LEED Storm Water Design (Project)

8/3/2019 LEED Storm Water Design (Project)

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Water Quality study in the city of San Fernando,Pampanga

1. Water QualitySewage and Industrial Liquid Wastes. San Fernando City is endowed with

abundant supply of groundwater. As shown in Figure 1, groundwater can be abstractedin its entire territory at depths less than or equal to 20 meters. In Sindalan forexample, water table can be as shallow as eight (8) feet or about 2.5 meters. This, aswell as due to its attractive location coupled by the establishment of infrastructuresupport facilities (road, rail, airport), San Fernando City became an importantindustrial location and urban destination. Today, San Fernando City may already beconsidered or classified highly urbanized. Some of its barangays especially those in thepoblacion have population densities ranging between 14,000 to 16,000 people/ square-kilometer, the same with the densities of Metro Manila today. This level ofurbanization if not properly managed will definitely put stress on the water resource ofthe City.

In the case of human waste or sewage disposal, septic tanks are one of themost efficient and economical methods of treating sewage. They provide biologicaltreatment for the solids and liquids by bacterial action. The sludge and scum areretained and broken down while the clarified effluent (liquid) is discharged to the drainfield for soil absorption. The process is shown Figure 2.


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However, the presence of too many household in a particular area increase the chancesof the sewage contaminating the groundwater. This is illustrated in Figure 3.


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While it is true that septic tanks can properly process sewage, the possibility ofseptic leaks especially in densely populated areas is high. This could easily reach thewater table especially the shallow well. Note that the shallow well depth in SanFernando City is within 3-meter deep. Industrial effluent contaminates thegroundwater in the same process shown in the figure above.

In 2005, the City of San Fernando conducted a socio-economic census namedOplan Pagtatala. It was found that of the total 45,995 households, about 34,135(74.3%) households have septic tanks, while 82 (0.1%) households only have sanitarypits, and the remaining 11,778 (25.6%) households neither have septic tanks norsanitary pits (Figure 4). The latter dispose of their sewage to any place convenient tothen such as waterways, open field, or vacant lots, among others. The sanitary pitreferred herein is a trench or ditch dug through the soil and is used to contain humanwastes without any fortification that will prevent effluents from seeping into the soil orthe water table.


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In the same census, the source of potable or drinking water of the City

constituents was determined. As shown in Figure 5, 23,446 households (51%) have waterdistrict connection, while 12,035 households (26%) and 10,514 households (23%) haveshallow wells and deep wells water sources, respectively.


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Relating this information with the data on sanitary waste disposal system, itcan be inferred that those utilizing shallow wells are at greater risk of usingcontaminated water if sewage seepage to the water table is considered. As such, theCity government may construct deep well systems in the affected communities or forthe local water district to expand its operation by providing at least Level II serviceconnections.

As regard to industrial liquid wastes, limited baseline data was generated in theOplan Pagtatala. The profile of waste water disposal systems of the major industrialplants located in the City of San Fernando particularly those in food and beverageproduction is not immediately available. Notwithstanding this, and in consideration ofthe issues discussed above, the City government at the interim may determine thequality of groundwater in potentially stressed areas (e.g. densely populatedcommunities and areas within the vicinity of industrial/manufacturing plants) byconducting a groundwater monitoring/testing activities.

In March 2004, the Philippine Clean Water Act of 2004 or Republic Act 9275was signed into law, which among others aims to protect , preserve, revive the qualityof our freshwater, brackish, and marine water under the framework of sustainabledevelopment. It mandated line agencies and local government units (Section 7) toestablish sewerage, septage, and sewerage-septage facilities in their respectivelocalities or jurisdictions. Within five (5) years following the effectivity of theAct, subdivisions, condominiums, commercial centers, hotels, sports and recreationalfacilities, hospitals, market places, public buildings, industrial complexes, includinghouseholds are required to connect to available sewerage system. The law alsoprovided the system of wastewater discharge permitting and wastewater chargesystem. RA 9275 and other relevant laws may be used by the City of San Fernando as a


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framework and guide to prepare its water quality and sewerage and septagemanagement plan.

Water Runoff. Another environmental concern that put stress on theenvironment in highly urbanized areas is surface run-off or rainfall not absorbed bythe soil that flows on the surface. During rainy or monsoon season, rain waterinfiltrates into the soil and the excess flows into creeks, then to rivers, down to the

seas and oceans. However, when most of the spaces are erected with dwelling(housing) units and cemented or asphalted, rain water can no longer seep into the soil.Impervious pavement reduce permeability and water retention capacity of soil. Thus,runoff readily goes into storm drainage canals and other water channels. As such, haveto carry stormwater beyond capacity inundating communities and becoming a surgingfloodwater downstream of the river basin.

As shown in Figure 6, installation of infiltration facilities such as rainwaterpercolation intakes, storm water can be allowed to seep into the ground. Thesefacilities help increase the retention capacity and thereby lessen the loads imposed onrivers by reducing total runoff to rivers. Note that San Fernando City is already heavily

built and concreted. Thus, water infiltration over a huge percentage of its total landarea is already minimal. At the rate the City is urbanizing, more and more lands will becovered with structures or paved. As mentioned above, this will increase surface runoffthat will overload the existing drainage systems. Unless capacity is upgraded, floodingwill be a perennial event becoming severe over the years.

In view of this, it may be necessary for the local government unit of the Cityof San Fernando to come up with its water-sensitive urban development plan. Theplan will be the basis of a local ordinance that will become the legal basis ofimplementing water-sensitive urban design measures. Such provisions will be then

incorporated to the local Building Permit System. No building permits will beapproved unless water-sensitive measures are incorporated in the design. The Citymay become the FIRST CITY IN THE PHILIPPINES to seriously implement the concept ofwater-sensitive urban design within the framework of sustainableenvironmental management.


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Another circumstance which aggravate flooding problem in the City of SanFernando includes formal and informal settler encroachment of water channels, creeksused as waste dump, and lahar sedimentation (Figure 7). These factors reduce thecapacity of the drainage channels in the City and have to be immediately addressed.


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Chapter IV, Article 51 of Presidential Decree (PD) No. 1067 also known as theWater Code of the Philippines states that the banks of rivers and streams and the

shores of the seas and lakes throughout their entire length and within a zone of three(3) meters in urban areas, twenty (20) meters in agricultural areas, and forty (40)meters in forest areas, along their margins, are subject to the easement of public usein the interest of recreation, navigation, flotage, fishing and salvage. No person shallbe allowed to stay in this zone longer that what is necessary fro recreation, navigation,flotage, fishing or salvage, OR TO BUILD STRUCTURES OF ANY KIND.

In view of such, the required easements encroached on by both formal andinformal settlers must be recovered in order to revive and restore the ecologicalfunctions of these water channels, and at the same time ensure the safety of theillegal occupants and the surrounding communities. There may also be a need to

prepare a waterways rehabilitation and improvement plan and come up with a doablewater channels clean-up projects. Interventions on proper wate disposal and laharsiltation are discussed in separately.


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Stormwater DesignQuality Control and Quantity Control

Intention:

-Limit the disruption of natural hydrology

-Increase on-site filtration

-Manage storm water runoff

-Eliminate sources of contaminants

-Reduce impervious cover

-Reduce/eliminate pollution

-Remove pollutants from storm water runoff

Some intentions in the list were not suffice based on the plans. So I suggest the followingstormwater solutions on the next pages...

***Sustainable design strategies should be low impact, environmentally sensitive design


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Stormwater Design (for reduction of impervious surface)

A. Alternative surfaces:

1. Rain Garden2. Swales3. Rainwater Recycling (Roof Tamks)

1. RAIN GARDENA rain garden is used to attenuate peak flows and to provide stormwater treatment. Rain gardens use theconcept of bio-retention, a water quality practice in which plants and soils remove contaminants. Raingardens are created in low-lying areas, with specific layers of soil, sand and organic mulch. These layersnaturally filter the stormwater. During the inter-event dry period, the soil absorbs and stores therainwater and nourishes the gardens grasses, trees and shrubs.

Rain gardens look and function like any other garden except they treat runoff and are specificallydesigned with a layer of 100 mm of mulch, 600 (minimum) to 1,000 mm of planting soil, and vegetation(grasses and shrubs). Figure 6-1 illustrates a typical layout of a rain garden. In clay soils, an underdrainshould always be incorporated into the design of a rain garden to provide adequate drainage during wet

weather. The underdrain must discharge to an approved stormwater outlet. To prevent the migration ofadjacent soil into the planting soil and the migration of planting soil into the underdrain material, filterfabric is required.

What to do?

The size of the rain garden depends on the area that drains into the rain garden. The area may includepervious areas as well as impervious areas. The rain garden depth should be 1.0 m deep unlessunderdrainage is difficult in which case the depth could be reduced to 0.6 m minimum.

The soil composition must be permeable enough to allow runoff to filter through the media. The planting


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soil should be a sandy loam, loamy sand, loam, or a loam/sand mix (35-60% sand). The clay contentshould be less than 25% and the permeability should be at least 0.3 metres per day. The soil should befree of stones, stumps, roots, or other woody material over 25 mm in diameter. Brush or seeds fromnoxious plants should not be present in the soils. Placement of the soil should be in lifts of 300 - 400 mmand loosely compacted (tamped lightly with a backhoe bucket). A mulch layer (standard landscape type)should be included on the surface of the rain garden.

The construction of a rain garden will require two inspections. The first inspection will be conducted

after the installation of the under drainpipe and drainage layer. The trench for the pipe connecting therain garden and dispersal device should remain open for the inspection. The final inspection will beconducted upon completion of the rain garden, including planting of vegetation.


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The Conceptual Layout of Rain Garden

2. SWALES

Swales can assist in preserving a sites predevelopment runoff characteristics by retarding flow andproviding some infiltration especially from larger areas of impervious surface like driveways and carparkareas. Swales also provide treatment of stormwater.

A bio-retention trench is similar to a swale on the surface, but includes a low flow trench underneath thegrassed surface that is filled with filter material. Runoff from driveways and carpark areas can bedischarged directly to this filter media. Reference should be made to ARC TP10 publication for detailson bioretention trenches.

Application

Both devices can be used to convey stormwater flows within the site. They may be used to divert andconvey overland flow associated with larger storm events.

Considerations

Swales are generally suitable for gradients between 1 and 4 percent. On steeper slopes check damsmay be required within the swales to prevent high velocities and subsequent erosion. A pipedunderdrain can also be incorporated to the design. Vegetative cover of swales generally consists of a dense and continuous cover of relatively longgrass. The grass should be maintained at a height of not less than 35 mm and typically 150 mm.Owners must be advised of proper maintenance requirements; swales should not be mown too short,or too frequently. The swale size should be based on the dimensions provided on Figure 8-1. The dimensions shownare for effective catchment areas of up to 1000 m2. The effective catchment area is equal to theimpervious area plus 0.72 times the pervious area.


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Typical check dam details for the swales on Figure 8-1, are shown on Figure 8-2 Driveways longer than 30 m should incorporate a swale with underdrain similar to the one shown inFigure 8-3.

Swale Design and Check Dam Location (Figure 8-1)


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Check Dam Details (Figure 8-2)


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Swale for Driveways (Figure 8-2)


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3. Rainwater Recycling ( Roof Tanks)

Roof tanks provide temporary storage and attenuation of stormwater flows generated on roof areas. Rooftanks can also be used to collect stormwater runoff for domestic use. In this regard use must be fornonpotable purposes including toilet flushing and garden irrigation. This section provides design detailsapplicable to both attenuation and reuse.

Stormwater is attenuated by holding stormwater within roof tanks during a rainfall event, and thencontrolling the release of stormwater through a small diameter orifice pipe. Roof tank sizes and orificediameters given in this section are designed to control flows from roof areas to a rate similar to grass.Stormwater discharging from the roof tank orifice must be connected into the drainage network or to an

WCC approved drainage outlet.

The roof tank volume and the orifice outlet diameter depend on the area of the roof. The tank volumemay also vary if it is proposed to reuse rainwater collected in the tank. In urban areas the Council does notsupport use of rainwater for potable water, however rainwater can be used for:

Flushing toilets; Laundry cold tap; Laundry; and Garden uses.

The amount of storage provided in a tank for reuse depends on which of the above the water is to be used

for.

Considerations

Consider the visual impacts of the building platform and tank for aesthetic reasons. The tanks can besupplied in a variety of colours, which will assist to blend in with the surrounding environment.Runoff from other impervious surfaces, such as driveways or paving will need to be managed by otherstormwater management methods.

Tanks should always be above ground unless approved otherwise by Council.


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B. Non-structural Surfaces:1. Drainage2. Permeable/Pervious Pavement3. Green Roofs

Flooded as a result of excess stormwater runoff, causing Installation of a channel drain as part of a storm waterdamage to the property and deterioration of the landscape. management system prevents damage to the house and

landscape from excess water.

1. DRAINAGE

Stormwater Drainage, downspouts and gutters will collect and send out hundreds of gallons ofwater during a storm. Splash blocks only serve as a way to absorb and spread the energy of

the falling water. Drain lines of durable 4 inch diameter plastic can capture and move thewater to a better place on your lot.


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Gravel Pavers

2. PERMEABLE/PERVIOUS PAVEMENT

Permeable paving has the potential to provide a number of beneficial functions within a stormwater

management system. Potential benefits are primarily associated with stormwater treatment and lesserrunoff rates and volumes being generated than conventional pavement due to infiltration and storage ofstormwater within the sub-base.

The design information provided in this document has been developed to assist with both the design andreview of permeable paving proposals. Permeable paving does not suit all sites and it is important thatsite characteristics are reviewed carefully. It is also important to define what the objectives are for usingthis type of system. Key considerations and design steps are outlined below.

What is Permeable Paving ?

It is important to note that these guidelines cover permeable surfacing only. The following distinction ismade between permeable and porous pavements: Porous surfacing is a surface that infiltrates water across the entire surface of the material formingthe surface. Examples include grass and gravel surfaces, porous concrete and porous asphalt. Permeable surfacing is a surface that is formed of material that is itself impervious to water but, byvirtue of voids formed through the surface, allows infiltration through the pattern of voids. Anexample is the concrete block paving.Both kinds of pavements have different service and maintenance requirements as well as surface designs.The demands for porous pavements are higher, because the failure usually results in reconstruction of thesurface after removing a completely section.In general three different configurations of these permeable paving are used (Interpave, 2003) as shown in


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Figure 7-1. The type of system is selected based on sub-grade conditions.

Figure 7-1 Principal system configurations for permeable pavements

Potential benefits include:

Removal of contaminants by filtration, allowing adsorption, microbiological breakdown andsettlement; and Attenuation of runoff.

Use

The situations where permeable paving might be used on a residential site include: Car parking areas;

Walkways; and Residential driveways.

Types

Permeable paving can be separated into the following broad categories: Grass paver /open cell paver: Small surfacing blocks with joints (gaps): Interlocking concrete blocks with voids: and Permeable blocks.

Land Use

Permeable pavement may be considered for light vehicle loading including parking areas and driveways.A common cause of permeable paving failure is clogging resulting from excessive sediment dischargeson to the permeable surface. For this reason, permeable paving is not suitable for use in catchmentswhere potential for sediment generation is high. This applies equally to hard surface catchments wherefrequent sediment tracking is expected (e.g. access roads within construction sites). In this regardconstruction sequence of permeable paving is important. Preferably, all pervious areas and high-sedimenthard surface areas must be excluded from the catchments treated by permeable paving.


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Permeable Paving Bedding Details


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3. GREEN ROOFS

A green roof is a roof system that incorporates soil and plants to minimise the impacts of the coveredstructure. The idea of the green roof is to mimic the natural environment by filtering rain through the soilwhile capturing some to be evapotranspired later. The infiltration and filtering of rain helps to limit thedecreases in the time of concentration that normally occur when a roof structure is built.

A green roof is a roof system consisting of waterproofing material covered with a thin protective layer ofsoil and vegetation. A green roof, also known as an eco-roof, can be used in place of a traditional roof.It is capable of capturing and evaporating between 10 and 100% of precipitation. The effectiveness isdependant on the soil type, soil thickness and vegetation. The season can also have an impact on theperformance.

Figure 9-1 shows the conceptual design of a green roof. Green roof designs must be specific to thestructure being considered. This detail is provided to illustrate the green roof option only.

Considerations

Adequate plant coverage needs to be established and maintained. Irrigation may be required during thesummer months and to aid in establishment.

The additional weight of the soil and water needs to be considered in the structural design of the roof.

The slope of the roof should not exceed 25% unless additional runoff control measures are incorporated.A registered Professional Engineer should be consulted in the design and construction of a green roofsystem.


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Figure 9-1 Typical Detail Green Roof

Documents

LEED Storm Water Design (Project)