Dear Mr. DiPietro,
   This letter is for the purpose of submitting more evidence toward the appeal of the above mentioned development project. 
   We appreciate the time you spent gathering information at the Powdermill Square sight.  I have a few points to bring to light and clarify following the sight tour.
   With regards to the increase in impervious cover:  I have revisited the Andover Conservation Commission (ACC) file on this project concerning correspondence with the 3rd  party consultant, Judith Nitsch Engineering, Inc (JNEI).  There is no correspondence in the record discussing the many areas of pervious surface within the area highlighted as impervious surface in the Merrimack Engineering (ME) drawings.  JNEI in the original critique, asked for a more clear delineation of the existing and proposed impervious cover.  The resultant map print generated by ME depicted a large shaded area as the existing impervious cover.  I showed this map to you and submitted this to Derek Standish on the day of the sight tour depicting clear areas of perviousness shown in green.  Some of the green area pertained to areas where clearly pavement had worn away, whereas other areas it was rather unclear of the history.  I have a few statements to make regarding this issue.
   According to the record, it is not clear if JNEI ever toured the sight.  Also the question of the classification if the green areas I have shown as pervious is not in the record as it relates to JNEIís independent study. 
   From my examination of the record, I have not seen mention as to the basis of the existing impervious cover. Is it from a field survey or an old map.
   I believe the ACCís interpretation of the green areas I have depicted to be classified as impervious due to the fact that ìhard pack substrateî underneath the worn away asphalt to be untrue and based on supposition rather than a field survey.  When I did my survey, I was careful to dig down a couple of feet in several areas, I found know such substrate.  You may recall that when you came to visit, this fact was made even more clear due to recent actions of excavation equipment.
   With regard to a redevelopment project in a floodplain, the law clearly states that the proposed impervious surface may not be greater than the existing.  I claim that the green areas are pervious.  The ACC claimed still impervious due to hardpack substrate.  If part of the law covers the fact if at one time a parcel of land was impervious, there is some time period in which it must still be classified as impervious regardless of its present condition, this was never mentioned in the record.  Due to the Wetlandís Protection Act in conjunction with the record of this proposal,  the DEP must uphold the appeal.
   With regards to the floodway, the proposed structure encroaches significantly upon the floodway.  This is clearly shown by superimposing the FEMA map to the relevant ME drawing.  In accordance with FEMA  National Flood Insurance Program regulations 44 CFR part, 60.3, a community can only permit encroachments if it has been demonstrated through hydrologic and hydraulic analysis that the proposed encroachment would not result in any increase in flood levels within the community during the occurrence of the base flood discharge.  This study was never done nor presented to the ACC.  Unfortunately the ACC never demanded it.  I do not recall the subject of the floodway even coming up, although I donít know this absolutely.  I recall during the tour, Mr. Stapinski of ME stating that the proposed building canít be in the floodway because a structure upstream is closer to the river than it is. This is neither factual nor does it qualify as a hydrologic and hydraulic analysis as dictated by the law.  On this basis, the DEP must uphold the appeal.
   This last point deals with the multitude of occurrences of 100 year floods in the last 2 decades.  We believe in this section of river, the 100 year flood levels will occur on a comparative 10 year interval, rendering the FEMA maps grossly inaccurate in this specific region.  I realize there may not be a legal statute for which you can uphold the appeal, but this fact is  significant to the Town of Andover and the quality of the environment in the Shawsheen River watershed.  We stated to you the empirical evidence of the high occurrences of 1% floods and gave reasons why  specifically, this section of the river was engineered not to flood which required regular dredging.  When this was stopped a few decades ago, significant sand and silt has built up impeding its discharge in this section in addition to significant development upstream resulting in more impervious surface in the watershed causing rainwater to flow into the river unabated.   Lastly, I searched for hard evidence.  I found my answer from processing precipitation data from the National Climatic Data Center (NCDC) which is part of the National Oceanic and Atmospheric Association (NOAA).  I looked up the amount of precipitation which prompted three different 1% flood levels in the past 25 years.  I then compared this to the NCDC data on the rate of occurrence for these precipitation amounts.  I found the following to be true of 3 recent floods in the Powdermill Square area designated by flooding which reached or surpassed the 1% flood elevations:

The Jan 26th 1987 flood corresponded to precipitation which was a 25 year occurrence

The Oct 22th 1996 flood corresponded to precipitation which was a 100 year occurrence

The June 15th 1998 flood corresponded to precipitation which was a 10 year occurrence

This leaves us with knowledge that on average, we can expect the 1% floodwaters as designated by the FEMA maps to occur on average every 10 years.  This will have a negative impact on the Town and the Shawsheen Watershed due to the following resultant events:

Chemicals from Automobiles leaching into the river

Greater likelihood of sewerage discharging into the river

10 in 20% chance of a flood occurring during the construction period resulting in environmental devastation (as opposed to 1 in 2% if the FEMA maps were accurate.)

Andover not able to enforce flood mitigation requirements on this project as is evidenced by the fact that Andover has not been able to enforce far fewer requirements on Marland Place, right across the river.

Solids as a result of sanding/salting due to snow discharging into the river.