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By using GIS to plan and maintain onsite systems, several Small New England communities are saving time and money.
By Don Talend
Several small New England communities, that have deemed traditional sewer infrastructure cost-prohibitive are meeting increasingly stringent environmental regulations by using geographic information systems (GIS), allowing them to identify and prioritize the most problematic parcels, and to plan appropriate onsite wastewater treatment solutions.
According to GIS.com, a GIS information portal compiled by GIS software developer ESRI, GIS is a collection of computer hardware, software, and geographic data designed to capture, manage, analyze, and display all forms of geographically referenced information. Using GIS, a city planner or public works director can link information to location data, e.g., building footprint, soil data, and groundwater elevation to land parcels. Layer upon layer of data can be added to a GIS, to generate color-coded visual displays that can greatly assist onsite wastewater treatment system design.
The power of such customizable information has allowed these resource-challenged New England communities to comprehensively plan and manage decentralized water treatment infrastructure, not to mention saving a great deal of time and money in the process.
Prioritization for Sewer Service
When its municipal wastewater treatment plant reached 80% of capacity in 1999, the town of Concord, MA was required to develop a comprehensive wastewater treatment plan, according to its EPA National Pollutant Discharge Elimination System Stage II Permit requirements. Elena Proakis Ellis, operations engineer with the town’s Water & Sewer Division, adds that the state also asked the town to prioritize for the remaining municipal sewer capacity those properties that had trouble meeting the requirements of Title 5 of the Massachusetts environmental code for onsite treatment systems. Although the community of about 17,000 is fairly small, more than two-thirds of it is served by onsite treatment systems, and the analysis of onsite treatment systems presented a considerable information-gathering endeavor.
Over the next two years, environmental consultants Stone Environmental, Montpelier, VT, and Lombardo Associates, Newton, MA, conducted a comprehensive analysis of every parcel in Concord using the town’s GIS database, which had been in its infancy. “They had information on the parcels, and on the buildings on those parcels, and they were able to take the area of the parcels and subtract out any setbacks, and subtract out the footprint of the building,” notes Proakis Ellis. “From there, they took out areas, that were known from our other GIS layers to be wetlands or on bedrock—areas where they knew you couldn’t site a system.”
Stone Environmental would add other data layers to the database, including soil test data, floodplain data, and groundwater elevations. “They ran this entire model for the entire town, and they were able to show on a map every lot in town that would be able to meet the Title 5 septic system regulations,” Proakis Ellis says, adding that, after eliminating these parcels, from the priority list, the town focused its attention on the remaining parcels in order to determine which ones were most in need of sewer hookups.
“It was just a much higher efficiency of the processing of all of that data,” says Proakis Ellis. “We never would have done field surveys on all 6,000 parcels; that would have been time—and cost—prohibitive.” By 2004, the town finished its comprehensive wastewater management plan, which made extensive use of the Title 5 analysis data.
Following the Title 5 analysis, the database evolved into an Integrated Wastewater Management System (IWMS), consisting of an up-to-date database of all of Concord’s onsite system information, and the type of data used in the analysis. As development conditions change, the IWMS is updated on a continual basis.
Simply converting old parcel maps, previously available in hard copies, into electronic files has benefited developers, says Proakis Ellis. “A developer could turn on all of those layers on the regular town GIS Web site and see if a parcel is all wetland and floodplain. It gives them some basic information before they even go in and try to site a system.”
The GIS has also allowed Concord to codify the management of onsite wastewater treatment more explicitly. In 2003, the town put into effect a new regulation, “CBHR 3.00: Onsite Disposal Systems,” which establishes standards for on-site/decentralized wastewater management and mandates that the Board of Health to rank all unsewered parcels according to potential impacts on the public health, and to prioritize those parcels for review purposes using the GIS.
“I think with the septic systems, it was so much more efficient to process the data from every parcel in town at once and manage that spatial data,” Proakis Ellis concludes. “Graphically, it’s also nice always having the data always available on a map so that visually you can see the areas that have problems. Are they scattered all throughout town, or are they concentrated? That’s something that you really only get with mapping software.”
Flexibility Yields Multiple Scenarios
The powerful organizational capability of a GIS can facilitate the development of various onsite wastewater treatment scenarios. That is the case in Colchester, VT, where city planners have zoned a planned “growth center” at the Exit 17 interchange along Interstate 89. Using an EPA grant, the Colchester Department of Planning and Zoning conducted a buildout analysis of the area, which was designated as a growth center in the town’s 1996 Master Plan. A decentralized wastewater treatment options study was conducted to determine if sufficient onsite wastewater treatment capacity exists for the growth center. Previous studies had focused on municipal sewer service for the growth center and recommended three scenarios. One recommendation was constructing a new municipal sewer collection system discharging to a treatment facility in the neighboring town of Milton, but Milton is planning to extend municipal sewer to an industrial park near Exit 17, and not beyond the Milton town line.
The buildout study completed in 2001 used input from the town planner and Planning Commission, utilizing a GIS. The resulting multiple scenarios, which incorporated sub-scenarios, such as modification of existing properties and owners’ possible plans, included all residential, all commercial, and mixed uses. The study indicated that about 1,000 residential and commercial units generating wastewater flows of 225,000 to 250,000 gallons per day (gpd) could be developed at Exit 17.
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Canaan Valley Institute |
| The Canaan Valley Institute is assisting local authorities in cleaning up the Upper
Guyandotte River Watershed, covering 260 square miles. GIS is a key part in this. |
Sarah Hadd, Colchester’s town planner, recalls that a 2002 state regulation, allowing the use of state-approved “innovative” onsite wastewater treatment systems, encouraged Colchester to look beyond municipal sewer treatment for Exit 17. The onsite treatment options analysis that was spurred on by this regulatory change followed the multiple land-use planning scenarios, and indicates that the GIS gave the analysis great flexibility. “Land-use planning drove the bus,” she acknowledges. “[The analysis] was pretty comprehensive as far as looking at the environmental constraints limiting where you could locate onsite systems.
“I think [Exit 17] is unique in that it’s an undeveloped interstate exchange, which is fairly infrequent nationwide. Exit 17 is a fresh start for us, in terms of the fact that it’s mostly Greenfield. There are definitely development pressures on it, because it is an interstate interchange and it’s in Chittenden County, which is in the Metropolitan Statistical Area for Burlington,” the largest city in a rural state. “What the town of Colchester attempted to do in 2001, was to say we have some responsibility as a municipality to ensure that the type of development that occurs here is in line with our larger land-use goals.”
Stone Environmental, which the town hired to evaluate the potential for onsite treatment of various land uses at Exit 17, took various soil samples and used remote sensing techniques to evaluate the area. Using the GIS and myriad data inputs, Hadd reports, several scenarios were generated. Although the growth center will not be developed for many years, the town has an idea of the various ways in which it could be developed—and what must be done to support development with onsite treatment infrastructure.
“The buildout analysis required a lot of inputs in various formats,” Hadd says. “We had the basic foundations of it as far as the zoning layers, the parcel maps, and the parcel data. The buildout analysis required quite a bit of tweaking of that data. During a buildout analysis, you have to proportionalize: Is it going to be 50% commercial, 50% residential, or 75% residential? Trying to develop those kinds of constraints was a little bit time-consuming.”
According to Hadd, the ability of a GIS to process a tremendous amount of data, and present a visual representation of the integrated inputs, is a major benefit throughout the course of a publicly transparent land-use planning process.
“I think GIS, first and foremost, allows you to not only visually comprehend things and build in the different layers and the different constraints, but also show the public what it all means,” she says. “The thing that GIS allows the town to do is to communicate different land-use concepts to the public visually. For instance, if we put down a layer showing all of the poor or marginal soils in Colchester versus all of the good soils in Colchester, you can start to see the parcel lines of single-family house developments and people start to understand land-use patterns—without the GIS tool, it’s very hard to communicate why we have the land-use patterns where we do.
“You run into so much in the public forum of, ‘Why can’t we have this type of development there?’ When you build these constraints into GIS and overlay them, and suddenly it creates a much clearer image of the different possibilities and the different perplexities—barriers that we have in land-use planning and development.”
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Canaan Valley Institute |
| Every parcel in Holliston, MA, was analyzed using a GIS populated with four “layers of data,” including buffers, building footprints, and bodies of water. |
For a planning or public works department, the information-processing capability can also aid internal decision-making, Hadd adds. “The benefits are really the knowledge that is created and the ability to manage that knowledge,” she says. “We’re the second-largest municipality in Vermont, but we’re a small town in many ways—you have so much institutional knowledge that stays with a person. In a small town in Vermont and rural areas, where one person has so much institutional knowledge, what GIS allows you to do is take that institutional knowledge and preserve it, graphically represent it, and continually update it.
“Why are the septic systems in one part of town working a lot better with this design than in other parts of town? Really, you can have the best land use plans in the world for any particular area, but, without knowing what constraints you’re working with, that land-use plan may never become a reality. It allows you to actually undertake comprehensive planning and land-use plans that can actually be enacted.”
As an implementer of plans, Colchester Public Works Director Brian Osborne echoes the advantages of GIS, insofar as its ability to show planners the feasibility of theoretical infrastructure development. “I believe that planning really needs to take into account not what you would ideally like to see, but what you can accomplish, and then have a plan that can actually be implemented, versus one that sits on the shelf because there’s no way to implement it,” he says. “Using GIS and doing the appropriate analysis, and seeing what the opportunities and constraints are, can be very helpful in developing a land-use plan that can actually be implemented.”
Every Parcel Analyzed
What began as an effort to identify land parcels, that could not meet the requirements of Title 5 of the Massachusetts environmental code for onsite treatment systems, and justify construction of a municipal sewer to serve them in Holliston, MA, in 2000-2001, ultimately identified which onsite systems needed upgrading to get them into compliance. Stone Environmental conducted a comprehensive analysis, using a GIS that assessed the condition of all 4,468 parcels in the town located 25 miles southwest of Boston over the course of more than a year.
Carolyn Dykema of Plymouth, MA-based environmental engineering firm Norfolk Ram Group, and a member of the town’s wastewater committee at the time, who now serves on the planning committee, reports that the issue of sewer construction was traditionally a controversial one in Holliston. The new Title 5 requirements led to the latest push. “There had been several sewer proposals,” she says. “The town had been talking about getting sewers for literally 100 years; we have no sewers at all. The reason Holliston had failed to get sewers previously was that there was some debate as to whether there was a true need for it, or it was a want. We don’t have a lot of industry in town—it was more to deal with a lot of areas with high groundwater.
Stone Environmental proposed an analysis of every parcel in town to determine which ones needed sewer service. Stone built buffers into the database, indicating setbacks required by local and state environmental regulations, and which were unsuitable for onsite systems. By subtracting the buffers from each parcel, and incorporating parcel soil characteristics and intended onsite system use, Stone was able to determine if a given parcel had enough useable land and suitable soils for its onsite treatment system. The consultant added another layer to the analysis by incorporating parcel-specific groundwater data from the Holliston Board of Health, or, when necessary, calculated a weighted average per parcel to estimate its groundwater depth using Natural Resource Conservation Service county-level soils data.
From there, Lombardo Associates put together a proposal to construct a pressure sewer system to serve the parcels with difficult soil, groundwater, and space conditions. The proposal consisted of centralized collection, treatment, and disposal facilities, with a capacity of about 125,000 gallons per day for the downtown area; seven cluster systems that would collect effluent in septic tanks, and dispense the effluent to cluster leach fields that would serve problem areas throughout Holliston; and maintenance and upgrade of septic systems in the remainder of the town. However, this proposal was voted down, and officials decided to upgrade out-of-compliance septic systems with more advanced secondary treatment systems instead—a process that has been completed since that time.
Dykema notes that the use of the GIS was critical to identifying the out-of-compliance parcels, but cautions that the tool should be used to save time, money, and effort in analyzing conditions for onsite wastewater treatment—not completely replace field surveys of some parcels. A consultant may offer to conduct an analysis with services beyond mere use of GIS, but the greater accuracy has a price.
“When we used the GIS data, we came up with what we called red lots—lots that were too small to accommodate a traditional septic system,” she says. “When we budgeted and planned to do this analysis, we didn’t take into account the fact that we should have added a second layer. We really needed to have somebody go out there and do an actual evaluation onsite of the lot to confirm that was the case.
“GIS is planning-level data. There was something about this premise of doing this lot by lot analysis where people just assumed that this was going to be 100% accurate, which was a challenge from a public communications standpoint. We did not have extremely accurate individual lot files, and we went into this understanding that our data was not going to be perfect. There has to be a broad understanding of what level of accuracy you’re hoping to get at the end of the day—if you need to be 100% accurate, just be aware that it’s going cost you a lot of money.”
For more information about GIS and related mapping/imaging resources, visit the following companies’ Web sites:
AirPhotoUSA
Bentley Systems Inc.
Black & Veatch Corp.
CDM
DeLorme
ESRI
Don Talend of Write Results, West Dundee, IL, is a public relations consultant.
OW - March/April 2008 |
