1. 7.6 Stormwater Management Near Water Supply Wells
    2. Stormwater infiltration BMPs near water supply wells
    3. Non-infiltration BMPs near water supply wells
    4. Appropriate BMPs
      1. 7.7 Surface Water Supplies and Special Protection Waters

Pennsylvania Stormwater Best Management Practices Manual
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restoration of new woodlands, because they offer the best method of healing and restoring these
damaged lands.
7.6
Stormwater Management Near Water Supply Wells
Pennsylvania ranks third in the nation for the total number of public water supply wells, and nearly
half of Pennsylvania’s 12 million residents get drinking water directly from ground water sources.
It is critical that stormwater BMPs be designed to remove pollutants from stormwater that is to be
infiltrated in close proximity to public or private water supply wells, and be sufficiently isolated
from ground water supply sources.
Water supply wells in Pennsylvania generally pump water from two types of aquifers,
unconsolidated aquifers and consolidated rock or fractured-bedrock aquifers. Unconsolidated
aquifers are composed of sands, silts and gravel. They are generally unconfined and close to the
surface, have high porosity and a high measure of permeability. Water moves into and through
unconsolidated aquifers readily. These aquifers are generally limited to major stream valleys, the
Atlantic Coastal Plain and the glaciated northeast and northwest regions of the state. Fractured-
bedrock aquifers are the most widespread and commonly exploited aquifers in the state. They
may be bedrock layers composed of sandstone, shale, or carbonate rocks such as limestone and
dolomite but they can also be layered or irregular bodies of crystalline rocks such as gneiss,
schist, granite and diabase. Ground water in bedrock aquifers can occur in either unconfined or
confined conditions. Fractured-bedrock aquifers have low primary porosity and ground water is
mainly stored in openings between rock layers and in fractures throughout the rock. Water moves
into and through these aquifers much more slowly than in unconsolidated aquifers. Exceptions
occur in limestone and dolomite where dissolution of the rock increases the size and frequency of
the fractures and therefore increases secondary porosity and permeability. Some Pennsylvania
public water supply wells in limestone and dolomite aquifers produce larger volumes of water
than do wells in unconsolidated aquifers.
Stormwater infiltration BMPs near water supply wells
Pennsylvania’s Safe Drinking Water Regulations (25 Pa. Code § 109) establish a three-tiered
approach to wellhead protection of public ground water supplies. Zone I is the innermost
protective zone surrounding a well, spring or infiltration gallery that may range from a radius of
100 to 400 feet depending on site-specific source and aquifer characteristics. The water supplier
must own this area or substantially control activities within the zone that could potentially harm
quality or quantity of the source. Zone II is the capture zone that encompasses the portion of the
aquifer through which water is diverted to a well or flows to a spring or infiltration gallery. Zone II
is defined as a one-half mile radius around the source unless a more rigorous hydrogeologic
delineation is performed. Zone III is the area beyond the capture zone that contributes significant
recharge to the aquifer within the capture zone. For more detailed information about protecting
underground drinking water supplies, please refer to the Department’s Source Water Protection
Program.
Infiltration BMPs should not be located within Zone I wellhead protection areas. In addition,
extreme caution must be exercised when planning stormwater infiltration BMPs for use in
delineated Zone II areas or for use in areas within one half mile
of public water supply wells. This
is especially important where the water supply wells are in unconsolidated aquifers or bedrock
aquifers of fractured limestone of dolomite. These easily recharged aquifers can become
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contaminated through stormwater infiltration BMPs unless adequate stormwater pre-treatment
occurs first. It is also essential that local government officials be contacted early when planning
infiltration BMPs within Zone II wellhead protection areas. Some municipalities have specific
ordinances that address land use within rigorously delineated Zone II areas.
To ensure that privately owned wells and ground water sources serving non-community water
supply systems are adequately protected, a minimum isolation distance of 50 feet must be
observed between the ground water source and all infiltration BMPs.
As always, the basic tenets of stormwater management should be applied:
All efforts should be taken to minimize the amount of impervious area on the site; and
Stormwater management should be designed to disperse runoff to a number of BMPs
scattered around the site rather than conveying and concentrating runoff to just a few
locations.
One of the most effective ways to pre-treat stormwater for infiltration is to pass the stormwater
through a layer of compost or a compost/soil mixture before allowing it to infiltrate into the ground.
(Compost is meant to be decomposed or composted organic material, not mulch.) EPA and
others report that organic materials in the compost and compost/soil mixtures have demonstrated
pollutant removal rates of over 90 percent for sediments, metals, bacteria and petroleum
hydrocarbons, and as high as 75 percent for total phosphorous. Pollutant removal effectiveness
increases with the amount of compost/soil mixture the stormwater has to pass through. Compost
or soil/compost mixtures are not effective in removing chlorides such those found in deicing salt.
The post-construction stormwater operation and maintenance plan should include limited use of
deicing salts in areas draining to infiltration BMPs. Sand or other inert antiskid materials should
be used in parking lots or roadways if stormwater infiltration is being used near water wells to
minimize water quality impacts from stormwater/melt water runoff.
Use compost or compost/soil mixtures in vegetated swales, bio-retention areas, and infiltration
trenches and basins so that stormwater must first pass through 18 to 36 inches of compost or a
compost/soil mixture before percolating into the ground. The type of vegetation planted in the
compost or compost/soil layer should be selected, in part, for its ability to replenish organic matter
through seasonal leaf fall, root die back etc. It is important to maintain a high percentage of
organic material in the soil because it is the organic material (compost) that has the cation
exchange capacity necessary to capture pollutants in stormwater.
Porous pavement and other sub-surface stormwater infiltration BMPs are not recommended for
use in areas close to water supply wells. These BMPs generally cannot be designed to allow
stormwater to percolate through 18 to 36 inches of compost or soil/compost mixture.
Non-infiltration BMPs near water supply wells
Non-infiltration type stormwater BMPs can be used in areas close to water supply wells. As with
all stormwater BMPs, they should be planned so that the stormwater runoff is spread throughout
a number of locations rather than conveyed and concentrated in just a few places. Stormwater
conveyance systems for loading docks, gas stations and other areas that have an increased
likelihood of hazardous spills should be designed with an emergency shutoff to contain spills if
there is an accident or release.
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Appropriate BMPs
Some appropriate BMPs to consider for stormwater management in areas within one half mile of
a water supply well are discussed below. These BMPs are detailed more thoroughly in Chapters
5 and 6.
Reduce Parking Imperviousness
:
Parking areas should be kept to the minimum allowed by
the municipality. Excess parking area increases the volume of runoff that must be managed.
Rooftop Disconnection
: Roof leaders (gutters) in residential and urban areas can be re-
configured to drain into Rain Barrels, or flow onto lawn areas. Multiple, smaller stormwater
elements placed around the home/structure can be combined to form a flexible design applicable
to confined areas. Larger, commercial buildings may have internal drainage systems, which can
still be disconnected into larger stormwater elements such as cisterns, planters, vertical storage
or infiltration BMPs. Roof runoff can often be routed directly to an infiltration BMP. Roof runoff is
generally cleaner than street and parking lot runoff and may not require as much pre-treatment
before infiltrating into the soil.
Vegetated Roof
:
A vegetated roof is one of the most effective (both cost and stormwater –
wise) methods to manage stormwater in an urban environment. Many buildings in urban areas
have large flat roofs that can be converted into vegetated roofs.
Rain Garden/Bioretention
: Rain Gardens are excellent applications for use around water
supply wells and can be designed to fit areas of various shapes and sizes. Common locations are
parking lot islands, landscaped areas around buildings, and plantings adjacent to streets. Runoff
can be directed into these areas either by a “bubbler” inlet or by graded surfaces. Curb cuts can
be utilized in parking areas and along roads to convey stormwater to these systems. Rain
gardens and bio-retention areas should contain 18 to 36 inches of compost or compost/soil
mixture. The pollutant removal capability of the BMP increases with the depth of the compost or
compost/soil mixture used.
Infiltration Trench
: Infiltration trenches can pick up runoff from parking areas and roads. A
variation of this theme is the planting of trees and other vegetation in the trench along sides of
roads, between the road and the sidewalk. This system promotes tree growth and facilitates the
evapotranspiration of stormwater through tree and plant uptake. Infiltration trenches must be
constructed with a layer of 18 to 36 inches of compost or compost/soil mixture for pollutant
removal. The efficiency of the BMP improves with the depth of the compost or compost/soil
mixture used.
Capture & Reuse of Rooftop Runoff
: Rain barrels can be used to capture runoff originally
coming from roof leaders. They are small enough to fit in yards and can easily be employed in
urban residential neighborhoods. Cisterns and vertical storage units can be placed in corners of
structured parking lots, inside buildings, on the outside walls of buildings, in adjacent alleys,
alongside elevator shafts, and other locations deemed feasible by the designer. Vertical storage
is well suited for use in urban areas where space is at a premium; the shape and location of this
BMP requires very little horizontal land area.
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Wet ponds
: Monitored performance of well constructed and maintained wet ponds has
documented efficiencies of greater than 90 percent removal for suspended solids, and ranges of
60 – 70 percent removal for nutrients and 60 – 95 percent removal for heavy metals. Wet ponds
can also be used to pre-treat stormwater before it is conveyed to infiltration and bio-retention
BMPs.
Vegetated swales
: Vegetated swales are excellent applications to attenuate stormwater
volume and provide effective pollutant removal while conveying and dispersing
stormwater
runoff. The swales should contain 18 to 36 inches of compost or compost/soil mixture to remove
pollutants from any stormwater infiltrating through the swale.
De-icing alternatives
:
Sand or other inert antiskid materials should be used in parking lots or
roadways in areas near water supply wells or upstream of surface-water intakes to minimize
water quality degradation from stormwater or melt water runoff.
7.7 Surface Water Supplies and Special Protection Waters
Antidegradation requirements for special protection waters (High Quality and Exceptional Value)
and for surface water supply (Potable Water Supply) will be met if the post-construction
stormwater infiltration volume equals or exceeds the pre-construction stormwater infiltration
volume, and that any post-construction stormwater discharge is pre-treated and managed so that
it will not degrade the physical, chemical or biological characteristics of the receiving stream.
Please refer to the Department’s
Water Quality Antidegradation Implementation Guidance
(document number 391-0300-002) for more information.
The project should be designed to minimize the amount of impervious area. Any resultant
stormwater should be infiltrated to the maximum extent possible
. Water quality treatment BMPs
should be employed for all stormwater that is discharged. Stormwater BMPs should be planned
so that the stormwater is spread out to a number of locations rather than conveyed and
concentrated in just a few places. Finally, the volume and rate of any stormwater discharge must
be managed to prevent the physical degradation of the receiving water, such as scour, and
stream bank destabilization.
Stormwater infiltration near surface water supplies and Special Protection waters
Care must be taken when planning stormwater infiltration BMPs for use in areas within two miles
* on either side of special protection waters or surface waters used for public water supply.
Infiltration BMPs in these areas must be designed to encourage maximum pollutant removal
before the stormwater is infiltrated into the ground or discharged to a receiving stream.
*[Pennsylvania also employs a three-tiered approach - for surface water source protection.
Zone
A
is a 1/4 mile buffer on either side of the river or stream extending from the area 1/4 mile
downstream of the intake upstream to the five hour time-of-travel (TOT).
Zone B
is a two-mile
buffer on either side of the water body extending from the area 1/4 mile downstream of the intake
upstream to the 25 hour TOT.
Zone C
constitutes the remainder of the basin. Please refer to the
Department’s Source Water Protection
Program for more information.]
One of the most effective ways to pre-treat stormwater for infiltration is to pass the stormwater
through a layer of compost or a compost/soil mixture before allowing it to infiltrate into the ground.
The organic materials in the compost and compost/soil mixtures have repeatedly demonstrated
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