OPERATION AND MAINTENANCE (O&M) REQUIREMENTS
The total projected yearly observation and maintenance review is projected to be less than five manhours. The twice-yearly observation should require less than two man-hours each visit including
observation for mosquito control. Sediment removal frequency is dependent on the drainage basin
size and sediment bed load. Projected pumping frequency of the forebay chamber is expected to be
five years or longer with an anticipated 6-8 hour equipment time requirement which is dependent on
the size and location of the unit.
Maintenance Observation:
The depth of oil sheen and floating debris can be estimated using visual inspection while gently
stirring the water in the micropool. The depth will typically be less than two inches and floatables
can be skimmed from the surface. Maintenance and observation should occur only after a
minimum of seven to ten days of non-flow dry weather. The recommended semi-annual
maintenance and observation sequence is described below:
1. Remove bypass headworks manhole access cover, observe for excessive trash and debris
and remove as required. Replace cover.
2. Remove Stormvault™ forebay access cover, observe flotsam in chamber and remove as
required. Replace cover.
3. Remove, in sequence (from influent to effluent) Jensen Precast Stormvault™ sediment
chamber access covers, observe for excessive flotsam and remove as necessary. The
sediment level can be determined by using a probe or stadia rod to determine the depth
of solids build up. Two measurements shall be taken: water depth (water surface to the
bottom), and water surface to the top of the sediment. The difference between the two
measurements is the sediment depth. To avoid underestimating the volume of sediment
in the chamber, the measuring rod must be lowered to the top of the sediment pile
carefully. Record sludge depth from several locations in each chamber. When average
recorded sediment depth is at or above six inches, it is time to remove the captured
sediments. Periodic removal of sand, silt, and other materials that collect at the bottom
of the first chamber will be more frequent than the remaining chambers. The time span
of when each Stormvault™ will need to be pumped will vary from site to site, and is
dependent on the frequency and volume of sediments flowing to the Jensen Precast
Stormvault™.
4. Observe color of sorbent mats; see “Replacement of hydrocarbon sorbent mats.”
5. Remove Stormvault™ screen access cover, observe screen and orifice plate for neutrally
buoyant materials, remove foreign materials as required. Replace cover.
6. Remove outlet box access cover, observe for excessive trash and debris and remove as
required. Replace cover.
Material Removal Methods (i.e., vac-truck, etc.)
Removal of accumulated sediment
Jensen Precast recommends that a professional pumping contractor trained and licensed to remove
and dispose of captured sediment material shall perform this task. The captured sediments are by
their nature very easy to resuspend. Great care shall be taken to prevent any turbulence that may
cause mixing of the micropools contents. Check with your local jurisdiction as they may require an
analysis of the sediments before disposal; however because of the dilution with the micropool
water, the harmful pollution concentrations levels are rarely reached. The recommended cleaning
process is as follows:
1. Place a fractional horsepower submersible pump or vacuum in the effluent chamber (last
access cover). Slowly decant the water above the sedimentation baffles, approximately
one foot of depth. The micropool water may be discharged directly into the outlet box
(check with local authority) or may be stored on site to be used to refill the Stormvault™
after the removal of the retained sediments.
2. In the selected chamber, lower the suction of a fractional horsepower submersible pump
to within one foot of the bottom. Decant this water slowly to the outlet box or store on
site to be used to refill the Stormvault™ after the removal of the retained sediments. The
easiest method to accomplish this is by providing the pump with tripod legs that will hold
the pump suction one foot above grade. After the chamber’s water level is lowered to the
one-foot depth, lower the pump to the bottom or use a Vactor™ truck or similar
equipment to collect the remaining liquid sludge. Discharge it to an approved disposal
site as required by the local authority.
3. Return water to Stormvault™, if set aside. Replace all access covers and return site to
operational condition.
Replacement of Hydrocarbon Sorbent Mats:
The Jensen Precast Stormvault™ is equipped with hydrocarbon sorbent mats that should be
observed for color change. These mats are solid white when they are initially installed, but will turn
darker as they absorb oils. The mats can absorb up to five times their weight in hydrocarbons, and
as they begin to absorb oil, they start to change color. When the mats are observed to be a uniform
dark brown or gray, replace them.
To remove the mats, find the lines for the mats attached to the appropriate access cover and pull
them out. Care should be taken in lifting the saturated mats out of the access way as they could
weigh up to five times as much as the replacement mats. The used mats should be disposed of as
directed by the local authority similar to used drain oil or other non-environmentally safe material.
Replacement mats can be obtained from the Jensen Precast office nearest you. The oil absorbent
mats are an essential component of a Stormvault™ and must be replaced and maintained for
efficient operation of the system.
Warning:
The Jensen Precast Stormvault™ is a confined space. The atmosphere inside may be
hazardous. Entry is not recommended! Atmosphere may be hazardous! Enter only with the
proper equipment, and follow OSHA confined space entry procedures if entry is necessary.
Also, refer to Jensen Precast confined space safety precautions. Please contact Jensen Precast
for additional information.