Spn H.010571.2 – Purpose and Need

SPN H.010571.2 – PURPOSE AND NEED

1.0 PURPOSE AND NEED

1.1 Description of the Proposed Project

The proposed project is to construct a detour roadway on new alignment in response to concerns associated with potential roadway instability as a result of the Bayou Corne/Grand Bayou Sinkhole. While a long-term solution to the sinkhole situation is being developed, further subsidence or subsurface instability could result in an immediate need to close Louisiana Highway 70 (LA 70). Figure 1 demonstrates the approved logical termini and location of the project study area, which begins near Gumbo Street/LA 70 and terminates at Louisiana Highway 69 (LA 69) just south of the Crosstex facility. The LA 70 Detour Route is proposed to be constructed to Rural Arterial 1 classification, which allows for two 12-foot travel lanes, eight-foot shoulders, and a 50 mile per hour design speed.

View of LA 70 looking west in front of Gator Gold Casino and Truck Stop.

1.2 Project Background

The proposed project involves the construction of an emergency detour route off LA 70 in the vicinity of LA 69. An emergency detour route is proposed in the event the Bayou Corne/Grand Bayou Sinkhole located to the south of LA 70 threatens the integrity of the highway.

There have been several past closures along LA 70 in or adjacent to the project area as a result of industrial and mining activities of the Napoleonville Salt Dome. The longest closure occurred on December 25, 2003 and lasted 1.5 months. Currently, when the road is closed residents must use one of the signed detour routes, one for passenger vehicles and one for truck traffic (see Figure 2). Truck traffic is required to take a different route due to bridge load/height restrictions. These routes are approximately 44 miles and 70 miles, respectively, and result in

040-014-076NG LA70DR_Final EA 1-1 SPN H.010571.2 – PURPOSE AND NEED

approximately an hour of additional drive time for each trip from the project area to Napoleonville, Labadieville, or Donaldsonville.

The LA 70 Detour Route Stage 0 Feasibility Study and Environmental Inventory (Detour Feasibility Study) was initiated in March 2013. The project was authorized to move forward into Stage 1 Planning and Environmental (Planning/Environmental) prior to the completion of the Detour Feasibility Study in an attempt to have an approved emergency plan in the event further collapse of the existing sinkhole were to impact LA 70.

1.3 Purpose and Need

The purpose of the proposed project is to provide an approved emergency detour route to be constructed only in the event that LA 70 requires immediate closure as a result of threats to structural integrity associated with the Bayou Corne/Grand Bayou Sinkhole. The project is needed to provide a safe, efficient detour of LA 70 in the vicinity of LA 69 if immediate closure of LA 70 is required.

040-014-076NG LA70DR_Final EA 1-2 ^

69 B a y o u C o r n Logical Termini e Latitude: 30° 01' 00.83" N Longitude: 91° 07' 56.42" W Logical Termini Latitude: 30° 00' 54.24" N Longitude: 91° 08' 49.67" W

ou ay

n a

Ê r G

2,000 1,000 0 2,000 Feet Legend C

Study Area Map L L

Project Study Area LA 70 Detour Route u o r G

Bayou Corne/Grand Bayou Sinkhole Area State Project No. H.010571.2 EA l

Ê a t

Assumption Parish, Louisiana n e m n o

Louisiana Department r i v n

of Transportation and Development E

Drawn By ECL 12/12/13 n a

g n

Checked By MEH 5/27/14 i r e

Approved By MEH 11/4/14 e n i g

Project Number n E

Reference e 040-014-000 c n e d Drawing Number 1 i v

Base map provided by CB&I on 4/15/14. o Figure r

040-014-000-A020 P 404

997

Primary Route ~70 miles Potential Area of Closure Truck Traffic

Local Route ~44 miles Vehicular Traffic 1

308

662

¤£90

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Legend C

Existing Road Closure Routes L L

LA 70 Detour Route u o Detour Route 2 r G

State Project No. H.010571.2 EA l a t

Assumption Parish, Louisiana n Existing Road Closure Routes e m n o r

Louisiana Department i

Local Route v n E of Transportation and Development d

Primary Route Drawn By ECL 6/30/14 n a

g n

Checked By MEH 11/4/14 i r e

Approved By MEH 11/4/14 e n Reference i g

14,000 7,000 0 14,000 Project Number n E

Feet e 040-014-000 c

Base map comprised of ESRI World Topographic Map last modified n e d June 26, 2014. Drawing Number 2 i v o Figure r

040-014-000-B069 P