City of Tucker Stormwater Assessment

Table of Contents Executive Summary

Introduction

Scope

Purpose

Existing Stormwater Assets

Pipe System Assessment

Background

Existing Conditions:

Recommendations and Estimated Costs

Stormwater Structure Assessment

Background

Existing Conditions

Recommendations and Estimated Costs

Detention Pond Assessment

Background

Existing Conditions

Recommendations and Estimated Costs

Dam Assessment

Background

Existing Conditions

Recommendations and Estimated Costs

Potential Additional Stormwater System Expenses

Conclusions

Appendix A: Cost Estimates

Appendix B: Erin Lake Dam Documentation

Executive Summary Atlas Technical Consultants, LLC (Atlas) was hired by the City of Tucker (city) to perform a document review and a limited field inventory of public stormwater assets within the city. The collected and reviewed information was used to provide a preliminary assessment of the state of good repair of the stormwater system. Four types of assets were assessed including structures, pipes, detention ponds, and dams. Conclusions from the condition assessment were used to develop a 5-year spending plan to improve and maintain the state of good repair of the system.

Existing data regarding pipe and structure condition was obtained from the DeKalb County Government database of stormwater assets. While this database appeared to be very comprehensive, its inspections were dated, with asset inspection dates ranging from 2007 to 2011. The detention pond document review was based on inspections performed by the City of Tucker in 2020. Dam reviews included various data provided by the City of Tucker.

The field stormwater assessment included the inspection of a limited sample of stormwater pipes, structures, and detention ponds. While all types of pipes were inspected to a very limited degree, a greater focus was placed on corrugated metal pipes over 30 years old. A variety of stormwater structures and detention ponds were inspected. The field inspections served to validate the data reviewed from other sources. While additional aging of the system was noted as expected given the timeframe of the prior inspections, the DeKalb County database was found to be accurate. The City of Tucker pond inspections were also found to be accurate. One dam was field inspected and was confirmed to have the deficiencies stated in prior reporting.

Both the prior inspection records and the Atlas inspections were used to establish replacement, repair, cleaning and other needs to be addressed over a 5-year period to improve and maintain the state of good repair of the system. Costs were estimated for these improvements using currently available unit rate pricing from local contracts.

The greatest concern found in the investigations of pipes, stormwater structures and detention ponds was the condition of some corrugated metal pipes. It is estimated that approximately 12 miles of this type of pipe requires replacement. Other, less costly improvements that were identified include pipe cleaning due to siltation, replacement of a very small percentage of structures, minor structure repair and cleaning, a small number of pond structure replacements and well as significant pond vegetation removal and fencing to secure pond sites. The total annual cost for these improvements in each of the five years in the plan had a range from a year 1 total of about $1.1 million to a year 5 total of over $1.3 million. These costs are more than offset by the annual stormwater utility collection from residents and businesses in the city in the amount of $1.84 million.

An initial review of materials provided by the city regarding the four dams within the city limits revealed that two of the dams have major planned rehabilitations projects that will restore them to good working condition. Of the two remaining ponds, the city requested that Atlas conduct a visual dam evaluation at the Lake Erin Dam. It was confirmed to have significant deficiencies both through the visual evaluation and review of other documentation from the Safe Dams program. While potential improvement costs have not been calculated, the scale of improvements that may be required at this dam could be in the $2 million range. If such improvements are required and are not supplemented with grant funding, their cost would significantly impact the remaining balance of funds generated by the stormwater utility fee.

Additional costs not considered as part of this assessment are an initial full inventory and assessment of the entire system, staffing for day-to-day management and operations of the stormwater system, and improvements to the capacity of the system as well as unexpected infrastructure failures due to unforeseen issues.

Introduction

Scope The Atlas Stormwater Assessment within the City of Tucker is made up of two parts:

1. Atlas performed a review of the DeKalb County GIS stormwater database that includes information regarding asset type, age, materials, size, and condition. The completeness of available data for stormwater pipes, structures and detention ponds was assessed. This information provides a preliminary analysis on the state of good repair of these assets.

Existing data from various sources provided by the city regarding the four dams in the city was also reviewed.

2. Atlas conducted field inspections of a part of the stormwater system in the city to verify the accuracy of the existing database. This inventory was limited in scope and focused on critical infrastructure such as aging corrugated metal pipe, system structures and detention ponds already identified to be in fair or poor condition. A visual inspection and research on one of the dams located in the city was also performed by a geotechnical engineer specializing in the review and assessment of category 1 dams in the state of Georgia.

Purpose The information gathered from the review of existing data and the field inspections provides for a general assessment of current and future maintenance and capital improvement needs related to maintaining and improving the state of good repair of the stormwater system. The cost of maintaining and replacing these assets can be considered against the current revenue available to DeKalb County provided by stormwater fees collected from City of Tucker property owners.

The study does not include an assessment of capacity needs of the stormwater system but is focused on the condition of the assets. Consequently, any capital improvements considered are related to the replacement of current assets, not upsizing any systems related to growth or other factors affecting stormwater control. Significant benefits would, however, be obtained related to flood control in that the current system would more fully function at or near its intended capacity.

Existing Stormwater Assets With an area of approximately 20 square miles and substantially well-developed residential and commercial areas, the City of Tucker has a large and significantly aging stormwater system. This system is currently managed and maintained by DeKalb County and, according to DeKalb County records, includes approximately 150 miles of stormwater conveyance pipes, over 13,800 drainage structures, 71 detention ponds, and four dams, including one category 1 dam at Lake Erin.

The stormwater system is comprised of facilities located on right of way and drainage easements and does not include assets on State of Georgia maintained right of way. Stormwater assets located on private property are also not included in the system maintained by the county. See the map below (Figure 1) of stormwater assets within the City of Tucker.

FIGURE 1: CITY OF TUCKER - STORMWATER ASSET MAP

Each type of stormwater asset (pipes, structures, ponds and dams) has its own maintenance concerns, and the assessment of each will be presented separately below.

Pipe System Assessment

Background Municipal stormwater systems are made up of both above surface and subsurface assets located in both the road right of way and in drainage easements. Drainage features located outside of right of way and easements are privately owned and are not typically maintained by the local government. Surface features that convey stormwater include roadside ditches and swales as well as curb and gutter and detention ponds. Ditches, swales and curb and gutter are normally maintained as part of the roadway and roadside shoulders and embankments, and do not typically add significant cost to the maintenance of those right of way features when compared to the costs associated with the maintenance of subsurface systems. Consequently, ditches and swales as well as curb and gutter drainage improvements are not included in this assessment.

Existing Conditions:

The City of Tucker contains an extensive network of DeKalb County maintained underground stormwater pipe systems. These systems include inlet structures, outlet structures, junction boxes and a variety of pipe types and sizes. According to the DeKalb County stormwater dataset, there are approximately 150 miles of stormwater pipe within the City of Tucker, constructed of aluminized steel, corrugated metal (CMP), plastic and reinforced concrete pipe, each with a different expected useful service life. The vast majority is either reinforced concrete (approximately 32%) and corrugated metal (60%), (see Table 1 below).

TABLE 1: PIPE AGE SUMMARY (BY MATERIAL TYPE)

Material Length (miles) Percent of Network

Average Age Average

Service Life

Aluminized Steel

2.8 2% 19 years 75-100 years

Corrugated Metal Pipe

90.5 60% 34 years 30-40 years

HDPE 6.5 4% 22 years 50 years

Reinforced Concrete Pipe

47.2 32% 33 years 70-100 years

Other 2.6 2% N/A N/A

Because the aluminized steel, plastic and concrete pipes were found to be in generally good condition in the DeKalb County database (as verified by the Atlas field inspections) and because their average current life is well below their expected useful life, they do not appear to require a significant financial investment in the near future to maintain their state of good repair. However, the condition of the corrugated metal pipe (CMP) is considered to be a significant maintenance concern. Much of the 90.5 miles of CMP under Tucker’s roads and roadsides has an age in excess of the typical expected life of this type of asset, (see Figure 2 below):

FIGURE 2: CORRUGATED METAL PIPE AGE SUMMARY

The 90.5 miles of CMP is made up of 5,500 segments that were assessed by the county between 2007 and 2011. A significant number of the segments of pipe exceeded their useful life at the time of the county assessment, and several hundred pipe segments were considered high or medium priority for improvements (approximately 10.6 miles) due to their condition as is shown in the CMP condition summary table (Table 2) below:

5%

15%

39%

36%

5%

<20 20‐30 30‐40 40‐50 50+ Age in years

Average Service Life of CMP Pipe: 30 to 40 Years

Table 2: Corrugated Metal Pipe Condition Summary

Condition Count (No. of Pipes)

Good 4244

Low Priority 390

Medium Priority 260

High Priority 389

Other 263

Over a decade has passed since the DeKalb County pipe inspections were performed and as should be expected, the Atlas field assessment indicated a significant percentage of pipes are now a high priority for full replacement. The length of CMP requiring replacement is estimated at approximately 12 miles.

The picture shown below is an example of an older pipe with significant rust damage along the pipe flowline, with the bottom of the pipe being completely rusted out. This example (Figure 3) is representative of the pipes identified for replacement.

FIGURE 3: EXAMPLE OF PIPE REQUIRING REPLACEMENT

The Atlas condition sampling also found that a significant number of pipes show some notable signs of rust and are not considered to be in good condition. These are not currently identified for replacement or even other improvements, but they could require maintenance or replacement as they continue to deteriorate. This condition level applied to the entire system indicates that approximately 14 miles of pipe would require improvements over a more extended timeframe. Options other than replacement such as lining, or invert paving may be available to extend the useful life of some of these pipes in the future.

Finally, according to the DeKalb County database, over 5% of the pipes of all types have siltation of over 25%. This equates to almost 8 miles of pipe. The Atlas field assessment confirmed a similar percentage of pipes with significant siltation.

Recommendations and Estimated Costs A full inventory and assessment of the entire stormwater pipe system is recommended as a first step in evaluating state of good repair and capacity needs of the stormwater pipes within the City of Tucker prior to implementing major capital and maintenance improvements. For purposes of estimating near term needs and their associated costs, the following is an estimate of potential short-range improvements to the CMP pipe system to allow it to continue to function in a reasonable state of good repair.

1. Replacement of 12 miles of CMP within the first 5 years of a maintenance and improvement plan implementation is recommended. These improvements are estimated using unit rate costs for various sizes of aluminized steel stormwater pipe. Aluminized steel pipe is recommended due to its durability and long life compared to CMP. Rates from the 2022 Gwinnett County annual contracts for stormwater replacement and repair are used as a reference. Material and labor costs have risen significantly over the past two years and this pricing captures those increases.

Additionally, pricing is inflated over each of the five years at 5% per year. A total cost over five years is estimated to be approximately $4.4 million. See Appendix A for cost breakdown.

2. Cleaning storm lines that contain a significant amount of silt for all pipe types is recommended.

This maintenance helps both to extend the life of the pipe and restore lost capacity to assist in flood control. Cleaning of 8 miles of pipe currently estimated to be significantly silted and an additional 4 miles of pipe that can reasonably be expected to become silted over 5 years is estimated at a unit cost of $4.75 per foot using the Gwinnett County 2022 annual rate. A total cost over five years is estimated to be approximately $300,000. See Appendix A for cost breakdown.

3. An additional estimated 14 miles of CMP that was identified in the Atlas field assessment as a low current priority for improvements should be planned for future pipe rehabilitation and replacement in years 5 through 15 of a potential maintenance and improvement plan implementation. Also establish a regular cleaning program so that system pipes remain clear of silt and debris.

The total cost over a five-year period for CMP replacements and pipe cleaning for all pipe types is $4,743,757.73. See Appendix A of this report for detailed cost estimates.

Stormwater Structure Assessment

Background Storm drain structures such as catch basins, drop inlets, junction boxes, headwalls, flared end sections, and manholes are used to receive water from roadway curb and gutter, ditches, ponds and low-lying areas. They are also used to discharge water from pipes into other conveyances in the stormwater system. These structures are typically made of either precast or cast in place concrete, but may also be made of cast iron, steel or even brick. Due to their materials of construction and their intended use, they can have a very long service life, particularly the underground box portion of the structure.

Existing Conditions According to the DeKalb County database, there are approximately 13,800 stormwater structures in the City of Tucker. The database categorized structures by four standard types and a miscellaneous “other” type as shown in Table 3 below:

Table 3: Stormwater Structure Type Summary

Structure Type # of Structures % of Total

Catch Basin 3,058 22.09%

Drop Inlet 2,893 20.90%

Headwall 3,806 27.49%

Junction Box 2,496 18.03%

Other 1592 11.50%

While the age of the structures generally corresponds to the age of the pipes described in the pipe section above, the DeKalb database indicates that they do not have the condition concerns that exist with the CMP system. Even the structures that are identified as high priority for improvements typically require only repairs and not full replacements, see age and condition information in the below Figure 4 charts:

The Atlas field assessment verified that the condition of structures is generally good and very few of the structures that were inspected needed any significant work. Because the Atlas inspections were limited and the DeKalb County database is over 10 years old, an assumption is made that a very limited number of the structures will require replacement over the first 5 years of a possible maintenance and improvement plan implementation.

Structure repair is also required based on condition assessments in the DeKalb Database and verified by the Atlas field assessment. Approximately 6% of structures (approximately 830) require some repair such as mortar grouting of cracks/joints. This is a relatively inexpensive repair that can increase the life of the structure and help avoid erosion around the structure that can lead to small sink holes.

In addition to structure replacement and repair, approximately 4% of structures are estimated to contain debris that requires removal in order not to impede flow or add to the deterioration of the structure.

Structure cleaning is a relatively inexpensive improvement to the stormwater system.

Recommendations and Estimated Costs As was stated in the Pipe System Assessment section above, a full inventory and assessment of the entire stormwater pipe system including structures is recommended as a first step in evaluating state of good repair and capacity needs of the stormwater structures prior to implementing major capital and maintenance improvements. For purposes of estimating near term needs and their associated costs, the following is an estimate of potential short-range improvements to the stormwater structure system to allow it to continue to function in a reasonable state of good repair.

20.13%

21.99% 41.08%

16.79%

Age of Structures

< 20 Years 20‐30 Years

30‐40 Years >40 Years

68.91%

9.50%

5.18%

4.48% 11.94%

Condition of Structures

G ‐ Good 3 ‐ Low Priority

2 ‐ Medium Priority 1 ‐ High Priority

Other

FIGURE 4: AGE AND CONDITION OF STRUCTURES

1. Although very few structures showed the need for replacement, a conservative assumption is that approximately 1% of the 13,800 structures (140) may require replacement over the first 5 years of a possible maintenance and improvement plan. An average unit rate cost for various stormwater structure replacements was taken from the Georgia DOT Mean Item Index.

A total cost for replacement of these structures over 5 years is estimated at approximately $487,000.

2. 830 of the structures (approximately 6%) are identified for repairs such as mortar grouting of cracks and joints. The cost of this repair is minor at approximately $275 per structure according to the Gwinnett annual contract. As part of improvements over the first 5 years of a maintenance and improvement plan, these repairs are estimated to cost approximately $265,000.

3 Approximately 4% or 550 of the structures are estimated to require cleaning to restore full flow and to help reduce structure deterioration. As part of improvements over the first 5 years of a maintenance and improvement plan, this maintenance is estimated to cost approximately $127,000.

The total cost over a five-year period for stormwater structure replacements, repairs and cleanings is $880,466.84. Inflation of 5% per year is used for each of 5 years beyond the initial estimate using 2022 unit rates. See Appendix A of this report for detailed cost estimates.

Detention Pond Assessment

Detention ponds serve an essential role in controlling flood waters by holding back a portion of stormwater runoff and allowing it to be released after the peak flow of a rain event. They are typically not designed for water quality, but can also at times, if designed to do so, reduce the release of sediment and pollutants. Their walls are typically made up of earthen embankments, but they can also be constructed of reinforced concrete. They contain inlet structures to allow stormwater to collect and outlet control structures that are designed to meter the flow back into the stormwater system.

Existing Conditions According to the DeKalb County database, there are 71 stormwater detention basins in the City of Tucker that are the County’s maintenance responsibility. The City of Tucker conducted inspections of the ponds that could be identified and accessed in 2020. The results of these inspections were verified as part of the Atlas stormwater field assessment. The majority of the ponds and their outlet control structures were found to be in good or fair condition. See the below condition summary from those inspections in Figure 5:

FIGURE 5: DETENTION PONDS CONDITION SUMMARY

The 2020 inspections revealed that 18 ponds contained vegetative growth that restricts the flow of stormwater. To account for additional ponds that may require clearing within the first five years of a potential maintenance and improvement plan, an estimate of 25 ponds is used to establish the cost needed to remove vegetation. General clearing costs obtained from the 2022 Gwinnett County stormwater annual contract were used to establish a clearing cost per pond.

The inspections also found that 8 pond outlet control structures had condition concerns. An estimate of 12 outlet control structures was used to establish a cost for required replacement/repair as part of the first 5 years of a potential maintenance and improvement plan. Costs for several potential components of an outlet control structure obtained from the 2022 Gwinnett County stormwater annual contract were used to establish a replacement cost per outlet control structure.

While both the city and Atlas inspections were focused on the stormwater ponds themselves, it has been noted that some of the ponds are not enclosed by fencing. Detention pond perimeter control may be considered as a necessary part of a stormwater system maintenance and improvement plan. An estimate of the cost to fully secure 25 ponds with a perimeter of 300 feet (equating to a moderately sized pond) is used to establish proposed funding to fully secure a portion of the detention ponds in the city.

Recommendations and Estimated Costs As was stated in the Pipe and Structure System Assessment sections above, a full inventory and assessment of the entire stormwater including detention ponds is recommended as a first step in evaluating state of good repair and capacity needs of the stormwater structures prior to implementing major capital and maintenance improvements. For purposes of estimating near term needs and their associated costs, the following is an estimate of potential short-range improvements to the stormwater detention pond system to allow it to continue to function in a reasonable state of good repair.

1. Although many of the detention ponds located in the City of Tucker contain significant vegetation, only 18 were identified with vegetation that impedes the flow of stormwater. An additional 7 ponds are assumed to also contain significant vegetation affecting water flow. The clearing of detention ponds to remove large vegetation that can affect the flow of water is

0 5 10 15 20 25

Unknown

Poor

Fair

Excellent / Good estimated at $3,000 per pond in the current year using unit rates from the Gwinnett County annual stormwater contract.

A total cost for vegetation removal over 5 years is estimated at approximately $87,000.

2. A total of 12 stormwater outlet control structures are assumed to require replacement over a 5 year maintenance and improvement plan. Eight structures were identified to have deficiencies and an additional four are assumed to require replacement. Costs for the various components of an outlet control structure were obtained from the Gwinnett County 2022 annual contract. A total cost of $10,000 per structure was used in the current year. As part of improvements over the first 5 years of a maintenance and improvement plan, these replacements are estimated to cost approximately $137,000.

3. Fencing of the perimeter of 25 moderately sized detention ponds with an average perimeter of 300 feet is estimated using a fencing installation unit rate of $22.33 per linear foot. As part of improvements over the first 5 years of a maintenance and improvement plan, this maintenance is estimated to cost approximately $194,000.

The total cost over a five-year period for detention pond outlet structure replacements, vegetation clearing, and fencing installation as described above is $418,927.02. Inflation of 5% per year is used for each of 5 years beyond the initial estimate using 2022 unit rates. See Appendix A to this report for detailed cost estimates.

Dam Assessment

The regulation of dams within the state of Georgia is the responsibility of the Safe Dams Program within the Georgia Environmental Protection Division. According to the Rules for Dam Safety, a regulated dam is defined as a water impounding structure with a height of at least 25 feet and/or maximum impoundment volume of at least 100 acre-feet. If the structure is defined as a “dam” under the law, then the dam can be classified as either a Category I (High Hazard) or Category II structure. A Category I dam is so classified based on an analysis that a failure of the dam would result in a probable loss of human life. If failure of that dam would not likely result in a probable loss of human life, then the dam is typically classified as a Category II structure. The Georgia Safe Dams Act and Rules for Dam Safety covers the design, operation and maintenance of dams which are classified as Category I (High Hazard). The Georgia Safe Dams Program does not regulate dams classified as Category II or “exempt” directly. However, dams classified as Category II may be re-classified to Category I if a residence or other occupied structure is later constructed downstream of the dam and which would be impacted by a dam failure.

Atlas and the City of Tucker discussed four dams within the city, all located within public parks, one of which is classified as a Category I dam. The remaining three are classified as Category II dams.

Existing Conditions Two of the dams in the city are referred to as the Twin Brother Dams and are located in Johns Homestead Park. They are both classified as Category II dams and have been well studied. A project has been established to improve both lakes and their dams. The project will also provide additional recreational opportunities. The projects rely on grant funding provided by the Georgia Department of Natural Resources and local matching funds.

Another dam within the city that was discussed, but that Atlas was not requested to inspect is the Kelley Cofer Dam. This dam is a Category II dam and is located in Kelley Cofer Park. It also serves as the road crossing for North Park Drive.

The final of the four dams is the Lake Erin Dam which is located in Henderson Park. Lake Erin Dam is classified as a Category I dam. This dam has a significant record of compliance and maintenance issues (See appendix B for documentation from the Safe Dams program). Atlas performed a Visual Dam Evaluation of Erin Lake Dam, as requested by the city. See Appendix B of this report for a full copy of the Evaluation.

Recommendations and Estimated Costs Recommendations for further action regarding the Lake Erin Dam are well documented in Georgia Environmental Protection Division letters dated April 4, 2018, and September 16, 2020. The Atlas Visual Dam Evaluation also provides conclusions and recommendations that are based strictly on the limited data available to us and our observations of surface features at the dam site, combined with past experience on similar projects.

Atlas has not prepared any cost estimates for a potential dam rehabilitation project at the Lake Erin Dam. For the purpose of providing an order of magnitude understanding of the potential cost of a major dam rehabilitation project for a dam with similar characteristics, a recent project cost estimate on another dam is $1.9 million including design, subsurface explorations, Georgia Safe Dams Program coordination and construction. This estimated cost is included in summary cost materials in Appendix A.

Potential Additional Stormwater System Expenses The above sections address the state of good repair of stormwater pipes, structures, detention ponds and dams located within the City of Tucker. A number of other costs and responsibilities must also be considered a part of the operation of a municipal stormwater system.

As was mentioned numerous times in the above sections, a comprehensive stormwater asset management assessment that includes an inventory, condition assessment and hydraulic capacity analysis off all assets within the system should be considered at the outset of a maintenance and capital improvement program. Such an assessment may require considerable resources and a significant budget to complete.

General operation of a stormwater system the size of the one in the City of Tucker would require budgeting for staffing and day to day operational expenses to serve the requests of the citizens of the city and the needs of the system outside of planned major maintenance and improvement initiatives.

Capacity improvements to the system may also need to be planned to account for additional storm flow volumes resulting from a number of sources such as increases in impervious surfaces. These improvements can be limited to a single culvert or pipe crossing of a road or can extend through a series of connected pipes and structures, resulting in significant capital costs.

Lastly, a fund balance may be desirable to allow for unexpected system failures.

Conclusions The existing DeKalb County database was found to be accurate in identifying stormwater pipe and structure assets properly in terms of their type, size and materials. Their condition characterization was also found to be accurate when the additional aging of the assets since the dates of the DeKalb assessment (2007-2011) was considered. The detention ponds were inspected by the City of Tucker in 2020 and that information appeared to be accurate as well. This information when combined with the limited Atlas inspections was useful in identifying needed repairs and improvements that could be implemented over a five-year improvement program.

Sufficient funds are generated by the current DeKalb County stormwater fee to support identified improvements to the pipe, stormwater structure and detention pond system in the above described 5-year investment. A fund balance would allow for a portion of several other potential needs such as improvements to the Lake Erin Dam, staffing for day-to-day operations of the stormwater system, establishment of a fund balance for unexpected system failures, and improvements to the capacity of the stormwater system. However, additional funding may be required to fund all of these additional needs. Pursuit of grant funding for improvements such as those that may be needed at Lake Erin should also be considered to offset local expenses. An assessment of the condition and capacity of the entire stormwater system is needed to fully implement a stormwater improvement program.

Appendix A: Cost Estimates

Pipe Diameter (Inches) Percent of Total CMP Network Total Replacement Length over 5

Years (Feet)

Total Replacement Length Per Year

(Feet) **Price Per Foot Total 1‐Year Base Cost

<18 10% 6,336 1,267 $49.62 $62,878.46

18 35% 22,176 4,435 $55.13 $244,512.58

24 20% 12,672 2,534 $60.64 $153,686.02

30‐42 25% 15,840 3,168 $60.64 $192,107.52

>42 10% 6,336 1,267 $88.20 $111,767.04

Total 100% 63,360 12,672 $764,951.62

Year 1 Subtotal Year 2 Subtotal Year 3 Subtotal Year 4 Subtotal Year 5 Subtotal Total Cost

$803,199.20 $843,359.16 $885,527.11 $929,803.47 $976,293.64 $4,438,182.58

Percentage of 150 mile pipe network with significant silt present

Total Miles of Pipe Requiring

Cleaning during 5‐year period

Assumed additional miles of cleaning due to siltation occuring over 5 years

Total Per Year Pipe Cleaning (Miles) ** Price Per Foot Total 1‐Year Base Cost

5% 7.5 2.5 2 $4.75 $52,668.00

Year 1 Subtotal Year 2 Subtotal Year 3 Subtotal Year 4 Subtotal Year 5 Subtotal Total Cost

$55,301.40 $58,066.47 $60,969.79 $64,018.28 $67,219.20 $305,575.14

Year 1 Costs Year 2 Costs Year 3 Costs Year 4 Costs Year 5 Costs Totals

$858,500.60 $901,425.63 $946,496.91 $993,821.75 $1,043,512.84 $4,743,757.73

5‐Year Total Replacement & Cleaning Cost

**Source: Gwinnett Co. 2022 Pipe Replacement Annual Contract

CMP 5‐Year Replacement Cost (Includes 5% per year Increase)

Year 1 CMP Replacement Cost (Based on Replacement of 12 Miles of Pipe over 5 Years)

Corrugated Metal Pipe (CMP) 5‐Year Improvements

5‐Year Cleaning Cost (Includes 5% per year Increase)

Year 1 Cleaning Cost (Based on Cleaning of 10 Miles of Pipe over 5 Years)

Number of Structures Replaced over 5 Years

Total Structures Replaced Per Year *Price Per Structure Total 1-Year Base Cost

140 28 $3,000.00 $84,000.00

Year 1 Subtotal Year 2 Subtotal Year 3 Subtotal Year 4 Subtotal Year 5 Subtotal Total Cost

$88,200.00 $92,610.00 $97,240.50 $102,102.53 $107,207.65 $487,360.68

Number of Structures Repaired over 5 Years

Total Structures Repaired Per Year ** Price Per Structure Total 1-Year Base Cost

830 166 $275.63 $45,754.58

Year 1 Subtotal Year 2 Subtotal Year 3 Subtotal Year 4 Subtotal Year 5 Subtotal Total Cost

$48,042.31 $50,444.42 $52,966.65 $55,614.98 $58,395.73 $265,464.08

Number of Structures Cleaned over 5 Years

Total Structures Cleaned Per Year ** Price Per Structure Total 1-Year Base Cost

550 110 $200.00 $22,000.00

Year 1 Subtotal Year 2 Subtotal Year 3 Subtotal Year 4 Subtotal Year 5 Subtotal Total Cost

$23,100.00 $24,255.00 $25,467.75 $26,741.14 $28,078.19 $127,642.08

Year 1 Costs Year 2 Costs Year 3 Costs Year 4 Costs Year 5 Costs Totals

$159,342.31 $167,309.42 $175,674.90 $184,458.64 $193,681.57 $880,466.84

*Source: GDOT Item Mean Summary **Source: Gwinnett Co. 2022 structure Replacement Annual Contract

Annual Stormwater Structure Cleaning Cost (Based on Cleaning of 4% out of 13,800 Structures over 5 Years)

Stormwater Structure Cleaning Cost (Includes 5% per year Increase)

Stormwater Structure 5-Year Improvements

Annual Stormwater Structure Replacement Cost (Based on Replacement of 1% of 13,800 Structures over 5 Years)

Stormwater Structure Replacement Cost (Includes 5% per year Increase)

Annual Stormwater Structure Repair Cost (Based on Repair of 6% of 13,800 Structures over 5 Years)

Stormwater Structure Repair Cost (Includes 5% per year Increase)

Stormwater Structure 5-Year Total Cost (Replacement, Repair, and Cleaning)

Number of Structures Replaced over 5 Years

Total Structures Replaced Per Year (Years 1 & 2)

Total Structures Replaced Per Year (Years 3 - 5)

**Price Per Structure Base Cost

12 3 2 $10,000.00

Year 1 Subtotal Year 2 Subtotal Year 3 Subtotal Year 4 Subtotal Year 5 Subtotal Total Cost

$31,500.00 $33,075.00 $23,152.50 $24,310.13 $25,525.63 $137,563.26

Number of Ponds with Vegetation Removal over 5

Years Total Structures Repaired Per Year ** Price Per Structure Total 1-Year Base Cost

25 5 $3,000.00 $15,000.00

Year 1 Subtotal Year 2 Subtotal Year 3 Subtotal Year 4 Subtotal Year 5 Subtotal Total Cost

$15,750.00 $16,537.50 $17,364.38 $18,232.59 $19,144.22 $87,028.69

Number of Ponds Requiring Fencing over 5 Years

Total Ponds Fenced Per Year Total Feet of Fencing per Pond **Base Cost Per Foot Total 1-Year Base Cost

25 5 300.00 $22.33 $33,495.00

Year 1 Subtotal Year 2 Subtotal Year 3 Subtotal Year 4 Subtotal Year 5 Subtotal Total Cost

$35,169.75 $36,928.24 $38,774.65 $40,713.38 $42,749.05 $194,335.07

Year 1 Costs Year 2 Costs Year 3 Costs Year 4 Costs Year 5 Costs Totals

$82,419.75 $86,540.74 $79,291.52 $83,256.10 $87,418.91 $418,927.02

Pond Security Fencing Costs (Includes 5% per year Increase)

Detention Pond Improvements 5-Year Total Cost (Structure Replacement/Repair, Pond Vegetation Removal, Pond Fencing)

Detention Pond 5-Year Improvements

Annual Pond Structure Replacement/Repair Cost (Based on Replacement/Repair of 12 Pond Structures over 5 Years)

Pond Structure Replacement/Repair Cost (Includes 5% per year Increase)

Annual Pond Vegetation Removal Cost (Based on Vegetation Removal of 25 Ponds over 5 Years)

Pond Vegetation Removal Cost (Includes 5% per year Increase)

Annual Pond Fencing Costs (Based on Fencing for 25 Ponds over 5 Years)

Improvement Type Year 1 Costs Year 2 Costs Year 3 Costs Year 4 Costs Year 5 Costs Totals

Pipes $858,500.60 $901,425.63 $946,496.91 $993,821.75 $1,043,512.84 $4,743,757.73

Structures $159,342.31 $167,309.42 $175,674.90 $184,458.64 $193,681.57 $880,466.84

Ponds $82,419.75 $86,540.74 $79,291.52 $83,256.10 $87,418.91 $418,927.02

Totals $1,100,262.66 $1,155,275.79 $1,201,463.33 $1,261,536.49 $1,324,613.32

Revenue $1,840,000.00 $1,840,000.00 $1,840,000.00 $1,840,000.00 $1,840,000.00

Revenue Remaining $739,737.34 $684,724.21 $638,536.67 $578,463.51 $515,386.68

*Fund Balance $739,737.34 $1,424,461.56 $2,062,998.23 $2,641,461.73 $3,156,848.41

Total Stormwater System 5-Year Improvements Cost

* Major dam rehabilitation at Lake Erin, if required, could be locally funded in Year 4 with the estimated fund balance.

Appendix B: Erin Lake Dam Documentation

VISUAL DAM EVALUATION

Erin Lake Dam Tucker, Dekalb County, Georgia

Atlas Project No.: 122209

PREPARED BY:

Atlas Technical Consultants, LLC

3000 Northfield Place, Suite 1100

Roswell, Georgia 30076

June 2, 2022

ATLAS Project No.122209

June 2, 2022

Mr. Alan Chapman

Atlas Technical Consultants

2450 Commerce Avenue, Suite 100

Duluth, Georgia 30096

Subject: Report of Visual Dam Evaluation

Tucker, Dekalb County, Georgia

Atlas Project No. 122209

State ID No. 044-004-00033

Dear Alan:

Atlas Technical Consultants, LLC (Atlas), has completed our visual evaluation of Erin Lake Dam. The following paragraphs briefly describe our understanding of the project, evaluation procedures used, site observations, and geotechnical engineering conclusions and recommendations.

This Scope of Work is intended to provide an overview of the dam's condition based strictly on our visual evaluation and the work likely required to bring any identified issues into compliance with current standards. It is not intended to be a full-scale dam evaluation report which would provide detailed specifics for dam redesign.

We appreciate the opportunity to provide you with this geotechnical engineering evaluation based on our visual assessment of Erin Lake Dam. We remain available to assist you with any recommended subsequent evaluations and any future evaluations of this dam. Should you have any questions concerning this report, or if we may be of additional service to you in any way, please do not hesitate to contact us.

Sincerely, Atlas Technical Consultants, LLC

Jonathan P. Sharpe, P.E.

Senior Registered Engineer

Registered Georgia 40573

GSDP Engineer of Record

Attachments: Dam Inspection Form

Photographic Log

GOVERNING RULES

As a result of the failure of Kelly-Barnes Dam in Toccoa, Georgia, the Georgia General Assembly passed the

Safe Dams Act in 1978. This act has had several amendments over the last 44 years. The regulation of dams within the state of Georgia is the responsibility of the Safe Dams Program within the Georgia Environmental

Protection Division. According to the Rules for Dam Safety, a regulated dam is defined as a water impounding structure with a height of at least 25 feet and/or maximum impoundment volume of at least 100 acre-feet. If the structure is defined as a “dam” under the law, then the dam can be classified as either a Category I (High

Hazard) or Category II structure. A Category I dam is so classified based on an analysis that a failure of the dam would result in a probable loss of human life. If failure of that dam would not likely result in a probable loss of human life, then the dam is typically classified as a Category II structure. Dams which fail to meet both the height and volume criteria stated above, even if their failure could result in a probable loss of life, are considered “exempt” from the overview of the Georgia Safe Dams Program. The Georgia Safe Dams Act and

Rules for Dam Safety covers the design, operation and maintenance of dams which are classified as Category

I (High Hazard). The Georgia Safe Dams Program does not regulate dams classified as Category II or

“exempt” directly. However, dams classified as Category II may be re-classified to Category I if a residence or other occupied structure is later constructed downstream of the dam and which would be impacted by a dam failure.

Erin Lake Dam is classified as a Category I (high Hazard) dam by the Georgia Safe Dams Program. The State

ID number is 044-004-00033.

EVALUATION PROCEDURES

The authorized study involves primarily a visual reconnaissance of the dam site and formulation of geotechnical engineering conclusions and recommendations concerning the observed condition of the dam.

Dam files archived and available for review by GSDP were located and reviewed. These conclusions and recommendations are based strictly on our review of the limited available information, observations made from a surface reconnaissance only on the date of the site visit in conjunction with our experience with similar projects.

No subsurface exploration of the dam was performed as part of this study. In addition, this study was not intended to evaluate the hydrologic and hydraulic (H & H) aspects of this dam. Any comments in this report referring to the dam, the spillway system and its hydrologic and hydraulic performance is based on visual observation and should not be taken as specific to any H & H evaluation of this dam.

PROJECT INFORMATION

Erin Lake Dam is located within Henderson Park in Tucker, Dekalb County, Georgia and is classified as a

Category I (High Hazard) dam by the Georgia Safe Dams Program (GSDP). From the GSDP dam inventory list, the dam is indicated to be 34 feet tall and have a maximum storage volume of 166 acre-feet. The dam is approximately 345 feet long.

SITE OBSERVATIONS

On May 19, 2022, Atlas engineer Jonathan P. Sharpe, P.E., a Georgia Safe Dams Engineer of Record, visited the site to perform a visual evaluation of the embankment. The weather was clear and approximately 80 degrees Fahrenheit and conditions were dry on this day and had been for the previous several days leading up to this inspection.

References to direction, left and right, are made facing downstream. The following items were noted in no particular order of importance:

1. The dam is estimated to be about 345 long and have a crest width of 15 feet. The crest alignment is generally straight. Many areas of the crest are bare dirt, with some areas being slightly depressed and would pond water during rain. It is estimated that the dam has about 10 feet of free board above the normal pool elevation. Based on review of the GSDP file, bare areas on the crest have been historically observed.

2. The upstream slope is heavily overgrown with thick brush that obscured the slope preventing visual evaluation of the slope surface. From observing the vegetation on the upstream slope, it looks to be slightly steeper than the typically preferred 3(H):1(V) configuration. Old stumps were visible near the water line, some of which have started to regrow. No wave protection was observed at the water line. A small diameter riser pipe was observed in the lake at about the midpoint of the dam. The downstream end of the pipe was not observed and is presumed to have been abandoned, but this has not been confirmed.

3. The downstream slope is estimated to be a 2.5(H):1(V) to 3(H):1(V) configuration and is irregular. There are large bare dirt areas that are eroding from rain and surface water. Where the slope is grassed the grassing is well-maintained. No obvious wet areas on the downstream slope that would be indicative of seepage were observed on this date. Past inspection reports reviewed in the GSDP file indicate seepage has been observed and the bare areas were suspected of sloughing. Indications of slope movement or instability were not observed on this date, only surface erosion in the bare areas. The left end of the slope, adjacent to the right spillway wall is overgrown with heavy brush. This area could not be visually observed.

4. There were six observation wells observed on the downstream slope. On the left end of the dam there was one well with a flush mount bolted cover observed at the crest and one well with a vertical riser cover at the toe. Towards the right-center portion of the dam a row of three wells with vertical riser covers were observed down the slope. Adjacent to the lowest riser cover was another flush mount well. Water levels at the left upper and lower wells were measured to be 22.3 feet and 2.4 feet below the ground surface, respectively. The water level in the right-center lowest riser covered well was measured at a depth of 7 feet below the ground surface. The remainder of the wells were locked and could not be measured.

5. The primary spillway is a corrugated metal pipe transitioning to a concrete pipe through the embankment that is placed at the pool elevation. The corrugated pipe controls the normal pool elevation and is also connected to a short riser pipe and trash rack for elevated lake levels. The upstream side of the spillway is partially obstructed with driftwood. The primary spillway pipe exits into a channel with rock masonry training walls and a concrete and bedrock bottom. The channel directs flows down the left abutment and to the creek channel. One location of the masonry rock walls was in poor condition with the mortar missing between the rock pieces and the rock becoming dislodged.

6. To the left side of the dam appears to be an emergency spillway channel. The emergency spillway channel is an earth channel that connects to the primary spillway channel. The emergency spillway channel is narrow at the entrance, not well defined, and has trees within the channel.

7. A presumed internal drain outlet was observed at the downstream toe, adjacent to the spillway channel. It appeared that the outlet pipe was cast in a concrete headwall. An animal guard was observed but was in poor condition. The drain outlet was flowing, though the end of the pipe was obscured and partially submerged, and flows could not be measured.

8. Along the right downstream toe of slope is a shallow toe ditch. The edges of the ditch are overgrown, and the ditch does not have any erosion protection. The lower portion of the ditch had some water and slight staining in the ditch. This water could be possible seepage.

9. The area immediately downstream of the dam and the toe ditch is wooded and overgrown.

CONCLUSIONS AND RECOMMENDATIONS

The following describes our conclusions and recommendations concerning this dam based on our visual observations. As discussed previously in this report, it should be understood that these are based strictly on the limited data available to us and our observations of surface features at the dam site, combined with past experience on similar projects. No other warranty, expressed or implied, is made. There may be issues internal to this dam that cannot be identified by surface evaluation alone that could impact the long-term integrity of this structure.

Based on our visual evaluation of Erin Lake Dam, we have identified the following concerns and/or deficiencies that should be addressed, they are as follows:

1. The upstream slope and a small portion of the left side downstream slope is vegetated with unsuitable vegetation. This vegetation should be removed, the areas uniformly graded, and low growing permanent grassing established.

2. Where the primary spillway channel walls are in poor condition or failing, they should be repaired.

The entrance to the primary spillway pipe should be cleaned of debris.

3. The bare areas on the crest and downstream slope should be smoothed and grassed with low growing permanent grassing.

4. The upstream slope should have erosion protection placed at the water line and the right toe ditch should be also protected from erosion.

5. The area downstream of the dam toe for about 25 feet, and the toe ditch should have the unsuitable vegetation removed and the area permanently grassed to aid in evaluation of the toe during future inspections.

6. If seepage and potential slope instability have been observed in the past, a subsurface investigation of the embankment is warranted.

7. Verification of abandonment of the assumed low-level pipe connected to the small diameter riser pipe should be provided and/or confirmed.

The Georgia Safe Dams Program and the geotechnical engineer should be notified of any work planned to this dam prior to the commencement of the work.

Attached to this report we have completed a check list suggested by the Georgia Safe Dams Program and attached photographs referencing the conditions at the time of our inspection. A site plan indicating the observation well locations has also been included.

Embankment (Earth) Dam Inspection Form

Name of Dam: Date:

Check if corrective action is noted/required. Version 1.0; Page 1 of 5

Location of Dam (County): Weather:

Inspected by (Print Name):

If an inspection item requires further action on your part, place a check mark to the left of the number of the item

A. Crest (refer to Glossary for description)

1. How would you describe the vegetation on the crest? (Check all that apply)

Recently Mowed______ Overgrown______ Good Cover______ Sparse______

Other/Corrective Action (describe):

2. Are there any trees or other inappropriate or excessive vegetation on the crest? Yes______ No______

If yes, describe (type of vegetation, size, location, etc.)/Corrective Action:

3. Is there a paved road or driveway on the crest?