2.1 Water Supply
Inventory
The Dennis Water District supplies drinking water to the entire Town. There are a handful of properties that are served by individual wells. The source of all the water is from the Monomoy Lens. The Monomoy groundwater lens is the sole sources of water for Dennis, as well as the Towns of Harwich, Brewster, Orleans and Chatham, as stated in the Monomoy Capacity Study, July 1996. Overall the lens supplies drinking water to over 40,000 homes and businesses that are served by 48 municipal public water supply wells and an estimated 1,000 private wells. In 1995 alone, municipal suppliers pumped an average of over 5.5 million gallons per day. In the summer season, this figure doubles or triples.
The Town of Dennis is served by 21 wells. These wells are all listed in Table 2.1.1. All wells are located north of Route 6. The information in this table and much of the data to follow on water use is from the Town of Dennis CWMP Needs Assessment. The table includes the well number, name, and location, daily pumping volume and the water treatment type.
Table 2.1.1 – Dennis Water District Public Supply Wells
|
Well Number |
Source Name |
Location |
Daily Pump Volume (MG) 1 |
Treatment Type |
||
|
01G |
Main Station |
80 Old Bass River Road |
0.58 |
CC, DI |
||
|
02G |
Well 1 |
Old Chatham Road |
0.5 |
CC, DI |
||
|
03G |
Well 2 |
Old Chatham Road |
0.36 |
CC, DI |
||
|
04G |
Well 3 |
Old Chatham Road |
0.43 |
CC, DI |
||
|
05G |
Well 4 |
Old Bass River Road |
0.322 |
CC, DI, IR |
||
|
06G |
Well 5 |
Route 134 |
0.36 |
CC, DI |
||
|
07G |
Well 6 |
Old Bass River Road |
0.155 |
CC, DI |
||
|
08G |
Well 7 |
Airline Road |
0.65 |
CC, DI |
||
|
09G |
Well 8 |
Airline Road |
0.43 |
CC, DI |
||
|
10G |
Well 9 |
Grassy Pond Road |
0.86 |
CC, DI |
||
|
11G |
Well 10 |
Airline Road |
1.02 |
CC, DI |
||
|
12G |
Well 11 |
Old Bass River Road |
0.587 |
CC, DI, IR |
||
|
13G |
Well 12 |
Airline Road |
1.01 |
CC, DI |
||
|
14G |
Well 13 |
ABANDONED |
0 |
|||
|
15G |
Well 14 |
Baker’s Pond |
0.619 |
CC, DI |
||
|
16G |
Well 15 |
Baker’s Pond |
1.01 |
CC, DI, IR |
||
|
17G |
Well 16 |
Timber Lane |
0.71 |
CC, DI |
||
|
18G |
Well 18 |
Hokum Rock Road |
1.008 |
CC, DI |
||
|
19G |
Well 19 |
Setucket Road |
1.008 |
CC, DI |
||
|
20G |
Well 20 |
Setucket Road |
1.008 |
CC, DI, IR |
||
|
21G |
Well 21 |
East of RTE 134 |
1 |
CC, DI |
||
|
22G |
Well 22 |
Old Bass River Rd |
1.008 |
CC, DI |
||
|
Notes: 1. Daily pumping volume from the Dennis Water District Public Water Supply Comprehensive Report dated 11-26-2003. 2. CC=Corrosion Control; DI=Disinfection, IR=Iron Removal |
||||||
The Town of Dennis CWMP Needs Assessment provides the following on water use:
Table 2.1.2 – Total Annual Pumpage
|
Year |
2001 |
2002 |
2003 |
|
Pumpage (Million Gallons) |
1034.5 |
1044.5 |
951.3 |
|
Percent Unaccounted For |
7.4 |
4.1 |
7.0 |
|
Notes: 1. Source – Dennis Water District – MADEP Public Water Supply Annual Statistical Report |
|||
Table 2.1.3 – Total Monthly Pumpage (Million Gallons) (1)
|
Month |
2001 |
2002 |
2003 |
2004 |
|
January |
39.4 |
38.3 |
48.4 |
48.1 |
|
February |
32.9 |
32.5 |
40.2 |
44.0 |
|
March |
38.4 |
40.4 |
41.5 |
44.9 |
|
April |
46.2 |
52.4 |
45.5 |
49.8 |
|
May |
120.1 |
84.5 |
78.9 |
87.1 |
|
June |
138.1 |
125.7 |
104.5 |
127.2 |
|
July |
178.9 |
225.0 |
189.0 |
180.8 |
|
August |
162.5 |
199.6 |
161.2 |
153.8 |
|
September |
120.0 |
100.8 |
100.0 |
114.7 |
|
October |
75.2 |
65.4 |
66.6 |
67.1 |
|
November |
43.4 |
41.0 |
43.5 |
42.2 |
|
December |
39.4 |
40.9 |
44.2 |
43.1 |
|
TOTALS |
1034.5 |
1046.5 |
963.5 |
1003. |
Source – Dennis Water District – MADEP Public Water Supply Annual Statistical Report
1. Analysis of Monthly Water Pumpage. The CWMP Needs Assessment analyzed monthly data, a usage statistic that was not in the previous Dennis Local Comprehensive Plan. The CWMP looked at the period 2001 through 2003. This monthly data is shown in Table 2.1.3, the table illustrates fairly consistent monthly demands over the three year period. Peak flows, as would be expected, occur in July. The peak monthly flow data not only illustrates the fluctuation of water use by year-round residents, with increases in water use during the spring when outdoor irrigation starts to occur, but also illustrates the significant jump in water usage as the seasonal population jumps during the summer months. This is illustrated by the peak summertime monthly water use being nearly five times the use in January or February, a pattern similar to the population trends discussed earlier in this document.
The CWMP reports that average monthly water use for 2001 was 86 million gallons, 2002 was 87 million gallons, 2003 was 80 million gallons, and 2004 was 84 million gallons.
2. Daily Water Pumpage Data. In the 2002 Local Comprehensive Plan the average daily water use was shown to be 2.78 million gallons per day (mgd). This figure had grown to 2.57 mgd in 2000. The average water use in 2001 and 2002 was 2.8 mgd, 2.6 in 2003, and 2.7 in 2004. The CWMP notes the maximum daily consumption in 2001 7.6 million gallons in August; in 2002 a maximum of 8.6 million gallons were consumed on July 4; in 2003, 8.1 million gallons were consumed on July 6 and 7.9 million gallons on July 10, 2004.
The CWMP provides the following peak pumping data:
Table 2.1.4 – Peak Water Use
|
Maximum Month |
Peak Day |
|
|
2001 |
2.06 |
2.7 |
|
2002 |
2.29 |
3.07 |
|
2003 |
2.00 |
3.11 |
|
2004 |
2.16 |
2.93 |
|
4 year average |
2.12 |
2.95 |
3. Analysis of Water Consumption Data. The CWMP analysis of 2004 Dennis Water District consumption data breaks down water use on generalized land use types (residential, commercial, industrial or institutional). The analysis also identified the use of irrigation systems.
Table 2.1.5 from the CWMP illustrates the existing water use (2004) by land use type. It also breaks out data for properties with irrigation use. As the table illustrates, about 28 percent of the total annual average water use is attributed to properties with irrigation systems.
Table 2.1.5 – Water Consumption Summary
|
User Type2 |
Total gpd with irrigation 3 |
Total gpd with no irrigation 3 |
Total gpd |
|
Residential |
629,000 |
1,397,000 |
2,026,000 |
|
Commercial |
23,000 |
235,000 |
258,000 |
|
Industrial |
0 |
6,000 |
6,000 |
|
Institutional |
2,000 |
57,000 |
59,000 |
|
Total |
654,000 |
1,695,000 |
2,349,000 |
|
Notes: 1. Values rounded to nearest thousand 2. User Type based on State Class Codes 3. Water accounts identified with irrigation system |
|||
Table 2.1.6 presents the average water use consumption in average gpd/property for each of the User type, based on the 2004 water data.
Table 2.1.6 – Water Consumption Summary in gpd/property
|
User Type1 |
with irrigation 2 |
with no irrigation 2 |
Total |
|
Single Family |
260 |
120 |
150 |
|
All Residential |
275 |
140 |
170 |
|
Commercial |
610 |
970 |
910 |
|
Industrial |
0 |
330 |
330 |
|
Institutional |
250 |
750 |
710 |
|
Notes: 1. User Type based on State Class Codes 2. Water accounts identified with irrigation system |
|||
The recharge areas for the wells are shown on Map 2.1.1. These areas have been approved by DEP. The Water District is now looking into and for a site for a future one million-gallon per day well. This well is needed to help get through peak demand periods as well as the town’s growth needs.
There are three irrigation wells within the Town of Dennis, all of which are located within the town’s golf courses. Each of these wells is registered with DEP.
The Future
The CWMP Needs Assessment makes projections regarding future waste water flow. The key aspect of this assessment is based upon estimations of future water demand. In the last LCP much of the analysis of future demand was based upon the Monomoy Capacity Study and growth expectations. The following discussion attempts to combine, compare and contrast these two analyses to provide ideas as to the future water demands.
Analysis
The Monomoy Capacity Study projected future demands for water usage. Water demand was calculated on the build out analysis conducted for the study and presented in the Land Use/Growth Management Section of the 2002 LCP. Development scenarios were conducted for the years 2005, 2010 and 2015, including a 50% shift from seasonal to year round units in the year 2015. Water demand was calculated separately for residential units (seasonal and year-round), and commercial units. Water use for each land use was figured at 330 gallons per day for each year round unit. For seasonal units, flow was lowered to one third of this amount taking into account seasonal occupancy. Commercial water use was estimated at 75 gallons per day per thousand square feet of commercial building area. Table 2.1.7 provides a summary of the water demand in each future development scenario from the 2002 Plan.
In 2002 water demand for the year 2020, based on population projections, was used as a comparison to the scenarios based on the build-out analysis. The 2020 figures were obtained from the forecasted needs assessment of October 1994 Department of Environmental Management Report. A summary of the average annual water needs forecast from the DEM report is included in Table 2.1.7.
Figure 2.1.1 includes a series of bar graphs that summarize the supply/demand results for 2002 “existing conditions”, 2015 with seasonal shift conditions, and the 2020 DEM forecast conditions.
The Monomoy Capacity Study provides forecast scenarios which illustrate a worst case future if the town and other surrounding towns do nothing to add capacity or conserve water (i.e. leak detection, etc). The only limiting factor relative to water supply for the Town of Dennis is the capacity of the Monomoy Lens itself.
TABLE 2.1.7
2002 SUPPLY AND DEMAND ANALYSIS
MONOMOY LENS – DENNIS
YEAR |
YEAR ROUND HOUSING UNITS |
TITLE 5 FLOW (330GPD/UNIT) |
Seasonal Housing Units |
Title 5 Flow (110gpd/unit) |
Commercial Area (sq.ft) |
Title 5 Flow (75gpd/1000s.f.) |
Total Water Use (GPD)1 |
Largest Well (MGD) |
|
DENNIS 1995 2005 2010 2015 (current mix) 2015 (seasonal shift) 2020 |
7,234 7,472 7,687 11,285 |
2,387,220 2,465,760 2,536,710 3,724,050 |
6,770 6,992 7,195 3,597 |
744,700 769,120 791,450 395,670 |
2,500,556 2,807,056 3,014,556 3,056,056 |
194,967 210,529 226,092 229,204 |
2,810,000 3,326,887 3,445,409 3,554,252 4,348,924 3,590,000 |
0.67 |
AVERAGE DAILY CONDITIONS(MGD) |
MAXIMUM DAY CONDITIONS(MGD) |
|||||||
|
Adjusted Demand2 |
Supply (wells pumping 16 hours/day) |
Excess/ Shortfall |
Adjusted Demand3 |
Supply (wells pumping 16 hours/day) |
Supply (wells pumping 24 hours/day) |
Excess/ Shortfall (16 hr. pumping) |
Excess/ Shortfall (24 hr. pumping) |
|
| DENNIS | ||||||||
1995
2005
2010
2015 (current mix)
2015 (seasonal shift)
2020
3.48
4.00
4.12
4.22
5.02
4.26
8.98
9.17
9.17
9.17
9.17
9.17
5.50
5.17
5.05
4.95
4.15
4.91
7.70
9.82
10.14
10.44
12.63
10.54
8.98
9.17
10.32
10.32
10.32
10.32
13.46
13.75
15.48
15.48
15.48
15.48
1.29
-0.65
0.18
-0.12
-2.31
-0.22
5.77
3.93
5.34
5.04
2.85
4.94
MONOMOY LENS TOTALS
1995
2005
2010
2015 (current mix)
2015 (seasonal shift)
2020
12.77
15.23
15.86
16.48
18.78
15.44
24.26
26.66
27.23
29.25
29.25
29.25
11.49
11.43
11.37
12.76
10.47
13.81
25.33
34.17
35.92
37.63
43.93
34.77
24.26
26.66
27.23
29.25
29.25
29.35
36.38
40.03
40.85
43.87
43.87
43.87
-1.07
-7.52
-8.69
-8.38
-14.68
-5.52
11.06
5.86
4.93
6.24
-0.06
9.11
1Water use calculated from capacity buildout analysis for 2005, 2010, 2015 and from DEM Water use forecast for 1995 and 2020. 2Water use adjusted for DEP recommendation of meeting demand with the loss of largest well. 3Calculated from 1993 ADD/MDD ration of 2.5. Adjusted for loss of largest well and 25 year error of 10%.
Well Wells may be pumped for 24hours/day only for a short period of time during times of extreme emergency. Planning should be based on pumping wells 16 hours/day.
Figure 2.1.1
2002 Supply and Demand Chart for Dennis
Wells may be pumped 24/day for only a short period of time in emergency situations. Planning should be based on pumping wells 16 hours/day.
As part of the CWMP Needs Assessment, a modified build-out approach was developed with the goal of estimating future water use, which for the CWMP was used to then project waste water.
The CWMP Needs Assessment estimated that waste water flow was 90% of a properties water use. This was used to project waste water flow in Table 6-4 of the CWMP Needs Assessment. Table 2-1-8 below uses this table in the Needs Assessment to convert back to water flow demands
Table 2-1-8 – Estimated Existing and Future Water Demand
|
Nitrogen Loadings 1,3Landuse |
Existing Wastewater (gpd) |
Future Wastewater (gpd) |
|
Multiuse 2 |
48,000 |
81,000 |
|
Residential |
1,723,000 |
2,036,000 |
|
Commercial |
267,000 |
421,000 |
|
Industrial |
6,000 |
26,000 |
|
Institutional |
57,000 |
109,000 |
|
Total |
2,101,000 |
2,673,000 |
The Monomoy Study used in the 2002 LCP suggested a 2020 “build-out” water use of about 3.6 million gallons per day. The CWMP Needs Assessment came to a much lower conclusion, estimating daily water use at “build-out” of about 2.7 million gallons per day.
The challenge of any projection is figuring out the trends, and being able to make “accurate” predictions of the future. In Dennis, a real challenge occurred in the past decade. Everyone anticipated an older population. However, projections all expected the town to grow at rates similar to the past several decades. Population shifts were also considered, but with a shift, toward more year-round housing, which had been the trend for several decades. No one anticipated a loss of year-round population, never mind the dramatic change which occurred. Also, no one anticipated that this population shift would actually result in a shift toward more seasonal housing. Interim population estimates by the Census Bureau held firm for the decade, showing population figures hovering near the 2000 Census figures. At the same time, in the early part of the decade, water use remained fairly flat on an average daily basis. All of this suggested projections made in the 2002 LCP and the CWMP Needs Assessment were not underestimating growth, and that the anticipated growth had simply been deferred given economic conditions in the decade.
Interpreting the 2010 Census is a challenge, while the housing number suggest that the housing “build-out” might be closer than anticipated, with 15,586 housing units constructed, versus 18,680 used in the needs assessment, the 2010 Census actually counts cottages for the first time ever. Actual housing numbers are significantly lower, 14,414, when building permit data is factored into the discussion. Either way, year-round housing occupancy has lagged behind as illustrated in the population drop for the decade. The end result being, far less water use presently in the winter season and a larger seasonal fluctuation. The range for future average daily demand would still be considered to fall somewhere between the 2.7 million gallons per day in the CWMP and the 3.6 million gallons per day of the Monomoy Study
Updated November 18, 2011
