Select 
Date,
Case_ID,
Site,
Dept,
Tech,
Start_Time,
ROW_NUMBER () OVER (PARTITION BY Date, Site, Dept, Tech ORDER BY Start_Time) as Row_Num
FROM
Logs
Where Date = Getdate()

Date	 Case ID   Site	        Dept	Tech	Start Time	Row_Num
7/28/14	 10023	   Tartville	Maintc	Amy P.	7:30	1
7/28/14	 56789	   Tartville	Maintc	Rem W.	8:05	1
7/28/14	 23098	   Tartville	Maintc	Amy P.	8:35	2
7/28/14	 70004	   Tartville	Maintc	Amy P.	9:10	3
7/28/14	 12708	   Tartville	Maintc	Mag O.	10:00	1
7/28/14	 10004	   Tartville	Maintc	Amy P.	12:30	4
7/28/14	 40056	   Tartville	Service	Joe F.	7:30	1
7/28/14	 23458	   Tartville	Service	Joe F.	7:55	2
7/28/14	 69200	   Tartville	Service	Rus T. 	7:30	1

Date	 Case ID   Site	        Dept	Tech	Start Time	Row_Num
7/28/14	 10023	   Tartville	Maintc	Amy P.	7:30	1
7/28/14	 56789	   Tartville	Maintc	Rem W.	8:05	1
7/28/14	 23098	   Tartville	Maintc	Amy P.	8:35	1
7/28/14	 70004	   Tartville	Maintc	Amy P.	9:10	2
7/28/14	 12708	   Tartville	Maintc	Mag O.	10:00	1
7/28/14	 10004	   Tartville	Maintc	Amy P.	12:30	1
7/28/14	 40056	   Tartville	Service	Joe F.	7:30	1
7/28/14	 23458	   Tartville	Service	Joe F.	7:55	2
7/28/14	 69200	   Tartville	Service	Rus T. 	7:30	1

declare @Logs table (
	Date		date,
	Case_ID		varchar(20),
	Site		varchar(20),
	Dept		varchar(20),
	Tech		varchar(20),
	Start_Time	time
	)

insert into @Logs
values
	('7/28/14', '10023', 'Tartville', 'Maintc', 'Amy P.', '7:30'),
	('7/28/14', '56789', 'Tartville', 'Maintc', 'Rem W.', '8:05'),
	('7/28/14', '23098', 'Tartville', 'Maintc', 'Amy P.', '8:35'),
	('7/28/14', '70004', 'Tartville', 'Maintc', 'Amy P.', '9:10'),
	('7/28/14', '12708', 'Tartville', 'Maintc', 'Mag O.', '10:00'),
	('7/28/14', '10004', 'Tartville', 'Maintc', 'Amy P.', '12:30'),
	('7/28/14', '40056', 'Tartville', 'Service', 'Joe F.', '7:30'),
	('7/28/14', '23458', 'Tartville', 'Service', 'Joe F.', '7:55'),
	('7/28/14', '69200', 'Tartville', 'Service', 'Rus T. ', '7:30')

--/**/ select * from @Logs

;with Logs
as	(
select l.*, dense_rank() over (partition by l.Date, l.Site, l.Dept order by l.start_time) rnk
from @Logs l
)
--select * from Logs
,Ranges
as	(
select
	l.Date,
	--l.Case_ID,
	l.Site,
	l.Dept,
	l.Tech,
	l.start_time,
	u.start_time End_time,
	row_number() over(order by l.start_time) rn
from
	Logs l		-- l = lower edge of range
inner join
	Logs u		-- u = upper edge of range
		on	l.Date = u.Date
		and l.Site = u.Site
		and l.Dept = u.Dept
		and l.Tech = u.Tech
		and l.Start_Time <= u.Start_Time
		and not exists (		-- where there is not an intervening tech
			select *
			from Logs m
			where
				l.Date = m.Date
			and l.Site = m.Site
			and l.Dept = m.Dept
			and l.Tech <> m.Tech
			and l.Start_Time < m.Start_Time and m.Start_Time <u.Start_Time
			)
		and not exists (		-- not a smaller lower edge in this range
			select *
			from Logs ll
			where
				ll.Date = l.Date
			and	ll.Site = l.Site
			and ll.Dept = l.Dept
			and ll.Tech = l.Tech
			and ll.rnk = l.rnk - 1
			)
		and not exists (		-- not a bigger upper edge of this range
			select *
			from Logs uu
			where
				uu.Date = u.Date
			and	uu.Site = u.Site
			and uu.Dept = u.Dept
			and uu.Tech = u.Tech
			and uu.rnk = u.rnk + 1
			)
)
--select * from ranges
select
	l.*,
	row_number() over (partition by r.rn order by l.start_time) row_num
from
	@Logs l
inner join
	Ranges r
		on	r.Date = l.Date
		and	r.Site = l.Site
		and	r.Dept = l.Dept
		and r.Tech = l.Tech
		and l.Start_Time between r.Start_Time and r.End_time
order by
	l.Dept,
	l.Tech,
	l.Start_Time