Page 137 - Villas at Savona Close-out Manual

The typical MaxWell Plus provides over 2,500 gallons of chamber capacity to process incoming water for
the removal of suspended solids and floating organic compounds. These chambers are constructed of
4000 PSI pre-cast concrete liner segments that are 48-inches I.D., 54-inches O.D. with a 3-inch wall
thickness. In constructing the chambers, these sections are carefully aligned, centered, and stacked in the
borehole to maximize bearing surfaces.

A filter sleeve made of non-woven geotextile fabric is placed inside the drilled shaft to encapsulate the
aggregate backfill, and inhibit the migration of fines from the surrounding soils into the gravelpack. Next, a
corrugated HDPE drainage pipe with a slotted Schedule 40 PVC drainage screen attached to the lower end
is inserted into the pilot-hole excavation. This component is then capped and suspended slightly off the
bottom of the borehole. Clean, washed aggregate sized between 3/8” to 1 ½” to best complement site soil
conditions is utilized for the backfill material surrounding the drainage pipe in the lower excavation of the
main well. The pre-cast concrete chambers are then erected in the 72-inch diameter reamed portions of the
upper excavation.

An overflow pipe constructed of Schedule 40 PVC is installed in the main chamber, and is mated to the
drainage pipe with a coupling under the chamber bottom. This vertical pipe is supported by a fusion-
bonded epoxy-coated galvanized steel bracket attached to the liner wall. Our PureFlo Debris Shield
®
equipped with an internal screen is then fitted onto the top of the overflow inlet. This cylindrical shield is
approximately 24-inches in length, and is fabricated from rolled 16-gauge galvanized steel. The component
is coated with fusion-bonded epoxy, and fitted with an anti-siphon vent. In operation, the shield forces
water to be drawn into the system from several inches beneath the surface, effectively isolating and
containing floating trash, paper, debris and pavement oils within the chambers. The internal screen
effectively filters out suspended material, and the vent prevents floating debris from being sucked into the
overflow pipe as the water level inside the chamber subsides.

The primary settling chamber is interconnected to the main well with a 4-inch diameter Schedule 40 PVC
pipe installed with a two percent slope between chambers. This connecting pipe is feed through a vented,
shielded and screened inlet that is fitted with a reduction orifice. This component narrows the opening of
the 4-inch pipe to 2-inches to manage excessive inflow velocity, and provide a manageable metered flow to
the main well. The restriction also increases the residence time of the water in the inlet structure, thereby
further enhancing the gravity settlement of suspended solids.

Each chamber of this design is equipped with two hydrophobic floating absorbent pillows, which will
remove a wide range of hydrocarbons and organic liquids. The sponges are 100% water repellant, and
literally “wick” floating petrochemical compounds from the surface of the water. Each pillow has a removal
capacity of at least 128 ounces to accommodate effective, long-term treatment.

At the surface of the ground, the inlet structure will be equipped with a 24” or 30” diameter cast-iron grate
and ring assembly, while the main well will be fitted with a 30-inch diameter cast-iron ring and solid cover.
See Appendix 1-A for MaxWell detail.

Installation

Once the locations of any utilities have been identified, the exact locations of the drywell chambers on the
jobsite are laid out and identified by the Civil Designer’s survey team. When installed with standard inverts,
the layout requires center stakes for each chamber, with (2) 10-foot offsets, 90 degrees apart.

The installation begins with the excavation of a pilot-hole boring, which will be accomplished using either a
bucket-auger drill rig, or a SoilMec machine. When a bucket-auger is utilized, the initial borehole is drilled
using a 48-inch diameter bucket. The upper part of this excavation where the chamber will be built must be
enlarged to 72-inches, in order to provide sufficient access to stack the liner segments, and place the
aggregate backfill around the outside of the chamber. In order to expand the upper portion of the drilled
4