newhall drainage study report

Newhall Area Drainage Study Hamden, Connecticut

DTC Job No. 11-140-106

Issued March 27, 2012

Table of Contents Appendix A - Public Information Meeting Documents .......................................................... 3

Appendix B - Public Observations (Fig. 1 - Map Pock et) ...................................................... 3

Appendix C – GIS Information (FIG. 2 & 3 – Map Pock et) ..................................................... 3

Appendix D - Closed Circuit Television Observations (Fig. 4 & 5 - Map Pocket) ................ 3

Appendix E - Maintenance Recommendations (Fig. 6 & 7 - Map Pocket) ............................ 3

Appendix F - Increased Pipe Capacity Recommendation s (Fig. 8 & 9 - Map Pocket) ......... 3

Appendix G – Storm Sewer Main Profiles .............................................................................. 3

Appendix H - Structure Identification Tables From S urvey (Fig. 10 - Map Pocket) ............. 3

Appendix I - Closed Circuit Television Pipe Inspect ion Reports .......................................... 3

Appendix J - Hydraulic Model ................................................................................................. 3

Study Area Description and Background ............................................................................... 4

Map 1 – Site Location ............................................................................................................ 5

Public Information Meeting ..................................................................................................... 6

Closed Circuit Television Inspection ..................................................................................... 6

Photo 01 – Accumulation of Cans & Bottles at Manhole NE04MH-0002 ................................ 7

Photo 02 – Sediment Accumulation at Outfall OF-0250 and OF-0391.................................... 8

Photo 03 – Rocks / Sediment Accumulation in Pipe ............................................................... 9

Photo 04 –Sediment Accumulation in Pipe............................................................................10

Photo 05 – Void in Catch Basin wall......................................................................................11

Photo 06 – Root Intrusion......................................................................................................12

Photo 07 – Root Intrusion......................................................................................................13

Photo 08 – Prior repair to broken pipe...................................................................................14

Photo 09 – Cracked Pipe ......................................................................................................15

Photo 10 – Pipe Collapse......................................................................................................16

Photo 11 – Utility Crossing Through Storm Pipe Section.......................................................17

Photo 12 – Utility Crossing Through Storm Pipe Section.......................................................18

Photo 13 – Lateral Tap Intruding into Storm Main .................................................................19

Photo 14 – Lateral Tap Intruding into Storm Main .................................................................20

Photo 15 – Typical Storm Inlet Without Sump & Outlet Located at Bottom ............................21

Photo 16 – Example of Cast Iron Inlet Grate .........................................................................22

Photo 17 – Clogged Inlet Grate .............................................................................................23

Hydraulic Model ......................................................................................................................24

General ....................................................................................................................................24

Stormwater Hydrology ............................................................................................................24

Hydraulic Analysis ..................................................................................................................25

Recommended Improvements ...............................................................................................26

Category 1 – Immediate improvement to drainage syst em function with minimal expense

.................................................................................................................................................26

Category 2 – Improvements with short term benefits gained at moderate expense ..........28

Category 3 – Long term solutions requiring signific ant capital investment .......................30

Preliminary Cost Estimate ......................................................................................................31

Appendix A - Public Information Meeting Documents Appendix B - Public Observations (Fig. 1 - Map Pock et) Appendix C – GIS Information (FIG. 2 & 3 – Map Pock et) Appendix D - Closed Circuit Television Observations (Fig. 4 & 5 - Map Pocket) Appendix E - Maintenance Recommendations (Fig. 6 & 7 - Map Pocket) Appendix F - Increased Pipe Capacity Recommendation s (Fig. 8 & 9 - Map Pocket) Appendix G – Storm Sewer Main Profiles Appendix H - Structure Identification Tables From S urvey (Fig. 10 - Map Pocket) Appendix I - Closed Circuit Television Pipe Inspect ion Reports Appendix J - Hydraulic Model

Study Area Description and Background The Newhall neighborhood is an approximately 140 acre area located in the southern end of Hamden, Connecticut on the border of New Haven. The area being considered in the study is bound by Prospect Street to the east, Goodrich Street to the south, The Farmington Canal Heritage Trail and Columbus Street to the west, and Mill Rock Road and Industrial Circle to the north. Included in the area are the former Hamden Middle School and athletic field, Rochford Field, Mill Rock Park, commercial buildings in the northwest corner, and residential area. The residential area constitutes approximately 65% of the study area and consists mostly of single and multifamily homes on small sized lots. The site contains high points to the north above Mill Rock Road and to the east above Prospect Street. Below Morse Street the topography generally slopes down to the west and becomes increasingly flat west of Winchester Avenue. The area above Morse Street and east of the middle school slopes toward low points in Rochford Field and Mill Rock Park. The northwest corner generally slopes toward the athletic field behind the middle school. The storm water drainage system is mainly set up with main line pipes running close to the center of the road with laterals branching off at manholes to catch basin inlets located at the curbs. The exceptions are the west end of Goodrich Street, Prospect Lane, and the middle school athletic field which have pipes running from catch basin to catch basin instead of using manholes. The types of the pipes used are clay, reinforced concrete pipe (RCP), corrugated metal pipe (CMP), and polyvinyl chloride (PVC), with the majority being RCP or clay. The drainage system was originally constructed between 1917 and 1964 with minor additions coming after. The entire drainage area has an ultimate discharge point through seven different outfalls into a pond just north of the middle school, which empties into Lake Whitney. The system uses both combination and curbless catch basins with single grates as inlets and curbs to direct water along roads to the catch basins. Curbless catch basins are used to collect water at low points in the fields and parking areas. The Newhall neighborhood is currently undergoing extensive environmental remediation to remove contaminated waste fill dumped there between the late 1800’s and 1950. Industrial and household waste was dumped in low-lying wetlands in the area in order to build homes. This waste contained lead, arsenic, and polycyclic aromatic hydrocarbons (PAHs) which are all harmful to human health. Work is currently being done to remove the top four feet of contaminated soil from private residences and replace it with clean soil. The construction has created an opportunity to improve the drainage system in the area. The available data given to DTC by the Town of Hamden included all available as-built drawings of the drainage system, GIS information for manholes, catch basins, outfalls, and pipes, 2 ft contours, and spot elevations. Additional information was acquired through a survey of all drainage structures which provided location and top of frame elevations for structures and elevations of pipe inverts. A closed circuit television inspection of the main line pipes was done to determine the condition of the pipes and to look for blockages or debris. A public information meeting was hosted by DTC prior to starting the study in order to locate specific flooding issues that affected residents. Site walks were also done to inspect the condition of catch basins and the outfall area.

Map 1 – Site Location

Public Information Meeting A public information meeting was held on August 31, 2011 from 3:00 to 7:00 pm at the Keefe Center in Hamden to inform residents of the Newhall neighborhood of the scope of the drainage study being performed in the area. Residents were also able to voice specific concerns related to flooding and drainage in the area. Maps of the area and questionnaires were provided for the residents to demonstrate the location and severity of the issues. Door hangers providing a summary of the study and information regarding the meeting were delivered to residents homes to inform them of the meeting. The door hangers also provided contact information for DTC to allow for residents who could not attend the meeting to also voice concerns. Drainage issues from public meeting:

• Intersection of Shelton Avenue and Marlboro Street: Ponding slow to drain • 472 Shelton Avenue: Vinyl layer 4ft below grade from environmental remediation

causing ponding in yard • Prospect Lane: Basement flooding and major backyard flooding. Drain in backyard

surcharges • Intersection of North Sheffield Street and Morse Street: Flooding reaches above car

tires. • Intersection of Marlboro Street and Newhall Street: Ponding slow to drain • Intersection of Newbury Street and Newhall Street: Ponding slow to drain • Intersection of Mill Rock Road and Prospect Street: Ponding slow to drain

The information received from the meeting was compared with findings from the study to determine if a specific issue was the cause for the flooding. Closed Circuit Television Inspection DTC contracted HydroMAX USA to perform light cleaning and closed circuit television (CCTV) inspection of the storm drainage pipe network within the Newhall study area. CCTV inspection was performed between September 29, 2011 and October 25, 2011. CCTV inspection reports are included in Appendix G. Specific findings of the CCTV inspection are illustrated on Figures 2 and 3 located in Appendix C. The CCTV inspection logs reference the Town of Hamden geographic information system (GIS) structure identification codes for future reference. Condition descriptions used by HydroMAX USA are consistent with the standards put forth by the National Association of Sewer Service Companies Pipeline Assessment Certification program. A number of pipes could not be inspected due to accessibility issues such as paved over manhole covers. Other pipes contained sediment accumulations, bricks, and rocks exceeding the capability of CCTV pipe cleaning equipment. Pipes which could not be inspected during this study are indentified on Figures 2 and 3.

Field Observations The following photographs illustrate typical concerns notes in the closed circuit television inspection logs and observations by DTC. Figures 2 and 3 identify specific locations within the storm drain conveyance system where problems were identified.

Clogged manhole structures

Photo 01 – Accumulation of Cans & Bottles at Manhole NE04MH-0002

This manhole is a good example of clogging resulting from floatable bottles and debris that travel through the storm drain pipe network from catch basins. Upstream catch basins without sumps or outlet hoods contribute to this condition.

Blockage located at pipe outfall

Photo 02 – Sediment Accumulation at Outfall OF-0250 and OF-0391

The outfall where the storm drainage system empties into the pond is blocked with sediment and debris. Sediment accumulation was observed inside each pipe effectively reducing the cross sectional area of the pipes and reducing their capacity. The outfall in the left side of the photographs is half full, whereas the outfall on the right is 90 percent full of sediment. The source of the sediment is primarily road sand applied for traction in the winter months and to a lesser extent soil erosion from disturbed areas during construction. Conditions within the pond are calm relative to turbulent flow in the pipe network allowing sediment to settle out of suspension. Over time the sediments accumulate at the bottom of the pond and eventually restrict flow as shown above. Upstream catch basins without sumps accelerate this condition.

Debris accumulation in pipes

Photo 03 – Rocks / Sediment Accumulation in Pipe

Large debris such as rocks, tree branches, household trash, and bricks were noted in several locations. Bricks are usually the result of catch basin inlet or manhole structural failure. After significant deterioration of drainage structures, rocks and soil surrounding the structure may enter the pipe system. Surface depressions or sink holes are usually evident on the surface. Pipe collapse also results in larger rocks entering the pipe at the failure location. Tree branches and household trash can enter curb inlets and eventually travel through the system if the catch basins are not equipped with sumps and hoods. Leaves and sediment that are normally scoured from the pipe invert during periods of high flow accumulate around the large pieces of debris as shown above.

Photo 04 –Sediment Accumulation in Pipe

Accumulation of very fine sediment in the pipe suggests a downstream obstruction has restricted flow. The increased residence time allows fine soil particles to settle out of suspension.

Catch basin Structural failure

Photo 05 – Void in Catch Basin wall

The catch basin above exhibits severe deterioration of the sidewalls affecting the integrity of the structure. After deterioration of the mortar joints, bricks from catch basins and manholes are pushed out by surrounding soil pressure enter the pipe network. These bricks create obstacles in the pipe since they cannot be conveyed to the outfall by stormwater flow. Voids remaining in the structure sidewalls allow soil to flow into the structure and lead to sink holes in the road surface above.

Root intrusion at pipe joints

Photo 06 – Root Intrusion

Roots will pass through very small gaps in the joints of the pipes and continue to grow. Root grow can damage the pipe by creating cracks. The roots create gaps between joints causing infiltration of water and soil into the pipes as well as exfiltration to the surrounding soil. Unattended, roots also create blockages in the pipe due to the increasing growth. The root mass will collect debris and sediment further restricting flow.

Photo 07 – Root Intrusion

Broken or cracked pipes

Photo 08 – Prior repair to broken pipe

This is an example of an existing point repair to a pipe. The repair appears to be composed of brick, clay pipe fragments, mortar, and possibly steel. The structural integrity of the pipe has been compromised and could lead to further problems. Replacement of the pipe segment rather than repair would be advisable in such an occurrence.

Photo 09 – Cracked Pipe

Cracked pipes have no distortion or missing pieces, but will lead to fractures and broken or collapsed pipes in the future. This example is a good candidate for cured in place pipe lined to stop further deterioration.

Collapsed Pipe

Photo 10 – Pipe Collapse

A collapsed pipe refers to more than 40% of the cross sectional area lost and the complete loss of integrity of the pipe. A significant portion of the flow area is obstructed by the remains of the pipe crown and debris snagged on the pipe fragments.

Pipe interferences

Photo 11 – Utility Crossing Through Storm Pipe Section

Two gravity sewer pipes crossing each other in an urban street setting occasionally result in pipe interferences which cannot be overcome with out significant pipe reconstruction. The pipe crossing the storm drain pipe above is unidentified. Significant groundwater infiltration or perhaps water leaking from the crossing pipe itself was observed in the video. These interferences create obstructions that impede flow through the pipe. Damage to the crossing pipe may occur if the pipe is struck by an object flowing through the storm drain pipe. If the crossing pipe is a sanitary sewer pipe, it could leak sewage into the storm water creating environmental issues.

Photo 12 – Utility Crossing Through Storm Pipe Section

Intruding taps into pipe

Photo 13 – Lateral Tap Intruding into Storm Main

Storm laterals protruding into pipes create obstacles that impede flow. Both examples shown in the photograph above and below were installed by breaking open the main pipe with a hammer to insert the lateral. This type of connection is susceptible to cracking and soil entry into the main pipe because the connection is difficult to seal.

Photo 14 – Lateral Tap Intruding into Storm Main

Storm drain inlets without sumps to trap sediment a nd debris

Photo 15 – Typical Storm Inlet Without Sump & Outlet Located at Bottom

Many drain inlets in the study area have no sump for sediment and debris to collect. Any trash, sediment or other debris entering through the grate or curb inlet will pass through the bottom of the structure directly into the main pipe.

Cast iron inlet grates with small inlet openings su bject to clogging

Photo 16 – Example of Cast Iron Inlet Grate

Older cast iron inlet grates within the study area have small holes relative to the openings found on modern steel grates. This will reduce the effectiveness of the inlet and can cause the grate to clog.

Photo 17 – Clogged Inlet Grate

Hydraulic Model General Stormwater runoff from the Newhall study area is intercepted by inlet structures and conveyed by a network of storm sewer main pipes to several outfalls. All pipes in this project were analyzed using the computer program Bentley StormCAD version V8. The following components were incorporated into the StormCAD model. The base maps used for determining drainage areas and location of storm drain pipe and structures was compiled from the following sources:

• Town of Hamden geographic information system (GIS) mapping • Town of Hamden record road construction plan / profile drawings • Field survey by Land Resource Consultants (LRC) performed in September through

October 2011. • Observation of landuse from aerial imaging sources such as Google Earth. • Field observation by DTC.

Stormwater Hydrology Runoff flows rates were determined for the 2 year, 5 year, and 10 year return periods by utilizing the Rational Method:

Q=CIA where: Q=peak rate of discharge, in cubic feet per second (cfs) C=weighted runoff coefficient I=rainfall intensity, in inches per hour (in/hr) for the selected design frequency and duration A=drainage area, in acres (ac)

Typical runoff coefficients are summarized in the following table taken from FHA “Design of Urban Highway Drainage, The State of the Art”, August 1979.

Character of Surface Runoff Coefficients

Pavement Asphaltic and Concrete 0.70 to 0.95 Brick 0.70 to 0.85

Roofs 0.75 to 0.95 Lawns, sandy soil

Flat, 2 percent 0.05 to 0.10 Average, 2 to 7 percent 0.10 to 0.15 Steep, 7 percent 0.15 to 0.20

Lawns, heavy Soil Flat, 2 percent 0.13 to 0.17 Average, 2 to 7 percent 0.18 to 0.22 Steep, 7 percent 0.25 to 035

The Newhall study catchment areas were subdivided into two subcategories – pervious cover and impervious cover for simplicity. Pervious cover was assigned a runoff coefficient of 0.4 which included lawn, trees, gardens, and bare soil. Impervious cover was assigned a runoff coefficient of 0.9 which included streets, sidewalks, driveways, and rooftops. The runoff coefficients were weighted in relation to the respective drainage areas to compute a composite runoff coefficient describing each drainage area. Times of concentrations were also entered into the model for each catchment area. The shallow concentrated flow method of determining the time of concentration was used as described in TR-55. This method takes into account land slope and paved / unpaved cover types. The minimum time of concentration used for this project was 5 minutes for rational method computations. Rainfall intensity values for short duration storm events (less than 180 minutes) were taken from Table B-2.1 located in Chapter 6 of the CONNDOT Drainage Manual. StormCad translates these tabular values into intensity-duration-frequency (IDF) curves thus allowing the program to interpolate intermediate time values. Hydraulic Analysis Once the runoff flow rate was established for a given pipe segment, the hydraulic grade line (HGL) was determined. Each pipe segment was analyzed using manning’s equation to determine velocity and depth of flow given the flowrate calculated by the rational method and physical pipe properties (slope, diameter, roughness coefficient). StormCAD then performs a standard step hydraulic analysis on the sewer network starting from the outfall and working in an upstream direction. A suitable tail water condition was selected for each outfall. Hydraulic grade line calculations account for pipe friction losses and headlosses that occur in manholes and catch basins. It calculates junction losses in one of several methods. HEC-22 was selected for calculating junction losses which is consistent with the procedure stated in the CONNDOT drainage manual. When applying HEC-22 to the model, structure headloss is related to the velocity head in the outlet pipe by the following equation:

hL=(K)(Vo2/2g)

Where:

hL=Headloss

Vo=Outlet velocity

g=gravitational constant

K=KoCDCdCQCpCB=Adjusted headloss coefficient

Ko=Initial headloss coefficient

CD=Correction factor for the pipe diameter

Cd=Correction factor for flow depth

CQ=Correction factor for relative flow

Cp=Correction factor for plunging flow

CB=Correction factor for benching

Recommended Improvements Field observations were studied to generate specific recommendations compiled on Figures 4 & 5. Recommendations were divided among three categories to reflect immediate results with the best return for each dollar spent (Category 1), longer term solutions to reduce maintenance burden with moderate initial investment (Category 2), and pipe replacement to increase system capacity with significant capital investment (Category 3). Detailed descriptions of recommended improvements are outlined below. Category 1 – Immediate improvement to drainage syst em function with minimal expense Drainage System Cleaning

Cleaning of all catch basins, inlet grates, manholes and pipes will result in an immediate improvement of the overall functionality of the drainage system. Many of the pipes TV inspected were clogged with sediment and other debris. These pipes were cleaned prior to inspection to allow passage of the inspection camera. Many components of the Newhall area drainage system were filled with large debris and sediment volumes exceeding the capability of the TV inspection crew. The middle school property, catch basin laterals, and main lines not inspected need to be flushed and cleaned with high pressure water jetting and a vacuum truck. The pipe inspection industry classifies this as “heavy cleaning”. A schedule should be put in place to have all pipes cleaned and inspected every 10 years. Many of the catch basins are full of debris and sediment not allowing storm water to reach the pipes. Catch basin sumps are designed to collect debris and sediment and keep it out of the pipes. When the sump fills up it blocks the outgoing pipe and does not allow the catch basin to drain. Some of the catch basins are filled completely to the top not allowing any storm water to enter. Cleaning of all catch basins is recommended in order to maintain their functionality. Several of the drainage inlets in the area do not have a sump. These inlets drain directly out of the bottom and will become clogged more frequently than catch basins with sumps. These catch basins should be indentified and the laterals to these catch basins should also be cleaned. Street sweeping twice a year during the spring and fall is recommended to reduce sand, leaves and other debris from entering catch basin inlets. All inlets not cleaned by street sweeping should be manually cleaned at this time.

Drainage System Cleaning Schedule

Item Action Frequency

Pipes

Removal of debris and sediment with high pressure water jetting and vacuum truck.

Initially and every 10 years

Catch Basins Removal of debris and sediment with vacuum truck. Annually

Inlets Removal of debris manually or with vacuum sweeping. Annually

Roads Removal of sand and debris with vacuum sweeping Twice annually (spring & fall)

Outfall Area Inspect and remove debris and sediment

Initially and when sediment accumulation encroaches on

outfall pipe. Excavate sediment and debris at outfalls OF-0391 an d OF-0250 Outfalls OF-0391 and OF-0250 are partially blocked by sediment preventing the system from draining properly (Photo 02). Sediment and debris within the pond must be excavated to an elevation lower than the inverts of the two pipes to allow unrestricted flow. More than half of the storm water runoff from the Newhall neighborhood passes through these two outfalls making it critical to clean and maintain the area. A significant amount of sediment must be removed and properly disposed of off-site to improve conditions downstream of the outfalls. An initial estimate of 400 cubic yards of sediment removal should be considered to maximize effectiveness of this improvement. Ownership of the property, rights to access, and jurisdiction of the local inland wetlands agency should be considered when executing this recommendation. After accumulated sediment is excavated and the outfall pipes cleaned, this area should be monitored at least every 6 months to establish sediment clean out frequency. Periodic removal of accumulated sediment will be required since the basin behaves similar to a sediment removal forebay. Reset manhole cover frames at locations where paved over Roadway resurfacing projects over the years have resulted in paving over several manhole covers. Others have become sealed shut by grit. Covers should be located, frames excavated and reset flush with the pavement surface. Manhole covers in the middle school field were covered with soil and grass. These manhole covers should be located and frames reset flush with grade. Remove roots from pipes Removal of roots from the system will have an immediate positive impact on the system. Unattended root infiltration is one of the leading causes of storm water system failure. Roots

enter pipes through joints seeking water and nutrients. Roots grow inside the pipe causing systemic failure such as joint separation, blockages, pipe fractures and collapses. There are several locations in the system where roots penetrated through joints and are causing blockages and broken pipes. Roots can be removed mechanically with the use of cutting instruments or chemically with different herbicides. When roots are cut back and removed they will likely come back in the future and will have to be removed again. Chemicals can be used to kill roots but can have a systemic effect and may kill the tree or shrub. Chemicals can also have negative environmental effects when they reach the outfall area. Once roots are removed cured in place pipe (CIPP) can be used to line the pipe in order to prevent further root growth. Lining the pipe will cover all joints leaving no place for roots to enter the pipe essentially making it one long solid pipe. Cut break-in taps flush with pipes After construction of the mainline storm sewer, additional laterals were added to accommodate additional catch basins and drains. These laterals were installed by breaking holes into the existing pipe and inserting the laterals without any special fittings. The ragged holes would then be sealed around the intruding lateral using mortar or nothing at all. The fractured nature of these penetrations encourages cracking in the main pipe around the lateral, impacting the structural integrity of the pipe. The intruding laterals will also obstruct flow through the pipe and may collect debris. Remote cutting tools used by cured in place pipe lining installers are available to trim intruding pipes flush with the storm main. Structural integrity of the lateral pipe-main pipe connection can be improved with the use of a “top hat” which is essentially a cured in place pipe product. The “top hat” can be installed remotely without excavation and reinforces the main pipe and lateral stub with resin impregnated fabric. Category 2 – Improvements with short term benefits gained at moderate expense Point repairs to existing pipes and catch basins Pipe fractures and broken pipes that have not collapsed can be point repaired by installing small sections of cured in place pipe over the affected area or chemical grouting. Excavation can usually be avoided for point repairs. Replace existing pipe section in kind Collapsed pipe sections, cracked pipes which are not longer circular in section, and pipes with large missing fragments must be replaced by open trench methods. Older pipe materials such as clay pipe and concrete pipe of non-standard size may warrant full replacement structure to structure rather than just pipe segments. Replace inlet structures with catch basins Many of the field observations can be linked to the existing style of stormwater inlet commonly found within the Newhall study area. The inlets structures are not catch basins since no depressed sump is provided for capturing sediment and debris.

Replacement of the existing inlets with precast concrete catch basins is recommended to reduce the need for periodic pipe cleaning and sediment excavation from the outfall pond. Sediment and debris would be captured in the catch basin sump where it could be removed by a vacuum truck. Connecticut Department of Transportation (CDOT) type ‘C’ or ‘CL’ precast catch basins with type ‘A’ grates are the recommended solution. CDOT catch basins and grates are commonly available from most local precast concrete manufacturers. Stock units are equipped with sidewall knockouts for pipe connections rather than custom designing each structure. This solution lends itself to easy replacement of catch basin tops and grates if they are damaged in the future since they are a standard product. Four foot deep sumps are desirable for collection of sediment but can be difficult to install at that depth. Cleaning deep catch basins is a challenge as well. A sump depth of two feet would be the minimum recommended. Hoods should be provided on each catch basin outlet pipe to prevent floatable materials such as bottles and sticks from entering the pipe network. Plastic and fiberglass hoods are an economical solution but subject to potential damage from vacuum truck cleaning equipment when compare to cast iron hoods. Areas of dense underground utilities may preclude the use of precast catch basins. Concrete block basins could be installed to fit the space available in these instances. Precast catch basin tops could be fitted to the block basin. Replace cast iron inlet grates with fabricated stee l grates All existing cast iron inlet grates should be replaced with CDOT type ‘A’ grates. The individual openings of the existing grate are too small subjecting them to clogging with debris of any size. The total open area of the grate is small relative to modern steel grates resulting in ponding during significant rainfall events. Caution should be exercised when replacing the inlet grates. The small opening size of the existing grates offers some protection against pipe clogging for the existing inlets without sumps. New inlet tops with larger opening steel grates will admit more debris into the storm drain pipe system if no sump exists. If the inlet does not have a sump, the entire structure should be replaced with a new catch basin equipped with a hood. Install cured-in-place pipe where needed Pipes with cracks, root intrusion, and consistent alignment can be renovated without excavating the pipe. Several pipe segments within the Newhall study area identified on Figures 6 &7 are good candidates for cured in place pipe lining, a popular form of trenchless pipe rehabilitation. Installation of cured in place pipe requires removing all roots, cutting back protruding lateral taps, and cleaning the pipe. A resin impregnated fabric liner is then pulled through the pipe and cured with hot water or steam. Lateral connections are restored with a remote cutter after curing. Few storm drain lateral connections exist in the Newhall area thus increasing the ease of installation. The finished liner is structurally independent of the host pipe after curing. Lack of soil excavation is the main benefit of cured in place pipe lining. This is advantageous in the Newhall neighborhood given the past history of environmental concerns of soil and groundwater in the area. The installation process is rapid, individual pipe segments between

drainage structures are typically completed in one day. Lining pipe diameters larger than 12 inches in diameter can be expensive, often exceeding the cost for open cut excavation if bury depth of the pipe is shallow. Category 3 – Long term solutions requiring signific ant capital investment Replace undersized pipes The hydraulic model of the Newhall area drainage network revealed several pipes which would benefit the entire network by increasing the pipe diameter. Figures 6 and 7 located in Appendix E identify specific locations where pipe replacement with a larger diameter is recommended. The existing storm pipe network has a widespread capacity failure for low intensity storms less than the 2 year storm frequency. Replacing the pipe segments as suggested would improve system capacity to handle a 2 year storm frequency at limited locations within the drainage network. Due to the lack of elevation change in the lower reaches of the storm drainage system and tailwater influences at the outfall pond, it is unlikely any combination of pipe size increases would improve capacity to handle a large storm event such as a 10 year storm commonly used in design of urban drainage systems. The pipe size increase recommendations are provided as a reference. Due to the high expense and low benefit relative to the other recommended improvements, DTC suggests increasing pipe sizes only when structural pipe conditions dictate replacement.

Preliminary Cost Estimate DTC quantified the costs for implementing each of the three categories of recommended storm drainage system improvements. This opinion of cost assumes public bid of a unit price construction contract in terms of 2012 dollars. Costs do not include contingencies, maintenance and protection of traffic, police coverage, insurance, bonding, or construction inspection services. It is likely that Town of Hamden staff could self-perform many of these tasks at a significantly lower cost.

RECOMMENDED IMPROVEMENTS

CATEGORY 1

Item Description Unit Price Estimated Quantity Total Price

Clean entire catch basin structure $200 16 ea $3,200.00 Clean catch basin sump $175 141 ea $24,675.00 Clean manhole sump $175 10 ea $1,750.00 Remove and dispose sediment at outfall area $60 400 cy $24,000.00 Heavy cleaning of pipe $10 6355 lf $63,550.00 Remove and dispose roots from pipe $50 345 ea $17,250.00 Cut back protruding lateral taps $300 3 ea $900.00 Locate paved over manholes & reset frame & cover $900 13 ea $11,700.00 Point repair of fractures and broken pipes $500 5 ea $2,500.00 Light cleaning of pipes $2 5134 lf $10,268.00 Total Cost: $159,793.00

CATEGORY 2


Replace broken pipe section $300 6 lf $1,800.00 Cured in place pipe lining $225 2813 lf $632,925.00 Replace inlet with CDOT catch basin $3,000 45 ea $135,000.00 Replace cast iron inlet grate with steel grate $800 88 ea $70,400.00 Total Cost: $840,125.00

CATEGORY 3


Replace existing pipe with 15" RCP $110 169 lf $18,590.00 Replace existing pipe with 18" RCP $120 1630 lf $195,600.00 Replace existing pipe with 24" RCP $140 3249 lf $454,860.00 Replace existing pipe with 30" RCP $150 2284 lf $342,600.00 Replace existing pipe with 36" RCP $225 3334 lf $750,150.00 Replace existing pipe with 42" RCP $270 908 lf $245,160.00 Replace existing pipe with 48" RCP $315 2232 lf $703,080.00 Replace manhole / catch basin $3,800 78 ea $296,400.00 Total Cost: $2,987,850

newhall drainage study report

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mill rock

mill rock

conndot drainage

catch basin

structure

curbless catch

storm pipe

upstream catch