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Multi-Family Housing Site Harbor Vista Apartments, Los Angeles, CA
TEAM MEMBERS
Landscape Architecture Graduate Students:
PROTOTYPE This is a typical multi-family residential site, with very high graywater discharge rates (1,500 gallons per day) and very high stormwater run off rates (95 to 100%). SITE PROFILE The Harbor Vista Apartments are located at 410-450 Wilmington Boulevard, in the Wilmington district of Los Angeles, within two blocks of the busy Port of Los Angeles. The surrounding residential neighborhood, built during the 1950s and 1960s, is a mix of single-family homes and 2-story apartment buildings. The 20-acre Dana Strand Village public housing development is located to the east, directly across Wilmington Boulevard. The neighborhood is well served by public schools and parks. Bus stops and a small retail district are located nearby. Currently, the site is being considered for redevelopment as a family-oriented housing community. Global Green USA used this site as one of its study sites for its Los Angeles Affordable Housing Charrette held April 18 and 19, 1997. Under the proposed plan, all of the existing wood-frame structures would be remodelled to provide a total of 132 2-, 3-, and 4-bedroom units, with improved community services and facilities for families with children. Coordinating with the Global Green effort allowed this team to focus on site related issues, assuring that the pressing social and housing issues were also being addressed simultaneously. The 3.4-acre Harbor Vista Apartment site occupies one city block and was developed as rental apartments in 1987. A total of 119 1-bedroom units and 64 2-bedroom units are housed in five 2- and 3-story buildings. The vacancy rate in the Harbor Vista Apartments is nearly 80%, and the site suffers from severe physical neglect. The few units that remain occupied are over-crowded and require basic maintenance and repair. Nearly 95% of the site not occupied by buildings is paved for parking or shared courtyard space. SITE DESIGN PROPOSALS Large buildings, high on-site parking requirements, and low rise/high density development produced a site that is covered with impervious pavement and roof surfaces. There are very few green areas on the site and none of these remnant green areas are useful for outdoor play or other activities. The underlying strategy of the team's design proposal is to reduce the amount of domestic water imported to the site, to re-use imported water on the site, and to allow the rain water that falls naturally on the site to flow back into the subsoil. The design proposals work with the existing buildings and basic organization of the site plan, and they propose the following construction and management measures: Reduce Paved Areas and Increase Plant Cover First, the parking area was reorganized to reduce some unnecessary pavement, mostly by repainting the parking stall stripes in order to create smaller (8.5' x 18') parking stalls, and by adding stacked bays (one car parked in front of another - appropriate where these two stalls are assigned to the same household) along the west edge of the property. Some paved area was eliminated in each courtyard and along a walkway between the parking area and the courtyard buildings. Trees, shrubs, and filter beds (see item 3, below) are proposed for these new openings in the pavement. On this property shade trees have been sacrificed to increase the number of cars that can be accommodated within the site. Using space gained by reducing the parking stall dimensions, the design team was able to add shade trees at the edge of the large parking area. In order to balance the need for shade with the design requirements for the subsurface infiltration basin located below the pavement, the design team proposed that a lightweight overhead trellis be installed over the center bays of the parking area. The trellis would support fast-growing vines that require limited amounts of growing medium. The vines would shade and cool the cars and pavement and filter out some airborne pollution. Posts for the trellis are strategically located at the corners of parking stalls to avoid potential damage to the trellis, vines, or vehicles. Vines are planted in two small islands of growing medium at the north and south edges of the infiltration basin area. These islands also help to organize vehicle movement within the parking area. In the courtyards and along the periphery of the property, trees, shrubs, and lawn areas work to filter run off and to provide shade and shelter. Trees are strategically located to shade the hot east-, south-, and west-facing walls, windows, and roofs of the residences. In addition to the water quality and flood control objectives described above, the design strategies in this proposal also address some important community livability issues. Reducing pavement and planting trees, shrubs, and vines helps to create a more humane environment and provides an opportunity to reorganize the site for the purpose of creating more useful outdoor spaces. Remodeling the site to provide grass or other landscape areas at the periphery of the property provides an opportunity to create more attractive and neighborly streets, yards, and alleys, while increasing safety and security through strategic planting, fencing, and lighting. Graywater Irrigation Graywater irrigation can be achieved by diverting residential graywater from the building's drain system and using it as a water-supply source in the landscape irrigation system. In multi-family housing, laundry rooms alone can supply a constant and abundant source of water for irrigation purposes. The graywater irrigation system used in this plan captures relatively clean water draining from the washing machines of the complex into closed tanks. These tanks hold an average of four days worth of graywater. An overflow drain returns any excess water to the building sewer drain system. A small electric pump, powered by a photovoltaic cell mounted on the south-facing roof of the apartment building, pumps the graywater to the landscaped areas using standard irrigation equipment. Because abundant graywater is available year-round at this site, there is no need to design a secondary system or to attempt to harvest stormwater for irrigation purposes. Irrigation lines are located below the surface and are operated with a standard remote electric valve system in order to limit human contact with the irrigation water. Graywater is stored in this system for very short periods of time. It contains mostly organic detergents, which can be broken down by soils. Phosphates, often a major ingredient in laundry-room waste water, provide nutrients to plants. With an estimated 530 residents at the Harbor Vista Apartments, laundry alone produces more graywater than the small landscape areas could use if it were to be recycled for on-site irrigation. The remodeling project will allow access to interior plumbing for the re-routing of graywater, providing an excellent opportunity to install a graywater irrigation system. Operation and maintenance of the system involves the following: (1) Monitor and clean the storage tank's inflow filter; (2) monitor landscape areas for indications of salt build-up, then irrigate with city water for two to three days to leach out such build-up; and (3) leaching bi-annually with municipal water to prevent salt build-up. Filter Beds A combined grass filter strip and organic filter bed remove solids and oils from the first-flush run off at the beginning of each rain event. By pre-treating run off, the downstream watersheds are protected from contamination and the subsurface infiltration basin (see item 4, below) is protected from clogging due to build-up of silt and other particulates. The sand filter medium is a peat-sand mixture that has the ability to filter out both solids and dissolved contaminants. A perforated pipe wrapped with filter fabric is placed at the bottom of the sand filter medium. The pipe then channels treated water to the nearby subsurface infiltration basin. Given space limitations, many filter beds on retrofit sites will not have enough storage capacity to treat all storms. In these instances, a standard storm drain inlet may be installed to handle excess flow, leaving behind solids and most floating constituents. The mulch filter medium is a leaf compost and peat mixture that has the ability to retain metals, oil, grease, and dissolved phosphorus. The mulch filter medium can be easily accessed and replaced with new material, as required. The material can be produced on-site, using the green waste produced by normal landscape maintenance activities. Operation and maintenance of the filter bed system involves the following: (1) monitor the mulch filter medium for declining infiltration rates (when water infiltrates slowly or becomes permanently ponded, the mulch filter medium must be replaced with new material, the normal replacement rate being twice every four to six years); (2) maintain the grass filter strip with irrigation and mowing; and (3) keep drain inlets free of debris. Subsurface Infiltration Basin The filter-treated run off flows or is channelled into the subsurface infiltration basin beneath the parking area. From there, any remaining water infiltrates the existing subsoil just like stormwater on an undeveloped or unpaved site. The 3-foot deep crushed stone infiltration basin in this location stores the equivalent of 4 inches of site run off. The dual filter system (surface and subsurface) reduces or eliminates this site's contribution to the region's stormwater and water pollution problems by treating water on-site and returning it to the underlying soil. The underlying clay loam subsoil on this site carries an assumed infiltration rate of 0.5 inches per hour. Given the holding capacity of the infiltration basin, this would allow it to empty into the underlying sub-soil within thirty hours of a major storm. The basin can be further vented to storm drains through an operable valve. This would assure available capacity when a major storm is predicted. A crushed stone material is used to fill the 3-foot deep subsurface infiltration basin. This stone is clean, local, crushed angular quarry material with a 40% water-holding capacity. During dry periods, the stone material at the bottom of the basin is aerated by the natural movement of air through inlets and pipes that work to break down any organic deposits and to regenerate the underlying soil's infiltration capacity. The existing asphalt in the parking area would be removed to install the infiltration basin and replaced with an impervious pavement. Impervious pavement is preferred over pervious pavement in this application so that storm water can be directed to the filter beds for cleaning before it enters the subsurface infiltration basins. Several considerations apply to the design and installation of subsurface infiltration basins. Existing underground utilities could raise installation costs and reduce the amount of the site's available water-holding capacity. Groundwater within 5 to 6 feet of the surface on this site is a constraint as it could lead to reduced infiltration basin volume, migration, and groundwater mounding, as well as problems concerning the overall dependability of the infiltration system. Lateral seepage into existing adjacent structures can be prevented with additional construction and expense. The potential seismic and structural behavior of the water-filled storage area should be investigated on a project-by-project basis. The operation and maintenance of the subsurface infiltration basin includes the following: (1) annual inspection for clogging by flushing the inlets and pipes; and (2) vacuuming or flushing the pipes clean, as required. Green Trellis Over Pavement Like a tree, a vine on a trellis shades the pavement, reduces ambient air temperature, humanizes the feel of the paved area, and intercepts airborne particulates that would become run off contaminants if they reached the ground. Vines have some additional benefits over shade trees in parking areas: (1) they require little or no rooting soil; (2) they grow very quickly; (3) their stems are narrower than tree trunks and can be supported on strong metal posts; and (4) since they shade the cars evenly and at all hours they are the most effective way to reduce gas fumes escaping from overheated gas tanks. The proposed trellis shown in this plan is a pole and vinyl-clad cable with posts located at the corners of parking stalls or at the ends of parking bays. This structure is probably the strongest, most lightweight, and least expensive type available. Many other designs and materials could serve the same purpose, given a variety of budgets and design considerations. Maintenance requirements include the following: (1) repaint metal posts, if required; and (2) irrigate and fertilize vines. SUMMARY The Harbor Vista team dramatically reduced the amount of domestic water imported to the site by re-using graywater for irrigation. The installation of low-flow shower heads and low-flush toilets, included as part of the renovation of the apartments, will further reduce the demand for imported domestic water. All rain water that falls on the site is treated within the boundary of the site in a subsurface infiltration basin located under the large parking area. Stormwater run off channelled to the infiltration basin passes through several stages of filtering in order to prevent future clogging of the infiltration basin. Trees are strategically planted to reduce energy use and to cool the interior spaces of the apartments. Ambient air temperatures are reduced in the parking area by vines suspended on the overhead trellis and by shade trees planted at the perimeter of the parking area. CONSTRUCTION BUDGET The charrette team provided a construction budget for the proposed work, rounded in 1997 dollars, as follows: All proposed site improvements, planting, graywater irrigation system, filter beds, and subsurface infiltration area = $500,000. Construction contingencies (30%) = $150,000. TOTAL ESTIMATED COST OF CONSTRUCTION: $750,000. Note: Additional professional design fees for engineering and landscape architecture (allow 20%) of the estimated construction cost = $150,000. Total project cost = $900,000. BENEFIT ANALYSIS The following benefit analysis provides a cost value per year; per thirty years; and a total value over thirty years for remediation of the entire property. This information was provided by the charrette team in 1997 dollars.
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