Thanks for this timely question.  Here is some advice:

Step 1.  Find a quiet relaxed place or mental space where you can take
Assignment 2.  Have a careful read of the assignment and what it asks you
to do.  When you're ready, engage in some creative visualisation of what a
new dairy processing plant might look like, in terms of its size, where it
might be located, possible proximity to a river, its likely rural location,
but possible nearness to other dwellings, whether there might be other
rural activities nearby, possibly even another dairy plant. If you've ever
used SimCity or SimTown you should feel right at home!

Step 2. Start making your list of possible environmental impacts that would
likely need to be considered when assessing the proposal. If you've taken
the RMA course or have an interest in an RMA focus, that's fine, but please
keep your lens fully back, not too close. This is an EIA course, not an RMA
course.  It's ok if you keep your knowledge about RMA processes a bit
hazy.  You're not expected to know them. For example, you might think that
the plant will need a regional council discharge consent, and definitely a
land use consent, but it's ok if you don't mention these in any specific
way, or refer to any specific sort of rural zoning issues. If they occur to
you in your mind, it's fine to make a note of them.  The case study itself
it purposefully a bit hazy on details so as to allow you the freedom to
consider a range of impacts.

3.  As you make your list, start thinking about how you might rank the
effects.  There are a couple of key course readings which will be helpful
in this regard, and there is extra advice on the course page for this
assignment.  I recently added a list of EIA tools, which you might wish to
run through as a reminder of potential effects.  The plant will need to be
constructed,  which will produce some short term effects, and then there
will be ongoing effects of one sort or another.  Generally speaking, what
might they be?

4. Benchmark your work by running a Google search.  I just ran one on
environmental impacts dairy processing plant and found a lot of information
from around the world.

5. Narrow your benchmark by restricting your Google search to NZ sites. 
As part of your search check out one or two news items to see the kinds of
impacts of a dairy processing operation that might get the local population
or environmental watchdogs a bit riled.  Flag these impacts (hint: EIA can
include positive effects. What are some positive effects from a new dairy
processing plant?)  and include them in your assignment as possible impact
bottlenecks that might add a weighting/loading in your ranking.  Include
them, and any other refs you have found useful, in a final reference
list. 

6.  Don't allow yourself to get distracted by trying to be too specific
about particular indicators you might run across in your searches, such as
actual permitted content of discharges, water chemistry, etc.   This
course doesn't expect you to be an engineer. Similarly, don't get
distracted by reaching too far.  You asked whether you need to consider
the environmental impacts of dairy farming. The short answer is "no". 
Having said that, your question is really interesting, but reaches too
far.  You might really be asking  "In assessing a possible resource
consent for a dairy processing plant, does the RMA include provisions for
considering the impact on the environment of producing the products it is
receiving, as part of the overall decision to grant consent, or as part of
any future consent conditions for the plant?"   This question is
interesting but goes beyond this assignment. Organisations like Greenpeace
really push for this sort of power, for example to try to require
reductions in greenhouse gas emissions in order to get consent for a
coal-fired electrictiy generating station.  But it's really an RMA issue
that goes beyond this course. 

Having said that, feel free to comment generally on environmental best
practice and how it might play out in terms of consent and monitoring
conditions for the actual activities of the dairy plant once it gets up and
running. This forms part of your assignment. If you're "RMA-keen", you'd be
looking here at something called a 'best practicable option' for minimising
discharge effects. Google the term and you'll find out more.  It's over to
you really in terms of how you want to use this course to gain general
knowledge, or as a tool in a quest to become an RMA-savvy environmental
practitioner.  We try to be flexible in our marking to cater to different
'angles' of approach.  Have confidence that any benchmarking you do in
Steps 4 and 5 will give you any additional support that you may need, or
contact me for more clarity.

Cheers and good luck with A2.