117
37.1%
55.6%
34.9%
39.7%
47.0%
51.4%
44.6%
33.0%
29.0%
37.0%
37.1%
22.2%
42.5%
34.4%
26.0%
25.7%
26.2%
42.0%
43.0%
41.0%
7.2%
22.2%
7.5%
6.9%
4.0%
5.7%
3.1%
9.5%
12.0%
7.0%
18.6%
15.1%
19.0%
23.0%
17.1%
26.2%
15.5%
16.0%
15.0%
English
Spanish
Children in HH under 18
No children in HH under 18
Phone [NET]
Landline
Mobile
Online [NET]
Email
Text
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by language, children in HH, and survey
mode
Question 22: The wastewater treatment system construction project would cost an estimate of $150 million. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system?
[AMONG TWENTYNINE PALMS VOTERS]
118
56% say they are more likely to support knowing
septic tanks can, overtime, contaminate groundwater
Question 23: Wastewater generated in Twentynine Palms and nearby communities is currently treated in septic tanks or leach fields and discharged into the ground which can, overtime, contaminate the groundwater. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
55.7%
26.0%
11.3%
7.0%
More likely to support
Makes no difference to me
More likely to oppose
Unsure
5.1%
17.9%
76.9%
More likely to support
Makes no difference to
me
More likely to oppose
10.0%
23.3%
36.7%
30.0%
More likely to support
Makes no difference to
me
More likely to oppose
Unsure
Among those who initially said unsure
Among those who initially said oppose
119
Among those who are more likely to support, 47%
are much more likely to support
Much more likely
Somewhat more likely 46.7%
53.3%
Among those who said more likely to
support
Much more likely
73.5%
Somewhat more likely
26.5%
Among those who said more likely to
oppose
55.7% 26.0%
11.3%
7.0%
Total
Question 23: Wastewater generated in Twentynine Palms and nearby communities is currently treated in septic tanks or leach fields and discharged into the ground which can, overtime, contaminate the groundwater. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
120
48.9%
61.6%
53.3%
55.1%
53.9%
49.2%
56.9%
51.2%
69.7%
49.2%
30.5%
22.0%
28.6%
24.7%
31.6%
36.9%
24.6%
34.1%
15.2%
22.2%
8.5%
5.7%
7.6%
11.2%
1.3%
6.2%
7.3%
6.1%
15.9%
12.1%
10.7%
10.5%
9.0%
13.2%
13.8%
12.3%
7.3%
9.1%
12.7%
Male
Female
Republican
Democratic
No Party Preference
18-29
30-39
40-49
50-64
65+
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by gender, party preference and age group
Question 23: Wastewater generated in Twentynine Palms and nearby communities is currently treated in septic tanks or leach fields and discharged into the ground which can, overtime, contaminate the groundwater. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
121
54.9%
54.6%
50.0%
62.5%
64.3%
23.5%
30.2%
25.0%
7.1%
5.9%
6.8%
12.5%
10.7%
15.7%
8.3%
12.5%
37.5%
17.9%
Latino/Hispanic
White/Caucasian
Black/African American
Asian
Other
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by ethnicity
Question 23: Wastewater generated in Twentynine Palms and nearby communities is currently treated in septic tanks or leach fields and discharged into the ground which can, overtime, contaminate the groundwater. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
122
63.4%
47.4%
69.4%
52.6%
54.7%
52.4%
33.3%
54.7%
54.7%
61.2%
58.8%
46.5%
18.3%
21.1%
19.4%
28.9%
30.7%
28.6%
47.6%
21.9%
26.6%
28.6%
22.5%
34.9%
9.9%
21.1%
5.6%
2.7%
9.5%
9.4%
6.3%
4.1%
7.5%
7.0%
8.5%
10.5%
5.6%
18.4%
12.0%
9.5%
19.0%
14.1%
12.5%
6.1%
11.3%
11.6%
5 out of 5
4 out of 5
3 out of 5
2 out of 5
1 out of 5
Newer perfect voter
New registrant
Council District 1
Council District 2
Council District 3
Council District 4
Council District 5
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by vote propensity and Council District
Question 23: Wastewater generated in Twentynine Palms and nearby communities is currently treated in septic tanks or leach fields and discharged into the ground which can, overtime, contaminate the groundwater. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
123
55.3%
66.7%
48.1%
60.3%
56.0%
57.1%
55.4%
55.5%
54.0%
57.0%
26.1%
22.2%
34.0%
22.2%
25.0%
25.7%
24.6%
26.5%
23.0%
30.0%
7.2%
3.8%
7.4%
1.0%
1.5%
10.0%
16.0%
4.0%
11.3%
11.1%
14.2%
10.1%
18.0%
17.1%
18.5%
8.0%
7.0%
9.0%
English
Spanish
Children in HH under 18
No children in HH under 18
Phone [NET]
Landline
Mobile
Online [NET]
Email
Text
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by language, children in HH, and survey
mode
Question 23: Wastewater generated in Twentynine Palms and nearby communities is currently treated in septic tanks or leach fields and discharged into the ground which can, overtime, contaminate the groundwater. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
124
48% are more likely to support knowing groundwater
is currently the only source of water for Twentynine
Palms and nearby communities have
Question 24: Groundwater is currently the only source of water for Twentynine Palms and nearby communities. Although there is currently no evidence of groundwater contamination, future risks of contamination are possible. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system?
[AMONG TWENTYNINE PALMS VOTERS]
47.7%
30.3%
12.7%
9.3%
More likely to support
Makes no difference to me
More likely to oppose
Unsure
12.8%
23.1%
53.8%
10.3% More likely to support
Makes no difference to
me
More likely to oppose
Unsure
16.7%
13.3%
16.7%
53.3%
More likely to support
Makes no difference to
me
More likely to oppose
Unsure
Among those who initially said unsure
Among those who initially said oppose
125
Among those more likely to support, 47% are much
more likely to support
Much more likely
Somewhat more likely 46.9%
53.1%
Among those who said more likely to
support
Much more likely
50.0%
Somewhat more likely
50.0%
Among those who said more likely to
oppose
47.7%
30.3%
12.7%
9.3%
Total
Question 24: Groundwater is currently the only source of water for Twentynine Palms and nearby communities. Although there is currently no evidence of groundwater contamination, future risks of contamination are possible. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system?
[AMONG TWENTYNINE PALMS VOTERS]
126
43.3%
51.6%
48.6%
48.3%
44.7%
46.2%
43.1%
39.0%
54.5%
52.4%
34.8%
26.4%
30.5%
30.3%
32.9%
41.5%
26.2%
39.0%
25.8%
22.2%
9.2%
9.4%
9.5%
12.4%
5.3%
1.5%
7.7%
12.2%
10.6%
15.9%
12.8%
12.6%
11.4%
9.0%
17.1%
10.8%
23.1%
9.8%
9.1%
9.5%
Male
Female
Republican
Democratic
No Party Preference
18-29
30-39
40-49
50-64
65+
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by gender, party preference and age group
Question 24: Groundwater is currently the only source of water for Twentynine Palms and nearby communities. Although there is currently no evidence of groundwater contamination, future risks of contamination are possible. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system?
[AMONG TWENTYNINE PALMS VOTERS]
127
49.0%
48.3%
37.5%
50.0%
42.9%
29.4%
34.1%
50.0%
7.1%
7.8%
8.3%
12.5%
12.5%
17.9%
13.7%
9.3%
37.5%
32.1%
Latino/Hispanic
White/Caucasian
Black/African American
Asian
Other
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by ethnicity
Question 24: Groundwater is currently the only source of water for Twentynine Palms and nearby communities. Although there is currently no evidence of groundwater contamination, future risks of contamination are possible. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system?
[AMONG TWENTYNINE PALMS VOTERS]
128
66.2%
31.6%
44.4%
39.5%
46.7%
47.6%
38.1%
45.3%
45.3%
49.0%
53.8%
41.9%
18.3%
34.2%
30.6%
31.6%
36.0%
23.8%
47.6%
26.6%
29.7%
28.6%
27.5%
44.2%
9.9%
18.4%
16.7%
2.6%
6.7%
9.5%
12.5%
7.8%
12.2%
10.0%
2.3%
5.6%
15.8%
8.3%
26.3%
10.7%
19.0%
14.3%
15.6%
17.2%
10.2%
8.8%
11.6%
5 out of 5
4 out of 5
3 out of 5
2 out of 5
1 out of 5
Newer perfect voter
New registrant
Council District 1
Council District 2
Council District 3
Council District 4
Council District 5
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by vote propensity and Council District
Question 24: Groundwater is currently the only source of water for Twentynine Palms and nearby communities. Although there is currently no evidence of groundwater contamination, future risks of contamination are possible. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system?
[AMONG TWENTYNINE PALMS VOTERS]
129
47.4%
55.6%
40.6%
52.4%
48.0%
54.3%
44.6%
47.5%
30.6%
22.2%
37.7%
27.0%
31.0%
28.6%
32.3%
30.0%
9.3%
11.1%
6.6%
10.1%
3.0%
4.6%
12.5%
12.7%
11.1%
15.1%
10.6%
18.0%
17.1%
18.5%
10.0%
English
Spanish
Children in HH under 18
No children in HH under 18
Phone [NET]
Landline
Mobile
Online [NET]
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by language, children in HH, and survey
mode
Question 24: Groundwater is currently the only source of water for Twentynine Palms and nearby communities. Although there is currently no evidence of groundwater contamination, future risks of contamination are possible. Does knowing this make you more likely to support or more likely to oppose the communitywide wastewater treatment system?
[AMONG TWENTYNINE PALMS VOTERS]
130
63% say they would support a 1.25% sales tax
increase to help pay for the treatment system
Question 25: A sales tax increase from 7.75% to 9% would raise $53 million over 20 years and cover more than one-third of the overall cost of a communitywide wastewater treatment system. Would you support or oppose a 1.25% sales tax increase to help pay some of the cost of a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
63.0%
29.7%
7.3%
Support Oppose Unsure
131
Among those who would support, 45% strongly
support
Strongly
Somewhat 45.0%
55.0%
Among those who would support
Strongly
75.3%
Somewhat
24.7%
Among those who would oppose
63.0%
29.7%
7.3%
Total
Question 25: A sales tax increase from 7.75% to 9% would raise $53 million over 20 years and cover more than one-third of the overall cost of a communitywide wastewater treatment system. Would you support or oppose a 1.25% sales tax increase to help pay some of the cost of a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
132
61.7%
64.2%
63.8%
60.7%
68.4%
73.8%
64.6%
65.9%
59.1%
52.4%
8.5%
6.3%
7.6%
9.0%
6.6%
1.5%
7.7%
4.9%
10.6%
11.1%
29.8%
29.6%
28.6%
30.3%
25.0%
24.6%
27.7%
29.3%
30.3%
36.5%
Male
Female
Republican
Democratic
No Party Preference
18-29
30-39
40-49
50-64
65+
Support
Unsure
Oppose
Support Oppose
Results by gender, party preference and age group
Question 25: A sales tax increase from 7.75% to 9% would raise $53 million over 20 years and cover more than one-third of the overall cost of a communitywide wastewater treatment system. Would you support or oppose a 1.25% sales tax increase to help pay some of the cost of a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
133
70.6%
65.4%
50.0%
50.0%
39.3%
5.9%
7.3%
14.3%
23.5%
27.3%
50.0%
50.0%
46.4%
Latino/Hispanic
White/Caucasian
Black/African American
Asian
Other
Support
Unsure
Oppose
Support Oppose
Results by ethnicity
Question 25: A sales tax increase from 7.75% to 9% would raise $53 million over 20 years and cover more than one-third of the overall cost of a communitywide wastewater treatment system. Would you support or oppose a 1.25% sales tax increase to help pay some of the cost of a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
134
57.7%
55.3%
72.2%
55.3%
69.3%
61.9%
71.4%
57.8%
60.9%
61.2%
71.3%
60.5%
9.9%
15.8%
2.8%
7.9%
4.0%
9.5%
7.8%
4.7%
12.2%
6.3%
7.0%
32.4%
28.9%
25.0%
36.8%
26.7%
28.6%
28.6%
34.4%
34.4%
26.5%
22.5%
32.6%
5 out of 5
4 out of 5
3 out of 5
2 out of 5
1 out of 5
Newer perfect voter
New registrant
Council District 1
Council District 2
Council District 3
Council District 4
Council District 5
Support
Unsure
Oppose
Support Oppose
Results by vote propensity and Council District
Question 25: A sales tax increase from 7.75% to 9% would raise $53 million over 20 years and cover more than one-third of the overall cost of a communitywide wastewater treatment system. Would you support or oppose a 1.25% sales tax increase to help pay some of the cost of a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
135
62.9%
66.7%
67.9%
61.4%
66.0%
71.4%
63.1%
61.5%
55.0%
68.0%
7.2%
11.1%
4.7%
7.9%
2.0%
5.7%
10.0%
15.0%
5.0%
29.9%
22.2%
27.4%
30.7%
32.0%
22.9%
36.9%
28.5%
30.0%
27.0%
English
Spanish
Children in HH under 18
No children in HH under 18
Phone [NET]
Landline
Mobile
Online [NET]
Email
Text
Support
Unsure
Oppose
Support Oppose
Results by language, children in HH, and survey
mode
Question 25: A sales tax increase from 7.75% to 9% would raise $53 million over 20 years and cover more than one-third of the overall cost of a communitywide wastewater treatment system. Would you support or oppose a 1.25% sales tax increase to help pay some of the cost of a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
136
44% are more likely to support knowing tourists
and visitors pay a large percentage of the sales tax
Question 26: Tourists and visitors pay a large percentage of the sales taxes in Twentynine Palms. Does knowing this make you more likely to support or more likely to oppose a sales tax increase to help pay for a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
44.3%
34.0%
16.0%
5.7%
More likely to support
Makes no difference to me
More likely to oppose
Unsure
13.5%
29.2%
51.7%
5.6% More likely to support
Makes no difference to
me
More likely to oppose
Unsure
40.9%
22.7%
36.4%
More likely to support
Makes no difference to
me
Unsure
Among those who initially said unsure
Among those who initially said oppose
137
Among those more likely to support, 49% are
much more likely to support
Question 26: Tourists and visitors pay a large percentage of the sales taxes in Twentynine Palms. Does knowing this make you more likely to support or more likely to oppose a sales tax increase to help pay for a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
Much more likely
48.9%
Somewhat more likely
51.1%
Among those who said more likely to
support
Much more likely
68.7%
Somewhat more likely
31.3%
Among those who said more likely to
oppose
44.3%
34.0%
16.0%
5.7%
Total
138
Question 26: Tourists and visitors pay a large percentage of the sales taxes in Twentynine Palms. Does knowing this make you more likely to support or more likely to oppose a sales tax increase to help pay for a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
38.3%
49.7%
34.3%
47.2%
53.9%
43.1%
55.4%
36.6%
45.5%
38.1%
39.0%
29.6%
40.0%
32.6%
30.3%
40.0%
27.7%
41.5%
27.3%
36.5%
6.4%
5.0%
7.6%
5.6%
3.9%
1.5%
3.1%
7.3%
12.1%
4.8%
16.3%
15.7%
18.1%
14.6%
11.8%
15.4%
13.8%
14.6%
15.2%
20.6%
Male
Female
Republican
Democratic
No Party Preference
18-29
30-39
40-49
50-64
65+
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by gender, party preference and age group
139
Question 26: Tourists and visitors pay a large percentage of the sales taxes in Twentynine Palms. Does knowing this make you more likely to support or more likely to oppose a sales tax increase to help pay for a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
51.0%
43.9%
37.5%
37.5%
39.3%
29.4%
37.1%
37.5%
12.5%
25.0%
7.8%
5.4%
7.1%
11.8%
13.7%
25.0%
50.0%
28.6%
Latino/Hispanic
White/Caucasian
Black/African American
Asian
Other
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by ethnicity
140
Question 26: Tourists and visitors pay a large percentage of the sales taxes in Twentynine Palms. Does knowing this make you more likely to support or more likely to oppose a sales tax increase to help pay for a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
53.5%
34.2%
47.2%
42.1%
44.0%
47.6%
28.6%
43.8%
45.3%
44.9%
47.5%
37.2%
26.8%
34.2%
38.9%
34.2%
34.7%
33.3%
47.6%
29.7%
35.9%
36.7%
30.0%
41.9%
2.8%
18.4%
7.9%
5.3%
4.8%
9.4%
3.1%
8.2%
3.8%
4.7%
16.9%
13.2%
13.9%
15.8%
16.0%
14.3%
23.8%
17.2%
15.6%
10.2%
18.8%
16.3%
5 out of 5
4 out of 5
3 out of 5
2 out of 5
1 out of 5
Newer perfect voter
New registrant
Council District 1
Council District 2
Council District 3
Council District 4
Council District 5
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by vote propensity and Council District
141
Question 26: Tourists and visitors pay a large percentage of the sales taxes in Twentynine Palms. Does knowing this make you more likely to support or more likely to oppose a sales tax increase to help pay for a communitywide wastewater treatment system? [AMONG TWENTYNINE PALMS VOTERS]
44.0%
55.6%
38.7%
48.7%
48.0%
48.6%
47.7%
42.5%
42.0%
43.0%
34.0%
33.3%
41.5%
30.2%
28.0%
28.6%
27.7%
37.0%
35.0%
39.0%
5.8%
4.7%
5.3%
2.0%
2.9%
1.5%
7.5%
9.0%
6.0%
16.2%
11.1%
15.1%
15.9%
22.0%
20.0%
23.1%
13.0%
14.0%
12.0%
English
Spanish
Children in HH under 18
No children in HH under 18
Phone [NET]
Landline
Mobile
Online [NET]
Email
Text
More likely to support
Makes no difference to me
Unsure
More likely to oppose
More likely to support More likely to oppose
Results by language, children in HH, and survey
mode
142
72% agree with Jones
Question 27: Here are two statements made by Twentynine Palms residents. Please indicate which statement you agree with more.
Smith: “The way we treat wastewater in Twentynine Palms is fine today. If it ain’t broke, don’t fix it. I oppose the effort to bring sewers to town.” Jones: “Investing a communitywide wastewater treatment system will improve property values and secure our local groundwater supply. It’s a smart investment for our future. I support the effort to bring sewers to town.”
[AMONG TWENTYNINE PALMS VOTERS]
22.0%
71.7%
6.3%
Agree with Smith Agree with Jones Unsure
143
23.4%
20.8%
21.9%
18.0%
19.7%
24.6%
26.2%
19.5%
13.6%
25.4%
7.8%
5.0%
5.7%
7.9%
6.6%
1.5%
3.1%
7.3%
9.1%
11.1%
68.8%
74.2%
72.4%
74.2%
73.7%
73.8%
70.8%
73.2%
77.3%
63.5%
Male
Female
Republican
Democratic
No Party Preference
18-29
30-39
40-49
50-64
65+
Agree with Smith
Unsure
Agree with Jones
Agree with Smith Agree with Jones
Results by gender, party preference and age group
Question 27: Here are two statements made by Twentynine Palms residents. Please indicate which statement you agree with more.
Smith: “The way we treat wastewater in Twentynine Palms is fine today. If it ain’t broke, don’t fix it. I oppose the effort to bring sewers to town.” Jones: “Investing a communitywide wastewater treatment system will improve property values and secure our local groundwater supply. It’s a smart investment for our future. I support the effort to bring sewers to town.”
[AMONG TWENTYNINE PALMS VOTERS]
144
13.7%
22.0%
25.0%
50.0%
28.6%
5.9%
4.4%
12.5%
21.4%
80.4%
73.7%
62.5%
50.0%
50.0%
Latino/Hispanic
White/Caucasian
Black/African American
Asian
Other
Agree with Smith
Unsure
Agree with Jones
Agree with Smith Agree with Jones
Results by ethnicity
Question 27: Here are two statements made by Twentynine Palms residents. Please indicate which statement you agree with more.
Smith: “The way we treat wastewater in Twentynine Palms is fine today. If it ain’t broke, don’t fix it. I oppose the effort to bring sewers to town.” Jones: “Investing a communitywide wastewater treatment system will improve property values and secure our local groundwater supply. It’s a smart investment for our future. I support the effort to bring sewers to town.”
[AMONG TWENTYNINE PALMS VOTERS]
145
14.1%
18.4%
16.7%
39.5%
20.0%
28.6%
33.3%
17.2%
26.6%
16.3%
25.0%
23.3%
5.6%
15.8%
13.9%
5.3%
1.3%
4.8%
10.9%
4.7%
8.2%
5.0%
2.3%
80.3%
65.8%
69.4%
55.3%
78.7%
66.7%
66.7%
71.9%
68.8%
75.5%
70.0%
74.4%
5 out of 5
4 out of 5
3 out of 5
2 out of 5
1 out of 5
Newer perfect voter
New registrant
Council District 1
Council District 2
Council District 3
Council District 4
Council District 5
Agree with Smith
Unsure
Agree with Jones
Agree with Smith Agree with Jones
Results by vote propensity and Council District
Question 27: Here are two statements made by Twentynine Palms residents. Please indicate which statement you agree with more.
Smith: “The way we treat wastewater in Twentynine Palms is fine today. If it ain’t broke, don’t fix it. I oppose the effort to bring sewers to town.” Jones: “Investing a communitywide wastewater treatment system will improve property values and secure our local groundwater supply. It’s a smart investment for our future. I support the effort to bring sewers to town.”
[AMONG TWENTYNINE PALMS VOTERS]
146
22.3%
11.1%
29.2%
17.5%
24.0%
22.9%
24.6%
21.0%
5.8%
22.2%
3.8%
6.9%
9.5%
71.8%
66.7%
67.0%
75.7%
76.0%
77.1%
75.4%
69.5%
English
Spanish
Children in HH under 18
No children in HH under 18
Phone [NET]
Landline
Mobile
Online [NET]
Agree with Smith
Unsure
Agree with Jones
Agree with Smith Agree with Jones
Results by language, children in HH, and survey
mode
Question 27: Here are two statements made by Twentynine Palms residents. Please indicate which statement you agree with more.
Smith: “The way we treat wastewater in Twentynine Palms is fine today. If it ain’t broke, don’t fix it. I oppose the effort to bring sewers to town.” Jones: “Investing a communitywide wastewater treatment system will improve property values and secure our local groundwater supply. It’s a smart investment for our future. I support the effort to bring sewers to town.”
[AMONG TWENTYNINE PALMS VOTERS]
147
72% support Twentynine Palms Water District
being annexed into the City
Question 28: The Twentynine Palms Water District and the City of Twentynine Palms cover almost the exact same service area and residents. There are hundreds of thousands of dollars in savings that can be achieved if the Twentynine Palms Water District were to be annexed into the City and consolidate operations. This means that the water district would become a City department and about seven hundred residents who live in the water district service area, but not currently in the City would become part of the City. Do you support or oppose Twentynine Palms Water District being annexed into the City? [AMONG TWENTYNINE PALMS AND DESERT HEIGHTS VOTERS]
71.7%
15.7%
12.6%
Support Oppose Unsure
148
Among those who support, 54% definitely support
Definitely
54.2%
Probably
45.8%
Among those who support
Definitely
69.1%
Probably
30.9%
Among those who oppose
71.7%
15.7%
12.6%
Total
Question 28: The Twentynine Palms Water District and the City of Twentynine Palms cover almost the exact same service area and residents. There are hundreds of thousands of dollars in savings that can be achieved if the Twentynine Palms Water District were to be annexed into the City and consolidate operations. This means that the water district would become a City department and about seven hundred residents who live in the water district service area, but not currently in the City would become part of the City. Do you support or oppose Twentynine Palms Water District being annexed into the City? [AMONG TWENTYNINE PALMS AND DESERT HEIGHTS VOTERS]
149
69.8%
73.5%
70.4%
72.6%
72.1%
76.5%
76.1%
80.4%
67.5%
63.4%
13.0%
12.2%
14.4%
9.4%
12.8%
7.4%
15.5%
13.0%
12.0%
14.6%
17.2%
14.4%
15.2%
17.9%
15.1%
16.2%
8.5%
6.5%
20.5%
22.0%
Male
Female
Republican
Democratic
No Party Preference
18-29
30-39
40-49
50-64
65+
Support
Unsure
Oppose
Support Oppose
Results by gender, party preference and age group
Question 28: The Twentynine Palms Water District and the City of Twentynine Palms cover almost the exact same service area and residents. There are hundreds of thousands of dollars in savings that can be achieved if the Twentynine Palms Water District were to be annexed into the City and consolidate operations. This means that the water district would become a City department and about seven hundred residents who live in the water district service area, but not currently in the City would become part of the City. Do you support or oppose Twentynine Palms Water District being annexed into the City? [AMONG TWENTYNINE PALMS AND DESERT HEIGHTS VOTERS]
150
80.7%
74.1%
80.0%
50.0%
44.1%
8.8%
12.6%
30.0%
17.6%
10.5%
13.4%
20.0%
20.0%
38.2%
Latino/Hispanic
White/Caucasian
Black/African American
Asian
Other
Support
Unsure
Oppose
Support Oppose
Results by ethnicity
Question 28: The Twentynine Palms Water District and the City of Twentynine Palms cover almost the exact same service area and residents. There are hundreds of thousands of dollars in savings that can be achieved if the Twentynine Palms Water District were to be annexed into the City and consolidate operations. This means that the water district would become a City department and about seven hundred residents who live in the water district service area, but not currently in the City would become part of the City. Do you support or oppose Twentynine Palms Water District being annexed into the City? [AMONG TWENTYNINE PALMS AND DESERT HEIGHTS VOTERS]
151
69.0%
71.4%
79.1%
59.1%
77.0%
71.4%
72.7%
75.0%
71.9%
73.5%
76.3%
74.4%
56.0%
11.9%
12.2%
14.0%
20.5%
9.2%
4.8%
18.2%
12.5%
7.8%
16.3%
15.0%
14.0%
10.0%
19.0%
16.3%
7.0%
20.5%
13.8%
23.8%
9.1%
12.5%
20.3%
10.2%
8.8%
11.6%
34.0%
5 out of 5
4 out of 5
3 out of 5
2 out of 5
1 out of 5
Newer perfect voter
New registrant
Council District 1
Council District 2
Council District 3
Council District 4
Council District 5
Desert Heights
Support
Unsure
Oppose
Support Oppose
Results by vote propensity and Council District
Question 28: The Twentynine Palms Water District and the City of Twentynine Palms cover almost the exact same service area and residents. There are hundreds of thousands of dollars in savings that can be achieved if the Twentynine Palms Water District were to be annexed into the City and consolidate operations. This means that the water district would become a City department and about seven hundred residents who live in the water district service area, but not currently in the City would become part of the City. Do you support or oppose Twentynine Palms Water District being annexed into the City? [AMONG TWENTYNINE PALMS AND DESERT HEIGHTS VOTERS]
152
72.0%
63.6%
73.9%
72.1%
75.4%
71.7%
77.4%
12.4%
18.2%
13.0%
11.4%
4.6%
6.5%
3.6%
15.6%
18.2%
13.0%
16.6%
20.0%
21.7%
19.0%
English
Spanish
Children in HH under 18
No children in HH under 18
Phone [NET]
Landline
Mobile
Support
Unsure
Oppose
Support Oppose
Results by language, children in HH, and survey
mode
Question 28: The Twentynine Palms Water District and the City of Twentynine Palms cover almost the exact same service area and residents. There are hundreds of thousands of dollars in savings that can be achieved if the Twentynine Palms Water District were to be annexed into the City and consolidate operations. This means that the water district would become a City department and about seven hundred residents who live in the water district service area, but not currently in the City would become part of the City. Do you support or oppose Twentynine Palms Water District being annexed into the City? [AMONG TWENTYNINE PALMS AND DESERT HEIGHTS VOTERS]
153
22% say they oppose the annexation due to less
regulations and government control
Question 29: Why do you oppose the City of Twentynine Palms annexing the Twentynine Palms Water District? [BASE: IF ANSWERED OPPOSE TO Q28]
21.8%
20.0%
18.2%
9.1%
5.5%
5.5%
20.0%
Less City/Government control/Less regulations
Fine the way it is/No issues/Better than the City
Higher cost
No more taxes
Water contamination
Other
Unsure
71.7%
15.7%
12.6%
Total
Demographics
154
Respondent demographics by ethnicity, gender, party and age group Ethnicity
52.0%
48.0%
Female
Male
Gender
30.0%
38.0%
25.0%
7.0%
Democratic
Republican
No Party
Preference
Other
Party Preference
19.4%
20.3%
13.1%
23.7%
23.5%
18-29
30-39
40-49
50-64
65 and
older
Age group
155
16.3%
68.3%
2.9%
2.9%
4.0%
5.7%
Latino/Hispanic
White/Caucasian
Black/African American
Asian
Other
Prefer not to answer
21.3%
21.3%
16.3%
26.7%
14.4%
Council Dist. 1
Council Dist. 2
Council Dist. 3
Council Dist. 4
Council Dist. 5
24.0%
14.0%
12.3%
12.6%
24.9%
6.0%
6.3%
5 out of 5
4 out of 5
3 out of 5
2 out of 5
1 out of 5
Newer perfect voter
New registrant
Demographics by Council District, propensity, children in HH, language and survey mode
Council District Vote Propensity
97.0%
3.0%
English
Spanish
Language
37.0%
35.0%
65.0%
63.0%
50.0%
50.0%
Phone [NET]
Landline
Mobile
Online [NET]
Email
Text
Survey Mode
Children in HH
156
32.9%
65.4%
1.7%
Yes
No
Prefer not to answer
Opinion Research on
Elections and Public Policy
Probolsky Research
23 Corporate Plaza Suite 150
Newport Beach CA 92660
Newport Beach (949) 855-6400
San Francisco (415) 870-8150
Washington DC (202) 559-0270
Questions?
Scarlett Isayo, Research Analyst
O: 949-855-6400
Adam Probolsky, President
O: 949-855-6400 | M: 949-697-6726
E: [email protected]
157
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: A. Schneider DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED:
COST
GRAVITY SEWER
(MILES)
LIFT
STATIONS
FORCE MAIN
(MILES)
2019-2020 AVG
WATER USE (MGD)
% OF STUDY AREA
WATER USE
% OF CITY
WATER USE
$ 37,000,000 11.3 0 0 0.180 12.9% 11.1%
$ 8,000,000 2.3 0 0 0.065 4.6% 4.0%
$ 18,000,000 5.1 0 0 0.146 10.4% 9.0%
$ 10,000,000 2.8 1 0.80 0.093 6.6% 5.7%
$ 17,000,000 5.3 0 0 0.073 5.2% 4.5%
$ 90,000,000 26.9 1 0.8 0.557 39.8% 34.4%
Assumptions/Notes:
4. Based on current pricing. Does not include inflation for future cost planning.
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject ITEM
Total
October 2022
Wastewater Feasibility Study - Rephasing - Collection System Cost Summary 227521-0000132.00 Phase A Collection System
Phase B Collection System
Phase C Collection System
Phase D Collection System
Phase E Collection System
2. Includes 30% construction contingency.
3. Includes 20% contingency for design and construction management. to change to reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
1. Cost opinion for preliminary planning information only. 15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL DRAFT
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 Mobilization / Overhead 1 LS $ 2,600,000 $ 2,600,000 10.3% 2 Install 8" PVC Gravity Sewer 52,000 LF $ 200 $ 10,400,000 41.1% 3 Install 10" PVC Gravity Sewer 2,800 LF $ 215 $ 602,000 2.4% 4 Install 12" PVC Gravity Sewer 2,600 LF $ 260 $ 676,000 2.7% 5 Install 12" PVC Gravity Sewer (15' to 20' Deep) 2,300 LF $ 390 $ 897,000 3.5% 6 Install 48" Dia. Manholes 160 EA $ 15,000 $ 2,400,000 9.5% 7 Install 60" Dia. Manholes 2 EA $ 20,000 $ 40,000 0.2% 8 Install Service Lateral (Public) 640 EA $ 5,000 $ 3,200,000 12.7% 9 Install Service Lateral (Private) / Abandon Septic 640 EA $ 7,000 $ 4,480,000 17.7% Subtotal $ 25,295,000
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 25,295,000
2. Assumes groundwater dewatering and rock excavation will not be required. CONSTRUCTION CONTINGENCY (30%) $ 7,588,500
3. Quantities of sewer & service laterals is based on existing parcels with active water use. DESIGN AND CM (15%) $ 3,794,250
4. Sewer unit prices include trench resurfacing.
5. Assumes only 1 service lateral for multi-unit parcels TOTAL PROBABLE PROJECT COST $ 36,677,750 FOR BUDGET PURPOSES $ 37,000,000
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
PHASE A COLLECTION SYSTEM
1. Cost opinion for preliminary planning information only. to change to reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
Wastewater Feasibility Study - Rephasing - City Collection System Phase A 227521-0000132.00 A. Schneider October 2022
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL DRAFT
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 Mobilization / Overhead 1 LS $ 500,000 $ 500,000 10.0% 2 Install 8" PVC Gravity Sewer 11,000 LF $ 200 $ 2,200,000 43.9% 3 Install 8" PVC Gravity Sewer (Deep) 1,000 LF $ 300 $ 300,000 6.0% 4 Install Concrete Encasement (Channel Crossings) 600 LF $ 150 $ 90,000 1.8% 5 Install 48" Dia. Manholes 40 EA $ 15,000 $ 600,000 12.0% 6 Install Service Lateral (Public) 110 EA $ 5,000 $ 550,000 11.0% 7 Install Service Lateral (Private) / Abandon Septic 110 EA $ 7,000 $ 770,000 15.4% Subtotal $ 5,010,000
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 5,010,000
2. Assumes groundwater dewatering and rock excavation will not be required. CONSTRUCTION CONTINGENCY (30%) $ 1,503,000
3. Quantities of sewer & service laterals is based on existing parcels with active water use. DESIGN AND CM (15%) $ 751,500
4. Sewer unit prices include trench resurfacing.
5. Assumes only 1 service lateral for multi-unit parcels TOTAL PROBABLE PROJECT COST $ 7,264,500 FOR BUDGET PURPOSES $ 8,000,000
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
PHASE B COLLECTION SYSTEM
1. Cost opinion for preliminary planning information only. to change to reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
Wastewater Feasibility Study - Rephasing - City Collection System Phase B 227521-0000132.00 A. Schneider October 2022
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL DRAFT
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 Mobilization / Overhead 1 LS $ 1,200,000 $ 1,200,000 10.2% 2 Install 8" PVC Gravity Sewer 17,000 LF $ 200 $ 3,400,000 28.9% 3 Install 10" PVC Gravity Sewer 5,000 LF $ 215 $ 1,075,000 9.1% 4 Install 12" PVC Gravity Sewer 3,000 LF $ 260 $ 780,000 6.6% 5 Install 18" PVC Gravity Sewer 1,500 LF $ 335 $ 502,500 4.3% 6 Install 18" PVC Gravity Sewer (Deep) 600 LF $ 503 $ 301,500 2.6% 7 Install Concrete Encasement (Channel Crossings) 150 LF $ 150 $ 22,500 0.2% 8 Install 48" Dia. Manholes 70 EA $ 15,000 $ 1,050,000 8.9% 9 Install 60" Dia. Manholes 10 EA $ 20,000 $ 200,000 1.7% 10 Install Service Lateral (Public) 270 EA $ 5,000 $ 1,350,000 11.5% 11 Install Service Lateral (Private) / Abandon Septic 270 EA $ 7,000 $ 1,890,000 16.1% Subtotal $ 11,771,500
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 11,771,500
2. Assumes groundwater dewatering and rock excavation will not be required. CONSTRUCTION CONTINGENCY (30%) $ 3,531,450
3. Quantities of sewer & service laterals is based on existing parcels with active water use. DESIGN AND CM (15%) $ 1,765,725
4. Sewer unit prices include trench resurfacing.
5. Assumes only 1 service lateral for multi-unit parcels TOTAL PROBABLE PROJECT COST $ 17,068,675 FOR BUDGET PURPOSES $ 18,000,000
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
PHASE C COLLECTION SYSTEM
1. Cost opinion for preliminary planning information only. to change to reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
Wastewater Feasibility Study - Rephasing - City Collection System Phase C 227521-0000132.00 A. Schneider October 2022
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL DRAFT
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 Mobilization / Overhead 1 LS $ 700,000 $ 700,000 10.5% 2 Install 8" PVC Gravity Sewer 15,000 LF $ 200 $ 3,000,000 45.2% 3 Install 48" Dia. Manholes 40 EA $ 15,000 $ 600,000 9.0% 4 Install Service Lateral (Public) 70 EA $ 5,000 $ 350,000 5.3% 5 Install Service Lateral (Private) / Abandon Septic 70 EA $ 7,000 $ 490,000 7.4% 6 Install Packaged Pump Station 1 EA $ 1,000,000 $ 1,000,000 15.1% 7 Install 4" PVC Force Main 4,200 LF $ 120 $ 504,000 7.6% Subtotal $ 6,644,000
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 6,644,000
2. Assumes groundwater dewatering and rock excavation will not be required. CONSTRUCTION CONTINGENCY (30%) $ 1,993,200
3. Quantities of sewer & service laterals is based on existing parcels with active water use. DESIGN AND CM (15%) $ 996,600
4. Sewer unit prices include trench resurfacing.
5. Assumes only 1 service lateral for multi-unit parcels TOTAL PROBABLE PROJECT COST $ 9,633,800 FOR BUDGET PURPOSES $ 10,000,000
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
PHASE D COLLECTION SYSTEM
1. Cost opinion for preliminary planning information only. to change to reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
Wastewater Feasibility Study - Rephasing - City Collection System Phase D 227521-0000132.00 A. Schneider October 2022
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL DRAFT
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 Mobilization / Overhead 1 LS $ 700,000 $ 700,000 6.0% 2 Install 8" PVC Gravity Sewer 28,000 LF $ 200 $ 5,600,000 48.4% 3 Install 48" Dia. Manholes 80 EA $ 15,000 $ 1,200,000 10.4% 4 Install Service Lateral (Public) 340 EA $ 5,000 $ 1,700,000 14.7% 5 Install Service Lateral (Private) / Abandon Septic 340 EA $ 7,000 $ 2,380,000 20.6% Subtotal $ 11,580,000
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 11,580,000
2. Assumes groundwater dewatering and rock excavation will not be required. CONSTRUCTION CONTINGENCY (30%) $ 3,474,000
3. Quantities of sewer & service laterals is based on existing parcels with active water use. DESIGN AND CM (15%) $ 1,737,000
4. Sewer unit prices include trench resurfacing.
5. Assumes only 1 service lateral for multi-unit parcels TOTAL PROBABLE PROJECT COST $ 16,791,000 FOR BUDGET PURPOSES $ 17,000,000
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
PHASE E COLLECTION SYSTEM
1. Cost opinion for preliminary planning information only. to change to reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
Wastewater Feasibility Study - Rephasing - City Collection System Phase E 227521-0000132.00 A. Schneider October 2022
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL DRAFT
ASSUMED LOCATION OF WWTP
INFLUENT LIFT STATION
SAMARKAND DR
PHASE E
0.073 MGD
PHASE A
0.180 MGD
PHASE B
0.065 MGD
PHASE C
0.146 MGD
PHASE D
0.093 MGD
ASSUMED LOCATION OF
PACKAGED LIFT STATION
DATE SUBMITTED: OCT 2022 227521-0000132
JOB NUMBER
EXHIBIT
1 SCALE
15092 AVENUE OF SCIENCE, SUITE 200
SAN DIEGO, CA 92128
P: 858.385.0500 WWW.NV5.COM
CITY OF TWENTYNINE PALMS - WASTEWATER FEASIBILITY STUDY 1 inch = 0.25 miles
Trunk Sewer COLLECTION SYSTEM RE-PHASING
Collector Sewer
Force Main
Package Plant
PhaseA
PhaseB
PhaseC
PhaseD
PhaseE
0 0.25 Miles
¹
Legend
DRAFT
S 1;. ,- ‘u .,
...s....,....u.... ._».w..m..ks..... —n....u...
.a.\.,...m....~x...._....,¢...m~......W _n....;....
Smrm M15 Mucnanm
7 ‘ Trunk Sewer System Project
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15092 Avenue of Science, Suite 200
San Diego, CA 92128
NV5 PROJECT NUMBER 227521-0000132
CITY OF TWENTYNINE PALMS
WASTEWATER FEASIBILITY STUDY
DRAFT REPORT
March 31, 2022
Prepared For:
City of Twentynine Palms
6136 Adobe Road
Twentynine Palms, CA 92277
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TABLE OF CONTENTS
1.0 Executive Summary.............................................................................................................1-1
2.0 Introduction And Study Objectives ....................................................................................2-1
3.0 Study Area and Background ..............................................................................................3-1
3.1 Study Area Limits And Land Use.................................................................................................3-1
3.2 Topography And Drainage ...........................................................................................................3-1
3.3 Population And Planning Horizons .............................................................................................3-2
3.4 Water Consumption and Supply .................................................................................................3-3
4.0 Wastewater Flows ...............................................................................................................4-1
4.1 Background And Assumptions for Wastewater Flow Projections .........................................4-1
4.2 Study Area Wastewater Flow Projections .................................................................................4-3
4.2.1 Study Area Wastewater Flow Projections – Based on Land Use ..................................4-4
4.2.2 Study Area Wastewater Flow Projections – Based on Water Use ................................4-4
4.2.3 Phased Study Area Wastewater Flow Projections...........................................................4-5
4.3 Joint-Use Wastewater Flow Projections.....................................................................................4-5
5.0 Wastewater Collection System..........................................................................................5-1
5.1 Topography Evaluation.................................................................................................................5-1
5.1.1 Low Point Locations: ............................................................................................................5-1
5.1.2 Study Area Gravity Flow Evaluation: ..................................................................................5-1
5.1.3 MCAGCC Pipeline Gravity Flow Evaluation:.......................................................................5-2
5.2 Preliminary Sewer Basins ............................................................................................................5-2
5.3 Preliminary Trunk Sewer System Layout...................................................................................5-3
5.4 Preliminary Joint-Use Pipeline Layout........................................................................................5-3
5.5 Preliminary Collection System Phasing Plan............................................................................5-4
5.6 Preliminary Collection System Layout – Phase 1 and Phase 2.............................................5-5
5.7 Collection System Capital Costs .................................................................................................5-6
5.8 Hydraulic Modeling .......................................................................................................................5-6
5.8.1 Hydraulic Model Limitations................................................................................................5-6
5.8.2 Hydraulic Design Criteria .....................................................................................................5-7
5.8.3 Model Elements and Development....................................................................................5-8
5.8.4 Model Scenarios Evaluated.................................................................................................5-9
5.8.5 Model Results and Estimated Pipe Sizes..........................................................................5-9
6.0 Wastewater Treatment Plant.............................................................................................6-1
6.1 Previous WWTP Studies and Documents..................................................................................6-1
6.1.1 2008 Joint-Use Study ...........................................................................................................6-1
6.1.2 2014 Wastewater Master Plan...........................................................................................6-1
6.2 Assumed WWTP Design Capacity ..............................................................................................6-2
6.3 City-only WWTP Alternative .........................................................................................................6-3
6.3.1 Potential City-only WWTP Sites ..........................................................................................6-3 DRAFT
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6.3.2 Anticipated Influent and Effluent Requirements .............................................................6-7
6.3.3 Conventional Activated Sludge Treatment Process ........................................................6-8
6.3.4 Treatment Process Technology Alternatives ....................................................................6-9
6.3.5 Conceptual City-only WWTP Facility.................................................................................6-11
6.4 Joint-Use WWTP Alternative ......................................................................................................6-12
6.5 Evaluation of WWTP Alternatives .............................................................................................6-12
6.5.1 Cost Comparison of WWTP Alternatives .........................................................................6-12
6.5.2 Other WWTP Considerations.............................................................................................6-15
7.0 Groundwater Recharge System.........................................................................................7-1
8.0 Conclusions and Recommendations................................................................................8-1
8.1 Wastewater Collection System recommendations..................................................................8-1
8.2 Wastewater Treatment Plant Recommendations ...................................................................8-1
8.3 Groundwater Recharge system Recommendations................................................................8-2
LIST OF FIGURES
Figure 1 – Study Area
Figure 2 – Study Area Land Use
Figure 3 – Study Area Topography
Figure 4 – Preliminary Trunk Sewer System
Figure 5 – Preliminary City-MCAGCC Pipeline
Figure 6 – Proposed Collection System Phases
Figure 7 – Preliminary Phase 1 & Phase 2 Collection System Figure 8 – Proposed City-Only WWTP Locations
Figure 9 – Conceptual WWTP Layout Design – Site 1
LIST OF APPENDICES
Appendix A – Preliminary Opinions of Probable Construction Cost Appendix B – Draft Preliminary Screening Study of Groundwater Recharge Sites DRAFT
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1.0 EXECUTIVE SUMMARY
2.0 INTRODUCTION AND STUDY OBJECTIVES
This feasibility study develops and evaluates a centralized wastewater collection (sewer) system and a centralized wastewater treatment plant (WWTP) for a portion of the City of Twentynine Palms (City).
Currently, wastewater generated in the City is treated primarily by individual septic systems and by several small, decentralized package treatment plants for newer residential and commercial developments. However, continued use of decentralized package treatment plants and septic systems is not a tenable long-term solution for the City. Decentralized treatment plants are expensive to construct, inefficient to maintain, have frequent compliance issues, and are a deterrent for new development, and although not currently an issue, it is anticipated that septic systems will eventually impact the quality of groundwater, which is the only source of water for the community. Implementing a centralized wastewater collection system with a WWTP provides the best long-term solution for the City.
At the north end of the City, the Marine Corps Air Ground Combat Center (MCAGCC, Base), currently operates its own centralized WWTP, the Mainside WWTP, which treats domestic wastewater from Camp Wilson and the main base “Mainside” area, most of which is located within the City limits. The MCAGCC is currently pursuing a design build contract to replace the aging Mainside WWTP with a new WWTP. The MCAGCC is still in the initial stages of that process which presents an opportunity to explore a new joint-use WWTP.
The primary objectives of this study are:
• To delineate a study area and to estimate wastewater flows for that area. • To develop a preliminary wastewater collection system for the study area, to evaluate the feasibility of gravity flow, to determine phasing for implementation, and to estimate costs for that system.
• To evaluate a separate-use (City only) WWTP alternative versus a joint-use (City and MCAGCC) WWTP alternative, by identifying potential WWTP sites, estimating the required infrastructure and associated costs for each, and comparing the advantages and disadvantages of each alternative.
• To evaluate potential groundwater recharge sites and to determine the next steps for development of a groundwater recharge system
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3.0 STUDY AREA AND BACKGROUND
3.1 STUDY AREA LIMITS AND LAND USE
In coordination with the City, the limits of the Study area were generally developed to exclude areas within the City limits that have very-low density residential land use (RS-E, RL-2.5, and RL-5 land use designations) which have a minimum lot size of 2.5 acres. These sparsely populated areas constitute a small portion of the City’s current water use and subsequently have a smaller impact on groundwater quality. A small portion of very-low density areas was included in the study area if adjacent to proposed sewer alignments. The study area includes the majority of all other residential, commercial, industrial, and public land use areas within the City limits, except for some small commercial and residential land use areas in the western portion of the City, colloquially known as the Indian Cove and Desert Life neighborhoods. The City’s Sphere of Influence (SOI) area was also excluded from the study area. See Figure 1 which shows the study area limits, the City limits, and the Twentynine Palms Water District (TPWD) service area.
The full City limits encompass approximately 37,650 acres (58.8 square miles) of land, including the MCAGCC. The study area encompasses approximately 12,800 acres (20 square miles) of land with approximately 66% designated for residential land use as shown in Table 1 below. See also Figure 2 which shows the various land use areas in the study area.
Table 1 – Study Area Land Use Areas
Land Use Area Approximate Percentage
of Study Area1
Single-Family Residential 59%
Multi-Family and High Density Residential 7%
Commercial 11%
Industrial 9%
Public 5%
Other (Right of Way, Floodways) 9%
Notes:
1. Obtained from City GIS Land Use File
3.2 TOPOGRAPHY AND DRAINAGE
The land within the study area generally slopes from the southwest to the northeast but has several hills and ridgelines throughout. A substantial portion of the study area drains to an earthen flood control channel which bisects the City. The channel was developed and is maintained by the San Bernardino County Flood Control District and drains to a natural desert wash area to the northeast. At the north end of the study area, a small area drains north towards the MCAGCC, north of the hilltop on Adobe Road between Raymond Drive and Mesa Drive. See Figure 3 which shows the existing topography with 20-foot contours and the flood control channel. DRAFT
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3.3 POPULATION AND PLANNING HORIZONS
Historical Population
Per the 2020 US Census, the total population of the City was 28,065, which includes the MCAGCC.
Table 2 below shows US Census population values and growth rates from 2000 to 2020.
Table 2 – US Census Population of Twentynine Palms
Source City
Population
MCAGCC
Population
Total
Population
10 Year
Growth2
Annual
Growth3
2000 US Census1 14,764 8,413 23,177 - -
2010 US Census - - 25,048 8.1 % 0.78 %
2020 US Census - - 28,065 12.0 % 1.14 %
Notes:
1. The City annexed the MCAGCC residential areas in 2000, but the 2000 US Census reported the City and MCAGCC as separate entities.
2. Calculated total growth of total population from previous Census total population.
3. Calculated compound annual growth from previous Census total population.
US Census data for 2010 and 2020 did not separate out the MCAGCC population. The San Bernardino County Transit Authority (SBCTA) Open Data website shows the 2020 population as 27,500 for the entire City, including 8,745 (32%) for the MCAGCC area and 18,755 (68%) for the remainder of the City.
Ultimate Buildout Population
The City’s 2012 General Plan lists an ultimate build-out population of 103,275 for the entire City, including 22,500 (22%) for the MCAGCC and 80,775 (78%) for the remainder of the City. No planning horizon is listed for ultimate buildout. Using the same methodology as the 2012 General Plan, which is based on land use area and projected average dwelling unit density, the estimated build-out population of the study area is approximately 66,100, approximately 82% of the City build-out population of 80,775, excluding the MCAGCC.
Population Forecast
Connect SoCal, The 2020-2045 Regional Transportation Plan/Sustainable Communities Strategy, developed by Southern California Association of Governments (SCAG), forecasts that the entire City’s population, including the MCAGCC, will increase to 33,300 by 2045. SCAG does not provide a population forecast past 2045, so population forecasts past 2045 were extrapolated for the purposes of this study.
See Table 3 below for population forecasts for the entire City (including the MCAGCC) Table 3 – Population Forecast for Twentynine Palms
2025 2035 2045 2050 2075
Population Forecast1 29,500 31,000 33,300 34,500 41,300 Notes:
1. 2035 and 2045 population forecast data is f DRAFT rom SCAG/SBCTA. 2025, 2050, and 2075 population forecasts were extrapolated.
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Planning Horizons
This study includes planning horizons for 2025 (Start), 2050 (25 years), and 2075 (50 years). For each planning horizon, Table 4 below lists the population forecast in comparison with the City’s ultimate build-out population forecast and shows that ultimate build-out will likely occur far beyond the 2075 planning horizon.
Table 4 – Study Planning Horizons
2025 2050 2075 Ultimate
Population Forecast1 29,500 34,500 41,300 103,2752
Calculated Ratio of
Population Forecast to Ultimate
Build-out Population
28.6 % 33.4 % 40.0 % 100.0 %
Notes:
1. For entire City (including the MCAGCC).
2. From City’s 2012 General Plan.
3.4 WATER CONSUMPTION AND SUPPLY
Potable water service for City customers is provided by the Twentynine Palms Water District (TPWD).
The TPWD service area includes both the City and the City’s SOI but does not include the MCAGCC. As mentioned previously the City’s SOI is not included in the study area or the City’s population. Refer to Figure 1 which shows the study area limits, the City limits, and the TPWD service area.
Water Consumption
Historical water consumption for the entire TPWD service area is presented below in Table 5. Water consumption which would not return to sewer, such as irrigation and fire protection uses, was excluded as much as possible by excluding consumption from dedicated irrigation and fire protection services.
These dedicated meters are typically only available for larger multi-family, commercial, industrial, and institutional users. Irrigation use for typical single family residential water services could not be excluded.
Table 5 – Historical Water Consumption For The TPWD Service Area 2000 2005 2010 2015 2019 2020
Annual
Water Use1,2 2577 AF 2572 AF 2449 AF 1996 AF 1950 AF 2129 AF Average Daily
Water Use1,2 2.30 MGD 2.30 MGD 2.19 MGD 1.78 MGD 1.74 MGD 1.90 MGD Notes:
1. Data from 2000 to 2015 is from the TPWD 2015 Urban Water Management Plan (UWMP) for residential, commercial, institutional, and industrial consumption and excludes irrigation, fire protection/non-potable uses.
2. Data from 2019 to 2020 is from bi-monthly consumption data and excludes irrigation meters, community park meters, fire service meters, and the TPWD pay station meter. Consumption from irrigation meters and park meters constituted approximately 6% of the total consumption. Consumption from fire service meters constituted less than 0.10% of the total consumption. DRAFT
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Study Area Water Consumption
To determine water consumption within the study area limits, average water use from 2019 to 2020 was input into GIS for each parcel and tallied by area. Table 6 below shows the average water use by area and relative ratios. As shown, the water consumption of the study area compromises the majority of the City’s water consumption, supporting the defined study area limits which exclude very-low density land use areas.
Table 6 – 2019 / 2020 Water Consumption By Area
Area 2019 / 2020
Average Water Use1
Ratio Of
TPWD Service Area Use
2 Ratio Of
City Use
3 TPWD Service Area 1.82 MGD - -
City of Twentynine Palms
(Excluding MCAGCC) 1.62 MGD 89.0 % -
Study Area 1.40 MGD 76.9 % 86.4 %
Notes:
1. Obtained from bi-monthly consumption data input into GIS and excludes consumption data from irrigation meters, community park meters, fire service meters, and the TPWD pay station meter.
2. Calculated ratio of average water use divided by total TPWD Service Area average water use.
3. Calculated ratio of average water use divided by City average water use (excluding MCAGCC).
Assuming a City population (excluding the MAGCC) of approximately 18,755, the average per capita water consumption, including residential irrigation use, from 2019 to 2020 would have been approximately 86 gallons per day (GPD). However actual per capita consumption could vary significantly since it is difficult to ascertain the exact populations of the TPWD service area or the MGAGCC area because available census population data does not separate out those areas.
Water Production
Water production data from 2020, for the entire TPWD service area, is listed below in Table 7 to show seasonal fluctuation of water demand. The maximum month production occurred in July and was approximately 38% higher than the average month production. The minimum month production occurred in February and was approximately 33% lower than the average month production.
Table 7 – 2020 Water Production For The TPWD Service Area1 Year Total Production
(AF)
Total Production
(MG)
Average Month
Production
(MG)
Max Month
Production
(MG)
Min Month
Production
(MG)
2020 2695 878.16 73.18 101.24 49.13
Notes:
1. Data provided by TPWD.
Water Supply
The TPWD relies entirely on pumping from groundwater wells to meet water demand. Groundwater is extracted from the Mesquite Lake, Indian Cove, Eastern, and Fortynine Palms subbasins. Per the TPWD 2015 Urban Water Management Plan (UWMP), the total combined pumping capacity from the basins is DRAFT
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limited to 6,995 Acre-Feet (AF) per year, as recommended by the California Department of Water Resources (DWR). The 2015 UWMP notes there could be a supply shortfall compared to estimated demands for 2035 and 2040 for single-dry year and multiple-dry year planning scenarios. However, no supply shortfall was anticipated for a normal water year scenario. Anticipated shortfalls were based on an estimated normal water year demand of 6,424 AF per year for 2035 and 6,987 AF per year for 2040.
Estimated future demands were based on target per capita water use and population projections from the SCAG 2012 Regional Transportation Plan.
The estimated future demands in the 2015 UWMP appear to be conservative as target per capita use is significantly higher than actual per capita water use and, as noted in the 2015 UWMP, did not account for future savings from codes, standards, ordinances, or transportation and land use plans or reductions from demand management practices. In addition, updated population forecasts are lower. Therefore, for the purposes of this study, future water demand was estimated less conservatively as follows. With the total water production in 2020 as 2,695 AF Per Year for the entire TPWD service area, and assuming a total production increase of 47%, based on the 2075 population forecast compared to the 2020 US Census population, the estimated 2075 water production would be approximately 3,962 AF Per Year.
This is significantly less than the groundwater basin limitation of 6,995 AF per year. Therefore, water supply is assumed to be sufficient until at least 2075, the long-term planning horizon for this study, and would not be a restriction for population/water consumption growth.
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4.0 WASTEWATER FLOWS
4.1 BACKGROUND AND ASSUMPTIONS FOR WASTEWATER FLOW PROJECTIONS Wastewater flow projections for the study area were developed based on multiple factors including land use area, wastewater generation rates developed for each land use designation, an assumed build-out ratio, existing water use, population growth, proposed system phasing, and other assumptions as described below.
Land Use Area:
Land use data for each parcel within the study area was obtained from the City’s GIS land use file, updated in July 2018 for Project Phoenix. As mentioned previously, residential land uses (including single family, rural living, multi-family and high-density) account for approximately 66% of the total.
Wastewater Generation Rates:
Future wastewater generation rates for each land use designation were developed based on a review of the City’s 2012 General Plan, the City’s 2014 Wastewater Master Plan (WWMP), the Hi-Desert Water District’s (Yucca Valley) 2009 Sewer Master Plan, and other sewer systems in Southern California.
Wastewater generation rates used for this study are summarized below in Table 8.
Table 8 – Wastewater Generation Rates
Land Use Designation
Projected
Average Density1
(DU/Acre)
Wastewater
Generation
(GPD/DU)
Wastewater
Generation
(GPD/Acre)
Single-Family Residential-Estate (RS-E) 0.32 202 65
Single-Family Residential (RS-1) 0.8 202 162
Single-Family Residential (RS-2) 1.6 202 323
Single-Family Residential (RS-3) 2.4 202 485
Single-Family Residential (RS-4) 3.2 202 646
Rural Living (RL-1) 0.8 202 162
Rural Living (RL-2.5) 0.32 202 65
Rural Living (RL-5) 0.16 202 32
Multi-Family Residential (RM) 6.4 172 1101
High Density Residential (R-HD) 24.0 172 4128
General Commercial (CG), Neighborhood Commercial
(CN), Office Commercial (CO), Tourist Commercial
(CT), Service Commercial (CS),
- - 800
Community Industrial (IC), Public (P) - - 680
Notes:
1. Obtained from City of Twentynine Palms 2012 General Plan, Table LU DRAFT -17.
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For residential land use, the wastewater generation rate is based on the projected average density values listed in the 2012 General Plan for each land use designation, an average persons per dwelling unit (per household) value of 2.75 per 2015-2019 US Census Data, and a future wastewater generation rate of 73.5 GPD per person as listed in the 2014 WWMP. A 15% reduction was applied for multi-family and high-density land use designations, which typically have lower flows per dwelling unit. For commercial, industrial, and public land uses, the generation rates are based on Hi-Desert Water District’s 2009 Sewer Master Plan which provides more specific and less conservative land use categories than the City’s 2014 WWMP.
The future per capita wastewater generation rate of 73.5 GPD, as listed in the 2014 WWMP, could be considered slightly conservative as water and wastewater generation rates continue to drop with the implementation of Green building standards, which have fixtures and appliances that use less water.
However, this value appears reasonable when compared to the existing estimated total per capita water use, including residential irrigation use, of 86 GPD discussed in Section 3.4. Some entities are going a low as 50 GPD/person for wastewater for new development, but that does not allow for a margin for planning purposes.
Build-out Ratio:
Sizing pipelines for ultimate build-out wastewater flows would result in pipelines that are excessively large for actual system flows, resulting in lower velocities, more solids deposition, and ultimately odor problems. These issues could be mitigated with increased pipeline maintenance but would result in increased operation costs. Furthermore, the pipelines sized for ultimate build-out would have higher capital costs associated with oversized construction.
To provide more reasonably sized pipelines, a land use build-out ratio of 40% was assumed for flow projections based on land use. This ratio aligns with the 2075 planning horizon, which has an effective build-out ratio of 40% based on the 2075 population forecast compared to the ultimate build-out population. With an estimated build-out population of 66,100 for the study area, a 40% build-out ratio corresponds to a population of 26,440 for the study area.
A build-out ratio of 40% effectively reduces flow projections based on land use by 60%. For the purpose of this planning level study, the build-out ratio was assumed to be the same for all areas. However, in reality, different areas of the City are more developed than others, such as the downtown area which is more developed than other areas of the city. In the preliminary design stage, this build-out ratio should be re-evaluated and applied to specific areas.
Existing Water Use:
As an alternate method to land use-based flow projections, existing water consumption was used to estimate future wastewater flows by using an assumed water to sewer ratio and an assumed population growth rate.
As described in Section 3.4, average water consumption from 2019 to 2020 was first input into GIS for each parcel and tallied by area. Then, to account for seasonal variation of water consumption, a 20% increase was applied to estimate average water consumption during peak season. As shown in Section DRAFT
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3.4, the maximum month water production was approximately 38% higher than the average month production. However, a substantial portion of this increase is likely attributed to summer heat with increased water use for irrigation and evaporative coolers, neither of which would return to sewer.
Therefore a 20% increase was assumed. Then, wastewater flows were estimated with the assumed water to sewer return-ratio described below. Then, future wastewater flows were estimated with the assumed growth rate described below. These calculated flows are listed as Average Dry Weather Flow (ADWF).
Water to Sewer Return Ratio
A water to sewer return-ratio of 86% was assumed for flow projections based on water consumption data. An 80% return ratio is commonly used to estimate wastewater flow and is referenced in the City’s 2014 WWMP. However, the water consumption from dedicated irrigation meters and large community parks has already been excluded and accounted for approximately 6% of the total consumption. Also, the estimated ratio of the per capita wastewater generation rate (73.5 GPD) to the estimated per capita water use rate (86 GPD) is 85.5%.
Growth Rate
An average annual growth rate of 0.80% was assumed for flow projections based on water consumption data. The is based on regional growth forecasts (SCAG and SBCTA) which used an annual growth rate of
0.80% for population projections between 2020 and 2035.
Peaking Factors
For Peak Dry Weather Flow (PDWF) conditions a diurnal curve was used to represent the variation and peaking of the calculated Average Dry Weather Flow (ADWF). A diurnal curve was created for this project based on a typical diurnal curve for an area consisting of 70% Residential flows and 30% Commercial flows. The curve has a maximum peaking factor of 1.8 and is similar to the diurnal curve referenced in the 2014 WWMP. For Peak Wet Weather Flow (PWWF) conditions a peaking factor of
1.15, a 15% increase, was included for potential inflow and infiltration. This assumes that watertight sewer manhole lids would be installed, which NV5 recommends because the summer monsoons can inundate a system.
4.2 STUDY AREA WASTEWATER FLOW PROJECTIONS
For comparison, wastewater flow projections for the study area are provided for two different approaches, one based on land use (See Section 4.2.1) and the other based on existing water use (See Section 4.2.2), using the background and assumptions listed above. Ultimately flow projections based on a combination of the two approaches is provided in Section 4.2.3, based on the proposed collection system phasing plan
DRAFT
described in Section 5.5
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4.2.1 Study Area Wastewater Flow Projections – Based on Land Use Study area average wastewater flow projections based on land use area, wastewater generation rates for each land use designation, and the assumed build-out ratio are listed below in Table 9 for the 2075 planning horizon.
Table 9 – Study Area Average Wastewater Flow Projections – Based on Land Use Area 2075 ADWF1
(MGD)
Calculated Ratio
of Study Area Total
Phase 1 0.27 10.0 %
Phase 2 0.26 9.6 %
Phase 3 0.38 14.0 %
Phase 4 0.32 11.8 %
Phase 5 1.48 54.6 %
Study Area Total 2.71
Notes:
1. 2075 planning horizon corresponding to an assumed 40% build-out ratio for each phase.
Residential land uses (including single family, rural living, multi-family and high-density) accounted for approximately 65% of the total calculated flow and commercial, industrial, and public land uses accounted for approximately 35% of the total calculated flow.
4.2.2 Study Area Wastewater Flow Projections – Based on Water Use Study area average wastewater flow projections based on existing water use, the assumed annual population growth rate, and the assumed water to sewer ratio are listed below in Table 10 for the 2075 planning horizon.
Table 10 – Study Area Average Wastewater Flow Projections – Based on Water Use Area 2075 ADWF
(MGD)
Calculated Ratio
of Study Area Total
Phase 1 0.37 16.4 %
Phase 2 0.42 18.6 %
Phase 3 0.54 24.3 %
Phase 4 0.35 15.7 %
Phase 5 0.56 25.0 %
Study Area Total 2.24
The projected 2075 ADWF based on water use was higher than the projected 2075 ADWF based on land use for Phases 1, 2, 3, and 4, whereas for the Phase 5 area, the projected 2075 ADWF based on water use was much lower than the projected 2075 ADWF based on land use. This indicates the Phase 5 area is currently much less developed than the other areas, which appears to be accurate based on the large areas of undeveloped land in the Phase 5 area. DRAFT
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4.2.3 Phased Study Area Wastewater Flow Projections
Study area average wastewater flow projections are listed below in Table 11 for each planning horizon based on a phased implementation of the wastewater collection system as described in Section 5.5.
For Phases 1, 2, 3, and 4, existing water use-based flow projections were used since they were higher than land use-based projections for those areas. For Phase 5, an average of water use-based and land use-based flow projections was used, since land use-based projections were significantly higher than water use based projections.
Table 11 –Phased Wastewater Flow Projections for Study Area Area
2025 2050 2075
ADWF
(MGD)
PDWF
(MGD)
PWWF
(MGD)
ADWF
(MGD)
PDWF
(MGD)
PWWF
(MGD)
ADWF
(MGD)
PDWF
(MGD)
PWWF
(MGD)
Phase 1 0.25 0.44 0.51 0.30 0.54 0.62 0.37 0.66 0.76
Phase 2 0.28 0.50 0.58 0.34 0.61 0.71 0.42 0.75 0.86
Phase 3 0.45 0.80 0.92 0.54 0.98 1.13
Phase 4 0.29 0.52 0.60 0.35 0.63 0.73
Phase 51
1.02 1.84 2.11
Total 0.53 0.95 1.09 1.38 2.48 2.85 2.70 4.86 5.59
Adjusted Total for City-only WWTP Alternative1 2.58 4.64 5.34 Notes:
1. Phase 5 includes the northern portion of the study area north of the hilltop on Adobe Road. This area drains towards the MCAGCC and would only be included for a Joint-Use WWTP alternative. Flow from this area was subtracted for the City-only WWTP alternative.
As compared to the City’s 2014 Wastewater Master Plan (WWMP), the flow projections listed above are much lower because the study area for this feasibility study is significantly smaller and because the 2014 WWMP projected flows for ultimate build-out conditions. As mentioned previously, a build-out ratio of 40% is estimated for the 2075 planning horizon, based on the 2075 population forecast compared to the ultimate build-out population.
4.3 JOINT-USE WASTEWATER FLOW PROJECTIONS
As mentioned previously, the MCAGCC is currently pursuing a design build contract to replace the existing Mainside WWTP with a new WWTP but is still in the initial stages of that process. Limited public information regarding the new WWTP is available, but the MCAGCC stated that the headworks will have (2) bar screen trains for redundancy, each with a maximum capacity of 3.0MGD, such that either train can handle peak loading. Also, per the latest RWQCB Waste Discharge Requirements (WDR) Order (No R7-2020-003) for the Mainside WWTP, certified in March 2020, the WWTP receives approximately 0.742 MGD of domestic wastewater and produces approximately 0.558 MGD of disinfected secondary-treated recycled water used for golf course irrigation and 0.184 MGD of untreated domestic wastewater is stored in ponds for reuse or disposal by evaporation. DRAFT
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Based on the available information, it is assumed that the new MCAGCC WWTP will be designed and constructed for an Average Dry Weather Flow (ADWF) of 1.0 MGD and that this includes capacity for both existing flows, assumed to be 0.75 MGD, and future growth at the MCAGCC. These assumptions have not verified with the MCAGCC.
Based on the assumptions above, combined (MCAGCC and Study Area) flow projections are listed below in Table 12 for each planning horizon with a calculated ratio of the study area flow projection to the total combined flow projection. Initially, City flows will be less than MCAGCC flows, but will eventually exceed MCAGCC flows as the City’s collection system expands.
Table 12 –Combined Wastewater Flow Projections for the Joint-Use Alternative 2025 2050 2075
ADWF
(MGD)
ADWF
(MGD)
ADWF
(MGD)
MCAGCC 0.75 1.00 1.00
City Study Area1
0.53 1.38 2.70
Combined Total 1.28 2.38 3.70
Ratio of Study Area Flow
to Combined Flow 2 41% 58% 73%
Notes:
1. Refer to Table 11
2. Calculated ratio of study area flow to combined total flow.
DRAFT
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5.0 WASTEWATER COLLECTION SYSTEM
A new wastewater collection system, consisting of trunk and collector sewers, lift stations, and force mains, will need to be constructed to convey City wastewater flows to a centralized City-owned wastewater facility (either a City-only WWTP or lift station that would convey wastewater to a Joint-use WWTP at the MCAGCC). Although the 2014 Wastewater Master Plan (WWMP) developed a conceptual trunk sewer system for the City, the proposed service area was much larger and the system was not developed with a focused study of ground contours, as noted in the WWMP. Therefore, a different preliminary wastewater collection system was developed and evaluated for this study, including a more focused evaluation of the existing topography as described below.
5.1 TOPOGRAPHY EVALUATION
An evaluation of the existing topography was conducted by analyzing contour and elevation data in GIS, using a 2017 USGS Lidar Digital Elevation Model (DEM). Lidar data was available for the study area but was not available for the MCAGCC area. The primary objectives of the evaluation were:
• To determine low points in the study area for a centralized City-owned wastewater facility (either a City-only WWTP or a lift station that would convey wastewater to a Joint-use WWTP at the MCAGCC).
• To determine which parts of the study area could have future wastewater flow by gravity to those low points, to determine where lift stations might be required, and to determine the best trunk sewer alignments for gravity sewer flow.
• To determine the feasibility of gravity flow for a pipeline to the MCAGCC WWTP.
5.1.1 Low Point Locations:
The evaluation identified two low point locations for the centralized facility, the low point on Amboy road between Adobe Road and Utah Trail, and the study area low point on Bagdad Highway, where the flood control channel ends and drains into a natural desert wash area. Both low points are shown on Figure 3. For the Amboy low point location, the undeveloped land north of the low point was assumed to be the location for the centralized facility. For the Bagdad low point location, the undeveloped land south of the low point was assumed to be the location for the centralized facility.
5.1.2 Study Area Gravity Flow Evaluation:
The evaluation found that future wastewater from the majority of the study area should be able to flow by gravity to either of the two identified centralized City-owned facility locations. The Amboy location would be more ideal for collecting the flow from the entire study area and for a lift station/force main to convey wastewater to the MCAGCC, for the joint-use alternative. It would require an additional lift station and force main for the industrial zoned “island” east of Bagdad Highway, but that area is currently undeveloped. On the other hand, the Bagdad location would require a deep gravity sewer, approximately 25 to 30 feet deep for a few thousand feet, to cross the small hilltop on Adobe Road DRAFT
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between Utah Trail and Bagdad Highway. Although feasible for the City-only WWTP alternative, the Bagdad location is not considered feasible for the joint-use alternative because of the topography and because it would add over 9,000 feet of force main. From a wastewater collection system perspective, the Amboy location is preferrable to the Bagdad location. However, for a WWTP there are many other issues to consider, which are discussed in Section 6.
5.1.3 MCAGCC Pipeline Gravity Flow Evaluation:
The evaluation found that it is not feasible to convey City wastewater flows to the MCAGCC WWTP solely by gravity, and that up to two lift stations would be required.
One lift station would be required near the Amboy Road low point road location, due to the hilltop on Adobe Road, between Mesa Drive and Raymond Drive, which is approximately 24 feet higher than the low point on Amboy Road. To cross this hilltop, a deep gravity sewer would need to be approximately 35 to 40 feet deep for a significantly long distance, which is not considered feasible. Therefore, a centralized lift station would be required to collect and convey wastewater up and over the hilltop.
Another lift station would likely be required near the MCAGCC main gate, because the existing WWTP inlet elevation is higher than the low point location south of the gate. Because of the long distance between the low point and the existing WWTP, approximately 10,000 feet, a deep gravity sewer would end up being approximately 20 to 25 feet below the existing WWTP inlet elevation. Lidar topography was not available in the MCAGCC area but based on google earth elevations it is estimated that a deep gravity sewer would need to be approximately 15 to 25 feet deep for approximately 5,000 feet and 25 to 35 feet deep for approximately 1,000 feet. With the significant elevation rise on Adobe Road south of the main gate, an inverted siphon (depressed sewer) pipeline may be another feasible alternative for this segment. However, there are significant operational risks with siphons including sedimentation which can lead to blockages and overflows. These alternatives should be evaluated further in the preliminary design stage, but for the purpose of this study, it is assumed that a lift station and force main will be required.
Gravity flow is feasible down Adobe Road between the hilltop on Adobe Road and the low point locations south and north of the MCAGCC main gate area. A gravity sewer in this segment would be used to convey wastewater from the Amboy road low point lift station and to collect wastewater from the northern-most sewer catchment basin described below in section 5.2.
5.2 PRELIMINARY SEWER BASINS
Preliminary sewer catchment basins were delineated for the study area and are shown in Figure 4.
Delineation of the basins was based primarily on natural topography, but adjustments were made for parcel lines, proposed system phasing, and the preliminary trunk sewer layout discussed below.
At the north end of the study area, there is a small catchment basin north of the hilltop on Adobe Road, which slopes towards the MCAGCC. For the Joint-Use WWTP alternative the majority of this area could be incorporated with the primary pipeline going to a MCAGCC WWTP. However, for a City-only WWTP alternative, a lift station and a long force main would be required to convey flow from this area back to DRAFT
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the main collection system. This is not considered feasible or cost-effective, especially considering how sparsely populated this area is. Therefore, for the City-only WWTP alternative, this area would be excluded and would remain a septic system similar to other areas outside of the study area.
5.3 PRELIMINARY TRUNK SEWER SYSTEM LAYOUT
A preliminary trunk sewer system layout was developed for the study area based on the topography evaluation discussed above and is shown in Figure 4. The low point on Amboy Road was assumed to be the location for the centralized facility for this layout. If the centralized facility were to be located near the study area low point, on Bagdad Highway, the layout would be similar.
Development of the trunk sewer layout focused on providing a system, including collector sewers, which would flow by gravity as much as possible to limit the number of sewer lift stations. This can be accomplished for most areas by running a portion of the trunk sewer along the flood control channel.
Preliminary locations for the few lift stations that would be required are also shown on Figure 4.
However, different alternatives may need to be evaluated for each trunk sewer alignment in the preliminary design stage. In some cases, unforeseen issues or project phasing changes could preclude proposed gravity sewer alignments and require additional lift stations. Small lift stations may also be required within some of the existing multi-family developments but were not identified as part of this study.
The proposed layout also took into consideration existing package wastewater treatment plants located within the study area and using existing or planned right-of-way corridors. Alignments in the Caltrans right-of-way for the Twentynine Palms Highway (State Route 62) were limited to perpendicular crossings as Caltrans does not currently allow for parallel alignments. In some limited cases, additional right-ofway will need to be required for the proposed trunk sewer alignments. In the preliminary design stage, alternatives for each trunk sewer right-of-way acquisition should be evaluated.
5.4 PRELIMINARY JOINT-USE PIPELINE LAYOUT
For the joint-use alternative, a preliminary alignment was developed for a pipeline to convey wastewater from a centralized City-owned lift station to the MCAGCC WWTP as shown in Figure 5.
As discussed in Section 5.1, a lift station and force main will be required to convey wastewater west on Amboy Road and then north on Adobe Road to the hilltop between Raymond Drive and Mesa Drive. At that point, the pipeline would transition to a gravity sewer running north down Adobe Road to another lift station located near the low point location south of the MCAGCC main gate. This lift station could also be located near the low point location north of the main gate to shorten the distance of the force main segment. However, it is assumed that this lift station would be owned and operated by the City and thus it would be preferable to have the lift station located outside of the MCAGCC. From this lift station a force main would convey wastewater towards the WWTP along Adobe Road inside the MCAGCC. Southwest of the intersection of Adobe Road and Del Valle Dr, the proposed force main alignment veers off Adobe Road, northwest towards the WWTP, paralleling an existing overhead electric line. This alignment has not been field verified or discussed with the MCAGCC but would be shorter than an alternate alignment on Del Valle Drive. The total length of the proposed pipeline is DRAFT
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approximately 28,000 feet (5.3 miles) long, with approximately 16,000 feet (3.0 miles) of force main and 12,000 feet (2.3 miles) of gravity sewer. Listed pipe sizes are based on the hydraulic model discussed in Section 5.8.
5.5 PRELIMINARY COLLECTION SYSTEM PHASING PLAN
Due to the large size of the study area and substantial capital cost for the entire wastewater collection system, the system will need to be implemented in several phases. The preliminary phasing plan proposed herein was based on many factors including the proposed sewer catchment basins, proximity to the proposed location for the centralized City-owned wastewater facility, eliminating package treatment plants, capturing dense areas with higher existing water use, minimizing lift stations, and input from the City. Five phases were developed, each with a geographical wastewater collection area as shown on Figure 6. The geographical limits for each phase are preliminary and will be modified as the design progresses.
This phasing plan proposes that Phases 1 and 2 be included as part of the initial 2025 planning horizon, that Phases 3 and 4 be included as part of the 2050 horizon, and that Phase 5 be included as part of the long-term 2075 horizon.
Collection system pipelines would be sized based on 2075 flow projections to provide capacity for all phases since the anticipated useful life of pipelines is much longer than the useful life of a WWTP or a lift station. However, a new centralized facility (either a WWTP or a lift station) would be a modular design. Initially (Stage 1) the facility would be sized for collection phases 1 and 2 but would be expandable (Stage 2) to accommodate the addition of phases 3 and 4. Another expansion (Stage 3) would be required for the addition of Phase 5.
Phase 1 includes:
• Trunk sewers for Phase 1, which are also required for the other phases. • Collector sewers for Phase 1.
• Two existing package treatment plants for the Turtle Rock and Desert Knoll Developments. • The two large dense military housing developments on Two Mile Road and Joe Davis Drive. • The residential area northeast of the Adobe Road – Two Mile Road intersection. • The commercial area on Adobe Road and Amboy Road north of Samarkand Drive. DRAFT
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Phase 2 includes:
• Trunk sewers for Phase 2, which are also required for Phase 3 and a portion of Phase 5. • Collector sewers for Phase 2.
• Two planned package treatment plants for Project Phoenix and the Wander Hotel. • The dense downtown area east of Donnell hill. This area has a balanced mix of both residential and commercial land use.
Phase 3 includes:
• Trunk sewers for Phase 3.
• Collector sewers for Phase 3.
• Two existing package treatment plants for the Fairfield Inn and the Holiday Inn. • The commercial strip on Twentynine Palms Highway west of Donnell Hill. • The dense residential area north of the Fairfield Inn.
Phase 4 includes:
• Trunk sewers for Phase 4, some of which are required for a portion of Phase 5. • Collector sewers for Phase 4.
• The sewer catchment basins located between two ridgelines which both run east-west. This includes the High School and the residential neighborhoods east and west of the High School and includes the commercial strip on Adobe Road between El Paseo Drive and Crestview Drive. • The sewer catchment basin north of the ridgelines, south of Samarkand Drive, between Adobe Road and Mesquite Springs Road. This area is mostly residential except for the commercial strip on the west side of Adobe Road.
Phase 5 includes:
• The trunk and collector sewers, lifts stations, and force mains for all remaining portions of the study area not in Phases 1, 2, 3, 4, and 5 except for the small catchment basin at the north end of the study area, north of the hilltop on Adobe Road, which slopes towards the MCAGCC. This catchment basin would be included as part of Phase 5 for the joint-use alternative but would not be included for the City-only WWTP alternative as discussed in Section 5.2.
5.6 PRELIMINARY COLLECTION SYSTEM LAYOUT – PHASE 1 AND PHASE 2 A preliminary collection system layout, including both trunk and collector sewers, was developed for the initial 2025 planning horizon which includes Phases 1 and 2, and is shown on Figure 7. Similar to the trunk sewer layout discussed in section 5.3, the preliminary collector sewer layout was developed based on topography and existing/anticipated right-of-way corridors. Listed trunk sewer pipe sizes are based on the hydraulic model discussed in Section 5.8. All collector sewers were assumed to be 8-inch diameter pipes, the minimum pipe size. DRAFT
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5.7 COLLECTION SYSTEM CAPITAL COSTS
Table 15 below provides the estimated length of sewer pipelines, the estimated number of sewer lift stations, and a preliminary opinion of probable construction cost for each phase of the preliminary collection system developed for this study. Refer to Appendix A for a cost breakdown of each phase.
These are rough order of magnitude cost opinions for preliminary planning information only and do not include inflation for future cost planning. Each cost opinion includes a 30% construction contingency and a 15% allowance for design and construction management.
Table 13 – Preliminary Opinion of Probable Construction Cost for Collection System Collection
System Phase
Estimated Length
of Sewer Pipelines
Estimated Number of
Lift Stations
Preliminary Cost Opinion1
(Million $)
Phase 1 10 miles 0 $31 M
Phase 2 20 miles 0 $58 M
Phase 3 26 miles 0 $83 M
Phase 4 17 miles 0 $51 M
Phase 5 40 miles 7 $133 M
Total 113 miles 7 $356 M
Notes:
1. Does not include costs for a WWTP or costs for a City-to-MCAGCC conveyance pipeline for the joint-use WWTP alternative.
5.8 HYDRAULIC MODELING
A hydraulic model was developed for the proposed Phase 1 and Phase 2 trunk sewer system and the City-To-MCAGCC pipeline to confirm the feasibility of gravity flow and to estimate pipeline diameters and profiles. The model was developed using InfoSewer, a GIS based sewer modeling software. The model does not include Phase 3, 4, or 5 trunk sewers or any collector sewers.
The previous hydraulic model prepared for the 2014 WWMP was not utilized for this study because the study area, wastewater flow projections, and the preliminary collection system developed for this study are significantly different.
5.8.1 Hydraulic Model Limitations
The hydraulic model developed is preliminary and is based on a large number of variables, assumptions, and projected wastewater flows. As the design progresses, the projected wastewater flows, and the physical elements of the hydraulic model will need to be adjusted and estimated pipeline sizes and slopes may change.
DRAFT
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5.8.2 Hydraulic Design Criteria
The design criteria used for hydraulic modeling is listed below in Table 13 for gravity sewers and Table 14 for force mains. This criteria was used to develop and evaluate the proposed system. The maximum depth of cover for pipelines was evaluated on a case-by-case basis. In general, a depth of cover of 15 feet or less is preferred. However, special situations warrant deeper pipelines, such as crossing under the flood control channel or avoiding the addition of a lift station.
Table 14 – Gravity Sewer Hydraulic Design Criteria
Criteria Value
Minimum Pipeline Diameter 8-inches
Maximum d/D Ratio for PWWF, Diameter < 12-inch 0.50
Maximum d/D Ratio for PWWF, Diameter > 12-inch 0.75
Minimum Velocity for PWWF 2 ft/s (feet per second)
Maximum Velocity for PWWF 10 ft/s (feet per second)
Pipeline Roughness Coefficient n = 0.013
Minimum Pipeline Slope
8-inch 0.4%1
10-inch 0.32%
12-inch 0.24%
15-inch 0.18%
18-inch 0.12%
> 18-inch 0.10%
Minimum Depth of Cover 4 Feet
Notes:
1. For gravity sewers in the upper reaches of the system that do not achieve the minimum velocity for PWWF condition a minimum design slope of 1.0% should be used.
Table 15 – Force Main Hydraulic Design Criteria
Criteria Value
Minimum Velocity for PWWF 3 ft/s (feet per second)
Maximum Velocity for PWWF 8 ft/s (feet per second)
Pipeline Roughness Coefficient
DRAFT
c = 130
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5.8.3 Model Elements and Development
The hydraulic model consists of a network of manholes, pipes, and outlets. These elements, user inputs, and development of the model network are described below.
Manholes
Manholes represent points in the collection system where wastewater loads (flows) enter into the system and where pipes link together. Manholes were located at junctions between different trunk sewers, junctions with collector sewers, and as needed to meet the maximum spacing per the design criteria. Manholes are also where pipe characteristics such as diameter and slope change. User inputs for manholes include rim elevation, manhole diameter, and wastewater load. Rim elevations were input for each manhole using InfoSewer’s Elevation Extractor tool which automatically extracted surface elevations from the 2017 USGS Lidar Digital Elevation Model (DEM). A manhole diameter of 5 feet was assumed for all manholes.
Pipes
Pipes represent links that convey wastewater from one point in the system to another and can be gravity sewers or force mains. User inputs for pipes include pipe diameter, a pipe roughness coefficient, and upstream and downstream invert elevations, which determine pipe depth and slope. Pipe length is automatically input from GIS. Pipe diameters and invert elevations were determined and input through an iterative process to meet the established design criteria with known constraints. As a starting point all invert elevations were set 6 feet below manhole rim elevations. Then invert elevations were adjusted lower as needed for known physical constraints. For this feasibility study, the flood control channel was the only physical constraint accounted for. For sewers immediately adjacent to and parallel with the channel, invert elevations were set so that top of pipe elevations would be approximately 1 foot below the flowline of the channel. For sewers crossing underneath the flood control channel, inverts elevations were set so that top of pipe elevations would be at least 5 feet below the flowline of the channel. These values are just assumptions that will need to be verified in design along with determining other physical constraints. Then pipe inverts, diameters, and slopes were adjusted to meet the design criteria, with consideration for the need to upsize pipe diameter versus increasing pipe slope. Pipe diameters were also adjusted so that a downstream pipe would be equal to or larger than all upstream pipes.
Outlets
Outlets represent points where wastewater flows exit the wastewater collection system and are the most downstream points of the system. For the hydraulic model, an outlet was located at the Amboy Road low point, one of the potential locations for the centralized City-owned wastewater facility (WWTP or lift station) and another outlet was located at the existing MCAGCC WWTP for the joint-use alternative. Similar to manholes, user inputs for outlets include rim elevation and manhole diameter.
Load Allocation
Wastewater loads (flows), based on land use areas and wastewater load factors (generation rates) for each land use designation, were allocated to specific manholes using InfoSewer’s Load Allocator tool. DRAFT
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The tool allocated loads by intersecting the City’s land use GIS polygon shapefile with a sewer subcatchment basin GIS polygon shapefile and by applying the load factors. Each manhole load was then reduced with the assumed build-out ratio value. Refer to Section 4.1 for wastewater generation rates and the assumed build-out ratio.
The sub-catchment basin GIS polygon shapefile utilized by the allocator tool was created for this study to approximate where flows from collector sewers would likely enter the trunk sewer system. The subcatchment basins, each a polygon for a specific area and an assigned manhole ID, were delineated based on the larger sewer catchment basins described in Section 5.2, and a preliminary collector sewer layout developed for Phases 1 and 2. Larger catchment basins were delineated to estimate future flows for Phases 3, 4, and 5.
5.8.4 Model Scenarios Evaluated
The developed system was evaluated for both Peak Dry Weather Flow (PDWF) and Peak Wet Weather Flow (PWWF) conditions at peak hour for the 2075 planning scenario. Peaking factors used are discussed in Section 4.1. Since PDWF is less than PWWF, PDWF was used to evaluate the minimum velocity design criteria and PWWF was used to evaluate maximum velocity, and the ratio of depth of flow to pipe diameter (d/D). For both conditions, the system was evaluated using a 24-hour extended period simulation (EPS) and fully dynamic flow routing to calculate water depths, head loss, and velocities.
5.8.5 Model Results and Estimated Pipe Sizes
Model results and estimated pipe sizes are discussed below. Estimated pipe sizes are preliminary. As the design progresses, the projected wastewater flows, and the physical elements of the hydraulic model will need to be adjusted and estimated pipeline sizes may change.
Phase 1 and Phase 2 Trunk Sewer System
The preliminary Phase 1 and Phase 2 collection system layout, including both trunk and collector sewers, is shown in Figure 7. The Phase 1 and Phase 2 trunk sewer pipe sizes determined from the hydraulic model range from 8-inches in the upper reaches of the system to 24-inches at the outlet. All pipes meet the required design criteria for the 2075 planning scenario except that some pipes in the upper reaches of the system do not meet the minimum velocity requirement because there is not enough wastewater flow. For these pipes, it is not possible to achieve the minimum velocity without substantially increasing pipe slope, which would create an undesirably deep system, so it is recommended to have a minimum pipe slope of 1% for these cases.
City to MCAGCC Pipeline
For the joint-use alternative, the preliminary layout for the pipeline from the centralized City-owned lift station to the MCAGCC WWTP is shown in Figure 5 with pipe sizes obtained from the hydraulic model.
Force main segments were modeled as dual force mains with a total combined capacity designed for the 2075 planning scenario. This will allow for redundancy and better velocities in a single pipeline for DRAFT
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smaller flows in earlier planning scenarios. For this feasibility study, it was assumed that the dual force main segments would have two equal diameter pipelines. However, having two different diameter pipelines should also be considered and evaluated in concert with the preliminary design of the lift stations, which should evaluate different pump configurations and sizes to assure proper force main velocities for both short-term and long-term flow scenarios. Based on the hydraulic model, dual force main segments would consist of two 10-inch diameter pipelines and the gravity sewer segment would consist of a single 24-inch diameter pipeline. All pipes meet the required design criteria for the 2075 planning scenario.
DRAFT
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6.0 WASTEWATER TREATMENT PLANT
As mentioned previously, a centralized wastewater treatment plant (WWTP) is the best long-term solution for treating the City’s wastewater and protecting the local groundwater supply, the only source of water for the community. This section discusses two primary WWTP alternatives, a separate-use (City-only) WWTP and a joint-use (City and MCAGCC) WWTP and evaluates the advantages and disadvantages of each alternative. It also evaluates potential sites and treatment processes and technologies for a City-only WWTP.
6.1 PREVIOUS WWTP STUDIES AND DOCUMENTS
Previous studies and documents regarding separate-use and joint-use WWTP alternatives for the City were reviewed for this study and are summarized below.
6.1.1 2008 Joint-Use Study
The Wastewater Treatment Plant Joint-Use Study prepared by Winzler & Kelly in 2008 compared three separate-use WWTP alternatives and two joint-use alternatives. Separate-Use Alternative #1 included the use of decentralized package wastewater treatment plants for new City developments of a certain size and maintaining and monitoring the City’s existing septic systems. Separate-Use Alternative #2 included a centralized City collection system and WWTP with an integrated free water surface pond system, a natural treatment process. Separate-Use Alternative #3 included a centralized City collection system and WWTP with a membrane bioreactor to treat flows, a mechanical treatment process. JointUse Alternative #1 included a newly constructed collection and trunk sewer main system to convey flows from the City to the existing MCAGCC WWTP. Joint-Use Alternative #2 also included a newly constructed collection and trunk sewer main system for the City but abandons the existing Mainside WWTP and redirects MCAGCC wastewater flows to a new centralized WWTP within the City.
After evaluating all five alternatives, the study recommended Separate-Use Alternative #1 and recommended upgrades to the existing Mainside WWTP. Joint-use alternatives were not recommended primarily due to the high capital cost and difficulty of owning and operating a joint-use facility.
Separate-use Alternative #1 (decentralized package treatment plants) was recommended over the other separate-use alternatives (a centralized WWTP) primarily due to the high cost of constructing a centralized collection system and WWTP. To address groundwater degradation concerns the study recommended regular monitoring of existing septic systems and recommended that the City actively participate with the RWCQB to regulate the construction and operation of package treatment plants.
6.1.2 2014 Wastewater Master Plan
The Twentynine Palms Wastewater Master Plan (WWMP) prepared by Kennedy/Jenks in 2014 developed and evaluated a conceptual centralized sewer collection and treatment system for the entire City and the City’s sphere of influence (SOI), including the entire TPWD service area, for the prevention of potential groundwater impacts from septic systems. The WWMP estimated wastewater flows and sized primary infrastructure (trunk sewers, lift stations, and a treatment facility) based on the ultimate build-out population for the City and the City’s SOI. DRAFT
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The WWMP was primarily focused on developing a City-only WWTP, the recommended long-term option, but also briefly discussed other options including decentralized treatment facilities and a jointuse facility at the MCGACC. The WWMP did not recommend decentralized treatment facilities due to the decreased ability to provide oversight and the difficulties of regulating private treatment facilities and did not recommend a joint-use treatment facility based on concerns about ownership and operation, control over treatment polices, water reclamation issues, and the prohibitive infrastructure costs to convey wastewater to the MCGACC and expand the existing WWTP.
Based on a siting selection criteria (available area, land use, non-proximity to residential areas, maximizing use of gravity flow, and drainage patterns) the WWMP suggested a general location for a City-only WWTP in the vicinity of Amboy Road and Bagdad Road.
The WWMP also assessed several wastewater treatment processes for a new City-only WWTP. Due to the high capital cost and difficulty of building a facility that immediately meets ultimate capacity, a “convertible” staging technique was recommended, with a treatment facility initially utilizing a sequencing batch reactor (SBR) process but later modified to a Modified Ludzack Ettinger (mLE) process, a subset of the extended aeration process, to treat additional flow more efficiently.
The final recommendation given by the WWMP was to improve groundwater monitoring and to implement a septic system management program based on the 2014 Salt and Nutrient Management (SNMP), which was prepared in conjunction with the WWMP. The WWMP did not recommend immediate implementation of a centralized sewer collection and treatment system. Instead, a comprehensive assessment of the impacts of septic systems on groundwater was recommended to be conducted after three to five years of monitoring and implementation of the SNMP.
6.2 ASSUMED WWTP DESIGN CAPACITY
As discussed in Section 5.5, it is assumed that a WWTP would be sized based on phased implementation of the collection system. Initially (Stage 1) the WWTP would be sized for collection phases 1 and 2, but would be expandable (Stage 2) to accommodate the addition of phases 3 and 4. Another expansion (Stage 3) could be considered for the addition of Phase 5 but is not included herein since the implementation of Phase 5 is assumed to be many years away and because the growth of the less developed Phase 5 area is more uncertain. As a basis for comparing the two WWTP alternatives, the assumed WWTP average design capacity for each alternative is listed below in Table 16, based on the phased wastewater flow projections listed in Sections 4.2.3 and 4.3. These capacities are based on a large number of variables, assumptions, and the preliminary phasing plan. As the design progresses, collection system phasing, projected flows, and design capacities may change significantly.
Table 16 –Assumed WWTP Design Capacity
Alternative
Stage 1 Stage 2
ADWF
(MGD)
ADWF
(MGD)
City-Only WWTP 0.7 1.4
Joint-Use WWTP 1.7 2.4
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6.3 CITY-ONLY WWTP ALTERNATIVE
The City-only WWTP alternative would include a new separate WWTP which would only treat wastewater from the study area near a low point within the City to facilitate gravity flow. This facility would be owned, operated, and maintained by the City with all capital and O&M costs borne by the City.
Under this alternative the MCAGCC would continue to operate its own WWTP independently.
6.3.1 Potential City-only WWTP Sites
Two potential sites, Site 1, and Site 2 were identified for a City-only WWTP. Both Site 1 and Site 2 were identified based on their proximity to low point locations in the study area as described in Section 5.1.
These low point locations are favorable for maximizing gravity sewer flow to the WWTP, which minimizes the number of lift stations in the collection system and reduces long-term O&M costs. Site 1 and Site 2 are shown on Figure 8.
Site 1 for the City-only WWTP lies north of Amboy Road immediately west of Desert Knoll Ave. There are four vacant parcels (APNs 0621-241-20, 0621-241-41, 0621-241-42, and 0621-241-64) near Site 1, that are designated as tourist commercial and single-family residential land use. Based on sizing needs of the WWTP, the site will likely only occupy a portion of one of the four parcels. For this study, APN 0621-241- 20 was the assumed location for Site 1 to maximize proximity to the area low point. However, the adjacent parcel to the west (APN 0621-241-42) is also suitable and a viable alternative to consider. Both of these parcels are 9.7 acres in size. APN 0621-241-41 further west is less suitable due to its uneven terrain and higher elevation and APN 0621-241-64 to the east is not recommended due to its close proximity to the TwentyNine Palms RV resort, located just east of Desert Knoll Ave.
Site 2 for the City-only WWTP lies near the intersection of Amboy Road and Bagdad Hwy. This general location was also identified in the City’s 2012 General Plan and the 2014 Wastewater Master Plan. At this location there are two large vacant parcels (APNs 0622-061-06 and 0622-091-02) on the north side of Amboy Road with suitable topography for a WWTP. However, APN 0622-061-06 is located adjacent to the residential development, identified as the Campbell Hill Tract. Therefore APN 0622-091-02 was selected for this study. The southern portion of this parcel (closest to Amboy Road) is designated for tourist commercial land use, whereas the northern portion is designated as rural living residential land use. The parcel is approximately 103 acres in size.
6.3.1.1 Comparison of Potential City-only WWTP Sites
Key considerations for the two potential City-only WWTP sites are compared below and include:
topography, collection system impact, proximity to a potential groundwater recharge facility, proximity to groundwater subbasins, proximity to residential areas, flood hazards, access, existing utilities, geologic faults, and environmental impact.
Topography:
Site 1 has relatively flat terrain with small sand mounds, with elevations ranging from approximately 1796 ft to 1802 ft, based on available USGS lidar data. The site is identified as a dry lake on USGS topographical maps. Site 2 has a sloping terrain (approximately 2 to 3 percent down towards the north) DRAFT
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with a high elevation of approximately 1792 ft near Amboy Road, based on available USGS lidar data.
This sloping terrain could be beneficial for certain gravity flow processes at a WWTP, but also could be more challenging for grading improvements.
Collection System Impact:
From a collection system perspective, Site 1 is preferable to Site 2. Due to its more remote location, Site 2 would add approximately 1 mile of trunk sewer on Amboy Road to the Phase 1 collection system, as compared to Site 1. Part of this additional trunk sewer would be a gravity sewer, approximately 25 to 30 feet deep for a few thousand feet, to cross the small hilltop on Adobe Road between Utah Trail and Bagdad Highway. It would also require crossing under the flood control channel. Assuming a 24-inch diameter trunk sewer, this additional segment would add roughly $5 million to the Phase 1 collection system preliminary construction cost opinion provided in Section 5.7.
As a counterpoint, Site 2 would reduce the length of the force main pipeline shown on Figure 6, by the same amount (approximately 1 mile), to serve the industrial zoned “island” east of Bagdad Highway.
However, that industrial area is currently undeveloped and therefore included in the last phase of the study area collection system phasing plan. Site 2 does offer one advantage in relation to the collection system, in that it would be easier to capture flows from the Campbell Hill Tract with the additional trunk sewer segment on Amboy Road. If Site 2 was selected for the WWTP location, it is recommended that the Campbell Hill Tract be included in Phase 1 of the collection system. A small lift station and force main pipeline would be required, but the residential area is relatively dense and worth including in Phase 1. However, this advantage is small in comparison to the large cost and challenges associated with the additional mile of trunk sewer necessary for Site 2.
Proximity to Potential Groundwater Recharge Site:
As described in Section 7, NV5 evaluated three potential sites for a groundwater recharge facility and concluded that the Fluoride Site was the best of the three sites. This potential site is preliminary, but for the purposes of this study, it is assumed to be the location for a potential groundwater recharge facility.
Based on this assumed location, WWTP Site 1 would require approximately 3,700 feet of pipeline to convey reclaimed water to the recharge site, whereas WWTP Site 2 would require approximately 8,200 feet of reclaimed water pipeline. This potential recharge facility is located south of the TPWD Fluoride Removal Water Treatment Plant as shown on Figure 8.
Proximity to Groundwater Subbasins:
Site 1 is located within the boundary of the Mesquite Lake Subbasin, a groundwater subbasin utilized by the TPWD for potable water use, whereas Site 2 is located within the boundary of the Mainside Subbasin, a groundwater subbasin not utilized by the TPWD. These subbasins are divided by the Mesquite Fault which runs between Site 1 and Site 2. Site 1 also is located closer to the other groundwater subbasins utilized by the TPWD, located south of the Mesquite Lake Subbasin. Please refer to Figure 3-1 in the TPWD 2015 Urban Water Management Plan (UWMP) which shows the location of groundwater subbasins and t DRAFThe TPWD active wells.
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Proximity to Residential Areas:
Approximately 400 feet east of Site 1 is the TwentyNine Palms RV resort, which has approximately 168 RV sites and 26 cottages. There is also a partially developed residential area and golf course, identified as the Green Acres Tract, directly northeast of the RV resort, with most residences on Saddle Horn Rd.
The area surrounding Site 2 is more remote and less developed than Site 1. The nearest residential area, the Campbell Hill Tract, is located approximately 1,900 feet east of Site 2.
For either site, advanced odor control technology should be implemented to address any residential concerns for potential odor from the WWTP.
Flood Hazard Areas:
The San Bernardino County Flood Control District’s flood control channel, also identified as the Twentynine Palms Channel, lies between Sites 1 and 2. Attributed to the channel are Federal Emergency Management Agency (FEMA) designated special flood hazard areas including a regulatory floodway and a 100-year floodplain.
Site 1 lies within the FEMA 100-year floodplain designated as Zone AO. Zone AO represents areas subject to inundation by 1-percent-annual-chance (100-year) shallow flooding where average depths are between 1 and 3 feet. The latest FEMA Flood Insurance Rate Map (FIRM) Number 06071C8195J lists an average depth of 1’ for this zone. It is anticipated that construction on Site 1 will require a conditional letter of map revision (CLOMR) from FEMA, likely entailing hydraulic modeling and analysis of the channel and surrounding area. It will also require mandatory flood insurance purchases and compliance with floodplain management standards, including floodproofing structures to an elevation at least one foot above the flood elevation, which would be determined as part of the CLOMR application.
Therefore, it is anticipated that some of the site will need to be filled and raised approximately 2 to 3 feet higher. For impact to construction cost, this may not be an issue as raising part of the site may help balance earthwork from underground excavations, especially considering the high cost to export and dispose of excavation spoils. In addition, most WWTP structures would be waterproofed regardless of the flood zone. However, being located in a 100-year flood zone is a significant disadvantage for Site 1 due to the flood insurance requirement and regulatory and permitting challenges.
Site 2 is not located in a FEMA special flood hazard area. However, a natural desert wash, the FEMA regulatory floodway, and associated 100-year and 500-year floodplain areas are located in the northern portion of the large parcel containing Site 2.
Access:
Both sites have good access and are both
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located along Amboy Road, a public paved road.
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Existing Utilities:
Both sites lie within the utility service areas for Twentynine Palms Water District (TPWD), Southern California Edison (SCE), and SoCal Gas. Utility mapping for water, power, gas, phone, and internet was not conducted for this study. However, DigAlert contact information indicates that there may be TPWD, SCE, SoCal gas, Spectrum (internet), and Frontier (internet) facilities on Amboy Road south of Site 1 and TPWD, SCE, and Frontier facilities on Amboy Road south of Site 2. Based on available TPWD GIS files there appears to be a 12-inch potable water line on Amboy Road south of Site 1, a 16-inch potable water line on Amboy Road south of Site 2, and a 12-inch potable water line on Baghdad Highway west of Site
2. Both sites appear to be well located in regard to existing utilities, but it appears that extending gas service, if needed, might be more costly for Site 2. However, utility mapping should be conducted in the preliminary design phase to determine required utility improvements for each site.
Geologic Faults:
According to the United State Geological Survey (USGS) Quaternary Faults database and maps, the Mesquite Lake Fault (Fault ID 123) runs between Site 1 and Site 2, and the inferred location of the Pisgah-Bullion Fault (Fault ID 122) runs just east of Site 2. A geotechnical investigation will need to be conducted to determine the impact of these faults on Site 1 and Site 2, but it should be noted that Site 2 appears to be located close to the inferred location of the Pisgah-Bullion fault which could be an issue.
Environmental Impact:
Both potential WWTP sites are undeveloped sites, however Site 2 is more remote and is located close to a wildlife corridor identified in the City’s 2012 General Plan. Site 1 also appears to be more disturbed by recreational off-road vehicle traffic, as evident by numerous tire tracks. Furthermore, Site 2 will require the construction of more collection system infrastructure and potentially more reclaimed water infrastructure, which inherently has some environmental impact. However, for either site, environmental impact and cultural studies need to be conducted to check for the presence of archaeological and historical sites, endangered species, and other potential environmental impacts.
6.3.1.2 Assumed City-only WWTP Location:
For the purposes of this study and development of the preliminary collection system, Site 1 was assumed to be to be the location of a City-only WWTP. However, potential sites for a City-only WWTP should be evaluated further in the preliminary design stage with consideration for the factors discussed above and the results of environmental and cultural studies, public input, geotechnical investigations, and as design of the groundwater recharge system
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progresses.
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6.3.2 Anticipated Influent and Effluent Requirements
The anticipated influent wastewater characterization parameters are shown in Table 17. Biochemical Oxygen Demand (BOD5) value provides information on the effect of wastewater on dissolved oxygen in water. It is generally assumed that the rate of oxygen consumed is in direct proportion to the concentration of degradable organic matter. Total Suspended Solids (TSS) is the dry weight of undissolved particles, typically composed of inorganic materials. Ammonia-Nitrogen is measured because ammonia is a pollutant often resulting from contamination by untreated wastewater discharges. Total Kjeldahl Nitrogen (TKN) measures the combined concentration of organic nitrogen and ammonia.
Table 17 – Anticipated Influent Constituent Levels
Constituent Average Concentration
BOD5 300 mg/L
Total Suspended Solids (TSS) 300 mg/L
Ammonia-Nitrogen 38 mg/L
Total Kjeldahl Nitrogen (TKN) 65 mg/L
The RWQCB typically requires the effluent to meet certain concentration levels for certain parameters.
Anticipated effluent discharge requirements are included in Table 18. Effluent discharge parameters will be dictated by the RWQCB Colorado River Region 7 once a treatment process is selected and discharge method/location is determined during design. Measuring these constituents assures that the treatment plant operated properly to remove necessary pollutants and protects the surface waters and groundwater that receive the effluent. The RWQCB Colorado River Region 7 Board will permit the Cityonly facility and develop Waste Discharge Requirements (WDR) with specific effluent concentrations for parameter of concern.
Table 18 – Anticipated Effluent Constituent Levels
Constituent Average Concentration
20°C BOD5 10 mg/L
Total Suspended Solids (TSS) 10 mg/L
pH 6.5 – 8.5
Total Nitrogen 10 mg/L maximum
Total Coliform
7-day median 2.2 MPN/100 mL
Single Sample Max
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23 MPN/100 mL
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6.3.3 Conventional Activated Sludge Treatment Process
A conventional activated sludge wastewater treatment process must undertake several processes to remove contaminants prior to discharging effluent into the environment. This section describes the main components of a conventional activated sludge WWTP, including pretreatment and headworks, primary treatment, secondary treatment, tertiary treatment, and disinfection.
6.3.3.1 Pretreatment and Headworks
The headworks of a wastewater treatment process is important for the initial screening of inorganics such as larger debris, trash, sticks, and rags. This removal reduces wear on the downstream equipment.
Pumps transport the influent wet well to the headworks, where mechanically cleaned bar screens physically remove larger solids in the influent raw wastewater. Wet screenings collected in the bar screen are washed and compacted to reduce their volume. Compacted solids are then collected in a portable bin container, where they are stored prior to being disposed of at a landfill. Before the influent wastewater is distributed to the primary clarifiers, flow is measured and logged.
6.3.3.2 Primary Treatment
Primary clarifiers hold the wastewater influent for a period of time, allowing heavier solids to settle and lighter materials to float. The size, detention time, and overflow rate are determined based on the influent flowrate. As the primary sludge separates and collects at the bottom of the clarifier, it is pumped to sludge handling and treatment units. Meanwhile, surface grease is skimmed and removed prior to secondary treatment. Effluent from primary clarifiers flows over weirs into launder troughs and into secondary treatment units.
6.3.3.3 Secondary Treatment and Sludge Treatment
Secondary treatment consists of the activated sludge system of aeration basins and secondary clarifiers.
Centrifugal blowers, pipes, and/or fine bubble diffusers pump air into the aeration basins.
Microorganisms fed by the oxygen will degrade the organic suspended solids and soluble biochemical oxygen demand (BOD) in the wastewater. Effluent then flows into sedimentation basins to separate activated sludge from the treated liquid. Sludge collected off these final clarifiers flows into the return and waste activated sludge pumping well, while the effluent continues on to tertiary treatment.
Sludge treatment typically consists of thickening, digestion, and dewatering. Gravity belt thickeners move sludge along a porous belt which drains the water using gravity. An optional belt filter press uses a similar process under pressure to achieve a higher dry solids concentration. Anaerobic digestion tanks use fermentation to break down the sludge. Excess water is removed before final disposal of the sludge using dewatering equipment, such as sludge drying beds. Stabilized sludge is typically stored onsite and transported to sites for land application or final disposal.
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6.3.3.4 Tertiary Treatment
Tertiary treatment consists of additional treatment steps to further remove organics from the secondary effluent. Tertiary treatment can consist of filtration (sand, dual-media, cloth), membranes, or physicochemical processes (coagulation), or a combination. The number and type of additional treatment steps will depend on the desired effluent quality, discharge limits, or effluent reuse.
6.3.3.5 Disinfection
The three most commonly used disinfection methods are chlorine, ultraviolet (UV) radiation, and ozone disinfection. Chlorine kills bacteria and viruses by direct contact when mixed with process water, requiring a certain amount of contact time. Process water disinfected with chlorine requires dichlorination before discharge.
Disinfection using UV units administer a radiation dose determined by flowrate. Ultraviolet radiation renders the remaining microorganisms sterile by damaging their genetic structures. Effluent undergoing UV treatment should be free of organic matter, which can shield microorganisms from the UV light.
Ozone is also used as a disinfectant by reacting strongly with microorganisms that come into contact.
Ozone can be generated on-site by using electrical energy to add an oxygen atom to diatomic O2.
6.3.4 Treatment Process Technology Alternatives
NV5 explored three technologies that would meet the anticipated effluent requirements. The technologies were selected based on their modular scalability to expand the treatment facility for future phases, flexibility to treat initial low flows, operational complexity, ability to meet effluent requirements, and required footprint.
The treatment technologies explored in this study include Aero-Mod SEQUOX®, Parkson Biolac®, and Membrane Bioreactor (MBR) systems. Both the Aero-Mod and Parkson systems utilize extended aeration activated sludge processes. The MBR system uses a conventional activated sludge process with membranes for separating liquid and solids, resulting in a small footprint but higher energy costs.
Treatment technologies are summarized in Table 19 and described further below.
Table 19 – Treatment System Alternatives
Manufacturer Treatment Technology Alternatives Treatment Process Aero-Mod SEQUOX® with cloth disc filters Extended aeration, suspended growth biological system
Parkson Biolac® Extended aeration, suspended growth,
long sludge age treatment process
Multiple
(Evoqua,
Dupont, Ovivo)DRAFT
Memcor®, Ovivo®MBR Membrane bioreactor
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6.3.4.1 Aero-Mod SEQUOX®
The Aero-Mod treatment system is an extended aeration treatment system that treats the wastewater to oxidize BOD and remove nitrogen, using their patented SEQUOX® nitrate removal process which also incorporates their patented ClarAtor® clarifier technology.
The system has a low level of complexity and is designed to handle varying flow conditions. The process sequentially oxidizes activated sludge in a two-stage aeration basin design. Influent wastewater first flows through an anoxic selector tank followed by two aerobic/anoxic reactors with an aerobic digestor in between. The anoxic reactor is a tank free of dissolved oxygen which aids in denitrification, where nitrate nitrogen is converted biologically to gaseous nitrogen and released from the process. In the Aero-Mod system, post-denitrification is used as a primary means of nitrogen removal. Lastly, flow enters the ClarAtor® clarifier where biomass is settled and clarified effluent is withdrawn and discharged. Airlift pumps transport return activated sludge (RAS) and waste activated sludge (WAS).
Solids are stored in aerobic digesters sized for up to 30 days of sludge storage.
6.3.4.2 Parkson Biolac®
The Parkson Biolac® treatment system is an extended aeration long sludge age treatment system. The activated sludge process takes place within lined earthen basins with a long sludge age of 40 to 60 days.
Longer hydraulic retention times with more biomass allows for a stable process that handles fluctuating loads and flow with minimal operator intervention.
BioflexTM floating aeration chains suspend fine bubble diffusers approximately one foot above the basin bottom. The suspended equipment is easily removable and maintained without dewatering the basins.
The process uses automatic dissolved oxygen and aeration control to create multiple oxic and anoxic zones in the treatment basin. This eliminates the need for separate anoxic mixers and suspended solids pumps. The unique and repeated cycling of environments also nitrifies and denitrifies the wastewater without nitrate recycle, separate staging, or additional external basins. After the long sludge age process, wastewater from the treatment basin flows into EZ ClearTM secondary clarifiers, reinforced concrete structures constructed with a shared wall with the lined earthen treatment basin.
An airlift sludge return system is used instead of mechanically pumping RAS and WAS. Automatic inbasin equalization dampens peak flow throughout the clarifier. The end result produces minimal quantities of stabilized, excess biomass that typically requires no further sludge treatment.
6.3.4.3 Membrane Bioreactor (MBR)
An MBR activated sludge plant includes a secondary biological treatment process followed by membrane microfiltration or ultrafiltration. After screening, wastewater enters the MBR plant’s anoxic tank with activated sludge to create mixed liquor. The anoxic tank is a tank free of dissolved oxygen which aids in denitrification, where nitrate nitrogen is converted biologically to gaseous nitrogen and released from the process. Mixed liquor then enters the aerobic tank where air is added to increase dissolved oxygen levels to aid in oxidation of BOD. DRAFT
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As the mixed liquor progresses through the tank, nitrifying bacteria convert ammonia in the wastewater to nitrates. A portion of the flow is recirculated back to the anoxic tank to complete the nitrogen reaction. The remaining mixed liquor enters the membrane tank where polymer is added and filtration takes place through filament-shaped membranes. The pore size of the membranes is approximately 1 micron. The membrane is helpful for separating out solids and liquids and eliminates the need for secondary clarifiers.
6.3.4.4 Odor Control Technology
For any of the treatment technology alternatives discussed above, advanced odor control technology should be implemented to address any residential concerns for potential odor from the WWTP.
6.3.5 Conceptual City-only WWTP Facility
This feasibility study does not recommend a site or a treatment technology for a City-only WWTP facility. The potential sites and treatment technologies listed above should be further evaluated in the preliminary design phase. However, to show an approximate footprint of a City-only WWTP facility, a conceptual layout at Site 1 is provided on Figure 9. This conceptual layout is based on using a modular Aero-Mod treatment system and an assumed WWTP average design capacity of 0.7 MGD expandable to
1.4 MGD, as described in Section 6.2. Based on this layout, the conceptual WWTP site would require approximately 5 acres of land, roughly half of the parcel’s size.
For this conceptual WWTP facility, wastewater from the collection system would first flow by gravity into a headworks consisting of screens to remove physical contaminants. Screenings would be dewatered, compacted, and transported to a nearby landfill for disposal. Screened wastewater would then flow to an influent lift station which would pump wastewater to multiple Aero-Mod treatment trains installed in parallel, each with a reinforced concrete structure with shared walls between different basins/tanks.
As described previously, the Aero-Mod system uses an extended aeration, suspended growth treatment process. Influent would first enter a selector tank which preconditions the raw wastewater for activated sludge treatment. The selector controls sludge bulking to inhibit filamentous growth and settleability for a more energy efficient plant. For each Aero-Mod train, the wastewater would flow through a first-stage aeration tank, a digester tank, a second-stage aeration tank, and a clarifier to complete the activated sludge secondary treatment process. Return activated sludge would be transported by airlift pumps from the clarifier back to the initial anoxic selector tank. Waste activated sludge would be stored in the digester tank for up to 30 days and then transported to sludge drying beds, where sludge is dewatered.
Dewatered sludge would then be hauled an offsite landfill for final disposal.
After leaving the Aero-Mod system, wastewater would enter the tertiary treatment process consisting of a series of disc filters and a UV disinfection tank. The cloth disc filters collect solids on stationary discs, while the filtrate flows inside the disks and towards an effluent weir. After a designated period, the discs are rotated slowly to backwash solids from the cloth media via vacuum pressure. Filtration is not disrupted during the cleaning process. Solids collected from the discs and settled at the bottom of the tank would be pumped towards the sludge drying beds for dewatering and disposal. The filtrate from DRAFT
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the disc filter tanks would then flow through UV disinfection units to inactivate the cells of microorganisms such as viruses and bacteria so that they are rendered harmless. After UV disinfection, the treated wastewater would then flow by gravity to an effluent pump station, which would pump the tertiary effluent to a designated groundwater recharge site.
6.4 JOINT-USE WWTP ALTERNATIVE
The Joint-use WWTP alternative would include a new WWTP which would treat wastewater from the MCAGCC and the City and would be located at or near the existing Mainside WWTP on the base. As mentioned previously, the MCAGCC is currently pursuing a design build contract to replace the existing Mainside WWTP with a new WWTP but is still in the initial stages of that process. This presents an opportunity for a new joint-use WWTP designed with capacity to treat wastewater from both the City and the Base.
This study assumes the new joint-use WWTP would have an average design capacity of 1.7 MGD expandable to 2.4 MGD, as described in Section 6.2. It is assumed that the joint-use WWTP would be owned, operated, and maintained by the MCAGCC with capital and O&M costs shared between the City and the MCAGCC.
For this alternative, as described in Section 5.4 and shown on Figure 5, two sewer lift stations and approximately 5.3 miles of pipelines, including two force main segments, and a gravity sewer segment, would be required to convey wastewater collected from the study area low point to the joint-use WWTP at the base. It is assumed that these lift stations and pipelines would be owned, operated, and maintained by the City with all capital and O&M costs borne by the City.
6.5 EVALUATION OF WWTP ALTERNATIVES
The section provides an evaluation of the City-only WWTP alternative and the joint-use WWTP alternative, including a comparison of costs and other key considerations.
6.5.1 Cost Comparison of WWTP Alternatives
Preliminary opinions of probable capital and operations & management/maintenance (O&M) costs and a life cycle cost comparison are presented herein for both WWTP alternatives. For simplicity, costs are based on the Stage 2 design capacities listed in Section 6.2. Stage 1 costs would be less for each alternative. Several other key assumptions used for estimating costs are presented below.
Assumptions:
For the joint-use WWTP alternative, an equal cost sharing split between the City and MCAGCC was assumed for both capital and O&M WWTP costs. An equal cost sharing split was assumed because initially, the City’s portion of the joint-use WWTP capacity (which includes City collection system Phases 1 and 2) would be approximately 41% (0.7 MGD of 1.7 MGD). However, after expansion of the plant (for the addition of City collection system phases 3 and 4), the City’s portion of the Stage 2 WWTP capacity would increase to approximately 58% (1.4 MGD of 2.4 MGD). DRAFT
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For the joint-use WWTP alternative, it is assumed that costs for special MCAGCC requirements for a new WWTP, such as increased security and anti-terrorism/anti-force features, would be paid for by the MCAGCC, and are therefore not reflected in the construction cost opinion.
6.5.1.1 WWTP Alternatives Capital Costs
Estimated WWTP capital costs for each alternative were approximated based on a similar size facility, the Hi-Desert Water District’s 1.0 MGD Wastewater Reclamation Facility which had a construction cost of approximately $30 million in 2017, with increases for inflation and the current bidding climate, and considerations for economies of scale in relation to the capacity of the WWTPs.
Table 20 below provides a preliminary opinion of probable construction cost for each WWTP alternative including the conveyance pipeline and lift stations that would only be required for the joint-use WWTP.
Refer to Appendix A for a cost breakdown. These are rough order of magnitude cost opinions for preliminary planning information only and do not include inflation for future cost planning. Each cost opinion includes a 30% construction contingency and a 15% allowance for design and construction management.
Table 20 – Preliminary Opinion of Probable Construction Cost for WWTP Alternatives – City Portion Alternative Estimated Length
of Conveyance Pipelines
Estimated Number of
Conveyance Lift Stations
Preliminary Cost Opinion1
(Million $)
1.4 MGD
City-Only WWTP NA NA $66 M
2.4MGD
Joint-Use WWTP 5.3 miles 2 $87 M
Notes:
1. For the joint-use WWTP alternative, the preliminary cost opinion only includes the City’s portion of the estimated total cost.
As shown, the joint-use alternative has a significantly higher capital cost, which is due the long pipeline and lift stations that would only be required for the joint-use WWTP.
6.5.1.2 WWTP Alternatives O&M Costs
Estimated O&M costs for each alternative were approximated based on interpolating known operating budgets of similarly sized facilities in Southern California, including the Hi-Desert Water District’s 1.0 MGD Wastewater Reclamation Facility and the City of Brawley’s 3.5 MGD Wastewater Treatment Plant, with increases for inflation and the current bidding climate. In general, WWTP O&M costs appear to correlate to the amount of flow for each facility, with some savings from economies of scale.
Table 21 below provides a preliminary opinion of probable annual O&M cost for each WWTP alternative including the O&M cost for the conveyance pipeline and lift stations which would only be required for the joint-use WWTP. These are rough order of magnitude cost opinions for preliminary planning information only and do not include i DRAFT nflation for future cost planning.
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Table 21 – Preliminary Opinion of Probable Annual O&M Costs for WWTP Alternatives – City Portion Alternative
WWTP
O&M Cost Opinion1
(Million $)
Pipeline and Lift Stations
1 O&M Cost Opinion
(Million $)
Total Annual O&M
Cost Opinion
(Million $)
1.4 MGD
City-Only WWTP $1.7 M NA $1.7 M
2.4MGD
Joint-Use WWTP $1.3 M $0.2 M $1.5 M
Notes:
1. For the joint-use WWTP alternative, the preliminary cost opinion only includes the City’s portion of the WWTP O&M cost.
2. Conveyance pipeline and lift stations required for the joint-use alternative. Does not include City collection system.
As shown, the joint-use alternative has a slightly lower estimated annual O&M cost for the City, due to economies of scale and cost sharing for a larger joint-use WWTP.
6.5.1.3 WWTP Alternatives Life Cycle Cost Comparison
The net present value (NPV) of each WWTP alternative was estimated for different life cycle periods as a comparative tool to evaluate the two alternatives. The estimated NPV was simply calculated using the estimated capital and O&M costs listed above in Sections 6.5.1.1 and 6.5.1.2, and with real discount rates obtained from Appendix C of the OMB Circular No. A-94 “Guidelines and Discount Rates for Benefit-Cost Analysis of Federal Programs”, updated in November 2020.
For a 25-year life cycle the calculated NPV was $111 million for the City-only WWTP alternative and $127 million for the joint-use WWTP alternative. For a 50-year life cycle the calculated NPV was $158 million for the City-only WWTP alternative and $168 million for the joint-use WWTP alternative. In both cases the City-only WWTP alternative has a lower estimated NPV, which shows that the potential annual O&M cost savings for the City, from a joint-use WWTP, are not enough to make up for the large capital cost difference between the two alternatives, which is due to the pipeline and lift stations required to convey City wastewater to the base.
A more detailed life cycle cost analysis including salvage values, repair, rehabilitation, and replacement costs was beyond the scope of this feasibility study but would unlikely alter the general conclusions above because of the large capital cost difference between the two alternatives.
Based on the various assumptions and preliminary design concepts presented in this Study, it is NV5’s opinion that the City-only WWTP alternative is preferable to the joint-use WWTP alterative for the City from a cost perspective. This conclusion could change if the large capital cost difference between the two alternatives could be reduced or mitigated, such as receiving grant funding for the conveyance pipeline and lift stations
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in an effort to consolidate systems, often a preference of regulatory agencies.
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6.5.2 Other WWTP Considerations
Other than cost, key factors considered for the two WWTP alternatives include reclaimed water, ownership, operations, coordination, operator availability, expansion capability, and environmental impact as discussed below.
Reclaimed Water:
Reclamation of the treated wastewater is important for both the City and the MCAGCC and both parties, which presents several issues for a joint-use WWTP. One issue would be the intended use of the reclaimed water. Currently the MCAGCC uses their disinfected secondary reclaimed water primarily for irrigation of their golf course and other restricted landscaped areas, whereas the City intends to use reclaimed water for groundwater recharge. Having separate intended uses would add complexity to regulatory and treatment requirements.
However, the main issue would be what to do with the City’s allotted portion of reclaimed water produced by the joint-use facility. Ideally, reclaimed water would be conveyed to a to a facility that could recharge one the groundwater aquifers used by the Twentynine Palms Water District (TPWD) which provides potable water service to the City. However, the MCAGCC is located within the boundary of the Mainside Subbasin, a groundwater subbasin not currently utilized by TPWD. Reclaimed water would therefore most likely have to be conveyed to a location that could recharge an aquifer used by TPWD in the adjacent Mesquite Lake Subbasin. Although the location of such a facility is unknown, the conveyance infrastructure for this situation would likely be substantial and may not be feasible for the City/TPWD. Alternatively, and assuming that recharge of the Mainside Subbasin would be beneficial to the MCAGCC, a framework of “water banking” could be established between the City and the MCAGCC, to assure the City and the TPWD benefit from reclaimed water use.
On the other hand, the assumed location (Site 1) for a City-only WWTP is located within the boundary of the Mesquite Lake Subbasin and close to the TPWD TP-1 production well which extracts groundwater from the Mesquite Lake Subbasin, which is then treated at the TPWD Fluoride Removal Water Treatment plant. Please refer to Figure 3-1 in the TPWD 2015 Urban Water Management Plan (UWMP) which shows the location of groundwater subbasins and the TPWD active wells.
As discussed in Section 7, additional hydrogeological investigations still need to be conducted before selecting a site, but assuming a groundwater recharge facility located close to a City-only WWTP is feasible, the City-only WWTP alternative would be preferable to a joint-use WWTP alternative from a groundwater recharge perspective. It would assure the City and the TPWD directly benefit from reclaimed water use without the need to develop a framework of “water banking”.
Ownership, Operation, and Coordination:
A joint-use WWTP would present challenges for both the City and the MCAGCC regarding ownership, operation, and coordination because there would be two agencies responsible for various aspects of wastewater treatment. Since the MCAGCC would own and operate the joint-use facility they would be responsible for assuring the treated effluent complies with all local, state, and federal regulations. DRAFT
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However, the City would be responsible for implementing policies for its own collection system and enforcing illicit discharges which could impact treatment. Detailed agreements and close coordination between the two agencies would be necessary to assure that the City’s wastewater meets the MCAGCC’s WWTP influent requirements, with periodic modifications over time as treatment regulations evolve. Agreements would also have to be made for cost sharing of O&M costs and capital improvements.
Continual close coordination will also be required between MCAGCC treatment operations and City collection system operations to ensure successful operation of the entire system and to prevent sewer overflows.
Operator Availability:
The availability of certified treatment system operators in the area is a concern. In this regard a jointuse WWTP would be advantageous for the City, since the MCAGCC would be responsible for WWTP operations. For a City-only WWTP alternative this issue could result in a premium for hiring new operators. A potential solution for this might be to share certified operators with another agency operating a wastewater treatment plant, such as the MCAGCC or the Hi Desert Water District in Yucca Valley. However, this would only work if the treatment plant types were similar as most operators are experts for a specific type of treatment process operation.
Expansion Capability:
Implementing the centralized collection system and a WWTP in multiple phases is a key aspect of this study due to the high estimated costs for a centralized wastewater collection system and also due to uncertainty regarding growth and development in the City. Therefore, a modular WWTP is recommended, and multiple expansions or plant upgrades are likely to occur in the future, particularly if growth in the City exceeds current forecasts.
With phased implementation in mind, the City-only WWTP alternative would be advantageous because the City would not have to rely on or negotiate with the MCAGCC for any expansion needs. The City would have sole discretion on when and how to expand a WWTP.
Environmental Impact:
The City-only alternative would be advantageous in that it would not require the construction of conveyance infrastructure to the MCAGCC, including approximately 5.3 miles of pipeline and two lift stations, which inherently would have some environmental impact. On the other hand, the City-only alternative might have more environmental impact at the actual WWTP site, since it would be at an undeveloped site, whereas the joint-use WWTP is likely to be at or adjacent to the existing Mainside WWTP, a developed site. However, for each alternative, environmental impact and cultural studies would need to be conducted to check for the presence of archaeological and historical sites, endangered species, and other potential environmental impacts. For the purposes of this study, environmental impact is not considered to be a discriminator between the two alternatives. DRAFT
Project Number 227521-0000132 NV5.COM | 7-1
7.0 GROUNDWATER RECHARGE SYSTEM
It is anticipated that the City’s allotted portion of reclaimed water (treated wastewater) from a centralized wastewater treatment plant (WWTP) will be used for groundwater recharge.
As an initial step, NV5 conducted a preliminary screening study of potential groundwater recharge sites in the City. A draft version of that study, dated January 26th, 2022, is included in Appendix B. As part of that preliminary study, NV5 evaluated criteria for screening sites including surface conditions (soil properties and surface geology), subsurface conditions (depth to groundwater, depth to crystalline basement, water quality, and hydrogeology), and location (distance to a potential WWTP, land use, land ownership, available land, and existing infrastructure). Using that broad screening criteria, three candidate sites were selected for further investigation: the Fluoride Site located off of Utah Trail, south of the Twentynine Palms Water District (TPWD) Fluoride Removal Water Treatment Plant, near the TPWD TP-1 production well; the Morongo Site located off of Morongo Road, north of Samarkand Drive and the Chocolate Drop residential area; and the Flood Site located south of Twentynine Palms Hwy (State Route 62), south of the Stater Bros. shopping plaza.
At each of the three sites, NV5 conducted field infiltrometer tests to determine the permeability (hydraulic conductivity) of surface soils. The field testing found that all three sites had surface soils with reasonable permeability and clay content with the Flood Site having the highest permeability results and the Morongo Site having the lowest permeability results. However, the field testing did not include complete subsurface investigations needed to fully evaluate the hydrogeology.
Based on the broad screening criteria and limited field testing, the preliminary screening study concluded that the Fluoride Site seemed like the best location for a recharge facility primarily due to its proximity to a potential City-only WWTP, but also due to the presence of favorable subsurface geological material, its location in the Mesquite Lake Subbasin, and the co-location of a TPWD well. The screening study also noted several potential issues for the Fluoride Site including the potential existence of an approximately 35-foot subsurface clay layer at 50 feet and that the Regional Water Quality Control Board could have an issue if the local groundwater levels interfere with leakage points of compliance for the evaporation ponds at the adjacent Fluoride Treatment Plant.
See Section 8 which provides a recommendation for continued development of the potential groundwater recharge system, including conducting a complete subsurface investigation.
DRAFT
Project Number 227521-0000132 NV5.COM
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DRAFT
Project Number 227521-0000132 NV5.COM | 8-1
8.0 CONCLUSIONS AND RECOMMENDATIONS
8.1 WASTEWATER COLLECTION SYSTEM RECOMMENDATIONS
NV5 recommends that the City move forward with preliminary design of Phase 1 and Phase 2 of the wastewater collection system as discussed in Section 5.5. As mentioned, a phased implementation of the wastewater collection system for the study area is suggested due to the substantial capital cost of the entire system. Phase 1 should be implemented first due to its proximity to the potential City-only WWTP sites and because Phase 1 trunk sewers are needed for other phases. Phase 1 will also allow for decommissioning of two existing package treatment plants and will serve two large dense military housing developments. Phase 2 would then be implemented to serve the core downtown area of the City, including two planned package treatment plants for Project Phoenix and the Wander Hotel.
Phased implementation will also provide the ability to collect data on actual wastewater flows from the initially constructed system, data that can be used to project future wastewater flows more accurately.
As mentioned previously, the projected wastewater flows included in this study are based on many variables and assumptions. These variables and assumptions should be further evaluated in the preliminary design phase, with a closer examination of the Phase 1 and Phase 2 areas.
The proposed trunk sewer system should be designed to accommodate projected wastewater flows from the Phase 1 and Phase 2 areas, but also with capacity for future phases 3, 4, and 5 considering the long useful life of pipelines and the ability to cost effectively rehabilitate gravity sewer pipelines with trenchless methods such as cured-in-place pipe and sliplining. The hydraulic modeling conducted in this study should be updated and used to design the system by evaluating both near-term and long-term flow scenarios using the pipeline design criteria provided in this study. Due to the significant difference between near-term and long-term flow projections, some pipelines could potentially have velocity issues initially. Pipelines with potential low flow issues should be identified and may need increased pipeline cleaning. The alternative, substantially increasing pipe slopes to accommodate low flows, would create an undesirably deep system and would likely result in additional sewer lift stations.
8.2 WASTEWATER TREATMENT PLANT RECOMMENDATIONS
NV5 recommends that the City move forward with preliminary design of the City-only Wastewater Treatment Plant (WWTP) alternative. This recommendation is given primarily due to the large capital cost that would be required to convey wastewater from the City to a joint-use WWTP at the MCAGCC, a conclusion consistent with previous studies including the 2008 Joint-use Study and the 2014 Wastewater Master Plan, and a result of the topography and the long distance between the core of the City and the MCAGCC, further exacerbated by current inflationary pressures and bidding climate.
The City-only WWTP alternative is also considered to be more favorable for the City in regard to reclaimed water, since a City-only WWTP would likely be much closer to a groundwater recharge facility that would benefit the Twentynine Palms Water District and the City. The anticipated multiple reclaimed water uses for the joint-use alternative could also add complexity to regulatory and treatment requirements. Furthermore, the City-only WWTP alternative would provide the City more flexibility for DRAFT
Project Number 227521-0000132 NV5.COM | 8-2
WWTP expansions, particularly considering the need implement the collection system in different phases and uncertainty regarding future growth and wastewater flows.
This feasibility study does not recommend a site for a City-only WWTP facility. However, based on the preliminary findings in this study, WWTP Site 1 initially appears to be preferable due to the additional collection system infrastructure and capital cost that would be required for WWTP Site 2 and because WWTP Site 1 is more likely to be located closer to a potential groundwater recharge facility, reducing the amount and cost of the groundwater recharge infrastructure. However, as mentioned previously, the potential sites should be further evaluated in the preliminary design phase, with consideration for environmental and cultural studies, public input, and a geotechnical investigation, all of which have not been completed yet.
NV5 recommends that the WWTP be a modular design and initially be designed for Phase 1 and Phase 2 wastewater flows (Stage 1) but be expandable to accommodate the future addition of Phase 3 and Phase 4 flows (Stage 2). This would be accomplished by designing multiple trains for some treatment process. Some of these trains would be constructed (Stage 1) and the others would be reserved for future expansion (Stage 2). Although the trunk sewer system would be designed for flow from all phases, the initial WWTP design would not account for Phase 5 flows, since the implementation of Phase 5 is beyond the planning horizon of this study and because the growth and projected wastewater flows of the less developed Phase 5 area is more uncertain. However, the City should periodically evaluate the entire system and implementation of future phases (3, 4, & 5) with master planning efforts.
As the City grows and as new developments are planned for, future phasing is likely to be modified and may look different than presented in this feasibility study.
8.3 GROUNDWATER RECHARGE SYSTEM RECOMMENDATIONS
For continued development of the potential groundwater recharge system, NV5 recommends investigating a potential fourth candidate site for a recharge facility that would be located closer to the City-only WWTP site, once a WWTP site is determined. Consideration of another recharge site is recommended to potentially reduce the amount and cost of reclaimed water conveyance infrastructure.
This fourth site should then be compared with the Fluoride Site discussed in Section 7 and then a complete subsurface investigation of one or both sites will need to be conducted to further evaluate the hydrogeology. The subsurface investigation, which would include a deep boring and laboratory testing of retrieved samples, will assist with preliminary design of the required infrastructure needed for a groundwater recharge facility including recharge basins and/or recharge wells.
DRAFT
Project Number 227521-0000132 NV5.COM
FIGURES
DRAFT
STUDY
AREA
MCAGCC
WWTP
UTAH TRAIL
AMBOY ROAD
TWENTYNINE PALMS HIGHWAY
TWO MILE ROAD
HATCH ROAD
MOJAVE ROAD
LERREAAVENUE
INDIAN TRAIL
BULL OI N MOUNTA NI ROAD
ADOBE ROAD
SUNR SI E ROAD
LEAR AVENUE
BASELINE ROAD
EL PASEO ROAD
WILSH RI E AVENUE
VALLE VISTA ROAD
CONDOR ROAD
NATIONAL PARK DRIVE
DESERT KNOLL AVENUE
MESQU TI E SPR NI GS ROAD
MORONGO ROAD
UTAH TRAIL
AMBOY ROAD
TWO MILE ROAD
UTAH TRAIL
ADOBE ROAD
AMBOY ROAD
VALLE VISTA ROAD
ADOBE ROAD
LEAR AVENUE LEAR AVENUE
TWO MILE ROAD
CONDOR ROAD
TWENTYNINE PALMS HIGHWAY
TWO MILE ROAD
INDIAN TRAIL
ADOBE ROAD
VALLE VISTA ROAD
TWENTYNINE PALMS HIGHWAY
BASELINE ROAD
Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community DATE SUBMITTED: MAR 2022 227521-0000132
JOB NUMBER
FIGURE
1 SCALE
15092 AVENUE OF SCIENCE, SUITE 200
SAN DIEGO, CA 92128
P: 858.385.0500 WWW.NV5.COM
CITY OF TWENTYNINE PALMS - WASTEWATER FEASIBILITY STUDY 1 inch = 7,500 feet
STUDY AREA
¹ Legend
Study Area Limits
City Limits
TPWD Service Area
MCAGCC
0 7,500 Feet
DRAFT
STUDY
AREA
UTAH TRAIL
ADOBE ROAD
AMBOY ROAD
TWO MILE ROAD
HATCH ROAD
TWENTYNINE PALMS HIGHWAY MOJAVE ROAD
BASELINE ROAD
LERREAAVENUE
INDIAN TRAIL
BULL OI N MOUNTA NI ROAD
LEAR AVENUE
CONDOR ROAD
MESQU TI E SPR NI GS ROAD
VALLE VISTA ROAD
NATIONAL PARK DRIVE
TWO MILE ROAD
TWENTYNINE PALMS HIGHWAY
UTAH TRAIL
DATE SUBMITTED: MAR 2022 227521-0000132
JOB NUMBER
FIGURE
2 SCALE
15092 AVENUE OF SCIENCE, SUITE 200
SAN DIEGO, CA 92128
P: 858.385.0500 WWW.NV5.COM
CITY OF TWENTYNINE PALMS - WASTEWATER FEASIBILITY STUDY 1 inch = 4,000 feet
STUDY AREA LAND USE
¹
Land Use Legend
Residential
Single-Family Residential-Estate - 2.5-acre minimum (RS-E) Single-Family Residential - 1 du/ac (RS-1)
Single-Family Residential - 2 du/ac (RS-2)
Single-Family Residential - 3 du/ac (RS-3)
Single-Family Residential - 4 du/ac (RS-4)
Multi-Family Residential - 8 du/ac (RM)
Multi-Family Residential-Specific Plan - 8 du/ac (RM-SP) High Density Residential - 20 du/ac (HDR)
Rural Living - 1-acre minimum (RL-1)
Rural Living - 2.5-acre minimum (RL-2.5)
Rural Living - 5-acre minimum (RL-5)
Open-Space Residential - 10-acre minimum (OSR)
Open Space Residential - 40 acre maximum (OSR-40)
Commercial
General Commercial (CG)
Neigborhood Commercial (CN)
Office Commercial (CO)
Tourist Commercial (CT)
Service Commercial (CS)
Industrial
Community Industrial (IC)
Public & Quasi Public
Military (M)
Public (P)
Other
Floodway (F)
Tribal Land
0 4,000 Feet
Legend
Study Area Limits
City Limits
DRAFT
RAYMOND DR
STUDY AREA
LOW POINT
1760'
MESA DR
ADOBE RD
HIGH POINT
1823'
AMBOY RD
LOW POINT
1799'
UTAH TRAIL
BAGDAD HWY
AMBOY RD
HIGH POINT
1809'
2600
2600
2600
2600
2560
2560
2560
2560
2360
2360
2360
2360
2360
2100
2100
2400
2400
2400
2640
2640
2640
2520
2520
2480
2480
1780
1780
2140
2140
2140
2420
2420
2340
2340
2340
2160
2160
2180
2180
2180 2180
2020
2020
2240
2240
2240
2960
2960
1800
1800
1800
1800
2260
2260
2280
2280
2200
2200
2920
2920
2160 2160
1760
1760
1760 1760
1820
1820
2240
2240
2800
2800
2840
2840
2880
2880
2960
2960
1840
1840
2280 2280
2240
2240
2160
2160
2680
2680
2280
2280
2280
1800
1800
1800
1800
1800
1800
1800
1820
1820
2260
2260
2120
2120
2380
2380
2840
2840
2300
2300
1820
1820
2260
2260
1760
1760
2280
2280
1800
1800
2320
2320
2320
2320
2080
2080
1900
1900
1740
1740
1780
1780
1840 1840
2120
2120
2120
1880
1880
2220
2220
1660
1660
2760
2760
2680
2680
2200
2200
2200
2720
2720
2720
1780
1780
1780
1780
1780
2440
2440
2440
2160
2160
2160
2160
2160
2160
2200
2200
2200
1740
1740
1740
2120
2120
2120
2120
1680
1680
1680
1680
2240
2240
2240
2240
2100
2100
2100
2100
2140
2140
2140
2140
1820
1820
1820
1820
1840
1840
1840
1860
1860
1860
1860
1860 1860
1700
1700
1700
1700
2020
2020
2020
2020
2040
2040
2040
2040
2040
1880
1880
1880
1880
1880
1720
1720
1720
1720
1720
2060
2060 2060
2060
2060
1900
1900
1900
1900
1900
1900
2080
2080
2080
2080 2080
2080
1980
1980
1980
1980
1980
1980
1920
1920
1920 1920
1920
1920
1920
2000
2000
2000
2000
2000
2000
2000
1960
1960
1960
1960
1960
1940
1940
1940
1940
1940
1940
1940
TWO MILE ROAD
SUNR SI E ROAD
VALLE VISTA ROAD
ADOBE ROAD
CONDOR ROAD DESERT KNOLL AVENUE
UTAH TRAIL
MESQU TI E SPR NI GS ROAD
LEAR AVENUE
TWENTYNINE PALMS HIGHWAY
AMBOY ROAD
UTAH TRAIL
LERREAAVENUE
BULL OI N MOUNTA NI ROAD
MOJAVE ROAD
TWO MILE ROAD
TWENTYNINE PALMS HIGHWAY TWENTYNINE PALMS HIGHWAY
BASELINE ROAD
HATCH ROAD
Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community DATE SUBMITTED: MAR 2022 227521-0000132
JOB NUMBER
FIGURE
3 SCALE
15092 AVENUE OF SCIENCE, SUITE 200
SAN DIEGO, CA 92128
P: 858.385.0500 WWW.NV5.COM
CITY OF TWENTYNINE PALMS - WASTEWATER FEASIBILITY STUDY 1 inch = 4,000 feet
STUDY AREA TOPOGRAPHY
¹ 0 4,000 Feet
Legend
FloodChannel
Drainage Boundary
Study Area Limits
City Limits
MCAGCC
DRAFT
ASSUMED
LOCATION OF
WWTP OR
LIFT STATION
MESA DR
ROCK AVE
MESQUITE SPRINGS RD
BUENA
BUENA VISTA DR
ADOBE RD ADOBE RD
DESERT KNOLL AVE
SAMARKAND DR
SAMARKAND DR
MESQUITE SPRINGS RD
SUN VALLEY DR S SLOPE DR
TWO MILE RD
JOE DAVIS
EL PASEO DR
VISTA DR UTAH TRAIL UTAH TRAIL
OLD DALE RD
UTAH TRAIL
DESERT KNOLL AVE
OLD DALE RD
SPLIT CACTUS DR
SULLIVAN RD
CLARE AVE
JUANITA DR CACTUS DR
MORONGO RD
ENCELIA AVE
RAYMOND DR
AMBOY RD
CALLE TODD LN
ADOBE RD
BASELINE RD
TWO MILE RD
LERREA AVE
EL PASEO RD
TWENTYNINE PALMS HIGHWAY TWENTYNINE PALMS HIGHWAY
HATCH RD
2060
2080
2060
2240
3040
2160
2180
2180
2640
2840
2760
2400
2100
2100
2680
2100
1820
2000
2220
2440
2800
2000
2040
2100
1820
2240
2000
3360
1800
1740
2080
2020
2480
2080
2160
2080
2400
2420
3120
2520
2040
2040
2920
2520
2180
2080
2760
2140
1820
3360
2760
2240
2440
2200
2680
2000
3200
2040
2480
1820
2420
2120 2440
2600
1820 2480
1800
2580
2120
1820
2120
2200
2220
2840
2560
2420
3160
2220
2220
2100
2020
1760
2440
3120
2200
2800
2100
2440
2080
3320
2180
1680
2080
2540
2040
2080
2160
2760
2520
2500
2140
2200
1740
2060
2480
2000
1740
2120
2080
2200
2440 2460
2400
3240
2080
3200
3280
2420
2400
2100
2720
1820
2040
2060
2040
3160
2160
2060
2120
2020
2400
1980
3120
2360
1980
1960
2180
3040
2020
1920
1940
2000
3080
1900
1860
2000
1820
1840
1880
1800
2160
2160
1700
2120
2920
1980
2140
2880
1780
1760
3000
2960
2320
2200
1740
1960
2280
2240
2040
2760 2800
2360
2840
1760
2280
2260
2300
2320
2380
2340
1800
2240
2080
2280
2220
2120
1720
2320
1780
2680
2200
2720
2360
2640
1820
2440
2160
2180
2160
2480
1840
1800
2520
2560
2400
2600
1860
2200
2120
2240
2080
2020
2100
1880
2140
2040
2060
1900
1980
1920
2000
1960
1940
DATE SUBMITTED: MAR 2022 227521-0000132
JOB NUMBER
FIGURE
4 SCALE
15092 AVENUE OF SCIENCE, SUITE 200
SAN DIEGO, CA 92128
P: 858.385.0500 WWW.NV5.COM
CITY OF TWENTYNINE PALMS - WASTEWATER FEASIBILITY STUDY 1 inch = 3,000 feet
PRELIMINARY TRUNK SEWER SYSTEM
¹
0 3,000 Feet
Legend
Package Treatment Plant
Proposed Lift Station
Proposed Force Main
Proposed Trunk Sewer
Study Area Limits
Proposed Sewer Basin
DRAFT
POTENTIAL
CITY-OWNED
LIFT STATION
LOCATION
1799'
1820
1800
1780
1840
1760
1780
DEL VALLE DR
DEL VALLE DR
ADOBE RD
6TH ST
5TH ST
4TH ST
3RD ST
1ST ST
2ND ST
7TH ST
DEL VALLE DR
(2) 10" 24" (2) 10"
MCAGCC
MAIN GATE
RAYMOND DR
ADOBE ROAD
HIGH POINT
1823'
POTENTIAL
CITY-OWNED
LIFT STATION
LOCATION
1762'
APPROXIMATE
LOW POINT
1760'
MCAGCC WWTP
WET WELL INLET
APPROXIMATELY
1765'
MESA DR
MESQUITE SPRINGS ROAD
DESERT KNOLL AVENUE
VALLE VISTA ROAD
CONDOR ROAD
ADOBE ROAD
AMBOY ROAD
INDIAN TRAIL
UTAH TRAIL
Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community DATE SUBMITTED: MAR 2022 227521-0000132
JOB NUMBER
FIGURE
5 SCALE
CITY OF TWENTYNINE PALMS - WASTEWATER FEASIBILITY STUDY 1 inch = 2,000 feet
PRELIMINARY CITY-MCAGCC PIPELINE 15092 AVENUE OF SCIENCE, SUITE 200 SAN DIEGO, CA 92128
P: 858.385.0500 WWW.NV5.COM
¹
0 2,000 Feet
DRAFT
Legend
Proposed Dual Force Main
Proposed Gravity Sewer
Study Area Limits
Drainage_Boundary
City Limits
MCAGCC
RAYMOND DR
MESA DR
ASSUMED
LOCATION OF
WWTP OR
LIFT STATION
UTAH TRAIL
BAGDAD HWY
SAMARKAND DR
AMBOY ROAD
EL PASEO DR
TWO MILE ROAD CRESTVIEW DR
SUNR SI E ROAD
VALLE VISTA ROAD
ADOBE ROAD
CONDOR ROAD DESERT KNOLL AVENUE
UTAH TRAIL
MESQU TI E SPR NI GS ROAD
LEAR AVENUE
TWENTYNINE PALMS HIGHWAY
AMBOY ROAD
UTAH TRAIL
LERREAAVENUE
BULL OI N MOUNTA NI ROAD
MOJAVE ROAD
TWO MILE ROAD
TWENTYNINE PALMS HIGHWAY TWENTYNINE PALMS HIGHWAY
BASELINE ROAD
HATCH ROAD
DATE SUBMITTED: MAR 2022 227521-0000132
JOB NUMBER
FIGURE
6 SCALE
15092 AVENUE OF SCIENCE, SUITE 200
SAN DIEGO, CA 92128
P: 858.385.0500 WWW.NV5.COM
CITY OF TWENTYNINE PALMS - WASTEWATER FEASIBILITY STUDY 1 inch = 4,000 feet
PROPOSED COLLECTION SYSTEM PHASES
Package Treatment Plant
Proposed Lift Station
Study Area Limits
Proposed Sewer Basin
Proposed Forcemain Sewer
Proposed Trunk Sewer
Phase 1
Phase 2
Phase 3
Phase 4
DRAFT
Phase 5 is all other
areas within the
study area limits
0 4,000 Feet
¹
Legend
ASSUMED
LOCATION OF
WWTP OR
LIFT STATION
TWENTYNINE PALMS HIGHWAY
EL PASEO RD
ADOBE RD
CALLE TODD LN
AMBOY RD
RAYMOND DR
SULLIVAN RD
CACTUS DR
SPLIT
OLD DALE RD
DESERT KNOLL AVE
UTAH TRAIL UTAH TRAIL
VISTA DR
JOE DAVIS DR
TWO MILE RD
SAMARKAND DR
DESERT KNOLL AVE
ADOBE RD ADOBE RD
BUENA VISTA DR
BUENA
MESQUITE SPRINGS RD
ROCK AVE
SAMARKAND DR
TWO MILE RD
AMBOY RD
18"
18"
15"
15"
15"
12" 12"
10"
8"
8"
8"
TWENTYNINE PALMS HIGHWAY
MESQUITE SPRINGS RD
21"
12"
15"
12"
8"
24"
DATE SUBMITTED: MAR 2022 227521-0000132
JOB NUMBER
FIGURE
7 SCALE
15092 AVENUE OF SCIENCE, SUITE 200
SAN DIEGO, CA 92128
P: 858.385.0500 WWW.NV5.COM
CITY OF TWENTYNINE PALMS - WASTEWATER FEASIBILITY STUDY 1 inch = 2,000 feet
PRELIMINARY PHASE 1 & PHASE 2 COLLECTION SYSTEM
¹ Legend
Study Area Limits
Package Treatment Plant
Proposed Trunk Sewer
Proposed 8" Collector Sewer
Phase 1 Area
Phase 2 Area
DRAFT
0 2,000 Feet
Note:
Existing collection sewers for package
treatment plants are not shown
FIGURE
SCALE
JOB NUMBER CITY OF TWENTYNINE PALMS - WASTEWATER FEASIBILTY STUDY 227521-0000132 DATE SUBMITTED: MAR 2022 DRAFT
PROPOSED CITY-ONLY WWTP LOCATIONS
8 1 inch = 800 feet
0 800 Feet
SELECTOR AERATION TANK (2ND STAGE) EMERGENCY STORAGE TANK
BLOWERS
DISC FILTERS
HEADWORKS
UV DISINFECTION
INFLUENT
PUMP
STATION
EFFLUENT
PUMP
STATION FUTURE EMERGENCY STORAGE TANK AERATION TANK (2ND STAGE) AERATION TANK (1ST STAGE) AERATION TANK (1ST STAGE)
CLARIFIER TANKS
DIGESTER TANK DIGESTER TANK FUTURE TREATMENT TANKS
FIGURE
SCALE
JOB NUMBER CITY OF TWENTYNINE PALMS - WASTEWATER FEASIBILTY STUDY 227521-0000132 DATE SUBMITTED: MAR 2022 DRAFT
0 40 Feet CONCEPTUAL WWTP LAYOUT DESIGN - SITE 1
9 1 inch = 40 feet
Project Number 227521-0000132 NV5.COM
APPENDIX A – PRELIMINARY OPINIONS OF PROBABLE
CONSTRUCTION COST
DRAFT
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED: FILE NAME:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 Mobilization / Overhead 1 LS $ 2,100,000 $ 2,100,000 9.9% 2 Install 8" PVC Gravity Sewer 35,000 LF $ 200 $ 7,000,000 32.9% 3 Install 12" PVC Gravity Sewer 5,300 LF $ 260 $ 1,378,000 6.5% 4 Install 15" PVC Gravity Sewer 6,400 LF $ 285 $ 1,824,000 8.6% 5 Install 15" PVC Gravity Sewer (15' to 20' Deep) 400 LF $ 428 $ 171,000 0.8% 6 Install 18" PVC Gravity Sewer 5,300 LF $ 335 $ 1,775,500 8.3% 7 Install 21" PVC Gravity Sewer 700 LF $ 370 $ 259,000 1.2% 8 Install 24" PVC Gravity Sewer 200 LF $ 425 $ 85,000 0.4% 9 Install 48" Dia. Manholes 110 EA $ 15,000 $ 1,650,000 7.8% 10 Install 60" Dia. Manholes 30 EA $ 20,000 $ 600,000 2.8% 11 Install Service Lateral (Public) 370 EA $ 5,000 $ 1,850,000 8.7% 12 Install Service Lateral (Private) / Abandon Septic 370 EA $ 7,000 $ 2,590,000 12.2% Subtotal $ 21,282,500
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 21,282,500
2. Assumes groundwater dewatering and rock excavation will not be required. CONSTRUCTION CONTINGENCY (30%) $ 6,384,750
3. Quantities of sewer & service laterals is based on existing parcels with active water use. DESIGN AND CM (15%) $ 3,192,375
4. Sewer unit prices include trench resurfacing.
TOTAL PROBABLE PROJECT COST $ 30,859,625
FOR BUDGET PURPOSES $ 31,000,000
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject to change to reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
PHASE 1 COLLECTION SYSTEM
1. Cost opinion for preliminary planning information only.
DRAFT Wastewater Feasibility Study - City Collection System Phase 1 227521-0000132.00 A. Schneider March 2022
J. Palacios
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400 DRAFT
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED: FILE NAME:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 Mobilization / Overhead 1 LS $ 4,000,000 $ 4,000,000 10.0% 2 Install 8" PVC Gravity Sewer 93,000 LF $ 200 $ 18,600,000 46.7% 3 Install 10" PVC Gravity Sewer 2,800 LF $ 215 $ 602,000 1.5% 4 Install 12" PVC Gravity Sewer 2,700 LF $ 260 $ 702,000 1.8% 5 Install 12" PVC Gravity Sewer (15' to 20' Deep) 2,300 LF $ 390 $ 897,000 2.2% 6 Install 15" PVC Gravity Sewer 2,200 LF $ 285 $ 627,000 1.6% 7 Install 15" PVC Gravity Sewer (15' to 20' Deep) 1,100 LF $ 428 $ 470,250 1.2% 11 Install 48" Dia. Manholes 270 EA $ 15,000 $ 4,050,000 10.2% 12 Install 60" Dia. Manholes 10 EA $ 20,000 $ 200,000 0.5% 13 Install Service Lateral (Public) 810 EA $ 5,000 $ 4,050,000 10.2% 14 Install Service Lateral (Private) / Abandon Septic 810 EA $ 7,000 $ 5,670,000 14.2% Subtotal $ 39,868,250
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 39,868,250
2. Assumes groundwater dewatering and rock excavation will not be required. CONSTRUCTION CONTINGENCY (30%) $ 11,960,475
3. Quantities of sewer & service laterals is based on existing parcels with active water use. DESIGN AND CM (15%) $ 5,980,238
4. Sewer unit prices include trench resurfacing.
TOTAL PROBABLE PROJECT COST $ 57,808,963
FOR BUDGET PURPOSES $ 58,000,000
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject to change to ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
PHASE 2 COLLECTION SYSTEM
1. Cost opinion for preliminary planning information only. reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
DRAFT Wastewater Feasibility Study - City Collection System Phase 2 227521-0000132.00 A. Schneider March 2022
J. Palacios
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400 DRAFT
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED: FILE NAME:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 Mobilization / Overhead 1 LS $ 5,700,000 $ 5,700,000 10.0% 2 Install 8" PVC Gravity Sewer 117,000 LF $ 200 $ 23,400,000 41.1% 3 Install 10" PVC Gravity Sewer 9,000 LF $ 215 $ 1,935,000 3.4% 4 Install 12" PVC Gravity Sewer 11,000 LF $ 260 $ 2,860,000 5.0% 5 Install 48" Dia. Manholes 370 EA $ 15,000 $ 5,550,000 9.7% 6 Install Service Lateral (Public) 1,460 EA $ 5,000 $ 7,300,000 12.8% 7 Install Service Lateral (Private) / Abandon Septic 1,460 EA $ 7,000 $ 10,220,000 17.9% Subtotal $ 56,965,000
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 56,965,000
2. Assumes groundwater dewatering and rock excavation will not be required. CONSTRUCTION CONTINGENCY (30%) $ 17,089,500
3. Quantities of sewer & service laterals is based on existing parcels with active water use. DESIGN AND CM (15%) $ 8,544,750
4. Sewer unit prices include trench resurfacing.
TOTAL PROBABLE PROJECT COST $ 82,599,250
FOR BUDGET PURPOSES $ 83,000,000
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject to change to reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
PHASE 3 COLLECTION SYSTEM
1. Cost opinion for preliminary planning information only. .
DRAFT Wastewater Feasibility Study - City Collection System Phase 3 227521-0000132.00 A. Schneider March 2022
J. Palacios
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400 DRAFT
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED: FILE NAME:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 Mobilization / Overhead 1 LS $ 3,500,000 $ 3,500,000 10.0% 2 Install 8" PVC Gravity Sewer 76,000 LF $ 200 $ 15,200,000 43.3% 3 Install 10" PVC Gravity Sewer 15,700 LF $ 215 $ 3,375,500 9.6% 4 Install 48" Dia. Manholes 250 EA $ 15,000 $ 3,750,000 10.7% 5 Install Service Lateral (Public) 770 EA $ 5,000 $ 3,850,000 11.0% 6 Install Service Lateral (Private) / Abandon Septic 770 EA $ 7,000 $ 5,390,000 15.4% Subtotal $ 35,065,500
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 35,065,500
2. Assumes groundwater dewatering and rock excavation will not be required. CONSTRUCTION CONTINGENCY (30%) $ 10,519,650
3. Quantities of sewer & service laterals is based on existing parcels with active water use. DESIGN AND CM (15%) $ 5,259,825
4. Sewer unit prices include trench resurfacing.
TOTAL PROBABLE PROJECT COST $ 50,844,975
FOR BUDGET PURPOSES $ 51,000,000
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject to change to ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
PHASE 4
1. Cost opinion for preliminary planning information only. . reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
DRAFT Wastewater Feasibility Study - City Collection System Phase 4 227521-0000132.00 A. Schneider March 2022
J. Palacios
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400 DRAFT
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED: FILE NAME:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 Mobilization / Overhead 1 LS $ 9,200,000 $ 9,200,000 10.0% 2 Install 8" PVC Gravity Sewer 204,000 LF $ 200 $ 40,800,000 44.5% 5 Install 15" PVC Gravity Sewer 8,300 LF $ 285 $ 2,365,500 2.6% 6 Install 48" Dia. Manholes 540 EA $ 15,000 $ 8,100,000 8.8% 7 Install 60" Dia. Manholes 20 EA $ 20,000 $ 400,000 0.4% 8 Install Service Lateral (Public) 1,570 EA $ 5,000 $ 7,850,000 8.6% 9 Install Service Lateral (Private) / Abandon Septic 1,570 EA $ 7,000 $ 10,990,000 12.0% 10 Install Packaged Pump Station 7 EA $ 1,000,000 $ 7,000,000 7.6% 11 Install 6" PVC Force Main 33,000 LF $ 150 $ 4,950,000 5.4% Subtotal $ 91,655,500
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 91,655,500
2. Assumes groundwater dewatering and rock excavation will not be required. CONSTRUCTION CONTINGENCY (30%) $ 27,496,650
5. Quantities of sewer & service laterals is based on existing parcels with active water use. DESIGN AND CM (15%) $ 13,748,325
4. Sewer unit prices include trench resurfacing.
5. Does not include potential collection system for study area sewer basin north of hilltop. TOTAL PROBABLE PROJECT COST $ 132,900,475 FOR BUDGET PURPOSES $ 133,000,000
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject to change to ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
PHASE 5
1. Cost opinion for preliminary planning information only. . reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
DRAFT Wastewater Feasibility Study - City Collection System Phase 5 227521-0000132.00 A. Schneider March 2022
J. Palacios
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400 DRAFT
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED: FILE NAME:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 1.4 MGD WWTP 1 LS $ 45,000,000 $ 45,000,000 100.0%
Subtotal $ 45,000,000
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 45,000,000
CONSTRUCTION CONTINGENCY (30%) $ 13,500,000
DESIGN AND CM (15%) $ 6,750,000
TOTAL PROBABLE PROJECT COST $ 65,250,000
FOR BUDGET PURPOSES $ 66,000,000
This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject to change to reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
CITY-ONLY WWTP
1. Cost opinion for preliminary planning information only.
2. Groundwater dewatering and rock excavation will not be required.
3. Does not include groundwater recharge system.
DRAFT Wastewater Feasibility Study - City-Owned WWTP Alternative 227521-0000132.00 A. Schneider March 2022
J. Palacios
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400 DRAFT
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL
PROJECT: PROJECT #
CLIENT: City of Twentynine Palms EST. BY: DATE:
TYPE OF EST. Preliminary (0% Design) CHECKED: FILE NAME:
Item No. DESCRIPTION QUANTITY UNIT UNIT PRICE COST SUBTOTAL SUBTOTAL % 1 1.4 MGD Lift Station 2 LS $ 4,500,000 $ 9,000,000 100.0% Subtotal $ 9,000,000
2 Mobilization / Overhead 1 LS $ 1,400,000 $ 1,400,000 10.0% 3 Install Dual 10" PVC Force Main 16,000 LF $ 400 $ 6,400,000 45.8% 4 Install 24" PVC Gravity Sewer 12,000 LF $ 400 $ 4,800,000 34.3% 7 Install New 60" Manhole 25 EA $ 20,000 $ 500,000 3.6% 8 Remove and Replace AC Pavement (4" Thick) 1,976 TON $ 300 $ 592,900 4.2% 9 1.5" Grind and Overlay 1,176 SF $ 240 $ 282,333 2.0%
Subtotal $ 13,975,230
10 City Portion (50%) of 2.4 MGD WWTP 1 LS $ 37,000,000 $ 37,000,000 100.0% Subtotal $ 37,000,000
Assumptions/Notes:
CONSTRUCTION SUBTOTAL COST $ 59,975,230
CONSTRUCTION CONTINGENCY (30%) $ 17,992,569
DESIGN AND CM (15%) $ 8,996,285
4. Assumes a cost sharing split of 50% for joint-use WWTP
5. Does not account for special MCAGCC requirements that might be required such as: TOTAL PROBABLE PROJECT COST $ 86,964,084 increased security and anti-terrorism/anti-force features FOR BUDGET PURPOSES $ 87,000,000 This opinion is limited to our best judgment of anticipated construction costs at the current stage of project development and is not a proposal or guarantee. All amounts are subject to change to reflect such items as changes in cost of labor or materials, contractor's methods of determining prices, project revisions, and general marketing conditions.
DRAFT Wastewater Feasibility Study - Joint-Use WWTP Alternative 227521-0000132.00 A. Schneider March 2022
J. Palacios
ENGINEER'S OPINION OF PROBABLE COST (0% DESIGN)
CITY-OWNED LIFT STATIONS
JOINT-USE WWTP
CITY TO MCAGCC PIPELINE
1. Cost opinion for preliminary planning information only.
2. Groundwater dewatering and rock excavation will not be required.
3. Does not include groundwater recharge system.
15092 Avenue of Science, Suite 200 | San Diego, CA 92128 | www.NV5.com | Office 858.385.0500 | Fax 858.385.0400 DRAFT
CONSTRUCTION QUALITY ASSURANCE - INFRASTRUCTURE - ENERGY - PROGRAM MANAGEMENT - ENVIRONMENTAL
Project Number 227521-0000132 NV5.COM
APPENDIX B – DRAFT PRELIMINARY SCREENING STUDY OF
GROUNDWATER RECHARGE SITES
DRAFT
Preliminary Screening Study
of Groundwater Recharge Sites,
Twentynine Palms, California
by:
NV5, Inc.
Phoenix, Arizona
for:
City of Twentynine Palms
Twentynine Palms,
California January 26th 2022
DRAFT
DRAFT
Table of Contents
1 INTRODUCTION....................................................................................................................... 3
1.1. Background....................................................................................................................... 3
1.2. Local Conditions............................................................................................................... 3 2 Preliminary Screening of Sites................................................................................................ 5
2.1.1. Surface soils .............................................................................................................. 6
2.1.2. Surface geology......................................................................................................... 8
2.2. Subsurface Conditions.................................................................................................... 12
2.2.1. Depth to groundwater............................................................................................ 12
2.2.2. Depth to crystalline basement................................................................................ 14
2.2.3. Water quality .......................................................................................................... 14
2.2.4. Hydrogeology.......................................................................................................... 16
2.3. Location.......................................................................................................................... 18
2.3.1. Distance to proposed WWTP.................................................................................. 18
2.3.2. Land use .................................................................................................................. 18
2.3.3. Land ownership....................................................................................................... 18
2.3.4. Size .......................................................................................................................... 19
2.3.5. Existing infrastructure............................................................................................. 19
2.3.6. Areas of preservation or open space...................................................................... 21 3 Candidate Sites ..................................................................................................................... 21
3.1. Field Work ...................................................................................................................... 21
3.1.1. Fluoride Site ............................................................................................................ 23
3.1.2. Morongo Site .......................................................................................................... 23
3.1.3. Flood Site ................................................................................................................ 24
3.1.4. Summary of Field Testing........................................................................................ 24
3.2. Application of Criteria .................................................................................................... 24 4 Conclusion and Recommendation........................................................................................ 28 5 References ............................................................................................................................ DRAFT31
Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California Figures
Figure 1.1 - - Map of locations cited in report............................................................................................................... 4 Figure 2- - Local soils data retrieved from NRCS SSURGO/STATSGO2 data series. ....................................................... 9 Figure 2.2 - - Local geology as generalized from Riley and Worts (1952), Dibblee (1968), and TPWD (2016)............11 Figure 2.3 - - Local groundwater basins from CalDWR 2021 and TPWD (2016)..........................................................13 Figure 2.4 - - Local depth to groundwater. Data from Dick and Kjos (2016)...............................................................15 Figure 6 - - Local depth to bedrock. Reproduction of figure from Li and Martin (2011). ............................................17 Figure 7 - - Local land ownership. Data from San Bernardino County Planning Department (2021)..........................20 Figure 3.1- -Location of three sites examined during infiltration measurement field work .......................................22 Figure 3.2 - - Detail map of Fluoride Site. ....................................................................................................................25 Figure 3.3 - - Detail map of Morongo Site. ..................................................................................................................26 Figure 3.4 - - Detail map of Flood Site. ........................................................................................................................27 Tables
Table 3.1 - - Criteria data used for the three sites.......................................................................................................29 Table 3.2 - - Ranking of the three sites........................................................................................................................30 Attachments (follows Section 5)
Attachment 1 - - Technical Memorandum on Infiltration Measurements.
Attachment 2 - - Well Completion Report for TPWD Well TP-1 DRAFT
Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California 1 INTRODUCTION
1.1. Background
This screening investigation of potential recharge sites near Twentynine Palms, California was contracted to NV5, Inc. by the City of Twentynine Palms (City) as part of a larger, wastewaterdesign, feasibility study in 2021 (Figure 1.1). The City lies in the Morongo Basin and similar to other developed parts of the Mojave Desert, groundwater levels are declining. The City is intent upon recycling treated wastewater, if practicable (TPWD 2016). NV5 was tasked under the feasibility study to recommend a site for the location of a surface-spreading infiltration basin to use for recharge of the regional groundwater system treated effluent.
Selection of a successful groundwater recharge basin requires the evaluation of multiple physical factors and criteria. Ideally, the selection would be entirely based upon the ability of the upper geological layers of the target area to accept infiltrated surface water and to allow gravitational and other site conditions to effect transmission of the water through percolation to the target aquifer. Despite this, there are additional variables that need to be considered, including the location of the basin, relative to the treatment facility, the availability and value of land, groundwater rights issues, water quality concerns, and cost.
NV5 examined each of these issues and developed a screening strategy using weighted factors appropriate to the importance of that concern. This analysis resulted in a candidate site that will be advanced to further and more detailed analysis.
1.2. Local Conditions
In 2014, the City and Twentynine Palms Water District (TPWD) commissioned a study of the wastewater option best suited to projected growth and revenue availability. At that time, dispersed sewer systems, primarily septic tanks, were the most common method for urban sewage disposal. The need for a centralized system was felt by City leadership, using a facility either owned by the City or shared with Marine Corp Air Ground Combat Station-Twentynine Palms (MCAGCC), located approximately 6.4 miles north of City Hall.
The recommendation of the report and plan was to focus on a 9.3-million-gallon per day (MGD) wastewater treatment plant (WWTP) central to the metropolitan area that could use City streets for collection alignments. The 2014 report did not recommend a joint-use facility with MCAGCC. Integration of these objectives with a water resource management plan, yet to be written, was also recommended (City and TPWD 2014).
page 3
DRAFT
Twentynine Palms Water District
Fluoride Removal Facility
Marine Corp Air Ground Combat StationTwentynine Palms BULLION MOUNTAINS
LITTLE SAN BERNARDINO MOUNTAINS
2 Mile Road
Adobe Road
Utah Trail
Amboy Road
Twentynine Palms Highway
Oasis of Mara
Twentynine Palms
City Hall
Fortynine Palms Canyon
Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Report Figures\Figure 1-1.mxd ¯ 8,100
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
Figure 1.1 - - Map of locations cited in report
page 4
DRAFT
Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California Subsequently, TPWD developed the anticipated water resource management plan (TPWD 2016). Under California Water Code (CWC) sections 10610 through 10657, and the Urban Water Management Planning Act (UWMP Act) of 1983, such a plan is required of an urban water supplier. From a water supply reliability analysis, the TPWD determined that it has adequate supplies to meet demands during normal, single-dry, and multiple-dry years throughout the 20- year planning period. Despite this, other State regulations require that a groundwater management plan be written and the Sustainable Groundwater Management Act (SGMA) passed in 2014 and amended in 2015, requires management of high-priority, local groundwater sources in California. The groundwater basins supplying TPWD are all considered low priority. under SGMA.
Despite this, the water resource management plan includes many suggestions and practices to extend groundwater resources as long as possible (TPWD 2016). These include conservation and stormwater recharge. Because there is no central WWTP available, effluent recharge (called “recycled water” in the report) was not considered.
Recharge of groundwater with treated effluent is uncommon but not unknown in the desert regions of San Bernardino County. Although most of the recharge facilities in the region use imported water from the Mojave Water Agency, Victor Valley Wastewater Reclamation Authority (VVWRA) recharges treated effluent along the Mojave River bed (Stamos, et al 2001).
The City of Barstow recharges wastewater and Mojave Water Agency imports and recharges 2,800 acre-ft of treated wastewater from the Lake Arrowhead and Big Bear areas (MWA 2020). 2 Preliminary Screening of Sites
At this level of study, a screening study must make a number of assumptions in order to make progress. The first assumption was in the location and management of the WWTP. Although previous investigations concluded that an MCAGCC joint-use facility was not feasible, the need for additional base capacity remains and the City requested that this location needs to be considered.
Sites in and around the Project Area of the current wastewater feasibility study, including MCAGCC were chosen for preliminary screening. The list of criteria were taken from Milczarek and co-authors (2014) and included:
Surface Conditions
• Soil Properties
page 5
DRAFT
Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California • Surface Geology
Subsurface Conditions
• Depth to Basement.
• Depth to Groundwater.
• Groundwater quality.
• Hydrogeology.
Location.
• Distance to proposed city-owned WWTP
• Distance to MCAGCC
• Land use
• Land ownership
• Existing infrastructure
• Recharged groundwater basin
• Areas of preservation or open space
Each of these criteria was applied to the list of available sites and three were chosen for ranking. Based upon infrastructure cost decisions of the City, the Area of Interest for the screening study was confined to a 1-mile “bubble” surrounding the City limits (Figure 2.1).
2.1. Surface conditions
Surface conditions criteria include the physical and geological description of soil and active alluvial sediment data.
2.1.1. Surface soils
Soil survey data was extracted from the regional descriptive data cataloged by the Natural Resource Conservation Service (NRCS) of the U.S. Department of Agriculture. NRCS soil data is found in the National Soil Survey, a compilation of field data mapped by NRCS soil scientists in each of the fifty states on a county-wide and Indian reservation basis. Currently, the data is stored digitally and available as downloadable, GIS data, or the SSURGO/STATSGO2 data series.
The soil survey data of interest used was the Mojave Desert Area, West Central Part (Figure
2.2).
Each of the area soil series was assigned a generalized set of physical parameters over the survey area by NRCS staff scientists. GIS covers of soil series spatial extent were used to map saturated hydraulic conductivity (Ksat) and clay content (%) over the area of interest. Ksat is a page 6
DRAFT
Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Report Figures\Figure 2-1 - Site Map.mxd LEGEND
City of Twentynine Palms 2-Mile Buffer ¯ 15,000
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
Figure 2.1 - - Limits of screening study
page 7
DRAFT
Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California parameter widely used to indicate the rate of infiltration of surface spread water. Clay percentage in the soil represents the presence of fine particles that might inhibit porous-media flow of water in the subsurface. These two estimated factors were used as criteria to select the candidate sites.
2.1.2. Surface geology
Surface geological maps were used to qualitatively extrapolate infiltration properties over a wider area and be used to interpret morphological features, such as ancestral streambeds that might offer abundant coarse-grained substrate. Alternatively, playas or other lakebed features would be expected to be underlain by finer-grained materials (Figure 2.3).
GIS geological maps were acquired from the USGS California Water Science Center. The USGS has done considerable work on the hydrogeology and geology of the area in support of the MCAGCC. Geological data was also extracted from the California Department of Conservation, California Geological Survey regional geologic map of the San Bernardino 30’ x 60’ sheet (1:250,000 scale). In addition, the geological sections of several hydrogeological reports were used, particularly, TPWD (2016).
The surface geology of the Twentynine Palms region is dominated by fault-bounded uplift of the surrounding mountains relative to the central basin. Riley and Worts (1952) defined the Mesquite Basin as a structural depression receiving sediment from the Little San Bernardino Mountains to the south, the San Bernardino Mountains to the west, and the Bullion Mountains to the east. The basin was part of a series of structural depressions that aligned in a northwesterly direction.
Bedrock geological units are exposed in all three of these bounding ranges and in smaller fault blocks aligned with larger mountains. The units were primarily composed of Jurassic granitics and Precambrian crystalline rocks. Riley and Worts (1952) assumed a Precambrian age for the older granitics, including gabbro-diorite, gneiss, granite, and monzonitic porphyry; however, age dating by Lanphere (1964) and mapping by Dibblee (1968) suggested that only the gneiss was Precambrian and distinguished an older Mesozoic granitic phase. Lying unconformably upon the crystalline rocks is a series of late Tertiary continental sedimentary rocks, chiefly sandstones and conglomerates, dipping to the east.
The youngest units are exposed extensively across the study area and are the principal target of this study. These Quaternary deposits include alluvial fan sands, silts, clays, and cobbles, extending from the mountain fronts to the basin axis and culminating in playa lake deposits. page 8
DRAFT
s1135
s1009
s1032
s1130
s1126
s1032
s1130
s1134
s1134
s1130
s1038
s1126
s1130
s1142
s1142
Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Report Figures\Figure 2-2 - Soils Map.mxd LEGEND
s1009 Ramona-Hanford-Greenfield
s1032 Wasco-Helendale-Bryman
s1038 Playas
s1126 Tecopa-Rock outcrop-Lithic Torriorthents
s1130 Rock outcrop-Lithic Torriorthents
s1134 Trigger-Rock outcrop-Calvista
s1135 Dune land-Cajon
s1142 Nickel-Bitter-Arizo ¯ 18,000
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
Figure 2.2 - - Local soils data retrieved from NRCS SSURGO/STATSGO2 data series. page 9
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Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California Dibblee (1968) separates several Quaternary deposits representing unique depositional facies.
An older alluvial unit fans outward across the city from Fortynine Palms Canyon, the main drainage feature, in a northeasterly direction. Lying on top of these deposits in the northeastern edge of the urban area is a younger alluvial unit, distinguished by a higher proportion of fine-grained sand and silt. Further to the northeast, this unit grades into windblown sand. The significance of these Quaternary units and their location will be developed in Section 3.
Structural elements clearly are controlling groundwater recharge and storage in the Area of Interest (Riley and Worts 1952, Li and Martin 2011, TPWD 2016)(Figure 2.3). At the northern boundary of the Mesquite Basin, a structural high (arch) in bedrock is used by Riley and Worts (1952) to limit the extent of groundwater flow. On the east, these authors conclude that the north-northeast trending Mesquite Lake Fault forms a groundwater flow boundary. On the south, the Pinto Mountain Fault has the largest effect of groundwater dynamics.
The Mesquite Lake Fault as a regionally extensive fault, exhibiting right-lateral, slip-strike motion (SCEDC 2013). Paleoseismic data suggest up to four prehistoric earthquakes since the latest Pleistocene, with three large, Holocene surface-rupturing events (Madden, et al 2006).
The Pinto Mountain Fault, exhibiting left-lateral, strike-slip motion, and an offshoot of it (Oasis Fault) have juxtaposed the Precambrian to Mesozoic crystalline rocks relative to the late Tertiary basin-filling sediments of the north (Riley and Worts 1952). Movement on the Oasis Fault is inferred from geomorphic evidence to have occurred five times since 13,600 years before present, the latest at 1700 years before present. The contrast in water-bearing properties between these units defines the southern boundary of the basin.
California Department of Water Resources (CalDWR) has designated two groundwater basins that cover the Area of Interest (CalDWR 2021), separated by the east-west running Oasis Fault, the Twentynine Palms Valley Groundwater Basin (DWR# 7-10), which extends north of the fault and the Joshua Tree Groundwater Basin (DWR#7-62), which lies to the south. Within the Twentynine Palms Valley Groundwater Basin, two subbasins are distinguished, the Main Subbasin which extends north from the Pinto Mountain Fault and which is separated from the Mesquite Lake Subbasin on the west by the Mesquite Fault (Riley and Worts 1952, Li and Martin 2011, TPWD 2016) (Figure 2.4).
Within the Joshua Tree Basin, three subbasins are defined between the Oasis Fault and the surface exposure of the crystalline rock (TPWD 2016). The Indian Cove Subbasin extends from the western edge of the Area of Interest eastward to a subsurface narrowing of the Tertiary page 10
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PINTO MOUNTAIN FAULT
PINTO MOUNTAIN FAULT
MESQUITE FAULT
OASIS FAULT
OASIS FAULT
BULLION MOUNTAINS
LITTLE SAN BERNARDINO MOUNTAINS LITTLE SAN BERNARDINO MOUNTAINS Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Report Figures\Figure 2-3 - Geology.mxd LEGEND
Quaternary Faults
alluvium
dune sand
gabbro
gneiss
granodiorite
intermediate volcanic rock
plutonic rock (phaneritic)
schist
City of Twentynine Palms Outline
2-Mile Buffer ¯ 18,000
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community"Preliminary integrated geologic map databases for the United States". http://pubs.usgs.gov/of/2005/1305 Original source of this data was the Arizona Geological Survey. USGS Geologic Hazards Science Center Golden, CO U.S. Quaternary Faults https://www.arcgis.com/apps/webappviewer/index.html?id=5a6038b3a1684561a9b0aadf88412fcf Figure 2.3 - - Local geology as generalized from Riley and Worts (1952), Dibblee (1968), and TPWD (2016)
page 11
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Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California sediments (TPWD 2016). The Fortynine Palms Subsection extends from this boundary westward to a boundary with the Eastern Subbasin, where the constriction between bedrock and the Oasis Fault widens. The Eastern Subbasin extend easterly to the end of the Area of Interest.
2.2. Subsurface Conditions
There are several primary data sets that have been used in the screening study. These are depth to groundwater, depth to basement, and groundwater quality.
2.2.1. Depth to groundwater
Depth to groundwater is used to estimate the thickness of the unsaturated zone. Presumably, introduced effluent will infiltrate and saturate this zone and therefore a greater thickness of unsaturated media indicates greater storage capacity. Shallow groundwater levels could indicate that recharged water will locally “daylight,” causing stability problems.
The USGS has monitored and interpreted water levels near MCAGCC for many years (Riley and Worts 1952, Schaefer 1978, Akers, 1986, Stamos et al 2004, 2007, 2009, Li and Martin 2011, Dick and Kjos 2016). In addition, the City has collected groundwater data for specific studies that was added to the analysis (TPWD 2016).
Groundwater elevations for this study were acquired from Dick and Kjos (2016). Depth to groundwater contours were mapped by subtracting topographic elevation from these data (Figure 2.5). These calculations suggest that the maximum depth to groundwater, <300 feet below ground surface (ft bgs), probably lies east of the Mesquite Fault, in the Main Subbasin. A second maximum occurs at the west side of the Area of Interest in the Mesquite Lake Subbasin.
The most shallow groundwater is found at the eastern edge of the city center, west of Utah Trail. For example, a set of TPWD wells near the Fluoride Treatment Facility produces a depth to water of 50 to 62 ft bgs.
These data suggest that there is a groundwater elevation maximum at the southern boundary of both basins (Figure 2.5) (TPWD 2016). A groundwater elevation greater than 2400 feet above sea level (ft asl) is measured at TPWD supply wells in the Indian Cove Subbasin. A second high is found at the eastern boundary of the Mesquite Subbasin (TPWD 2016). Groundwater elevations in wells in that part of the Area of Interest exceed 1850 ft asl. The lowest elevations are just west of MCAGCC at about 1760 ft asl.
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Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Report Figures\Figure 2-4 - Groundwater Subbasins.mxd Figure 2.4 - - Local groundwater basins from CalDWR 2021 and TPWD (2016). page 13 DRAFT
Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California In 1993, TPWD drilled a 1,250-foot-deep monitoring well (TP-1) in the vicinity (Amboy Road and Utah Trail) of the proposed WWTP (Attachment 2). The well was screened from 350 to 440 and from 460 to 620 feet below surface (fbs). Static water was measured at 50 fbs. See section 2.2.4 for a discussion of the probable source of the groundwater sampled by this well.
2.2.2. Depth to crystalline basement
Depth to the Mesozoic and Precambrian crystalline rock is used to establish the relative thickness of potentially water-bearing formations in the subsurface among candidate sites.
Although some water is certainly available in the fractured granitic rocks, the difference in yield is great enough to preclude them as the location of an effective aquifer. Geological cross sections developed by Riley and Worts (1952) and Dibblee (1968) indicate a range in depth to bedrock from 0 ft bgs along the southern boundary of the Area, to over 2000 ft bgs adjacent to the Mesquite Lake Fault. Subsequent gravity surveys by Roberts and co-workers (2002) allowed Li and Martin (2011) to infer depth to basement that exceeded 16,000 feet in the northeastern part of the Area of Interest (Figure 2.6); however, basement rock depth across most of the Area ranges from 0 to 4000 ft bgs .
2.2.3. Water quality
Water quality is dependent upon the depth, screen position, and location of monitoring wells.
In general, it is not a critical determinant in siting a recharge area, unless a specific area or plume of contamination exists in the subsurface.
It is generally recognized in the Area of Interest that the only groundwater components of concern are nitrates from septic tank discharge and naturally occurring high fluoride and arsenic concentrations. Presumably, nitrate contamination would be reduced across the city subsurface as residents switched from septic tank use to the proposed City sewer system.
Isolated areas of remnant nitrate contamination would remain, as would residential areas not connected to the City system. Currently, the average nitrate concentration in the Mesquite Lake Subbbasin is 3.5 mg/L and in the three subbasins south of the Oasis Fault, 6.5-11.3 mg/L, well below the maximum contamination level (MCL) of 45 mg/L (TPWD 2016).
Fluoride exceedances are common in shallow Western aquifers. Fluoride concentrations in the Indian Cove, Fortynine Palms and Eastern Subbasins generally average 1.3 to 2.7 mg/L, while the Mesquite Lake Subbasin averages more than twice that at 5.9 mg/L, above the MCL of 4.0 mg/L (TPWD 2016). The difference probably reflects the presumed recharge source of the two page 14
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200
300
400
100
100
300
300
400
200
200
300
200
300
100
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MojaveWater
Groundwater Direction
Quaternary Faults
Depth to GW
City of Twentynine Palms Outline
2-Mile Buffer ¯ 18,000
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
Figure 2.5 - - Local depth to groundwater. Data from Dick and Kjos (2016) page 15
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Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California basins, with the Mesquite Lake Subbasin water leaching fluoride salts from buried evaporite deposits (Robertson 1991).
Arsenic concentrations show the opposite relationship between the subbasins. The Indian Cove, Fortynine Palms and Eastern Subbasins average 1.8 to 5.7 µg/L of arsenic and the Mesquite Lake Subbasin averages 2.4 µg/L. The MCL for arsenic is 10 µg/L.
All of the water introduced by the recharge system would be treated to drinking water standards, as set by the California State Water Resources Control Board, Indirect Potable Reuse program. In that sense, the recharged water would be of better quality than the existing groundwater. In any case, there would be little difference in the location of the recharge basin for water quality concerns.
2.2.4. Hydrogeology
These distributions of elevations suggest that groundwater flow is principally from west to east in both basins in the west and from southeast to northwest on the eastside, mimicking the topographic gradient and structural discontinuities. This was also the conclusion of TPWD (2016). These groundwater dynamics would also suggest two principal recharge areas for the greater basin: the western bounding ranges of the San Bernardino Mountains and the northern margin of the Little San Bernardino Mountains. In fact, several springs emerge from the northern trending canyons of the Little San Bernardino Mountains. Springs are reported from Fortynine Palms Canyon, in addition to the historically flowing Oasis of Mara in the Eastern Subbasin (Cadena 2014).
The recognized water-bearing formations in the subsurface have emerged from deep borings that have been constructed across the area and the recognition of these formations by the USGS and other hydrogeological investigations (Li and Martin 2011). Li and Martin define three water-bearing formations in the Project are subsurface. The Upper system is hosted by the younger Quaternary, fan-deposited sands and gravel (Qtf2, Li and Martin 2011). It ranges from 250 to zero feet in saturated thickness, thinning from west to east. Underlying the Upper system are an older set of Quaternary (Qtf1, Li and Martin 2011) fan-deposited units that contain intercalated clay layers. These beds make up the Middle unit of the regional aquifer.
Saturated thicknesses of the Middle unit range from 100 feet in the north basin to 500 feet in the southeast direction. The Lower unit is found within the poorly-sorted sands, gravel, silt, and clay of the Tertiary unit (Ts, Li and Martin 2011).
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Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Report Figures\Figure 2-6 - Depth to Basement Li&Martin2011.mxd Service Layer Credits: Li and Martin 2011
¯ 18,000
Feet
City of Twentynine Palms Outline
2-Mile Buffer
Figure 2.6 - - Local depth to bedrock. Reproduction of figure from Li and Martin (2011) page 17
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Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California The permeability of the Middle unit is much lower than Upper unit. Despite this, most watersupply wells in the region are screened in coarser-grained, water-bearing beds of the Middle unit. In some parts of the Project area, recharge to the Middle unit may be acting as an aquatard, restricting downward movement of surface infiltration.
As discussed in Section 2.2.1, monitoring well TP-1 (Attachment 2) was logged as ‘sand’ or ‘sand and clay’ in the driller’s record from 0 to 65 fbs. At 65 fbs, the log records ‘clay,’ which extends down to 100 fbs. Given the stratigraphic data reported by Li and Martin (2011), the upper 65 feet of the boring probably encountered Qtf2 and the Upper unit of the local aquifer. The clay encountered between 65 and 100 fbs is probably the aquitard that marks the top of Qtf1 and the Middle unit. The Middle unit in the southeast corner of the Mesquite Subbasin is reported to be approximately 500 feet thick (Li and Martin 2011). Thus, it is likely that the screened interval is primarily sampling groundwater extracted from the Middle aquifer, although the integrity of the upper confining clay is unknown.
2.3. Location
Location takes in all of the factors that would make the recharge basins economically and operationally feasible under City financial and administrative constraints.
2.3.1. Distance to proposed WWTP
The location of the proposed WWTP is just south east of the corner of Amboy Road and Utah Trail.
2.3.2. Distance to the existing MCAGCC WWTP
Although a joint-use WWTP has been discussed, the location has not been selected (1/2022).
The existing plant is used as a proxy. The current WWTP serving MCAGCC is located on Del Valle Street on base and directly across the road from Marine Corps Exchange -29 Palms.
2.3.3. Land use
Land use was important in that changes in zoning might cause delays or generate public opposition. A land use GIS cover was retrieved from the San Bernardino County Planning Department web site.
2.3.4. Land ownership
page 18
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Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California Land ownership could also cause delays and potential opposition (Figure 2.7). Private land would necessitate establishment of a purchase or lease agreement. Public land administered by the Bureau of Land Management (BLM) would require a lease agreement and additional potential permitting requirements, including National Environmental Policy Act (NEPA) documentation and compliance. State or county land would also require use authorization from the responsible agencies. The simplest land ownership situation would be the use of City land.
Regardless, any of these options would most likely trigger California Environmental Quality Act (CEQA) requirements.
2.3.5. Size
The size of the available land is also critical, as surface-spreading basins require a relatively large, moderately undisturbed, flat topography. For example, the Bighorn-Desert View Water Agency estimated that a spreading basin of five acres was required to recharge 1500 acre-feet over six months at an infiltration rate of 1.64 feet/day (BDVWA ). Ideally, three basins are used for normal operation in order to allow for scarification and cleaning of 25% of the infiltration surface while 75% remains in operation. Thus, the size of the facility needs to be much greater than the actual basin surface area.
Hi-Desert Water District has been recharging imported Mojave Water Agency water at its Warren Valley Basin Groundwater Recharge facility in Yucca Valley since 2015 (HDWD ). The District recently constructed a new wastewater treatment plant and began discharging water into its three percolation ponds in February of 2020. The facility occupies approximately 30 acres in Yucca Valley, including the three ponds and other supporting infrastructure.
Green Valley Municipal WWTP is operated by Pima County in southern Arizona. The Green Valley WWTP averages 2335 acre-feet per annum of treated effluent to be infiltrated in 7.1 acres of pond. The size of the entire complex is approximately 50 acres (Pima County RWRD 2021).
2.3.6. Existing infrastructure
Once again, the required effluent infrastructure has not yet been determined by the City and it is unknown where these alignments will be located. In all likelihood, buried collection pipelines will follow major road rights-of-way and effluent return lines would most likely be proposed for the same corridors. Therefore, distance to existing major City streets would be one proxy for this criterion.
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Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Report Figures\Figure 2-7 - Land Use.mxd LEGEND
Private
United States of America
Government Land
County of San Bernardino
City of Twentynine Palms
City of Twentynine Palms Outline
2-Mile Buffer
¯ 18,000
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
Figure 2.7 - - Local land ownership. Data from San Bernardino County Planning Department (2021)
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Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California Another important infrastructure component would be groundwater wells that could serve as monitoring wells or locations for new points of compliance. Under California State Law the permitting of a Department of Public Health Groundwater Replenishment Reuse Project (GRRP), monitoring of the aquifer receiving treated effluent is required.
2.3.7. Areas of preservation or open space
Although the recharge basins would not require much in the way of built structures, they would be a disruption of the natural topography and vegetation. Location in an area of well-known cultural resource distribution could also cause issues in permitting and approval of the facility. 3 Candidate Sites
Using these broad data sets on currently available land areas, three sites were chosen for sitespecific fieldwork (Figure 3.1). These sites included a section of land owned by TPWD directly north of the well TP-1, south of the Fluoride Removal Facility, and adjacent to Utah Trail (Fluoride). The City-owned parcel that comprises Section 19 of Township 1N, Range 9E and that is bordered on the west by Morongo Road and on the south by Two Mile Road (Morongo) was another site. The third site is located south of Twentynine Palms Highway (SR62), east of Encelia Drive on San Bernardino County Flood Control property (Flood).
3.1. Field Work
The percolation rate of introduced water through the surface soils is of paramount importance in locating a recharge facility. Although the NRCS Soil Survey database includes saturated hydraulic conductivity values for each represented soil series, a better estimate is required from the actual surfaces used, on site. Three candidate sites were surveyed as part of the field investigation. . Attachment 1 is a detailed description of the field activities. A summary of field activities is provided in this section. .
Field work at the three sites occurred during the period of August 17-19, 2021. The methodology of Bouwer et al (1999), as modified by Rice et al (2014), was used during this effort. The Bouwer method employs a single-ring infiltrometer to generate a series of estimates of the saturated hydraulic conductivity of surface soils. The principal source of error in the method, which was corrected by Bouwer and co-workers (1999) is the lateral expansion of the wetting front as it progresses downward. The measurement of the lateral expansion is accomplished by digging exterior to the ring and measuring the radial extent of saturation with a soil moisture probe. For soils similar to the candidate sites, this methodology has been demonstrated to improve the estimates by a factor of 3.4 to 7.0 (Rice, et al 2014). page 21
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2 Mile Road
Twentynine
Palms City Hall
Amboy Road
Morongo Road
Adobe Road
Utah Road
Twentynine Palms Highway (California 62)
Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Report Figures\Figure 3-1 revised.mxd LEGEND
Infiltration Test Location ¯ 4,000
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
Morongo
Fluoride
Flood
Figure 3.1 - - Location of three sites examined during infiltration measurement field work.
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Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California Measurements were made at four locations at each of the three sites. Locations were chosen based upon the general topography and field texture inspection of the sites to be representative of the general area. The measurements were straightforward. At each location the 50-cm-diameter, steel ring was driven a few inches into the ground. Water was introduced carefully so as not to disturb the ground surface. The water level was maintained at a few centimeters below the rim of the steel rim in order that a constant head was maintained at the soil surface. The drop in water was recorded as infiltration progressed until 21 to 62 centimeters of entry was recorded or four hours of measurement occurred. Approximately six hours per site was necessary for the test.
Upon conclusion of the test, excavations were made in three direction from the ring and lateral divergence of the wetting front was recorded. Finally, the cylinder was drained, the center of the wetted soil was hand augered to the depth of the wetting front, and a sample was recovered for textural analysis.
3.1.1. Fluoride Site
The site was accessed from Utah Trail on a dirt road (Figure 3.2). The topography was flat with mildly eroded drainage to the west. At the surface, loamy sand makes up the most common material supporting a mixture of creosote bush, yucca, annual grasses and forbs. The NRCS soil survey assigned this site to the Duneland-Cajon 1135 map unit and estimated the mean K(sat) to be 4.23E-05 to 1.41E-04 cm/s with 10% clay. The four Fluoride site K(sat) values ranged from
7.8E-04 cm/s to 1.4E-03 cm/s, with a median of 8.7E-04 cm/s and a geometric mean of 9.51E04 cm/s.
3.1.2. Morongo Site
The Morongo Site was located within the City-owned Section 19 parcel, adjacent to the dirt extension of Morongo Road and approximately 0.8 miles north of 2 Mile Road (Figure 3.3). The land slopes off approximately 3% to the north-northeast. The surface soil is a loamy sand; however, the location is bisected by a 2-meter-deep gully that appears to have formed from adjacent stormwater runoff. The gully exposes an approximately 0.5-meter layer of whitishgrey, firmly cemented, calcareous caliche. Sparse surface vegetation includes creosote bush. bursage, joshua tree, annual grasses and forbs. The NRCS describes the area as WascoHelendale-Map 1032 map unit, estimating the mean K(sat) to be 1.41E-05 to 4.23E-05 cm/s with page 23
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Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California a clay content of 0.8%. This investigation produced K(sat)ranging from 3.5E-04 cm/s to 1.2E-03 cm/s with a median of 4.9E-04 cm/s and a geometric mean of 5.63-04 cm/s and.
3.1.3. Flood Site
The Flood Site was within the San Bernardino County Flood Control District property (Figure
3.4). The area is topographically much more rugged than the previous sites and includes a number of off-channel gullies and terraces. The site is located within a mountain-front alluvial fan associated with Fortynine Palm Canyon, a major through-going drainage. The texture is also coarser and poorly graded, ranging from cobbles to fine sand; however, the four locations tested were more uniform, ranging from medium sand to loamy sand. Vegetation includes the same community as the Morongo Site with the addition of abundant smoke tree shrubs. The NRCS mapped the locations as part of the Ramona-Hanford-Greenfield 1009 map series. For this series, a K(sat) of 1.41E-05 to 4.23E-05 cm/s was estimated by the NRCS at a clay content of
0.2%. The results of the current study for the Flood Site ranged in K(sat)from 1.1E-03 cm/s to
9.5E-03 cm/s, with a median of 1.5E-03 cm/s and a geometric mean of 2.24E-03 cm/s.
3.1.4. Summary of Field Testing
While all three sites were within a reasonable range of K(sat) and clay content, the Flood Site was more than two times more permeable than the Fluoride Site and infiltration was almost 4 times faster than the Morongo Site. Permeability at the Morongo Site was probably inhibited by the thick layer of caliche exposed in the stormwater gully. Coarser material composing the alluvial fan at the Flood Site appears to contribute to the faster infiltration rate at that locality.
3.2. Application of Criteria
The data used in making the selection are summarized in Table 3.1. Each site was ranked from one to three, with three being the highest score relative to the others in fulfilling that criterion (Table 3.2). In some cases, the criterion weighed heavier in importance to the needs of a surface-spreading, groundwater recharge facility. In these cases, the criteria was multiplied by a weighing factor. Hydrogeology, land ownership, and the presence of existing water conveyance, ground transportation, and power infrastructure were weighted heavier than most other criteria. The results of the field infiltration testing were considered to be of even greater importance.
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Fluoride 4
Fluoride 3
Fluoride 2
Fluoride 1
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Infiltration Test Location ¯ 250
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
Twentynine Palms Water District
Fluoride Removal Facility
Utah Trail
Figure 3.2 - - Detail map of Fluoride Site.
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Morongo 4
Morongo 3
Morongo 2
Morongo 1
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Infiltration Test Location ¯ 500
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
Morongo Road
Samarkand Drive
Figure 3.3 - - Detail map of Morongo Site.
page 26
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Flood 4
Flood 3
Flood 2
Flood 1
Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Report Figures\Figure 3-4.mxd LEGEND
Infiltration Test Location ¯ 400
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
Encelia Road
San Bernardino County Twentynine Palms
Flood Control Channely
Figure 3.4 - - Detail map of Flood Site.
page 27
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Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California These component scores were summed for the cumulative score (Table 3.2). Using this system, all three sites were very close. The Fluoride Site was highest, scoring very high on existing infrastructure and proximity to the proposed WWTP site. The Flood site was very close, receiving high marks for the hydrogeology, surface conditions, and field infiltration data.
Measured infiltration values were reasonably good. The Morongo Site scored highest in land ownership and use but was limited by its low infiltration rate and the presence of caliche layers in the subsurface.
4 Conclusion and Recommendation
Based upon the results of the screening study, the Fluoride Site seems to be the best location for a recharge facility. The presence of favorable subsurface geological material, its location in the Mesquite Lake Subbasin, and the co-location of several TPWD wells would all be helpful; however, the proximity to the proposed City-only or joint-use WWTP is probably the main discriminator. If and when a joint-use facility location is selected, this conclusion may need to be revised to accommodate a site closer to the alternate WWTP.
Presumably, the required land used for the existing Fluoride Treatment Plant could be leased from the TPWD and the basins sited off of Amboy Road. Despite this, the potential existence of an approximately 35-foot clay layer at 50 feet might be an issue. There are many ways to accommodate subsurface fine-grained units subjacent to a recharge spreading basin. A combination basin that includes several deep dry wells is one possibility. Regardless, it will be important to initiate a complete subsurface investigation before the Fluoride site is advanced to the design phase.
There may also be an issue with the Regional Water Quality Control Board (RWQCB) regarding the Fluoride facility evaporation ponds. If an elevation of the local groundwater levels interferes with the pond leakage points of compliance, the RWQCB might object to the facility. The hydrogeology of this issue should be analyzed further and discussed with the RWQCB before finalizing the choice of this site.
NV5 has proposed a single boring to 100 feet bgs as part of the Twentynine Palms WWTP project. This boring will allow laboratory testing of retrieved samples for texture, moisture content and laboratory K(sat) . These data can support estimates of basin size and capacity can be calculated, as can the impact of the recharge facility on local groundwater levels. It may be necessary to expand this investigation before a decision is reached. page 28
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Soils Survey Data (NRCS)
Surficial geology (Dibblee)Depth to groundwater Depth to crystalline basementWater quality*HydrogeologyDistance to proposed WWTP siteLand useLand ownershipAvailable SizeExisting infrastructureGroundwater BasinAreas of preservation or open spaceMeasured K(sat) Fluoride
Duneland-Cajon,
K(sat) = 4.23E-05 to 1.41E04 cm/s 10% clay.
Qa, Detrital sediments ranging from
subangular boulders and cobbles in small
alluvial fans adjacent to mountains, through
pebbly arkosic sand down slope, to arkosic
sand and silt in valleys; includes sand and
gravel of stream washes.
50 to 60 ft bgs 4,300 to 6,700 ft
bgs
Ave F = 5.9 mg/L
Ave NO3 = 3.5
mg/L
Upper aquifer,
GW flow to east 1.5 miles industrial
Twentynine
Palms Water
District
84 acres
adjacent streets
and power,
existing TPWD
wells
Twentynine Palms
Valley Groundwater
Basin, Mesquite Lake
Subbasin
none
Morongo
Wasco-Helendale,
K(sat) = 1.41E-05 to 4.23E05 cm/s 0.8%
clay.
Qoa, Old weakly consolidated alluvial
deposits that fill valley and former valley
areas; dissected where elevated. May be as
thick as a thousand or more feet. Light-gray,
poorly bedded to non-bedded, fine to coarse,
arkosic sand and minor pebble-cobble gravel;
in places a little micaceous silt or clay.
100 to 200 ft bgs 2,200 to 4,300 ft
bgs
Ave F = 5.9 mg/L
Ave NO3 = 3.5
mg/L
Upper aquifer,
GW flow to east 2.3 miles single-family residential
City of
Twentynine
Palms
472 acres adjacent streets
and power
Twentynine Palms
Valley Groundwater
Basin, Mesquite Lake
Subbasin
none
Flood
Ramona-HanfordGreenfield,
K(sat) = 1.41E-05 to 4.23E05 cm/s 0.2%
clay.
Qa, Detrital sediments ranging from
subangular boulders and cobbles in small
alluvial fans adjacent to mountains, through
pebbly arkosic sand down slope, to arkosic
sand and silt in valleys; includes sand and
gravel of stream washes.
200 to 300 ft bgs 0-400 ft bgs
F = 1.3-2.7 mg/L
NO3 = 6.5-11.3
mg/L
Upper aquifer,
GW flow to east 2.5 miles public facilities County of San Bernardino 203 acres adjacent streets
and power,
existing TPWD
wells
Joshua Tree Basin,
Fortynine Palms
Subbasin
Joshua Tree
National Park
* same data characterizes both sites.
2.24E-03 cm/s
Surface Conditions Subsurface Conditions Location Field Work
9.51E-04 cm/s
5.63-04 cm/s
Table 3.1 - Selection criteria used to rank sites. See text for discussion. page 29
DRAFT
Soils Survey Data
Surficial geologyDepth to groundwater Depth to crystalline basementWater qualityHydrogeologyDistance to proposed WWTPLand useLand ownershipSizeExisting infrastructureGroundwater BasinPreserve or open space issuesTOTAL RATING Fluoride 2 3 2 3 3 4 6 3 4 1 6 1 3 49
Morongo 1 2 3 3 3 2 4 2 6 3 2 1 3 39
Flood 3 3 3 1 2 6 2 3 2 2 2 3 1 45
4 12
Surface
Conditions Subsurface Conditions Location
Field
WorkMeasured K(sat)
8 page 30
Table 3.2 - - Ranking of the three sites. DRAFT
Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California 5 References
SCEDC, Southern California Earthquake Center
SCEDC (2013)
BDVWA, Bighorn/Desert View Water Association
______, 2012, Groundwater Management Plan Pipes and Reche Groundwater Subbasins of the Ames Valley Groundwater Basin San Bernardino County, California. Bighorn/Desert View Water Association Consultant Report, 175 p.
Bouwer, H., Back, J.T. and Oliver, J.M., 1999. Predicting infiltration and ground-water mounds for artificial recharge. Journal of Hydrologic Engineering, 4(4), pp.350-357.
Cal DWR, 2019, California's Groundwater (Bulletin 118), https://water.ca.gov/programs/groundwater-management/bulletin-118, visited 9/9/2021 City and TPWD, City of Twentynine Palms and Twentynine Palms Water District ____________, Twentynine Palms Wastewater Master Plan, Consultant Report, 98 p.
Dahlke, H.E., LaHue, G.T., Mautner, M.R., Murphy, N.P., Patterson, N.K., Waterhouse, H., Yang, F. and Foglia, L., 2018. Managed aquifer recharge as a tool to enhance sustainable groundwater management in California: examples from field and modeling studies. In Advances in Chemical Pollution, Environmental Management and Protection (Vol. 3, pp. 215-275). Elsevier.
Dibblee T.W., 1968. Geologic map of the Twentynine Palms quadrangle, San Bernardino and Riverside counties, California. US Geological Survey, Miscellaneous Geologic Investigations Map I-561, 1 sheet and explanation.
Dick, M. and Kjos, A., 2017. Regional water table (2016) in the Mojave River and Morongo groundwater basins, southwestern Mojave Desert, California. U.S. Geological Survey Scientific Investigations Map 3391, scale 1:170,000,
HDWD, Hi-Desert Water District
_____, Hi-Desert Water District 2020 Urban Water Management Plan, Consultant Report, 85 p.
Hutchinson, A.S., Rodriguez, G., Woodside, G. and Milczarek, M., 2017. Maximizing infiltration rates by removing suspended solids: Results of demonstration testing of riverbed filtration in Orange County, California. Water, 9(2), p.119.
Lanphere, M.A., 1964. Geochronologic studies in the eastern Mojave Desert, California. The Journal of Geology, 72(4), pp.381-399.
page 31
DRAFT
Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California Madden, C.L., Rubin, C.M. and Streig, A., 2006. Holocene and latest Pleistocene activity on the Mesquite Lake fault near Twentynine Palms, eastern California shear zone: Implications for fault interaction. Bulletin of the Seismological Society of America, 96(4A), pp.1305-1320 MWA, Mojave Water Agency
-------, 2020, 2020 Urban Water Management Plan, 109 p.
Pima County RWRD, Pima County Regional Water Reclamation Department, website Rice, R, Milczarek, M and Keller J. 2014. A Critical Review of Single Ring Cylinder Infiltrometers with Lateral Flow Compensation. 14th Biennial Symposium on Managed Aquifer Recharge, Orange, CA, July 31–August 1.
Riley FS and Worts Jr GF., 1952. Geologic Reconnaissance and Test-Well Drilling Program, Marine Corps Training Center, Twentynine Palms, California. US Dept. of the Interior, US Geological Survey; Open-File Report 98-166. 71 p.
Roberts, C.W., Katzenstein, R.C., Smith, A. and GA Johnson, R., 2002. Gravity map and data of the eastern half of the Big Bear Lake 100,000 scale quadrangle, California and analysis of the depths of several basins. U.S. Geological Survey Open-File Report 02-353 Robertson, F.N., 1991. Geochemistry of ground water in alluvial basins of Arizona and adjacent parts of Nevada, New Mexico, and California (Vol. 1406). US Geological Survey. Geological Survey Professional Paper 1406-C, 102 p.
TPWD, Twentynine Palms Water District
--------, 2016, 2015 Urban Water Management Plan Update Amended Final. Consultant Report, 340 p.
page 32
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Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California Attachment 1 - - Technical memorandum on infiltration testing.
DRAFT
TECHNICAL MEMORANDUM
To: Mark Murphy Date: August 26, 2021
From: Kirk F. Creswick, RG Project: 227521-0000132.00
CC:
Subject: Infiltration Testing – 29 Palms
This Technical Memorandum discusses the estimation of soil hydraulic conductivity (K) from cylinder infiltrometer testing.
Theory
The rate of infiltration of water into soil is directly proportional to the hydraulic conductivity (K) of the soil and the hydraulic gradient. Cylinder infiltrometer testing estimates the hydraulic conductivity by measuring the infiltration rate and estimating the hydraulic gradient. The hydraulic conductivity is then calculated based on these measurements/estimates.
Measuring the infiltration rate from the cylinder (in) is fairly straightforward: the change of water level in the cylinder infiltrometer (yn) is measured over time (tn) and the infiltration rate is yn/Δtn, for any nth measurement.
The hydraulic gradient is a little less straightforward since it involves both direct measurement and estimation. The following equation shows the pertinent parameters:
𝑖𝑖𝑤𝑤 = 𝐾𝐾 𝑧𝑧+𝐿𝐿−ℎ𝑤𝑤𝑤𝑤
𝐿𝐿 (Equation 1)
where:
iw – the infiltration rate of water in the soil (L/T)
K – the hydraulic conductivity (L/T)
z – the head of water in the cylinder (L)
L – the depth to the wetted front from ground surface (L) hwe – the water entry pressure of the soil (L)
The values in the numerator of Equation 1 (z+L+ hwe) make up the head over the length (L) in the denominator that represent the hydraulic gradient. The value z is measured directly in the cylinder during the test. The value L is measured directly after the test. The value hwe is, however, estimated based on soil type. The water entry pressure is the head required to force water into the pore space.
For most soil, the value of hwe is negative since capillary suction pulls water into the soil. Generally, the finer the soil, the greater the capillary suction and the more negative the water entry value.
Values for hwe reported in Bouwer et al., 1999 are:
• Coarse Sand, -5 cm
• Medium Sand, -10 cm DRAFT
• Fine Sand, -15 cm
• Loamy Sands, -20 cm
• Sandy Loams, -25 cm
• Loams, -35 cm
• Structured Clay Soils, -30 cm
• Nonstructured Clay Soils, -100 +
As the wetting depth (L) increases, the water entry value (hwe) becomes less significant as an overall percentage of the head, such that a 5 cm misestimate of hwe would result in about 4.2 to 6.5% error in overall head (and gradient) in this particular study.
The capillary suction responsible for hwe values also causes lateral wetting (divergence, x), which much be accounted for since it impacts the downward infiltration rate of water in the soil (iw). The relationship between cylinder infiltration rate (in), the infiltration rate in the soil (iw), and divergence (x) is shown in Equation 2:
𝑖𝑖𝑤𝑤 = 𝑖𝑖𝑛𝑛𝜋𝜋𝑟𝑟2
𝜋𝜋(𝑟𝑟+𝑥𝑥)2 Equation 2
where r is the radius of the cylinder.
This shows that the volumetric flow through the area of the cylinder (with a radius, r) will flow through a greater area of soil (with a radius, r+x), thereby reducing the downward infiltration rate in the soil (iw) relative to the infiltration rate in the cylinder (in) by the ratio of the areas.
Similarly, the increase in cross-sectional area caused by divergence (x) affects the depth of the wetted front (L) as shown in Equation 3:
𝐿𝐿 = 𝑦𝑦𝑡𝑡𝜋𝜋𝑟𝑟2
𝑛𝑛 (𝑟𝑟+𝑥𝑥)2 Equation 3
where:
yt – total length (depth) of water from through the cylinder n – soil fillable porosity
Note that fillable porosity is porosity not already occupied by water or by entrapped air.
Field Work
Field methods for measuring/estimating parameters for use in the above equations are described in this section.
Three areas were predetermined for this study (see Figure 1):
• Adjacent to the Fluoride Removal Plant, south of Amboy Rd. and west of Utah Trail (see Figure 2)
• North of the Morongo neighborhood, east of Morongo Rd and north of Samarkand Dr. (see Figure 3)
• On Flood Control property south of Hwy 62 and east of Encela Ave. (see Figure 4) DRAFT
Locations were selected for testing within each study area that were relatively free of vegetation, rocks or local disturbance (trail compaction, animal/insect burrows, etc.).
The following procedure was used for conducting the test:
Four different cylinder infiltrometers were used in this study, with diameters of 50.8, 50.9,
50.9 and 52.5 cm. All where 30.5 cm tall.
The cylinders were secured 4-8 cm into the soil using a sledgehammer. The soil around the interior of the cylinder was tamped against the cylinder wall with the handle of the sledgehammer and the soil on the exterior was tamped with the head of the sledgehammer and/or foot pressure.
A wooden ruler was clipped vertically to the inside of the cylinder with one end at the soil level to allow for water level measurements.
A foam pad was placed in the cylinder during filling to limit soil disturbance. Two buckets of water (10-12 gallons) were poured into the cylinder and the foam was removed.
A reading of the water level was taken from the ruler and recorded with the time on the field data sheet.
As the water level dropped, additional water level and time readings were collected and recorded. Where wind caused fluctuation of water levels, the average reading was approximated.
Additional water was added to maintain head in the cylinder with readings collected immediately before and after the filling.
40 cm of cumulative water drop was the goal for a test. The actual range was 21 to 62 cm. Immediately after the test, three trenches were hand-dug at approximately 120° spacing to approximately 6 to 9 inches depth to locate the divergence (x) of the wetted zone beyond the cylinder. This was generally visually observable, but a moisture meter was also used to reduce the potential for error due to smearing the interface during excavation. Dry soil read 0% moisture and wetted soil generally read 10% or more (up to about 22% next to the cylinder).
After draining any remaining water from the cylinder, a hand auger was used to determine the depth (L) of the wetted front. In practice, this was the depth that either dry material was found in the bottom of the hand auger, or the depth that non-cohesive material would not be retained in the hand auger due to lack of moisture.
The second auger bucket of material (from approximately 6-12 inches below ground surface), was retained for visual soil description. Additionally, a portion of the retained soil was placed in a jar with water above the sample surface and shaken/swirled to determine relative percentage of silt and clay. Silt settles within several seconds while clay settles overnight.
The thickness of silt and clay layers in the jars were compared to the total sediment thickness to determine silt and clay percentages.
Spreadsheet Analysis
Values of yn, tn, x (average), and L were entered into a spreadsheet that uses the three equations above to calculate the hydraulic conductivity, K.
• The value for iw is calculated from the final in value (yn/Δtn), the radius of the cylinder (r) and the average divergence (x) using Equation 2.
• Although L is measured directly, an iterative approach using Equation 3 and adjusting fillable porosity (n) is used until the measure value of L is approximated. • Equation 1 is then solved for K. The water entry value in Equation 1 is approximated from soil type and manually entered. The value of head in the cylinder (z) is taken from the starting head value for the last yn pair. Note that z should actually be the average value during that DRAFT
interval, but this error is small, particularly if frequent measurements were made during the latter part of the test.
Note that the ruler used for measurement of the head in the cylinder was installed with the larger values at the bottom. This would result in improper values of z in the calculations if used as is.
Therefore, these values were corrected by subtracting the field values from 30, effectively flipping the ruler to the proper orientation.
Results
Table 1 shows some of the measured and modeled values from the testing for discussion. These values are reported to two significant digits.
Table 1 - Results of Infiltration Testing
Location Soil Type hwe
(cm)
X
(cm)
L
(cm) n K (cm/s)
Fluoride 1 Loamy Sand -20 24 56 0.14 1.4E-03
Fluoride 2 Loamy Sand -20 30 56 0.15 8.8E-04
Fluoride 3 Loamy Sand -20 28 54 0.11 8.6E-04
Fluoride 4 Loamy Sand -20 27 55 0.14 7.8E-04
Morongo 1 Sandy Loam -25 63 38 0.14 3.5E-04
Morongo 2 Sandy Loam Sandy Clay Loam -27 56 49 0.11 5.0E-04 Morongo 3 Loamy Sand -20 42 58 0.11 1.2E-03
Morongo 4 Sandy Clay Loam -30 16 72 0.11 4.9E-04
Flood 1 Medium Sand -10 42 55 0.12 1.7E-03
Flood 2 Medium Sand -10 23 101 0.13 9.5E-03
Flood 3 Sandy Loam -25 30 82 0.12 1.1E-03
Flood 4 Medium to fine sand -13 19 88 0.15 1.4E-03
With respect to hydraulic conductivity:
• Fluoride Area hydraulic conductivity values ranged from 7.8E-04 cm/s to 1.4E-03 cm/s, with an average of 9.8E-04 cm/s and a median of 8.7E-04 cm/s. • Morongo Area hydraulic conductivity values ranged from 3.5E-04 cm/s to 1.2E-03 cm/s, with an average of 6.3E-04 cm/s and a median of 4.9E-04 cm/s. • Flood Area hydraulic conductivity values ranged from 1.1E-03 cm/s to 9.5E-03 cm/s, with an average of 3.4E-03 cm/s and a median of 1.5E-03 cm/s.
These values are in general agreement with their soil types.
Some observations on the data in Table 1 include:
• The value of divergence exceeds the water entry value in all tests except Morongo 4. • Divergences exceeds the water entry value significantly in Morongo 1, Morongo 2, Morongo 3, Flood 1, and Flood 2.
• Divergence does not show a high degree of correlation with hydraulic conductivity, but hwe correlates fairly well.
• Fillable porosity values range from 11% to 15%, but average site values are not much different. DRAFT
These observations suggest that lateral divergence is being affected by factors other than water entry pressure. For homogeneous material, these values would be expected to be more predictable. In most of the tests, the content of fines appeared to increase from soil observed at the surface. If the infiltration rate of the shallow soils is in excess of the infiltration rate of the soil below, this would cause lateral spreading that may be observable during investigation of divergence in the shallow soil.
Additionally, the fillable porosity is somewhat lower than a suggested value of 0.3 for dry, uniform soil. Having both visual and quantitative confirmation of very dry soils, this suggests a high degree of air entrapment during testing is responsible for the reduced fillable porosity.
Reducing the porosity will result in more lateral and vertical spreading of the moisture front until the air is effectively purged from the pore space. It may be that this occurs to a large extent during the test, but that the extent of the divergence is expressed by the early effects of the lower porosity. This higher apparent divergence will reduce the calculated value of iw and K.
Bouwer et al., 1999 acknowledges that saturated hydraulic conductivity (Ksat) is generally two times the K value for sandy soils and four times the K value for finer soils determined by cylinder testing.
Conclusions
Flood Area soils appear most favorable, with average conductivities 3.5 times the Fluoride locations and 5.5 times the Morongo locations, and median hydraulic conductivities 1.8 times the Fluoride Locations and 3.1 times the Morongo Locations; however, all three locations have good permeabilities.
The lack of significant clay and silt at the Flood site would help to limit surface clogging. It is also likely that the Flood location would have less fines at depth since fines tend to wash down further into the basin. The Morongo and Fluoride locations are further into the basin, and therefore likely have more fines, although the Morongo area appears to have a higher surface gradient than the Fluoride site, resulting in coarser surface texture.
Saturated hydraulic conductivity values would likely be two to four times higher.
Recommendations
Cylinder infiltrometer testing of these sites has evaluated the short-term, unsaturated hydraulic conductivities of the upper 38 to 101 cm of soil at the sites. Additional geotechnical investigation should be conducted to investigate the possibilities of less permeable layers at depth that could cause mounding.
DRAFT
FIGURE 1
SHT 1 OF 1
DES: RDD DR: RDD
1 W DEER VALLEY ROAD
BUILDING 2, SUITE 305
PHOENIX, ARIZONA 85027
Tel: 623.374.6637 Fax: 623.738.3690
FOR: SITE MAP
Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Figure 1 - Site Map.mxd CHK:
LEGEND
Infiltration Test Location ¯ 4,000
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
PROJECT NO. 227521-0000132.00 DATE: 9/2/2021
TWENTYNINE PALMS WWTP SUPPORT
Morongo
Fluoride
Flood
DRAFT
Fluoride 4
Fluoride 3
Fluoride 2
Fluoride 1
FIGURE 2
SHT 1 OF 1
DES: RDD DR: RDD
1 W DEER VALLEY ROAD
BUILDING 2, SUITE 305
PHOENIX, ARIZONA 85027
Tel: 623.374.6637 Fax: 623.738.3690
FLUORIDE FOR:
INFILTRATION TEST LOCATIONS
Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Figure 2 - Fluoride.mxd CHK:
LEGEND
Infiltration Test Location ¯ 250
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
PROJECT NO. 227521-0000132.00 DATE: 9/2/2021
TWENTYNINE PALMS WWTP SUPPORT
Twentynine Palms Water District
Fluoride Removal Facility
DRAFT
Morongo 4
Morongo 3
Morongo 2
Morongo 1
FIGURE 3
SHT 1 OF 1
DES: RDD DR: RDD
1 W DEER VALLEY ROAD
BUILDING 2, SUITE 305
PHOENIX, ARIZONA 85027
Tel: 623.374.6637 Fax: 623.738.3690
MORONGO FOR:
INFILTRATION TEST LOCATIONS
Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Figure 3 - Morongo.mxd CHK:
LEGEND
Infiltration Test Location ¯ 500
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
PROJECT NO. 227521-0000132.00 DATE: 9/2/2021
TWENTYNINE PALMS WWTP SUPPORT DRAFT
Flood 4
Flood 3
Flood 2
Flood 1
FIGURE 4
SHT 1 OF 1
DES: RDD DR: RDD
1 W DEER VALLEY ROAD
BUILDING 2, SUITE 305
PHOENIX, ARIZONA 85027
Tel: 623.374.6637 Fax: 623.738.3690
FLOOD FOR:
INFILTRATION TEST LOCATIONS
Document Path: E:\227521-0000132.00 29 Palms WWTP Support\Figure 4 - Flood.mxd CHK:
LEGEND
Infiltration Test Location ¯ 400
Feet
Service Layer Credits: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
PROJECT NO. 227521-0000132.00 DATE: 9/2/2021
TWENTYNINE PALMS WWTP SUPPORT DRAFT
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Preliminary Screening Study of Groundwater Recharge Sites, Twentynine Palms, California Attachment 2 - - Driller’s Log for Monitoring Well TP-1.
DRAFT
DRAFT
DRAFT
Delivering Solutions
Improving Lives
TWENTYNINE PALMS
WASTEWATER PROJECT
Frank J. Luckino
City Manager
November 8, 2022
PROJECT OVERVIEW
• The City is with the exception of 6 package treatment plants are on septic tanks to process wastewater;
• This is a sustainability project and not a result of any water quality issues;
• The impetus of the project is to access state funding ($350M) that has the ability to pay 100% of the initial phase(s) of the project; • The initial phase(s) of the project will be collecting and treating approximately 34.4% of the City’s usage;
• The initial treatment plant will treat approximately a .56 MGD (Million Gallons a Day) Plant or 20% of what is needed by 2050. 2
PROJECT TEAM
• City and Water District Staff (Oversight and Direction) • Carollo Engineering (Owners Representative and Wastewater Design)
• NV 5 Engineering (Collection System Designer)
• Terra Nova - Environmental
• Wildan Financial
• CV Strategies (Outreach)
3
TWENTYNINE PALMS WASTEWATER PROJECT
What money do we have for planning?
4 Funded Agency Amount
Clean Water State Revolving Fund $983,000
Clean Water State Revolving Fund (USGS) $1M
Olbernolte Earmark (STAG funding) $663,224
Olbernolte Earmark (22/23 Federal
Budget, not approved yet)
$1,275,000
City Surplus $500,000
County ARPA $1M
Water District Contribution (USGS) $100,000
TOTAL PLANNING $5,521,224
TWENTYNINE PALMS WASTEWATER PROJECT
What money do we need for completing design and construction (big picture)? 5 Funding Task Amount
Hard Construction (Plant and Collection) +/- $137M
Add Advanced Treatment $20M
Land Acquisition TBD
Additional Planning Dollars needed $1.5M
Private Lateral Connection ($12K average per
connection)
Included in Hard Cost
TOTAL PLANNING $158.5M
TWENTYNINE PALMS WASTEWATER PROJECT
Timeline
6 • November/December 2022- City will submit a pre-application so they (State Water) knows of our needs; • Environmental Analysis – Complete however, needs to finalize plant location which would require more studies;
• December 2022 – Anticipated the Olbernolte budget request ($1.275M) and Federal budget approved; • December 2022 – Engage Financial analysis to determine potential rate payers' costs (operations and capital);
• February 2023 – Anticipated State Water contract agreement amendment that will include the USGS monies
• February 2023 – Outreach on project and costs;
• March 2023 – Full and complete funding package to State Water, that needs to include environmental; • June 2023 – After environmental review, state potentially could give us an amount that we are eligible to receive within six months however it will take up to 12 months for the entire underwriting review and contracting
• July 2023 – Collection system designed to a percentage to bid; • Late 2024/Early 2025 Construction, if funding is successful. Page 878 of 885 • USGS Study that will begin in 2023; the science will give us the specificity of how the Nitrates are traveling in the unsaturated zone and where in the City;
• And the science to predict when density creates the loading that hits the saturated zone, among many other things;
• Wastewater Treatment and Sewers are a tried-and-true piece of infrastructure that protects the water supply that dates to the Romans;
• It is a proactive project; although not on an order by the Regional Board or imminent threat of groundwater
contamination, but why wait for that?
7 TWENTYNINE PALMS WASTEWATER PROJECT
WHY ARE WE DOING THE PROJECT?
• Money is here and now; State has allocated $350M for septic to sewer conversions. From a California only perspective, in my 18 years searching for Wastewater grant dollars, this is the single highest amount (Hi-Desert Water District, Blythe, and Twentynine Palms);
• In a public professional poll by Probosky Research (attached) refer to page 40, question #10, 90% of people polled support infrastructure that benefits the residents;
• Also, page 100, question #20, 77% of the people polled support sewering the City, but then later the percentage goes down when money is discussed, which is natural, so cost is the barrier;
8 TWENTYNINE PALMS WASTEWATER PROJECT
WHY ARE WE DOING THE PROJECT?
•No Water Quality issues;
•Limit growth and density to reduce and/or limit the threat •Hope the Science from the ultimate USGS report (5 years) will show Nitrates NOT traveling into our water source;
•As per the SNMP, we have not done the monitoring and analysis to determine we need it
•Some cannot afford it and/or no public support.
9 TWENTYNINE PALMS WASTEWATER PROJECT
WHY NOT TO DO THE PROJECT?
TWENTYNINE
PALMS
WASTEWATER
PROJECT
10
Tertiary treatment (water used for recycled purposes, purple pipe) is the next wastewater treatment process after secondary treatment (current treatment process by Lake Bandini on the base). This step removes stubborn contaminants that secordary treatment was not able to clean up. Wastewater effluent becomes even cleaner in this process through the use of stronger and more advanced treatment systems.
11 TWENTYNINE PALMS WASTEWATER PROJECT
Advanced Water Treatment (potable re-use) is the final step in the treated water/natural water mix undergoing standard purification processes. Indirect potable water is entirely safe to drink and places across the world use this process.
12 TWENTYNINE PALMS WASTEWATER PROJECT
DISCUSSION
Questions?
13