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HomeMy WebLinkAbout1985-07-18 Town of Nantucket Conservation Commission Town and County Building Nantucket, Massachusetts 02554 Agenda July 18, 1985 Public Hearings 1. Woodbury Lane Realty Trust 2. Revisions of the Nantucket Wetlands By-Laws ~..~ ..~~llTUCIr~~ ~~;r... l!f~--- ~~\ ~.-\... ~~i' : . ~\~~~~/::I ~.. ~~=-- il\. ;: ~..... -"i't=~. ......~'O~;: () ~ p........;. f:> . ~~ ORA1~.... .........- Town of Nantucket Conservation Commission Town and County Building Nantucket, Massachusetts 02554 July 18, 1985 The public hearings of the Nantucket Conservation Commission began at 7:30 p.m. Members present were: M. Arnold, P. Waine, P. Dunwiddie, L. Dunn, L. Leske and D. Visco. 1. Public Hearings: a. Woodbury Lane Realty Trust - SE48-312 - P. Waine - Why is it necessary to install injection wells? Daylor- Because of the clay layer, water saturates the ground above. Needed a system to drain this. An underdrain system was designed that would intercept and lower the ground water three to four feet. The water must go somewhere could (1) have as a surface discharge into existing wetland and tie into surface drain system into Lily Pond or (2) take the ground water and break through the clay area into the underground water Dunwiddie- If the ground is so saturated why isn't the whole area considered a wetland? Daylor - The water fluctuates so much that I believe it is not wet long enouth to support wetland vegetation. Lily Pond is already taking all this water. Why should there be an objection of drying the surface area and rerouteing the water that eventually ends up in Lily Pond as it does now. The Planning Board allows underdrains around the corner on N. Liberty Street.So why not Woodbury Lane? The water is breaking out and discharging into wetlands and drains today so whatever quality it has, it is a surface quality that soaks in about three or four feet. Arnold - The Board of Health recommends unfavorable action for reasons of ground water pollution. What is your response to this? Dunn - There seems to be more danger when the water:'is going straight down to the aqua layer, than having it travel in the upper layer 100 or so ft. Daylor - The underdrains will make it as if the clay layer did not exist. All there would be is the regional ground water. This is a much larger water shed going to Lily Pond, about 90 acres. There is a much smaller water shed on the surface. The bottom does not see the fluctuations as the the top layer does. Whatever is put on your lawn will end up in Lily Pond either way. ~.."~ ~~llTUCIr~~. ~.. ~;r... t \~\ o :l/la ~'-X" - i.. i . ., -I.. fill!. .. "'=- - ;,it" I ~C'... -"i't=--=-" ........'O,i () ~;;-.......~ f:>. ,,' ORAl.. ,... .........,,' Town of Nantucket Conservation Commission Town and County Building Nantucket, Massachusetts 02554 July 18, 1985 page 2 Arnold - There is a feeling that there won't be adequate filtering with this system. If the clay layer was not there a sand and gravel layer would be in its place. Daylor - All of the surface features runoffs stay on the surface, none get caught in the infiltration system. All discharges into suface areas. Only the water that soaks into the ground would get injected. L. Leske - Where would a gallon of poison go if dumped now and with new system? Daylor - Now it would trav~l approx. 350 ft. to the edge of the pond, deposit in catch basin by the wetland and drain at N. Liberty Street into Lily Pond. If it went into the underdrain it would travel through about four ft. of soil and travel by pipes into the aqua flow and discharge into Lily Pond. Dunwiddie- What is happening with well #5? Daylor - This shallow hole is acting strangely. We question the readings. It is acting as if we have been having a lot of rain. Other holes are consistant with long term levels. During summer and fall will find the underdrains will most likely be dry. It is not designed to make basements dry. Basements are to be of the nature of basements downtown, above ground. P. Waine - Where are the natural springs in this area? Daylor - The ground water has a slope to it. Sheet 2 shows that it breaks out in fwo or three locations on the site. In each of the four wetlands have breakouts. Ditchs and drains with catch basins were put in these areas some time ago. During dry period you see two to three inches of water in these catch basins, but assume that these dry up in the fall. Waine - Is there any way the water can go up hill? Daylor - Not with the forces that are in effect now. If this was so they would see the regional ground water to revers~,flatten or get equal to allow this. We don't see this in our observations. Waine - What is the total water shed and is it possible for there to be hydrostatic pressure somewhere off site where there is no clay layer, where water will come up and become surface water? Daylor - The water shed for this land is 24 to 25 acres. It is possible, but the high point is on our property except for Main Stree and if it were so, there is a vally where water would spring up and it is not. ...~~ ~~llTUCIr~~ ;r-\, t:r- ,'. i \~- I......~ ~~... ,,-. il\. ;: -,^, ~ . .''0;: .., .. ....... ~ () -9::........;. f:>. ~ ",-'-ORA1.. ,...... -.......",,' Town of Nantucket Conservation Commission Town and County Building Nantucket, Massachusetts 02554 July 18, 1985 page 3 Dunwiddie - Your plans are to use surface runoff to maintain the wetlands. If you reduce the ground water level wouldn't this change the level where it intercepts the wetland? You have tryed to design so that this does not happen but if it does change and due to very wet years or failure of the system and ground water comes up and we see wet basements, and a larger wetland. If it gets dryer are we going to lose the ' wetland? How do you balance these so that we don't lose it. Daylor - We have engineered to maintain the surface runoff. We have increased the total area of wetland by 27,00 sq. ft. One elbow of the wetland could become dryer in years of drought but with the total increase of wetland it won't make the total area smaller. At the Planning Board meeting Monday night we will give evidence of the safety of injection systems. There are approximately 278 areas where these are being used. Borchert - would like to see the commission request a water budget to see where the water comes from and how much water this wetland gets. If the clay layers are not at a constant layer water may be feeding into the wetlands from off site areas. Waine - There are 4 or 5 abbutters who say they have water in their basements when there has been no rainfall recently. Haines - Water is stored and then discharged slowly through the sand and gravel layer. Daylor - There is more of a water shed by Mr. Blairs and others, around 90 acres of ground water from other areas. Brock - Have the issues of the Nantucket By-Laws been addressed? Daylor - We are putting these in writing for a formal presentation. Haines - John Roe's water table line shows more water contributing to the large wetland, I don't see this as a reality. Daylor - If we interpert well five as it is dry, we wouldn't have a problem of saturated land. We should see it with water as we do the other wells. Brock - Will all of the surface runoff go directly to Lily Pond or is it possible for it to go around it and flow elsewhere? Daylor - It is possible and probible that some of the water will be picked up by currents and taken elsewhere. Town of Nantucket Conservation Commission Town and County Building Nantucket, Massachusetts 02554 July 18, 1985 page 4 Poor - What is the opinion of the Commission about the retention crrea ? Daylor - Because of the depth, there would be an increase in the wetland area. Dunwiddie - If the extended wetland is going to be fed from surface runoff with a short residence instead of a steady flow of ground water how will having just peaks of runoff support any vegetation? If you are going to introduce some ground water to keep it wet, what will grow on this clay layer without some kind of peat sub- strate ? Daylor - We would put down an organic layer, and species of plants will do well. Leske - Moved to have applicant bring plans for new retention system. So voted. Also want details of plant replication. Suzanne Howard - A list of proposed conditions for people buying homes in this area will be given to the Planning Board. Visco - Moved to continue the hearing. So voted. b. Nantucket By-Laws - Septic system setbacks were discussed. Title V was never intended to protect wetlands or ground water. It is a health and sanitation oriented law. Daylor says there is evidence that 50 to 100 feet is a reasonable setback for bacterial dillution. Believe that density is a dillution factor more than seperation. Borchert - Nitrogen and phosphates concentrations make the wetlands fill in with more vegetation which eventually fill a body of water. Daylor - Every lot should have a nitrogen model showing how these will be dilluted. Wetlands are a dillution role in figuring nitrogen concentrations in an area. The commissioners voted to continue the hearing and to review the materials presented to them. The meeting was adjourned at 11:00 p.m.