Amherst Department of Public Works


Construction Storm Water Pollution Prevention Plan

(SWPPP)


Permit # NHR-100000


The Amherst NH Construction Storm Water Pollution Prevention plan is implemented and enforced to limit the discharge of pollutants during the reconstruction of town roads. The project is engineered and supervised by the Amherst Department of Public Works.


By Bruce W. Berry
Public Works Director


Typical road reconstruction consists of the following work.

  1. Reestablishment of shoulders by removal of roadside winter sand buildup (typically four feet for edge of road). Disturbed areas are protected with silt fencing, hay bales, and/or erosion matting. Materials removed are given a visual exam for contamination prior to disposal. If found unsuitable, prior to disposal, material will be tested under the guidelines of ENV-Wm 502.

  2. Remove brush and trees interfering with shoulder work, line of sight, blocking sunlight towards the road within the right of way. On a designated scenic road, prior approval by the Amherst Planning Board and when appropriate, Historic District Commission will be sought.

  3. Culvert replacement, with as needed additional piping perpendicular to road edge and connected to catch basins, to channel Stormwater runoff underground in a managed environment.

  4. Reclamation of asphalt road surface is done following, but not limited to the process listed below:

    1. The road asphalt is ground ten to twelve inches into the base material during the first pass of the reclaimer.
    2. The new road base is reshaped with a grader and compacted with a vibratory roller.
    3. A compaction agent is introduced into the new base material at the rate of approximately three quarters of a gallon to the square yard at a depth of approximately ten inches using the second pass of the reclaimer as a mixer.
    4. The new base material is reshaped with a grader and compacted using a vibratory roller.
    5. The new road base is capped with the compaction agent at a rate of approximately one quarter of a gallon to the square yard.
    6. New asphalt is laid out at a minimum of two inches of ¾” base paving.
    7. Where deemed appropriate Cape Cod style asphalt curbing is used to keep water on the edge of the road, channeled towards catch basins to limit erosion.
    8. One and one half inches of ½” asphalt top locks in the curbing and acts as a finish coat.
    9. Erosion straw woven matting, composted loam, and grass seed gives us a finished and environmentally safe look along the road edge.

  5. At the start of the construction season, a meeting is held with all Public Works employees. An overview of upcoming construction projects is presented. During this meeting information packets are handed out.

  6. During the Public Works morning briefing held at the start of each work day, the daily assignments are issued. All pertinent work is discussed and employees have a clear understanding of their assignments.

  7. Natural chain of command within Public Works is Director, Lead Foreman, Buildings and Grounds Foreman, Heavy Equipment Operator, and Light Equipment Operator, Laborer.

  8. Work is managed on site by experienced senior public works personnel. Grassett Excavation operates an excavator installing catch basins and culvert pipe on this project, with onsite town employees and reports to senior public works personnel who review work in progress.

  9. Our paving / road reclamation is put out to bid each paving year. Throughout the paving / reclamation process, Amherst Public Works supervisory personnel are on site and in charge of the process.

Project and Activity Description

The Georgetown, Williamsburg subdivision is approximately thirty-five years old and built into and along the edge of Walnut Hill. The ditches were allowed to fill in and water saturated the road sub-base causing the road asphalt to breakup. It appears water either runs down the road, draining into a small stream that in turn runs into English Brook or travels through a series of culverts and poorly maintained ditches constructed through residential property (without the benefit of drainage easements) in turn running into English Brook.

Our project involves draining the water away from the road base by either improving the roadside ditches, or a series of connected culvert and catch basins. Culvert pipes are bedded in sand or three quarter inch stone and rapped with geotextile fabric. Some catch basins have porous lower sidewall rapped with geotextile and the outer ditch is filled with three quarter inch stone. This process gives water an avenue to follow without entering the roadbed. After a storm, catch basins drain slowly eliminating standing water and West Nile virus concerns. Where not appropriate, catch basins are solid.

In the appropriate areas, underdrain piping or French drains are added to drain naturally flowing springs away from under road surfaces using a combination of six inch perforated pipes and ¾”stone. Where appropriate, geotextile fabric is used either on top of the stone or to totally rap around the stone and pipe. The road base is compacted in twelve inch lifts and the top six to ten inches has a compaction agent added to improve stability and keep dust particles from becoming airborne.

This department renews its leases yearly for a satellite weather system which included storm imagery in fifteen minute increments and five day projections. This information is available to all senior staff. Care is taken not to excavate roads during projected severe weather periods and to take appropriate precautions where excavations have already taken place. This is covered during the morning crew briefing and crew assignments.

A combination of silt fencing, hay bales, and where necessary coffer dams using three quarter inch or five inch processed stone are used to manage Stormwater runoff. The results of this process is monitored daily by senior Public Works employees and adjusted as necessary. Inventories of the materials listed above are stored, managed, and monitored at the Public Works garage in concrete bunkers and or undercover.

Site Map

During the planning process, all culverts, catch basins, and connecting culvert pipes are marked out with road paint on the road itself. Residents are able to comment and question the layout. All work is done within the right of way unless prior arrangements are made with documented easements.

Prior to starting major work projects, all affected residents in the area of the proposed work zone are invited to an information hearing with power point presentation explaining the project. Proposed culvert work is mapped out and the process listed above under “typical road construction” is explained to all attendees.

Hand drawn sketches with dimensions of pipe size, length of run, direction, etc are posted and available for inspection. Every effort is made to manage and channel the flow of water runoff, similar to its flow prior to road renovation.

Controls to reduce pollutants

Newly renovated roads with reestablished center crown will channel water to the curb edge. This process creates a smoother road surface and it controls and minimizes winter icing. A smoother road uses less winter deicing chemicals, is easier to scrape clean, and therefore creates a minimal negative environmental impact.

By adding parallel pipe and catch basins in appropriate places as roads are renovated, water is channeled from an unmanaged state (with unpredictability oftentimes creating erosion) to a managed environment. Yearly catch basin management (catch basin cleaning, more often if needed) captures sand which harbors pollutants such as hydrocarbons, salt residue, heavy metals, animal waste, and motor oils.

Endangered Species

There are no recorded occurrences of rare species and exemplary natural communities near the area identified. A negative result does not mean that a sensitive species is not present. On-site monitoring will continue throughout life of the project.

Inspections

As stated above, this is a town managed project. Inspections of the whole project, by the DPW supervisory staff are done at a minimum of twice a week. We own these projects and are directly responsible to the taxpayers, they vote on our budgets and we are a phone call away. There is no greater motivation!